ELEMENTS
or
C H E A I S T R Y9
INCLUDING TIIE
%1I'2  RECENT DISCOVERIES AND APPLICATIONS OF THE SCIENCE TO
MEDICINE AND PIHARMACY, AND TO THE ARTS.
BY ROBERT KANE, M.D., MI.R.T.A.,
PROFESSOR OF NATURAL PHILOSOPIHY TO THE ROYAL DUBLIN SOCIETY;
PROFESSOR OF CHEMISTRY TO THE APOTHECARIES' HALL OF IRELAND; MEMBER OF THI
SOCIETY OF PHARMACY OF PARIS, AND OF THE GERMAN PHARMACEUTICAL
SOCIETY, ETC., ETC., ETC.
AN AMERICAN EDITION,
WITH ADDITIONS AND CORRECTIONS, AND ARRANGED FOR THE USE OF
THE UNIVERSITIES, COLLEGES, ACADEMIES, AND MEDICAL
SCHOOLS OF THE UNITED STATES,
BY JOHN WILLIAM DRAPER, M.D
PROFESSOR OF CHEMISTRY IN THE t'NIVERSITY OF NEW-YORE, FORP0MERLY
PROFESSOR OF PHYSICAL SCIENCE AND PHYSIOLOGY IN HAMPDEN SIDNEY COLLEG]S,
VIRGINIA; MEMBER OF THE LYCEUM OF NATURAL HISTORY OF NEW-YORKI
&C., &C., &c.
NEW YORK:
HARPER & BROTHERS, PUBLISHERS.
1854.




entered, according to Act of Congress, in the year 1842, b3
HARPER & BROTHERS,
i the Clerk's Office of the Southern District of New-York.




PREFACE TO THE AMERICAN EDITION.
IN preparing the work of DR. KANE for the use of Amierican students, I have preserved the original entire, and have
only made those alterations in it which the system of instruc.
tion pursued in the United States seems to require.
This work, which, as a text-book, is undoubtedly the best
extant in the English language, representing the present condition of chemical science, necessarily contains much detail.
To give it completeness, it was needful to include the deseription of many bodies of little technical importance, to
describe experimental processes, and sometimes to dwell on
facts of minor value.
The period of instruction in the schools of this country is
short, so that many standard books are unavailable from
their extent. From an experience of several years in public
teaching,  I have perceived the importance of separatingj for
ilce student, the leading principles from the accompanying
detail.  This will, perhaps, to a certain extent, be accomr
plished by the mechanical contrivance of printing such works
vwitlh different types, the important matter being in the larger
letters.
The magnitude of the original prevented me from making
additions to any great ex-tent; what has been introduced in
this way will be readily distinguished, from being inserted
lbetween brackets.
From its having been repeatedly and carefully read, and
thle errors and misprints revised, this will probably be found
tnore correct than the foreign edition.
JOHN WILLIAMX DRAPER.
University of VNew-,York, June 1st, 1842.








PR EFACE.
Mv object in the following pages is to present to the student an account of the general principles and facts of Chem.
istry, and of its applications to Pharmacy, to Medicine, and
to the Useful Arts.
In the arrangemtent of a work like the present, if the general principles of the science are first described, it is impossible to avoid the difficulty of introducing the names of many
substances with whose history the reader cannot be supposed
conversant; and by entering, in the commencement, on the
description of individual substances, reference to the principles of atlinity and the laws of constitution is continually necessary, in order that the reactions of these bodies may be
understood. In both cases the student is liable to some embarrassraent, but I believe it to be greater in the latter, and
hence I have adopted the plan of fully describing all the
general principles and laws of chemical action, before entering on the description of the chemical substances in detail.
Chem-istry being itself but a department of Natural Philosophy, altho.lgh the most extensive in its objects and the most
important in its uses, it is connected so intimately with the
other branches of Physics, that a knowledge of at least their
general principles is necessary for the proper understanding
of the nature of chemical phenomena.  I have consequently embraced within the design of the present work a de.
scription of the physical properties of bodies, so far as they
serve to complete their chemical history, or influence their
chemical relations; and thus, upon the one hand, supply
characters by which chemical substances may be recognised,
and, upon the other, modify the affinities by which the action of chemical substances upon each other is determined.
With this twofold object, the chapters on Cohesion, Light,
Heat, and Electricity have been drawn up.
The portion of the work which treats of the general laws
of chemical combination, is followed by an account of the
mode of preparation and properties of all inorganic substances of interest to Science, to Medicine, or to the Arts. But
in this part I will pass over very briefly the history of numerous bodies which, from their rarity, are objects only of




Vi                    PREFACE.
scientific curiosity, referring those who would wish to study
their history more closely to the extended works of Thompson, of Graham, of Dumas, or of Berzelius.
In the department of Organic Chemistry my object will be
fully to discuss the history of all such bodies as are of importance, from their bearing upon general principles or existing theories, from their use in medicine or pharmacy, their
employment in the arts or in ordinary life.  The numerouls
series of bodies which are every day discovered in Organic
Chemistry, but which do not come under any of the above
heads, shall be dismissed with only a notice of their existence.
The relations of chemical action to the functions of organized matter, the applications of Chemistry to Physiology and
to Pathology, will be treated of so far as our accurate knowledge extends; and, finally, a succinct description of the mode
of analysis of organic and inorganic bodies will be given.
As this work is not intended to be a complete system of
Chemistry, nor to satisfy the wants of those who wish to make
Chemistry their special study, I have in almost all cases
avoided references or quotations, which would needlessly
occupy much space; for, in the larger works already menltioned, the original authorities on all subjects will be found.
The object of a work like the present being to represent
faithfully the general aspect and extent of science at the time
of publication, its details must be in great part founded on
the results of others. Hence originality cannot in any great
degree be either expected or desired; but I have not hesitated, in many instances, where the best consideration I
could give the subject induced me to dissent from views
generally held, to make this work the vehicle, in a popular
form, of such suggestions as I thought deserved to be adopted.
The processes given for the preparation of the various
substances described are, with very few exceptions, those
followed either in my private laboratory or in the manufacturing laboratory of the Apothecaries' Hall of Ireland; and
the apparatus figured in the woodcuts are generally similar
to those which I employ in experiments of research or at
lecture




CONTENTS.
Page                                   kag
INTRODUCTION.                  Radiation of Heat... 94
Origin and Objects of Chemistry     9   Absorption and Reflection of Heat 96
Researches of Melloni and Forbes  98
CHAPTER I.                   Polarization of Heat... 01
OF GRAVITY AND COHESIVE FORCES, AS   Relations of Heat to Light.. 102
CHARACTERIZING  CHEMICAL  SUBSTAN- SECTION VI.
CFS.                                   Of the Cooling of Bodies.. 103
Specific Gravities of Bodies.1   Theory ofDew and Frost.. 104
Central Heat of the Earth.    105
Constitution of Matter... 17
Capillarity and Elasticity.      19              CHAPTER IV.
Phenomena of Solution..    22 OF ELECTRICITY CONSIDERED AS CHACqystallization... 23   RACTERIZING CHEMICAL SUBSTANSystems of Crystallization. 26  cEs..100
CHAPTER II.                SECTION I.
OF THE PROPERTIES OF LIGHT AS CHAR-   Of Statical Electricity.. 107
ACTERZING CHEMICAL SUBSTANCES.  Distribution of Electricity.. 110
Electrical Attractions and RepulReflection and Refraction of Light. 32    sions.112
Double Refraction...        34   Theories of Electricity. 114
Polarization of Light... 38   Electrical Induction.       118
Circular Polarization.. 4120
Wave Theory of Light... 42   Nature of Induction. 122
CHAPTER III.                  Atmospheric Electricity. 125
SECTION II.
OF HEAT CONSIDERED AS CHARACTERIZING    Of Dynmical Electricity           126
CHEMICAL SUBSTANCES.            Simplu Galvanic Circles. 128
SECTION 1.                               Of Electrotype Copying. 130
Of Expansion. 46   Theory of the Galvanic Battery. 131
Nature of Temperature.    49   Volta's Theory of Contact.. 133
Thermomleters.      50   Construction of Galvanic Batteries 134
Pyrometers.    54   Constant Batteries... 136
Expansion of Air and Gases. 56   Thermo-electric Currents.. 139
-  -  iquids..   58   Magnetism.. 143
-   -  Solids... 60   Electro-magnetic Phenomena. 145
SECTION II.                              Of the Galvanometer...   147
SPecific Heat                    63              CHAPTER V.
Connexion of Specific Heat and
the Chlemical Constitution     66       OF CHEMICAL NOMENCLATURE. 149
Specific Heats of Gases.     69 Names of the Simple Bodies.. 150
SECTION II.                                        - Primary Compounds. 152
Of Liquefaction..    70                Secondary Compounds [54
Latent Heat of Liquids           71 Symbolical Nomenclature..1 56
Freezing Mixtures... 73
SECTIoN IV.                                        CHAPTER VI.
Of Vaporization.               75 OF CHEMICAL AFFINITY, AND ITS RELALatent Heat of Vapours.       76   TIONS TO HEAT, TO LIGHT, AND TO COElasticities of Vapours.. 78   HESION.
INature of the Boiling Point. 83 Elective Decomposition.. 157
Spontaneous Evaporation.       87 Order of Affinity not Constant. 159
Of Steam as a Moving Powver      89 Relation of Affinity to Cohesion. 163
SECTION V.                             Influence of Elasticity on Affinity. 168
Of the Transmission of Heat through  Influence of Light on Affinity.. 172
Bodies...            91 Influence of the Chemical Rays of
Conduction of Heat.            92   Light....173




Viii                         CONTENT S.
Page                                 Pap
Photography  and  Daguerreotype      3. Of Nztrogen... 260
Drawing.. 175   Of the Atmosphere... 262
Nitrous Oxide. 272
Nitric Oxide.... 273
OF THE HEAT AND LIGHT DISENGAGED       Hyponitrous Acid, Nitrous Acid.275
DURING CHEMICAL COMBINATION. 178   Nitric Acid.277
Products of Slow Combustion. 179 4. Of Sulphur. 282
Constitution of Flame... 181   Sulphurous Acid. 284
Of tile Saflety Iamp..   183   Sulphuric Acid                 286
Theories of Combustion... 185   Hyposulphurous and HyposulphuCHAPTER VIII.                  ric Acids.290
Sulphuret of Hydrogen. 292
OF THIE INFLUENCE OF ELECTRICITY     5. Of Selenium. 294
ON CHEMICAL AFFINITY.. 187
Its Compounds with Oxygen, HyElectro-chemical Classification. 189  drogen, and Sulphur. 294
Electro-cheinical Theories.. 190 6. Of Phosphoruls..295
Electrolysis and Electrolytes.. 194   Oxide of Phosphorus, PhosphorOrigin olfthe Galvanic Current. 197   ous Acid                     296
Synthetic Action of Electricity. 199   Phosphoric Acid. 297
Relations of Electricity to Affinity. 201   Phosphuret of Hydrogen. 299
CHAPTER IX.               7. Of Chlorine.... 300
Hypochlorous and Chloric Acids. 304
OF THE LAWS OF COMBINATION. 202   Chlorous Acid.     305
Scales of Chemical Equivalents. 205   Hydrochloric or Muriatic Acid. 307
Law of Multiple Proportions.. 207   Chlorides of Sulphur and PhosphoDefiniteness of Composition.. 210   rus.. 310
Theory of Volumes... 213 8. Of Iodine.                         311
Iodic and Periodic Acids.  313
CHAPTER X.
Hydriodic Acid.. 315
OF THE RELATIONS OF CHEMICAL CONSTI-  Iodine with Phosphorus, Sulphur,
TUTION TO TIIE MOLECULAR STRUCTURE     &C..  316
OF BODIES.                           Hydriodate of Phosphuretted HySECTION I.                                drogen..316
Of the Atomic Theory... 217 9. Of Bromine. 317
Physical and Chemical Atoms. 218   Bromic and Hydrobromic Acids. 318
SECTION II.                            Other Compounds of Bromine. 318
Of Isomorphism.. 221 10. Of Fluorine...  319
Isomorphous Groups... 223   Hydrofluoric Acid. 320
Relation of Form to Constitution 226 11. Of Silicon... 321
SECTION III.                           Silicic Acid or Silica. 322
Of Dimorphism and Isomerism, and     Chloride of Silicon. 323
of the Theory of Types. 227   Fluoride of Silicon.. 324
Approximate Dimorphism.      230 12. Of Boron..       325
Principle of Isomerism.     231   Boracic Acid...  326
Compound Radicals. 233   Chloride and Fluoride of Boron. 326
Theory of Organic Types.. 234 13. Carbon  referred  to  Organic
SECTION IV.                              Chemistry... 327
Of Catalysis...      235
Communication of Motion. 237           CAPTE  XII.
OF THE GENERAL CHARACTERS OF THU
CHAPTER XI.                 METALS, AND OF THEIR  COMPOUNDS
OF THE CLASSIFICATION OF THE ELOf THE: CLASSIFICATION OF THE EL-       WITH TIlE NON-METALLIC BODIES.
EMENTARY BODIES.. 238 Classification of the Metals; their
State in Nature; the Mode of ReCHAPTER XII.                 duction of their Ores.. 327
OF THE SIMPLE NON-METALLIC BODIES,
AND OF THEIR COMPOUNDS WITH EACH             CHAPTER XIII.
OTHER.                             OF THE INDIVIDUAL METALS, AND OF THEIR
1. Of Oxygen: Its Preparation and      COMPOUNDS WITH  OXYGEN, SULPHUR,
Properties.      241   SELENIUM, AND PHOSPHORUS: TIIEIR
2.: Of IHydrogen: Its Preparation. 246   ALLOYS.
The Hydro-oxygen Blowpipe.251 SECTION I. Metals of the First Class.
Of Water: its Composition. 253   Potassium: its Preparation. 336
Peroxide of Hydrogen.. 258   Potash, Peroxide of Potassium. 33"




CONTENTS.                                  i x
Page                                  Pae
Sulphurets of Potassium.. 339   Sulphurets and Alloys of Lead. 395
Sodium and Soda.     340   Bismuth and its Compounds. 397
Sulphurets of Sodium           342 SECTION VI. Metals of the Sixth Class.
Lithium: its Oxide and Sulphuret 342   Of Silver, its Natural State and
Barium: its Preparation.. 342     Properties.        399
Barytes, Hydrate of Barytes. 342   Oxides and Sulphurets of Silver. 401
Sulphuret of Barium.        344   Of Mercury: its Preparation and
Strontium: its Oxide and Sulphu-,       Properties.              402
ret... 344   Oxides and Sulphurets of Mercury 403
Calcium: its State in Nature. 345   Of Gold: its Oxides and SulphuPreparation and Properties of Lime 346  rets..              405
Sulphurets of Calcium.. 347   Of Palladium and its Compounds 406
Maognesium, Magnesia, &c..   348   Of Platinum: its Oxides and Sul3Ec'rmoN II. Metals of the Second Class.  phurets.407
Aluminum: its State in Nature. 349:   Of Iridium and Rhodium.     409
Alumina, Sulphuret, &c... 350            C
Glucinum aind its Compounds. 351 
Yttrium, Thorium, Zirconium. 351  OF THE GENERAL PROPERTIES AND COL
Cerium, Lanthanum... 351            STITUTION OF SALTS.
Of Manganese... 352 Neutral, Acid, and Basic Salts; DouOxides of Manganese.          353   ble Salts; Sulphur Salts; TheoTechnical Valuation of Manganese      ries of the intimate Constitution of
Ore...             ~ Acids and Salts; Binary Theory
Manganic and Permanganic Acids 356   of Salts                        410
Other Compounds of Manganese. 357
SECTION III. Metals of the Third Class.
Of Iron: its State in Nature. 357 SPECIAL HISTORY OF THE MOST IMPORTANT
Manufacture of Cast and Soft Iron 359   SALTS OF THE INORGANIC ACIDS AND
Manufacture of Steel... 360   BASES.
Passive Condition of Iron.. 361 Of the Salts of Potash.-Chloride, Io
Oxides of Iron...      362   dide, Bromide, and Fluoride of PoSulphurets of Iron... 363   tassium; Fluosilicate of Potash;
Of Nickel and its Compounds. 365   Sulphates of Potash; Nitrate of
Of Cobalt and its Compounds. 366   Potash; Manufacture of GunpowOf Zinc and its Compounds. 367   der; Hypochlorite and Chlorate of
O0 Cadmium. Of Tin. 369   Potash; Perchlorate, Iodate, and
Oxides and Sulphurets of Tin. 370   Silicato of Potash.. 421
Of Chrome: its Oxide. Chromic       Of the Salts of Sodium.-Chloride of
Acid..371  Sodium; of Sea-water.; Bromide
Of Vanadium. 373   and Iodide of Sodium; Sulphate,
SECTION IV. Metals of the Fourth Class.  Nitrate, Hypochlorite, and HypoTungsten and Molybdenum. 373   nitrite of Soda; Various PhosOsmium and its Compounds. 374   phates of Soda; Borate and SiliColumbiuf: and Titanium. 375   cate of Soda..           426
Of Arsenic..376 Of the Salts of Lithium-Salts of BaArsenious Acid, Arsenic Acid. 377   rium.-Chloride of Barium; SulArseniuret of Hydrogen. 378   phate and Nitrate of Barytes. Salts
Sulphuret of Arsenic.. 379   of Strontium.-Chloride of StronDetection of Arsenic.. 380   tium; Sulphate and Nitrate of.
Of Antimony..           384   Strontian.429
Compounds of Antimony with Ox-      Of the Salts of Calcium-Chloride,
ygen..385   Bromide, Iodide, and Fluoride of -
Sulphurets of Antimony. 386   Calcium; Sulphate and Nitrate of
Antimoniuret of Hydrogen.. 388   Lime; Phosphate of Lime; HypoOf Tellurium and its Compounds 389   chlorite of Lime; Manufacture of
Of Uranium and its Compounds. 390   Bleaching Salt; Chloromletry. 430
8ECTION V. Metals of the Fifth Class.  Salts of Magnesia.-Epsom Salts. 434
Of Copper, Reduction from  its      Salts of Aluminum.-Manufacture of
Ores.390         Alum...           435
Oxides of Copper... 392   Constitution of Glass and PorceSulphurets of Copper.. 393      lain; Manufacture, of Glass;
Brass, Bronze, Gun Metal, Specu-        Manufacture of Earthenware. 437
luim Metal... 393   Of the Salts o! Manganese.. 443
Of'Lead: its Oxides.. 394 Of the Salts of Iron.-Chlorides of




X                           CONTENTS.
Page                                 Pag
Ironi; Manufacture of Copperas;    balt, Silver, Palladium, Platinum,
Nitrates of Iron..   444   and Mercury; White Precipitate 498
Salts of Nickel and Cobalt.. 446 Ammonia and Anhydrous Acids;
Salts of Zinc and Cadmium. 447   Common Ammoniacal Salts; TheSalts of Tin..          448   ory of Ammonium; Sal AmmoniSalts of Chrome and Vanadium;        ac, Sulphates, Phosphates, OxalChromates.... 449   ates, &c., of Ammonia; Double
Salts of Tungsten, Molybdenum,       Chlorides of Ammonium. 507
Osmium, and Columbiur. 451           C
Salts of Arsenic, Arsenites, Ar-             CHAPTER XIX.
seniates.         452
Salts ofeniAntimony, Antimoniates... 452 OF CYANOGEN AND ITS COMPOUNDS, AND
Salts of Antimony, Antimoniates 45,OF THE BODIES DERIVED FROM IT.
Salts of Titanium, Tellurium, and
Uranium.                  454 Cyanogen. Cyanic, Fulminic, and
Salts of Copper.- Manufacture of       Cyanuric Acids. Prussib Acid:
Blue Vitriol; Scheele's Green;     its Preparation and Detection;
Emerald Green.          455   Valuation of its Strength. ChloSalts of Lead; Chrome Yellow;        rides and Iodides of Cyanogen. 513
Chrome Rted                 457 Of the Metallic Cyanides, Potassium,
Salts of Bismuth... 458   Mercury, Iron. Complex CyanSalts of Silver, Lunar Caustic    459   ides; Prussian Blue; Yellow and
Salts of Mercury. —Corrosive Subli-    Red Ferroprussiates of Potash;
mate, Calomel, Iodides, Sul-       Theory of the Complex Cyanides 520
phates, and Nitrates of Mercury 461 Of Sulphocyanogen and its ComSalts of Gold.... 465   pounds; of Mellon, Melam, MelaSalts of Palladium and Platinum 466   mine, and their Derivatives. 525
Salts of Iridiumn and Rhodium. 466CHAPTER XX.
CHAPTER XVI.               OF STARCH, LIGNINE, GUM, AND SUGAB,
OF THE GENERAL PRINCIPLES OF THE CON-   WITH THE PRODUCTS OF THEIR DECOMSTITUTION OF ORGANIC BODIES.       POSITION BY ACIDS AND ALKALIES.
Elements of Organic Bodies; Rela-    Varieties of Starch; Lignine; Varition of Vital Force to Affinity;     eties of Gum; Varieties of Sugar;
Compound Radicals; Theory of         Action of Acids on Sugar; Saccha.
Organic Acids; Theory of Types;      rine Fermentation; Lactine; MuDecomposition of Organic Bodies 467   cic Acid; Mannite; Lactic Acid;
Glycyrrhizine.... 527
CHAPTER XVII.
CHAPTER XXI.
OF CARBON AND ITS COMPOUNDS WITH OXYGEN, SULPHUR, AND CHLORINE.     OF THE ALCOHOLIC AND ACETIC FERMENTATIONS. OF ALCOHOL; THE ETHERS;
Forms of Carbon; Organic Analysis 476   ALDEHYD; ACETIC ACID, AND OTHER
Carbonic Acid; Carbonates of Pot-      BODIES DERIVED FROM IT.
ash and Soda; Manufacture of
Potashes and Sodla-ash; Alkalim-   Vegeto-animal Bodies; Yeast; Manetry; Earthy Carbonates; Car-        ufacture of Spirit; Preparation of
bonates of Iron, Copper, Lead,       Ether; Theory of the Process;
&c.; of Carburets... 485   Nature of Ether; its Compounds
Carbonic Oxide, Oxalic Acid, and the   with Acids; Sulphovinic Acid;
Oxalates; Chlorocarbonic Acid;          of Wine; Compound Ethers;
Oxycarburet of Potassium; Rho-       of Olefiant Gas and the derived
dizonic, Croconic, and Mellitic      Compounds.... 537
Acids; Sulphuret of Carbon; Chlo-  Oxidation of lcohol; Aldehyd; Acerides of Carbon.... 492   tous Fermentation; Acetic Acid,
Acetates of Potash, Lime, &dc., SuCHAPTER XVIII.                gar of Lead, Verdigris, other AceOF THE COMPOUNDS OF NITROGEN iND lY-   tates; of Acetone; Compounds of
DROGEN. OF AMMONIA, ITS DERIVATIVES   Kacodyl; of Marsh Gas.553
AROGEN. OF AMMONIA, ITS DEmV,~TIVES  Action of Chlorine on Alcohol, and
the Bodies derived from it; TheAmmonia; Amidogene; Iodide and         ory of the Ethers. 564
Chloride of Azote; Ammoniurets,    Secondary Products of the Alcoholic
Amidides; Azoturets; Ammonia-        Fermentation:'CInanthic Acid;
Salts of Zinc, Copper, Nickel, Co-   Amilic Alcohol; Corn Oil.. 567




CONTENTS.                                 xi
Page                                1'~
CHAPTER XXII.                       CHAPTER XXVI.
OF THE ESSENTIAL OILS, CAMPHORS, AND      OF THE COLOURING MATTERS.
RESINS.               Of Madder; Anchusa; Carthamine;
Of the Oils forming Acids, not exist-  Carmine; Logwood; Persian Bering in the Plants; Oil of Bitter     ries; Anotta; other Yellow BodAlmonds; Amygdaline; Benzoic        ies; Indigo, and the Substances
Acid; Benzyl; Oils and Acids of      derived from it; Lichen Colours;
Cinnamon, Cloves, Mustard, and      Archil and Litmus;  Colours of
Spirea.                       569   Leaves and Flowers; Theory of
Oils pre-existing in the Plant, Prop-  Dyeing.613
erties not Acid...    574          CHAPTER XXVII.
Camphors or Stearoptens of the Oils
of Resins.  576 OF THE VEGETABLE ALKALIES AND OF
Amber, Succinic Acid, Succinates;                THEIR SALTS.
Caoutchouc... 579 Quinine; Cinchonine; Aricine; Morphia; Narcotine; Codeine; TheCHAPTER XXIII.                baine; Narceine; PseudomorOF TIIE SAPONIFIABLE FATS AND OILS.    phine; Strychnine; Brucine; Delphinine; Veratrine; Sabadilline;
Glycerine, Stearine, Oleine, Marga-    Jervine; Colchicine; Emetine;
rine; Products of the Action of      Solanine; Chelerythrine; CheliAcids on Fatty Bodies; Vegeta-       donine; Aconitine; Atropine; Belble Fats and Oils; Fish Oils: Man-   ladonine; Daturine; Hyoscyaufacture of Soaps and Plasters. 581   mine; Coneine; Nicotine; MenSpermaceti, Ethal, and the derived     ispermine; Cissampeline; GlauBodies. Wax.... 591   cine; of the Constitution of the
CHAPTER XXIV.                 Vegetable Alkalies... 623
OF TIlE ORGANIC ACIDS WHICH DO NOT           CHAPTER XXVIII.
PRE-EXIST IN PLANTS, AND DO NOT BE- OF THE PRODUCTS OF THE DECOMPOSITION
LONG TO ANY ESTABLISHED SERIES.       OF WOOD AND THE ALLIED BODIES.
Tartaric Acid; Tartrates of Potash,  SEcrION I.
Soda, Iron, Antimony, &c...592   Of the slow Decomposition of Wood.
Action of Heat on Tartaric Acid;         Constitution of Ulmine. Of Turf
Racemic Acid.       595      and Coal.63
Citric Acid; Citrates; its Decompo-  SECTION II.
sition by Heat..597   Of the Produects of the destructive
Malic, Maleic, and Fumaric Acids. 598  Distillation of Wood, Coal, and
Meconic, Komenic, and Pyromecon-         Resin.646
ic Acids.          599   Pyroxylic Spirit; Compounds of
Tannic Acid; Valuation of Tannin;        Methyl; Formic Acid; Coal
Tannates..... 600           Gas; Napthaline; Kreosote, &c. 647
Gallic Acid; the Products of its De-          CHAPTER XXIX.
composition. 601 OF THE CHEMICAL PHENOMENA OF VE~GO
Tannic Acid from Catechu, Cincho-                  TATION.
na, and Kino...         603
Other Vegetable Acids           603 Germination, Assimilation of the
Food of Plants; Sources of CarCHAPTER XXV.                 bon and Nitrogen; Ashes of Plants;
1FP THE NEUTRAL ORGANIC                Composition of Soils and Manures;
AND OF THE N PRODUCTS OF SUBSTANER    Rotation of Crops; Action of Light
AND OF THE PRODUCTS OF THEIR DE- on Plants                          650
on Plants..650
COMPOSITION.
Pectine; Salicene; Phloridzine; As-           CHAPTER XXX.
paragine;  Caffeine;  Piperine;            OF ANIMAL CHEMISTRY.
Cantharadine; Anemonine; Ce-       SECTION I.
trarine; Picrotoxine; Columbine;     Of the Composition of the Animal
Cusparine; Elaterine; Meconine;        Tissues.'Peudecanine; XEsculine; Popu-       Of the Albuminous Constituents;
line; Quassine; Santonine; Sapo-       Albumen; Fibrine; Proteine;
nine; Scillitine; Senegine; Smi-       Gelatine; Chondrine; Fats of
lacine; Absinthiine; Lactucine. 605   the Brain; Ozmazome; ZomiOf Extractive Matter; Apotheme;          dine..                      663
Extracts.612   Skin, Epidermis, Hair, Horn,




xi                           CONTENTS.
Page                                  1~
Feathers; Cellular and Serous         Acids; Bilifulvine; Chyle and
Tissues; Tendons; Muscular            Lymph, Saliva and Pancreatic
Tissue; Brain; Composition of         Juice..679
Bones, Teeth, and Enamel;         SECTION IV.
Shells..670    Constitution of the Urine in Irealth
SECTION II.                               and in Disease.
Of the Composition of the Blood, and  Urea; Uric Acid; Allantoine, A1the Phenomena of Respiration.         loxan, Alloxantine, and other
Blood Globules and Serum; Clot;          Products of the Decomposition
Hematosine. Blood in Disease;         of Uric Acid; Hippuric Acid;
Respiration; Modes of Action          Urinary Deposites and Calculi;
of the Air; Animal Heat. 673      Mode of recognising Calculi;
SECTION III.                              Urine in Diabetes and other
Composition of the Digestive Or-        Diseases..... 683
gans, and of their Secretions;    SECTION V.
Chemical Phenomena of Diges-        Of various Natural and Morbid
tion.                                 Products.
Miucus; Gastric Juice; Pepsine;       Milk; Caseine; Eggs; Amnios;
Analyses of the Bile; Bilin;          Tissues of the Eye; Earwax;
Taurine;  Cholic  and  other    )    Pus; Ambergris..     l




ELEMENTS OF CHEMISTRY.
T'rr science of chemistry has its origin in the principle, that tie
bodies which constitute the external world are composed of a variety of elements, united according to certain laws. If we could
conceive a universe consisting only of iron, or quicksilver, or sulphur, the objects of the astronomer might still remain as extensive
and as sublime as they are in the actual state of things; for, in
tracing the constitution of planetary and satellitic systems, or reducing to precise laws the forces by which the motions of the
heavenly bodies might be produced, all the resources of his science
would still be brought into play. In like manner, the physical sci
ences could attain perfection, for the relations of these bodies to
heat, to light, to electricity, the various problems and laws of statical and dynamical forces, could have been known, and thus all
that is essential to the science of natural philosophy might be
attained. But not even an idea of chemistry could have been
formed. The duty of chemistry is to find the constituent elementary substances, which, by uniting, form the various compound
bodies which we observe; to ascertain the nature of the force! by
which they unite, and the laws by which their union or separation
may be regulated; to trace the effects of their mutual action in
the properties of the new substances formed by their combination,
and in the phenomena, independent of composition, which accompany the exertion of chemical force.
This object of chemistry has been at all periods fully recognised;
for the earliest philosophers, even before the science had received
a name, considered its objects as well defined in the arrangement
of the elements of fire, air, earth, and water. When the methods
of chemistry, and the reasonings to which they led, acquired a
better form, these elements, which had been assumed from speculations in natural history and metaphysics, gave way to others, as
sulphur, spirit, salt, oil, and earth, equally incorrect, but still those
which, in the rough trials of the period, were obtained by decomposing compound bodies. As more accurate ideas and better processes were acquired, these elementary principles changed again
their character, until, finally, the philosophical idea of chemistry
was clearly stated and established by Lavoisier: 1st, that we study
to resolve the various compound bodies found in nature into others
which resist our power, and which we term undecompounded or sintpie substances, without pretending that they are elements; for the
advance of science enables us to decompose, in each generation,
bodies which to our own predecessors had appeared simple; 2d,
that w-e study to effect the recomubination af those simple bodies,




10        ORIGIN AND USES OF CHEMISTRY.
either in the same proportions, and thus regenerate the natural
compound bodies, or in new proportions, and fhus add to the catalogue of bodies which may exist in nature.
Of these two operations, the first, or separation of a compound
body into the simple substances which constitute it, is termed anal.
ysis. The second, or combination of simple to form a comipound
substance, is called synthesis. All chemical processes are conducted
upon the principle of one or other of these two, and occasionally
they are both, successively or- synchronously, accomplished.
The objects of chemistry cannot, however, be considered as
limited to the mere abstract study of the laws of elementary composition; to it also belongs the improvement of processes in the
useful arts by the more accurate knowledge of their theory which
chemistry confers, and the invention of new processes or of new
arts, by the application or discovery of substances previously neg
lected or unknown; the alleviation of disease, by new remedies
which may be placed at the command of the physician, or by more
correct ideas of the origin and results of morbid action, to which
the attentive study of the chemical processes of the great laboratory of the human frame may ultimately lead, ranks also among
the most important of its applications: and, although an abstract
science, which reveals some of the most beautiful of nature's laws,
deserves our best attention, yet it becomes invested with more
general interest, and commands more universal homage, when, as
with chemistry, it appears to be the basis of those practical arts on
which so much of health, of national prosperity, and of civilization
may depend.
The origin or derivation of the word chemistry is unknown. It
was first found as Xq:?/Ea, indicating the art of making gold and
silver among the Egyptians and Greeks of the Empire, at the commencement of that extraordinary perversion of the idea of elementary constitution which fascinated mankind for nearly five hundred years. From the Greeks it was naturally adopted, with the
vain pursuit which it denoted, by the Arabians, and, passing with
the Arabic prefix into the languages of modern Europe, became
alchemy. When the just objects and powers of the science were
finally recognised, it was termed chenmia or chemistry.
In studying those properties of the different kinds of matter by
which they are recognised to be distinct and independent chemical
substances, it is unavoidable to include those qualities which, although common to all forms of matter, yet differ in decree among
the different kinds, and thus serve as distinguishing characteristics
of them. The physical properties of various bodies are hence in
common use among chemists, as serving to perfect their description;
and, indeed, the limit between properly physical and properly chemical properties of substances is not always capable of being dis.
tinctly drawn.




SPECIFIC  GRAVITY  OF GASES.                   11
CHAPTER I.
OF GRAVITY AND COHESIVE FORCES AS CIIARACTERIZING CHEMBIICAL SUB
STANCES.
TIIHE physical forces which are of most importance in determining the characteristic properties of bodies are gravity and cohesion.
These differ, however, remarkably in principle from  each other,
and are applied to quite independent purposes. Gravity is common to all forms of matter, and is totally independent of its nature.
It is exerted at all, even the greatest conceivable distances, and is
the invisible yet insuperable tie, which, connecting together the
satellites and planets of our system with the central sun, assigns to
each of the tenants of our boundless skies its place and motions.
Acting thus only on the mass, gravity is a measure of the quantity
of matter present in a body; and what we term weight is only the
gravitating force exerted by the substance which we weigh. By
no natural operation can the smallest particle of matter be annihilated or destroyed; throughout the most complicated processes the
quantity of matter remains constant, and hence we are enabled to
verify the accuracy of our chemical operations, by proving the
weight of the bodies ultimately formed to be equal to the weight
of the substances by whose action they have been produced.
Under the same volume different bodies have very different
weights, atnd hence contain different quantities of matter. Bodies
are said to be more or less dense, according as in a given bullk they
contain a greater or less quantity of gravitating matter; and when
a certain body is taken as a standard, and their density reduced to
numbers, there is obtained the specific gravity of each body, or the
comparative quantity of matter it contains in a given bulk, which,
being almost always the same for the same body, is an important
element in its history, and mnay often serve for its recognition.
The determination of specific gravities is easily performed where
the volume of the substance can be exactly measured. Thus. for
liquids, as water, oil of vitriol, or alcohol: if a small bottle be
taken containing an ounce of water, or 480 grains, it will contain
343 grains of sulphuric ether, or 885 grains of sulphuric acid. Now
the densities will be as these numbers; or water being taken as the
standard, and its specific gravity being assumed as 1000, the spocific gravities of the others become proportional to it; as,
Water... 480: 1000
Ether... 3443: 715
Sulphuric acid  885: 1845
To save this little calculation, the bottle in use is generally made
to hold 1000 grains of pure water, and then, filling it with the fluid
to be tried, the weight gives directly the specific gravity.
Where the substance exists naturally in the state of gas, a precisely similar process may be had recourse to; in place of a bottle




12         s PEcIFIC  GRAVITY OF GASES.
with a ground glass stopper, there is used a globe, g, with a stop
cock, capable of holding from twenty to thirty cubic inches. A
-"  quantity of air having been removed
\ from the globe, the gas, which must preY   J viously be either perfectly dried or perfectly saturated with moisture, is adimit-'e  ted to supply its place; and as the volume
d  of gas which passes in is exactly equal to
the volume of air which had been taken
c    out, the relative weights give their (len~ "" -fi~-     k  sities, and hence the specific gravity of
the gas. For, suppose that the globe full
1111  11111 of air weighed 656 grains; that, having
been exhausted of air, it weighed 647'5,
and then, having received 28 cubic inches of carbonic acid gas, it
weighed 660'3 grains. We thus know that the 28 cubic inches of
air had weighed 8'5 grains, and that 28 cubic inches of the gas had
weighed 12'8; hence the densities are as 85 to 12,8, and the specific
12.8
gravity of the gas, air being taken as 1000, is -8-510001'06.
This brief description being intended only to explain the principle which the words " specific gravity" involve, it has been considered as not liable to alteration; but, in reality, the volumes of bodies,
particularly of gases, are constantly in a state of change. According as the air is warmer or colder; according as the pressure to
which it is subjected, as indicated by the barometer, diminishes or
augments, the volume which a certain weight occupies is altered,
and the specific gravity is changed. Hence, when we talke air as a
standard of specific gravities for gases, we do so only with reference to a certain standard of temperature and pressure, as at 32 on
the scale of Fahrenheit's thermometer, and at 30 inches of m'ercury
in the barometer tube. It is only by accident that an experiment
might happen to be made at this standard temperature and pressure,
and hence it is necessary to reduce the observed result to what the
result should have been at the standard points. If the gas be damp,
it is necessary also to correct for the presence of the watery vapour, and hence the determination of the specific gravity of a gas,
although so simple in theory, is in practice a most delicate opera.
tion. Under the proper heads of the constitution of gases and
vapours, with regard to heat and pressure, the mode of making
these corrections will be described.
The determination of the specific gravity of a solid body involves
in practice some principles in addition to those above stated. We
cannot regulate the bulk of a solid body as we wish, and hence the
volume must be determined indirectly. This is done by finding how'much water it displaces. Thus, if the solid be in many small fragments, weighing altogether, for example, 357 grains, they may be
introduced into a specific gravity bottle containing 1000 grains of
water. A quantity of water overflows exactly in bulk to the solid
which is introduced. The bottle being fiill, the solid body and thel
remaining water are then found to weigh 1285 grains. Now, if no
water had been expelled, the water and solid body should have




SPECIFIC  GRAVITY OF SOLIDS.                      13
weighed 1357 grains.  The difference 72 is the weight of the water
expelled; and, consequently, the weights of equal volumes, or the
densities of the water and of the solid, are as 72 anid 37; or, the
specific gravity of the water being taken as 1000, that of the solid
357
is  7 x 1000, or 4958.  If the solid be unsuited for that method, its
72
volume is next determined by the principle that a solid body immersed in a fluid is partly supported by the upward pressure of the
liquid which it displaces.  The solid, in order to silli in the liquid,
has to displace and push upward a quantity of it equal to its o wn
bulk, and to resist its weight or tendency to sink down again; for
this purpose a portion of the weight of the solid must be eup!loyed,
and it is only the overplus that is counterpoised by the weinghts
when we proceed to weigh the solid body immersed in any fluid.
A solid weighs, therefore, less when immersed in a flUid than when
weighed in the ordinary manner, the difference being the portion
of the weight of the solid which is employed to sink it, or to resist
the force of the liquid which tends to float it up, and this is equal
to the weight of the liquid which the solid pushes out of its place,
and which is of the same volume as the solid.  To effect this oporation, a balance, as in  a..........
the figure, is taken, generally with one scale dish.  b
The solid is hung to the
other extremity of the
beam  by a fine hair or
thread of cocoon-silk, b,
and is thus weighed as
usual; let us suppose that
it weighed 295 grains.  
A vessel of pure water is then so arranged that the. solid shall be
immersed as nearly as possible in the centre of it (as a in figure),
and it, being then again weighed, is found to be lighter than before;
let us suppose that it shall  weigh 243 grains.  This is the overplus
of its weight after having neutralized the tendency of the water to
float it up.  The difference of the two weighings 295 —243=52
grains is therefore the amount of the upward pressure, or the
weight of the water which the solid displaced.  Equal volumes
thus of the solid and of the water are found to weigh respectively
295 and 52 grains, and the comparison of these numbers, water
being taken as 1000, gives the specific gravity of the solid, which
is --- x 1000=5673.
52
A variety of other instruments are made use of for measuring
the specific gravities of solids and of fluids, as areometers, hydrometers, &c.; but. as here it is rather the general principles than the
practical details of such operations that are of importance, I shall
not enter into their description.
The specific gravity of compound gases is found to have a highly important rela.
tion to their ultimate constitution, and throws great light upon some of the most
general laws of chemistry; but as yet, notwithstanding some interesting specula
tions of Perzoz and of Boullay which I shall hereafter notice, no connexion be
B




14          SPECIFIC  GRAVITY  OF  VAPOURS.
tween the chemical properties or composition of liquid or solid bouies and their
specific gravities has been discovered. The physical constitution of vapours and
gases being, however, identical, those bodies which, being volatile, are capable of
assumint the form of vapour, may render, by the examination of the specific gravities of their vapours, most interesting indications of the manner in which their
elements are combined, and methods of performing this operation have been contrived by some of the most illustrious of chemists, as by Dumas and by Gay Lussac.
The method of CGay Lussac is the simpler of the two, and, for substances which
are volatilized at moderate temperatures, easily applied. A basin, c, is
taken, which rests upon a little furnace, and contains mercury. In
this basin the graduated bell glass, a, is inverted full of mercury. Let
us suppose we wish to determine the specific gravity of vapour of wab   ter. One or two little bulbs are taken and filled with water as follows:
the bulb is warmed with a lamp, and allowed to cool with the point
dipped into the water; in this manner a little water gets admission;
this is then boiled in the bulb until all air has been expelled, and the
bulb is filled with pure steam; the point being then dipped under the
surface of the water, as the steam condenses, the water rushes up to
supply its place, and the whole becomes fill; the point being then
touched to the flame of a lamp, it is melted, and the orifice is closed.
A small quantity, three or four grains, of water being thus enclosed,
the little bulbs are passed under the edge of the jar, a, and1 rise to the
top, where they float upon the mercury; a glass cylinder, b, open at
both ends, is now placed round the jar, resting on and secured to the
dish, c, and into it is poured so much colourless oil as shall completely cover the
jar, a, but allow of the graduation being distinctly seen; the furnace is then light
ed, and as the temperature of the oil and mercury rises, the water in the little bulbs
forms steam, which at last bursts the bulbs, and the level of the quicksilver in the
jar immediately falls, tile steam occupying the space above it. When the mercury
ceases to descend, it is known that all liquid has been converted into vapour; the
temperature of the oil, which is necessarily the same as that of the vapour inside,
is ascertained, and by the graduation on the jar the volume occupied by the vapour
is accurately read off; the weight of the vapour is known, for it is the weight of
the water in the bulbs, and its volume at this high temperature is thus found.
Knowing thus the volume of a few grains of steam at 250~, the volume at 320 may
be calculated; and as the volume of so many grains of air at 32~0 is already known,
the specific gravity of the vapour of water is obtained. The temperature of the
oil must be at least thirty or forty degrees above the boiling point of the liquid. and
hence it is likely to become coloured, to fume, or even to risk taking fire, unless
great caution is employed.
The method invented by Dumas has the advantage of being applicable to all tem
peratures below the melting point of glass, and it is consequently by its application
that the greatest benefit has been conferred on science. It is, however, more complex in principle, though not less delicate in practice. A globe holding from ten to fifteen cubic inches, and drawn out at its beak to a capillary orifice, is carefully weighed, containing, as usual, atmospheric air. It is then warmed, and its beak being
dipped into the fluid to be tried, it is allowed to cool, until by the contraction of the
air a sufficient quantity of thb
fluid has made its way in. The
globe is then fitted in a sort of
cage, by which it is securely held
in the centre of the liquid bath,
by which the heat is to be applied, and which may be water or
oil, a solution of chloride of zinc,
or, best of all, the fusible alloy
of bismuth, tin, and lead. The
capillary beak of the tube just
projects over the surface of the
bath, as in the figure. WVhen the
globe becomes sufficiently heated, the liquid boils, and its vapour, in passing away, carries off
the air which had previously fill



DIVISIBILITY   OF  MATTER.                            15
ed the globe. The liquid should be present in such quantity that its vapour, after
carrying off all air, should occupy the interior of the globe completely pure. The
excess of vapour is known to have passed away when there is no longer a jet proceeding from the capillary beak, and then by means of a blowpipe the orifice is
closed, and the temperature of the bath being taken at the same moment, the glo!.e
is removed from the bath, perfectly cleaned and weighed. The liquid condensing
as soon as the globe grows cold, leaves its interior practically empty, anil, on breaking off the capillary beak under the surface of quicksilver, this last enters into the
vessel, and, if the operation had been well managed, fills it completely. The globe,
fiull of quicksilver, is then emptied into a graduated jar, by which the quantity of
the qulicksilver being measured. the volume of the globe is known; when'this has
been done, all requisites for calculating the specific gravity of the vapour have been
obtained. For, knowing the volume of the globe, the weight of the air it contained
is known, and, subtracting that from the first weighing of the globe, the weight of
the globe when empty is obtained. Subtracting this from the second weighing of
the globe, the weight of the vapour is obtained; and as the air and vapour occupied
the same volume, the densities should be as these weights, if they had been at the
same temperature; but, as this was not the case, a farther calculation is required
to reduce them to the standard, and obtain the numerical specific gravities.
No process has been more firuitful in important results than this mode of detelmining the specific gravity of vapours, for it is only in this way that such sub)stances
as sulphur, arsenic, phosphorus, and mercury, as well as numerous compound bodies
with high boiling points, could have been tried.
The force of gravity is thus of importance in chemistry, by giv.
ing a measure of the quantity of matter upon which we experiment.
and by affording characteristics of individual substances, by the
comparison of the quantity of matter they possess in a standard
volume. The force of cohesion, although not so universally existant as that of gravity, is of equal interest, from the numerous peculiarities in its activity which almost everybody is capable of presenting, and by which bodies are remarkably distinguished fronm
each other. To understand, however, the nature of cohesive forces,
and the causes of the variation of their energy, it is necessary to
notice those ideas of the peculiar constitution of matter on which
philosophers have generally agreed, and which result from, while
they best serve to explain, those remarkable phenomena.
From the earliest period in science, discussions have arisen as to
whether the masses of matter which we ordinarily employ should
be considered capable of infinite division, or whether, by continuing
to divide, a term should ultimately be found at which no farther subdivision could be made; that thus the ultimate constituent and indivisible particles, or atoms, which, by their aggregation, form sensible
masses, should be discovered. By no appeal to experiment can this
question be resolved; when we call in the assistance of our most
powerful means of mechanical division, we attain only to producing
powders, of which the finest particle is, in miniature, all that the
mass from which it had been formed was upon a larger scale, and
capable evidently of just as much subdivision, if our mechanical
processes were perfect enough to enable us to proceed.
That this divisibility may actually occur to an almost incredible
degree, may be easily demonstrated by experiment.  In gilding silver wire, a grain of gold is spread over a surface of 1400 square
inches; and as, when examined in a microscope, the gold upon the
thousandth of a linear inch, or one millionth of a square inch, is
distinctly visible, it is proved that gold may be divided into particles
of at least r. oo.0oo.ooo of a square inch in size, and yet possess




16            DIVISIBILITY OF MATTER.
the colour and all other characters of the largest mass. If a graln
of copper be dissolved in nitric acid, and then in water of ammonia,
it will give a decided violet colour to 392 cubic inches of water.
Even supposing that each portion of the liquor of the size of a grain
of sand, and of which there are a million in a cubic inch, contains
only one particle of copper, the grain must have divided itself into
392 million parts. A single drop of a strong solution of indigo,
wherein at least 500'000 distinctly visible portions can be shown,
colours- 1000 cubic inches of water; and as this mass of water contains certainly 500-000 times the bulk of the drop of indigo solution,
the particles of the indigo must be smaller than  *.ow  0l o.o 0 0 the
twenty-five hundred millionth of a cubic inch. A rather more dis
tinct experiment is the following: if we dissolve a fragment of sil.
ver, of 0'01 of a cubic line in size, in nitric acid, it will render distinctly milky 500 cubic inches of a clear solution of common salt.
Hence the magnitude of each particle of silver cannot exceed, but
must rather fall far short of, a billionth of a cubic line. To render
the idea of this degree of divisiona more distinct than the mere mention of so imperfectly conceivable a number as a billion could effect,
it may be added, that a man, to reckon with a watch, counting day
and night, a single billion of seconds, would require 31.675 years.
In the organized kingdoms of nature even this excessive tenuity
of matter is far surpassed. An Irish girl has spun linen yarn of
which a pound was 14,32 English miles in length, and of whicl, consequently, 17 lbs. 13 oz. would have girt the globe; a distinctly visible
portion of such thread could not have weighed more than as'.-  -., 0 o 
of a grain. Cotton has been spun so that a pound of thread was
203'000 yards in length, and wool 168'000 yards. And yet thfese,
so far from being ultimate particles of matter, must have contained
more than one vegetable-or animal fibre; that fibre being itself of
complex organization, and built up of an indefinitely great number
of more simple forms of matter.
The microscope has, however, revealed to us still greater wonders
as to the degree of minuteness which even complex bodies are capable of possessing. Each new improvement in our instruments
displays to us new races of animals, too minute to be observed be.
fore, and of which it would require the heaping together of millions
upon millions to be visible to the naked eye. And yet these animals live and feed, and have their organs for locomotion and prehension, their appetites to gratify, their dangers to avoid. They possess
circulating systems often highly complex, and blood, with globules
bearing to them, by analogy, the same proportion in size that our
blood globules do to us; and yet these globules, themselves organ
ized, possessed of definite structure, lead us merely to a point where
all power of distinct conception ceases; where we discover that
nothing is great or small but by comparison, and that presented by
Nature on the one hand with magnitudes infinitely great, and on the
other with as inconceivable minuteness, it only remains to bow down
before the omnipotence of Nature's Lord, and own our inability to
understand Him.
These proofs of great divisibility, however, leave the question of
infinite divisibility quite untouched. There are, however, many and




MOLECULAR  CONSTITUTION.
powerful reasons which have decided almost all modern philosophers
to consider the possible division as being finite. On the other view
the mind has no resting-place, until, by the total disappearance ot
material conceptions, the constitution of bodies resolves itself into
a collection of mathematical points, from which, as centres, certain
forces are exerted; but with such abstract speculation chemistry
has no connexion. Its fundamental condition, that there exist many
kinds of elementary matter, of which the quantity is measured by
their weight, is totally independent of our abstract idea of what mat
ter is, or how its properties have their source.
In proof of the division of matter having a limit, experiments
made principally by Faraday and Wollaston have been quoted. Thus,
it is ascertained that our atmosphere does not extend into space,
but is confined within comparatively a trifling distance from the
earth, about 4~5 miles. Wfollaston, considering the particles of air
as being balanced between their mutual repulsion and the general attraction towards the earth, suggested that, if these particles could be
divided to an infinite degree, there should be an infinite source of
repulsive power, and hence, at a certain distance, this repulsion overcoming the gravitating force, the atmosphere should spread fintao
space, and, being attracted to the other planets in proportion to their
masses, should form round the larger, as Jupiter, and especially the
Sun, vast and dense atmospheres, the existence of which should
easily be recognised. No such atmospheres exist, and hence, as
was argued by Wollaston, the force of repulsion must have a finite
limit, and the number of repelling particles cannot be infinite. In
like manner, Faraday found that bodies, in evaporating, form atmospheres of certain definite depths above the surface of the body, and
drew from hence the same conclusion.  This argument cannot, however, be considered as decisive. It is not at all certain that, because
the elasticity of air is thus found to have a limit, the number of
particles of air, in a given space, might not be infinite.
I shall consider the masses of matter, whose properties we purpose to examine, as being made up of a great number of lesser masses,
to which the name of molecules or particles may be assigned. It
is totally indifferent whether these molecules may be infinitely divisible or not; there is no fact in either chemistry or physics which
requires the positive adoption of either one side or the other. These
molecules are subjected to the influence of two forces, which oppose
each other, and by the relative balancing or preponderance of which,
all the forms and physical properties of ordinary substances are produced. One of these forces is attractive; it is the attraction of aggregation, as it has been termed, or cohesion. If it acted unimpeded,
the molecules of every portion of matter would cohere with insuperable power; unconquerable solidity, hardness, and tenacity would
alone characterize external nature. The other force is one of repulsion, which, from a variety of evidence, is assumed as identical with
the cause of heat. If it alone prevailed, no other form of matter
could exist but that of gas; the solid globe, the liquid waters, would
change to atmospheres of vapours, and the beneficent uses to which
our earth is now adapted could not exist.
Such is, perhaps, approximatively what occurs in those extreme
C




18            STATES OF AGGREGATION.
members of our planetary system, Herschel and Mercury. The former receiving from the Sun but 4 part of the heat which our earth
derives, must be reduced to the temperature of empty space; and,
with few exceptions, the bodies which on this earth are gaseous or
liquid, if they exist, are there as rocky masses.  The latter must at
certain periods be so hot, that quicksilver would naturally be a gas
upon its surface, and those metals which here constitute our examples
of solidity, should there form liquid oceans. On this earth, however,
according as the forces of heat and cohesion vary in different bodies,
they pass through different states of aggregation. Those bodies in
which cohesion prevails are solid, and by their tenacity and resistance to breakage or change of form, display the force which binds
their molecules together. Where cohesion has been suppressed, and
the repulsive agency of heat acts uncontrolled, the body becomes
gaseous, and its particles, devoid of the least trace of cohesive power,
repel each other. In intermediate cases, where the two forces appear balanced, the particles do not cohere, and hence may move
upon and separate from each other without any external force; but
they do not repel, and thus remain in contact if no external force
tends to disturb them. This is the liquid condition; it is that of
water, of alcohol, of oil, while air and steam are gaseous, and iron,
wood, and stone are instances of the solid form.
The peculiar nature of each body determines whether, under common circumstances, it shall have one or the other of these forms;
but there are few bodies which are not capable of assuming all the
three. This is artificially effected by diminishing or increasing the
degree of heat, and thus by cooling a liquid, it may, by the cohesion
becoming greater, be converted into a solid; or by increasing the
heat to which a solid is subjected, it may be converted into a liquid, and from thence into a gas. One liquid, pure alcohol, has not
yet been frozen; some solids, as charcoal, have not yet been melted:
organized bodies are generally decomposed too easily to allow of
a change of state; but, with these exceptions, the principle of the
change of form, artificially caused by the increase or diminution of
the quantity of heat, is universal. These forms of matter, considered as effects of heat, will require and obtain hereafter a more
extended notice.
This force of molecular cohesion acts only at distances so minute
as to escape the most delicate examination. The fragments of a
piece of glass or metal which has been just broken, when laid ever
so closely together, have no tendency to unite again; but, if the
surfaces be pressed together, union may take place, though only
in a few points, and imperfectly. Yet, when pieces of plate glass,
laid flat on each other, and subjected to considerable pressure, are
allowed so to remain for a certain time, they are found to grow together so completely, that thick masses may often be ground as if
they had always formed a single piece. If two surfaces of lead be
cut quite clean and bright, and forcibly pressed together, they unite
also, and may require a force of eighty or one hundred pounds to
effect their separation. In fluids, altbhough the force of cohesion
is very nearly absent, yet it is not entirely so; the viscidity of
fluids depending upon the traces of it which remain. The globular
form of a rain drop, or of a drop of any fluid allowed to fall from




CO  E SIO N.-C AP I  L LAItR I T Y.            19
a point, arises also from the cohesive attraction of its particles, and
different fluids differ remarkably in their relations to heat, fromn the
various decrees of force with which this residue of cohesion is exerted.  The particles of a fluid cohere not only to each other, but
even more powerfully to solid bodies in many cases.  It is thus
that solid bodies are wetted by fluids.  If the finger be dipped into
water, the particles of the water in contact with the finger adhere
to it more powerfully than they do to the other particles of the
fluid, and when the finger is removed, they accompany it, and thus
it becomes wet. Mercury does not wet the finger, for its particles
cohere too powerfully to each other; but mercury adheres to, or
wets a piece of gold, as water wets the finger.  From this cohesion of fluids to solids, all the phenomena of capillary attraction
result, as the filtering of liquids in pharmacy and chemistry, to separate solids which had been mixed with them; the absorption of
liquids by porous solid bodies, and many others.
The existence of this form of cohesion may be very simply shown
by an experiment, such
as is illustrated in the
figure. A disk of any
substance. which may
be wetted by water is
to be hung evenly from
the extremity of the
beam  of the balance,
and  brought exactly
into contact with the                       -
water in the cup below. It will be found necessary to augment considerably the weights
in the scale dish opposite, to separate them; and, when the disk has
been torn away from the surface of the water, the force overcome
will be found to have been, not that of the solid to the liquid, which
was still more intense, but the cohesion of the liquid particles to each
other; for the solid is found to be wetted by a layer of liquid particles which it had torn from the general mass of liquid underneath.
If the experiment be tried with a disk of polished iron, and mercury
as the fluid, there is no wetting, and the force measured is really
the cohesion of the solid to the fluid.
[Clairaut found, as the result of his mathematical investigations,
that all the phenomena of capillary tubes depend upon the relation
of two forces: 1st, The cohesion of the particles of the fluid for
each other; and, 2d, The attraction of the particles of the solid for
those of the fluid.  When a glass tube is dipped into different
liquids: if the force of attraction of the glass is less than half the
force of cohesion of the fluid, the fluid will be
depressed, and not rise to its hydrostatic level;       d
if it be equal to half, the fluid will come pre-a  
ciselv to its level; and if it be more than half,
the fluid will rise in the tube.                     a -
Connected with these conditions is the figure
of the boundary surface of the fluid.  If three
glass tubes, b c, d e, fg, be placed in fluids which a  e 
respectively are depressed, at the true level, or at




20                   C   P RE S SI B I L I TY.
an elevation, it will be seen that in b c the surface a a of the fluid
is convex, in d e it is plane, and inafg it is concave.]
The particles of a body being held at certain distances from each
other by the balance of their attraction and repulsion: if, by the application of an external force, as pressure, they be brought nearer,
so as to occupy a smaller volume, the body is said to be compressible.  If, when the external force is removred, the body, by the mu tual
repulsion of its particles, regain its original volume, it is said to be
elastic; if, on the contrary, it remains as when compressed, it is
called inelastic. In nature there are few bodies perfectly elastic, and
none which can be said to be perfectly inelastic. In solid bodies,
when pressure produces a change of volume, some traces of it are
permanent; but in liquids and in gases, the restoration to the original bulk appears to be complete.
The amount to which solid and liquid bodies may be compressed
is very small, so much so that very delicate methods are necessary
to determine it.  Thus it requires a pressure of about 400 lbs. upon
each square inch of the surface of water to diminish its volume by
the T-0j-10 part. In gases, however, the repulsive force acting without
interference, and the particles being at much:greater distancesfrom
one another than in the liquid or solid form, the amount of compressibility becomes very much increased, and the law by which it
is regulated extremely simple, being, that the volume of any gas
varies inversely as the pressure upon it; that it is doubled if the
pressure be diminished to one half, and reduced to one half if the
pressure upon its surface be doubled. Thus, sutpposing a gas to
measure 100 volumes under the pressure of 20 lbs.,
Then with pressures of 80. 40. 20.  10.   5 lbs.
The volume becomes  25. 50. 100. 200. 400.
The gases which are used in chemical operations are liable to
constant changes of volume, from the alterations in the weight of
the surrounding atmosphere, by which they are always pressed; and
hence, before we can tell how much of a gas we really have obtained
by any process, it is necessary to ascertain the amount of atmospheric pressure, and to allow for it.  The pressure which the air
exercises is measured by the barometer, in which a column of quicksilver balances the pressure of the air, and varies in height according
as this changes; the height of this mercurial column being accurately
measured by a scale applied to the tube of the barometer.  In these
countries, the height of the barometric column fluctuates between
28 and 31 inches, but the average height of a year is about 29'8
inches.  For simplicity, a number very near this, 30 inches, is taken
as the standard pressure; and whenever the specific gravity, or the
volume of a gas is given, without particular remark, this standard
height of the barometer is understood to be the pressure.
If, therefore, we have a gas at a different pressure, it is usual, and often necessary, to reduce its volume to what it should have been under the standard pressure,
or, as it is generally termed, to correct for pressure: to do this, we use the rule
given above for the change of volume with the pressure. Thus, if, in an analysis
of morphia, we obtain 4'54 cubic inches of nitrogen gas when the barometer is at
28'5 inches, we say that, expressing the volume at 30 inches by V,
28.5
V   28.5:  454: 30, or Y-    X4'54=4'313.




LIQUEFA'CTION  OF  GASES.                         21
Knowing, then, the weight of 100 eubki inches of nitrogen gas at 30 inches, the
weight of 4:313 is easily obtained.
In this manner, the corrections for pressure, alluded to in the description of the
modes of taking the specific gravities of gases and of vapours, are introduced.
Thus, in taking the specific gravity of steam by Gay Lussac's process (page 14),
the vapour occupying but a portion of the tube, there remains a column of mercury,
suppose 5 inches high: the pressure on the vapour is therefore only the difference
between that and the external pressure, and if this be 30 inches, is (30 —5)-25.
Then the measured volume of the steam is to what it should be at the standard
pressure, as 30 to 25.
In certain cases, of which atmospheric air may be taken as an
example, this rule, of the volume being inversely as the pressure,
holds exactly; but there are many other gases, in which, when the
compression is very great, the particles appear to be brought within
the sphere of their respective cohesive forces, and the volume diminishes more rapidly than it ought by the rule.  Thus, if a tube
full of air and a tube full of sulphurous acid gas be exposed to exactly the same pressure, the volumes will not diminish in the same
degree when the pressure becomes high, but as follows:
Tlhe air as..      1000.  853.  559.  314.
Sulphurous acid as 1000.  851.  554.  301
In some other gases the same variation has been observed.
If such a gas be still more violently compressed, its particles may
be brought so completely within the sphere of cohesive action, that
this force comes into active play, and the body changes from  the
gaseous to the liquid form. Thus many gases have been liquefied
by a degree of pressure which differs for each gas, and is at 3~o
Fahrenheit as follows:
Name of gas.        Atmospheres.  Pouthe Inch. 
Nitrous Oxide........   44        660
Carbonic Acid........   36    540
Muriatic Acid........   24       360
Sulphuretted Hydrogen.....   15    225
Ammonia..........    5            75
Cyanogen..........    3           45
Sulphurous Acid.......     2      30
Other gases, such as oxygen, hydrogen, and nitrogen, have been
subjected to a pressure of 800 atmospheres, not only without becoming- liquid, but without even deviating from the rule which implies
perfect elasticity, and hence without even approximating to the
term at which they should abandon the gaseous state. Notwithstanding this, we cannot consider that there is any physical difference of constitution between those liquefiable and non-liquefiable
gases, and hence the conclusion i%, that, by a suitable increase of
prt ssure, the molecules of all gases might be so brought into coherent approximation, and converted into liquids.
With regard to the means of applying such pressure, and actually
obtaining those gases in the liquid form, it is necessary to consider
the manner in which such gases are generated, and such methods
will consequently be described in the history of those bodies.
Cohesion is thus antagonistic to the force of heat, which tends to
render the molecules of a body repulsive to each other, and to separate them to greater distances from each other than they had been




22                PHENOMENA OF SOLUTION.
before.  Cohesion is therefore diminished, and even annulled, by
applying heat.
When the cohesion between the particles of a solid and those of
a fluid is more powerful than between the particles of the solid itself, the latter is not merely moistened by the fluid, but it abandons
altogether the solid form, and, becoming liquid, mixes uniformly with
the fluid, and is said to have been dissolved by it. By this peculiarity of cohesion, bodies are divided into the soluble and the insoluble.
Thus common salt and Glauber's salt are soluble, while chalk and
white lead are insoluble, in water. These classes are, however, connected by a series of intermediate degrees of sparingly soluble
bodies, such as cream of tartar and plaster of Paris. Bodies which
are insoluble in water may be yet easily dissolved by other fluids;
thus, resinous bodies, which do not dissolve in water, dissolve in alcohol.  A great deal of the success of vegetable proximate analysis
depends on the skill with which the solvent powers of various fluids
may be successively applied.
From the tendency of heat to diminish the force of cohesion, it naturally results
that the solubility of' most bodies is increased by heat; thus, 100 parts of water, at
60~ F., dissolve 11 of sulphate of potash, and at 212 dissolve 25. At 60~, 32 parts
of dry sulphate of magnesia are dissolved by 100 of water, but 74 at 212~. This,
however, is not always the case; some bodies, as common salt, are exactly equally
soluble in water at all temperatures, while in other cases the solubility is greater at
particular temperatures than either above or below them. Of this peculiarity, the
sulphate and nitrate of soda are examples. Thus, 100 parts of water dissolve of
dry sulphate of soda, at 32~, 5'02; at 520, 10-22; at 760, 28; at 93~, 53; at 122~,
47; and at 2120, 42: the solubility increasing up to 930, and from thence diminishing.  100 parts of water dissolve of nitrate of soda, at 210, 63; at 32~, 80; at
50~, 23; 60~, 55; and at 246~, 218 parts. Here the peculiarity is of the opposite
kind to what occurs with sulphate of soda: the solubility diminishing up to 500~,
and from thence progressively increasing.
The solubility of bodies in water may be strikingly represented to the eye by
means of a kind of map, such as is given in the figure. The horizontal lines represent the quantities of the salt dissolved by 100 parts of water, while the vertical
lines represent the temperatures. Thus the line of sulphate of soda commences
70                                                - 
20                                7 / -726 90s  1  1  15-i 7 10 2_
35          I.,       ~, I I         Les -" " I
100   t
32~  52~  72~   92~  112~  132~ 1520 172~ 192~  212~  2320




FORMATION OF CRYSTALS.                            23
at the temperature of 320 at the horizontal line 5, mnd, rising rapidly, cuts the horizontal line 10 at 52~, cuts the line of 40 at 88', and attains its highest point of 53
at 93~; from thence it commences to redescend, until at 2320 there are only 42
parts dissolved. The line of chloride of sodium is horizontal, showing that it is
equally soluble at all temperatures, and in the other cases the construction of the
scale is easily seen on inspection.
In general, when solid bodies dissolve in a fluid, there is cold produced, but occasionally the solution is accompanied with a remarkable evolution of heat; this
last occurs when bodies which naturally contain water, chemically combined, are
deprived of it by heat, and when thus dried, dissolved; in such cases, it is probable
that the one portion of water is taken by the salt into a state of intimate chemical
combination, and thus more heat produced than counteracts the cold which should
arise from the mere solution of the hydrated salt thus formed. Such examples may
be found in dry chloride of calcium, the dry sulphates of copper, or of zinc and iron.
Solution is very much promoted by agitation, by the minute division of the solid, and generally by all causes which tend to facilitate the contact of the solid and liquid particles.  WThen the liquid
has dissolved as much of the solid as possible, it is said to be saturated.  The cohesion of the liquid to the solid having been reduced
to an equality with that of the particles of the solid for each other,
it can dissolve no more.
If a saturated solution be so circumstanced as to diminish the
cohesion of the particles of the solid to each other, a portion of
the solid separates, the amount of which depends on the new conditions under which the liquid is placed.  Thus, if to a solution of
nitre in water there be added spirits of wine, the water mixes with
the spirits of wine and abandons the nitre, which is precipitated
If strong muriatic acid be added to a solution of chloride of barium
in water, the water is taken by the acid, and the salt falls down as a
white powder. But the most usual case is where the separation
of the solid is produced by the cohesion of its own particles, which,
slowly abandoning the liquid, dispose themselves according to certain laws, and, assuming regular geometrical forms, are termed
crystals. Solid bodies, in separating slowly from liquids in which
they had been dissolved, in general thus crystallitze, and the figures
of these crystals being, to a great extent, characteristic of the
bodies, deserve minute attention.
To obtain substances regularly crystallized, several processes
may be followed, according to the nature of the body.  Where the
substance is soluble, and more soluble in a hot than in a cold liquid,
a saturated boiling solution may be made and allowed to cool.  The
excess of the solid body crystallizes out on cooling. Thus, if 151
parts of sulphate of magnesia in crystals be dissolved in 100 parts
of boiling water, and allowed to cool to 600, a quantity of crystals
will be obtained weighing 86 parts; for at 60' the 100 of water can
only dissolve 65, and the difference between that and the 151,
which had been dissolved by the boiling water, must crystallize.
If the body be, like common salt, equally soluble in water at all
temperatures, the above process cannot be applied, and a quantity
of the liquid must be removed by evaporation; the portion of salt
corresponding to the quantity of water which has passed away, is
thus obtained solid. If the evaporation be slowly carried on, so
that the formation of the crystals is not disturbed by the boiling of
the liquid, they form regularly, and may attain to considerable size.
In many cases the bodies which it is necessary to obtain crys



24                 CRYSTALLIZATION.
tallized are not soluble, or it may be wished to obtain crystals oth
erwise than by solution. By melting a solid substance, its particles
are allowed liberty of motion; and when it again commences to
solidify, they may arrange themselves regularly, and crystallize.
Almost all bodies, when melted, and then allowed to solidify, do
thus crystallize; but the spaces left between the crystals which
first form being completely filled up by the portions which solidify
afterward, there remains only a general crystalline structure, visible in the fracture of the body. Thus cast iron, sulphur, zinc, &c.,
have crystalline fractures. The beautiful feathered appearance
given to sheet tin by washing with dilute acid, and which was so
popular some years ago under the name of moiree metallique, was
simply this crystalline structure, displayed by removing the thin
layer of metal on the outside, which had solidified too rapidly to
have acquired any trace of crystallization. To obtain, therefore,
the metals crystallized by fusion, the excess of liquid metal must
be removed from around the crystals that are first formed. A
quantity of the metal or of sulphur, having been melted in a cup,
is to be allowed to cool until a solid crust has formed upon the
surface and at the sides to a certain depth; two apertures must
then be made in the upper crust, and the fluid metal
~ ~~;~   remaining be poured out at the one aperture, while
the air enters at the other to supply its place. On
then breaking the vessel, the interior of the solid
layer of metal or sulphur is generally found lined
-'       with well-formed and characteristic crystals, as represented in the figure.
Bodies may also be crystallized by sublimation. When a substance has been converted into vapour, and that, in condensing, it
assumes at once the solid form, its particles arrange themselves so
as to form crystals. Thus are obtained in fine crystals, arsenic,
arsenious acid, corrosive sublimate, benzoic acid, &c.
It frequently happens that the same body may be obtained crys.
tallized by more than one of these processes. Thus, corrosive sub.
limate may be crystallized by solution or by sublimation; sulphur
may be crystallized either by fusion or by solution. It is remarkable that, when this occurs, the crystals obtained by the two pro.
cesses are never of the same shape; they have not even any simple
relation of figure to one another, but indicate a totally different
mode of arrangement of particles, induced probably, at least in
part, by the different temperatures at which the change of state of
aggregation may have occurred. A body which crystallizes thus
in two ways is said to be divnophous, and this character will be
found hereafter of the highest importance in the theory of the
atomic constitution of compound bodies.
The more slowly the change of state occurs, the more regular,
and the larger, are the crystals that are formed. Hence, in practice,
solutions are left to cool very slowly, or to evaporate spontaneously; 
and sublimation is effected by the most gentle heat that can be ad"
vantageously applied. To favour the deposition of the particles,
a variety of artificial acids may be applied, Thus, crystallization
takes place better in a pan with some little roughness at the sides




CRYST ALL I ZA TI O N.                    25
than when it is quite smooth, and threads are hung in sirup to pro
mote the crystallization of the sugar-candy; a little crystal of the
same kind of salt is often introduced, to serve as a nucleus round
which the new crystals may gather; and, in a solution containing
many salts, the nature of the salt which shall crystallize may be
determined by the nature of the little crystal introduced: thus, if
equal parts of nitre and of Glauber's salt be mixed and dissolved
in five parts of water, and the solution divided between two similar
dishes; on a crystal of nitre being laid in one dish and a crystal
of Glauber's salt being laid in the other, a crystallization of pure
nitre will occur in the former, while nothing but Glauber's salt will
crystallize in the latter dish.  Salts which are mixed together in
solution may also be separated from one another by their respective
solubilities: thus, if sea-water be evaporated, common salt alone
will be deposited according as the liquor boils away; when it has
been removed from the fire no more common salt separates, but
Epsom salt will crystallize, and, after it has been removed, the liquor
will be found to contain chloride and iodide of magnesium.  The
liquor from which crystals have separated is called the Mlother
liquor.
Crystals occasionally form  in a body, although it may remain
completely solid. Thus, when copper wire has been kept some
time in the laboratory, it becomes a mass of cubical crystals, and
its tenacity is almost completely lost. When sugar is melted and
allowed to cool, it forms a perfectly transparent hard mass, destitute of any trace of crystalline arrangement, but after some months
it becomes opaque and white, having changed into ordinary crystallized sugar. In eases, also, where bodies are dimorphous, one
form is generally unstable, and the body, when crystallized in it,
changes after some time into the other form. This takes place remarkably with sulphur, and will hereafter be again referred to.
A solution of a salt, saturated at a high temperature, is found
occasionally to remain without crystallizing, although cooled to a
very low degree. In such case, on introducing a little crystal, or
agitating the liquor, it suddenly crystallizes, and frequently solidifies into one mass. Sulphate of soda is remarkable for its tendency to assume this indifference to crystallization.  If two parts of
crystallized sulphate of soda be dissolved in one part of water, at
93', and the solution be laid aside to cool, without being disturbed,
it remains quite clear and liquid; but, on producing crystallization
by any of the means just stated, the whole becomes solid.
In all cases of crystallization there is heat evolved, consequent
on the general law of heat being given out when a liquid or vapour becomes solid. There is sometimes a remarkable evolution
of light, to which I shall refer again, Indeed, crystallization is
sensibly afeected by the presence or absence of light. If a dish,
half covered by paper, be set aside with a solution to crystallize,
but few crystals will form  in the dark, although there may be an
abundant crop on the illuminated portion of the vessel.
It has been noticed, that when a body has been obtained, crystallized at different temperatures, as by solution and fusion, the
crvstalline form is generally different, and the body is said to be
D




26      PRIMARY  AND  SECONDARY  CRYSTALS.
dimorphous.  In this case, the two forms are totally diflerent in
their geometrical character.  But independent of this, a body may,
even simply by solution, be obtained, crystallized in a great variety
of forms. In a crop of crystals of sulphate of iron or of alum, obtained by cooling from a hot solution, a great many different figures may
be observed, which, however, are, on examination, all referrible to
one more regular and fundamental form.  Each substance has thus
a characteristic form of crystal, which is termed its primary form;
and it may assume a great variety of figures; produced by modifications of this form: these are termed secondary forms. Thus,
carbonate of lime has been found crystallized in more than six
hundred different secondary forms, all derivable, however, from the
one original primary figure, the rhombohedron. The growth of a
crystal depending on the deposition of new layers of particles
over its external surface, any change in the quantity deposited on
each side will naturally produce a change of form. It is therefore necessary, when crystals are left long in a solution, to turn
them, and change their position frequently, as otherwise the growth
would take place on some sides rather than others, and secondary
forms would be produced, by which the characteristic figure of the
crystal would be injured.
The most ordinary source of change of figure consists in the replacement of an
edge or of an angle by a plane. Thus one of the simplest figures of crystals is
the cube a; it has eight edges and eight solid angles. The effect of substituting
plane surfaces for the edges is to produce the secondary form b, and by replacing
the solid angles by planes, the form c; when these replacements occur together,
XC                      b i I   b            c
the more complex figure d is produced. If the edges of the cube be replaced until
all traces of the original planes disappear, the figure e, the rhombic dodecahedron,
is produced; and if the replacement of the solid angles by planes be carried on to
d                              /
tne same extent, there is formed a regular octohedron f. These last are again simple and primary forms, for by a similar move of replacement they may be reduced
to each other or to the cube.
When a crystal augments in size by the deposition of layers of
fresh material upon its faces, the moleculax cohesion in each new
layer is greater than its cohesion to the laver. underneath, and hence,
by skilful splitting, a crystal may be separated into a number of
plates, exhibiting the order of its formation. The direction in
which a crystal may be split is termed its cleavage, and it is of great
importance in the determination of the primary form of the crys



REGULAR  SYSTEM.                                27
tal, for it often occurs that the same secondary form may be produced by two different primary forms, and in such case, the cleavage being simply related to the surfaces of the true primary form,
determines which it is.
Notwithstanding the immense variety of forms of crystals which exist, they may
yet be reduced to a very few classes, by conceiving them to be formed by their particles being built up around certain axes, which pass through the centre of the crystal, and the relative position and magnitude of which determine the manner in which
the particles are arranged.
In this way there may be formed six systems of crystallization, characterized as
follows:
1st System.  The Regular System. The three axes are all equal in length, and
are at right angles to each other.
2d System.  The Rhombohedral System has three axes equal in length, which
are placed, however, at equal angles (600) with each other, and are all in the same
plane, while a fourth and unequal axis is at right angles to that plane.
3d System.  The Square Prismatic System has the three axes at right angles to
each other, but there are only two of them equal; the third is either longex or shorter
than the other two.
4th System.  The Right Prismatic System has the three axes at right angles to
each other, but there are no two of them of the same length.
5th System.  The Oblique Prismatic System has two of the axes making an acute
angle with each other, while the third is placed at right angles to both. The three
axes are all unequal in length.
6th System.  The Doubly Oblique Prismatic System has all the axes unequal in
length, and making acute angles with one another.
The various actual forms of crystals, both primary and secondary, are derivable
from the manner in which the plane surfaces of the crystals may be applied around
these axes. In order to conceive the application of the planes, the axes shall be
considered as placed with one in a vertical position, and it is called the principal
axis. The nature of the system determines which axis should be selected.
In the Regular System, the axes being all equal, it is a matter of indifference
which is chosen as the principal axis, and their perfect symmetry is also a reason
that the portions of the crystal around each axis must be completely similar. The
number of forms belonging to this system is consequently not very large, and they
are remarkable for their simplicity. Thus, when each plane cuts the axes at equal
distances from the centre, the forin is the octohedron, and as the planes must be
equally inclined to all the axes, it is the regular octohedron f, of which each plane
is an equilateral triangle. When each face of the crystal cuts one axis at right angles, and is hence parallel to the other two, the form is the cube a. When each
face cuts two axes at equal distances from the centre, and is parallel to the third,
the figure which results is the rhombic dodecahedron e. By the combined positions
of sets of planes, other and more complicated (secondary) b, c, d, forms are produced,
arising from the partial coexistence of the conditions of the formation of two simple forms.
The crystals belonging to this system are generally very well defined and easily
recognised: a great number of important bodies crystallize
in the forms belonging to it: thus common salt, fluor spar,
galena, and iron pyrites, are found in cubes; alum in octohedrons; the garnet is found in dodecahedrons. When pure
metallic substances are found crystallized, it is always in    9..      g
forms belonging to this system; thus, bismuth, copper, silver, gold, crystallize in cubes, and lead in octohedrons.     /
A peculiarity of crystals, belonging particularly to this system and to the next, is, that every alternate face shall become
developed to such a degree as to obliterate the intervening
planes, and thus to generate a new form, having one half of            /
the number of planes. Thus a crystal of alum is very sel-            /
dom truly octohedral; it has usually the figure of g where        //
four of the sides of the octohedron have become very large,
while the other four remain very small. When the obliteration becomes complete, there is produced the tetrahedron, or
three-sided pyramid of fig. h, which is hence properly called




28     RHOM.BOHEDRAL  AND  SQUARE  SYSTE MS.
the hemioctohedron.  Such crystals are called hemihedral, from their containing
half the proper number of sides. Certain bodies have a natural tendency to hemihedral crystallization, and are but very rarely found with the proper number of
planes. The diamond is a remarkable instance of this. Its proper form is the regular octohedron, but its crystals are universally hemihedral.
In the Rhombohedral system, the supplementary, or fourth axis, is taken as the
principal axis, and the crystals are formed
by the planes being applied to these axes,      \ ] k
as in the former system. If the planes
be all inclined at the same angles to the
three horizontal axes, and cut the vertical axis, there is formed a double sixsided pyramid (i); and when the planes
are perpendicular to the horizontal axes, |
\\ \ ///  and parallel to the vertical axis, the sixsided prism (k) is produced. These forms
generally coexist in quartz, as in the figure
k. By the replacement of the edges in these forms there may
be produced others with twelve sides in place of six; as a twelvesided prism and a twelve-sided pyramid, of which quartz also
affords examples.
This system is more remarkable for its modified forms than for those simple figures above described, although the six-sided prism and sixsided pyramid are characteristic of very many substances.  If
we suppose, in the terminal six-sided pyramid, every alternate.   side, above and below, to grow at the expense of those next
it at each side, I will be formed. Ultimately the sides of the
prism  disappear, and there will remain 
a figure of six planes, of which all the
sides shall be equal and similar rhombs,
the rhombohedron, m, which gives its
name to this system, although it be but
a hemihedral modification of the true
typical form. The principal axis of the
rhombohedron is the vertical axis of the
pyramid, and the horizontal axes are found by joining the
solid angles to the centres of the opposite faces, where originally the lateral angles of the pyramid had been.
The carbonates of lime, of iron, and magnesia are remarkable for crystallizing
with this hemihedral figure. Even in the six-sided prism of carbonate of lime, the
rhombohedral tendency is evident by the crystal being terminated, not by the six-,
sided prism, as in quartz, but by its three hemihedral replacing planes.
3. The Square Prismatic System.-The crystals of this class differ from those of
the regular system in the vertical axis not being necessarily
~n              equal to the other two; but, on the contrary, being in almost
all cases either longer or shorter. VWhere there is formed
-   an octohedron, n, it di.ffers fiom the regular octohedron in
\  f/    the terminal angle of each plane being not 60~, but more or
\\  //   less. Its basis is, however, a square; and
to distinguish it from the octohedron of the
following system, it is termed the octohedron with the square base.
By the application of planes perpendicular to the horizontal axes, a
tour-sided pyramid with a square base is formed, o, and by the replacement of the terminal edges of this prism, four-sided pyramids
may be formed on its base and summit. By this property the square
prisms and octohedrons are distinguished from all modifications of
the cube and octohedron of the regular system. When the edge
of a cube is replaced, the plane substituted for it gains equally on  /
the two surfaces, and hence, when one is effaced, the other must
be so also. But in the square prisms the replacement may efface the terminal plane,
giving a four-sided pyramid, and yet the lateral planes be but little encroached upon.
The sides of the crystal in this system are thus independent of the top or bottom,
and may be modified, while the top and bottom remain unaltered; this never takes
place in the regular system, where, there being no one side particularly upper or
ower, all modifications must affect all sides alike.




PRIS MAT IC SYSTEMS.                                 29
4. The right Prismatic System.-In this system the three axes
being all unequal, the length, breadth, and thickness of the crystal may be different from each other.  Thus, in the octohedron,p,
formed by the application of planes, each connecting the extremi-       \ P
ties of the three axes, the three dimensions of the crystal, as in
the figure, which is the primitive form of sulphur, are unequal;
the octohedron has a rhombic base; and by planes which are in- 
clined to the horizontal axes, and parallel to the vertical axis, a
prism with a rhombic base may be produced.  This also, by combination of the two forms, may obtain pyramidal terminations, as
in some forms of native sulphur.
An important character of this system, which arises from there
being no necessary connexion between the two
horizontal axes, is, that the lateral edges may be
alternately modified -in a different manner; or, in other words, that,
/     looking at the crystal, its back and front may be differently affected
from its sides.  Of this an example may be found in a common
modification of the sulphur octohedron given in figure q.
\ I \  // 5. The oblique Prismatic Systemn..-From the manner in which
the crystals belonging to this system form. one of the oblique axes
is generally by much the most developed, and is taken as the principal axis.  The remaining axes, which are at right angles to each
other, are taken as horizontal, the principal axis making with them the acute angle,
which belongs to the peculiar body.
By means of planes which are inclined to all the axes, there is formed the oblique rhombic octohedron, such as characterizes gypsum
~f'~.. \... (sulphate of lime), as in figure r; and by means of planes'...- "~  -'"] —- which are inclined to two axes, but parallel
to the third, an oblique rhombic prism may
be formed, s. A remarkable character of
these crystals is, that from the crossing of the axes and their independence of each other, the front and back of the crystal may be
quite different in relation to the sides.  The crystals of sulphate
of soda, of carbonate of soda, of borax, of sulphate of iron, and of
feldspar, may be taken as examples of the numerous forms derivable from this system.
6, The doubly oblique Prismatic System.-The axes are all unequal, and all form acute angles with each other, and it is hence indifferent which is taken as the principal axis of the crystal.  The
consequence is complete absence of symmetry between any two surfaces of the
crystal, except such as, being at the ends of the same axis, are parallel to each other.
The complexity of crystals of this system is hence usually
t /               very great.  The simplest forims are the oblique rhombic
_/...... octohedron, t, and the oblique rhombic prism, formed by
planes inclined to all the axes, or to two, and parallel to the
third, respectively.  The soda feldspar (albit) and sulphur
of copper are examples of this system; the octohedron of
this system is figured in the margin.
It might be at first supposed that the assumption of these axes, or lines round
which we have supposed the crystalline particles to be regularly arranged, was
merely a geometrical fiction, by which the form of the crystal might be more easily
represented to the mind; but such is not the case. Evidence derived from a variety of sources agrees in demonstrating that this diversity of crystalline systems
arises from fundamental differences in the laws of molecular cohesion, by which
the formation of the crystal is regulated, and that these axes, which have been so
much alluded to, are real centres, the proportion and position of which determine
all the physical properties of the body. It is peculiarly from the action of crystallized bodies upon light that accurate and extraordinary information has been obtained of their internal structure, and the discoveries that have been made in this
department were the means of advancing the physical theory of light to its present
almost perfect state.
Substances may assume crystalline forms which do not properly belong to them
in many ways.  Thus, a group of crystals being imbedded in a rock, they may, by
the filtration of the water of springs across the rock, be dissolved out, leaving a hol



30    FORMS  MODIFIED  BY  FOREIGN  BODIES.
low mould of their form; and, subsequently, substances of another kind may be introduced into this cavity, and, solidifying there, may simulate the external form of
the original inhabitant. But these are no more real crystals than a mass of plaster
of Paris, which has solidified in a hollow mould, and comes out as an Apollo's head,
can be said to have so crystallized. By cleavage, and by the operation of polarized
light, the unsuited internal structure is recognised, and the crystal is stated to have
been merely pseudomor7phous. Another mode in which a body may come to have a
form not its own, is by remaining behind after the decomposition of the substance
which had really crystallized. Thus, when hydrated chloride of copper, which
crystallizes in fine green prisms, is carefully heated, the water is expelled, and the
chloride of copper remains dry, and of a fine yellowish-brown colour, in the original
crystalline form, and with the surfaces quite bright. The red iodide of mercury
combines with ammonia to form a substance which crystallizes in long prisms of a
snow-white colour; these, when exposed to the air, lose all ammonia, and the
iodide of mercury remains behind, pure, and of a brilliant red, but with the perfect
figure, and bright, smooth surfaces and sharp angles of the body originally crystallized.
It has been thought that the presence of foreign bodies in a solution, even where
they did not enter into combination with the substances which crystallized from it,
might modify their form. Thus, when common salt crystallizes in a solution of
urea, it is! deposited in octohedrons, and by dissolving alum in a solution of urea, it
may be obtained crystallized in cubes. But in this case, the substances which crystallize are no longer common salt nor alum, but the one, a combination of urea with
common salt, and the other, a basic alum produced by the mutual decomposition
of the urea and the alum. The presence of a trace of lead or tin in a large quantity of iodide of potassium, has been supposed to modify its form; but it is more likely
that the mechanical presence of an impurity of the kind may be supposed to produce
a tendency to macled crystals, and thus the external form be somewhat altered, although the true constitution of the crystal may remain the same.
Certain bodies, when they exist together in solution, may rermlarkably modify each other's form, by crystallizing together so
completely that every individual crystal shall contain a quantity of
each. Yet these bodies will not have combined chemically with
each other, for the quantity of each present in each crystal is quite
indefinite; they are mixed together mechanically in the crystals,
and hence the form of the actual crystal is intermediate between
those which the separate bodies should have had if they were
pure. In order that bodies may so crystallize together, it is not
only necessary that they should be of the same crystalline system,
but the crystalline forms must resemble one another very closely
in all their angles and sides. Thus, not only will iodide of potassium  and sulphate of soda, which belong to different systems of
crystallization, not crystallize together, but Glauber salt a-id carbonate of soda, which do belong to the same system, will not crystallize together, because the relations of their angles and sides being completely different, they cannot mix together so as to form  a
uniform solid. But sulphate of zinc and sulphate of mafgnesia belong not merely to the same crystalline system, but they are almost identical in their figures; the eye cannot make any distinction
between their crystals; and hence, when a crystal is being formed
in a solution containing these two bodies, the molecular and crystalline forces being the same for both, they concur in the building
of the crystal without interfering with each other. Hence, as there
is a very small difference between the angles of the rhombic prisms
of the two salts, the one being 90~ 30', and the other 91~ 8', if they
be mixed in equal proportions in the crystal, its angle must be 90~
439'. Carbonate of lime and carbonate of magnesia are, like the




ISOMORPH ISM.                            31
suiphates of zinc and magnesia, almost identical in crystalline form,
and they exist in nature mixed together, forming the dolomite or
magnesian limestone. The quantity of carbonate of lime is to the
quantity of carbonate of magnesia as 50'6 to 42'8; and as the angle
of the rhomb of carbonate of lime is 105~ 4', and that of carbonate
of magnesia is 107' 40', the angle of the mixed crystal is found
by mu'ltiplying the angle of each constituent by its quantity, adding
these products together, and dividing by the quantity of the mixture,
and the result is 106:) 15', the angle of the rhombic crystal of magnesian limestone.
The peculiarity of crystallization which such bodies possess may
be illustrated in another manner.  Ordinary alum  is a sulphate of
alumina and potash; but there are a great variety of other double
sulphates which crystallize in the same form, and which constitute
a well-defined crystalline genus. If an octohedral crystal of common alum be placed in a solution of the sulphate of alumina and
ammonia, the crystal augments in size by the addition of layers of
it.  If it be then removed to a solution of sulphate of potash and
peroxide of iron, it acquires another layer; by a solution of sulphate of ammonia and peroxide of iron another still; and by means
of solutions of the alums, which consist of oxide of chrome united
to potash or ammonia, with sulphuric acid, the crystal may grow to
a still greater size. The chemical constituents of the crystal may
thus vary, but it retains its form; the number of equivalents of
chemical substances contained in it remains also the same, although
they may not remain identical in nature. The potash and the ammonia on the one hand, the oxide of iron, the alumina, and the oxide of chrome on the other, agree in producing the same crystalline arrangement of particles; in impressing upon their compounds, with the same bodies, the same crystalline form. Bodies
so related are called isomorphous.'Oxide of zinc and magnesia, are
isomorphous; while lime is a dimorphous body, being in one form
isomorphous with magnesia, and in the other with oxide of lead.
Isomoypihous bodies are remarkably similar in their chemical properties; they follow generally the same laws of combination, and
hence, as shall be farther shown in the chapter on chemical affinity,
the principle of isomorphism has been of the highest importance
in developing the true relations of chemical substances to each
other, and the intimate connexion of the forces which produce the
chemical combination, and those which direct the crystalline arrangement of the particles of bodies.
It was, some time ago, considered an important question, whether the ultimate
particles of bodies had the same figure as their primary crystalline form, or whether they were glotbular or ellipsoidal. The law of isomorphism was considered, at
one time, to result from the ultimate particles of those bodies, being themselves
isomorphous; and hence, when entering into siinilar combinations, giving to them
also the same form. It was at another time referred to the principle that, in any
chemical combination, the crystalline form was determined by the number of molecules or atoms present, and was independent of their nature. Neither of these
ideas has been found sufficient; but the complete discussion of the relations of the
isomorlphous bodies will be found in a future chapter.
The angular dimensions of crystals being thus the measures by
which they are recognised and compared with one another, the
instruments by means of which their measurement is effected re



32              G O NI O ME TE RS.-L I G IT.
quire a few words' notice. They are called goniometers (yovtoc, an
angle; ytep(o, I measure).'The simplest form consists of a semicircular scale of degrees attached to a pail of blades, which, crossing
each other at the centre, allow of the crystal being adjusted exactly
to their edges, and then show the value of the angle by the  irnber
of degrees intercepted on the scale between the blades. For all
purposes requiring accuracy, the goniometer of Wollaston must be
applied. In it, the angle of the crystal is determined by measuring
the number of degrees through which it is necessary to turn the
crystal in order that two rays of light, reflected successively from
the two surfaces, including the angle, may be in exactly the same
direction. To the adoption of this principle of measurement we
owe almost all the great advance that has been lately made in the
relations of the crvstalYine forms of bodies to their chelical and
molecular constitution.
In all that has formed the subject of the chapter which has now
closed, the forces brought into play, and the effects which were produced by means of their action, were not such as to involve the
principle upon which all purely chemical phenomena are based, the
existence of a variety of elements. The laws of cohesion, from its
simplest action in a liquid to its most complex manifestation in a
double oblique crystal, might have existed in nature, and, being
studied, make a part of science, independent of any consideration
of true chemical force, although serving most usefully for the identification of chemical substances, and capable of modifying the circumstances of their mutual action in an eminent degree.
CHAPTER II.
OF THE PROPERTIES OF LIGHT AS CHARACTERIZING CHEMICAL SUBSTANCES
I SHALL not attempt to enter into the details of the history of the
mechanical properties of light, as they constitute one of the most
purely mathematical of the physical sciences, and have but indirectly
a relation to chemical phenomena: a short notice of these properties
is, however, necessary, in order that the means of recognising chemical substances may be fully given.
Light, emanating from any luminous body. moves in straight lines;
the smallest portion of it which can be admitted through an aperture
being termed a ray. When a ray of light falls upon the surface of
a body, it is either bent back again, or it passes into the substance
of the body; the bending back is termed reJfection, and is regulated
by the law, that the angles of incidence upon the surface, and of
reflection from it, are always equal. It is thus that the images are
formed in a looking-glass; for we see objects in the direction in
which the ray of light arrives at the eye, and hence we judge the
image to be as much behind the mirror as the object is before it.
When the ray of light has passed into the substance of the body,




PROPE RTIES OF  LIGHT.                        33
it may be absorbed, in which case the substance, not sending any light
to the eye, appears completely black, or is, rather, totally invisible,
except by contrast with some other body placed behind it; or the
light may be transmitted, in which case the body is said to be transparent, as the light may arrive at the eye after passing through the
substance. Bodies which do not transmit light are said to be opaque;
but there are two kinds of opacity, that of blackness, where the light
which falls upon the object is totally lost by being absorbed, and that
of whiteness, where the light is reflected, and we can see the object
itself, though we cannot see anything through it.  Where, in an
opaque body, the light is partly reflected to the eye and partly absorbed, there arises the diversity of colours which opaque bodies
may possess.
When the ray of light is neither totally reflected from the surface
nor lost within the substance of the body, but passes through it, it
is refracted; that is, its direction is changed; and if its path be represented by a line, it is broken at the surface of the medium, and
hence ihe name.  It is thus that an oar, partly immersed in water,
appears broken at the surface.  Any substance through which light
is moving is termed a medium, and the refraction occurs at the limiting surface of the two media, as air and water, air and glass, though
not to the same degree as' if the light had passed into the most refractive medium directly from an empty space. This refractive
power is of importance as a characteristic property of bodies, but
to the chemist it is specially of use in the study of crystallized bodies;
and it is hence with reference to the principles of the molecular
structure of those substances already noticed, that the refraction
of white lioht shall be examined.
This reflection, absorption, or transmission of the luminous rays
which fall upon the surface of a body is, however, in no case absolute and simple. All bodies reflect some light, and there are none
which allow light to pass through them without its undergoing some
absorption. In general, light incident upon a body is divided into
three unequal parts, of which one is reflected, another absorbed, and
the third transmitted, and the nature of the body determines which
action shall be most powerful.
In uncrystallized bodies, a ray of light, in passing from a rarer
te, a denser medium, is generally bent towards a line perpendicular
to the surface of the medium, and in passing from a denser to a rarer,
niedium, the refraction is from the perpendicular. In this case, the'
law of refraction is such that the sines of the angles of incidence
and refraction are to each other in a constant proportion, no matter
how the direction of the incident ray may change, and the number
which expresses this ratio is called the index of refraction.
T'he velocity with which light is transmitted is exceedingly great;
the light of the sun arrives at the earth in eight minutes, being at;
the rate of 195,000 miles in a second.  This, however, is but the
mean velocity of the coloured lights which a solr ray contains, for
these differ in velocity, those which are least refrangible being transmitted with the greatest quickness. The velocity of light is changed
when it passes from one substance to another, and it is this change
in which originates refraction.  In general, the denser the imedium.
E




34                      RE F RACT ION.
the more is the velocity diminished; and it was by the experimental
proof of this that one of the most triumphant testimonies in favour
of the undulatory theory of light was found.
The refractive power of a body is not connected with its chemical
constitution in any positive manner; but inflammable substances
are generally possessed of high refractive powers.  It was this
which led Newton to the celebrated prophecy that the diamond
should be combustible, and that water should possess an inflammable
constituent; but many bodies of high refracting powers are not at
all combustible.
The refracting power, as measured by the refractive index, is given for some of
the more remarkable bodies in the following table:
itealgar... 2549        Garnet... 1815
Octohedrite... 2500      Oil of cassia.  1 614.
Diamond.. 2'439      Plate glass.. 1542
Nitrate of lead..  2322      Oil of turpentine. 14-75
Phosphorus... 2224       Water... 1.336
Sulphur.... 2148       Chlorine... 1000772
Flint glass, from.. 2028   Air.... 1000294
to... 1830        Vacuum... 1 000
In uncrystallized bodies, the molecular arrangement being irregular and indefinite, the action upon light is the same in every direction, and hence a ray of light undergoes, when passing from air into
water or glass, simple ordinary refraction; it is bent out of its path
by an angle which depends upon the angle of incidence, by the law
of the proportionality of their sines. In bodies which crystallize
in the regular system, where there are three precisely similar axes,
the molecular constitution, although subjected to definite laws, must
be the same in all directions, and hence a ray of light will be acted
upon, in such a crystal, in the same manner, no matter in what direction it may go. Hence, in crystals of the regular system, there
is only ordinary refraction and a single image.
When a ray of light passes, however, into a crystal of the rhombohedral system, it is differently acted upon, according to the part
of the crystal it passes through. If it pass along the principal axis,
it is equally related on all sides to the crystalline forces, and hence,
as in the crystals of the regular system, there is only a single refracted ray.  But if the light pass in any other direction, it is divided into two portions, one of which is refracted according to the
ordinary law of the sines, while the other, following a totally new
law, is termed the extraordinary ray.  The angle which these two
rays make with each other increases according as the path of the
incident ray is farther from the principal axis; and when the light
falls perpendicular to the sides of the prism, and hence to the principal axis, the divergence of the two refracted rays is the greatest
possible.  In the square prismatic system, the same peculiar action
upon light exists; when a ray of light passes along the principal
axis of the crystal, it undergoes simple refraction according to the
ordinary law, but in any other direction the ray is subdivided into
two, of which one is refracted in the ordinary way, and the other
follows anew and peculiar law.
The existence of double refraction, and the change in its amount,
according to the, direction in which the light passes through the




DE C OMPOSITION  OF  LIGHT.                           35
crystal, may easily be observed.  If a round dot be marked with
ink on a sheet of paper, and a rhomb of calc-spar be laid upon it,
the dot will appear double, and on moving the crystal round, one
image will be seen to revolve round the other. By changing the
position of the eye, the distance between the two images of the dots
will be found to change; it will be greatest when the eye is in a line
connecting a solid angle and the centre of the opposite plane; but
to efface the double image and obtain single refraction, new surfaces would require to be cut perpendicular to the principal axis. In
a natural crystal there are, therefore, always two images of an object
seen through it.
In the remaining three classes of crystals, where the rhombic octohedron,
whether right or oblique, gives the predominant character to the forms, the existence of a molecular constitution, regulated by the same cause as the external figure, is displayed in a peculiarly striking manner. There is no longer a single line
in the crystal, in Mwhich ordinary refraction alone occurs, but there are two such
lines, or axes of simple refraction. These axes, however, do not now coincide
with the principal crystalline axis, as was the case when there was only one,. but
their position is so dependant on that of the crystalline axes as to show that they
are the resultants of the forces which emanate from them, and which govern all
the molecular actions of the crystal. If the ray of light does not pass exactly along
one of these axes, but at some distance from it, it is divided into two rays; and
of these rays, both follow.new and peculiar laws of refraction,.the proportionality of
the sines being totally abandoned. The real distinction of the crystalline systems
is thus completely proved by the existence of these remarkable optical properties
by which they are characterized; and so perfect is this distinction, that in cases
where the external form and cleavage would lead us totally astray, the optical
properties of the body may show us its true crystalline position.. Thus the mineral
boracite (borate of magnesia) crystallizes in cubes, which. are remarkable, however, for an anomalous replacement of the opposite solid angles by triangular planes.
When, however, horacite was optically examined, it was found to possess double
refraction, and to appear cubical only from the accidental circumstances of its rectangular axes being exactly equal to each other.
When a ray of white light, S, P, admitted into a darkened room
[nalro..C..                       Ic "~Lc  through an aperture,
Violet                                        $ HI, passes into a reBlue.... S j 9>i             fracting substance, a,
Grelen    I  =                                    A, B, C, whose surfaYellow..                                    A     Al.
Orange.e....''-.                                 ces are  parallel, its
R eod     L...,,-,,''t.        path after refraction
is parallel to its original course, and the
ray continues white;
C.i.-]                           but if the surfaces of
the refracting  medium  be not parallel, if it be a prism, A, B, C, the
ray of white light is separated into a number of rays of light, of
different colours and of different refrangibilities, as at g-; and if it
has been-derived from  the sun, in place of a round white image, P,
there is formed a series of solar images of differentcolours, which,
overlapping each other, produce a long band, which is termed the
prismatic spectrum, or image of the sun. The order of colours, the
same as that seen.in the rainbow, is, commencing with the rays of
greatest refrangibility, violet, indigo, blue, green, yellow, orange,
and red; the length of the spectrum, and the space otlcupied by
each colour, varying with the nature of the refracting body, according to what is termed its dispersive power.  White light is,
therefore, not a simple, but:a -highly complex phenomenon, con



36                PRISM-ATIC  COLOURS.
sisting of impressions made simultaneously on the eye by the
lights of these various colours. This may be verified by experiments of very simple performance: if a circular disk be painted
with the colours of the spectrum, in segments proportional to the
spaces which each colour occupies in the length of the spectrum,
and then be made to revolve rapidly on a central axis, the eye loses
the sensation of the individual colours, and a uniform grayishwhite tinge is produced: if we had colours as perfect as those of
pure solar light, their reunion would form pure white, and this actually may be produced by receiving the spectrum  on a lens, by
which all the coloured rays are brought to bear upon a single point,
the focus, where reproduction of the original white light takes place.
Herschel has recently discovered that there exists in the spectrum, beyond the limits of the violet rays, other rays of a still
higher refrangibility, and of a colour which he proposes to term
lavender.  This lavender light cannot be merely a weaker form of
violet light; for, on concentrating it by means of a lens, it remains
still unaltered, and appears to have no tendency to assume a violet
tinge when it becomes more intense. If this proposal be adopted,
there are then eight prismatic colours; and although some peculiarity of vision, with regard to colours, may cause a difference of
opinion,'yet the evidence obtained by Herschel of the real existence of simple lavender-coloured light appears to be satisfactory.
Of the seven prismatic colours, there are four which cannot be
considered as simple lights, but as being formed by the mixing of
rays of two different colours having the same refrangibility: these
are orange, green, indigo, and violet; the first being the mixture
of the superposing extremes of the red and yellow, the second of
the yellow and blue, and the third and fourth of blue with red remaining in excess. There are, in fact, blue, red, and yellow lights
spread over every portion of the spectrum; and if they were so in
equal quantities, the spectrum would be white, and we could not
have any decomposition of light by refraction; but, although there
are blue rays of every degree of refrangibility, yet the larger proportion of them  have a refrangibility greater than those of any
other colour, and they are hence collected nearer the upper extremity of the spectrum. A portion of red light is spread also over the
yhole surface, but the majority of the red rays, having low refranMNI3::      Crgibility, are thrown to the opposite extremity, while
the great proportion of the yellow rays, having a mean
-  R    refrangibility, occupy the centre. In every portion of
the spectrum there is therefore mixed, blue, red, yellow, and hence white light; but where these simple
lights prevail, the colours of the spectrum are produced, and where two are present in excess over the
quantities which form white light, the secondary colours, orange, green, indigo, and violet, are formed.
-  13    The intensity of these spectra of simple light in each
portion of the prismatic spectrum  is represented in
the figure by the distance of the curved lines, R, Y, B,
N           from the ground, M, N. Where the red rises beyond
the yellow and blue, the red space of the spectrum  is produced;
where the curve of the yellow light prevails, the space is coloured




ABSORPTION.-NATURAL COLOURS  OF BODIES. 37
yellow, and similarly in the blue; at the point where the curves
of the red and yellow meet, the tint is orange; where the yellow and
blue are equal, the colour produced is green; and where the red and
blue are both in excess over the intermediate yellow, there is violet.
This view of the constitution of the solar spectrum, leading to
the remarkable and unexpected consequence that there may be
white light unalterable by the prism, its coloured rays having all the
same degree of refrangibility, was obtained by Brewster, by means
of the absorbing power of coloured bodies. If a ray of white light
be incident upon a glass coloured red by suboxide of copper, it is
decomposed in passing through it, the yellow and blue lights being
intercepted or absorbed, and the red rays alone being transmitted.
A glass does not possess this property of absorbing certain kinds
of light, because it is coloured; but it appears coloured to our vision, because it acts so upon white light. The colours so given to
glass are of great importance, from the use which is made of them
for ornamental purposes in the arts; but they afford also to the
chemist one of the most delicate and most certain means of detecting many metallic substances, thus:
Cobalt is known by colouring glass blue.
Nickel    "   orange.
Chrome and vanadium       "       green.
Copper    "               r       green or red.
Iron    yellow or green.
Manganese  purple.
Silver     "   yellow or orange.
Gold    crimson.
And these are not the only cases in which colours are produced.
The colours of chemical compounds are so varied, that there
cannot be laid down any principle by which they could bearranged:
thus, lead forms with other simple bodies compounds which are
brown, or red, or yellow, or white; mercury has a still greater
range. There are, however, certain general facts worth bearing in
mind, in which classes of bodies, to a certain extent, are characterized by colour: thus, the ordinary compounds of copper are us',
ally green or blue; those of nickel, green; those of cobalt,.lrir
or blue; those -of chrome, green or purple. A singular property
of certain bodies consists in what is termed dichroism, that is, when
seen by light which has passed in different directions, they appear
of different colours, which are often complementary, or such as,
when mixed together, would form white light. This dichroism occurs only in crystals which refract doubly, and in which the absorption takes place unequally along the two refracted rays.
The colours of natural bodies, seen by transmitted light, depend
thus upon the analysis which they effect of the light incident npon'
them, and of which they absorb one portion and transmit another
Where the object is seen by reflected light, its colour is generally
different from that given by transmitted light, for it frequently reflects, in considerable quantity, the light which it does not transmit
Thus, solution of litmus, when seen by transmitted light, is of a
rich reddish purple, but, seen by reflected light, of a fine, pure blue.
In general, a portion of the light is reflected from the second sur



3S              POLARIZATION  OF  LIG HT.
face, tinged like the transmitted portion, which, mixing with that
properly reflected at the first surface, modifies its colour. The
transmitted and reflected lights are sometimes truly complementary; thus, sea-water, seen by reflection, is of a fine green, but the
light which it transmits is pink.
When a ray of light is reflected from any surface at a particular
angle, which is for glass 56~ 45', and for water 533 11i, it acquires
peculiar properties which it had not previously possessed, and is
said to be polarized.  If the ray be then: made to fall upon a second reflecting surface, the effect varies according to the position
of the plane of the second reflected ray.-  The reflection, if it be
in the same plane as the first, is complete; but if it be at right angles to the first, there is no light- reflected: in intermediate positions,
the quantity of light reflected varies according to the angle which
the second: makes with the original plane.  Light is thus said. to be
polarized by reflection.  In all cases of' reflection there is some of
the light thus modified; for, although the angles above mentioned
are those at wvhich alone: the polarization is complete, at all other
angles the light reflected is partially polarized in a degree, according to its deviation on either side from the proper angles.
Polarization may be effected by various other means, as by refraction or absorption. Even in ordinary refraction some of the
light transmitted is polarized, but it is mixed with so much ordinary light that its properties are obscured: however, if the same
quantity of light be refracted often, it may be polarized completely;
and hence, transmitting a ray of ordinary light, at a certain angle,
through a pile of parallel glass plates, is a usual mode of polarizing it. In double refraction, the polarization of the refracted light
is perfect, and the two emergent rays are found to be polarized in
planes at right angles to each other.  If these proceed together to
the eye, they mix again, and thus recompose the original ray of
common light; but by contrivances, such as in Nichol's prism, one
may be turned aside or absorbed, and then the other used. In polarizing light by absorption, the mineral tourmaline is generally
used; this is a doubly refracting substance, of such a nature that
it absorbs completely one refracted ray and transmits the other. It
therefore gives only a single image of any object, but this image
is formed by light completely polarized.  If two pieces of tourmaline.be: -laid together, and the direction of their crystalline axes
be-the samei in:both, they:act similarly upon the light, and, the-same
polarized ray being transmitted by both, the brightness of: the image is- almost the same with the two as with only one; but if they
be placed-with their: crystalline axes at right anoles to each other,
the ray that is transmitted by the first is absorbed by the second,
and no light can pass.  If a ray: of light be polarized by reflection
or refraction, it is known that the polarization has been complete
when the -ray is totally absorbed. by a t-ourmaline,ithe axis of which
is perpendicular to the plane of polarization of the ray.
When. a ray of light.so polarized passes through a doubly refracting substance, it
undergoes double refraction like, a beam-of ordinary light, being divided into two
rays, polarized in two new planes at right angles to each other; and when these
two rays are-received upon another polarizing instrument, they are each divided
inito twod portions, again at right angles, which unite, as the planes of polarization
coincide two and two, and by their union produce some of the most beautiful phe



POLARIZED LIGHT.                                   39
moinerena in optics; for as, in the doubly refracting substance through which the ray
has passed, the two portions move with different velocities according to the refractive indices of the body, one issues in advance of the other by a certain distance,
and according to this distance, which depends on the difference between the two
refractive indices of the body, a series of colours is produced the most gorgeous
that can be imagined, for every little difference of thickness a different colour is
shown; with the same thickness the colour passes through all the prismatic tints,
according as the plane of polarization of the ray of light is altered, and thus the asction exercised upon the ray by the doubly refracting substance, shows itself in a
manner equally beautiful and strange.
The apparatus used, in so employing polarized light to exhibit these properties of
bodies, consists in, first, a means of polarizing the ray, which may be any of those
before described, but which is generally a flat plate of obsidian or blackened glass,
by which a polarized reflected ray is given.  The substance to be examined is supported upon a frame, in a plane perpendicular to the direction of the ray; or, if it be
fluid, a glass tube is filled with it, and, being closed by plates of glass with parallel
surfaces, it is so placed that the ray shall pass along the axis of the tube. The ray,
after emergence, is examined in order to detect the modifications which it has undergone, by an apparatus termed the analyzing piece, which may be, where two
images are required, a doubly refracting prism, or, where only one, the Nichol's
prism, a doubly refracting prism in which one image is destroyed; a tourmaline
might also be used, but the brown or olive colour which tourmalines possess would
deprive the phenomenon to be observed of much of the interest it derives from the
-beautiful display of colours.
Tn nothing is the action of polarized light so interesting as in the evidence which
it gives of the internal constitution of crystals
of the different systems that have been descri-'Z     cji~i,; 1~ill        bed; for the real difference of molecular arrangement in crystals belonging to these various
0i",111,ll; I'I l,,  systems, is rendered still more remarkably disil'l I~, M[ L,,,~,,&,i  timnct by the action which they exercise upon
4   lI d  Al~j11 11!l       light in this peculiar state of plane polarization.
10'lffll\iih, I.""..'';.;;i;'iIf a ray of polarized light pass along the princihI                   0$lidli.IwI l   palpal axis of a crystal belonging to the rhombo"I( +ih ittII11  lf M11    $1'hedral or to the square prismatic system, and
4 j$I!JtV~ ili- i f5 i  on issuing be examined by means of an analytiItIIIl,,    ii il',  zing plate, the axis of the crystal is seen to be,,::,i,! it lj,,',  surrounded by a series of beautifully rainbowcoloured rings, the centre being occupied either
by a cross which is alternately black and white,
according as the analyzing plate revolves, as
with cale spar, fig. a, or a circular space which is occupied successively by a series
of colours similar to those which form the rings, as in quartz.
If the crystal belong to any of the more complex systems, and its optical axes
be not much inclined to one another, there will'b _-'             be seen, on transmitting a ray of polarized light
along the  crystalline
axis intermediate to the  _.sf —- - - two, a double system rn_
--     -~3 — ~" —~-. _.... of rings, which, uniting,   i
#-$ G-   ~-'_-'_  =~.-= -=L  ~- =form  a very beautiful   g _     V _- 
= — -- -- - -    curved figure, such as - - =   a- -:        _ = -- is represented in figure'......_. -''-v:~_;_f __.....   b, which is the phenom-l,-":_'' ~=;-.- ~~' —T= —~ienon as seen with ni-i -                        i
-—' -- ----  —.,   _:tre.  The curves are.    =..'.
"'A —— t= ~ ~~ — crossed by two ballds,. -   - 
- ___-_ black or white, accord- -.-_ _.-.-.    - - = uing as the analyzing     i  — 3 — 
-:-. B —= —- f —f       plate  revolves,  but          -
___=   ~     which, when the crystal is turned round on        ___:
its principal axis, open    -— ==_~
out, revolving each on      N-'
its axis, A or B, and




40        OPTICAL  PROI. ERTIES  OF CRYSTALS.
bend with the convexity towards the centre of the figure. In substances, as topaz
and carbonate of soda, where the axes make a large angle wnith each other, thte
complete system of rings cannot be at once seen, and only one half; or the portion.
round one axis, as in the case of topaz in figure c, is visible in one direction.
The angle of the axes in topaz is 18~ 30', but in other cases it may be much greater;
thus with green sulphate of iron they are at right angles with each other.
The physical production of these beautiful phenomena involves optical principles
too recondite to be here introduced.  It is, for the purposes of the chemist, sufficient
tosay that they arise from the mutual action of the two rays, which are produced
by the double refraction of the crystal; and hence, if there be not double refraction,
there can be no colours produced. With crystals of the regular system there is
consequently no such result, and hence such crystals are recognised by the com
plete absence of coloured rings.
The optical properties of the different systems of crystallization may be thum
summed up.
1. Regular system.                Single refraction.  No rings by polarized light
2. Rhombohedral system..  Double refraction i Simple system of rings b)
3. Square prismatic sy stem  4..    with one axis.    polarized light.
4. Right prismatic system        I Double refraction  Double system of rings by
6. Doubly oblique prismatic system  with two axes.   polarized light.
6..Doubly oblique prismatic system
When crystals form in a crowded or confused manner, it frequently happens that
not merely are their surfaces modified in a complicated way, but that several crystals become soldered together so completely as to simulate a single form which
does not belong to the substance of which the crystal is composed. These crystals
are called macles, or twin or hemitrope crystals. Some bodies have a remarkable
tendency to crystallize in this way; thus, sulphate of potash had been long considered as crystallizing in six-sided prisms, terminated by six-sided pyramids; and
such crystals of it occur with almost exactly the proportions of the rhombohedral
system; but by optical examination, this figure was ibund to be composed of three
or six of the true crystals, which are right rhombic prisms of the fourth system.
These being laid together, form, by their angles exactly joining, a six-sided prism;
but when tested by polarized light, they show, in place
of the system of rings which a true crystal should pro-~____~__ ~~_. duce, the tesselated structure of the figure. In many
cases, the agglutination of the crystals is less complete,
and irregular figures, with the sides channelled by the
imperfect joints, are found.  A substance which illustrates remarkably this tendency to the macled form
is the mineral analcime, which is termed also c.ubizite,
from its forms belonging most perfectly, so far as external characters go, to the regular system. It has,
however, no distinct cleavage planes, and refracts
doubly. When examined by a ray of polarized light, the cube of analcime gives a
most beautiful appearance. The diagonals of each
surface become occupied by lines, which are alter-.....I   nately black and white, according as the analyzer
is made to revolve, and in the intervening triangull"';    -:.....  lar spaces the richest colours of the rainbow sue.l:'',[Ji.Zl.l / lceed one another, according to the optical laws.
This crystal is therefore made up of a great number
of other crystals belonging to some one of the
more complex systems; but its structure is so extraordinary, that the determination of the form of
its real crystal has been as yet impossible  In
this instance, and in that of boracite alrep,y no.
ticed, the optical properties have been the means
of showino the true nature of bodies which. from their external form, should oth.
erwise have been ranked among those which crystallize in the forms of the regular
system.
It has been noticed as a general character of the crystals of tile rhombohbtiral
and square prismatic systems, that by the analysis of a beam of polarized light
transmitted along the principal axis, there is seen a system of coloured rings traversed by a cross, alternately black and white, as the analyzing plate revolves, but




ROTATIVE  POWER  OF  LIQUIDS.                             41
farther, that in the case of quartz the cross is not produced, the central space being
occupied in succession by all the prismatic colours. Even in quartz there have
been found two modifications of this property; with one, the analyzing plate must
be turned from right to left, to obtain the spectral colours from red to violet; but
with the other, the rotation must be in the opposite direction, to show them in the
same order. The molecules of the quartz cause these colours to appear along the
axis by turning the plane of polarization of each colour round in a different degree,
and thus opening out into a fan shape those combined lights, which had previously
affected the eye only as white or black. This faculty does not depend upon the
manner of arrangement of the particles of the quartz; it involves the chemical na
ture of the molecules; and, although some observations appeared to connect it with
the crystalline structure, it is now fully establislhed to be independent of it. In
fact, this property of circular polarization, as it is termed, belongs to certain bodies,
independent of their arrangement, and even in many cases accompanies them whew
they enter into combination. It is even found in liquids, particularly the volatil,
oils; and when oil' of turpentine is converted into vapour, its molecules preserve
unaffected their rotative power. Its existence is, however, subjected to remarkable anomalies; thus, when oil of turpentine combines with muriatic acid and forms
artificial camphor, it retains its power of rotation; but when the artificial camphor
is decomposed and the oil of turpentine got back again, its power of changing the
plane of polarization of the ray of light has totally disappeared.
[These phenomena of circular polarization may be readily traced. If from a
crystal of quartz a disk is cut transversely, a system of rings will be seen enclosing
a circular coloured space. If the disk be turned round, no change takes place; but
if the analyzing plate turns, the colour passes through a series of tints, which, after
100~ of rotation, may end in a sombre violet. If, now, we cut from the same crystal another disk twice the thickness of the former, and make use of it, we shall find
the tint different from what it last was; but, by turning the analyzing plate 100~,
we may bring it back again to the same sombre violet: with a plate three times
as thick, we should have to turn 1000 still farther to produce the same tint, and for
each additional thickness an additional 100~. We therefore infer that, when polarized light passes along the axis of a crystal of quartz, its planes of polarization rotate circularly, or, rather, spirally, in the crystal; and this takes place in some specimens from right to left, and in others from left to right. Under these circumstances, light is said to undergo circular polarization.]
In cases, therefore, where bodies exhibit this action upon light, their power of
otation becomes an important numerical fact in their descriptions, and it may be
measured by the angle through which a certain thickness of the body is capable of
moving the plane of. polarization of a ray of homogeneous light, such as the pure
red given by glass coloured by sub-oxide of copper. It may also be expressed,
when white light is used, by the angle at which the pure violet is produced, and the
direction of rotation is expressed by an arrow turned either to the right or left, according as it is necessary to make the analyzing crystal revolve to the one or the
other side. Thus, the rotative power of oil of turpentine, contained in a tube six
inches long, is for red light 45~0 —, and of oil of lemons, in the same length,
841~ m —. The rotative power of quartz is about 68 5 times greater than that of
oil of turpentine. This property is beautifully applied to trace the changes which
occur during the saccharine fermentation: a solution of starch possesses a high
- power; but it gradually changes into the sugar of grapes, the rotative power
of which is H-.    Hence the action of the starch, when fermentation has commenced, rapidly diminishes, until there is so much sugar fornied that the   -   and
-— 6~    exactly balance, and the solution is totally without action upon a polarized
ray; after that, the quantity of sugar still increasing, the rotation becomes <4 —,
and increases until all the starch has been decomposed. With such a solution,
knowing the total quantity of starch originally dissolved, the measure of its rotative
power enables the quantity of sugar present to be at once calculated. The juices of
plants which contain sugar, as the beet-root, the maple, the sugar-cane, may be exactly valued by a simple determination of their rotative power compared with their
specific gravities. This property of the circular polarization of a ray of light, which
at the first aspect might appear so far removed from proper chemical inquiry
or useful application, becomes thus an instrument from which the distiller or sugarboiler may every day derive advantage; and when we come to discuss the means
by which we endeavour to learn the internal constitution of bodies produced by?hemieal affinity, we shall find that the light which ordinary polarization throws upon
F




WAVE THEORY OF LIGHT.
the inteinal mechanical structure of the crystal is not more brilliant than that which
we obtain of the arrangement of the chemical constituents by their circularly polarizing power.
Some specimens of quartz appear destitute of this rotative power: the purple
quartz, amethyst, is generally so, and gives with polarized light the ordinary black
cross. But these peculiarities of quartz are related to their crystalline arrangement.
Thus, in those specimens which possess rotative power, the solid angles of the pyramid (k, page 28) are generally replaced by planes which are unequally inclined to
the axes; anld where these planes are present, the direction of the rotation can be
foretold, it being to the right or to the left, according as these unsymmetrical faces
are inclined.  Such crystals are termed plfgi/zdral; as in the cases where no such
faces can be traced, the rotative power is generally absent, and this arises, as is remarkably evident in amethyst, from the crystal being formed of separate crystals
rolled utp together; and as these may possess opposite rotations, and so neutralize
each other, the action on light should be like that of calcareous spar, which has no
rotative power. Such crystals are truly macles; and hence the circular polarization
may show a still more intimate crystalline arrangement than could be detected by
light in its ordinary polarized condition.
~ With such an example, it was not difficult to conclude that the power of rotation
depended on the crystalline arrangement, particularly as quartz, in all its uncrystallized conditions, is devoid of all rotative power; and, accordingly, until the discovery of the power of rotation in liquids, and that this property was found to accompany the molecules of the body through all states of aggregation, it was considered to have its-origin in the mechanical structure of the body; but we must now
invert the argument, and infer that the difference of rotative power in right-handed
and left-handed quartz does not result fiom the difference of crystalline arrangement,
but that this last is caused by actual differenc(e of properties in the molecules them;
selves, of which the most remarkable is detected by the opposite actions upon light.
The impression of light was at one time considered to be produced by a series of exceedingly minute particles, of- a- peculiar substance, emanating from the sun and from burning or luminous bodies,
and which strike upon the eye.  This idea has been, however, now
almost totally abandoned, and all the phenomena are considered to
arise from the vibrations of an exceedingly attenuated medium,
thrown into waves by luminous bodies of every kind, and which, filling all space, and being diffused through the substance of the most
solid bodies, and occupying the spaces between their more substantial molecules, transmits and modifiesthese vibrations, and confers
upon substances transparency or opacity, colour, and all other properties of acting upon light which they may possess.
This medium, or luminiferous ether, as it is termed, is supposed
capable of vibrating in waves of different lengths, and from this
difference in length of wave arises the difference in colour of the
light produced.  The shortest wave produces violet, the most refrangible light; the longest wave, red, the least refrangible light:
the length of the wave being in all cases inversely proportional to
the refrangibility of the light.  The impression of the different colours arises, therefore, precisely as the impression of different sounds
is produced, by a difference in the length of the waves in the vibrating air; the shortest-wave, in sound, giving the highest note  and
in light (giving the violet colour   The actual length of these waves
of light is extremely small: for violet lioht there are 57'490 in an
inch; for red, 39'180; the average of the different colours being
50'000; and hence, in white light, there acts upon the eye in every
second 610'000000'000000 luminiferous vibrations.
In the case of doubly refracting crystals with one axis, that is,:hose'be longing to the rhombohedral and the square prismatic sys.




WAVE  THEORY  OF LIGHT.                       43
tem, the elasticity of the ether is supposed to be so far modified
by the arrangement of the molecules of the body, that the velocity
of propagation of the waves is more rapid in one direction than in
another at right angles to it, and hence there are two refracted rays.
In the three systems, the crystals of which have double refraction
with two axes, the elasticity of' the ether is supposed to be different in each of three perpendicular directions, and hence neither
refracted ray can follow the ordinary law. It is thus, as has been
already stated, that the classification of all crystallized bodies in
these systems is shown, not to be an arbitrary assumption, but a
principle based upon our most decisive evidence of molecular ar
rangement.
The rays of light derive some of their most-remarkable proper
ties from the principle that the vibrations are accomplished in a
direction perpendicular to the direction of the rays.  Thus, if we
conceive a ray of light moving from north to south, the little vibrations which constitute it are effected in a direction east or west,
and in every other direction equally perpendicular to its path; and
ordinary light is characterized by the fact that its vibrations are
accomplished in every imaginable plane. If we reduce these vi
bratory movements to a single plane, the light becomes polarized,
and is then in the condition:for:dissecting the interior of crystallized bodies, and exhibiting the beautiful illustrations of their structure that:have been already noticed.  But it would lead us too far
away from our proper subject to enter into the description of polar —
izing: apparatus, or even of its principles, in detail, as the indication
just given of its nature is sufficient.
Perhaps the most remarkable and the most important principle
of the theory of waves is, that two portions of light may act on
each other so as to interfere and produce darkness, though at another point they may form light of double brilliancy. To effect
this, it is only necessary they should be in opposite states of vibration, that is, while the waves of one ray should be rising up, those'
of the other should be falling down: these motions then compensate each other, and the result is the same as if no vibratory motion had existed, that is, as if no light had arrived at the points
where the rays met. It is only, however, when one of the simple
coloured lights is employed, that actual blackness occurs by the
mutual destruction of the rays: if white lightebe used, there is produced a brilliant series of prismatic colours;' for at the moment
when the red light is destroyed, the remaining blue and yellow form
a bright green; when the yellow is destroyed, the red and blue produce a purple.  Cases of this kind of interference are extremely
common: it is thus that the coloured rings of crystals, and the
colours of the soap-bubble or oil-film are produced.  The brilliancy
of the plumage: of birds, the lustre of many minerals, as of labradorite, arise from the interference of the portions' of light which after:
reflection thus act on each other.
Under ordinary circumstances, light is always associated with
heat; the sun, the source of warmth to the: surface' of our globe,
being also the' natural origin of light: and in most cases where light
is -artificially produced, it is'associated with heat, which is also ca



44                PHOSPH ORE SC ENC E.
pable of being transmitted in a radiant form. It was, indeed, once
considered, that at certain temperatures heat became converted
into light, and that the colour of the light depended on the degree
of heat; a body, when first rendered luminous by being heated,
emitting a dull red light, which gradually becomes brighter as the
temperature rises, until at the highest degree of heat the light
emitted is pure white, and similar in constitution to the solar ray.
The powers of emitting heat and of emitting light are, however,
although so frequently associated, quite independent and distinct;
and the rays of heat and those of light may be perfectly separated
from each other. It would anticipate too much the account of radiant heat to describe the means of separating the heating from the
luminous qualities of ordinary light; but elsewhere they will be
described in full. A body may become luminous when very moderately heated, as is the case with many iminerals, as fluor spar
Light may be produced also by the friction of bodies, as by rubbing
two pieces of sugar briskly together, or by striking together two
pieces of quartz; and ini these cases it is difficult to assign its true
origin, as, possibly, a minute trace of the substance may be very
intensely heated. There are also many bodies which, when exposed to the light of the sun after having been made red hot, appear to absorb a portion of it, and become capable of emitting it
slowly, giving a pale bluish light for some time afterward in the
dark. This occurs particularly with chloride of barium, native sulphate of barytes, carbonate of lime, and a great number of other
bodies. Such substances are said to be phosphorescent.  Thus fluor
spar is rendered so by heat, sugar and quartz become so by friction,
and the electric spark is capable of conferring the phosphorescent
property on a great variety of bodies.
Organized substances become phosphorescent in the first stages
of their decay; thus, rotten wood, and fish before actual putrefaction has commenced. The light emitted is, in such cases, the result of an exceedingly slow but distinct process of combustion; it
requires the presence of atmospheric air, or oxygen, although an
exceedingly small quantity may suffice, and it is extinguished and
revived by all such means as facilitate or retard the chemical action of the air upon organic bodies. The light emitted by the glowworm and the fireflies, as well as by the great variety of marine
zoophytes, appears also to be not merely an evolution of light as a
product of vital action, but to arise similarly from the secretion of
a substance, which, slowly combining with the oxygen of the at
mosphere, produces the light as a consequence of combustion
Animal phosphorescence is, therefore, to be ascribed to chemical
action.
The white light, derived from different sources, does not always
possess the same physical constitution. If the coloured spectrum
produced by the solar ray be closely examined, it will be found
crossed by a multitude of black lines, indicating the total absence
in the sun's light of rays of certain refrangibilities.  That this is
inherent in the light is shown by the fact, that when we change
the nature of the prism, the position of the space in which these
black lines occur may alter, but the lines preserve all their relative




CHEMIICAL RAYS IN THE SPECTRT.M.    45
listances from each other totally unchanged. Hence, in place of
referring to the colours of the spectrum in order to characterize its
properties, those lines, of which the most remarkable is a double line
situated in the yellow space, are used as marks. The light of the
sun, of the moon and planets, as well as white light produced by
our processes of combustion, all consist of the same elements of
yellow, red, and blue, and all are distinguished by the same set of
lines. In the light of some of the fixed stars the same lines are
found, as is the case with Pollux; but in the spectrum formed by
rays from Sirius or from Castor, this double line does not occur,
but is replaced by one broad line in the yellow space, and two re
markable dark lines in the blue. It is very curious, that if we examine the spectrum through certain coloured media, as the vapours
of iodine or bromine, we find additional black lines, and by using
gaseous nitrous acid these become almost innumerable,. and increase so much when the gas is heated that the spectrum is obliterated and the gas becomes opaque. It is possible that such
takes place at the origin of the light of the heavenly bodies, and
that the sun and the fixed stars are involved in absorbing atmospheres, which allow only certain rays to pass, andthat hence there
may exist in nature kinds of light from which the eye of man is
screened forever by means of such an impervious veil.
Some classes of chemical substances are, to a certain extent,
characterized by the facility with which they are decomposed when
under the influence of light. The salts of silver, of gold, of platina, and, in. some instances, of mercury, are subject to this influence.
A great variety of vegetable and animal bodies undergo important
changes in their constitution by the action of the solar rays, the
development of certain colours requiring the agency of light, and
the majority of colours being destroyed when its action is too great:
hence the fading of dyes arises. The power of light thus to modify the affinity by which chemical combination is produced, has
been found to be exercised specially by the violet or more refran..
gible extremity of the spectrum, and' even with great intensity by
invisible rays quite outside of the luminous space, and extending
beyond the lavender-coloured prismatic space of Herschel. It has
been also considered that the rays of the red extremity of the spectrum possessed chemical properties of an inverse kind, and that the
decomposition produced by violet light might be counteracted, and
the elements brought to recombine by the red rays. This is not
certain. All that has been established is, that there exist in solar
light, and probably in all light derived from sources of combustion,
three distinct sets of rays, the one of proper light, which produces
only luminous effects, the second of radiant heat, the nature of
which will be specially examined in the following chapter, and the
third of rays which, though neither luminous nor heating, exercise
an influence on chemical affinity, and the nature of which will be
discussed withl more detail when the subject of chemical affinity
and its relations to the other physical forces has been described.




A41                 EFFECTS OF HEAT.
CHAPTER III.
OF HEAT CONSIDERED AS CHARACTERIZING CHEMICAL SUBSTANCES.
AT almost every step of chemical inquiry it is necessary to introdnee the action of heat, either as modifying the results of the
chemical action of bodies upon each other, or as affording characters by which the substances we operate upon may be distinguished.
The doctrine of heat and the history of its effects have consequently, at all periods, formed an important portion of the studies of the
chemist; and it is, indeed, only lately, since the brilliant course ot
discoveries that was opened, and so successfully prosecuted by
Melloni and by Forbes, has identified the theories of heat and light,
that this subject has been contemplated in its proper aspect as a
physical science, and its application and influence in chemistry have
ceased to be considered as making up the science, properly so called, of heat.
Of all the physical sciences, however, that of Heat, or T/zermotic.:
as it is now termed, is the most important to the chemist in guiding
him in his operations, and in the accurate description of their results
On this account it will be necessary to describe the properties of heat
more in detail than those of any other of the physical agents, an,,
to illustrate these properties by more numerous references to cases
in which their utility in chemistry is apparent.
The effects of heat, by which, according to their degrees, bodies
may be characterized, are,
1st. Changre of volume for a given change of temperature. El.l
pansion.
2d. Quantity of heat required to produce a given change of tern.
perature. Specific heat.
3d. Temperature necessary for liquefaction.  MJlelting points.
4th. Temperature necessary for giving a certain elasticity to A
vapour. Boiling points.
5th. Quantity of heat required to produce a given change of az.
gregation. Latent heat of liq-uids and vapours.
6th. Manner and rapidity of communicating or receiving heal
Conduction and radiation of heat.
The subject of heat will therefore be studied specially under
these heads; and it will be necessary to introduce an account of
our mode of measuring heat and temperature by the thermometer
and pyrometer, and to add some observations on the physical rela.
tions of heat and light, and on the physical theory of heat.
SECTION I.
OF EXPANSION.
When describing the effects of cohesion, I have already notices
that the molecular constitution of all bodies might be considered




REPULSIVE POWER OF HEAT.                                47
to depend on the relative power of the attractive force, cohesion,
and the repulsive force of heat, upon their particles. That wher'e
the attraction was in excess, the molecules were knitted firmly together to form a solid body; but that where repulsion was most powerful, all cohesion was lost, and the body assumed the form  of a vapour or a gas. In the intermediate condition, where the forces appeared to be nearly in equilibrium, the liquid state was produced,
in which the molecules of the body appeared still to unite by a trace
of remaining cohesion, but that they moved among one another
with perfect ease, and the slightest external force might disarrange
them entirely. Now the change from one to the other of any two
of these conditions is not quite abrupt. If a cold body be gradually heated until it shall begin to liquefy, its particles do not remain
in the same condition up to the moment when they separate so far
as to chance their state of aggregation; on the contrary, from the
instant that the substance becomes warm, the change begins; the
molecules of the body gradually separate, occupy more space than
before, and from the very commencement of the increase of heat,
the body, though it may remain solid, yet expands.  In the same
manner, if a liquid be heated, the change of aggregation does not
commence until the increase of heat has reached a certain degree;
but from  the beginning a change of volume occurs, the increase of.
which marks the gradual diminution of cohesion.  In gases there
can take place no farther change of form, and the only effect which
heat can produce upon them is expansion.
This power of repulsion which we suppose heat to exercise, in causing the transition from one state of aggregation to another, as well as the expansion which occurs without change of form, may become directly evident to the senses, at least
in a partial way, in many cases. Thus, many powders, if sprinkled on a warm
capsule, or, still better, on a silver plate, are thrown into violent motion, and dissipated by the mutual repulsion of their particles, independent of any currents of air
which might affect them. When liquids, particularly alcohol and the oils, are
brought to boil, the drops which are mechanically thrown up out of the liquid do
not mix with it on falling back, but roil about on the surface, and appear to repel
each other, and to be repelled by the hot glass of the vessel in a remarkable degree. If a brass poker, strongly heated, be allowed to rest against a cold iron bar,
or, still better, if a rounded bar of brass be made very hot and laid upon a fiat block
of lead, the surface of the cold metal becoming heated, repels the warmer brass,
which instantly falls down again, by its weight overcoming the repulsion, when the
metal cools. When the brass again touches the metal or lead, the latter is again
heated at the point of contact, and again there is repulsion succeeded by a new
contact, and these repeated motions throw the bar of brass into a state of tremulous
agitation, which being conveyed to the ear by the intervening air, gives a remarkably distinct and agreeable musical tone. The better conductor, the heated body,
and the worse conductor (provided both are metals), the cold body can be, the more
successful is the result.
This force of repulsion is mrade still more distinct, and even measurable, by an
experiment devised by Powell. When a flat and a convex glass plate are strongly
pressed together, they still do not touch, but are separated by an exceedingly thin
space, by the action of light on which there are produced coloured rings, like those
seen on the surface of a soap-bubble, or in a film of oil floating upon water. Each
colour belongs to a distinct and measurable thickness of this space; and when such
an apparatus is gradually heated, the rings close in towards the centre, showing
that the glass plates recede from one another, and the degree of repulsion may bih
determined from the narrowing which occurs in the breadth of any particular col
oured ring, according as the temperature rises.
In gases, the expanding effect of heat is unaffected by any disturbing cause; there is no cohesion remaining to impede its oper



48                ME, A SURE  OF HEAT.
ation; hence a certain increase of heat affects all gases alike; and
rno matter how hot or how cold a gas may be, a certain increase of
heat produces the same increase of voluime in every case. In solids and in liquids, however, it is different; the expansion which occurs is but the result of the opposing forces of cohesion and of
heat, and hence the amount of expansion depends not only on the
quantity of heat which is applied, but also on the power of cohesion by which it is resisted, and which depends upon the nature of
the body. Consequently, every fluid and every solid expands in a
degree which is peculiar to it. There is yet another consequence
of the influence of cohesion upon the expansion of solids and of
liquids. Let us represent the cohesive force of a certain substance,
for example, copper, by 10, and let us suppose that we apply to it a
quantity of heat which will expand it through a space which we
will call 1, and will diminish its cohesion from 10 to 9. If, then,
we apply another quantity of heat exactly equal to the former, it
will not have to contend against a cohesion of 10, but of 9, and
will, consequently, be able to produce an expansion of more than
1, say 1', and it will reduce the cohesion more than it did before,
as from 9 to 7'. If, then, another equal quantity of heat be added,
it having still less opposing force to overcome, will act still more
powerfully, reducing, for example, the cohesion from 7' to 5, and
the increase of volume becoming, in place of 1}, 2. In solids and
liquids, the rate of expansion increases thus, with the temperature,
from the diminution of cohesion; but in gases, where the cohesion
remains the same, or, rather, is-completely absent, the expansion is
proportional to the additional quantity of heat, no matter how much
may have been sensibly present in the gas before.
I shall now proceed to consider in detail the rates of expansion
of various bodies, commencing with those of gases, for which the
simplest results have been obtained. Before doing so, however, it
is necessary to study the means by which we ascertain the quantities of heat which we add or subtract from bodies to effect their
expansion or contraction; to investigate, in fact, the principle on
which the thermometer and pyrometer are founded, and such details of their construction as shall hereafter be found necessary to
be known.
Tet a b be a glass bulb with a long and narrow neck, which is divided
by a scale, as in the figure, of which each division is a certain part, as
T-,'W.. of the volume of the bulb. Let us suppose the bulb a to be filled with pure dry air, at the same degree of heat as that at which ice
melts, and separated completely from the external air by means of
a globule of mercury, c, which is exactly settled at the commence.
ment of the scale. If, now, the instrument be warmed, the air in
the bulb expands, and, according as it increases in volume, pushes
before it into the tube the globule of mercury. This last serves,
therefore, as an index of the increase of volume which the air gains
as it is heated, and by its position we can read off the exact propor



NATURE OF TEMPERATURE.                       49
tion. If the source of heat be water boiling, under ordinary circumstances, at Dublin, at the level of the sea, as soon as the air
has been heated to exactly the same degree as the water, the globule will be found to have arrived at the 365th division on the scale.
Therefore, 1000 measures of air, on being heated from the degree
of melting ice to that of boiling water, become 1365. Now as, from
the constitution of air and gases, the effect of each increase of
heat is the same, we may consider the whole quantity of heat which
it received from the boiling water to be divided into 365 parts or
degrees, and each of these parts being applied separately to the
bulb, should have increased the volume of air by TW  part, or should
have converted the 1000 volumes into 1001. There is thus obtained a scale of expansion which is quite artificial and arbitrary certainly, but which, having been once contrived, may be with perfect
accuracy applied to measure different quantities of heat. Thus, if
we warm water to blood heat, and immerse in it the air bulb as described, the expansion of the air will move the globule of mercury
to the degree 122, which is almost exactly the one third part of
the 365, and hence the water, in being heated from the degree of
melting ice to that of blood heat, received almost exactly one third
of the quantity of heat which should have made it boil, and its temperature is one third as high.
I have here spoken of measuring the successive quantities of
heat which the air received, and in this case the manner of expression is sufficiently accurate, as well as the most simple. But it is
necessary to explain the true meaning of the words quantity of heat
and temperature. The amount of expansion which a hot body is
capable of producing in the air or mercury of the thermometer,
measures truly what is called its temperature. The temperature has
nothing whatsoever to do with the quantity of heat whicli the body.
may contain, it refers only to its expanding power. If a quantity
of water, of oil, of ether, of mercury, or of iron produce all the
same amount of expansion in the air or mercury of the thermometer,
we say they have the same temperature, without pretending to know
anything of the quantity of heat which they may actually possess.
The thermometer and pyrometer are therefore instruments for
measuringr, not heat, but temperature, and we denote by degrees of temperature the amount of expansion produced, marked off on any arbitrary scale which we may thirlk proper to adopt.
Gases expanding more than any other bodies, the air thermometer is the most sensible that can be made, and in the form just
described it is an exact measure of heat, subject only to one correction, which is, that although the air, in being heated from the
degree of melting ice to that of boiling water, actually expands
3:6, of its volume, yet that expansion is not all visible, for the glass
bulb expands also on being heated, although in a very small proportion, and holds l-go  more than it did when cold; the visible expan
sion on the scale is therefore only 363 degrees, and this must be
allowed for to have complete accuracy. The form of the air thermomneter which has been just described is, however, quite unfit for
ordinary use; the adjustment of the index globule, the necessity
that the instrument should be perfectly horizontal, which is quite
G




50                AIR  THERMOMETER.
impossible in the majority.of practical cases, renders this kind of
an air thermometer too unmanageable; and since the air changes its
volume very much for every change of pressure, and our atmosphere varies in its weight almost every.hour, an air thermometer
left open, as at the. orifice b, would change continually without ref
erence to the degrees of heat at all, and would thus give false indications. The end of the tube must therefore be accurately
closed.
When, however, the air inside is thus confined, the simple rule
of the dilatation being proportional to the increase of heat, ceasesl completely. For if the point b be closed, and the bulb a be
heated, the globule of mercury, in moving along the scale, condenses the air before it, and thus generates an elastic force, by
which the expansion is resisted and diminished in amount; the degrees would therefore be no longer equal, but rapidly diminish in
size, so that on the upper parts of the scale they could not be distinguished from one another, and would hence be useless. But by
having a second bulb, in the next figures, the elasticity of the air
-ompressed in the cold bulb increases much less rapidly, and the
scale to be applied to the stem connecting the bulbs is easily constructed. As the stems of these air thermometers are generally
upright, mercury would be too heavy a fluid to introduce in a column,
and the mere globule which we supposed in the example first taken
would not answer, fromn the facility with which it might be broken
or displaced: to any watery or spirituous fluid there is also an objection, that the amount of expansion would be increased to an
uncertain degree by the portion of fluid converted into vapour. To
avoid these errors, oil of vitriol may best be employed, and it is
generally coloured. red to render the motion of the fluid column
more easily visible.
An air thermometer, closed perfectly, indicates a change of temverature only by the difference between the elasticity of the air in
the two bulbs. No matter how high or how low
the temperature may be, if it affects both bulbs to
the same degree, the air in each bulb presses on
the liquid column with the same force, and exactly
A   balances the other.  The            c
instrument indicates, there-   lD
fore, such temperatures only
as affect one bulb and vet
the other; the difference, in
fact, between the tempera.
tures of the two bulbs, an(
hence is properly called the
differential thermometer.  In
fig. A the one bulb is much above the other
In fig. B the stem which terminates above in
a bulb is open below, and plunges into the
fluid which the inferior bulb. contains. This
lower bulb is soldered or cemented at its or-  -
ifice round the tube, so as perfectly to pre-.- i
vent the action of the air. Fig C represents'     =G-:




MER CIRIAL  THER MOMETER.                             51
the most ordinary form; the bulbs are on a level, and are connected
by a U-shaped stem.
The air thermometer is thus, in all its forms, liable to so many inconveniences from  the limited range of its scale, if it be not open
to the air, and from  the complex form  which the scale assumes if
the external air be prevented from  communication, that it is never
made use of in practice except in some particular cases, which
shall hereafter be specially noticed.  We are therefore obliged to
have recourse, for our accurate measures of temperature, to other
bodies, which, though not so sensible as air, ofler more practical
advantages.
The liquids which are generally used to measure, by their expansion, change of temperature, are alcohol and mercury. The former,
in being raised from the melting point of ice to that at which itself
boils, expands — PT,, whereas air within the same limits would have
expanded,(14,  being about three and a half times as much as alcohol: and mercury, in having its temperature raised from the melting point of ice to the boiling point of water, expands  I-,,, or
about -'- of the quantity of air.  Hence these liquids are much less
sensible, as thermometers, than air; but their other advantages are
decidedly in their favour.  Alcohol is only employed  where the
object is to measure very great degrees of cold; and for this purpose it is admirably fitted, as it is the only liquid that has not yet
been frozen.  Mercury, on the other hand, may be applied to an
extensive range of temperatures, as it freezes only by the application of an intense cold; and it does not boil until it arrives nearly
at a red heat. It has the largest interval between its freezing and
boiling points of any liquid that is known.  Mercury is also admirably suited to be a measure of heat, by the accidental circumstance
that its expansion, when contained in a glass bulb, is accurately
proportional to the temperature, and its indications therefore absolutely true.
This is occasioned by the circumstance that, as in all liquids and solids the expansion increases with the temperature, the rate of increase of the capacity of the
glass bulb exactly corresponds to the increase of the rate of expansion of the nlercury, and absorbs it; so that the visible expansion of the mercury is uniform, and a
degree in every part of the scale is of the same length. For instance, if mercury
and air be together heated from the fieezing to the boiling point of water, 1000
measures of air become 1'365, and 10'000 measures of mercury become 10'180.
If, then, they be both heated as much more, the air, expanding at the same rate,
becomes 1'730; but the mercury, expanding more rapidly, becomes 10'363: and
hence, if a scale was so applied, there would be shown 180 degrees in the lower,
and 183 degrees in the upper part of the scale, to the same quantity of heat. This
is corrected by the expansion of the glass bulb which holds the mercury. At the
temperature of melting ice, the bulb holds, for example, 10'000 measures of mercury; but, on being heated to that of boiling water, it holds 10'026. The mercury,
however, having become 10'180, the difference, (10'180-10026)-1 54 measures,
passes into the stem, and makes the rise of temperature upon the scale. When,
now, the second portion of heat is applied, the mercury becomes 10'363; and the
glass bulb, expanding at the same time, becomes able to hold 10'055: and hence
the difference, (10-363 —10055) —308 measures, passes into the stem and moves
along the scale. Thus the visible portion of the expansion is rendered exactly proportional to the increase of heat; and the mercurial thermometer becomes, not
merely the most convenient, but the most accurate measure of heat which we
possess.
In constructing a thermometer, the first requisite is, that the bore of the tube
shall be perfectly uniform, for otherwise the result above described, which gives all




52              OF THE STANDARD INTERVAL.
its real value to the quicksilver thermometer, would be completely inapplicabie in
practice. This is ascertained by finding that a small quantity of mlercury,, mi  red up
and down the tube, occupies exactly the same length in every part.  A proper tube
having been thus obtained, one extremity is closed, and a bulbt) is blown upon it
another is formed near the open end, leaving a space between the two bulbs somnewhat longer than the thermometer is intended to be. The tube and bulbs having
been heated, are allowed to cool, with the open end immersed in pure and recentlyboiled mercury.  By the contraction of the internal, and the pressure of the external air, a quantity of mercury is forced into the first bulb, and ultimately the bulb
at the closed end is filled completely by a repetition of the process.  When the introduction of the mercury has been completed, the open end of the tube is closed
by a little sealing-wax, to prevent the admission of air or dust, and the tube is allowed to cool with the terminal bulb down. VWThen it has cooled completely, it is
again heated to the highest degree it is intended to indicate; and the fine flame of
a blowpipe being directed upon the point which is to be the extremity of the tube,
it is melted, and the orifice completely closed. When the instrument then cools,
there remains over the mercury in the stem a perfectly empty space.
It remains, then, to attach the scale. When describing the general principle of
the thermometer, in the example of dry air, pushing, by its expansion, an index
globule of mercury along the stem, the scale which included the interval from the
freezing to the boiling points of water was supposed to be divided into 365 palrs.
This was, however, merely because the 1000 measures of air, in being heated
through that interval, expand in that proportioni.  The scales that are actually used
are different, although quite as arbitrary.  The simplest scale is that in which the
interval between the freezing and boiling points of water, which is universally taken as the standard, is divided into 100 parts; it is termed the centigrade scale,
and is employed in France, and generally in Germany and the north of Europe. In
it ice is said to melt at 00, and water to boil at 1000. On the scale generally used
in this country and Great Britain, the standard interval is divided into 180 degrees,
but the melting point of ice is not taken as 0~, but as 32~, from a very absurd idea of
Fahrenheit, who was the inventor of this scale. Hle mixed together snow and salt,
and having thus produced a more intense cold than anybody before him had done,
he imagined that he had attained a point at which the bodies had no heat at all,
that he had arrived at what was afterward called the absolute zero, and he called
that point 0~; the melting point of ice was then 320, and water boiling at 180~
higher, its temperature was marked 212~.  There is another scale, sometimes, but
not often used; thaf of Reaumur, in which the melting point of ice is the commencement or 00, and the boiling point of water is marked 80~.  The first step in
the graduation is to mark the extreme points of the standard interval: the melting
point of ice, and the boiling point of water. To do this correctly, some precautions
must be taken. I have frequently spoken of the melting point of ice and the fi'eezing point of water as meaning the same temperature, and under ordinary circumstances they c; so; but they do not so necessarily.  The freezing of water is a
crystallization, and, like all 5ther cases of crystallization, may take place with greater or less facility. If water be agitated, or if it be contained in rouglh vessels, affording prominences to which the crystals of ice may attach themselves, it freezes
exactly at 32~ on Fahrenheit's scale; but if the water be kept carefully at rest, and
be contained in smooth glass vessels, free from dust, it may be easily cooled to 25~,
and has been cooled even to 150, without becoming solid. Hence, if we wished to
determine the zero by means of freezing water, an error might easily be committed.
Ice, however, under all circumstances, melts at 32~0; and hence, by plunging the bulb
of the thermometer into a mixture of ice and water, and marking on the stem the
point at which the level of the mercury settles, the first fixed point upon the scale is
had. To determine the second point, that at which water boils, it is necessary to attend to the condition of the barometer. It will be hereafter described how the boiling point of every liquid varies with the atmospheric pressure; it is here enough
to notice, that either the boiling point must be determined when the barometer
stands at 29'8 inches, or a correction, which will be hereafter given, applied for any
difference of height which may exist. The water must boil also in a metallic vessel, for water in a glass or porcelain vessel has its boiling point somewhat raised,
and as the thermometer is to be used for chemical purposes, the bulb and only a
small portion of the stem should be immersed in the boiling water. The two fixed
points having been thus obtained, the interval is to be divided into 180 equal parts
or degrees for the ordinary scale of Fahrenheit, and then 32 of these degrees
counted downward from the point of melting ice to obtain the zero; for the zero




THER M OMETRIC  SCALES.                              53
cr..;o be truly got in the manner in which Fahrenheit is supposed originally to
have nlvented it, for a mixture of snow and salt is found to produce always a cold
of about 20 below zero, or -2~. As our range of temperature passes far below
the zero of the scale, wv. count downward precisely as we count upward, only
prefixing in the former case the - minus sign, whereas, in the degreecs above zero,
the + plus sign is usually omitted. Thus, +500, or simply 500, is fifty degrees
above zero, but -501 is the same number below zero. To construct the centi
grade scale, the method is precisely the same, except that we make the point of
melting ice 0~, and that of boiling water 1000, and a degree being the T-I  of tile
interval, we count up and down from zero, precisely as in the other case.
It is generally proper to lay a thermometer aside for a few weeks after having
filled it before proceeding to apply the scale. For it is found that as there is a vacuum in the instrument above the mercury, the external pressure acting on the thin
glass of the bulb gradually changes its form a little, and would move up the fixed
points, sometimes through one or two degrees, if they had been marked before the
change.
The centigrade scale is of such extensive use in the works of most distinguished
chemiSts, that it is well to show more closely its relation to the ordinary scale of
Fahrenheit, and the means of reducing one to the other. The standard interval is
divided into 180~ Fahrenheit, and into 100 centigrade degrees, and hence a degree
of the former is equal to I 0,9 or 5ths of a centigrade degree. To reduce any interval in centigrade degrees to Fahrenheit's, it is therefore to be multiplied by 9 and
divided by 5; and for the reduction from Fahrenheit to centigrade, the number is
to be multiplied by 5 and divided by 9: but as the degrees do not in number start
from the same point, the Fahrenheit scale being already 32~ when the centigrade
begins, it is necessary to add 32~ to the number of Fahrenheit degrees which have
been attained by calculation from the centigrade, and to subtract 32~ from the number of degrees on Fahrenheit, which are to be converted into degrees upon the other scale.
Thus, to reduce 1670 of Fahrenheit, we proceed:
167-32 —=135, and 135 X5=-75C,
Tan find it to correspond to 750 centigrade. And to reduce 650 centigrade to Fahrenheit's scale, we say,
65X=Ill7, and 117+32=149~,
Corresponding, therefore, to 149~ of Fahrenheit.
Reaumur's scale being to the centigrade scale as 4 to 5, similar reductions are
made to and from it, by using 9 in place of 5, as has been employed in the example.
The range of temperatures observable with a mercurial thermometer on Fahrenheit's scale is from — 39  to +-630~.  The mercury
freezes a little below —400; and though it does not boil until it arrives at 660~, yet the quantity of vapour which it forms when very
near its boiling point, prevents its indications from being quite exact between that point and 630~.
Our means of estimating temperatures above the boiling point
of mercury are not at all so perfect as those that have been described for the lower degrees of heat.  Mercury, when boiling, is
not in the slightest degree luminous, but the temperature at which
a heated body becomes visible in the dark, by emitting a dull red
light, is not much higher.  Numerous instruments have been invented for the purpose of determining the higher temperatures,
particularly of furnaces, and hence they have been called pyrometers. Of these, the only one which appears to give accurate re.
sults, and hence deserves description, is that of Daniell.
In this pyrometer, the change of temperature is shown by the excess of the expansion of an iron bar over the expansion of a black-lead case in which it is enclosed. The iron rod a is somewhat shorter than the black-lead-ware case, and a
plug of earthenware, b, which fits tight in the case, abuts against the iron rod inside, and projects as at c in the figure. Let us suppose the length of the case to be
5 inches, that of the iron rod 4- inches, and that of the earthenware plug to be 1
inch. If the whole be heated until the case shall have expanded by 12 parts, the
iron rod will have increased in length by 44, and the earthenware piece by 7, which,




5;4               -D ANIELL'S  PYROMETER.
added to 44, makes 51. If the black-lead case did not increase in size, all these
51 parts should project; but as there is additional room made for 12, the projecting portion is only 39. If the parts of the apparatus were all free to move, each
contracting again on cooling, the result would be that all would be restored to their
original position; but this is not the case. The bar of iron, in expanding, pushes
out before it the plug of earthenware, which, however, is held so tight in the case
that it cannot go back again when the apparatus has become cold. The protrusion
of the earthenware plug is therefore a permanent index of the greatest amount of
expansion that had been produced while the instrument was exposed to heat. This
expansion is, however, very small. The three pieces being, as stated, 5, 4~, and 1
inch, the expansion, when heated from 32~0 to 2120, is only' -03 of an inch; and as
this indicates 180 degrees, the expansion for a degree is only about 4    of an
inch. It is therefore necessary to magnify this expansion, in order that the indication may be read off; and this is done by means of a graduated circular arch, d e
f, with a movable index, kept by means of a spring constantly at 00 when undisturbed. On fitting this scale to the pyrometric black-lead case, after it has been
in the fire, the projection of the earthenware plug, c, catches in the prolonged heel
of the index, e, and moving it round, the point of the index travels over a portion
of the graduated scale, and indicates the number of degrees through which the
temperature had been raised. This instrument is not always made of the same
size, and hence the absolute amount of expansion may vary, which, however, is reduced to the same proportion on the scale, by which, also, the increase in the rate
of expansion of the metallic bar at very high temperatures must be allowed for.
By means of this very ingenious and useful instrument, Professor Daniell has determined the melting point of most of the important metals, and also several other
temperatul es at which remarkable phenomena occur.
The p'rometers of Wedgewood, of Guyton, and many others
that have been proposed, must be considered as now totally abandoned, and do not require notice.
The most delicate, and. perhaps the most important, measure of
heat that has been contrived, is one totally independent of expansion, and founded on the measurement of an electric current which
a change of temperature produces under certain circumstances.  It
is the The,-mo-multiylier invented by Nobili.  The principle which
the instrument involves in its construction and its form will be described under the head of electricity, and the remarkable results
obtained by means of it, and which have completely remolelled




TABLE  OF' T:E:MPERATURES.                       55
our ideas of the physical constitution of heat, will be noticed in
another place.
It may be of interest to subjoin the temperatures on Fahrenheit's
scale at which some of the most remarkable effects of heat are
produced:
135~. The greatest cold that has been produced.
-    121~. The solid compound of alcohol and carbonic  acid
melts.
91~. Greatest cold by ordinary freezing mixtures.
- 580. Temperature of the planetary spaces.
60~. Greatest cold observed in the arctic regions.
473. Sulphuric ether congeals.
450~ Nitric acid conceals.
39?. Mercury congeals.
+      10. Oil of vitriol freezes.
+     14~. Oil of turpentine freezes.
+    200. Wine freezes.
+    25. Blood freezes.
+    32'. Ice melts.
+    360. Olive oil freezes;
+    983. Heat of human blood.
+   1080. Phosphorus melts.
+   174~. Alcohol boils.
+   201~. Rose's metal melts.
+   2110. Newton's metal melts.
+   212". Water boils.
+   218~. Sulphur melts.
+   662. Mercury boils.
+   8100. Antimony melts.
+   980~. Red heat.
+  11410. Heat of a common fire.
+  1869~. Brass melts.
+  18730. Silver melts.
19960. Copper melts.
2200~. Gold melts.
2786~. Cast iron melts.
(Che details which have been given, regarding the construction of the air tlherr,'meter, will show sufficiently the principle upon which the determination of the
ra.e of expansion of gaseous bodies has been effected. The exact amount of dila.
ta ion was first ascertained by Dalton and Gay Lussac nearly at the same time.
Te apparatus of Gay Lussac consisted of a tin vessel, A, having five apertures.
y means of the aperture in the side, o, there is introduced the tube with the bulb,
By means of the aperture in the side, o', there is introduced the tube with the bulb,




56                    EXPANSION   OF  AIR.
g g', containing air dried by the tube h h', and arranged with the graduated scale asri
index globule of mercury m, as described in page 48. By the opposite orifice, o, is
fixed a thermometer, b s, the bulb b of which is on the same level as the bulb of
the air tube. By means of the central orifice in the top, a second thermometer, v,
*is introduced, the bulb of which is situated exactly in the centre of the box. The
other orifices in the top are for the free escape of steam. The apparatus so being
arranged, water, rendered ice-cold by some snow or ice floating on it, is introduced,
until the thermometers and the air bulbs are covered to the depth of la couple of
inches, and the index globule of mercury is thus brought to the zero of the scale.
The box is then placed on a furnace, B, and gradually heated: the rise of temperature is indicated by the thermometer, t, the expansion by the motion of the index
globule, and at each degree the thermometer and air bulb may be compared together until the water is brought to boil.
By substituting other substances for water, such as oil, or a bath of fusible metal,
the rate of expansion may be determined for still higher temperatures, and has been
thus ascertained by Dulong and Petit up to the boiling point of mercury.
From such experiments, conducted by Dalton, Gay Lussac, and Dulong, it resulted, that 1000 volumes of air, when heated from 32~ to 2120, became 1375, and that
the change was in proportion for higher or lower temperatures. The numbers actually obtained may be stated as in the following table:
[Temperature on a 10000 Volumes Expansion for one
IMercurial  Ther-   ofAirat 32    D)egree on F. Scale
monmeter by Fall-  become  in Parts of the Volrenheit's Scale.  ecome me at 320.
-  33       8650      20 77
-- 32      10000
212      13750      20'83
300      15576      20'70
387      17389      20-82
473      19189      20'84
559      20976      20-83
660      23125      20'90
The mean of these results gives the expansion for one degree at 20'81, or almost
exactly:F' of the volume at 32~0, which result had been'adopted universally, with.
out any suspicion of its being imperfect. Circumstances having, however, induced
Rudberg to submit the subject to an accurate reinvestigation, conducted with ex.
ceeding care and attention, particularly to the state of dryness of the air employed,
he has found that the amount of expansion assigned by Gay Lussac and Dalton is
somewhat too great, and that a volume of air, in being heated.from 320 to 2120,
expands from 1000 volumes to 1365.
The method which he employed was almost exactly the inverse of that of Gay
Lussac. Having dried with great care the air in a glass bulb, the tube of whic:.
was drawn to a fine point, like that described, page 14, for taking the specific gravity
of vapours, he heated it for a long timne in a vessel of boiling water, taking care
that all parts of the bulb and tube were equally heated, and then, being completely
certain that all the air had attained the maximum temperature, he sealed, by the
blowpipef the minute orifice, and thus had the bulb containing air in the expanded
state. The vessel being then removed to a trough of Inercury, the orifice of the
-tube was placed deep below the surface, and carefully opened; a quantity of ice
was then laid upon the globe, and being supplied as fast as it melted, the whole
was thus left for some hours until the temperature was well established at 32~,
and all the mercury which would rise into the globe by the contraction of the air
by cooling, had entered. The height of the mercury was then noticed, and the
height of the barometer, and the corrections necessary for its positive amount, or
for any change which occurred during the experiment, allowed for, as already described. The volume of the mercury which had entered into the globe was then
ascertained, and the volume of the globe itself also determined; and by a compar.
ison of these, corrected for the expansion of the glass, and for any variation in the
boiling point from 2120, the rate of expansion and its amount were calculated.
From very numerous experiments, Rudberg inferred that, in being
heated from 32~ to 2123, 1000 volumes of air became between 1364
and 1366'4; we may consider 1365, which is between the two, as




CORRECTION  FOR  CHANGE  OF  TEMPERATURE. 57
being absolutely the most correct, and hence that for each degree
1000 volumes expand 3 —-2'028, or I-~ of its volume at 32'.
In all operations upon gaseous mixtures, the rate of expansion
of air comes into play; for as all gases expand alike, and the vapours,
even of these bodies which are least volatile, as camphor and corrosive sublimate, expand, while in the elastic form, precisely as
gases do, their volumes are corrected for temperature and pressure
in the same manner. In determining the: specific gravity of a vapour, it is also usual to reduce it to the same standard as those of
gases, that is, air at 32', even where the substance is of such a naturje as that at 32~ it may not produce any sensible vapour at all.
In doing so, it is assumed that the vapour should, in cooling to 320,
follow the same law as common air; and hence an error, even though
very slight, in the rate of expansion of air, might lead to incorrect
results in many cases.
The application of such corrections follows very simply from what has been described. If there be a certain quantity, as 155 cubic inches of hydrogen gas at 1420
Fahrenheit, and we wish to know the volume there should be when cooled to 32c,
we say that, as 1420 is 1100 above 32~, the 155 cubic inches are equal to the volume at 320, and in addition to 4 I 0 of it; that being the quantity by which it is expanded from 32~ to 142~. Thereftbre, denoting the volume at 32~ by the letter V,
there is the equation:
110      493 x155
155=V+V113, or V=-4   o=1291 5:
129'5 cubic inches are therefore the volume at 32~.
If, on the other hand, we have a gas at a low temperature, and we wish to ascertain what its volume should be at 32~, it is evident that the mode is the same,
except that, in place of subtracting the amount of expansion, we add it to the original volume. Thus, if the 155 cubic inches of hydrogen had been at 6~ Fahrenheit,
then the equation should have been 320~-6 being 26.
26       155 x493
155=V — V3 or V    93          168-3 cubic inches in exact numbers.
493'      493-26
It frequently happens that it is necessary to reduce a gas at one temperature to
Its volume at another, neither of which being 32~, it would require two different sums
to be worked by the above process. But it may be effected as follows by a single
calculation.
The volumes at the two temperatures are to one another in the same proportion as the standard' volume, 493, increased by the amount of expansion proper to
the temperatures. Thus, at the temperatures of 75~ and 420, the standard volume,
which is 4930, at 32~ becomes respectively 536 and 503. Now any volume of
gas, when heated from 420 to 750, or cooled from 750 to 420, changes its volume
in these proportions; and hence, if we have, for example, 127 cubic inches of a gas
at 75~, and we wish to calculate its volume when at the temperature of 42~, we
say, calling the unknown volume V:
V: 127: 503: 536, and V  127X503= 119'2.
536
The formulae for these corrections may be very simply written in a general form.
thus, to reduce a volume to 32~, denoting the temperature on Fahrenheit's scale
by t; by V, the volume of gas which we have measured at that temperature; and
by VI, the volume at 32~, the formula is:
493. V
V1=
493 + (t —320'
And to reduce, without reference to 32~; denoting the known volume by V, and
the unknown by Vi; the temperature of V by t, and that of V1 by tl, there is found:
V, 493~ (t-132) and         493z-f (ti-32)
V — 93~ (t-32)              493+ —  (t —-32)
Air which has been heated becomes, from  its great increase in
volume, specifically much lighter than cold air, in which it therefore ascends with a velocity due to the difibrence between their
H




58                E-X-PANSION  OF  LIQUIDS.
specific gravities. It is thus that over every lamp or candle there
may be felt a current of heated air ascending from the flame; that
the heavy dark smoke rises in its heated form from the chimneys of
our houses; and that, in crowded apartments or theatres, the upper
portion of the space will be occupied by oppressively hot air, while
that near the floor will be quite cool. By the ascent of the heated
air from  our furnaces and fireplaces, there is generated the draught
which gives the supply of air necessary for continued burning; and
as the intensity of the combustion and consequent heat produced
depends on the rapidity of draught, the hot air is kept from being
cooled by mixing Writh the cold external air, by being collected in
the chimney, where it obtains an ascensional powver corresponding
to its height, and by which we are enabled to regulate with accuracy the temperature which shall be produced. On this ascensional
power of heated air is founded also the construction of the fire or
Montgolfier balloon, a bag of hot air, rising in the surrounding colder
atmosphere, precisely as a light flask, filled with oil or alcohol,
would ascend if let loose at the bottom  of a vessel full of water.
It has been already noticed that liquids do not, in expanding,
follow any simple proportion, such as that -which exists for gaseous
bodies, but that each fluid has a peculiar dilatability of its own, and
that the rate of expansion varies with the temperature, being greater
in the higher portion of the thermometric scale than in the lower.
Liquids expand much less than gases, but much more than solids;
for, as is particularly instanced in the thermometer, the visible expansion of a fluid is, in most cases, only the excess of its expansion
over the expansion of the solid vessel in which it may be contained.
To measure the amount of expansion in liquids, they may be introduced into
graduated thermometer tubes; and then, when exposed to the same degree of heat,
they will indicate temperatures proportional to their expansibilities. Thus alcohol
rising more into the stem than water, and water more than mercury, will stand at
different marks on the stem, although the temperature be really the same. It may,
however, be more easily and more accurately done by means of the apparatus in
the figures. a d b is a glass tube, the neck of
| za.'d  which is very narrow, and bent as in either figure. This tube is to be filled completely, at the
lowest temperature, with the liquid, whose expansion is to be examined and then
weighed, the weight of the tube itself being previously
c  known, and the quantity of liquid which it contains is thus:,r....  determined. The tube is to be then placed upright in a
i    w'Hlljii |cylinder of water or oil b, to which heat may be applied!il  by a furnace below; and the liquid expanding according
i a'         as its temperature is raised, the excess of volume flows
out at the capillary beak c, and may be collected as in d, or
let to waste. When the apparatus has been brought to the
highest temperature required, and all farther expansion has
C  ceased, as is known by no more liquid passing out at c, the
L tube is to be removed from the bath, carefully cleaned, and,
i     -       when again cool, accurately weighed. The loss of weight
is the quantity of liquid that had been expelled, and this,
compared with the whole original quantity of liquid, gives the proportion of expansion. In this manner, however, the result appears to be less than it really is, for
the expansion of the glass tube itself diminishes the quantity of liquid expelled.
Such results require, therefore, to be corrected for the expansion of the glass, which
is, however, so small, that in the more dilatable liquids it may be neglected. In
mercury, however, it affects the apparent expansion very much: mercury expanding
in glass through 180~, augments in volume only A, while its real expansion is;
The amount of expansion of different fluids in passing through 1800 of Fahren
heit is thus found to he:




EXPANSION   OF  LIQUIDS.                             5
Alcohol.......                 Oil of turpentine...
Nitric acid...                      Sulphuric acid....  r
Fixed oils.                        Water..           
Sulphuric ether           4            Mercury...... 
The actual amount of expansion, independent of the expansion of the containing
vessel, is best observed by the apparatus used by Dulong and Petit. It consists of
a glass tube a b c, bent in the form of a
A_.   ~ ~ tU, of which the horizontal portion c is narrow, but the vertical legs pretty wide.
When mercury is poured into the tube, it
l,           stands at the same height in both legs if
the temperature be the same; but one leg
being immersed in a vessel of oil or water
g_ __ _ ____Ho.      1, by which heat can be applied to it, and
thereby the mercury in it caused toexpand,
the height of the liquid column must in.
crease in order to balance the colder column of mercury in the proportion of the
augmented volume. The difference between the heights being read off, by means of
an accurate scale, with a telescope o, the amount of absolute expansion may be easily calculated front it.
By means of this instrument Dulong and Petit determined the rate at which the
expansion of mercury increases with the temperature, as has been noticed generally
in the description of the thermometer. Their result was, that between 32~ and 212~,
measured on the air thermometer, the expansion is,  From 2120 to 3920, it is
4.1;; and from 3920 to 5720, it is t   The consequence is, that, measured by
its own expansion, mercury boils at 6800 Fahrenheit; but from the expansion of
the glass of an ordinary thermometer bulb, it boils at 6600 on the visible scale,
which coincides almost exactly with 662~, the temperature given by the dilatation
of air. The apparent expansion of mercury in glass is therefore taken as being
uniform for 1800. ~ of its volume.
Considerable simplicity is given to the laws of'dilatation of liquids by an observation of Gay Lussac, that, in order to obtain any common rule for them, such as is
found for gaseous bodies, we must examine them when in the same molecular condition; that is to say, the cohesive powers of the liquids we employ must be brought
into the same state. This is most nearly done by taking these liquids when heated to their boiling points, for then the cohesion of each liquid is about to cease altogether. Thus alcohol boils at 1730, water at 212~, sulphuret of carbon at 1340, and
sulphuric ether at 96-30; and, taking 1'000 volumes of each at their boiling points,
and allowing them to cool, they contract as follows:
By cooling Water  Alcohol iSuphuren  Ether
through    contracts  con[nets  contracts
contracts
18   6.61  11-43  12[01  16 17
360  13'15  24-34  23'80  31'83
540  18'85  34'74  35'06  46'42
720  24,10  45'68  45-77  58'77
900  28 56  56.02 {56-28  72.01
1080  32-42  65.96  66,21.
We by this means find a very interesting relation between alcohol and sulphuret of carbon, two fluids remarkably different in their specific gravities, and in
their chemical constitution and properties. It appears that their molecular force
must increase at the same rate; for in cooling the same number of degrees below
their boiling points, they contract to exactly the same amount: and a still farther
connexion is exhibited between their molecular conditions by the remarkable fact
that, in being converted into vapour, the augmentation of volume which they undergo is the same.
Many liquids possess the property of contracting, by reduction
of temperature, only to a certain point; below  which, if the cooling be continued, they expand. As the volume at this temperature
is the least possible, it is called the point of maximum density.
This peculiarity was first recognised in water; but it has since been




60               EXPANSION  OF SOLIDS.
found in many other fluids, even in a still more remarkable degree
It is, however, in water that the phenomenon is of most importance,
in consequence of the extensive agency of that fluid in natural operations. The point of maximum density of water has been determined by the experiments of very many persons to be 39.50 of Fahrenheit. When water below that temperature is heated, it contracts; when heated above it, it expands: when cooled from above
it, it contracts; when cooled below it, it expands: and when the
experiment is made in glass vessels, the contraction of the glass has
ne effect of rendering the expansion of cooling below, or of heating above, through the same number of degrees, exactly equal. Thus
100'000 volumes of water become 100'012 equally by being cooled
from 39.5 to 32~, or by being heated from 39'5 to 46~, and the specific gravity of water at 46' and at 30?' is consequently the same.
A great deal of the permanence of the existing order of nature
depends upon this property of water: it is by means of it that the
great mass of water in our lakes and rivers is preserved from being
converted into solid ice. When, by the cooling process of the
winds, the water has been all reduced to the temperature of 39.5~,
the surface acts as a screen to prevent the farther loss of heat, and
thus retains the deeper portions at a temperature sufficiently high
for the existence of its organized inhabitants; for, by the continued
action of the cold wind, the superficial water being cooled below
39.5~0 it becomes lighter, and floats upon the heavier and warmer
water'underneath; and from the bad conducting power which water
will be hereafter demonstrated to possess, the loss of heat is effectually prevented. If it were not for this property of water, all large
collections of it in lakes and rivers would, with few exceptions,
be permanently frozen.
I'he dilatation of solids is much inferior in amount to that of
liquids, and as with these, the rate of dilatation is not uniform, but
increases with the temperature. The increase is, however, so exceedingly minute, that in almost all cases it may be neglected, and
hence need not occupy much attention. The dilatation of solids,
although so small, may yet be demonstrated to be real by many
simple experiments. Thus, if an iron rod be made to fit, when cold,
in length and breadth, an exact scale, it will be found, when heated,
to be, too large to enter it. An iron ring, which is, when cold, too
small to pass over a cylinder, becomes sufficiently large on being
heated; and if the cylinder could have passed through when cold,
its diameter becomes too great to allow its passage when its temperature is raised. In the arts, the expansion of solids, particularly
of the metals, in this way becomes the source of numerous inconveniences, and of many useful applications.  Thus, the iron rim of
a carriage wheel is secured by the power of its own contraction,
it having been slipped upon the wooden frame while in a hot and expanded state. The force of contraction of iron bars in cooling has
been applied successfully to restore to the proper position buildings
which had been about to fall, and the rate of expansion has also, as
in the pyrometers of Daniell and others, served as a useful measure of high temperatures; on the other hand, by the alternate expensions and contractions, under the successive influence of win



EXPANSION  OF SOLID S.                       61
ters and summers, of the metallic bars which had imprudently been
laid in the masonry of some important public buildings, with the
idea of giving additional security, the courses of stone or brick
have been loosened from one another, and reconstruction rendered
necessary, in order to prevent their being gradually pulled to pieces.
In estimating the amount of expansion of a solid body, the great
difficulty is the accurate measurement of the small increase in
length which takes place. For this purpose, a great variety of mechanical arrangements have been constructed. As they are all in
principle the same, and the detailed description of any exact form
would occupy too much space, it will be sufficient to notice one,
which, though not that by which very accurate numbers may be
obtained, is calculated to give a very satisfactory idea of their general construction: a
b is the bar of which
the expansion is to
be determined; it is
fastened securely at
the extremity a, and
rests at b in a groove
along which it is free
to move, as in the
fig ure.  This end of
the bar at b presses
4.'2    -!.J- against a rod c, which
e  is a lever of the second order, very near..-J   e                  m               the fulcrum, and this
transfers its motion
to the end of the lever, increased in the proportion of the distance. This lever acts on
another similar one, d, the extremity of which serves as an index
on the graduated circular arc e, by which the amount of expansion
is read off. Thus, if the acting lengths of the arms of the levers
are respectively 1 and 20, and the end of the bar a at b moves
1 0 0, of an inch, the end of the index d will move on the scale e
20x20 4
through  10  -10   of an inch, a space capable of being divided
by'a microscope and vernier into 200 measurable spaces, so that an
expansion of the two hundred thousandth of an inch can be accurately determined. For a popular illustration, the source of heat
may be lamps, as in the figure; but for accurate experiments, the
bar is completely immersed in a bath of oil or water, and the temperature ascertained by a suitable arrangement of thermometers.
The most important results thus obtained are the following. The temperature
being raised from 32~ to 2120, the increase in length of a bar of
Glass varies from..            Steel.......
to....  0        Gold...... 
Copper....                Silver.......     4
Brass..                        Lead...3...
Soft iron.............. i
The increase in length is called the linear dilatation of a sub




62 EXPANSION INCREASES. WVITH TEMPERATURE.
stance, B:t its increase of volume is called the cubical dilatation,
and is three times the former. Thus the cubical dilatation of glass
is  -38,  or 4.  - Hence a glass ball which holds 428 measures at
32~, becomes capable of holding 429 at 212'; or if it hold 10'000 at
320, it holds 10'023 at 212~. In this manner the correction for the
expansion of glass is in all cases made. But it is necessary to apply the amount of expansion belonging to the particular sort of
glass; thus, in the account of the thermometer in page 51, the
cubic dilatation of glass was taken,. not as 10'023, but 10'026.
[The reason that the cubic dilatation may be taken as equal to three times the
linear, without sensible error, is due to the circumstance that the linear dilatation
is always a small fiaction of the primitive length. If' 1-+1 represent the dilated
length, (1+1):, or 1+3 1+3 12+13 will be the true volurne; but as l is a small
fraction, its triple square and cube may be neglected.]
Although it is abundantly proved that solid bodies expand Inore rapidly at high
than at low temperatures, yet, except in the case of some particular substances, as
glass, iron, and platinum, whose utility as measurers of heat rendered a knowledge
of the law of their expansion necessary, the subject has been little examined; the
degree to which the rate of expansion is affected by temperature will be sufficiently
shown in the table which follows. At the temperature of 212~ Fahrenheit, as given
by an air thermometer, the dilatation for one degree is thus, for
Glass.   I Platinum. I   Iron.  Copper.
-— I       I -    i
)6  6    8 6 () 51 6 0 3 4 1 412 )
while at 572~ of Fahrenheit it becomes, for
Glass.  1 PlatinniD.  Iron.  C opper 
5 9. 2 0i 6. 324 0 1 7' fI -'I i31 6' T i1
and the temperature deducible from the expansion of a thermometer made of each
of these substances should be, in passing firom 212~ to 572~, as compared with air,
Air.   1   Glass.    P rlillI.nM.     Iron.   [ Coppe:r.5720 | 667~  5920 I 701' 6230
Platinum expands thus the most regularly of those bodies, and should, therefore; be
best fitted for a metallic thermometer.
It is remarkable that the rate of expansion is not increased by
rise of temperature for all solid bodies, but, on the contrary, in
some cases there exists, for solids as for liquids, a point of maximum density, so that the body shall expand whether it be cooled
or heated from that degree. This is peculiarly the case in Rose's
fusible metal, which has been so often mentioned as a means of applying a steady heat.  TWhen heated from  320 to 111~, this metallic
alloy increases in volume from 100'000 to 100'830 parts, but there
the expansion stops, and when farther heated it contracts, until,
when at 156', the volume is only 99,291, being less than at 32~
By a farther rise of temperature it again expands, and at 1780 is at
its original volume of 100'000, and continues expanding until, being
100.862 at 201~, almost exactly what it had been at 111', it begins
to'melt. It is curious that it has no point of maximum density
when in the liquid state.
The different rates of expansion of different solid bodies are subservient to some very important uses in the arts and in scientific
research. Thus, the difference between the expansibilities of platinum and brass, or any other two metals which differ much, may be
used as a very delicate thermometric means.  If we take a flat rule




EXPANSION  OF COMPOUND  METALLIC  BARS. 63
of platinum exactly ten inches long at 32~, and lay it on a similar
rule of brass, to which it is firmly screwed at one extremity, asnd
on which, at the free end, there is engraved a scale of parts of an
inch for a small space, the compound rule will serve as a thermometer. For the two rules being exactly of the same length at 320, if
we place them, fastened together, in boiling water, the brass rule
will be elongated by 0'019, while the platina rule will expand only
through 0'009; hence the end of the brass rule will project beyond
the platina rule by 00 10 of an inch; and as the expansion is uniform
for these moderate temperatures, each degree of Fahrenheit's scale
will be indicated on the scale of the brass rule by 0,9=0j  of
an inch. In this form the spaces would be too minute to be easily,determined; but by modifying the form, and connecting the rules
through their whole length, the beautiful metallic thermometer of
Breguet has been invented. Its principle is as follows: if the two
rules be soldered completely together, as in a, in place of being connected only at a single point, the result of the unequal expansion is
to bend the bar, as in b, until, the most expansible metal being on
a manMMm!tnrnlalFnnthe outside, it forms an arch longer than that
formed by the inside rule, by the difference
_    _     _       of their expansions. If the compound bar be
already bent into a circle, the ends of which
are not opposed, the effect of the expansion is to make these edges
project, and to diminish the diameter of the circle; by having a
number of such circles, the expansion of all being added together,
a considerable circular motion is produced in the extremity. In
the thermometer of Breguet there is such a
compound spiral b, b, fastened at the upper end,
and having attached to its lower extremity an
index, c, which moves round a dial, d, d, and
indicates the temperature of the instrument.
On this relative expansion is also founded the
1 b g  ) construction of the compound pendulum. A
metallic bar, when used, as in an ordinary clock,
to measure time by its vibrations, being condstantly changing in length according as the external temperature varies, affects the rate of the
clock, making it'go too fast or too slow by its
shortening or elongation.  This is corrected by having two or more
bars, by the expansion of one of which the vibrating length of the
pendulum is increased, while by the expansion of the other it is
just as much shortened; the consequence of this opposing action
is, that the pendulum remains indifferent to all changes of temperature, and the clock becomes an exact measure of time at all seasons.
SECTION II.
OF SPECIFIC HEAT.
It is now necessary to examine into the quantity of heat which
each substance requires to raise its temperature a certain number
of degrees; for, although it be quite impossible to assign the absolute




64              METHOD  OF MIXTURES.
proportion, yet; by obtaining the relative proportions, we may arrive
at results which may serve to characterize those substances, and
may, as shall be hereafter shown, lead.s to important views of the
relations between their physical and chemical constitution. The relative quantity of heat necessary to raise the temperature of any
body through a certain number of degrees, as ten, for example, is
termed its specific heat.
If we take a pint of water at 150', and another pint of water at
50', and mix them well in a very thin vessel, the telnperature of
the mixture is found to be, if we allow for some sources of error to which this process is exposed, exactly 100'. Thus the one
part of the water has transferred to the other a quantity of heat
sufficient to raise its tempe'rature 50'; and whether this addition was
from 50 to 100l, or from 100: to 150, the result was the same. In'
water, therefore, the specific heat does not change within these
limits; but it will be found that in high temperatures a trifling increase does occur; for the present purpose, however, it may be neglected. If, now, a pint of water be taken at 1500- as before, and a
pint of mei cury at 50', and they be well and rapidly mixed together
until both have attained the same temperature, this will be found to
be 1180. The mercury here rises from 50" to 118', through 68*,
while the water cools only through 32', or not quite half as much,
so that the same quantity of heat can raise the temperature of mercury through twice as many degrees as that of water.
Taking thus equal volumes, the specific heats of water and mercury are as 68: 32; or water being adopted as the standard for
liquid and solid bodies, and its specific heat taken as 1, the specific
heat of mercury is 0'47 nearly.  Such bodies are, however, generally taken, not in equal volumes, but in equal weights, and hence
it is necessary to divide the 0'47 by 13'5, the specific gravity of mercury, and'thus there is obtained 0'035, its specific heat.
-he process now given is known as the method of' mixtures, and
has been selected for example, as that by which the meaning of the
term specific heat is best explained; but it is not the only one, nor
even, perhaps, the best, by which specific heat imay be determined.
The sources of error are, that a certain quantity of heat is absorbed
by the vessel in which the mixture is made, and that, as the mixture
requires some time to make, a certain loss occurs by. the cooling
power of the air. But it is, however, in skilful hands, capable of exceeding accuracy; and, with the recent improvements that have been
made in its details by Regnault, it has yielded results of the highest
value to science. The various forms of apparatus used in such experiments need not be described. For the usepof: the method of
mixtures, it is not necessary that the two bodies should be liquid.
Thus, if a pound of pure copper in a bar be heated in an oil bath to
3000, and be then immersed in a pound of water at 50', the copper
will give out its excess of heat to the water, and both will arrive at
a temperature of 72'. The copper.has therefore lost 228;:, and the
water has gained 22", and the specific heats being inversely as these
numbers, that of copper is found thus to be 2 —0'096, water being
1.000.
One proces employed by Dulong and Petit consisted in heating




THE  CALORIMETER.                              65
to the same degree the bodies to be tried, and allowing them to cool
exactly under the same circumstances. It is evident that, if we know
exactly the rate at which a body cools, and the time which it talces to'
cool, we can calculate exactly how much heat it parts with.  Thus,
if we have two bodies heated to 300, and circumstanced in all respects alike, one requires 15 minutes to cool to.50, and the other
25, the latter will have parted with more heat, in the proportion of
25 to 15, and the specific heat is expressed by the quantity of heat
the body gives out in cooling.  Hence those substances which have
high specific heats require more time to heat or cool, through a certain number of degrees, than those bodies whose specific heat is less.
It was by a process of this kind that the relative specific heats of
bodies was first discovered.  Boerhaave having remarked that, when
two thin glass vessels, containing, one a pound of water and the
other a pound of mercury, were equally exposed to -the heat at the
front of a strong. fire, the temperature of the mercury rose much
more rapidly than that of the water, and that it attained its greatest
degree in one half of the time which the water required; and also,
when both, equally hot, were removed from the fire, the mercury
cooled twice as fast.  For accurate purposes, however, there are
many precautions necessary in order to place the substances under
the same conditions, so as to render the rapidity of cooling depend
ant only on their different specific heats; thus, equal weights of
the different bodies are placed in the same thin polished silver vessel, so that their external surface may be the same in extent and nature, and this vessel cools in an exhausted receiver in order that
there may be no loss of heat from  contact with the external air.
The internal surface of the receiver must also be always in the same
state, that the heat given out may pass off in all cases with equal
facility.
An extensive series of researches on the specific heats of bodies, conducted by
the illustrious associates Lavoisier and. Laplace, has been found on repetition to
have been rendered useless by the imperfections of the apparatus they employed:
it was termed the Calorimeter, and consisted of a vessel containing ice, in the centre
of which the heated body was placed, and the quantity of heat this gave out in
cooling was measured by the quantity of ice which was melted into water. Outside
there was another case of ice to defend the instrument from the action of the air.
It was found in practice impossible to collect all the water. A quantity remained
infiltrated among the ice, some solidified in one part of the vessel after having been
melted in another, and, consequently, the numbers given' by two of the greatest men
that have ever been attached to science must be considered as quite without authority. In cases, however, where the quantity of heat was very large, as when
the Calorimeter was: employed to determine the quantity of heat produced in combustion, these sources of error became less influential, and such results will be utilized in a future chipter.
The specific heats of a number of the most important solid and
liquid bodies, determined by such methods, are given in the following table:
Water...=1'000         Iron...... — 0114
Ether..0. o.  =0520           Copper...... =0095
Alcohol...      =0660          Lead......  0031
Sulphuric acid.. =0'333          Gold.... 0 032
Nitric acid.... =0442            Antimony... =0'051
Sulphur.....=0-202                Tin.. =0056
Carbon..... -0241            Iodine...... =0054
Mercury..... =-0033           Phosphorus.... =0188




66  SPECIFIC  HEAT.- CHE MICAL  CONSTITUTION.
Arsenic.....  — 0 081       Glass...... -0177
Platinum.....=-0032         Calomel.... — 0,041
Silver.. =-0'057                  Common salt... — 0225
Zinc...         -0095         Nitrate of soda.. =0'240
Tellurium..... =0051         Lime....  =0'205
Nickel...... =0109          Magnesia......  0-276
Cobalt.. -0'107
The numbers given are generally those lately obtained by Reg.
nault.
The specific heats of bodies are not the same at all temperatures;
thus Dulong and Petit have found that the specific heats, calculated
from the change of temperature from 32~ to 212', and from 329 to
572', differ, as in the following table:.Substance  Sp. Heat from  Sp. Heat from
320 to 2120.   320 to 5720.
Mercury...  0-0330  00350
Zinc.....  00927  01015
Antimony...   00507  0'0549
Silver...    0.0557  0'0611
Copper....  0:0949  0 1013
Platinum...  0'0355  0.0397
Glass.... 01770  0'1900
Iron...... 0-1098  0.1218
The specific heat increases, therefore, with the temperature, and
Nauman and Regnault have found that this holds, even with water;
for, according to their experiments, the specific heat of water at 32'
being 1'000, that water at 2129 is 1.010, consequently the equal distribution of heat between warm and cold water, which was described
at the commencement of this section, does not exactly hold; the
temperature of the mixture should be a very little above the mean.
This was, however, omitted, in order not to complicate the account
of that manner of finding the specific heats.
The specific heats of bodies are connected very intimately with
their chemical and molecular constitution, although we are not yet
able to trace the exact cause of this connexion in all its forms. The
discovery of such connexion was the most remarkable result of the
experiments of Dulong, and it may be expressed as follows.  If we
take the specific heats of any of the bodies given in the table, and
divide by each of them the number 3'1, we obtain a series of numbers which are found to be either those which shall be hereafter
described as the chemical equivalents of the bodies, or to stand in
some remarkably simple relation to those equivalents, thus:
Substance.  Sp. Heat.    3  a  Troe
l______Suhstanc____ _p. _  Heat.l  Equivalent.
Lead.... 0031 1000  103 —6
Tin..      0'056  55 4  57'9
Zinc.... 0095  32 6  32'3
Bismuth.... 0 030 1007  71-)
Carbon....024   12-9   6-1
Iodine.... 0 054  57-4 126-3
Phosphorus..   0'188  165  31'4
Silver.. 0'057  54'4  108In the first division of this table, the quotient is so close to the
true equivalent as sufficiently to show that, were it not for the un




SPECIF IC H EATS  OF  ATOMS.                       67
avoidable errors of experiment, they would coincide. In bismuth
the result is 1~ times the true equivalent. In carbon it is double
the true equivalent.  In iodine, in phosphorus, and in silver, it is
one half.  Each of these illustrations might be much extended, their
numbers being only intended as examples of the fact.
The above are all simple bodies; but Nauman and Avogadro have
shown, that also in compound bodies this connexion between the
equivalent number and the specific heat exists, although the connecting dividend is no longer 3-1, but is a different number for each
class of bodies.
Thus, for the following carbonates, the specific heats being made
the divisors of the number 10,4, there isSubstances.  Sp. Hei.i S Tr Equivlent
Carbonate of lime.. 02044 50 9  506
Carbonate of iron.. 0'1819 57 2  58'1
Carbonate of zinc.. 0'1712 60'7  62'4
Magnesian limestone. 0'2161 48'1  46'7
For certain sulphates the number is 12-4  Thus:
Substances.  Sp. Heat.  1  Equiatent.
Sp. Heat._
Sulphate ofbarytes. 0-1068 1161 1161
Sulphate of strontia:.- 01300 95'4  91'9
Sulphate of lime..   0 1854 66-8  68,6
For a number of metallic oxides, the constant appears to be 5.4
Thus:.
Substances.  Sp. Heat. -I  t  Equivalent.
Magnesia....  10 276  19.6  207 
Red oxide of mercury.0049 110 2 1094 
Oxide of zinc 0...  132  40.9  403 1
Oxide of copper.. 0137  39'4  39'6
The relation between the specific heats of bodies and their chem
ical equivalents is thus remarkably shown to extend not merely to
the simple substances, but even to saline bodies, and indicates a connexion between the chemical equivalents and the molecules upon
which the heat exerts its action, of an intimate description.  In fact,
the specific heat of a certain weight of any body is thus shown to be
proportional to the number of chemically equivalent masses contained in that weight; and the constant numbers, which were divided
by the specific heats, are the specific heats of the ultimate chemically equivalent particles. Thus, the specific heat of chemical molecules of zinc, of lead, and tin, is 3'1; that of the oxides of zinc, of
copper, and of mercury, 5'4; the specific heat of the chemical atom
or ultimate particle of carbonate of lime or of zinc, 10'4; and that of
the sulphates of barytes, strontia, and lime, 12'4 Attempts have been
made to connect these constants together, but without good foundation; for 5,4 and 12'4, although nearly the double and quadruple
of 3.1, are yet too far removed to show any necessary connexion,
and 10'4 is completely out of the series of 3 1, though nearly the
double of 5'4. 
I shall have occasion to discuss this remarkable relation between the physical and




68       HEAT BY CHEMICAL C O M BINATION.
chemical characters of these bodies when I come to examine the subject of the laws
of chemical combination in their full extent. For the present, the details now given
are sufficient.
It is not likely that any law connecting the specific heats of different bodies can be obtained perfectly consistent, for the various
bodies necessary cannot be examined exactly in the same state
Regnault has well observed, that the quantity of heat which we
measure as specific heat consists of several different portions: 1st,
the true specific heat; 2d, the heat which produces dilatation; 3d,
the heat which causes the rise of temperature; and, 4th, when a
solid is near its fusing point, the quantity employed in giving the
softness and ductility, which most bodies at certain temperatures acquire. These last three portions being very small, do not conceal
the law by which the true specific heat is regulated; but they influence it so far as to prevent the law from being verified in its numerical results with the accuracy which otherwise might have been
obtained.
When bodies combine chemically, there is generally found to be
a diminution of specific heat; and it has been attempted to account
thereby for the rise of temperature, by which combination is in most
cases accompanied.  Thus, the specific heat of sulphuric acid is
0'33;. and when mixed with an equal weight of water, the specific
heat of the mixtures should be, were there no action, I33=0,665;
but the true specific heat of the combined acid and water is found
to be only 0'587.  The excess, therefore, 0'665-0'587-0.078, becomes free, and shows itself by raising the temperature of the mixture; and, accordingly, on mixing together sulphuric acid and water,
it is well known that a temperature higher than that of boiling water
may be produced. It was even supposed at one time, when heat
was looked upon as being a positive substance which combined with
bodies in different proportions, that the absolute quantity of heat
which a body contained might be determined by such an experiment, thus: if the rise of temperature produced by 0.07S of heat
becoming free is expressed by 180' above 32', then the quantity of
heat which stays behind must be greater than that in the proportion
of 587 to 78; and hence is equivalent to 7 180  1335': and thus, at
the temperature of — 1303~ of Fahrenheit's scale, a body should contaih no heat at all; it should be the absolute zero. But no two such
experiments, with different bodies, ever gave the same result: and
it is evident, from the fact of the specific heat diminishing as the
temperature sinks, that the term at which the two quantities should
vanish must be infinitely iemote, and that there is no such thing as
an absolute zero at all. In fact, the physical existence of an abso
lute zero is inconsistent with the more accurate ideas of the nature
of heat, which modern investigation has suggested.
The development of heat, in chemical combination, is also only
in some cases accompanied by a diminution of specific heat; in at
least as many it is, on the contrary, remarkably augmented.
The specific heat of gases and vapours has obtained considerable
attention; and yet, from the extreme delicacy of the processes necessary, and the small quantity of material which can be operated on,
the results hitherto obtained have not acquired that degree of posi



SPECIFIC   HEATS OF  GASES.                         69
tive accordance which should render repetition unnecessary. The
principal experimenters in this department have been Delaroche and
Berard, Delarive and Marcet, Haycraft, Dulong, and, latterly, Apjohn
and Suerman.
The method adopted by Haycraft, and by Delaroche and Berard,
c:nsisted in heating a quantity of gas to a certain temperature, and
then, by passing it through a tube in a vessel of water, determining
how much it raised the temperature of the water in being cooled
through a certain number of degrees.  In principle, this mode is
perfect; but the extreme accuracy necessary in the management of
the apparatus does not appear to have been attained by Haycraft:
and Delaroche and Berard deprived their results of most of their
value by the oversight of using the gases in a damp state.  The process of Delarive and Marcet was not such as could lead to results
worthy of much confidence.  A glass globe full of gas, to which
was attached a thermometer, with the bulb exactly in the centre,
was plunged into a vessel of hot water, in the expectation that the
time occupied by each gas, in having its temperature raised a certain number of degrees, would be proportional to the specific heat
under a constant volume. But the communication of the heat
would be so much and so variously affected by currents, according
to the density of the gas and the quantity of heat absorbed by the
gas, so trifling in comparison to that which would be required to
heat the globe, that the amount of liability to error was very great.
The process employed by Dulong was very beautiful in principle,
and calculated to give experimental results of great accuracy.  It
consisted in determining the velocity bf sound in each gas, which
was measured bv finding the note the same organ-pipe gave with
each: from this, by very ingenious methods, which, however,
need not here be introduced, farther than that the gases with higher
specific heats give more acute tones, he calculated the specific heats.
The calculations were, however, based on certain other principles,
which are not necessarily true.
The method contrived by Apjohn is that which appears to be the
best calculated to give accurate results, and those which he obtained
have been verified by the experiments of Suerman.
Apjohn's method cannot be completely described until we come to speak of the
latent heat of vapours and their relation to space; but the general principle of it is,
that if several gases be employed to convert a certain quantity of water into vapour,
the gases will be cooled thereby in inverse proportion to their specific heats. Thus,
if one gas have double the specific heat of another, it will saturate itself with vapour by cooling through only half the number of degrees necessary for that with
the less specific heat; and thus, by measuring simply the cooling power of each
gas, the specific heat may be calculated.
The numbers obtained by Delaroche and Berard, by Dulong and by Apjohn, for
the specific heats of the gases in equal volumes, are given in the following table -
Gases..Apjohn. Delaroche. Dulong.
Air...    1.000 1000 11000
Nitrogen...   1;048 1'006 1'000
Oxygen.... 808 -976 1/000
Hydrogen.... 1459.900 1300
Carbonic acid... 1-195 1'258 1'172
Carbonic oxide.   - 996 1'034 1'000
Nitrous oxide      1. 1193 1-350 1-159
I~~                      ~     ~~~~~~~~~~~~~~.  




70                    LiQUEFACTIO N.
These numbers show the diversity which exists among even the best expen
renters; and they also show that the different gases follow no simple law regarding their-specific heats. The principle laid down by Haycraft, Delarive, and Marcet,
that in equal volumes all gases have the same specific heat, is thus shown, by the
combined evidence of all the best results, to be totally unfounded.
It is sometimes necessary to compare the specific heats of gases
with that of water; this being 1'000, that of air is 0'267 for equal
weights, and so on for the other gases in proportion.
We do not know the specific heats of many bodies in the state
of vapour. For watery vapour, however, it is found to be 0'847,
water being 1'000, or 3'172, air being 1P000, for equal weights.
Water is thus the only substance of which we know the specific
heat in the three states-of aggregation, that of ice being 900, water
1'000, and steam'847, for equal weights.
When the volume of a gas or of a vapour increases, its specific
heat increases also, and vice versa. Hence, when air is suddenly
condensed, so much heat is evolved that tinder may be lighted, and
the barrel of a condensing syringe may become too hot to hold;
thus, also, in some kinds of machinery where air suddenly expands,
so great a degree of cold is produced that water may be frozen.
The exact degree of connexion between the amount of expansion
of the gas and the increase, or of condensation and the diminution
of specific heat, has not been ascertained.  They are not proportional; that is to say, when the volume of a gas is doubled, its spe.
cific heat is not doubled, and' vice versa; and yet it would appear
that it does not fall much below that ratio.
SECTION III.
OF LIQUEFACTION.
It has already been frequently explained, that by the application
of heat to a solid body, it commences, when its temperature has
risen to a certain degree, to become liquid, and that this point, the
melting point of such solid body, is one of the most determinate
and characteristic of its physical properties. Accordingly, the
melting point is often used as a means of distinguishing and recognising substances otherwise very similar in properties; as, for example, the numerous fatty acids can scarcely be otherwise distinguished from each other, exclusive of analysis, than by the temperatures atvwhich they melt.  There has been already given a list
of the melting points of a number of solid bodies, and, in the history of each individual substance, its fusibility will be described.
The change from the solid to the liquid state is accompanied,
however, by a phenomenon differing from any yet described, and
deserving of great attention from the' important consequences which
flow from it. It is, that at the moment of liquefaction a very large
quantity of heat is absorbed, combining, as it were, with the solid
to form the liquid body, and after combination being insensible to
the thermometer, and having thence obtained the name of latent heat.
A pound of water at 32~ and a pound of ice at 32: give on the
thermometer precisely the same degree, and yet, independent of all
considerations of specific heat discussed in the last section, and
which we now lay aside, the water contains, in a state of intimate




ABSORPTION OF HEAT DURING LIQUEFACTION. 71
combination, a great quantity of heat, by virtue of which it is liquid
water, and by losing which it would be reduced to the state of solid
ice. In melting, therefore, every body renders latent a quantity of
heat.
This principle may be demonstrated by experiments of a very sim
ple kind. Thus, if a pound of ice be taken at 32', and added to a
pound of water at 172', the ice dissolves immediately, but the temperature of the resulting two pounds of water is found to be 320
There has thus disappeared a quantity of heat, which had previously raised the temperature of the water to 172?, or through 140~.
This heat has been absorbed by the ice in becoming'liquid, and rendered latent; and it is therefore said that the latent heat of liquid
water is 140'. If a vessel of water, at the temperature of 520, be
exposed freely to air below the freezing point, it will rapidly cool
until it arrives at 323, but there the lowering of the temperature
ceases; it begins to freeze, and, until the entire mass is reduced to
solid ice, no loss of heat sensible to the thermometer is observed:
yet it must still be giving out heat precisely as it was when it cooled from 52' to 320, this heat being, however, that which gave to it
the form of liquid water, and which had been perfectly insensible,
or latent, until the formation of ice commenced. If the water had
taken ten minutes to cool from 520 to 32~, it will be found to require
one hour and ten minutes to become completely frozen; and hence,
as in the same time it loses the same quantity of heat, the external
air remaining equally cold, the latent heat is 20~ x 7=140C, as in the
former experiment. Another mode of verifying the result consists
in exposing a pound of ice at 32', and a pound of water at the same
temperature, to the same source of heat, as on a steady fire, and it
will be found that, by the time the ice has completely melted, the
temperature of the water will have risen to 1720.
Water is, of all liquids, that which contains the greatest quantity
of latent heat, and hence that which changes from the liquid to the
solid state most slowly; and inversely, ice is the solid which ab.
sorbs most heat, and requires most time to liquefy. This property
of water is of the highest importance in the economy of nature,
for by means of it the change of seasons is rendered much less
sudden than could otherwise occur. If water passed from 320 to
31~, and became solid by losing only the same quantity of heat as
it gives out in cooling from 33' to 32', the change of seasons would
be so rapid and so uncertain as to interrupt almost entirely the
proper cultivation of the soil, and, by the vicissitudes of heat and
cold, become injurious to the health. But, as these properties of
water are now arranged, each particle, in freezing, becomes a source
of warmth to all around, and mitigates the severity of the cold;
there can be but a comparatively small quantity of water rendered
solid; and when, on the return of a warmer season, a sudden liquefaction might prove equally injurious, ice and snow, in melting, ab
sorb all excess of heat, and render the change gradual, and suitable
to the functions of those plants and animals to which a sudden transition might pr6ve fatal.
We do not know the latent heat of many liquid bodies, but those
give' in the following table will suffice to show the remarkable




72      fIEAT EVOLVED IN  SOLIDIFICATION.
pre-eminence of water in that respect.  The numbers are given in
two columns; the first showing the interval through which the
body itself, in its liquid form, would be heated by the heat it absorbs
in melting, and the second showing the interval through which
that heat would elevate the temperature of an equal weight of water
Thus:
Latent Heat of     Measured by itself.    Measured by Water
Water...... 140.140
Sulphur.....-.    144.......    2714
Lead.......         370........    11.0
Zinc......  493........   483
Bismuth......  550........  2325
in every case a solid body begins to melt at the same temperature
Thus, ice never begins to melt until it arrives at 32~, and can never
be raised above 32' without melting; consequently, the fixed point
is the melting point of ice, and not the freezing point of water; for,
if water be cooled carefully without agitation, its temperature may
be lowered easily to 25~, and has been reduced to 15' without solidifying.  This is a phenomenon like that which has been (page 25)
noticed in the crystallization of sulphate of soda, where the solution
may remain perfectly liquid until agitated, and then suddenly crystallizes with the evolution of considerable heat. If water, so cooled
below 320, be agitated, it freezes suddenly, and the temperature
rises to 32~; the latent heat of that portion which freezes becoming
sensible, and thus warming the entire mass.
Substances which crystallize easily generally expand in solidify.
ing, and in doing so exert great force.  Thus water is capable of
bursting the strongest vessels if they be filled completely with it,
and tightly closed so as to prevent expansion otherwise.  It is by
the agency of this force that the gradual deterioration of the surface of rocks, and the formation of the soil on the lower grounds,
depends; the rain-water being absorbed into the pores and small
cavities which even the hardest rocks contain, and being there, in
winter, frozen, breaks open the substance of the rock, and causes
it gradually to fall to powder, thus generating the soft and porous
soil fitted for the reception and sustenance of the seeds and roots
of plants. It is also by the action of this force of expansion, exert.
ed by many bodies when they crystallize, that we are enabled to
take accurate copies of the moulds into which such substances, in
the liquid state, are poured.  Cast iron, antimony, and the alloy of
antimony used for printers' types, the alloy used for stereotype
plates, brass, bronze, and all such bodies, are capable of making
good castings by virtue of this expanding power; while bodies
which do not distinctly crystallize, as gold, silver, and copper, are
not capable of giving accurate castings, and hence the coinage of
these metals is made by stamping the necessary marks upon themr,
by means of a violent blow.
By the addition of small quantities of salts or vegetable acidls,
the freezing point of water may be considerably lowered: thus, sea.
water does not easily freeze. When such a solution is brought to
solidify, it is pure ice which first crystallizes out. Thus, from  a
strong solution of potash, ice has been obtained in large six-sided
prisms; and the ice mountains which form in the Polar Seas are




COLD BY  LIQUEFACTION.                          73
found to be almost completely fresh. This principle has been applied also to the concentration of vinegar and lemon-juice by freezing, a large quantity of mere ice being formed round the sides of
the vessel, and a central cavity remaining filled with concentrated
acid.
The principle of latent heat has been applied to the production
of artificial cold. For if a solid body suddenly liquefies without
the application of external heat, it must abstract from the surround
ing bodies the heat necessary to its liquefaction, and thus reduce
their temperature and its own.  Hence, when salts are dissolved irn
water without any chemical combination, there is cold produced.
Thus, by mixing nitrate of ammonia with an equal weight of water,
the thermometer sinks 46'; and carbonate and sulphate of soda,
dissolved in three times their weight of water, reduce the temperature, the first 16', and the second 12'.
In many cases where, by double decomposition, those soluble
substances may be formed, more powerful effects are produced by
mixing two salts together than by either separately.  Thus neither
nitre nor sal ammoniac produce much cold, but when mixed they
generate nitrate of ammonia, which is very powerful, and hence
cause a reduction of 40". In other cases the cold results from a
quantity of water of crystallization being set free and suddenly
liquefying.  Thus, when crystallized sulphate of soda is dissolved
in muriatic acid, there~'are formed bisulphate of soda and chloride
of sodium, with which but I of the quantity of water remains; and
the remaining I being disengaged, and abstracting from  the surrounding bodies the heat necessary for their liquefaction, depress
the temperature through 50'.
By using snow or pounded ice, freezing mixtures of still greater
power may be produced.  The cold is the greatest when a substance
is employed which contains itself a large quantity of water in a
combined from. Thus crystallized chloride of calcium contains
half its weight of water, and, when mixed with an equal weight of
snow, the whole becomes liquid, and the quantity of heat absorbed
is proportionally large.  By combining such freezing mixtures intense degrees of cold have been produced; Mr. Walker, to whom
the invention of most of them is due, having obtained a depression
of temperature to — 91 of Fahrenheit.
The following table contains the proportions for some of the most useful freezing
mixtures, and the degree of cold which can be obtained by means of them. It is to
be remarked, that in using freezing mixtures a great deal of the success depends on
the rapidity with which the liquefaction is produced; the thinnest possible vessels,
and a tolerably large quantity of materials should be used. For producing a great
degree of cold, it is also necessary to cool the materials previously as much as possible; thus, to produce the intense cold of — 91~, Mr. Walker had cooled the substances to be mixed dowr to -68~ by means of other freezing mixtures.
K




74  ARTIFICIAL  COLD  BY  FRIGORIFIC  MIXTURES.
FRIGORIFIC MIXTURES WITHOUT ICE.
Der
Mixtures.      Parts.   Thermnometersinks  of cold.
Nitrate of ammonia             fiom +500 to +40   46O
Water.......               fiom -[50~ to -_40  460
Muriate of ammonia..
Nitrate of potash...   5   from +50~ to +10~ 400
Water...                16
Sulphate of soda...frm 350~ to-30  530
Diluted nitric acid.     2..
Sulphate of soda... 6
Muriate of ammonia             from +500 to  10~ 600
Nitrate of potash 
Diluted nitric acid 4...        _.    __
Sulphate of soda...   6
Nitrate of ammonia..        from 500 to -140   640
Diluted nitric acid...   4
Sulphate of soda...         from +50  to 00    500
Muriatic acid..
Phosphate of soda...   5
Nitrate of ammonia..   3   from 0~ to -340    340
Diluted nitric acid.
FRIGORIFIC MIXTURES WITH ICE.
Mixtures.      Parts.   Thermometer sinks  Degree
of cold.
Show or poundedice..   2            to  50 
Common salt....
Snow or pounded ice..   5'
Common salt....   2              to —12         *
Sal ammoniac....   1    
Snow or pounded ice..  24  E                     _
Common salt....  10
~ to-180
Sal ammoniac      0        5 /
Nitrate of potash...   5
Snow or pounded ice..12
Common salt....                  to -250
Nitrate of ammonia.      5
Sno.                     _. 7
Snow...                    from +320 to -300 600
Diluted nitric acid...      fom         o     _  60o
~~Snow ~.~~ from +320 to — 50~ 820
Crys. muriate of lime......Snow...33 2f              0 to _510  830
Potash......
Snow..3                                    0rom 0- to -46-    460
Diluted.nitric acid..             0 to  6         46
Snow..                   from0   to — 66.0
Crys. muriate of lime     2 from 00 to  660         66
Snow...           8.-...
Diluted sulphuric acid    10
In the ordinary experiment of freezing mercury by a mixture of snow and crystallized chloride of calcium, success is seldom obtained unless by having two portions of the mixture, and either cooling the materials for the second by means of the
first, or plunging the tube of mercury, when it has exhausted the cooling powers of
the first, into the second and freshly-mixed portion of materials.
There are many cases in which heat is evolved from solid bodies
without our being able positively to ascertain its source, and where,




NATURE OF SPECIAL  HEAT.-VAPORIZATION. 75
consequently, it may be considered as having previously been latent
Thus, by the friction of two different bodies together, as when the
axle of a carriage becomes hot, or when, as among savage nations,
fire is obtained by rubbing two pieces of wood together. But it is
rather a misuse of words to say that the heat evolved had previously
been latent, for the latent heat of a body should properly be considered as that by which the fluid condition is conferred upon it, and
hence a solid body cannot be said to have such latent heat at all.
It is most likely that, as a diminution of specific heat accompanies
the increase of density which occurs when oil of vitriol and water
are mixed together; so where, by compression, the density of a solid
body is increased, its specific heat may be diminished, and hence
sensible heat evolved. Although our knowledge of this subject is
not at all as satisfactory as its importance merits, it has been ascertained that, when iron is violently compressed, as in boring cannon
or by repeated hammering, its specific heat becomes much less, and
the heat evolved is so considerable that the metal may easily be
made red hot. It would be well to distinguish between heat, certainly before latent, which may thus be rendered sensible, and the
true latent heat which is absorbed during liquefaction, and which
can be only given out again by the reassumption of the solid form;
and this might be done, perhaps, and its connexion with specific heat
made evident, by adopting the word special heat, or heat peculiar to
the body. Thus liquids and vapours only can contain latent heat;
but every body contains a quantity of special heat, equally insensible
to the thermometer, but becoming manifest when the specific heat
is diminished. The special heat is thus the heat which gives to the
body the temperature which it possesses, and the quantity of special
heat necessary to produce a rise of temperature measures the specific heat.
Many bodies undergo, before liquefaction, remarkable changes in
their molecular constitution: thus iron, wax, and glass become
soft and pasty, so that different pieces may be perfectly united into
one; and it is, indeed, on this property that the most useful applications of glass and iron in ordinary life depend. This has been
referred to a certain quantity of latent heat having already entered
into the body, and giving an intermediate condition, that of semifluidity. There is no proof either for or against this view, as no exact
experiments have been made upon such bodies. In other cases,
where semifluidity is produced, as in lard, tallow, &c., it is plainly
seen to arise from the substance being a mixture of two bodies, of
which one melts easily, and, being then liquid, forms with the other,
which remains still solid, a kind of pulp, which gradually becomes
less thick, according as the temperature rises, until all is liquefied
SECTION IV.
OF VAPORIZATION.
By the application of a higher temperature than that which was
necessary for liquefaction, the generality of fusible bodies are capable
of being converted into vapour. In this form they resemble, in molecular constitution, the most permanent of the gases, and are subjected




76             LATENT  HE-AT  OF  VAPOURS.
to precisely the same laws of change of volume, for. any alteration
of temperature or pressure, as atmospheric air, as long as the elastic
form is preserved. This passage from the solid or liquid to the
gaseous state of aggregation, may occur either slowly and silently,.
or with violence and rapidity; the body may either evaporate or
boil. The evaporation may go on at any temperature, even at the
lowest; but boiling commences only at a certain temperature, which
depends on the nature of the body, and upon the pressure to which
it is subjected.  Each of these modes of generating vapour will require to be specially examined; but it is necessary to attend, in the
first place, to the phenomenon which accompanies and may be supposed to produce the change of form, the absorption of the heat of
vaporization; for precisely as a solid absorbs heat in becoming liquid,
so does a liquid, in assuming the vaporous condition, render heat latent, and even in still greater quantity.
If we place upon a steady fire or over a lamp a cup of water, we
shall observe that its temperature rises until it begins to boil, but
then remains perfectly stationary until the last drop of the water.
shall have been boiled away.  if we remark the time, we shall find
it to be in the following proportion. Let us suppose the temperature
of the water to have been originally 62~, and that at the end of six
minutes it began to boil, having attained the temperature of 212~.
In each minute,' therefore, there entered into the water a quantity
of heat sufficient to raise its temperature 22 62=25o. Now, the
source of heat remaining perfectly steady, it will be found necessary to apply it during 40 minutes to boil away all the water; and
as in each minute there enters heat enough to raise the temperature
of the same weight of water 25~, the total quantity of heat absorbed
by the water in being converted into steam  would have raised its
temperature, had it remained liquid, 25 x 40= 10000, or just to redness. And yet this becomes perfectly latent, the temperature of the
vapour formed, that is, of the steam, being exactly 21o2, that of the
water it is formed from.
By the inverse process a corresponding observation may be made. Thus, water
being boiled in a vessel, as in
the figure, the steam may be
conducted bv a tube into a glass
containing a weighed quantity
of cold water, the temperature
of which is accurately marked.'.-I.' The steam, by condensing in
the cold water, raises its tem-..........li         perature; and when a sufficient rise has been produced,
the steam may be shut off, and
the glass with the warm water
weighed again. It is found to
be heavier than before, from
the quantity of water added to'l      ~ it by the condensation of the
steam; and the quantity of heat
o.....             %1Iu, 24   given out by the steam in so
condensing may easily be calculated. Thus: let us suppose that there were eight ounces of water, at 60~, originally used, and that, at the termination of the experiment, there were nine ounces
at the temperature of 1880~. It is then evident that one ounce of steam, in conden



INCREASE  OF  VOLUME  IN  VAPORIZATION.   7r7
sing, had raised the temperature of the eight ounces 1280. The temperature of one
ounce might have been, therefore, raised 128X8=10240: but this was not all la
tent heat; Ibr the steam, by merely condensing, should have formed liquid water at
212~, whereas it cooled to 1880. The difference, =24~, must be subtracted from
the 10240; and thus the latent heat of steam determined to be 1000~, as it had been
found by the previous process.
The great quantity of heat thus contained in an insensible form in
steam is very generally made use of for warming apartments and
for chemical operations, in which exposure to the direct action of a
fire, or even to a sand bath, might be injurious.  By means of a
series of pipes, steam from a boiler, placed at a distance, is brought
to circulate through every part of the most extensive buildings, and
condensing gradually as it passes along the cooling surfaces, the
liquid water is conducted back again to the boiler, there to be reconverted into steam. In large manufacturing laboratories, such as those
of the Apothecaries' Halls of Dublin and of London, there are steam
ranges, or series of evaporating pans and stills, set in cast-iron cases,
within which steam  is introduced, and thus the most delicate vege-,
table preparations, such as extracts and inspissated juices, prepared
at temperatures which, being completely under the control of the
operator, allows all the freshness and active properties of the plants
to be perfectly preserved.
By means of apparatus similar in principle to that in the last figure, the latent
heats of the vapours of many fluids have been determined. It has been found that
the latent heat of equal weights of the vapours of the following bodies would have
raised the temperature of an equal weight of water in condensing:
Water...... 1000~
Alcohol...........                  376
Ether...                             163c
Oil of turpentine........ 1380
Nitric acid.......... 335~
The latent heats of bodies, such as vinegar and water of ammonia, which have no
definite chemical constitution, but contain mixed water, do not possess any value
or importance.
In changing from the liquid to the gaseous state, the volume is
increased in a very great degree; the amount of increase, in some
instances, which may be taken as examples, is given in the following
table.
Substxnce. Spe. Gra. Boiling of V oi r  une. p' ci c
Substance.  wa~err    joint, at boiling of Vapour Girooiy of
Point.at   at21 -   V- apour.
Water...  100 2120 1696  1696   620
Alchol....   907 1720  488   519  1601
Ether...    715 970  240   289  2583
Oil of turpentine.   867 3150  221   192  4763
Mercury...13500 6600 3395  1938  6969
In the first column are the names of the bodies; in the second, theil specific
gravities, water being 1000; in the third, their boiling points; in the fourth, the
number of volumes of vapour furnished by one volume of each fluid at its boiling
point; in the fifth, the number of volumes of vapour reduced to a standard temperature, 2120, which one volume of fluid may produce; and in the sixth, the specific
gravity of the vapour, air being 1000.
It has been imagined that there should exist some physical connexion between
the increase of volume produced by the change from the liquid to the gaseous
state, and the quantity of heat rendered latent during the change; and it is, in
fact, generally true, that those bodies which have small latent heat expand least, as
oil of turpentine and ether. But, as yet, from the few experiments that have been




78 DETERMINATION OF ELASTICITIES OF VAPOURS.
made upon latent heats, with substances sufficiently pure to be taken as the basis
of calculation, nothing positive can be considered to be known.
The passage from the liquid condition to the state of vapour is
distinguished from the change of a solid to a fluid, by the important fact that, while liquefaction is definitely produced at one temperature, and at that alone, vaporization occurs at all temperatures; and it is only from the influence of external circumstances
that the change is accompanied, at a particular temperature, by the
phenomenon of boiling. The coldest water is capable of forming
vapour; even ice evaporates; and, in order to do so, it is not necessary that it shall previously melt; it is thus that snow will gradually
disappear from the ground, even when shaded from the sun's rays,
and though the air shall have continued'below the melting point.
Other solid bodies also evaporate without previous melting, as camphor; and arsenic cannot be inelted; for, when heated, it is converted at once from the solid to the vaporous condition. The particles
of volatile bodies appear thus, at all temperatures, to repel each
other to a certain degree, and to spread abroad, in the form of vapour, until they occupy completely the space in which the body is
contained, and exercise a pressure which is equal to the force of
their mutual repulsion, and which is termed the elasticity of the vapour.
The amount of elasticity, or, as it is often called, tension of a vapour, is. determined by very simple methods.  Thus, for elasticities
spatP C- a     below that of atmospheric air, a. series of. barometer tubes arranged in a stand, P P a a, are to be
oi carefully filled and inverted in a basin of mercury,
c c, as in the figure.  One such tube, d d, is to be
kept untouched, to measure the elasticity of the external air. If a little water be allowed to pass up
into the next tube, and there float upon the surface
of the mercury, it immediately forms vapour, which
spreads through all the empty space, and, pressing
against the upper surface of the mercurial column,
counteracts a portion of the pressure of the external air.  The remaining pressure of the air is able
to support, therefore, only a shorter column of mercury, and the height of the mercury in the tube
diminishes. If into another tube some alcohol be
introduced, there is a similar, but still greater depression of the mercurial column caused, and with
ether the height of.the mercurial column is still
c  more diminished. The atmospheric pressure in
lP - e~. Cthese cases balances the shortened column of merP~:_           cury added to the elasticity of the vapour, and this
last is consequently measured by the height of the
column of mercury which it is capable of replacing, that is, by the
space through which the mercury has been depressed, which is
read off by the rule and index, r v r. Thus, if the barometer be at
30 inches and the temperature 800, the mercury will stand in the
tube with watery vapour at 29 inches, in that with alcohol at 28'1,
and in Ihat of ether at 10 inches. The elasticities of these vapours
are therefore at the temperature of 80~.




DETERMINATION OF ELASTICITIES OF VAPOURS. 79
Vapour of water............  0 inch.
4"  of alcohol.............    19
of ether............. 200
In order to ascertain how the elasticity of a vapour changes with
the temperature, it is only necessary to enclose the upper part of the
tube in a cylindrical case containing water or oil heated to the
necessary degree. As the heat increases the height of the mercurial column will diminish, and at each temperature the elasticity is
so determined.  The apparatus may be modified by bending the
tube so as to immerse the bent portion containing the vapour into
a globe of water or oil to Which heat may be applied, but the principle remains the same. In this way a table of the elasticity of a
vapour at all temperatures below their boiling points may be formed; and as there will be frequent reference hereafter to the tension
of the vapour of water, the following table is introduced for use
and as an example:
Temperature.    Elasticity.'l'emperature.l   Elasticity.
32~   0 200  A900    1 36 
400   0 263 g  1000    186;
500   0375  } 120~   3'33  {
550   0443    1400   5-74 
600   0,524 ~  1600   9'46 ~
650   0 616.  1800   1515.15
700   0'721.  2000  23'64.C
800   1-000.d  2120  30.00.5
When a liquid, in such an apparatus, is heated until the vapour
formed occupies all the tube-and expels the mercury, the elasticity of the vapour is equal to that of the air, and the liquid exposed
to the air boils; the phenomenon of boiling arising simply from
the fact that the elasticity of the vapour balances the pressure
of the air while the bubble is passing through the fluid: thus,
suppose a vessel of water exposed to the air at 200^, and a bub
ble of steam to form in it; the pressure exercised by that bubble
being equal to its tension, is equivalent to a column of 23'64 inches
of mercury; but the external pressure being 30 inches, the bubble is crushed in by a force equal to the difference (6.36 inches
of mercury), and, consequently, dispersed. If the water, however,
be heated to 212', the elasticity becomes equal to 30 inches, and
then the external and internal pressures being equal, the bubble
rises in the liquid without injury, and maintains itself at the surface
until its investing film of water is ruptured by other causes, when
the vapour mixes uniformly with the air.
It is the burstingr of the steam  bubbles that are first formed in
this manner that constitutes the simmering of a boiler or the singing of a kettle on the fire. The bottom of the vessel heats more
strongly the layer of water in contact with it, so that the steam has
there a high degree of elasticity, and forms a multitude of minute
bubbles; when these separate from the hot metal, they are immediately burst in by the greater external pressure, and the mass of
water is thus thrown into a state of exceedingly rapid and uniform
vibration, which fall upon the ear so regularly, in many cases, as to
produce a musical and often agreeable tone, which may become




80 DETERM IINATION OF ELASTICITIES OF VAPOURS.
graver or more acute, according as the bubbles burst more or less
rapidly after one another.
The elasticity increases very rapidly with the temperature, as is
seen in the table, where, in rising from 180' to
2.'12, the elasticity is doubled. For high temperatures the rate of increase is still more rapid.
To determine the elasticity at temperatures
above the ordinary boiling point, an apparatus
completely cut off from the external air is made
use of. In the figure there is a globular vessel
of strong metal, a, into which is introduced by
the stopcock d, the fluid to be experimented on,
as, for example, water. In the aperture c is
fitted a thermometer, the bulb of which dips
into the fluid near the centre, and shows its temperature. A quantity of mercury.being in the
bottom of the vessel, the tube b dips under its
c      ~ A      d. surface, and, rising to the necessary height, has
attached to it the scale divided into inches and;fi d    their parts.  When the apparatus is heated, as
the vapour produced cannot escape, all junctures being perfectly steam-tight, the temperature rises continuously in place of stopping at
the boiling point, and the vapour formed pressing on the surface of the remaining liquid, and
by it on the mercury underneath, forces the
-' mercury up the tube b until the mercurial column shall have attained such a height as to counterbalance by its
weight the elasticity of the vapour.  In these cases the elasticity
is generally reckoned by atmospheres, each atmosphere being equivalent to a mercurial column thirty inches high. In this manner the
vapour of water has been found to exert a pressure of
I atmosphere at 212~'         16 atmospheres at 3980
2 atmospheres at 2500         20  "4         418~
3   "         275~            25   "   "   4390
4   "   "    294              30   "   " i 457~
6   i"        3200            40   " "       4860
8 "i   it  3420               50  "i   "    510~
12  s"   "    3740
It is necessary, in order to understand such tables, to observe
that this great increase of the elasticity of steam, as the tempera.
ture rises, results not from the expansion of steam already formed,
but from the constant addition of new quantities of steam for every
variation of temperature.  If a globe full of steam  at 212', but
containing no liquid water, were heated to 294~, it would tend to
expand. precisely as air or any other gas, and the increase of elasticity would be only from 30 to 34 inches, or from  1 atmosphere,
to 1i; but if the globe contain liquid water, there is sach an additional quantity of vapour formed and compressed into the same
space, that the elasticity becomes equal to four atmospheres, or to
120 inches of the mercurial column. Also, when the pressure on
vwpour is made to vary, the result deviates from the rule laid down




RELATIONS  OF  VAPOURS  TO  PRESSURE.    81
in page 20, for the action of pressure upon gases; for the elasticity
of a vapour cannot be really increased by any increase of pressure:
it remains the same, but a quantity of the vapour becomes liquid,
and there continues in the state of vapour only as much as occupies
with the saine elasticity the diminished volume which the column
of rnercury leaves.  Thus, if we consider the bent           b
tube a b, of which the extremity at a is closed,.............
and the leg a occupied from  the dotted line c d
by vapour of ether at its boiling point, and balancing in the leg b a column of mercury thirty
inches high.  If, now, without allowing the tern-..... 
perature to change, mercury be poured in at the
orifice of b until it shall rise in a up to the line f
g, and occupy exactly one half of that leg, the va-               i
pour will not be compressed into half its volume,
and, acquiring  a double  elasticity, support 60
inches of mercury as a gas should do, but one
half of the ether will assume the liquid form, and....
the remainder, occupying the remaining half of                 f.
the original volume, will balance 30 inches of mercury precisely as it did before, and the pressing
column, counting from  the line fg, will terminate c                     i
at h.
If, however, in place of attempting to increase the pressure on a
vapour, we diminish it, then the vapour preserves its elastic form,
and its elasticity diminishes in all respects as if it were a gas.
The specific gravity of a vapour, formed at any certain temperature, should be
proportioned simply to the elasticity, if the volume were not altered by the change
of temperature, and it should be inversely as the volume if it could all remain uncondensed; but, in reality, the relation is more complex, and may be calculated
upon the following principles. Thus, if we wish to know the specific gravity of vapour of water having an elasticity expressed by 7'42 inches of mercury, and the
temperature 150~, we proceed as follows: the specific gravity of steam at 30 inches
and 212~ is 620'2; and hence, if the volume did not change, the specific gravity of
the vapour at 1500 should be 620-2X   o%~-L-15339; but in cooling from 2120 to
1500, the portion of steam which retains its elastic form is compressed within a
smaller volume, and hence has its specific gravity increased in proportion to the
change, and therefore the 153'39 obtained above must be increased in the proportion of the volume at 1500 to the volume at 212~, or as 611: 673, and thus becomes
169.24. The subjoined table contains specific gravities for some temperatures calculated in that way, and accompanied by the temperatures, the elasticities, and the
weight in grains of 100 cubic inches of the vapour.
Elasticity in specific Gravity  Weio'htof I0
Temperature. Inches opecfic.r..y.  Weig ne. 100
SMiercurv.  ilAOOO.  cubic Ieetles.
320    0'200     5.68 0I1361
500~   0'375    10-17   0'2474
600    0:524    14'06   0'3387
100~ 0    1'860    46'36 - 1'1028
150~    7'420   16924 4/0543
212~   30.000   620 20  )1496)00
There is some reason to suspect, however, that vapours do not follow exactly the
theoretic rules upon which such tables are constructed, and which, in reality, apply
only to gaseous bodies. Thus, Despretz has found the specific gravity of the vapour of water to be at 670 7'72, while by this calculation it should be 17 26, air at
212~ being 1000; his results cannot be considered as decisive, although they show
the necessity for an accurate re-examination of the subject. At very high temperaL




82   PROPERTIES OF COMPRESSED VAPOURS.
tures, the elasticity does certainly not increase with the specific gravity when the
volume remains constant. Ether is found to become gaseous, and to occupy only
twice the volume it had when liquid, at the temperature of 320~, and its elasticity
in that state equals 38 atmospheres, whereas, by calculation, its elastic force should
be 168 atmospheres. Alcohol, enclosed in tubes hermetically sealed, is totally converted into vapour, occupying only three times the volume of the liquid at 404~, and
then exerts a pressure only of 129 atmospheres, while by theory the pressure should
equal 221. Water, also, was obtained by Cagniard de la -Tour gaseous in foul
times its liquid volume at 7730, and should then, by theory, have an elasticity of
780 atmospheres, a force far above what the glass tube employed could possibly
have resisted. It would appear, therefore, that vapours, so far as the relation between their specific gravity and their elasticity is concerned, do not follow exactly
the same law as gases except within certain limits; but that, when the elasticity is
much smaller or much greater than the atmospheric pressure, variations which are
very remarkable, though not as yet well understood, present themselves.
When a vapour, as, for example, steam, which has been generated
in close vessels, and attained a great elasticity, is suddenly allowed
to escape into the air, its temperature is suddenly reduced in a remarkable degree, even independent of condensation.  If the steam
had been formed under a pressure of four atmospheres, its volume
is, but one fourth of what it should become when free, and hence,
on escaping, it expands in that proportion; under that pressure
its temperature bad been 294P, but by the increase of latent heat
it falls immediately to 212;'; there, however, the expansion does
not stop; the impulse of the particles of vapour carries them much
farther; and as the specific heat increases so as nearly to be doubled
when the volume becomes doubled, a considerable reduction of the
temperature below 212~ occurs, which is still farther increased by
admixture of cold air which presses into the rarefied space left by
the expansion of the steam.  Hence it is that steam  escaping into
the air from under considerable pressure possesses much less heating power than steam arising from water boiling in an open vessel:
it is much less liable to scald.
The principle of the conversion of a solid or liquid body into a
vapour at all ordinary temperatures is true, even where the body
may be very little volatile. Thus the space over the mercury in the
best barometers is not truly empty, but contains a quantity of mercurial vapour, exercising a certain elasticity, and, by d.cpressing the
liquid column, making the pressure of the external a'r appear smaller than it really is. It would appear, however, that there are, for
some bodies at least, temperatures below which evaporation does
not go on; thus no mercurial vapour can be detected unless the
temperature be above 40', and oil of vitriol requires to be heated to
120' before any vapour forms from it: it is probable, however, that
even in these cases the general principle holds good, and that it is
only from the minute quantity of vapour eluding our means of re
search that the existence of a limit to evaporation was believed.
The boiling point of a liquid being that at which its vapour can
support the external pressure, it is liable to constant fluctuation as
the pressure changes, and hence the fixing of the temperature of
boiling water upon the thermometer requires the care and attention
already noticed.  If the barometer stood at 23'64, water would boil
at 200' in place of 2123; and so close is the connexion between the
pressure and boiling point, that the height of any place aba ve the
level of the sea may be determined by the temperature at which




NATURE  OF THE  BOILING POINT..                  -86'
water boils there. Thus, if, on heating some water on the summit
of a mountain, it be found to boil at 203', we find, by reference to a
table, that the elasticity of its vapour is then 25-1 inches, and hence
that in the same place, at the same moment, the column of mercury
in a barometer should have been at that height. Then, by the ordinary calculation, the height of the mountain may be found with
as much accuracy as if the barometer itself had been carried up. On
the summit of Mount Blanc, the highest point of Europe, water has
been found to boil at 184o.
By reducing,; artificially, the amount of pressure upon a fluid, as
by placing the vessel containing it under the receiver of an air-pump
and exhausting the air, the boiling point is lowered in a remarkable
degree. If the vacuum were perfect, a fluid would boil even at the
lowest possible temperature; but this is not practicable, as the vapour formed cannot be so perfectly removed but that it will exer
cise some pressure; but, with a good air-pump, fluids may be got
to boil 145~ below their ordinary boiling points;- thus water will
boil at 67T, alcohol at 32~, ether at a temperature at which quicksilver would freeze. If, at the moment that such a fluid is in violent
ebullition, the working of the pump be stopped, the vapour accumulates, and, exercising on the surface of the fluid an amount of pressure corresponding to its elasticity at the existing temperature, raises the boiling point, and thus stops the ebullition. This fact may
be shown in a very simple and singular manner, by half filling a
flask, B, with water, and boiling the water until all the air in the
flask shall have been expelled, and then carefully closino the mouth of the flask, b, by an airtight cork. On removing the source of heat,
p   the upper part of the flask, B, when inverted
as in the figure, remains full of vapour, which,
pressing upon the liquid water, arrests the ebul_'81    }         lition. If, then, p jet of cold water, p, be allowed
to play upon the flask, the -vapour is condensed,
and, a vacuum being thus produced, the water
begins to boil; if a jet of warm water be employed, the vapour retains its elastic form, and
the ebullition ceases, so that in this apparatus
the application of cold may appear to cause,
/7/b ~and that of heat to prevent, the water's boiling.
The temperature at which a liquid boils is thus totally dependant
on the amount of pressure to which it is subjected. But the limits
within which that pressure varies near the level of the sea, in ordi-:
nary cases, are so small, that the boiling point may be looked upon
as one of the most important characteristic properties of a volatile
substance; and from the facility with which it may be determined,
it is almost universally capable of being applied. Hence, in describing such bodies, the boiling point will be in all cases given; but,
for illustrating the present subject, a table of the boiling points of
some of the most remarkable liquids is subjoinefd:




-84      ANOMALOUS PROPERTY  OF LIQUIDS.
Muriatic ether..      52~   Water...2126
Sulphuric ether..  96~      Nitric acid..... 2480
Sulphuret of carbon..116~    Oil of turpentine... 3150
Pyroacetic spirit.  1320       Phosphorus.... 5540
Water of ammonia.. 1400      Sulphur.6...01
Pyroxylic spirit... 151~    Sulphuric acid.... 630o
Alcohol.....            173~ Mercury....     660The boiling point is influenced by some other circumstances than
the atmospheric pressure; the nature of the vessel may alter it several degrees. Thus, in a glass or glazed porcelain vessel, water
boils, under a pressure of 30 inches, not at 21w', but 214P; and in
graduating a thermometer, it is hence necessary to use a metallic
vessel. This latter appears to favour ebullition by the minute irregularities on its surface, affording a nucleus for the steam to form, as
a crystal dropped into a saline solution facilitates the crystallization;
and if the smooth surface in the glass vessel be removed in a single
point by a scratch with a diamond, the bubbles of steam will be seen
to form there before the general mass of liquid comes to boil.  The
influence of roughened or angular surfaces in thus favouring the
escape of steam, may be shown very well by heating water in a glass
flask to boiling, and then allowing it to cool a little, so that the boiling shall completely cease; if, then, a little filings of copper, or a
platina wire, be dipped into the liquid, if the cooling had not gone
too far, the boiling will immediately recommence, the steam forming
at the edges and angles of the rough substances introduced.
Tlie temperature of the steam  produced is not affected by the
boiling point of the liquid. Thus, although by dissolving salts, such
as chloride of calcium, in water, its boiling point may be raised to
264~, the temperature of the vapour immediately over the solution
is found to be but 212~; for, though the temperature of a steam bubble which rises up through such a solution must be 2642, yet, as its
elasticity and latent heat are proportional to that temperature, it expands on mixing with the less elastic atmospheric air, and is cooled
down instantly to the ordinary boiling point.  The heat of a waterbath may thus be increased by the addition of saline bodies; but
the temperature of a steam-bath depends only on the elasticity of
the steam.
A curious, though only apparent, anomaly in the relations of liquids
to their boiling points consists in the possibility of the vessel containing the liquid being heated even to redness without the liquid
boiling, though exposed only to the ordinary pressure.  This may
easily be shown by heating a platina crucible to redness, and dropping into it al small quantity of water; the water remains on the redhot metal without disturbance, and appears scarcely to evaporate;
but if another crucible be heated to 300~, and the water be poured
out of the first into the second, it instantly boils, and is dissipated
in a gush of vapour.  The reason is, that in the red-hot crucible the
water is not really in contact with the metal, and hence the heat
passes to it with extreme slowviess; but the water wets the colder
crucible, and, absorbing from it all the necessary heat, is instantly
converted into steam.  The cohesive force of the metal to the water
being diminished considerably, this lies in a red-hot crucible as a
clean steel needle floats on water, or a globule of mercury moves




ARTIFICIAL  COLD  BY  EVAPORATION.                   8
cupon glass, and is not affected by the heat until it wets the vessel,
just as the needle does not sink in the water until it is wetted by it.
At certain temperatures all liquids manifest the same peculiarity.
When a liquid evaporates at a temperature below its boiling point,
it still absorbs and renders latent a great quantity of heat, and, indeed, more heat than it would render latent when converted into vapour by ordinary boiling. It has been found, by accurate experiments with water, and there'is good reason for supposing it to hold
also with liquids in general, that no matter at what temperature a
liquid vaporizes, it absorbs the same total quantity of heat. The
more of this that becomes sensible, the less is the portion which remnains latent, the sum of the latent and sensible heats of the vapour
being at all temperatures the same. Thus, with vater evaporating at
32~, the latent heat is 1180. the sum being 1212
1000,    4   "   1112,   "   "   1212
212~, "'   "   1000,   " "        1212
30O~,    "   "    912,   "   "   1212
There is, therefore, no economy in evaporating or distilling at one
temperature rather than another, as the same absolute quantity of'
heat is necessary for the formation of the steam; but, for other
reasons, the formation of vapours at low temperatures affords to the
chemist processes of the greatest value.  Many vegetable substances
undergo important alterations in their chemical constitution and medicinal properties if they be exposed for a long; time even to a heat
of 212'; and hence, in the preparation of extracts and inspissated
juices of plants, in pharmacy, formns of apparatus are sometimes
employed, in which the evaporation is carried on in close vessels
connected with an air-pump, and in which a partial vacuum, measured by a barometer gauge, may be established. In the manufacture
of sugar, this principle of evaporation at low temperatures, by removal of the atmospheric pressure, was the source of great improvement, as the true crystallizable sugar is converted into the uncrystallizable sugar (treacle) with great rapidity at the temperature. of
boiling sirup, and was hence, to a great extent, lost to the manufacturer. By later improvements in the mode of applying heat, the
necessity of evaporating the sirup in vacuo has been, however,
completely obviated.
The absorption of heat in the conversion of a liquid into a vapour,
at ordinary temperatures, may become the source of considerable
cold; and it is, indeed, in this way that the greatest cold yet generated has been produced. The cold which is felt when a little ether
or spirits of wine is dropped on the hand, arises from this fact; and
by surrounding the bulb of a mercurial thermometer with some loose
cotton, and moistening it with liquid sulphurous acid, the quicksilver
in the bulb may easily be frozen. By placing some ether in a shallow, thin metallic cup, which rests in a glass vessel containing a
small quantity of water, and producing, by the air-pump, the rapid
vaporization of the ether, the water may be so frozen that the two
cups shall adhere firmly together by the intervening sheet of ice'.
Water may be even frozen by its own evaporation, as in the cryophorus, which consists of a long tube terminating in bulbs which
contain some water, and from which the air had been carefully ex



86 S Y NCHRONOUS F REEZING AND. EVAPORATION
pelled by boiling before the apparcatus Aras completely closed. The
=.~ ~:~:~ -' —- a........ space above the water remains then oc| H g icupied only by watery vapour. If all
the water be brought
into one bulb, and
the other bulb be im-., i'/_.: mixture, the vapour
will condense there,
~./i/i./I///////                   and new vapour be-"=  ing formed, a distillation will be produced from the one to the other bulb. The vapour
which forms in the warm bulb must derive its latent heat from the
water which remains behind, and this is gradually cooled to the
freezing point, and ultimately completely frozen; the latent heat
of about eight parts of water being given up to form the latent heat
of one part of vapour at 32~. Even without the application of artificial cold, water inay be frozen by its own evaporation.  Thus, if under the receiver of an air-pump
we arrange two flat dishes, the upper containing
water, the lower containing oil of vritr;rl -ar- then,
having removed the air, we leave the -apparatus Ior
a sliort time to act, we shall find the water in the
upper vessel converted into ice. Accordingly, as
any portion of vapour forms, it is immediately absorbed by the sulphuric acid, which has a great affinity for water; and the vapour being thus prevented
from collecting, the loss of heat by evaporation proceeds unceasingly, until so much heat has been removed that the residual water is converted into ice.
In fluids more volatile than water, this synchronous freezing and
evaporation may occur still more simply. Thus, if strong prussic
acid be allowed to form a pendant drop from a glass rod, the drop
will become solid by the evaporation of one portion of it, and the
cooling of what remains. The remarkable phenomenon of the solidification:of carbonic acid arises from the same principle. A jet
of liquid carbonic acid being allowed to escape into the air, one
portion instantly flashes into the state- of gas, and absorbs so much
heat that the portion which remains is converted into a compact
solid mass..
In: warm climates, the evaporation of water is commonly employed to moderate the sultriness of the- air, by the agreeable cold and
freshness it produces. The Spanish alcarrazas are earthen vessels,
so porous that any liquid which is put in them  gradually filters
through, and, evaporating from the outer surface, cools the interior
mass. In chemical operations, the same mode of. refrigeration is in
constant use;.and when- describing these operations, the action of
this principle, in the construction: of the apparatus used, will be referred to.
-'*he conversion of a liquid into- vapour at ordinary temperatures




SPONTANEOUS EVAPORATION.                         87
IS often called spontaneous evaporation; and in the case of water,
from the great extent to which it becomes subservient to the economy of nature, this process is one of high importance.  It was formerly supposed that the atmosphere was necessary to evaporation;
and this idea was strengthened by the fact, that by a current of air
the evaporation is much assisted; but it is now established that the
pressure of air is really an obstacle to evaporation, and that a current is useful, not by supplying new quantities of air, but by removing the vapour according as it is formed, and leaving fresh
spaces into which it may expand. When a liquid forms vapour,
the quantity formed is determined only by the space into which
the vapour may spread, and by the temperature. It is no matter
whether the space be occupied before by other vapours or by air,
or whether it be a vacuum; the quantity of vapour which can form in
it is in all these cases the same.
Dalton was the first who clearly showed that different gases and
vapours offer no resistance to each other's elasticity: thus, that the
particles of watery vapour in the air are not subjected to the pressure of the atmosphere, but only influenced by the pressure of the
particles of the same kind; and hence, that at 32'., when the elasticity of vapour is only 0'200 inch, it retains perfectly its elastic
constitution, though diffused through an atmosphere, the elasticity
of which may equal thirty inches. If we moisten the interior of a
bell glass, filled by air, with ether, alcohol, sulphuret of carbon, and
water, all mixed together, there will be formed in the bell as much
of the vapour of each substance as if the bell had been completely
empty of the others; each vapour will exercise a pressure proportional to its elasticity, and by the sum of all these pressures, the
pressure of the external air will be equilibrated. It is, consequently, possible to produ'ce the rapid evaporation of one fluid, while another beside it, or even mixed with it, shall not evaporate at all; it
being only necessary to remove the vapour of the one as rapidly as
it is formed, while the portion of the vapour of the second produced in the first instance shall remain, and prevent its farther change.
Thus, by placing a shallow dish of dilute alcohol under the receiver of an air-pump, with a quantity of quicklime, the latter combines
with and absorbs. the watery vapour as fast as formed; and there
is, hence, a continual evaporation of the water, while the alcohol,
after generating as much vapour as once fills the receiver, is pressed upon by it, and cannot form any more. In this manner, alcohol,
almost quite pure, though much the more volatile, in the ordinary
sense, may be obtained by the evaporation of its solution in water,
as it were to dryness.
If the liquid be in excess, the vapour possesses the elasticity
belonging to its temperature; but if there be not liquid enough to
form so much vapour, the vapour formed then expands, so as to occupy the entire space, and its elasticity diminishes in proportion to
the increase of volume; vapours being regulated by the same law
of pressure which holds with gases.
If, thus, a bell glass of atmospheric air be confined over water at the temperature of 800, a quantity of vapour diffuses itself through the air, and, as there is
water in excess, the elasticity of that vapour will be 1'00 inch. Now if we suppose
the elasticity of the air to have been previously 30 inches, it will become, by the




88               MOIST-BULB  HYGROMETER.
addition of the vapour, 29, for the vapour counteracts one inch of the external atmospheric pressure; the air in the bell glass will then expand in the proportion of
30 to 29; or, what is the same in practice, the volume of the damp air is thle same
as the volume which the vapour should occupy, if condensed in the proportion of its
own elasticity to the atmospheric pressure, added to the volume occupied by the
air when dry'. It is thus that the volumes of gases collected over water are corrected for the watery vapour that is mixed with them. Thus, in the analysis of a
substance containing nitrogen, let us suppose that 8'54 cubic inches of nitrogen have
been collected over water at the temperature of 630, and the barometric pressure
being 29'35 inches; at that temperature the elasticity of vapour is 0'58, and hence
that of the dry air is 29'356-058-28'77. The volumes which they occupy are as
these numbers, and hence the 8'54 of damp gas consists of ~ —534 X8 54=-017 of
watery vapour, and 2 8,  X 8'54-8 37 of dry nitrogen.
This volume should still' be corrected for temperature and pressure before the
quantity of nitrogen by weight could be obtained from it.
Where the air is not completely saturated with the watery vapour, it is not so easy to determine the exact quantity of vapour
which it contains.  One of the best methods consists in cooling it
until its volume is so much diminished that the quantity of vapour
is sufficient to saturate it, and from  the temperature at which this
occurs the quantity of vapour may be calculated.  This temperature
is termed the dew point of the air or' -gas, because, if cooled in the
least below that point, a quantity of liquid water is deposited in the
form of dew upon the neighbouring cold bodies.  This may be easily done by takinog a tumbler of water somewhat too warinm, and
cooling it gradually by dissolving in it a little mixed nitre and sal
ammoniac, until a slight deposition of dew is perceptible on the exterior of the glass; the water is then at the temperature of the dew
point. Another method consists in observing the rapidity of evaporation from the surface of the bulb of a thermometer which is
covered with muslin kept wet by water. The thermometer so arranged is always at a lower temperature than an ordinary thermometer, from the quantity of heat carried away by evaporation, and
the temperature will be lower in proportion to the amount of evaporation.  In dry air, evaporation is quickest; in air saturated with
moisture evaporation ceases, and in all intermediate degrees there is
a connexion between the quantity of moisture already present in the
air and the depression of temperature, which accompanies the formation of as much more as will saturate it.  This method is peculiarly
of interest from the means which it afforded to Apjohn of ascertaining the specific heats of the gases already noticed, and it is easy
now to understand the general principle upon which his process
was established. If we consider a certain space which may be filled by the different gases in succession, and these gases being dry,
they are made to saturate themselves with watery vapour, for the
formation of which they themselves supply the heat, it will be easily seen, that'as the quantity of heat to be given out is the same
for all, their temperatures will be reduced in a degree inverse to
their specific heats.  Hydrogen with a high specific heat will only
require to cool about one third the number of degrees necessary for
air or other gases. The numerical results obtaine'd by this process
have been already given.
Instruments for the purpose of determining the quantity of the watery vapour
which the atmosphere contains are termed hygrometers, and that of Daniell is one
of the most elegant and most useful. It is a cryophorus, a b c, which in place of




S-TEALM  AS  A  MOVING  POWER.                          89
- water contains ether, and in one bulb of
which, b d, is fixed a very delicate thermom&Cf  dl  eter. This bulb is made of blackened glass,
and the other bulb, a, is covered with a little
bag of muslin. All the ether having been
made to pass into the black glass bulb, a little
ether is poured on the muslin envelope of the
other. This, by condensing the vapour inside,
causes the ether to distil from the blackened
i   bulb, and thus cools it and the air in contact
with it, until it arrives at the point of satura1iX!! i         tion, when a dew of liquid water begins to be
deposited, which is at once observed upon the
~:~d a   btlackened glass. The internal thermometer.b'i~' shows the temperature of the bulb, which is
0t\Y    the dew point, and a thermometer which is
attached to the support of the instrument
shows the temperature of the external air.
When the dew point has been thus determined, the subsequent calculation is very
simple.  Thus, if there be air at'72~, of
which the dew point is 450, the barometric pressure being 30 inches, the elasticity
of steam at 450 is 0'316; and as the elasticity diminishes according as the volume
increases from 450 to 720, the elasticity of the vapour in the air at 72~ is 0'30; and
the atmospheric pressure of 30 inches is produced by the dry atmosphere, which
balances 29'70, and the watery vapour which balances 0'30; and the respective
volumes are as these pressures.
Gay Lussac has sought to establish a close relation between the manner in which
solid bodies dissolve in liquids, and that in which vapours diffuse themselves through
space. Thus, if a solid body dissolved only because the liquid diminished the cohesion of its particles, the diminution of that cohesion in another way should increase the solubility very much: this, however, does not occur. When paraffine
dissolves in alcohol, the solubility increases steadily with the temperature, and does
not change more rapidly at the temperature when the paraffine melts than at any
other. This is the case also with many other easily fusible bodies. Hence he compares the diffusion of particles of the solid through the liquid to the diffusion of particles of vapour of water through the air, which is not affected by the solid or liquid
form of the water, but depends only on the temperature; and certainly this view,
though not applicable to all, or even the majority of cases of solution, is of much interest, as pointing out a similarity between solution and vaporization previously unnoticed, and which may be applied to the explanation of many anomalous facts.
The employment of steam  as a moving power is of so much ilgportance to science and to the arts, that it would be improper to
terminate a discussion of the properties of vapours without any
allusion to the manner in which it is utilized.  The little steam cylinder of Wollaston figured in the margin contains all
that is essential to the application of steam, in principle, to produce motion. A glass tube, terminating below in a bulb, is fitted with a little steam-tight piston,
which slides up and down, the lrod passing through the
brass cap at top.  If, now, a little water be placed in
the bulb and boiled, its steam, pressing on the bottom
of the piston, forces it up; and when at top, if the bulb
be dipped into cold water, the steam  condenses, and
the pressure of the external air forces the piston down
again.  This may be repeated any number of times,
and is the essential element of the atmospheric steam
engine of Newcomen.  It was in this form when Watt
commenced his improvements on it; and by applying
all the resources of the exact knowledge of the properties of heat
M




90    BOILING  POINTS  OF  CONDENSED   GASES.
then first obtained by himself and his illustrious associate Black,
he converted it, though still without chancing its fundamental principle, from  the machine of Neweomen, which had been rejected
from  practice for its inefficiency and expense, into the instrument
which, after the art of printing, must be considered as the most
powerful material agent of human improvement and civilization of
which mankind has ever obtained possession.
The similarity of constitution of gases and vapours has been already pointed out
on many occasions, and particularly, in page 21, the conversion of gases into liquids
by the application of great pressure has been detailed. A liquefied gas so contained in a close vessel is precisely in the condition of water heated in a digester,
as in the apparatus figured in page 80, far above its boiling point, and generating
steam possessed of considerable tension.  On this analogy has been founded an interesting speculation concerning the temperatures at which the gases would, at ordinary pressures, assume their liquid form, that is, their boiling points when liquid,
thus:
At 44'50 the tension of liquid nitrous oxide is 50 atmospheres.
At 32'00                 " "               44      "
For 12'50 an increase of tension of...    6 atmospheres.
Steam exerts a pressure of 50 atmospheres at... 51.15~0
and of 44..... 497.50
For six atmospheres the difference is....      14.0, or just the same.
Liluid carbonic acid exerts a pressure of 25 atmos. at    320 } Difference 20
and of 20  "  120
The tension of steam is 25 atmospheres at...   4. 39  50~
20     "   "                  418 5~   Difrerence, 210
Muriatic acid exerts, when liquid, a tension of 25 atmos. at  25~  Difference
and of 20      "     30  Difference, 220
Steam balances 25 atmospheres at.439'50  Difference, 21~
20      "      "                      41850 
Ammonia liquefies and exerts a pressure of 6'5 atmos. at    50~  Difference, 18~
and of 5    "   "    320 
Steam exerts a pressure of 6'5 atmospheres at... 32      Diference   8
5'0... 30750 -Difference, 18'50
It is hence evident that, in every case, the rate of increase of elasticity of these
gases with the temperature follows the same law as that of steam; and there is,
therefore, good reason to believe that, if the elasticity were diminished to one atr-osphere, the reduction of temperature necessary to effect it should be regulated
by the same law as that of watery vapour; the gases should then, under the ordinary pressure of 30 inches, become liquid, and when liquid, their boiling points
should be:
Nitrous oxide.= - 2524~0 Fahrenheit.
Carbonic acid.                -   230'80      "
Muriatic acid.......         -     202.00      "
Ammonia.....- - 634~ "
The great increase of elasticity which these liquefied gases acquire by a change
of temperature, limited to a very few degrees, has led to sanguine opinions of their
advantages as a source of power in machines. No experiments at all sufficiently
satisfactory to be decisive upon the question have as yet been made.
There are some other properties of gases which, although closely connected with
the subject now discussed, I shall postpone, in order to introduce them where they
are found to be of'the most practical importance. Thus, the manner in which
gases spread through each other, in virtue of their diffusive power, will be descri
bed under the head of Atmospheric Air, to the proper constitution of which this
law is indispensable.  The relation of gases to water, their solubility in that and
other liquids, and the various modes of depriving them of moisture for the purpose
of chemical experiments, shall enter into the history of the physical and chemical
properties of water.




CONDUCTION OF HEAT.                       91
SECTION V.
OF THE TRANSMISSION OF HEAT THROUGH BODIES.
It is a matter of every-day experience, that heat may be propagated
from one part of a body to another, and also that this propagation
takes place in unequal degrees with different bodies. Thus, if one
extremity of a poker be heated to bright redness, the oth!~r wvill become so hot as to be intolerable to the hand; while, 1' a stick of
the same length be inserted in the fire, the heated extremity may be
completely burned of, without the farther extremity having its temperature raised in any remarkable degree. The extremity of a glass
rod may be melted by the flame of a blowpipe, though held in the
fingers scarcely an inch from the flame: but we shall find it difficult
to melt the extremity of a silver wire, from the heat spreading itself generally through its mass, and elevating the temperature of
its entire length almost to the same degree. Bodies which act like
silver are said to conduct heat well, and are termed conductors.
Bodies which intercept it, like wood or glass, are termed non-conductors. It is only a difference of degree, for there is no body
which prevents totally the passage of heat across its mass.
The propagation of heat through a body, in virtue of its conducting power, is supposed to take-place from particle to particle, precisely as, when we apply a heated to a cold ball of iron, the latter
becomes warmed at its point of contact. If, in place of using balls
of iron, cubical masses were employed, touching by their surfaces,
the communication of heat would be much more rapid, from the
greater number of points at which transmission could take place.
In the interior of a body we should expect, therefore, to find the
degree of approximation of the particles to have some influence on
the rapidity of transmission, that is, on the conducting power, or, in
other words, that the power of conducting heat should have some
relation to the density and the cohesion of each body.
3Many series of experiments have been made to determine the conducting power of different bodies. Such experiments may be arranged in a variety of ways. Thus, if a number of similar rods, of
different substances, be coated to a certain distance from one extremity with wax, and then heat be applied to the other extremity,
the wax will melt according as the temperature of each rod rises,
from the transmission of the heat along it; and the length of the
coating melted at the end of a certain time will be a measure of its
conducting power. Another mode consists in forming the substances to be tried into disks, and, having placed a small morsel of
phosphorus upon each, warming all equally by laying them on: a
heated surface. The phosphorus inflames first upon the disk which
transmits most readily-the heat, and on the other disks in- the order
of the conducting power of their substance. But suchexperiments
are only useful in giving the order of conducting power in a general way, and are inapplicable to exact purposes.
The best results are those which have been obtained by Despretz,
whose method was the following. All the bars used in his experiments-were square prisms, and were all covered with the same black




92  RELATIVE  CONDUCTING  POWER  OF SOLIDS.
varnish, in order that the loss of heat from their surface might be
exactly similar. At every four inches of their length was a hole
bored to half the depth of the bar, which was filled with oil or mercury, into which the bulb of a delicate thermometer dipped, so as
at every instant to show the temperature of the bar at this series of
points. By means of a lamp applied to one extremity of the bar,
it was strongly heated, and the steadiness of the heat secured by
finding the temperature of the thermometer nearest the lamp to be
stationary for six hours, the usual time of an experiment.  The
temperature of the air of the room, which should scarcely at all
vary during that time, is known by a thermometer.
After the bar has been heated for two or three hours, each ther
inometer arrives at a temperature which thenceforth continues the
same as long as the source of heat is kept up. This temperature
depends on the difference between the quantity of heat that is propagated along the bar from the lamp, and the quantity which is lost
by cooling. The excess of the temperatures of the thermometers
attached to the bar above the temperature of the room, forms, therefore, a series, the ratio of which depends upon the conducting power of the bar in a manner which, though not simply proportional,
is easily deduced from  it by calculation.  By these principles, of
which the theory was given by the celebrated Fourier, Despretz has
deduced, from his experiments, the following conducting powers,
gold being assumed as the standard for comparison.
Gold.. 1000  Tin.304
Silver.             973        Lead...   180
Copper...... 898         Marble......   236
Platinum...    381          Porcelain......   122
Iron....... 374         Fire clay...    11'4
Zinc.363
Although this series presents, when compared with the specific
gravities, or other physical properties of these bodies, very great
diversity, yet it is remarkable that the more expansible and more
fusible metals, tin, lead, and zinc, are those which conduct heat
worst. The position of platina is, however, quite anomalous, and
must prevent any attempt at generalization.
The difference of the conducting power of solid bodies is of daily
utility in ordinary life, as well as in chemical operations. It is thus
that substances of exactly the same temperature may produce quite
opposite sensations to the hand. If we grasp in one hand a piece
of metal, and in the other a piece of wood, both at 180~, the hand
will be reddened and blistered by the former, but the latter will feel
only moderately warm. If the metal and wood be both cooled to
32~, the former will feel intensely cold, but the latter scarcely at all
so. In the first case, the metal gives out its heat to the hand, and
in the second, abstracts it from the hand so rapidly that the nerves
and circulation become acutely sensible of the change; but with
the wood, from its low conducting power, the flow of heat takes
place so gradually in each direction as almost to escape notice.
The brickwork of a fireplace or of a furnace is for the purpose of
keeping the heat generated by combustion f-om spreading to the
surrounding bodies, and so being lost. It wormld be difficult to light




CONDUCTING  POWER  OF LIQUIDS.                    93
a fire in a massive metallic grate, for the heat would be so rapidly
carried off by its conducting power, that the fuel, if not well lighted
before being introduced, would be cooled down and extinguished.
Liquids conduct heat but very slowly; so slowly, that they were
long considered to be true non-conductors. It is now satisfactorily
proved, however, that they do conduct; and although no accurate
numbers have been obtained, their power appears to be generally as
their density; mercury being the best conductor, and alcohol and
ether being the worst. This low conducting power may easily be
demonstrated by experiment. Thus, if in ajar of water an air ther
mometer be inverted, so that its bulb shall be very
near the surface, and the cup containing ether be laid
floating on the water, as in the figure, the ether may
be set on fire, and allowed to burn for a considerable,
time before any action on the thermnometer becomes!?l
sensible, and even then the heat, appears to have    I |.
travelled rather by the solid material of the glass i l
than by the water. If a little water be frozen in the
bottom of a narrow tube, and a solid adherent piece   if
of ice being so obtained, if more water be poured in i.,
so as to cover the ice to the depth of a few inches,,  _ _
on inclining the tube, and applying the flame of a
lamp to the water near the surface, it may be kept boiling violently,
and for a long time, before the ice begins to liquefy, and even then
it is by the glass material of the tube that the heat is conveyed.
Notwithstanding such facts, it is still well known that heat may
be communicated through large quantities of fluid, so that the mass
shall be rapidly and uniformly heated. It occurs, then, not by conduction, but by diffusion; and the source of heat cannot be applied
indifferently to any surface of the fluid, as it might be to a solid
body, but must be applied underneath. When any portion of a
liquid is heated, it expands, and, becoming specifically lighter, ascends in the mass, and is replaced by the colder and heavier portions, which, being in their turn heated, ascend also, and,..:"
thus generate a circulating current of ascending warm, 1
and descending cold liquid, as in the figure, by which
every particle of the liquid is brought in succession into. ii
contact with the source of heat, and the resulting tem-  i............
perature quickly and uniformly gained.                      i II
In the case of water, and such liquids as have a point    fi
of maximum density, this communication of heat, by as-! f
cending and descending currents, occurs in the inverse  
order below that point. Thus, to warm water which is        l
below 39'.5, the heat should be applied above, or to cool' 
it farther the heat should be abstracted below. On this.  A
property depends the preservation of the lakes and rivers
of these countries from  total and eternal congelation.
When the mass of water becomes cooled to 395, the su-!i 
perficial layer becoming lighter as it cools more, prevents, i    i
by its non-conducting power, the farther abstraction of
heat from the deeper portions; but when the warm air of
spring plays on it, the heat is rapidly diffused from above down.
ward, until the temperature of the entire mass is raised to 3953'




94  COMMIUNICATION  OF  HEAT  BY  RADI.ATION.
In their mode of communicating heat, gases resemble liquids.
Their true conducting power is quite insensible, but by the currents
which are produced by the ascent of warm and the descent of cold
particles, they abstract and communicate heat with great rapidity.
The difference is easily felt by holding the hand first at the side
and then over the, flame of a candle, the distance beingT the same.
In the latter case the great increase of heat arises from the ascendin(r current of heated air,which does not affect the hand wvhen at
the side.
The non-conducting power of gases is practically of great importance. The different kinds of clothing owe their warmth to the fact
that they prevent the heat of the body from escaping; this they effect not so much by the power of their proper solid substance, as
by being of a loose and spongy texture, they imprison, ill their pores
a quantity of air, which, not being able to form those continual currents, acts as a non-conductor.  The more loose and spongy, therefore, the tissue of a cloth may be, the more air does it confine and
the warmer it is. This is fully supported by the experiments of
Rumford, who, having heated to the same degree a thermometer
imbedded in the materials of which clothing is generally made,'found that it cooled through 135" with
Air        in  576"      I       aw silk  in 1284'
Fine lint   " 1032"             Beaver's fur- "  1296"
Cotton wool  " 1046" E- ider (down "  1305"
Sheep's wool " 1118"           Hare's fur  "  1315"
When these bodies are tightly compressed, so as to diminish the
quantity of air confined within their tissue, the power of retaining
warmth diminishes in the same degree.
On standing before a fire, the influence of the heat is felt even
at a considerable distance, although the air is, as has.been just stated,
so bad a conductor that the warmth cannot be ascribed to direct.,transmission through its mass; and since a current of air is passing
to the fire in order to supply its conduction and produce the draught
of the chimney, no heat can arrive at the body by the current from
the fire. Also, if a heated iron ball be suspended in a room, it
propagates heat in all directions, although the current of air which,
so far 4s has been yet described, alone can convey any great quantity of heat, is directed only upward. Heat is therefore propagated
by a third mode, distinct from diffusion and from combustion; and
the heated body being supposed to emit actual quantities of heat in
straight lines or rays from every point of its surface, this mode is
termed radiation.
Radiation is remarkably distinct from conduction and diffusion
in not requiring for its existence any material medium.  On the
contrary, the existence of any coherent substance. in their path is
an obstacle to the transmission of the rays of heat, and hence in
most'solids and liquids there is little heat transmitted by radiation,
unless we look upon conduction as a kind of radiation from particle
to particle in the interior of the mass, and it is only with gases that
radiation is equal to what takes place in empty space. A heated
body throws off rays of heat precisely as a luminous body throws
off rays of light; and in every detail of physical constitution that




PROPERTIES OF RADIANT  HEAT.                       95
has yet been discussed, there exists a perfect similarity between
heat and light in these radiant forms.
Different bodies radiate heat with different powers, which appear
to depend more upon the mechanical nature of the surface than
upon the internal constitution of the body. When any substance is
interposed in the path of the rays of heat, these are either reflected,
or are absorbed, or they pass through the body without loss. In
general, all these eflects are in part produced; that is to say, one
portion of the incident rays will be transmitted, another portion reflected, and a third will disappear by being absorbed.  There are
thus in relation to radiant heat four qualities, which various substances possess in different degrees, the radiating, the absorbing, the
reflecting, and the transmitting power.
The rays of heat may, like those of light, be concentrated by reflection or refraction. By the former mode, that originally used by
Prevost and by Leslie, the properties of radiant heat may be demonstrated in a simple manner.
The form of apparatus generally employed for demonstrative experiments on radiant
heat consists of refleeting mirrors of pol-    A                               B
ished  silvered  copper,..............
of a paraboloid form,         C....    l
A B; the property of'...
this figure being that
rays emanating from
the focus- of one mnirror are reflected from
it in parallel directions, and falling thus parallel upon the other, are
brought to convergence in its focus. In this manner the heat radiating from a body may be concentrated upon a single point, and
all its properties determined with great precision. Thus, a hot iron
ball may be placed at a distance of a few feet from a bit of phosphorus for any length of time without affecting it; but if the hot
ball be placed in the focus of one mirror, C, and the phosphorus in
the focus of the other, D, this immediately begins to melt, and after
a moment bursts into flame. If the hand be
held in the focus, it feels hot; but, on moving      {ii!tD
it much nearer to the source of heat, the iron
ball, it feels cooled. It is thus not by the direct conduction of the air, or by diffusion of
warm  currents, that the effects are caused,
but from the radiation of heat in a form which,
like light, admits of being reflected from polished surfaces, and concentrated upon a focus,
and which will be found to follow the analogy
of light through all its branches.
If a thermometer be placed in the focus of
the mirror opposite the heated ball, it immediately indicates the rise of temperature, and
may serve to measure it. But it is only the
air thermometer which is delicate enough for  




96           OF  THE  RADIATING, ABSORBING,
such experiments, and it is specially for this use that the differen
tial air thermometer is constructed.  One bulb being placed in the
focus, the difference of temperature between the two bulbs is instantly shown; and it is thus also proved that the rise of temperature is local, that it is confined to the point where the rays of heat
are brought to meet, for the instrument is insensible to every general change of temperature, no matter how extensive.
By means of this apparatus, the radiating and absorbing, as well
as the reflecting and transmitting powers of bodies may be examined.  The radiating power may be conveniently exhibited by filling
a tin cube, a, with boiling
rc      water, and applying to the....... —        surfaces of the cube the bod-;tL~_I_____~__~_             4 E o-//   a ies which are to be exama.                                 -      ined.  Thus, one side being
left brightly  polished, another dimmed by being rub~__ X             bed with sand paper, a third
covered by paper, and the
- fourth being blacked by the
smoke from  a candle, each
side, on being turned towards the mirror c, gives out a quantity of
heat proportional to its radiating power, and this being reflected
and brought to bear upon the thermometer in the focus, is measured
by its indication.  Leslie thus found the radiating power of the
following surfaces to be relatively,
Lampblack......         100         Plumbago.....  75
Writing paper..          98         Tarnished lead.... 45
Crown glass.....   90              Clean lead......    19
Ice........ 85              Polished iron.            15
Red lead.....    80      Other bright metals... 12
It is here evident that the radiating power is quite independent of the colour of
the body, and that, in all cases, those bodies with bright metallic surfaces radiate
least, the radiating power of lead being doubled by simply tarnishing its surface.
It has been rendered probable, however, by recent observation, that it is not the
degree of polishing of the surface which influences the radiating power, so much as
the closeness and density of the exceedingly thin surface layer, on which the quantity of radiant heat depends. In the process of polishing, the surface of a metallic
plate, particularly if it be rolled, is very much compressed, and in this state radiates
in the lowest possible degree; but if, by rubbing with sand-paper, that dense film of
compressed metal be removed, the softer material underneath radiates with nearly
double the power. If a plate of silver be cast without being subjected to any pressure, the surface, although perfectly bright, radiates with a power of 22; but if it be
dimmed by rubbing with sand-paper, the compression, even though so slight, diminishes the radiating power to 12. Substances which are highly elastic, as ivory,
or very hard, as agate, radiate in the same degree, no matter what may-be the
rough or smooth condition of the surface.
That. the texture of the surface should influence the radiating power is easily
comprehended, when we know that it is not from the external surface, but from a
little depth below it, that radiation actually takes place. If radiation were truly
from the surface, every point of it emitting rays in all directions equally intense,
there should oc cur inequalities in the temperature of the surrounding bodies of the
most remarkable and intolerable kind. Thus, let us suppose two surfaces at right
angles radiating heat, as, for instance, two surfaces' of a red-hot poker. A body A,
at a certain distance from the angle, should have its temperature raised much
more thaii a body, B or C, directly opposite either side, for it should receive the rays
A M and A Nl' ecually intense, while the bodies B and C should receive from the




AND  REFLECTING  POWERS  OF  B ODIES.    97
same pointst only the rays B M or C M'. But the rays
emanatinl not from the surface at M or M', but from N' and
N, at some depth below, the oblique ray N A has to pass
througrh so much a thicker stratum of solid matter from N       _P
to P than the direct ray fi'rom N to M, that the conjoint. 
action of the two does no more than enable the surrounding bodies to attain an equable temperature.  Bodies
obliquely exposed to a flat radiating surface receive Iess C    M}\!i
heat; not that a smaller number of rays impinge upon them,
but that a greater proportion of heat is lost in escaping
from below the surface of the body.
The radiating powers of bodies are the foundation of numerous
applications in the  arts.  Those bodies which radiate least cool
slowest; and hence, if it be required to keep any material hot for a
considerable tine, it should be enclosed in a vessel with a bright
metallic surface, that being the kind which retards most the escape
of heat.  If, on the contrary, the object be to diffuse heat, the best
radiating surface should be made use of.  It is thus that the tubes
by which heated air, or water, or steam is supplied to buildings, for
the purposes of warmth, should be bright and polished until they
arrive at the precise locality where the heat is to be given out, but
should there be painted with whitelead or lampblack, the surfaces by
which the heat is most rapidly given out.
If two tin vessels, precisely similar in form, but one being painted
and the other polished, be filled with warm water and placed in a cold
room, that which is painted will cool more rapidly than the other, in
consequence of its greater power of radiation.  If the two vessels,
when cold, be placed opposite a steady fire, the temperature of the
water in that which is painted will be observed to rise more rapidly
than that of the other; it will absorb the heat of the fire, precisely
as it had given out the heat of the water, with most rapidity.  The
bodies, therefore, that radiate best, absorb heat, likewise, with greater
power, and those which, when hot, cool most slowly, are those also
which have least tendency to receive radiant heat.
aThe absorbing and radiating power may even be proved to be exactly propor
tioned to one another by the following experiment. A large differential thermometer is arranged, whose bulbs are chambers of considerable size, presenting large
and equal plane surfaces on the sides that are towards each other. Of these, one
is polished and the other coated. Midway between them is placed a canister having equal plane surfaces, facing each of the former respectively, and one polished,
the other coated with the same pigment as before. This canister is filled with hot
water, and is capable of turning on a vertical axis; thus the coated surlace of the
canister can be turned to the coated bulb or to the polished; in the former case, a
great effect is produced upon the coated bulb, and a very small effect upon the
plain; in the second case, the better radiating surface is directed to the worse absorbing one, and tihe worse radiating to the best absorbing, and the liquid in the tube
remains perfectly stationary, establishing thereby the exact equality of the absorbing and radiating powers.
Although colour is without influence on the radiating power, it yet
appears to influence the absorbing power in a remarkable degree.
If pieces of cloth of various colours be laid upon snow, and exposed
to the direct solar rays, that which is black will, by absorbing more
heat, melt the snow away from  under it, and sink deepest.  White
will sink least, and the others in the order of their depth of colour.
It is, therefore, with reason that dark-coloured cloths are preferred,
for winter use, and light colours for summer. It is, however, to be
N




98                TRANSMISSION  OF  HEAT.
noticed, that it is only upon the absorption of those rays of heat
which accompany rays of light that colour has this power.
The great difference of Absorbing power of a blackened and of a
metallic surface may easily be shown, by coating one bulb of a differential thermometer with silver leaf and blackening the other.
W hen, with the same source of heat, the rays are received upon the
silvered bulb, scarcely any rise of temperature can be observed; but
when the blackened bulb is placed in the focus, the rise is much
more than would have occurred with the thermometer in its ordinary
condition of the bulb with a glass surface.
The mirrors which are used in those experiments do not become
sensibly heated until after a long time; they absorb but very little
heat: but if the surface of the mirror be smeared with glue, it loses
to a great degree its power of reflecting; and having thus obtained
an absorbing and radiating power, it very soon becomes warm.  If
it be coated with lampblack, its reflecting power vanishes, and its
surface becomes highly absorbent. The reflecting property is therefore possessed by the surfaces of bodies in the inverse degree to the
absorbing and radiating powers, and hence the best absorbers are
those which reflect least.
The heat which is naturally associated with light in the sun's rays
is capable of being so concentrated by reflection, that in the focus
of a burning mirror, results equal to those of the most intense artificial heat may be produced. The heat of the sun's rays may also be
concentrated by refraction, the heat accompanying the rays of light
in their passage across lenses; hence the use of the burning glass.'
But when we thus come to discuss the property possessed by bodies
of transmitting heat through their substance, it becomes necessary
to look farther to the source and intimate structure of the heat. For
the results which have as yet been described, we are indebted al.
most exclusively to Leslie, but the power of transmitting heat could
only have led to the important consequences deduced from  it by
Forbes and Melloni more recently, when the advance of other sciences had placed at the disposal of the experimenter measures of
temperature infinitely more sensible than any form of thermometer
formerly in use.
It is by means of the thermo-multiplier and galvanometer that the effects of the
transmission of heat require to be observed.
The apparatus employed by Melloni was, in its general arrangement, such as is
represented in the subjoined figure.
On a steady table there rests a frame M M, along the middle of which a slip R R
is cut, by which the various stands and supports may be moved back and forward,
so as to vary their distances from each other. On the stand S is placed the source
of heat; in the figure it is a coil of platina wire ignited by a spirit lamp; but the
flame may be surrounded by a cylinder of blackened copper, or it may be a vessel
of boiling water, or an argand or Locatelli lamp. The rays proceeding from it are
received by the thermo-multiplier P, from which the wires F F convey the electricity generated to the4galvanometer G, which for steadiness is placed at a distance,
and on brackets secured against a wall. These parts, P and G, will be represented
in full in the chapter on electricity. If it be required to study the action of a plate
of any substance upon the rays of heat; the screen E is interposed, having an aper
ture 0, somewhat smaller than the plate to be employed. This last is then supported immediately behind the aperture by means of the little frame S', so that no
heat can reach the thermo-multiplier unless after having passed through it. As it
is of great importance to have the end of P farthest from the lamp uninfluenced by
any disturbing causes, the screen E" is placed immediately behind it, to protect it




TRANS.MISSION  OF  HEAT.                             99... -                        n
from irregular radiation and from currents; and as the action of the heat upon the
pile must be limited to the actual time of the experiment, the double screen E' is
interposed immediately next the lamp, and, being provided with a hinge, is raised
or lowered at the moment when the rays of heat are to be allowed to pass or are
to be intercepted.
The orifice of the thermo-multiplier is occasionally fitted with a conical tube of
plated brass, for the purpose of collecting the rays of heat in greater number; but
that is not often wanted.
The reflecting power of.bodies has been exactly determined ty
Buff to be as follows. Of 100 rays incident at an angle of 60~ from
the-perpendlcular, there are reflected, by
Polished gold..........   76
"  silver........62
"'  brass........                          62
Brass without polish........                52
Polished brass varnished....                       41
Glass plate blackened on back.....      12
Looking-glass....              20.Metal plate blackened.............  6
The power of a body to transmit heat is termed transcalescence,
and of intercepting heat intranscalescence.  These properties are totally independent of the power of transmitting light, as will be at
once seen from the following table. Of 100 rays proceeding from
theb flame of an argand lamp, there are transmitted by
Rock salt...  colourless 92 Glass coloured.  yellow  22
Calc spar....    do.   62         Do....    blue   21
Smoke topaz..      brown  57 Sulphuric ether. colourless 21
Plate glass....  colourless 40 Gypsum..    do.   20
White agate...    do.   35 Tourmaline..   green  18
Glass coloured... violet  34 Opaque glass..   black  16
Do..               red   33 Citric acid... colourless15
Chromate of potash.  orange  33 Alcohol....    do.   15
Borax...... colourless 28 Alum....         do.   12
Glass coloured...  green  23 Water....    do.   1
Rock salt is thus the most transcalescent substance that has been




100      PER M EABILITY -OF BODIES TO HEAT.
found.  Glass arrests more than one half of all the heat which it receives, while colourless and transparent alum, and the most limpid
water, arrest more of the heat which they receive than the deepest
coloured glasses, or topaz, or quartz, so brown as to be quite
opaque.
But not merely do different bodies act differently on rays pro.
ceeding from the same source, but the same body may allow the
heat from one source to pass freely through its substance, and intercept partially or completely the heat radiating from another.  Thus
using, in his experiments, the heat emanating from  five kinds of
source, first, the argand lamp; second, the lamp of Locatelli, which
is remarkable for the steadiness of its flame; third, a red-hot spiral
of platina wire; fourth, a blackened copper plate heated to 734~;
and, fifth, a blackened copper plate heated to 212' by boiling water,
Melloni found the heat arising from these sources to be transmitted
In the following proportion per cent.; the results with the argand
lamp, having been given in the last table, are here omitted.
Substance.  Locatelli Ignited  Copper  Colpper
___ _Substance_ _  Lamp.  Platina. at 734~. at 212~.
Free radiation. 100 100 100 100
Rock'salt...  92  92  92  92
Fluor spar..  78  69  42  33
Calc spar..    39  28   6   0
Plate glass..  39  24   6   0
Agate...  23  11   2   0
Gypsum..    14   5   0   0
Alum...    9   2   0   0
Ice.....   6   0   0   0
Rock salt is thus not only the most transcalescent body, but it is
that which alone is equally transcalescent to heat of all temperatures. The rays of heat evidently acquire a greater power of transmissibility as the temperature of the source increases, and hence
glass arrests scarcely any portion of the direct solar heat, while
from the argand lamp it intercepts 47; from Locatelli's lamp, 61;
from ignited platina, 72; from copper at 734~, 94; and from copper at 212~, 100 per cent.  The action of these media upon radiant heat consists not merely in stopping a certain portion of it, but
in separating it into two portions, physically distinct, of which one
is capable of transmission, while the other is absorbed. Hence a
second plate, of the same kind of substance, exerts but a very slight
action upon the heat which has already passed through the first.
Thus, though a plate of alum allows only 9 in 100 of the direct rays
of the lamp to pass, yet it admits of the passage of 90 in 100 of
rays which have already passed through a plate of the same substance; and cale spar, which transmits only %9m of the direct heat,
transmits 91 of that which had passed through alum, and 89 of that
which had passed through gypsum. On the other hand, a green
tourmaline, which transmitted IS out of 100 rays directly incident
upon it, intercepts -0-9% of those Wvhich had previously passed through
alum, but gives passage to,0  of radiant heat which had passed
through black glass.
The nature of the physical distinction between the intercepted
and the transmitted portions of the heat is to be found in the differ




ANALOGY  OF  HEAT  TO COLOURED  LIGHT. 101
ent refrangibility of the rays of heat emanating from sources of va
rioils temperatures. If the rays of heat emanating from a lamp bc
incident upon a rock-salt prism, they will undergo refraction, subject to the same law of the sines as in the case of ordinary light,
and there will be obtained a band or spectrum  of rays from  the
lamp; the most refrangible will coincide with about the middle of
the luminous spectrum, while the least refrangible will extend far
beyond the limits of the least refrangible rays of light. The mean
refrangibility of heat is therefore less than that of white light, and
the length of its undulation, if that theory be adopted, longer in
proportion.
If, now, the heat spectrum so obtained be examined by means of
the media which have been already noticed, the explanation of the
peculiarities in their action will be at once observed.  Rock salt allows the rays of all degrees of refrangibility to permeate its mass;
it is to heat what perfectly colourless glass is to white light; it acts
equally on all portions of it. Alum stops all but the very least refrangible rays; it is to heat what ruby-coloured glass is to light,
which allows only the rays of the least refrangible extremity of the
spectrum to pass through.  Glass, gypsum, and such bodies as give
passage to the rays of least and of mean refrangibility, resemble
those orange-coloured glasses which exclude the blue and violet
rays of light, but admit the others.
After long search, Melloni at last found that by coating with soot
the surface of a plate of rock salt, it became to heat what blue glass
is to light; it excluded the rays of inferior refrangibility; and when
a plate so prepared was combined with a plate of alum, all heat was
intercepted, precisely as when, by laying a plate of blue and a plate
of orange glass together, perfect opacity is produced, the one absorbing the portion of light which alone the other is capable of
transmitting.
The rays of heat derived from sources of different temperatures
are thus analogous to the rays of light of different colours. The
higher the temperature of the source, the more does it resemble red
light; the lower its temperature, the greater is its analogy with the
violet rays. Hence alum absorbs all the heat from boiling water,
but gives passage to that from the argand lamp; but alum is like a
glass so deeply coloured red that it is almost opaque, and transmits only a small portion even of its own coloured light that may
fall upon it.
When a ray of heat is incident upon a doubly-refracting substance, it follows
precisely the same law as light, and is refracted doubly. In this case, also, the
rays after emergence are found to be polarized in planes perpendicular to each
other; and all those consequences of the mutual action of polarized rays which give
rise to such magnificent phenomena of colours in the case of light, must occur with
heat, and be made sensible if our organs or our instruments were of a construction suitable for their appreciation. As yet, however, the fact which alone remains
wanting towards a physical theory of heat has not been observed-that of interference; up to the present time, the actual production of cold by the combined action
of two rays of heat has not been seen; but the closeness of the analogy, which in
this case alone requires additional observation betweenlight and heat, is so remarkable, that we can have little hesitation in referring these agents, in their radiant
form, to the same kind of physical arrangement.
There is no difficulty in conceiving radiant heat to consist in vibrf'liXng i f the
same ethereal medium which produces light, and in considering that th- d f-lence




102   RELATIONS  BETWVEEN  HEAT  AND  LIGHT.
between heat and light should be m the magnitude of the vibrations, and the consequent refrangibility of their rays. On the contrary, it is not reasonable to suppose, that while we are conscious. of the waves in air, although they may vary in
length'from 32 feet to I of an inch, the limits of our sensibility to the ethereal
waves should be so narrow that the shortest (violet) is to the longest (red) as 60 to
38; it is more consonant to our idea of the various and beautiful uses to which
every object of creation is made subservient, to believe that, while the waves within these limits produce upon the eye the sensation of coloured light, another range
of lengths, greater than those of light, should give to our organs the sensation,of radiant heat; and that a third order of vibration, still shorter, and more refirangible
even than violet light, is capable of acting upon the elementary constituents of bodies, and constitute the chemical rays. The coexistence of these three kinds of rays
in solar light is an argument remarkably in favour of this view; for we can well
imagine that, by whatever means the sun communicates to the ether-eal expanse
the vibrations of various lengths which constitute the rays of light, that vibrations
of other magnitudes, greater or less, should be at the same time produced; and
thus the light, which exhibits to us the beauty of the external world, be accompanied by the heating power which animates all living nature, and without which the
universe would be a tenantless and barren void.
These arguments, however natural, and in appearance sound, are met by facts
which, if not positive against light and heat differing only in the length of the
waves by which they are produced, are. at least of so much importance as to deserve attentive study. If it were so, then the heating rays of the spectrum should
be thrown always below the coloured space, being less refiangible; and it is found.
that, with a flint glass prism, the greatest heat is produced outside the visible confines of the spectrum at the limit of the red light. This is, however, only accidental, from the nature of the prism; for if a prism of crown glass be employed, the
rays of heat are collected in the middle of the red space: with a prism of sulphuric
acid, in the orange; and by a prism of oil of turpentine or water, they may be collected into the centre of the yellow light.
The rays of heat, therefore, although generally less refrangible than those of
light, are still not necessarily, or even always so. There is distributed over the entire visible spectrum a heating spectrum, which has its peculiar point of greatest
energy, and which may be refracted more or less quite independently of the luminous space, and may be brought to overlap it at either end, or to lie evenly upon it.
The ethereal medium, if it be the means of transmitting radiant heat, must be capable of two distinct methods of vibration, by which rays of equal refrangibilities,
but totally different properties, may be produced.
The physical independence of solar light and heat was beautifully shown by Melloni, who, using quartz and black mica, perfectly
opaque, upon the one hand, and rock salt made perfectly opaque by
soot upon the other, obtained radiant heat of all refrangibilities'totally free from light; and on the other hand, by combining a plate of
alum with a glass coloured green by oxide of copper, he obtained a
brilliant beam of light, which, when concentrated by a lens upon the
most delicate thermoscope he could apply, exhibited no trace of any
heating power whatsoever.
An interesting property of radiant heat, and one which shows the remarkable
distinction between it and light in a very evident manner, is, that the heat may
change its degree of refrangibility; and hence, if it be vibrations, one wave may
break it up into several, or several smaller waves may unite to form one. The
light of the sun, deprived of all the more refrangible rays by passage through a
plate of alum, may be received on a blackened. surface, the temperature of whclth
will be thus elevated, and Which, in turn, will become a source of radiant heat.
But the heat so radiated is found to have totally changed its properties; it can no
longer pass through alum; it has passed from the state of heat of the lowest to the
state of heat of the highest refrangibility. In like manner, if the most refrangible
rays emanating from a source at 2120 be concentrated by a rock-salt lens, and
brought to act on a small' surface, they may raise the temperature of this surface
above 2120, and radiate'from thence in a less refrangible condition than before.
The parallel case to this has never been found with light. Red light has never
changed into blue, nor violet into orange; and there must be in the physical theory




EQUILIBRIUM OF TEMPERATUR-E.    103
ot radiant heat some general principle of so high an order, that the physical optics
of the present day is but a particular case of it.
This change of radiant heat from one degree of refrangibility to another occurs
in nature very often, and is the source of some remarkable phenomena. Thus the
heat of the sun's rays, being of low refrangibility from their intensely-heated source,
is transmitted easily by ice or snow, and hence a layer of snow upon a field, exposed even to the powerful action of the sun, is but slowly melted; if, however, a
dark-coloured object, as a branch of a tree, be laid upon the surface, it absorbs the
solar heat, and becoming a source of radiation of heat of great refrangibility, which
the snow absorbs completely, this is melted under the stick, which sinks and
gradually disappears beneath the surface. The earlier melting of snow upon the
branches and round the stems of plants, which was supposed to demonstrate a
kind of natural warmth belonging to the living vegetable, arises from this merely
physical conversion.
From this results also the influence of colour on the power of bodies to absorb
the heat of the sun or of a fire; the strips of coloured cloth (page 97) melted the
snow beneath them, not merely because they absorbed more heat in proportion to
the depth of colour, but because they in that proportion possessed the property of
changing the heat, which would be transmitted into the heat which would be absorbed by the snow on which they rested.
The construction of a theory of heat would be, even were an undulatory hypothesis adopted for its radiant form, involved in difficulties which may require many
years of research to render them even clearly understood. The relation between
radiation and conduction; the connexion between specific and latent heat; the
laws of cohesive force against which heat acts in causing the expansion of a body,
will all require to be comprehended within the folds of whatever principle shall
hereafter be made the basis of thermotics. But it is no disrespect to the illustrious
names that have been connected with speculations on this subject, to conclude, that
none of the views brought forward appear positive or clear enough to be described
in a work of an elementary nature like the present.
SECTION VI.
OF THE COOLING OF BODIES.
Bodies at an elevated temperature are capable of giving out the
heat which they contain by every method by which, when cold, they
become heated at the expense of the surrounding warmer bodies.
Cooling may occur, therefore, by contact or by radiation. The rapidity of cooling by the immediate contact of the hotter with the colder
body depends on the degree of intimacy of the contact, and on the
conducting powers of the bodies.  Thus solids, which merely touch
at a few points, communicate their relative temperatures but very
slowly, while with liquids or gases which may mix completely with
each other, the establishment of a uniform temperature is almost
instantaneous. The colder body becomes heated to the original
temperature of the hotter only when there is a continual supply of
heat to maintain that temperature, as in a furnace; in other cases
the hotter body cools in proportion as the colder becomes warm, and
the resulting temperature depends on the specific heat of each, as has
been described, page 62. In determining, therefore, the temperature
of a body by a thermometer, it must not be forgotten that the thermometer, in becoming hot, cools, the body, so that, unless there be a
continuous source of heat, the true temperature of a body is never
given by the instrument.  Where the substances, being solid, can
only come into external contact, the rapidity with which heat passes
from one to the other depends upon their conducting power; thus,
a cold brick may be laid upon a heated brick for a considerable time
without much heat changing place, but a plate of red-hot iron laid




104         THEORY  OF DEW  AND  FROST.
upon a plate of cold iron, abandons its excess of temperature so
rapidly, that a mean temperature is attained by both in a very short
time.
The cooling. of bodies by radiation is governed by the principle
that all bodies in nature are in a continual state of interchange of
heat; no matter how hot or how cold a body may be, it is constantly
giving out radiant heat to other bodies, and receiving in exchange,
and absorbing the heat which radiates from them. The quantity of
heat thus radiated depends on the temperature of the body; the
higher this is, the greater quantity of heat is thrown off; the lower
the temperature, the less heat does a body radiate in a certain time.
Hence, if we conceive a ball heated to redness, and suspended in the
centre of a number of similar but colder balls, each will radiate and
absorb, but the hotter ball will give out more than it can gain in return, and will hence cool, while the surrounding colder bodies, absorbing more of the radiant heat than they return, will have their
temperature raised. Every body in nature, therefore, no matter how
its temperature may, by peculiar or local means, be elevated or depressed, tends ultimately to an equilibrium with all the neighbouring
bodies; and hence, the instant we remove a substance from our furnaces or freezing mixtures, it begins to cool or to become less cold.
This principle explains, in a very perfect manner, a singular but instructive experiment which may be made with the concave mirror
apparatus described, page 95. In the ordinary form, the thermometer and the heated ball tend, by radiation, to assume a common
temperature, and the thermometer, being the colder body, becomes
heated; but if, in place of the heated iron ball, a mass of ice be substituted, the temperature of the thermometer in the focus of the opposite mirror immediately sinks below that of the surrounding air.
The explanation consists simply in the fact that the thermometer
is now the hotter body, and hence, giving out to the ice more heat
than the ice gives back, has its temperature reduced. At first this
effect appeared to demonstrate the existence of rays of cold, which
were reflected, radiated, and absorbed like rays of heat.
In this principle of the uniformity of temperature being sustained
by the equivalent radiation and absorption of the bodies at the surface of the earth, we find the solution of many interesting natural
phenomena. The production of dew and frost are to be thus accounted for. In the absence of the sun, the surface of the earth
losing by radiation a great quantity of heat, would have its temperature considerably lowered, were it not that the canopy of clouds
which generally lies above it radiate in return, and thus maintains the
temperature almost the same. If, then, the clouds be absent, all the
heat radiated by the earth is lost in the planetary spaces, and the
temperature of its surface brought many degrees below that of tlhe
atmosphere. The stratum of air which lies in contact with the sur.
face of the ground is then cooled by contact, and a portion of the
watery vapour which it had possessed in its elastic form is depos.
ited as liquid water. If the temperature of the air be itself low,
and the night very clear, the cooling may proceed so far that the
drops of dew at the moment of their deposition shall be frozen, and
thus form frost. The truth of this explanation is demonstrated by




CENTRAL HEAT OF THE EARTH.                               105
the fact that it is only on the surface of good radiators, and during
clear starlit nights, that dew or frost is found.  If a plate of polished metal be laid on the centre of a rough board, and exposed to
the air of a frosty night, the rough surface will be found in the
morning covered with copious frost, but on the bright metal no trace
will be deposited.  It is thus that, by lightly covering a thin layer of
water with straw to increase the radiating power, a sheet of ice may
be obtained in a single night between the tropics, where the actual
temperature of the air may have continued far above the freezing
point. That the cooling effect is produced by the loss of heat in
its radiant form, and not by the contact or diffusion of the particles
of the air, may be proved by the interposition of a screen of any
substance which intercepts the passage of radiant heat, when the deposition of dew or frost instantly ceases, and the surface cools no
more. Thus plants are protected by mats from the frost of spring
and autumn, and thus the screen of snow, which covers the surface
in the depth of winter, prevents the loss of heat from the soil below,
and favours the vegetation of the seed.
The rapidity of cooling depends upon the difference ot' tempera
ture of the radiating bodies, but it is not proportional to this difference except within a very narrow range of temperature. Newton
having experimented only within that limit, announced that law as
general; but the establishment of the true law is due to Petit and
Dulong. It is, that the rapidity with which a body cools, for a constant excess of temperature, increases in a geometrical proportion,
of which the ratio is 1'161, when the temperatures increase in an
arithmetical proportion. Bodies at moderately high temperatures
cool, therefore, much more rapidly than they should do by Newton's law.
The heat, by means of which we produce a rise of temperature, or any other of
the effects which have been described, may be derived from any one of a variety of
sources. To the earth at large the sun is the source of warmth; and by his varying position in the heavens, by which his rays strike upon the surface with different
inclinations, and, passing through the different thicknesses of atmosphere, undergo
absorption to a variable amount, the change of seasons as to temperature is produced; and the alternation of vital activity and torpor which characterizes the vegetable world, and a great portion of the animal creation, is occasioned. Although
at the surface the temperature of the earth is solely dependant upon the radiating
power of the sun, yet it is found that it contains within itself a source of heat, which,
in ages excessively remote, must have retained the general mass of all constituents
of the mineral globe in igneous liquefaction. In fact, if we dig below the surface
of the earth, we arrive, at a depth of about forty feet, at a layer of which the temperature is in winter and in summer exactly the same. It is termed the stratum of
invariable temperature, and is in general of the mean temperature of the place; that
is, the temperature of the surface falls in winter as much below that of the invariable stratum, as in summer it is raised above it by the excessive action of the solar
rays. The heat of the sun, falling upon the surface, is transmitted inward in virtue
of the conducting power of the ground; and thus, each summer, a thin layer of elevated temperature moves inward, those of successive summers being separated
from each other by the intervening colder shell, which marks the period of diminished heat in winter, until they mix and confound themselves in the layer of constant temperature, below which the influence of the sun is felt no more. But, on
descending beyond this depth, the temperature steadily increases, and, although
subject to irregularities consequent on the different conducting powers of the rocks
of different countries, the augmentation is in general about one degree for every
forty-two feet, or about 1200 for every mile. At a depth of two miles, therefore,
water could not exist as a liquid, unless from the great pressure to which it would
0




106           PROPERTIES  OF  ELECTRICITY.
be subjected: at four miles' depth tin and bismuth would naturally be liquid; ana
at five miles, lead. At a depth of thirty miles the temperature would be so high as
to melt iron; and still more easily, almost without exception, the rocks, which constitute the solid earth which we inhabit. The central heat, therefore, although insensible at the surface, is still, there is every reason to believe, in violent activity
at a small depth below: we live upon a pellicle of solid crystalline rocks, with which
the melted mass has become skinned over, and which extends but to 1-aw of the
distance to the centre.  Hence we can well imagine, that in many places where
orifices or cracks in this solid crust might form, violent manifestations of the internal fire should be produced, and the magnificent phenomena of volcanoes and
earthquakes should thus arise.
For artificial purposes, the source of heat is generally chemical combination.
The details of this mode of generating heat will require to be carefully and minutely
considered hereafter, under the heads of Combustion, and the Relations of Heat to
Chemical Affinity. By mechanical causes. as percussion and friction, heat may
also be set free; but such cases arise from a change in the specific heat of the
bodies before and after the mechanical action; and hence, although once considered
as influencing our ideas of the nature of heat, do not now require special notice. A
very interesting source of heat consists in the respiration of certain kinds of animals,
and constitutes an important branch of chemical physiology, which shall be discussed in its proper place: and, finally, one of the most remarkable sources of heat
is to be found in the properties of electricity, in its various forms; and to the de
scription of this interesting and important agent we shall now proceed.
CHAPTER IV.
OF ELECTRICITY CONSIDERED AS CHARACTERIZING CHEMICAL SUBSTANCES.
AMONG the various forces which concur to the production of natural phenomena, there are few whose agencies are more remarkable
or more general than those of electricity; and so intimately does it
appear to be connected with chemical action, becoming sensible in
all cases of union or decomposition, and being even developed in
a degree proportional to their amount, that the most eminent philosophers have not hesitated to consider electrical and chemical
agencies as beingo if not identical, at least intimately connected with
each other.
It is not the object of this work to enter into the minute description of electrical
phenomena, nor to attempt the detailed discussion of their causes; as for a complete
examination of the subject, it must be considered as one, and certainly not one of
the least extensive branches of natural philosophy; it is only with regard to the in
fluence which electricity exercises in the operations and the theory of chemistry,
and the means which the electrical properties of bodies afford for their recognition,
that it requires notice here; and hence, although it is necessary to describe the peculiar origin and characters of each form which electricity assumes, yet that shall
be accomplished within the shortest limits that are consistent with the importance
of this branch of science. In the present chapter the subject will be studied in its
general history, and considered as affbrding useful characteristics of substances, the
properties of which we have to learn; and in a future place the influence which it
exercises upon chemical affinity, and the opinions which have been advanced concerning its relation to purely chemical forces, shall be carefully discussed.
Of the true nature of electricity nothing is positively known;
whether it be a mere property of matter like attraction or cohesion, a
mere force acting independently of all interposed material, or whether, like light, it consists in the undulations of an ethereal medium fill



NATURE OF ELECTRICITY.                      107
lng space, cannot be determined. Indeed, the ordinary views of its
nature consist in supposing the existence of one or of two fluids of
electricity, of exceeding tenuity and of perfect elasticity; and that,
according as ordinary bodies were supposed to contain more or less
of these fluids of electricity, they acquired or lost the properties of
electrical excitation. Of these opinions it is exceedingly difficult
to say which is the more reasonable or more consonant to experimental truth, so far as the explanation of phenomena is concerned;
but no positive evidence has ever been obtained of the existence of
such an electric fluid: it has never been found capable of being separated from the ordinary particles of matter, of which it appears
always as an additional property assumed under peculiar circumstances, and not as a superadded constituent. I consequently incline to
the idea that, in the phenomena of electricity, we have exhibited
only the results of new mechanical conditions of the ordinary particles of matter, produced by the action of forces which may be called
into play in a variety of ways, and which may be either totally new
forces which are first generated at the time, or modifications of the
forces of gravity and cohesion which exist already. But, although
such may be the true condition of the electric properties of bodies,
yet such views are far too abstract and indefinite to be as yet carried
out into the detailed explanation of experiments; and hence, in the
present chapter, I shall adopt the language of that view, which has
been so long in use as to have become incorporated with science,
and speak of an electric fluid uniting with or separating from ordinary bodies, without being considered as at all believing in its actual
existence.
This electric fluid, whether it be looked upon as of one or of two
kinds, may, like air or water, be examined in a state of rest or in'
motion; and the science of electricity nay be thus divided into
electrodynamics and electrostatics. The electricity generated by}
friction, or by change of state of aggregation, is ranked under thei
latter head; while the effects of electricity in motion are found to,
include the phenomena of magnetism, of galvanism, and their relations to each other, electro-magnetism and magneto-electricity, and
also those of the electricity produced by a change of temperature in
bodies. Under these heads, therefore, the subject will be treated of
at present.
SECTION I.
OF STATICAL ELECTRICITY,
Electricity, in its statical condition, may be evolved in various
ways, of which one of the most remarkable, and that most commonly
employed, is friction. If a piece of silk, or a handkerchief, warm
and dry, be rubbed briskly against the surface of a dry glass rod, a?
peculiar odour will become manifest; and in the dark, the surface,
of the glass rod will appear covered with a peculiar phosphores-(
cent glow. If the rod be brought near the cheek, a sensation as if
a spider's web had been drawn across the face will be felt; and on
approaching to the rod, as in the figure, any very light bodies, as a
silk thread, a feather, balls of elder pith, or little bits of paper, they




108   ELECTRICITY PRODUCED  BY FRICT IO N.
will suddenly spring towards the rod, and become attached to it for a moment; after
which they will spring from it, and fall away'  with equal power, assuming the positions of
the dotted lines. The rod which has acquired
-\ /~  ~these properties is said to have been electrifled by friction with the silk handkerchief; it
has become excited, and the phenomena produced are known; the phosphorescent appearance, as the electrical light; the motion to
and from the rod by the light bodies, as electrical attraction and repulsion; in which also, acting on the minute
down of the cheek, the sensation above described has its source.
it is not alone by rubbing together silk and glass that these phenomena may be produced; two pieces of silk, by their mutual friction,
become electric also, particularly if they be of different colours;
thus, on laying flat together slips of black and of white riband, and
drawing them  smartly through the fingers, each will attract the
feathers or pith balls; and being both light bodies, they will also
attract each other. A piece of sealing-wax, or any other resinous
body, when rubbed with flannel or a woollen cloth, becomes similarly excited. Sulphur and amber, in which last, indeed, the property
was first discovered, and from the Greek name of which, qjXe1r'pov,
the science electricity has its name, assume this excited state with
remarkable facility and power.
It is not every substance which may be thus electrified by friction, and even the same substance may often become incapable of
being excited; thus, if the silk or flannel be not completely dry,
if the glass rod be damp, no electric properties can be conferred
upon them. But it matters not how much care we use in drying a
metallic surface which rests upon the ground, or which we support
by the hand, it cannot be electrically excited by any amount of friction. Such a body is termed a non-electric; dry glass, resin, sulphur, silk, &c., being called electrics. Excitation may therefore be
produced by rubbing together two electrics, but by the friction of
non-electrics no electrical effects can be observed. This distinction
is, however, not real; it arises from the construction of the apparatus; for if, in place of resting the metallic rod or plate upon the
ground, or grasping it in the hand, we support it on a piece of sealing-wax, or hold it by a glass or resinous handle, it becomes, when
rubbed with the silk, as highly electrified as any of the electrics;
and in this way, by suitable arrangement of supports, all bodies in
nature may be made to assume electric properties by friction.
To account for this diversity of character, bodies are supposed to
retain the electric fluid upon their surface with different degrees of
power, according to their nature. When by friction electricity has
been accumulated upon the surface of a glass rod, it being a highly
elastic fluid, its particles repel each other, and tend, consequently,
to escape from the limited space which it occupies, precisely as air
tends to escape from a vessel into which it has been powerfully
condensed. Glass, resin, sulphur, amber, silk, flannel, and such
bodies, do not allow of such escape of the electricity, and it is hence




RELATIVE  CONDUCTING  POWERS.                       109
retained in its elastic form upon their surface, and produces anll the
effects of excitation.  They are electrics because they are non-conductors of electricity.  But such is the molecular constitution of the
metals, that they allow of the escape of all that is set free upon
their surface, unless its passage away to other bodies is intercepted
by the interposition of some non-conducting substance. A metal
is thus a non-electric because it is a conductor of electricity; and
when, by supporting it upon a non-conductor, we oblige it to retain
its charge of electricity, it is said to be insulated.  Ice is a non-con-'
ductor of electricity, and by rubbing a, stick of ice it becomes excited; but it must not melt upon the surface, for liquid water, although inferior to the metals in conducting power, is yet so excellent a conductor, that it allows the electricity which we might de-.
velop to pass totally away. Hence the necessity of drying carefully the substances which are, by their friction, to produce the
electricity, and also the reason that insulating bodies must be kept
free from damp; for if the thinnest layer of moisture be deposited
upon their surface, the electricity will instantly escape by the path
so opened for it.
The conducting powers of bodies have as yet been scarcely as.
certained with accuracy enough to justify their being expressed in
numbers, at least for the non-metallic bodies.  The ogeneral order
appears to be, commencing with the best insulators or worst conductors: -
Dry air.              Glass.                 Strong acids.
Shell-lac.            Spermaceti.            Fused saline bodies.
Resins.               Damp organic bodies.   Charcoal.
Oil of turpentine.    Damp air.              Metals.
Sulphur.              Water.
The worst metallic conductor is many thousand times better than
water, and by the following method an idea of their relative power
may be formed. A wire, across which an electric discharge is passed,
becomes heated in proportion to the resistance offered to the motion
of the electricity, and therefore the rise of temperature is inversely,
proportional to the conducting power.  By such experiments Harris
found that, with
The Heat           The conductevolved.           ing P'ower.
Silver......  6....... 120
Copper...... 6.......              120
Gold.... 9          80
Zinc....          18.-.40
Platinum..... 30....... 24
Iron.... 30.24
Tin.... 36.-.20
Lead......72.12
These numbers are merely comparative, and can only be looked
upon as approximations.
The difference of the conducting power explains the fact that,
when we excite by friction the surface of a glass plate or rod, it is
only at the points actually rubbed that electricity at first appears,
and it requires considerable time to creep over the other portions;
but on exciting an insulated metallic rod or plate, no matter how ex



110        DISTRIBUTION OF ELECT.RICITY.
tensive or how long, the electricity, when evolved by friction at a
single spot, appears uniformly distributed over the entire. Hence,
also, a spark may be obtained by electricity passing instantly along
a great extent of metal surface, but is interrupted by a narrow interval filled by any non-conducting matter.
The rapidity with which the electric impulse is propagated has
been examined by Wheatstone in a very ingenious manner, the details of which could not be well introduced here, but which enabled
him to determine an interval of the,,    of a second; he found
that the impulse of the shock of a Leyden jar is transmitted from
each end of an interposed wire, and arrives latest at the centre, so
far appearing favourable to the idea of the existence of two fluids
rather than of only one, and that the velocity of transmission of this
impulse is greater than that with which light passes through the
planetary space, that is, at the rate of more than 195,000 miles in a
second of time.
The electricity, when thus evolved, accumulates upon the surface
of the body, not penetrating to any appreciable depth, but forming a
layer of fluid, which by its elasticity, and hence expansive power,
tends constantly to break away and pass to other bodies which
are not excited. It thus passing through air produces the electric
spark, and is accompanied by a snapping report. The tendency to
escape under the form of the spark depends upon the thickness of
the layer of electricity, and is accurately proportional to its square;
so that if we excite a brass ball with double or treble the quantity
of electricity, the force of the electricity to pass away will be quadrupled, or increased ninefold. Hence it requires exceedingly good
insulation to retain electricity of great intensity.
C                                 a
B         A          B
These principles may be easily demonstrated by means of the apparatus in the figure. A is a hollow sphere of some conducting substance, and B B are hemispheres of gilt paper or thin metallic foil,
which, when closed upon the globe, cover its surface accurately.
They are provided with insulating handles, C C. The hemispheres
being placed on the globe, if the whole be excited by friction or by a
spark front the machine, the electricity will be found uniformly diffused over the whole external surface; and if the hemispheres be suddenly removed by means of the handles, the globe A will remain totally deprived of its electricity, which will be found all collected on the
surfaces of B and B; but it will be no longer uniformly spread; its
intensity will be found much greater on and near the edges of the
hemispheres, and towards the centres of the surfaces the signs of
excitation will be extremely feeble.
The form of a body has a remarkable influence upon the manner
in which the electricity is distributed upon its surface. In a sphere
the layer is everywhere of equal thickness, but in an elongated body




OPPOSITE  CONDITIO.NS OF  EXCITATION.  111
it accumulates more at the extremities of the longest axis.  Hf ace
on a wire or a needle, the electricity is accumulated almost exclusively on the ends; and even though the total quantity of electricity
may not be large, it is there so thickly heaped that it breaks off and
rapidly escapes. Hence electrical apparatus should be completely
smooth except where a point or projection is intentionally attached,
and many remarkable experiments are founded upon the escape of
electricity from points.  Electricity is not merely prevented from
accumulating upon a pointed body itself, but it cannot collect upon
any surface near it, the point abstracting the electricity'.'hus, a
point held near to the excited glass tube used in the experiments
first described may prevent the attraction of the light bodies, which
demonstrates its excited state, by concentrating all the action upon
itself. The detailed theory of this power of points to dissipate their
own electricity and to absorb that of other bodies, will be hereafter
fully noticed; at present it is sufficient to refer it to the thickness
and high elasticity of the layer of electric fluid which forms upon
them.
It has been already stated that, when two slips of silk riband are
excited by rubbing against each other, the electricity appeared to be
equally evolved upon each.  This ocedrs in all cases of excitation
by means of friction. Thlus, when silk and glass are rubbed together,
the silk acquires as much electricity as the glass, but by the silk
being held in the hand, the electricity escapes by the dampness which
is always present, and is lost.  If, however, the silk be insulated;
if a disk of dry wood covered with some folds of silk be held upon
an insulating handle, and rubbed against a similar disk of glass, then
the same phenomena are produced in an equal degree by both. T.hle
attraction and repulsion of light bodies, the odour and the phosphorescence belong to both, and thus in every case where bodies are
rubbed together, the excitation is completely mutual. There is,
however, a profound and curious difference between the two conditions: separately they attract and repel other bodies exactly in the"
same way; together they produce neither attraction nor repulsion:
separately they may manifest the most remarkable evidence of tension, giving sparks and shocks; but when combined, all signs of free
electricity are lost, and the body on which they are collected appears
as destitute of excitation as if the power had never been called into
existence.  The states of the two bodies are therefore so far opposed that they may interfere; and as from the action of two lights
there may be produced total darkness, so from the coalition of the
excitation of the two bodies which had been rubbed together, absolute indifference may result.
This neutralizing power of the excitation of each body for that of the other may
be shown by very simple means. If a feather be suspended by a silken string, and
upon the one side there be presented to it the disk of glass, and upon the other the
disk of silk, which had been rubbed together, it may be brought to remain, by managing the distance, perfectly at rest. If there be the glass alone, it instantly attract8 the feather; the silk alone acts in the same way; but no matter how strong
the power of each may be, when at equal distances the feather remains indifferent
to both. In order, however, to obtain perfect demonstration of this principle, it is
useful to examine it by means of more exact instruments than the feather or other
light bodies, which hitherto have been sufficient, and for this purpose the gold-leaf,shctroscope is best adapted: deferring the description of its principle to ai.other




112    ELECTRICAL  ATTRACTIONS  AND  REPULSIONS.
place, I shall here only notice its construction and the indications which it gives
elg! E-3 A glass jar, A, is closed at the top by a metallic (brass) plate,
B, to which are attached below, by a wire, two slips of gold leaf,
lying, when unexcited, flat on one another, and reacliing below
the middle of the jar. The jar rests on a wooden or metal ioot,
with which are connected two slips of till foil, applied to Lile inA  LI V'I     side of the glass, and rising so far that the gold leaves,on opening out, may come into contact with them.  When thi's occurs. -   there is evidently a free conducting medium fromll the upper me-- -        tallic pllate to the ground; but, except whe,n the gold leaves touch. —,    -      -- the slips of tin foil, the cap and leaves are perfectly insulated,
if the instrument be kept dry. When this electroscope is brought near to an excited body, the gold leaves diverge, and remain so, in the position of the figure, as
long as the excited body be kept near. But if the instrurrent be not touched, the
leaves collapse on its removal, and all remains indifferent, as it had been before.
By the divergence of the gold leaves, therefore, the existence of free electricity acting on the electroscope is made known.
No matter what may be the nature of the excited body acting on this instrument,
it gives the sanme indication of its presence, but when exposed to the action of the
two bodies which had been rubbed together, the gold leaves remain quiescent. If
they be made to separate by the influence of the glass, and the excited silk be then
slowly approximated, the divergence gradually diminishes, until at last the leaves
lie close together. If the silk be then brought still nearer, there is a new divergence,
but it is due to the excess of power of the silk after the neutralization of the glass.
On removing either of the excited bodies when the instrument is in the neutralized
condition, the leaves diverge, from that remaining being free to act. Not merely
is the excitation assumed by the two bodies immediately rubbed together, of these
opposite kinds, but it may be shown that this peculiar power may exist in the conditions of two bodies rubbed by a third, as if a glass be rubbed with silk, and an insulated metal rod be likewise excited by rubbing with silk, the glass and metal rod
assume electricities which destroy each other, or the silk is related to the metal as
the glass had been to the silk. Bodies rubbed by different other substances are also
so circumstanced; if a stick of sealing-wax be rubbed by flannel, it will assume opposite excitation to that of glass when rubbed with silk, and would counteract its
influence; and, consequently, the condition of the flannel in the one case, and the
silk in the other, would be opposite also. This assumption of opposite states of excitation may be caused by trifling mechanical conditions: thus, if smooth glass and
muffed glass be both rubbed with silk, they become oppositely electrified; and two
pieces of silk, which differ markedly in colour, neutralize each other when electrified
by their mutual friction. The peculiar characters of these two forms of excitation
extend, however, much farther than the principle of mutual destruction. If we hang
by a dry silk thread, varnished with shell-lac in order to render it a better insulator,
a little cylinder of gilt paper, and bring near it an excited body, the cylinder is attracted, and moves towards the body until it touches, when.it is immediately and
forcibly repelled. It has by contact participated in the state of excitation of the
body, and, when that is so, they mutually repel each other. In all cases, bodies
which are in the same electrical condition repel each other; and it is thus that the
gold leaves of the electroscope become an index of any electricity which may be
present; for as both slips of leaf are necessarily excited in the same way, they repel
each other, and, consequently, they diverge.
It; now, the insulated gilt paper cylinder which has been, as above described, repelled by the glass rod, after having shared its electricity, be brought near the silk
against which the glass rod had been rubbed, or to any body which is in the same
state of excitation as the silk, attraction will ensue, and this will be found more
powerfful than if the body had previously been neutral. If two such gilt paper cylinders be touched, both with the glass rod or both with the silken disk, they will
repel each other; but if one be touched with the glass and the other by the silk,
they will attract each other, and move until they touch, when the states of excitation neutralize each other, and they become inactive.
When bodies are rubbed together, therefore, they become electric, and with such properties, that while each when separate gives
signs of powerful excitation, together they  destroy each other's
power. Bodies when thus oppositely electrified attract each other;




LA W   OF. ELECTRICAL  ATTRACTIONS.                           113
bodies which are excited in the same manner repel each other;
and these attractions and repulsions arise from the exertion of a
force which, like that of gravitation, diminishes in intensity according as the square of the distance between the bodies becomes
greater.
This law, which is of the greatest importance for the theory of electricity, was
discovered by Coulomb by means of the torsion electrometer. The gold-leaf apparatus, though exceedingly sensible as a test of the presence of free electricity, is yet
not susceptible of being used to measure its amount.  It is an electroscope, but not
an electrometer.  The torsion balance of Coulomb consists of a
glass drum, a, on the centre of which rises a glass tube, b, to the
height of one or two feet. From the top of this tube is hung, by
a fine thread of glass or of cocoon silk, a very light wooden beam,
c, to which is attached at one end a ball of dry elder pith, and at
the other a piece of gilt paper, which serves as a counterpoise,
and by its surface prevents irregular motions of the beam. The
pith ball is usually gilt, to give it a more uniform surface.  In'!
the top of the drum there is an aperture, by means of which a   I
second gilt pith ball, d, may be introduced, and Bmade to touch
that of the balance; and around the centre of the drum is fixed
a scale of degrees, by which the angular distance to which the
balls separate after repulsion may be measured.  Now let us I". ""
suppose that, by touching the second, or, as it is called, the carrying ball, to an- excited body, we charge it with electricity, and,......::::::..
having inserted it in the aperture, it touches the ball of the bal- A
ance, which is immediately repelled: in moving away, thistwists
the thread by which it is suspended, and the amount of the twisting which is necessary in the opposite direction to bring it back again, and maintain it at a certain
distance, measures the force of repulsion the balls then exercise. This measurement is effected by the glass or silken thread being attached, not to the tube, hut to
a stem carrying an index, which shows, on a graduated circle, the number of degrees through which the thread is twisted; and as the thread is exceedingly long
in pr.oportion to its thickness, and its elasticity almost exact, the force of torsion is
taken as proportional to the angle through which the inde.x moves.
By this instrument, into the detail of experiments with which it would be improper
here to enter, Coulomb established the fundamental law of electrical attraction and
repulsion; and it has been found, that from this law all the results of the distribution of electricity on bodies, its accumulation on and escape from points, that have
been noticed, might be deduced.
The fundamental principles of electrical excitation, the distribution of electricity
on bodies, and the manner in which the electric states of the excited bodies are related to each other, having been thus described, I shall pass to the explanation of
the general principles under which those phenomena and laws have been arranged,
and a knowledge of which we shall find necessary to our future progress.  I shall
lay aside all consideration of the more abstract theories of electricity, which refer
it to mere molecular disturbance or to vibrations, and consider only those views
which suppose the existence, in the one case, of two electric fluids, the theory of
Dufay, and, on the other, that of a single fluid, the theory of Franklin.
Theory of two Fluids.-It is assumed that there exist in nature two
kinds of electricity, each a highly elastic fluid, whose particles repel
each other according to the law  of the inverse square, while they
attract the particles of matter, and also attract each other, according to the same law: that every body in nature contains usually
an exactly equal quantity of each fluid; that bodies then are in their
ordinary state; and hence, manifesting  no unusual properties, we
look upon them  as being quiescent: but if a body contains more
of one fluid than of another, it comes into an extraordinary state,
and, acquiring new properties, we say that it has become excited.
Upon this view, the phenomena of electricity are capable of very
simple explanation.  When two bodies are rubbed together, the re-.
P




114          THEORIES (}F ELECTRICITY.
suit is, that one electric fluid accumulates in excess upon the one,
and the other upon the other body. They are thus both brought
into a state of excitation; and as the excess of the one fluid must
be exactly equal to that of the other, the excitation of both is equal,
and, being opposite, must neutralize each other when they are
brought to reunite. Of these electricities, that which passes to
glass when it is rubbed with silk is termed, in the language of Du.
fay, vitreous electricity, and that which accumulates on resin when
rubbed with flannel is called resinous. There are few bodies which
may not assume vitreous or resinous excitation, according to the
substance by which the friction is produced, and hence these names
are liable to some objection, and are not much employed.
Since the electric fluids and matter attract each other, the bodies
upon which the electricities become free appear to attract or repel
each other according as they are invested by the same or opposite
fluids, in consequence of the necessity of accompanying'these fluids in their action on each other. Hence the electric attractions
and repulsions which manifest themselves in all cases of excitation,
and hence the bodies return to their indifferent condition as soon
as the excess of electricity they contain is neutralized. It was for
a long time supposed that the atmosphere, by its mechanical pressure, assisted in retaining the free electricities upon the surface of
the excited bodies; but this is not the case. The air acts as an insulator of the excited body, without which no accumulation of free
electricity could occur; but the mechanical pressure of the air may
be removed without affecting the electrical conditions.
Theory of one Fluid. In the hypothesis of Franklin there is assumed to exist but one electric fluid, of which, in its ordinary state,
every substance contains a certain quantity. This fluid is considered to be highly elastic, to repel its own particles with a force
varying as the inverse square of the distance, and to attract the particles of matter according to the same law. A substance with its
proper share of electricity is therefore in its indifferent condition,
possessing no properties beyond what we ordinarily attribute to it.
But when two such bodies are rubbed together, a quantity of electricity abandons one and collects upon the other, and thus both are
brought into an abnormal state, and assume the unusual properties
which constitute excitation. The excitation is equal, for the one
has gained precisely what the other lost; and by recombination
they destroy each other's action, for they are brought to their original ordinary state. The excitation being produced, according to
this view, by one body having electricity in excess, while that of
the other is deficient, one is said to be;plus and the other minus
electrified; or, more generally, the one to be positively, the other
negaftively excited, and the signs -+- and - are often -used as abbreviations for these words.
The particles of the electric fluid being mutually repulsive, and attracting those of matter, it is natural that two bodies having electricity in excess shall mutually repel, and that a body having an
excess of electricity shall attract one having an excess of matter.
GBodies both + therefore repel, a + and a;- body attract each other.
But, to explain the mutual repulsion of bodies both in the negative




ELECTRICAL  MACHINES.                              115
condition: an assumption is required which at first sight appears to
militate considerably against our reason; for as it is matter which
is in excess in that condition, we must consider that the particles
of matter mutually repel each other, according to precisely the same
law, as it is demonstrated by the whole construction of the universe,
that the particles of matter mutually attract each other. There is
not, however, any real contradiction in these principles; the law of
gravitation applies to matter in its ordinary state, in which it contains its natural quantity of electricity; and it affords no grounds
for supposing that, if matter were deprived of that natural electricity, it would continue to attract. There is, consequently, nothing
illegitimate in that assumption; and the theory of a single fluid may
be as easily and successfully applied to the explanation of phenomena as that of the two fluids before described.
Already, indeed, considerable progress has been made towards a theory of electricity upon this idea. In order to account for the ordinary molecular constitution
of matter, it is necessary to suppose that the forces which act upon its particles
may cllange from attractive to repulsive, and again from repulsive.to attractive, according as the distance between the particles is made to vary; and Mosotti has
shlown that it is only necessary to assume that the mutual repulsion of matter,
when destitute of' electricity, is inferior to its attraction for electricity, and to the
mutual repulsion of the electricity itself, and the law of gravitation becomes a necessary consequence of the conditions under which alone electrical equilibrium can be
establiished.
Such are the theories of electricity that have hitherto met with most general accepltation. In the succeeding portions of this work, I shall adopt the language of
the tieory of the two fluids, except that I shall use the words positive and negative
fluids in place of vitreous and resinous; but I do so merely from convenience, and
seek not to connect the idea of a fluid in any way more intimately with the true,
causes of the electrical properties of bodies.
Before passing to the description of the phenomena, and the discussion of the principles of electricity which yet remain, it is necessary to notice the construction of some electrical apparatus, which
is employed in all cases where it is desirable to operate upon
this agent in a state
of high intensity ali'
power. Of these the
most important is the
electrical machine.
The machine is in
principle only a modification of the glass
tube which, by friction with a piece of
silk, evolved the electricity in the first experiments described.
It consists of a glass
having such a form
as to expose a great
extent of surface, and
generally being used
in the shape of a cyl



116             ELECTRI iAL MACHINES.
inder, A, or of a plate. There are hence the cylinder and the plate
machines. To produce the friction, an elastic rubber, B, is covered
with silk, and made to press against the surface of the glass according as the plate or cylinder is turned round by means of the handle.
The rubber being generally insulated, the electricity evolved upon
it is at once collected, and may be transferred along conductors, or
drawn as sparks from the knob of brass attached to it at the back.
The electricity which is diffused upon the glass passes fromn its surface to that of a brass cylinder, termed the prime conductor, C, being collected by
means of a series of pointed
wires, which graze the surface of the cylinder according as it is turned round. The
prime conductor is also insulated; and in the case of a
cylinder machine, the glass
itself is often supported upon
insulating pillars, by which
the loss of electricity is prevented. To increase the energy of the machine, the silk
of the rubber is generally
smeared over with a mixture
of grease and an amalgam of
tin and zinc, and a silken
apron extends from the rubber half over the cylinder or plate to conduct the electricity to the points: and prevent its being carried away
by the air.
Although I shall have occasion, when we have examined the relative action of excited bodies and  conductors somewhat better, to
notice the true theory of the prime conductor, yet for the present it
may be considered as simply,ofrom its proximity, collecting the free
electricity on its points from the surface of the glsss cylinder or plate,
and by thus accumulating it upon a confined surface, enabling the
experimenter to apply it or carry it to other bodies at his pleasure.
When the machine is worked, the two portions of electricity become
developed, as in the rubbing of the tube and handkerchief, upon the
silk and glass; and if all be insulated, they attract each other so intensely that they break through the intervening air, and recombine
across the surface of the cylinder, or round the edges of the plate,
presenting the appearance of a brilliant spark, and accompanied by
a snapping noise and a peculiar phosphorescent odour.  To prevent
this recombination, which would, of course, render accumulation upon the prime conductor impossible, the rubber, when the machine is
required for active work, is connected with the ground by a wire
or chain, through which the electricity which forms upon the silk
makes.its escape; and as new quantities are then liberated at each
moment, those passing from the glass to the prime conductor, by
the projecting points with which it is always furnished, collect upon
it, and, acquiring a high degree of tension, pass under the form of
sparks to any conducting body which may be brought near.




PHENOMENA  OF THE ELECTRICAL.MACHINE. 117
By means of a machine of such construction, the opposing properties of the electricities of the bodies rubbed together may be simply and completely shown.
The degree of excitation of the prime conductor is generally,
though not very, accurately, shown by means of the quadrant electrometer. This consists of a stem of brass, which
rests in a socket in the prime conductor, or, when not in
use, in a wvooden foot, as in the figure. To this is attached
an ivory semicircular scale, of which a portion is graduated,
from whence the name; on an axis at the centre of the
ivory scale there is hung, by a light arm of whalebone, a
pith ball, which, when the apparatus is unexcited, lies in
contact with the brass stem, and thus assumes the same electrical condition with it when the instrument is placed on the
prime conductor and the machine worked. The stem and the pith
ball then repel each other, and the ball being consequently set in motion by the united repulsion, its radius moves through an angular
space on the graduated scale, which serves in rough experiments as
an index of the intensity of the excitation. Now if, when this instrument is fixed on the prime conductor, the latter be connected with
the insulated rubber by a chain or wire, no matter how vigorously
the machine may be worked, no signs of excitation can be produced;
the electricity collected from the glass by the prime conductor
passing along the chain or wire to unite with that which is developed on the rubber, and the two being evolved in equal quantities,
complete neutralization is produced. That bodies similarly electrified repel each other, is shown by the principle of this instrument,
as its indications of free electricity depend upon the stem and ball
being both excited in the same way, and the repulsion being the
same, whether it be fixed upon the rubber or the prime conductor.
To prove on a large scale, by means of the machine, that the opposite electricities attract each other, it is only necessary to place
in connexion with the conductor on each side a metallic wire, tc
which is hung, by a wetted thread, a ball of pith, or a cylinder of
gilt paper. When the machine is turned, the balls attract each oth
er across the cylinder, and touching, interchange the electricities
by which they are excited, and thus the fluids, separated by the
friction, are continually recomposed, being brought together by
their mutual attractions. If to each wire there be hung two such
balls, those of each side will be seen to repel each other, while
they move towards those oppositely excited. Numerous experiments of an amusing kind, which it would be foreign to my purpose
to in*roduce, are founded on these principles.
There have been now noticed four methods by which bodies may
be electrically excited. 1st, by friction, which is, indeed, the only
true direct excitation. 2d, by contact; as when an insulated
brass disk excited by friction is touched to another, also insulated
and neutral, a spark passes between them at the moment previous
to actual contact, and the first is found to have divided its electricity with the second in proportion to its surface. In this case the
two bodies, after contact, are in the same state of excitation. 3d,
ts where the prime conductor, which is neither itself rubbed, nor




118          EXCITATION  BY  INDUCTION.
does it touch the cylinder of the machine, yet gathers from it the
electricity which is evolved thereon, and allows it to be transferred,
under the form of the spark, to other bodies; and, finally, all the
attractions and repulsions which have been observed indicate a powder of action and excitation even at considerable distances; and this
mode, which results from the attraction and repulsion of the electric fluids for each other, is, when examined, found really to comprehend the second and third modes of excitation, by contact and
by gathering with points. There are, therefore, truly, only two
means of excitation, this at a distance, which is termed induction,
and that by friction.
It is not difficult to understand how bodies come to be excited by
induction. Let us consider the insulated cylinders, B C, as being
C    -                - B       neutral, and having
their natural electriD                                        cities combined, and
distributed uniformA  ly over their surface.
If a globe, A, exci-......._.._....,._-        ted, say with positive electricity, be brought near, it will attract the opposite electricity of B to the end which is nearest it, and repel the electricity
of the same name to the farthest extremity; both electricities of
B will thus become free, and B will be excited by the influence of
the electricity of the body, A, at a distance; and the condition of
B is characterized by its two extremities being in opposite states,
and hence, at a certain point between them, perfect neutrality remaining. The positively excited end of B influencing C in a corresponding way, brings it also into an excited state, and this communication of action would go on through any number of bodies,
the force set free being regulated by the law of the inverse square
of the distance fromn the original disturbing cause at A. As long
as A remains in its place, the state of electrical excitation is kept
up; if A be totally removed, the natural electricities of each body
recombine, and all become neutral; if A be brought very close to
B, or B to C, the attractions between the opposite electricities become so great that they unite across the intervening space of air,
and a spark passes. The bodies are then found to be in the same
state, and the communication by contact, or the excitation which
occurs, is shown to be only the termination of the inductive action.
For suppose that A had 10 parts of +- electricity, and that, by induction, it set free 5 of the - and 5 of the + fluid on the surface
of the body B; then, when the spark had passed, the -5 destroying +5 of the body A, the two bodies should remain each with
+5, and thus the results of contact described already should be.
produced.
The distance at which the combination of the electricities of the
inducing and the induced body may occur, depends upon the intensity of the fluids collected on the parts of the surface nearest to
each other; and hence, when there is on the body a point on which
the great proportion of the liberated fluid, as has been already described, becomes accumulated, the fluid escapes from thence before




THEORY  OF  THE   GOLD  LEAF  ELECTROSCOPE.  119
it is in sufficient mass to break its way under the form of a spark,
and thus the permanent and similar excitation of the body silently
occurs.  This is the true theory of what has hitherto  been described as the power of points to gather and to disperse the electric fluid. If a pointed body be excited by friction, it induces an
opposite state in the particles of air by which it is surrounded, and
communicates to them, with great rapidity, the charge which it had
received. The prime conductor of the machine, being insulated,
has its electricities separated by the inductive action of the excited
glass cylinder or plate; the negative electricity collected on the
points turned towards the glass escapes from thence, and unites
with the positive fluid which had been set loose by friction, and
proportional quantities of the positive fluid of the prime conductor
being left free upon its surface, it serves the same purpose as a
source of electricity as if it had come directly from the glass. A
point placed on the prime conductor prevents the accumulation of
the electricity, because it gives the +- to the air as fast as the other points give the - to the glass; a point held near the prime conductor also prevents its excitation, by giving to it by induction -
electricity as fast as it obtains + electricity from the glass of the
machine.
In all these cases of induction where the electricities attract and
repel each other, the bodies on which the electricities are collected
will accompany them  in their motions if they be not too heavy.
Hence all the singular motions of bodies, when excited, are explained upon this principle. The variety of dancing figures, ringino bells, revolving wheels, affrighted heads, and so on, that are exhibited in popular lectures on this subject, will serve to practise the
ingenuity of the student in tracing out their theory in the detail,
with which it would be quite improper to occupy this work.
The theory of the Bennet's gold leaf electrometer, with which some of the most
important principles of statical electricity are demonstrated. must not, however, be
omitted. When an excited rod is brought over the electroscope, it separates the
electricities of the metallic portions of the instrument, attracting the opposite to the
upper surface of the cap, and repelling that of the same name into the gold leaves,
which, being thus excited with the same electricity, repel each other, and hence
diverge. If' the exciting body be -+-, it is the + fluid by which the instrument appears affected; if it be -, the leaves diverge from the presence of - electricity.
Hence if, when it is under the influence of a glass rod rubbed with silk, a stick of
sealing-wax which had been rubbed with flannel be brought near, the divergence
diminishes, until at last the leaves collapse completely, the resin having driven down
as much negative electricity as there had been positive brought into action by the
glass, and hence the gold leaves coming into their natural and indifferent condition.
That it is by this inductive process that the gold leaves act, may be thus shown. If
the cap of the electroscope be rubbed with a dry silk handkerchief, it becomes excited,
and the leaves diverge with negative electricity; if then an excited glass rod be
brought near, the divergence is neutralized, showing that positive electricity had been
sent down by the glass; but if an excited resinous body be approached, the divergence increases, indicating the superaddition of electricity of the same name from
the inducing power of the resin.
If, as in the figure (page 118), the cylinder C be connected with the ground by
means of a wire or a wetted thread, D, the positive electricity passes from that body
through the wire into the earth, where, from the enormous surface of the globe, it
may be looked upon as lost, and the surface of C is altogether in a state of negative
excitation. If, now, the exciting body A be taken away, the quantity of positive fluid
returns along the wire, and brings the body C into its neutral state; but if before the
body A be taken away, the conducting communication with the ground be cut off by




120      CONSTRUCTION  OF  THE LEYDEN  JAR.
the removal of the wire or thread, the body C cannot get its positive electricity back,
and hence remains in a state of negative excitation. In this manner a substance
may, by induction, be made to receive a permanent charge. This is often useful in
experiments with the electroscope, and the manipulation to charge it permanently is
as follows: If it be desired to charge it positively, an excited stick of resin is held
near, and the cap of the electroscope is touched with the finger. The negative electricity then escapes by the hand into the ground, and the positive electricity, accumulating over the cap and leaves, these last diverge. On then removing the finger,
the leaves are insulated; and. when the stick of resin is taken away, the permanent
charge remains. To charge with negative electricity, an excited glass rod is to be
used; and it will be recollected, that where the charge of the leaves is temporary,
its electricity is the same as that of the exciting body; but where the charge is permanent, the electricity is of an opposite kind.
After the exciting body, in the latter instance, has been withdrawn, the divergence
of the gold leaves becomes much greater than it had been before. This arises from
the charge being increased by its action on the surrounding bodies, particularly on
the glass by which the leaves are enclosed. By taking advantage of the increase
of charge, by secondary inductive action, various forms of the electroscope have been
contrived for rendering it more sensible, and are described in special treatises on
electricity under the name of Doublers and Condensers. As they do not add anything
to our knowledge of principles, and have no peculiar chemical relations, I shall not
enter on their farther consideration.
One of the most interesting instruments in statical electricity,
founded on the principle of induction, is the Leyden Jar, so called
from  the city where its construction was discovered.
It consists of a glass bottle, which is coated inside and:::-    outside, to a small distance from  the top, with tin foil,
ii. and has fitted to the orifice a wooden or cork stopper,
through which passes a stout wire, touching at the bottom  the internal coating, and terminated outside by a
metallic knob.  When this jar is insulated, and the knob
-,l is  touched to the prime conductor of the machine, and
_.~     ~.-~.,: the handle turned, the positive electricity passes to the
internal coating' of the jar, and excites it to an equally powerful degree. This, then, reacting by induction upon the electricities of the
external coating, separates them, attracting the negative to the side
next the glass, repelling the positive to the outer side. The position becomes, therefore, +  -   +-; and when the +  fluid inside
makes up by its greater quantity for the thickness of the glass by
which it is separated from the -- fluid, no more can enter into the
jar. In this case the inside of the jar may be considered as being
merely an extension of the prime conductor; and the electricities
of the external coating, although separated from  each other, are
only in the quantities -which had been always present. But if the
external coating be connected with the ground, the +  fluid, being
repelled by that inside, passes away, and another quantity, entering
from the prime conductor into the jar, decomposes a new quantity
of the natural fluids of the external coating, of which also the positive escapes and the negative remains behind, held by the attraction
across the glass to the positive fluid inside. New quantities of positive electricity entering continually from the machine, the accumulation of negative electricity on the outer coating proceeds, until the tendency of the two to combine is so intense as to break
their way across the glass, cracking the jar, or to creep over the
mouth from the edge of one coating to that of the other, and thus
the jar discharges itself.  To discharge a jar in which the eleec




ELECTROPHORU S     OF VOLTA.                 121
tricities are so accumulated, it is only necessary to connect by a
wire the internal and external coatings; when the extremities of
the wire, which are generally terminated by brass balls, approach,
a large brilliant spark passes, accompanied by a loud report, and the
jar returns to its original neutral state.
By thus collecting great quantities of electricity in large jars or
in sets of jars (electrical batteries), the most beautiful and remarkable phenomena of electrical force may be exhibited.
The principle of the construction of the Leyden jar may be experimentally demonstrated as follows: First, it has been already
explained that the jar, when insulated, is incapable of receiving any
other charge from the machine than what its internal coating obtains
by forming part of the surface of the prime conductor; the principle
of induction requiring, in order that one electricity may accumulate upon its outer surface, the other shall be dissipated on the ground.
Second, a light body placed between two balls, connected, one with
the internal, and one with the external coating, is alternately attracted and repelled by each, and thus the accumulation on the two
coatings is shown to be of opposite kinds. Third, the quantity of
electricity which passes from the external coating may be shown
to be equal to that which passes into the internal coating from the
machine, by insulating the jar, and applying the knob of a second
jar which is not insulated to its outer surface; this second jar will
be found charged to the same degree as the first, and the inner and
outer coatings will be respectively in the same state.
Statical electricity, thus accumulated in the Leyden jar, is capable of giving violent shocks to the animal frame, of evolving light
and heat, and producing also powerful mechanical effects.
An instrument founded on the principle of induction, and which
is of frequent use in chemical experiments, when an electric spark
of moderate power is required, is the electrophorus of Volta. It consists of a flat cake of resin, b, which is generally spread on a circular board of eight or ten inches diameter. There is laid on this
anotheer circular plate, a, somewhat smaller, and which may be either
of brass or tinned iron, with the edges turned up over a thick wire,
so as to round it, or a board covered with tin foil. To this upper
plate is attached an insulating handle of glass, c, and from its edge
projects a wire terminated by a knob. The resinous plate, being warmed, is to be strongly excited    IC
by friction with a warm  flannel cloth or a cat's
skin, and then the upper plate is to be laid on it, and
is touched with the finger. The negative electricity,('a
of this passes, then, into the ground, and the positive
accumulates on the surface next the resin, of which:
it, by induction, increases the negative charge. This new portion
of negative fluid decomposes a new quantity of the electricities of
the upper plate, which again reacts, and thus the plates are mutually
brought into a state of very intense excitement. If, then, the finger
be removed, the upper plate is insulated, and its charge of positive
electricity retained upon it; and on applying the knob of the wire
to any conductor or to the knuckle, a strong spark may be obtain.
ed from it; the instrument may be repeatedly charged and dischar.
Q




122         TR ANS1',1S SION BY INDUCTION.
ged in a few minutes, and retains its charge better than the electrifying machine.
This inductive action of electricity would at first appear to be
exercised at a distance, altogether independent of the interposed
substances, and to produce the motions to which it gives rise, as
gravity causes the revolutions of the planets and their satellites,
without the existence of any interposed medium; but a more exact
exramination shows that this is not the case. The substances inter
posed in the path of the inductive action are necessary to its transmission, and modify, by their nature, its direction and amount; and
it is, indeed, only from molecule to molecule of any substance, gaseous or solid, that the decomposition of the natural electricities can
take place.
This may be beautifully shown by plunging in a vessel of oil of
turpentine, which is an excellent fluid insulator, two brass balls, of
which one is in connexion with the electrical machine, and the
other with the ground. On turning the machine, the latter becomes excited by induction. If, now, a number of short shreds of
sewing- sillk be mixed with the oil of turpentine, the mechanism of
the inductive action is shown by each little bit of silk acting like
the bodies B and C in the figure (p. 118); and attaching themselves
mutually by their extremities, they transmit the electricity of the
machine, by a series of decompositions, to the ball which is connected with the ground. If the excitation be very violent, the attractions and repulsions become too strong to be regularly transmitted; and this induction is accompanied by a powerful current
of the particles of the oil from the first ball to the second. The
particles immediately in contact with the directly excited ball acquire its state, and, being repelled, immediately pass off to that which
has obtained, by induction, the opposite condition, and there become
neutralized. Now what here occurs with the oil of turpentine takes
place in ordinary induction with the air; every molecule of it interposed between the solid bodies becomes itself subjected to the inductive action, and forms a chain of alternate positive and nWa:gative
poles, by which the effect may be transmitted to any distanc;e. If
the excitation be very great, the neutralization may occur with violence and rapidity, and generate currents, as in the oil of turpentine. It is these currents which, being produced by the repulsion
of the particles of air from excited points, are rendered sensible in
the effect termed the electrical aura, and are shown by the experiments of revolving flies. A still more violent and rapid recomposition of the electricities of the air molecules, which had been separated by induction, gives the electric spark in its various forms,
such as the star, the brush, &c., according to the manner in which
it is received and generated.
That the excitation by induction of a body at a distance is eftected in this manner, from particle to particle of the interposed substance, is beautifully shown in the results obtained by Faraday concerning the influence of the nature of the medium on the amount
of inductive charge transmitted. The instrument, which he has
termed an inductometer, consists of a hollow sphere of brass, a a b,
and a sphere of smaller size, A, also of brass, which is placed exact



SPECIFIC  INDU CT'IVE CAPACITY.                 123
ly concentric with it. The interval between        (0)
these, o o, may be occupied by any substance,
as air, or glass, or sulphur; and then the central
sphere being insulated from  the outer by the    b
shell-lac column b, and having been excited from
the machine through the ball and vire B, the
outer one is uninsulated, and the whole becomes   (//
a Leyden jar, in which the. material may be varied at the will of the experimenter. By means
of the tube and stopcock f d, the air in o o may
be removed, and. any other gas substituted for it.            b
The outer sphere opens at b in two, so that          h
melted sulphur or shell-lac may be poured in to
form the inductive niedium.                      I
When the internal sphere is excited always
to the same degree, the charge of the external
coating should be the same, no matter what
might be the nature of the intervening substance,
if the action took place simply at a distance, after   Jf'j
the manner of gravitation. But this is not the
case. With the same internal charge, the excitation of the external sphere was found to be,          X
that with air being 100, with shell-lac 150, xvith 
flint glass 176, and with sulphur 224. In these cases, therefore,
the molecular excitation was transmitted in proportion to these
numbers, which express, therefore, the degree of excitation that a
common amount of inductive influence is able to produce in masses
of these bodies. All gases, no matter how different in chemical
properties and constitution, even though the temperature and pressure do not remain the same,' possessed the same specific inductive
capacity as air.
This principle is farther shown in an interesting manner by the
fact that the induction is not exercised only in
the straight line connecting the solid inducing      M
and induced bodies, but that at every intervening    )
point there is a lateral action exercised by the    (
interposed molecules of air, which may be them- A\ 
selves considered centres of inductive force.
Thus, if a cylinder, a, of shell-lac be excited by
friction, and a brass hemisphere, h, placed on top
of it, the intensity of the induced electricity will
be found to depend not merely on the distance Cg 
from the excited source and the nature of the
interposed material, but to be more energetic
in certain positions in the air, as when the carrier ball of Cotulomb's torsion electrometer was
placed at o, than when it was lower or higher at
n or p.
Faraday has been led by his experiments to conclude that the
cifference between conducting and non-conductinog bodies is, that
the former assume with exceeding rapidity, under an inductive influence, this condition of molecular excitation, and hence appear to




24 OTHER C AUS E S OF'STATICAL EXCITATION.
allow the electricity to pass actually and instantly through their
substance, whereas, in reality, it is only that the separation and recomposition of the electricities of the chain of molecules has been
so accomplished. They lose also this condition as soon as the exciting cause has been rem oved, whereas non-conductors, when their
particles have acquired electrical excitation, remain in that state of
tension for a certain time. Thus, if the internal and external coatings of a Leyden jar were connected by a metallic wire, the inductive action would be propagated immediately across it; but the instant that the source of the excitation was removed, the electricities of the two coatings would recombine, from the facility with
which the molecules of the wire can assume the inverse condition.
But with an interposed plate of glass the result is different; the inductive action is propagated equally, but more slowly; and that it
is the particles of the glass that really produce the charge by their
excitation, is demonstrated by the fact that the metallic coatings
may be removed, and yet the accumulated electricities be not disturbed; the tin foil serving only to discharge at the same moment
every particle of the glass, as if a wire had been individually applied
to each. That the induction has acted on the substance of the
glass explains also the peculiarity of what is called the secondary
or residual charge. When the particles at the surface have been
discharged, they are acted on by the deeper molecules which are
still excited, and hence acquire a second inductive charge; and with
thick glass, and particularly with bodies which do not insulate quite
so well as glass, there may be even a third or a fourth charge of
this kind.
Conduction is therefore only the highest, most intense, and most
rapid form of induction; and it appears from Faraday's investigations that the permanent excitation of an electrified body has its
origin also in the inductive influence of the bodies that are around.
The source of the electricity evolved by the electrical machine
cannot be considered as being positively known. Wollaston instituted a series of' experiments, by which it appeared to be demonstrated that there was no electricity evolved except where chemical
combination took place, and the superior power given to the machine by the amalgamn of tin and zinc being spread upon the rubber
was supposed to verify this idea. These experiments of Wollaston
have been latterly repeated with great care by Peltier, and with
different results; he found that the electricity evolved was proportional only to the amount of friction, and was the same under va
rious circumstances of liability to the presence or absence of chem
ical action of the materials rubbed. It is therefore likely that, at
least, the electricity of the machine may be generated by the simple molecular derangement and vibration which friction necessarily
produces; and this view is very much supported by the undeniable
fact, that by other agencies purely molecular, where no trace of
chemical action can be pretended, the same form of statical electricity may be produced.
In almost all cases where the particles of bodies are suddenly and violently disarranged, the separated surfaces are found to be electrically excited; for instance,
if a piece of mica be torn into thin leaves, these are powerfully electric. In many
mineral substances a change of temperature causes a manifestation of electrical




ATMOSPHERIC  ELECTRIC IT Y.                            125
polarity in a very remarkable degree; thus, if a long prism of tourmaline be heated,
one extremity becomes positive and the other negative; when the temperature attains its highest point and becomes stationary, all symptoms of electricity disappear,
but on cooling they return; in the inverse order, however, the end which had
been positive becoming negative, and so on. In this case it appears as if the particles, in the internal motion which the expanding force of heat produces in them,
acquired the same condition of polarity as they would have done by an external
friction. If the expansive effect of heat and the consequent change of position
among the particles of the tourmaline had been the same throughout, there would
have been no reason for electrical disturbance; but this mineral, and some others
which likewise become electric on being heated, as baracite, are exceptions to the
general law of crystalline symmetry, and in other respects, as with regard to light,
indicate a kind of structure which is very complex and peculiar. In such cases, an
internal friction by the action of expansion on the unsymmetrically situated mole
cules of the crystal is the origin of the electrical excitation.
The source of statical electricity, which is of the greatest importance in nature
fronl the universality of its action, is that of change of state of aggregation.  When
any body passes from the liquid to the solid, or fiom the liquid to the vaporous con
dition, or in the reverse order, from being solid or being gaseous becomes liquid, disturbance of the previous electrical equilibrium results. Thus, if a little melted sulphur be poured into a glass, or if melted tallow or resin be poured out on a metallic plate, the bodies after solidification will be found excited. If a cup of watet
be placed on the plate of the electroscope, and a red-hot ball of metal, or even a
red-hot cinder, be dropped into it, the gold leaves immediately diverge by the influence of the negative excitement which is assumed by the water which remains,
and which communicates itself to the metallic cup and to the instrument; if the
gush of vapour had been allowed to impinge on the plate of another instrument, it
would have shown excitation by positive electricity. This last is one of the nir st
abundant sources of electricity; for as at all ordinary temperatures evaporation
takes place from the surface of all the water of the globe, and the vapour produced,
carrying with it the prodigious quantity of positive electricity which is thus set free,
mixes with the air, our atmosphere is almost continually in an electrical condition,
generally positive, but at some times, from interfering causes, negative. The great
body of vapour, when condensed by the more elevated and colder regions of the
air, collects into the peculiar condition which constitutes a mass of cloud, and
therein is thus concentrated all the electricity evolved by evaporation at the surface. The clouds are, therefore, intensely electric; and when attracted by indue
tion to each other, or to some prominent object on the earth, as a mountain-peak
or an elevated building, the discharge and neutralization of the electricities take
place with the brilliancy and destructive agency of the lightning, while the report,
re-echoed from the surfaces of the remaining clouds, or by the sides of the adjacent mountains, produces the effect upon the ear of the continuous rattle of the
thunder.
There is no doubt, however, but that in many cases of chemical combination
and decomposition electricity in its statical form may be evolved; thus Pouiliet
proved decisively, that when charcoal is burned, the carbonic acid which passes off
is in a state of positive excitement, and the residual mass of charcoal becomes negatively charged. When hydrogen burns in air, the vapour of water carries off the
positive electricity, while the negative fluid distributes itself on the hydrogen remaining, and the vessel from which it issues. There is thus, in the combustion
of our ordinary fuel, a vast source of the electricity of our atmosphere, in addition
to that evolved by water in evaporating; and it has been found that the evaporation
of a saline solution, as sea-water, produces a much greater degree of excitement
than when the water is completely pure, owing, perhaps, to the destruction of the
condition in which the salt and water had been united. The evolution of statical
electricity occurs, also, when the chemical action is of a much more complex and
obscure kind; thus, in the growth of a seedling plant, the carbonic acid which it
evolves is in a positively excited state, and the substance in which the'seed is imbedded becomes negative.  It would appear, however, that frequently electricity
that had been imagined to arise from the chemical relation of the bodies brought
into contact, arose from their merely mechanical action on each other; thus the
electricities produced by sifting lime and oxalic acid together on the plate of the
electrometer are produced.
The mere contact of bodies has been supposed sufficient to evolve electricity upon




126             DYNAMICAL  ELECTRICITY.
their surface. The trace of excitation in such experiments is so small, and diminishes so much in proportion as care is taken to avoid friction and other causes,
that we may consider contact as being in itself without power.
The remarkable characteristic of statical electricity developed by any of these
methods, is the amazing energy of its action on bad conductors, and on the best
conductors if their substance be not of sufficient mass to give it free passage from
one point to another; while it is only with difficulty that we can obtain, by means
of it, the slightest chemical decomposition. In the language of the theory of electrical fluids, the electricity is developed in exceedingly small quantities by friction
e.r change of aggregation, and hence can perform but feebly such offices as chemical decomposition, which depend on the quantity that passes in a given time; but
this small quantity is gifted with immense tension; the few molecules which become polarized are so to an intense degree, and the attractive and repulsive forces
which they exert are then sufficient to cause the, greatest mechanical effects
SECTION II.
OF DYNAMICAL ELECTRICITY.
The sources from which electricity is derived in a continually
circulating form, so that its properties shall result from its uninterrupted motion, must necessarily consist in arrangements from which
all insulating substances are to be carefully excluded. In statical
electricity, the connexion, by a conducting medium, of the opposite
extremities of an inductively excited body, caused all electrical indications instantly to disappear, while that kind of connexion is absolutely necessary to the continuous flowing of the electricity which
constitutes its dynamical condition; and when the conducting circle
is broken by the intervention of the smallest portion of insulating
matter, either all electrical excitation ceases, or at most a feeble
trace of it remains, with the properties which characterize its statical condition.
1st. Electricity  thus circulating through  conductors is found
naturally existing in those substances which thereby possess magnetic properties.  There is every reason to believe that the native
loadstone, as well as all our artificial steel and iron magnets, are
closed circles of dynamical electricity, set in motion by forces
which depend on the chemical and mechanical constitution of these
bodies.  2d. When any closed conducting circuit is at the same
time unequal in mechanical constitution and in temperature, so that
the current may pass more easily through one point than another,
such a current is generated, flowing from the portion where the obstacle is greatest to that part where it is least.  3d. TWhen substances capable of mutual chemical combination or decomposition
act on one another, there is a current of electricity produced. In
the case of simple union or double decomposition, the circle is internally closed, like that of a steel magnet; but where there is simple decomposition  or replacement, the current may be directed
through any kind of circuit; and thus constituting the most important branch of dynamical electricity, is called Galvanism or Voltaism,
from the names of its most illustrious investigators.
4th. By means of organized structures, of which it is only lately,
by the researches of Matteucci, that the true nature and functions
have become known, certain fishes possess the power of transmnitting a current of electricity across even imperfect conductors, and
employ, instinctively, the effect of this current upon the living
frame of smaller animals in order to obtain them for food. The




GALVANIC ELECTRICITY.                        127
identity of the electricity from this animal origin, wvith the fluid of
the other dynamic sources, has been completely proved, particular
ly by Faraday; and as the question of the anatomical structure of
the electric organ, and of the peculiar part of the brain from which
the electric nerves arise, interests the physiologist rather than the
chemist, I shall merely state that the current so obtained possesses
all the properties that will be described as characterizing galvanic
electricity of very high tension, and allude nc farther to it.
To the chemist, the electricity of the Galvanic or Voltaic battery
is the most interesting of all the forms which this agent may assume, from the intimate relation which exists between it and the
force by which the elements of bodies are bound together in chemical combination.  rTo it, therefore, I shall especially direct attention, and consider the remaining sources only so far as the electricity which they yield may differ from it.  I shall endeavour, also,
to consider it only as characterizing bodies by their properties of
exciting the current, or of' conducting it when excited, deferring
the imlportant topic of the action of the current upon compound
bodies until the nature of chemical afnities has been described.
Galvanic Electricity.-The manner in which this form of excitation occurs  may be very simply shown.  If a slip of perfectly pure
zinc be partly immersed in a cup of dilute muriatic acid,
this last remains totally without action on it, and there
is no appearance of electrical disturbance; but if a slip   C
of copper be introduced, which touches the zinc at C,
out of the liquid, active decomposition of the muriatic
acid begins, the chlorine combining with, and dissolving
the metallic zinc, and the hydrogen making its appearance under the
form of' minute bubbles on the surface of the copper.  At the'samne
moment a reinarkable state of electrical excitation is produced, in
which the zinc resembles a body to which negative electricity, in a
state of exceedingly low tension, is uninterruptedly supplied, while
an equal quantity of the positive fluid flows along the copper, and
these, uniting at the point of contact, produce the effects which are
spoken of as those of' the electric current, the passage of which may
be rendered evident in a great variety of wAays.
The precise manner in which the electrical excitement is here
produced, may be explained sufficiently well without involving rany
consideration of the theory of chemical decomposition, which at
the present moment would require a knowledge of principles that
ehave not been as yet described.  We may suppose, simply, that the
chemical relations of the zinc and muriatic acid are such, that when
placed in contact they mutually indu:ce on each other a development
of elect'ricity: that part of the zinc which is immersed becomning  A-,
and that out of thle acid -, while the molecules of the acid near tlie
zinc become  -, and the general mass of the fluid obtains - excitationl; the q- electricity of the zinc being, however, balanced between
the fui'ds of its own mass and of the acid, and the -  fluid of the
acid being in equilibrium between the +- fluids of'the zinc and or
its own particles, it results that this condition of induced excitation
may remain for any length of time without increasing  or diminlishing
in intensity, the apparptus being in the condition of a very feebly
charged Leyden jar: and on applying the slip of copper by which




128           SIIPLE GALVANIC  CIRCLES.
the excited surfaces, the zinc and acid, are placed in communication,
the negative electricity of the zinc unites with the positive of the
copper, whether by direct translation or by inductive action, and the
positive electricity of the liquid unites with the negative of the copp.:r to produce neutralization; at the same time t the a- of the zinc
and the - of the acid combine. As, on the theory of Franklin, the.<,~.~.   single electric fluid is supposed to pass from  the
ZiNC       body which is positively to the body which is neg
atively excited, it is usual to imagine this exchannge
of electricities to take place by a current, which in'~'1 /* this case, as shown by the arrows in the figure, is
from the copper to the zinc at the superior junction,
but from the zinc to the copper in the acid underneath. At every moment, according as the neutral
Aj 4  \ization of the electricities is effected, the system is
competent to generate new quantities, and hence the
analogy of the weakly-charged Leyden jar, noticed above, does not
completely hold; for, to be accurate, it vwould require the jar to possess a power of charging itself as rapidly as it could be discharged
The passage of the current is accompanied by the solution of the
zinc and the liberation of the hydrogen.  This hydrogen accompa
nies the positively electrified molecules of the acid across the fluid,
and is discharged under the form  of gas upon the surface of the
copper plate.
The essential elements of an arrangement by which a current of
electricity may be produced are, therefore, first, two bodies, one
simple and one compound, which act chemically upon one another
in such a way as that the simple element shall be substituted for a
constituent of the other, which shall be expelled; and, second, a
conducting substance, which is indifferent in a chemical point of
view, and only furnishes a route for the fluids of the
tZi   4 /e-  actual elements to recombine continually with each
other. In the example given just now, this conductor was a slip of copper; but it may be of any form, o~
almost any substance; thus, as in the figure, a -wire
may be soldered to the end of each slip, and on bringing these wires into contact at X, the current passes
precisely as if the contact of Z with C had been direct.
Such an arrangement is termed a sinmple circle.
It is not even necessary that the conductor should be solid or metallic; it is, indeed, only for convenience that the ordinary conducting plates and wires are metallic.  Thus, in the figure,
A Z \W, a plate of zinc is in contact on the one side'with
muriatic acid, A, and on the other with water, W, to
which a better conducting power has been given by disA    —.... solving in it a little common salt. The current is then established, being from the conductor to the zinc, and from
the zinc to the acid, precisely as in the former instances.
The passage of the current under these various circumstances
may be shown, and also that, for its origin and transfer, metallic
communication between the plates Z and C is not necessary, by
a very simple experiment. If the slip of zinc be bent, as in B, and




GALVANIC  AND  CHE M ICAL  ACTION.                       129
a bit of paper moistened with iodide of potassium be laid
upon it, and the wire from A be then brought to touch the
upper surface of the moistened paper, the current passes in \i
the direction of the arrow, and iodine is evolved at the.
point of contact of the wire.  If the surface of the paper i %       B
next the zinc plate, B, be examined, it will be found to be  |
alkaline, from free potash.  Thus the chemical action of  K
the current, which will hereafter assume so important a
position, may here be simply used as a test of its having  I!
passed.
The direction of the current depends upon the nature of the chemical action which is produced at the period of its passace, and on
this principle is founded one of the most cogent and reasonable arguments in favour of the idea that the current is produced by the
chemical decomposition, and not by the contact of thle metals, as
has been maintained.  Thus, if a slip of iron and a plate of copper
be immersed in muriatic acid, the action is altogether on the iron,
and the current passes from the copper to the iron at the po{int of
contact.  But if the metals be immersed in a strong solution of ammonia, which acts upon the copper, but not upon the iron, the current is produced in the reverse direction.  If persulphuret of lime,
dissolved in water, be used as the exciting fluid with iron and copper, the current is from  the copper to the iron through the fluid;
but on using zinc and copper with the same fluid, the direction of
the current is reversed; in the first case the copper, and in the last
the zinc, is acted on: with acid solutions the copper would have escaped action, and the current would be in both cases from  the iron
or zinc to it, through the liquid.
It thus appears that the relation between the current and the
chemical action is of the most intimate nature possible; the one, as
Faraday and others have decisively shown, cannot exist in such arrangements without the other, and the nature and tendencies of one
determine the power and the direction of the other; for the quantity
of electricity which is set in motion in such an arrangement depends
strictly on the amount of chemical decomposition which occurs in
the liquid element, and is simply proportional to it.
It is usual to arrange the various bodies in a list with relation to a fluid, in which,
if they be immersed and brought to touch outside, a current is generated from that
of the two metals which stands highest in the scale to that which is below; the
current through the fluid is, of course, in the opposite direction. The metals arrange themselves, however, very differently with different fluids, according to their
liability to chemical action from them, as may be seen in the ibllowing table ~
Dilute Nitric  Strong Nitric    Muriatic  Acid.    SAuibu  of  Yeliow Hidr:m;u-l
Acid.    Acid.            Caustic P:.sIL  pht.ret of totassltll.
Platinum. Platinum. Platinum. Platinum.  Platinum.
Silver.   Nickel.   Antimony. Silver.    Iron.
Copper.  Silver.   Silver.   Nickel.    Nickel.
Antimony. Antimony. Nickel.   Copper.    Bismuth.
Bismuth. Copper.  Bismuth. Iron.        Antimony.
Nickel.   Bismuth. Copper.  Bismuth.   Lead.
Iron.    Iron.    Iron.      Lead.      Silver.
Tin.     Tin.      Lead.    Antimony. Tin.
Lead.    Lead.    Tin.       Cadmium. Cadmium.
Cadmium. Zinc.     Cadmium. Tin.        Copper.
Zinc.    Cadmium. Zinc.      Zinc.      Zinc.
R




130    PRINCIPLE  OF  ELECTROTYPE  COPYING.
At the head of each column is placed the name of the exciting fluid; on taking
any two of the metals of the list beneath, and making them the solid elements of
the circle, the current is, at the point of contact, from the upper to the lower, and
is more powerful in proportion as the metals are farther separated from one another
in the list; thus, with dilute nitric acid and with solution of' caustic potash, the
most powerful current is, after platinum, by silver and zinc; with muriatic acid by
antimony and zinc, and with persulphuret of potassium with iron and zinc.
If the metals in contact with the exciting liquid be such as that one is totally
without chemical action on it, it serves only as a means of mechanically transmitting the inductive force, and the current is simply due and is proportional to the
electricity evolved by the action of the acid on the other. - But if both metals be
such that either would act upon the acid if by itself, and thus produce excitation,
as when zinc and copper are placed in dilute nitric acid, then the molecules of acid
are submitted to two polarizing forces in opposite directions, which, if equal, would
exactly neutralize; but in practice they are not equal, and a current is produced
proportional to their difference. Hence, the more nearly the metals resemble each
other in their chemical relations to a given liquid, the weaker is the current they
produce; but, though acting similarly to one liquid, they may be oppositely related
to another, with which, therefore, they become a source of powerful excitation.
Thus copper and zinc, being both acted on violently by sulphuret of potassium,
generatebut a feeble current, while with dilute acids, which act very differently
on each, the current is very powerful; and thus platinum, which is inattackable by
almost all liquids, forms the best possible element in every instance.
The metal which is used as the conducting medium conducts by having its natural polarity inverted; and hence, in place of a disposition to combine with the oxygen or chlorine of the liquid, it would, if already combined, abandon it; hence this
metal remnains clean and bright. On this principle was founded the mode of protecting the copper sheathing of ships, by attaching small portions of iron of about.
of the surface; the chlorine of the salt in the sea-water being thus transferred to
the iron, and the copper,- in place of becoming covered with the green rust of
oxychloride of copper, remaining completely bright. This process succeeded in
practice somewhat too well; for the negative elements of the sea-water being
transferred to the iron, the- positive bases present, lime and magnesia, were deposited upon the copper, and thus affording points of adhesion for marine plants and
shell-fish, caused the bottoms of the vessels to become so foul as materially to injure their sailing powers. The process at present so extensively employed, of fixing a layer of zinc upon iron surfaces, acts in protecting them from rust in the
same manner.
This transfer of the elements of the exciting liquids has become recently, inr the
hands of Spencer, the basis of one of the most beautiful and important of the applications of science to the arts. If pne of the exciting liquids be a solution of sulphate of copper, as in Daniell's battery (page 136), the metallic copper which separates is deposited upon the surface of the plate to which the current passes in the
liquid, and there is formed a layer of metal, which may be obtained, by slow and
long-continued action, as dense and homogeneous as the best hammered copper.
Any prominences or depressions, even a scratch of a pin, drawn on the plate on
which the deposite forms,; are accurately represented on its internal surface: and it
is only necessary to use as the negative metallic element a medal' in relievo or intaglio, to reproduce, with an accuracy equalling the powers of the most finished
hand or machine, the finest works. of art. This principle has been shown. by Mr.
Spencer to be applicable to the copying of all varieties of designs, and may be looked
upon as the most important means of facilitating the possession of works of art,
and thus elevating public taste, that has been made since the discovery of the method
of transferring engravings to any number of steel plates.
The electricity which is evolved by the chemical action of such
simple circles is remarkably different in its characters from that
form which has been described as its statical condition. Although
present in much greater quantity than can be developed by friction
with the most powerful machines, yet, from  its state of continued
recombination, it cannot acquire intensity; it hence can pass only
through good conductors; pure water, which, from the facility with
which it allows of the passage of machine electricity, proves the




COIMIPOUND  VOLTAIC  CIRCLES.                  131,great source of failure and uncertainty in our experiments, intercepts almost completely the current from a simple circle, and the
wires which are used to effect communication may be touched with
the fingers without any tendency to lateral shock becoming evi
dent; and yet the disproportion in quantity between the fluid, which
bursts through the strongest insulating bonds of our apparatus, or
breaks from the clouds, devastating forests, as the lightning, and
that which passes silently across the wires of the voltaic circle, is
such as almost to surpass belief. By actual experiment,'the immersion of two wires, one of platina and the other of zinc, each
0'06 inch in thickness, to a depth of five eighths of an inch, in dilute sulphuric acid for three seconds, gave as much electricity as
could be generated by thirty turns of the most powerful machine
of the Royal Institution. indeed, Faraday has shown. that, in the
current which passes during the decomposition of a grain of water,
there is contained more electricity than in the brightest flash of
lightning.
If the metallic elements of a simple circle be connected, not directly. by metallic contact or by a wire, but by means of one or more
other similar simple circles, interposed in the course of the current of
its electricity, it is not at all interfered with, but the quantity of electricity which circulates is precisely equal to what is generated by
the chemical action which takes place in each cell. For, considering the circle of four cells, represented in the figure, consisting of
c  zn                 + b
_d       -
copper and zinc plates, acted upol by muriatic acid, the copper of
each cell discharges its positive electricity upon the negative fluid
of the zinc in the adjoining cell, and hence there is neutralization
of effect at the points a, b, and c, and it is only the amount of electricity liberated upon the copper and zinc plates in the terminal
cells that passes along the wires, and, recombining at d, produces
ihe phenomenon of the current; but this is the same quantity as
should be evolved by any one of these simple cells by itself, and
hence the remarkable result, which has' been fully demonstrated by
experiment,' that no matter how we may increase the number of the
elements of a galvanic circle, the quantity of electricity passing in
the current is equal only to that evolved by a single cell. If:the
chemical action be nit of the same energy in all the cells, there
passes little more electricity than what is generated where the decomposition is least active; for, as the excess would have to penetrate through the liquid conductor in all the cells, the obstacle afforded to its progress is so great that it is almost totally absorbed.
Although the increase in number of the elements of the galvanic




132 REL.\ TION  OF  INTENSITY  AND  QUANTITY.
circuit is intfftlicient towards augmenting the quantity of electricity
which passes, yet it changes the character of the current in a very
remarkable degree, and confers upon the fluid an intensity which,
in a simple circle no matter of what magnitude, it never can possess.
It has been seen, that by the state of mutual excitation into which the
zinc and acid are thrown before the circuit is completed, the intensity of the evolved fluids is limited  to that wAhich will
Z    - not suffice to enable the excited particles of acid to discharge themselves upon the oppositely excited particles
of zinc; for if this discharge occurred, all should be
brought back to the neutral condition.  Now, if there be
interposed a second cell, containing an equal quantity of
the same liquid as the first, its particles must be brought into an
equally excited state before discharge can occur; and as the electricity has then to pass through a bad conductor of double the
length, it will require much greater intensity to penetrate it. The
process, in virtue of which, therefore, the electric equilibrium  is in
the first instance disturbed, continues, even before contact is made,
until the intensity accumulated is sufficient to propel the current
across the interposed retarding liquid, and is hence proportional
to the number of cells, or, as it is usually stated, to the number of
pairs of plates.  The peculiar character of intensity may be supposed to arise, also, from the electricity generated by the outside
plates obtaining additional velocity, in passing across the intermediate cells, in each of which it meets an equal quantity of fluid moving
in the same direction, and whose motion it absorbs, restoring them
to rest, and'being thereby hurried itself onward in proportion.
The intensity of the electricity which is thus excited is very slight, even where
the number of combinations is considerable; thus, it requires a series of at least
200 pairs of plates, four inches Square, immersed in dilute sulphluic  acid, to cause a
sensible divergence of the gold leaves of the most delicate electroscope. It is only
where the arrangement involves some thousands of couples that electricity is
evolved of sufficient tension to produce a spark across a non-conductor, such as that
given by the electrical machine, or to cause any of those attractive and repulsive
motions by which the feeblest form of statical electricity is recognised; to obtain
these effects also, the circuit must be broken, for even with the most powerful combinations the current of electricity is without any action of intensity.  Where. however, by means of a sufficient number of elements, intensity has been given, the
quantity of electricity which accumulates, and the qua.ntity of chemical action fiom
which it has its origin, are exceedingly minute.  This is exemplified in the dry piles
of Zarmboni, the form in which electricity may be considered as connecting its purely
dynamical and properly statical. conditions. The pile of Zamboni contains no apparent liquid element; it consists of disks of gilt paper, and of exceedingly thin zinc
foil, laid alternately over one another, to the number of from five to twenty thousand,
care being taken to turn all the gilt surfaces
-=      the same way. These are enclosed in a glass
tube, and terminated at each end by a brass
cap with a pressure screw.  The paper containing in its pores, when not artificially dried,
a small quantity of water, this gradually acts
upon the zinc, and electricity is evolved, which
from the great obstacle presented to its recom
ii ll    0,ll lbination through the disks internally, and by.  the atmospheric,air outside, attains a degree
of intensity so high that it acts decidedly upon
the electroscope, as shown in the figure. and
is amusingly applied to produce various at-.. —..._ —-___..;.;:._~=.__  tractive and repulsive motions, such as ringing




VOLTA'S  THEORY  OF  CON'TACT.                          133
bells, &c.; for there being a continual source of electricity in the action of the
moisture of the paper on the zinc, these phenomena may continue manifested for
years without diminution.
Such a dry pile, when insulated, shows opposite electrical excitation at the two
extremities, these being, however, of equal force, and hence producing neutrality
when combined. If, therefore, the two ends of a dry pile be connected by a wire,
the electricities which had accumulated recombine, and the pile becomes inert, and
requires a certain time. before it can recover a charge equal to that which it had
lost. When the pile is examined at a distance from its ends, the excitation is found
to be less powerful, until at the centre it is exactly neutral. This arises from the
action at each point being the resultant of the opposing actions of the two extremities, and vanishing at the centre where these last are equal, precisely as there exists a neutral place upon the surface of any body inductively excited by ordinary
electricity. If the pile be held in the hand by one extremity, the electricity of that
end is dissipated, and the other end becomes capable of acting more powerfully
upon the electroscope, from the opposing influence being removed.
No principle has ever been discovered in science more rich in consequences than
this of the increase of tension given to electricity in motion by the connexion of a
number of simple galvanic circles. Hence, deservedly, the instrument so formed
has obtained the name of the Voltaic pile. It has enriched chemistry with a crowd
of important substances discovered by its means, and has led, by its results, to the
suggestion of the most plausible theory of chemical combination that has been as yet
proposed. In physical science it became the origin of all subsequent improvement
in the domain of electricity, for without its agency it is hard to see how the steps
which followed could have been made.
The form  in which the Voltaic pile was first constructed was similar to that of the dry pile noticed above.  The disks were of zinc
and silver or copper. The fluid conductor, which was rendered
more capable of acting on the zinc by the addition to it of some
acid or of common salt, was imbibed in disks of common cloth,
which were interposed between every pair of metallic disks. There
were thus, copper-zinc, acid, copper-zinc, acid, copper-zinc, and so
on to an indefinite extent. It is a peculiarity of this instrument,
which, as it extends to many forms of it even now in use, and affects
our chemical nomenclature remarkably, it is necessary to notice,
that the current in the connecting wires appears to be in a direction
opposite to that described in the battery of cells of page 131; for
the outer copper plate at the one end, and the outer zinc plate at
the other, having no communication with the exciting acid, transmit the current merely as portions of the attached wires, and hence
the direction of the current is in appearance from the zinc to the
copper end, while it is properly the copper from  which the positive
fluid emainates, and it is the negative which arises from  the zinc.
This diversity had its origin in the circumstance that the theory of
the pile maintained by Volta, and even at the present moment supported by some illustrious men, ascribed the origin of the electricity not to the action of the acid upon the zinc, but to the contact
of the zinc with the copper; the point where the metals touched
being supposed to be a continual source of positive electricity to
the copper.  It was even attempted to prove this by soldering together plates of zinc and copper, and testing their electrical condition by the gold-leaf condenser, which was supposed to indicate a
permanent state of excitation, independent of all fluid or chemically
acting media. It has been fully proved, however, that, according
as such contact experiments are made with increased care, the results become less evident in favour of that theory. Such trials tend
to show the evolution of minute traces of statical electricity, where



134  vARIO-US FORMS OF G ALVANIC BATTERIEII.
as the simple galvanic circle is characterized by the great quantity
of electricity-it may yield, and by its total want of statical intensity.
Even, therefore, if it were proved, which it is not, that the mere
conltact of bodies evolved electricity affecting the gold-leaf electroscope, it'would be as far from accounting for the tot.ally different
kind of electrical excitement by which the galvanic battery is created, as it would be from giving a true or satisfactory theory of the
cause of magnetism.
But the pretended excitation by contact, or the electromotor force,
as it was termed by Volta, must be carefully distinguished from the
capability of inductive excitement, which bodies capable of chemical action, as a slip of zinc and muriatic acid, mutually confer upon
each other.
This last arises from the possible substitution of the zinc for the
hydrogen of the acid, which does occur as soon as the interchange
of the electricities allows of the transfer of elements; for on the
first immersion of the zinc, the equilibrium of the chlorine and hydrogen, which had previously been totally engaged with each other,
is interrupted, and that of the particles of the zinc, which had before been all circumstanced alike, is disturbed by some of them being nearer the acting muriatic acid than the others, and thus the induced condition of both arises.  On this positive and necessary
principle, the theory of the simple and compound circles already
described has been given; and although it will require to be again
noticed in describing the phenomena of decomposition which accompany the passage of the current, yet, for the only purpose which
we here require, of studying the manner. in which the current of
electricity of the battery has its rise, the, peculiar and important influence exercised by the chemical reaction among the elements of
which it consists has been sufficiently described.
It is now necessary to notice more in detail the construction of
some of the more usual forms of
/I~    =    the Voltaic or Galvanic battery.
_  The first improvement on the pile
of Volta consisted in placing it
- D   horizontally in a wooden trough,.is-__ _ —-—. ——. -   and replacing by cells containing
dilute: acid the moistened disks of cloth employed by the original
inventor.  It being difficult to cleanse the surfaces of the plates,
which in that form were permanently cemented into the
trough, this was made of delftware divided into cells, and the
plates, being soldered together
by projecting bands at the top,
were hung upon a rod, as in the
figure, so that, when wanted,
they may be immersed with
great rapidity, and withdrawn
as easily from'the liquid when;-__ -,. 11    the battery is not wanted. The:_"'.    power of such troughs is in.




INTE.RFERING  ACTION  OF COMMON  ZINC.  135
creased by one half when the copper slip is doubled over so as to
oppose both surfaces of the zinc. Batteries intended rather for in.
tensity than for quantity, and which consequently consist of a great
number of plates of moderate dimensions, are generally employed
on this last construction: each delftware trough holding ten pairs of
plates, and any number of troughs that may be required being rapidly and easily arranged together. When a current of electricity
of great quantity, but not of intensity, is required, it is usual to employ a few, or even only one pair of plates of considerable size. Thus,
a sheet of copper and a sheet of zinc, each of from 80 to 120 square
feet of surface, being kept separated by ropes of horsehair, have
been rolled up together and immersed into a large tub of acid, forming thus a simple circle, giving a current so feeble in intensity as to
pass with difficulty through a short column of distilled water, and to
be quite insensible to the feeling, but which fused down into globules
the most refractory metals, and gave with charcoal points a light of
brilliancy insupportable to the eye. The copper plate may be very
conveniently made to act as the cell containining the acid: cylindrica_
batteries of moderate size are very frequently so constructed.
I have supposed, in the description of the nature of simple and
compound Voltaic circles, that the zinc employed was completely
pure, in which state, when first immersed in the acid, there is no chemical action, but only the preparatory inductive state produced, the
decomposition of the acid by the zinc commencing only when the
circuit is completed. But such pure zinc is too expensive for ordinary
use, and the commercial zinc contains always traces of impurities,
particularly iron, from which it acquires a power of generating a
multitude of little secondary currents across the fluid, and thus preventing to a great extent the formation of the proper current. For
suppose that there is on the centre of a plate of zinc a little piece of
iron or of copper, this serves to return to the zinc from the acid the(
positive electricity, which had passed away from it precisely as if'
it had been a copper wire, which touched the acid with the one end,"
and the zinc plate with the other. Such a plate is therefore occupied almost solely with its own self-contained currents, and scarcely
assists in generating the electricity which is brought into play in the
battery at large. To this cause must be assigned the property which
ordinary zinc possesses of dissolving readily in an acid, and of evolving hydrogen upon its own surface. It evolves the hydrogen upon
those points of its surface on which foreign metals being deposited,
serve to complete its circuits. This injurious property of ordinary
zinc is remedied by coating the surface of the plate with mercury,
or, as it is termed, amalgamating it. By this means the whole surface of the metal is brought into the same state, and must hence act
in the same manner on the acid. Any secondary current which
might arise could therefore find no means of discharge, and such
zinc is not acted on until the circuit is completed, and then all hydrogen is carried by the excited molecules of acid to the copper
plate, and there evolved as gas.
To amalgamate the zihc plates of a battery, a quantity of mercury
is to be laid in a flat dish, sufficient to cover the bottom; moderately
dilute nitric acid, to which a small quantity of nitrate of mercury




136       FORMS OF  CONSTANT  BATTERIES.
has been added, is to be then poured on the mercury, so deep that
the zinc plate, when floating on the mercury, shall be covered by
the acid. Before immersing the zinc plate, it should be, if not new,
cleaned as well as possible with sand-paper from adhering dirt, and
then it combines with the mercury very rapidly, so as to form a surface which, by rubbing with a little flannel, may be rendered completely uniform.  The zinc should not be too highly mercurialized,
for then it becomes extremely brittle, and requires considerable care
in using it. The power of a battery may often be quadrupled by
this method. A source of great inconvenience in the ordinary batteries arises from the hydrogen acting on the oxide of zinc which
is dissolved, and reducing it to the metallic state, when it is carried,
with the remaining hydrogen, to the copper plate, and deposited upon
it. In this way there is gradually formed a second zinc surface
opposite to the proper zinc plate, and which, tending to transmit a
current in the reversed direction, neutralizes a certain proportion of
the power of the circle, and may even destroy it altogether. Hence
an ordinary battery is most active when first brought into play, and
diminishes very rapidly in power until, after the lapse of some hours,
even though the acid be not saturated, its action ceases.
This disadvantage has been beautifully removed by the principle
of absorbing the hydrogen by means of a solution of sulphate of
copper, which it decomposes, and precipitates upon the surface of
the copper plate a layer of clean, new, metallic copper, in the best
possible condition for supporting the action of the battery. The
simplest arrangement of this kind is that of Mullins; the mechanical construction is most perfect in Daniell's constant battery.  Mul~ lins' battery consists of a delftware trough, D, in; Fe   -.c:X3 which the cylindrical zinc plate B, of nearly the
same diameter, is placed, and inside of which, again,
- is the copper cylinder A, which is close, and acts
D  only by its external surface; round the upper edge
[If?,,f'iP,~  of the copper cylinder C is tied a bladder, into which
fluid may be introduced by means of a row of apertures in the rim to which the bladder is attached.
A solution of sulphate of copper is poured into the
bladder, and its state of concentration is kept up by
heaping some coarsely-pounded crystals on the top of the copper
cylinder:  Into the trough in contact with the
I' I!    zinc is then poured dilute sulphuric acid. When
the action commences, the hydrog-en is transfer.
a |    iii 0  lk,;,! red through the membrane, and., meeting there
the solution of sulphate of copper, is absorbed
I         am!liii in the production of metallic copper.  The cop.
per cylinder never wears nor dirties. The metal
il 1i Iti  is all recovered from the sulphate of copper,
and the only thing necessary  is that the plates
~.'i1: ~ of zinc shall be renewed  from  time to time.
Daniell's battery has the advantage that the cop.
per is outside, and hence i~s capable, with ex.'~'i"i'! posure of the same surface of zinc, of producing' mi7   - a much more powerful current.  The cell con.




CONSTA, NT BATTERIES.                      137
sists of a copper cylinder, a, c, near the top of which is attached
a perforated plate, P, on which, when the cell has been filled with
the solution of sulphate of copper, a quantity of crystals are laid,
to be dissolved according as they are required. A solid zinc rod,
Vn, supported at the top of the copper cylinder by a wooden crosspiece, is contained in a membranous bag, formed of the gullet of an
ox, g, h, and into this is poured the dilute acid, which consists of
one part of oil of vitriol and eight parts of water. Any number of
these cells may be arranged together so as to give a battery, which,
if all the coppers be connected upon the one hand, and all the zinc
rods upon the other, will evolve large quantities of electricity of
low tension; but when the copper and zinc elements are alternately
connected with each other, the tension of the electricity evolved is
much increased, though at the expense of the quantity generated.
The great advantage of such batteries is the perfect uniformity
of their action, by which they deserve fully the name applied by
Daniell to his construction, of the constant battery; with such an
instrument, the conditions of the current may remain for days perfectly unaltered; and thus the laws of action of the current have
been determined, particularly in its chemical relations, with complete success,. and views of the analogies between affinity and electricity, equally novel and important, which will be discussed in another place, have been arrived at by its means.
Latterly, the membranous bags, originally used by Daniell and
others as the diaphragm between the acid solution and that of the
sulphate of copper, have been with great advantage replaced by
porous cells of biscuit-ware, such as is represented in the figure by
g, h.
Some forms of battery have recently been proposed, in which,
under a small compass, very great power is obtained, by, 1st, bringing the plates very near each other; 2d, selecting solid elements,
which differ as much as possible in their chemical relations; and,
3d, using as the exciting fluids those of the most intense action,
and of the highest conducting power. In this way, the most powerful Voltaic combination that has been yet made is that of Mr.
Groves. Plates of zinc and platina are separated by diaphragms of
porous earthenware, the zinc being acted upon by dilute sulphuric
acid mixed with some nitric acid, and the platina being in contact
with tolerably strong nitric acid. The hydrogen evolved by the
zinc is completely absorbed by the nitric acid on which it acts,
forming nitrous acid which remains dissolved; and the metals, being
those most opposite in their electrical relations, give the most powerful current possible.
The conducting powers of various bodies for this form of electricity has been determined with great care by Pouillet, whose results
are, that the relative conducting powers of the various metals are
expressed by the following numbers:
Palladium... 5791      Brass from....  900
Silver           5152             to....  200
Gold..   3975        Cast steel from..  800
Copper.... 3838             to....  500
Platina...  855       Iron.....  00
Bismuth.         8384      Mercury'.. o.    100
S




138       RELATIVE CONDUCTING POWERS.
He ascertained, also, the relative conducting powers of the saline
solutions usually contained in the cells of the Galvanic battery;
and it appears that the conducting power of platina is two million
and a half times that of a saturated solution of sulphate of copper,
and hence that of copper is sixteen million times'as great. The
conducting power of the saturated solution of the sulphate of copper being taken as 10'000, he found that of
a saturated solution of sulphate of zinc to be. 4'170
distilled water.                           0,025
distilled water with ~   of nitric acid. 0-150
The great retardation which occurs when the current has to pasb
through any considerable length of liquid, will now be easily understood. Pure-water may be considered, with feeble circles, as an
absolute non-conductor; and even with the most powerful combinations that have been yet made, the current is unable to force its
way through the smallest measurable interval of air. It was not
long ago believed that, even with simple circles, a spark indicating
the passage of a current was seen on making contact, and hence
that the electricity had passed before the metals had touched, and,
consequently, that the chemical action should be alone considered
as the source of the electricity. It is, however, now acknowledged,
that no spark can pass until the wires have touched and are again
separated, and the passage of the electricity is then accomplished,
not by the action of the excited molecules of air, as occurs with the
machine, but by the violent inductive polarization of the particles of
the terminal conductors, which are torn off and pass from one pole
to the other.
When the current of electricity is retarded by means of an insufficient conducting medium, the centre of the conductor becomes
hot, and thus the most brilliant effects of heat and light may be produced; even the most refractory metals, as gold and platina, being,
when in thin foil or wire, dissipated actually in smoke. By terminal points of well-burned charcoal, this phenomenon is beautifully
produced, the ignition being totally independent of combustion, for
it takes place in vacuo or in carbonic acid gas; and when the points
are separated from one another to a certain distance, the interval
becomes occupied by a splendid arch of light, formed by the inductively excited particles of charcoal, which, in a state of intense ignition, abandon the positive to attach themselves to the negative
extremity of the conductor.
The action of galvanic electricity upon the animal frame does not
properly fall within the scope of the present work, but in terminating the subject, the mode in which the
first view of this important science was
I/";XlNt        <       obtained may with propriety be noticed.
Galvani was professor of anatomy at Bo\';Filt!- I;/        logna, and, while preparing frogs for
~ilil _~I:,~.!~' csome physiological experiments, he happened to touch, by one extremity of a
metallic wire, the lumbar nerves which
still remained attached to the spine, while




GA LV AN I S M. —T HERMO - E L E CT RIC IT Y.    139
the other extremity of the wire was in contact with the muscles of
the leg; these last were instantly thrown into strong convulsions.
To perform this experiment with success, the legs of the fiog are
to be left attached to the' spine by the crural nerves alone, and then
a copper wire and a zinc wire being either twisted or soldered together at one end, the nerves are to be touched with one wire,
while the other is to be applied to the muscles of the leg.
Galvani erred in the explanation of this remarkable effect; he looked upon the body as being in the state of a charged Leyden jar, of
which the nerves'and muscles were the external and internal coatings, and that, on connecting these by the conducting wire, the electricities recombined, and the passage renewed for the instant the
phenomena of life. Volta pointed out, however, that, in order to
produce full effect, the presence of two metals in the conductor was
required, and he ascribed the origin of the electricity not to the
body, but to the contact of the two metals, and supposed the convulsive motions to be merely the indication of the passage of the
current across the body of the frog. This view has also been since
modified by ascribing the electricity to minute traces of chemical
action on the wires; but it was so fruitful in results, of which the,construction of the Voltaic pile is the most remarkable, that Volta
is, with justice, looked upon as the true originator of this branch of
electricity as a science, although it was Galvani who observed the
first fact belonging to it.
The frog so prepared is a most delicate test of the passage of a
Galvanic current; it is truly a galvanoscope, corresponding to the
gold-leaf electroscope for ordinary electricity;'but it does not measure the quantity or intensity of the electricity which passes. As
yet we have no exact measure of the intensity of Galvanic electricity; but that its quantity may be exactly determined, two of its
properties may be applied: the first consists in determining the
quantity of a given chemical substance, as water, which the current
can decompose in a certain time, for the quantity decomposed is
proportional to the quantity of electricity which passes; the second
consists in observing the degree to which the current is able to deflect the magnetic needle from its natural position of north and
south, for the angle of deflection is connected with the quantity of
electricity in the current by a very simple lawv; we are not yet in a
position to understand fully the theory either of the chemical or
the magnetic galvanometer, and hence I merely indicate, for the
present, their existence and their names.'Thermo-electricity.-If heat be applied to a wire, uniform in texture and thickness, bent into a ring, there is no disturbance of electrical equilibrium; but if any obstacle to the transmission of tha
heat, such as a knot or a coil in the wire, exist, a current will be established, of which the direction will be
from the point of the circuit to which the heat is applied
towards the point where the retarding cause exists. If
in place of merely causing an artificial obstacle on a
uniform wire, two metals, a b, be selected, which differ
in conducting power, and the point at which they touch
one another, c, be kept at a different temperature from
the rest, a current is also produced from the latter point towards




140         THE RMO-ELECTRIC CURRENTS.
the metal which is the worst conductor. The more unlike the metals are in molecular constitution, and the greater the difference between their conducting powers, the more energetic is the current.
The best combinations are therefore of a crystalline and a noncrystalline metal, or of two metals which crystallize in different sys.
tems. Bismuth and antimony, which are the worst conductors of
the metals, are also among the most crystalline; and while bismuth
crystallizes in cubes, the form of antimony is a rhombohedron; these
metals, therefore, combine all the essential qualities for generating
a current when unequally heated, and they are, consequently, the
most powerful sources of thermo-electricity that have been found.
The results obtained with other metals will be understood by writing them down in the following order, any two of them  being
capable of forming a current when their junctions are unequally
heated, the current being from the metal highest to that which is
lowest in the list, and the power of the current being greater in
proportion to the distance between the metals in the following order: bismuth, platinum, lead, tin, copper or silver, zinc, iron, antimony. The molecular texture would appear from this list to have
more influence on-the production of the current than the mere difference of conducting power.
The intensity of the thermo-electric current so excited is exceedingly small; it is only capable of passing through very good conductors, and it requires the combination of a number of exciting
couples to give sufficient tension to enable it to produce a spark, or
to show any signs of chemical influence. It then, however, agrees
in all respects with the electricity of the Galvanic battery when in
an excessively feeble state of tension, and it resembles remarkably
the hydro-electric current, in being able to reproduce at a distance
the circumstances in which it originates; for precisely as a current
passes through a combination of antimony and bismuth when its
junctions are at unequal temperatures, so, when a similar current
from any other source is passed through the metallic couple, a change
of temperature is produced at the place where the two unite; if the
current pass from the bismuth to the antimony, the junction becomes
heated; but if the electricity pass in the opposite direction, the junction is cooled to a remarkable degree, so that, if a little hole be
bored where the metals touch, and a drop of water be laid therein,
it is frozen after a few moments. This result, which was first obtained by Peltier, and has been confirmed by B6ttger, is one of the
most remarkable proofs of connexion between the physical sources
of temperature and electrical equilibrium that has been as yet discovered, and may influence our theories of the nature of heat in no
inconsiderable degree.
The principle of strengthening the thermo-electric current, by
combining together the action of a
number of metallic couples, is due to
Nobili. If we consider a number of
bars of antimony and bismuth, a b,
Ub  bab a ~b acb ab 1\\ ~soldered together alternately at their
ends, so that every alternate soldering
shall be in the same plane, and the
extremities of the terminal bars be




CONSTRUCTION OF    THE THERMOSCOPE.   141
connected by a wire, on applying heat to the alternate solderings,
a current is generated at each, which, being all in the same direction, travel together through the system, and thus increase its energy in proportion to the number of combinations. The important
distinction between this and the combination of elements in the
Voltaic pile is, that in the latter the increase of number affects only
the tension of the current, but leaves the quantity the same as the
single couple; but in the thermo-electric pile, although the intensity
is increased, yet the quantity which passes in the current is augmented also.
It is this principle which has been applied by Nobili to the construction of the thermo-multiplier or thermo-electroscope used by
Melloni and Forbes in their researches on radiant heat, of which a
sketch has been given in the last chapter. The thermoscope consists of fifty small bars of bismuth and antimony, placed parallel beside one another, and forming a single prismatic bundle, F, F', about
1 inch long and,- inch square in section. The two terminal faces
are blackened. The bars of bismuth, which are arranged alternately
with those of antimony, are soldered at their extremities, and separated all through their length by an insulating substance. To the
A
first and last bars are attached copper wires, which terminate in the
pins C C, of the same metal, passing across a piece of ivory fixed
on the ring A A. The space between the interior of this ring and
the elements of the pile is filled by insulating material. The free extremities of the two wires are put in communication with the terminal wires of a magnetic galvanometer, the needle of which indicates by its motions when the temperature of the anterior surface
of the thermo-electric pile is raised or lowered, in comparison to that
of the posterior surface. (See P in figure, page 99.)
By means of a jointed support, the axis of the pile may be. turned
in any direction that may be wished; and to protect its surface from
lateral radiation, the metallic tubes B. B, brilliant externally and black
ened on the inside, are attached to the extremities of the ring A A.
If by changing through one degree the temperature of a single
soldering, a current of a certain power be obtained, there should be
with fifty solderings a current fifty times as strong, or an equal
current when the temperature of the solderings varies through one
fiftieth of a degree. It has been ascertained that instruments of
this kind may be made to indicate a variation of temperature of3 0la o
of a degree on Fahrenheit's scale.
The electricity which is thus evolved by change of temperature
in conducting bodies, although so feeble in quantity and intensity
as to be utterly devoid of those brilliant qualities which attach much
popularity to the phenomena of Galvanism and of machine electricity, has thus been found the means of assigning the true laws of
some of the most interesting and important branches of the physical
sciences; and it will be hereafter seen that thermo-electric currents,




142  E IATION S OF THERMO- E L ECT R IC CURRENTS.
excited in the superficial stratum  of the globe by the inequality of
temperature which arises from  the action of the sun, may generate
not only the magnetic properties on which are founded the commercial intercourse of civilized nations, but, by influencing the affinitary powers of the elementary constituents of our planet, may have
been the agent in silently, but effectively, regulating the constitution
of inorganic nature.
[From the extensive employment of thermo-electric currents as measures of temperature, it is desirable to understand their lhabitudes. Dr. Draper has shown that
equal quantities of heat do not set in motion equal quantities of electricity; with
certain combinations of metals the proportion increases, and with others decreases.
For this reason, temperatures estimated in this way must always undergo correction, as the following table shows:
Water bolls. Mlercury boils.
Mercurial thermometer.   212     662
I (Copper and iron...   202       257
I Silver and palladium.   235     880, Iron and palladium..   211      539
Hi   Platina and copper..   244    1030
Iron and silver...   170       279
k  itr.on and platina...   212      829
We therefore infer, that in these six systems of metals, the developments of electIi.
city do not increase proportionally with the temperatures, but in some with greater
rapidity, and in others with less.
The tension of these currents undergoes a slight increase with increase of temperature: a phenomenon due to the increased resistance to conduction of metals
when their temperature rises. In hydro-electric pairs, the quantity of electricity
evolved depends on the surface of the plates; but in thermo-electric arrangements,
the quantity of electricity is independent of the amount of heated surface, a mere
point being just as efficacious as an indefinitely extended surface. And in a compound series of many pairs, the quantity of electricity evolved is directly proportional
to the number of pairs.
Thermo-electric currents traverse metallic masses only on account of differences
df temperature existing at different points. When a current flowing from the poles
of a battery is made to traverse a wide metallic sheet, the whole of it does not
pass in a straight line from one pole to
1erf i                      f2   the other, but diffuses itself through the
metal, diverging from one pole and converging to the other. For these reasons,
a   -  C   -b           L_          there are certain forms of construction
which give thermo-electric arrangements
d                           peculiar advantages. For example, the sur3                   faces united by soldering must not be too
massive. Let a, fig. 1, be a bar of antimony, and b a bar of bismuth; let them be
a       c                    soldered together along the line c d, and at
the point d let the temperature be raised,
a current is immediately excited; but this
does not pass round the bars a b, inasmuch as it finds a shorter and readier channel through the metals between c and d, circulating, therefore, as indicated by the
arrows. Nor will the whole current pass round the bars until the temperature of
the soldered surface has become uniform.
An obvious improvement on such a combination is shown in fig. 2, which consists of the former arrangement cut out along the dotted lines; here the whole current, as soon as it exists, is forced to pass along the bars. And because the mass
of metal has been diminished along the line of junction, such a pair will change its
temperature very quickly.
One of the very best forms for a thermo-electric couple is given in fig. 3, where a
is a semi-cylindrical bar of antimony, b one of bismuth, united together by the opposite corners of a lozenge-shaped piece of copper, c. From its exposing so much
surface, the copper becomes hot and cold with the greatest promptitude; and from
its good conducting power, it may be made very thin without injury to the current.]




AM AGNEA TIC PRROPERTIES OF IRON AND STEEL. 143
Jaggnetic Electricity. The properties which are now known as
magnetic were first recognised in a peculiar ore of iron, found in
the vicinity of the town Magnesia, in Asia Minor, from which the
names of the substance and of the science have been derived. The
native magnetic ore or loadstone consists of iron and oxygen. This
mineral, although quite inert with regard to all other bodies, attracts
iron and steel with great power; and the pieces of iron and steel,
while in contact with the loadstone, participate in its powers, and
are capable of attracting other pieces to themselves. Iron and steel,
though both attracted by the magnet, differ remarkably in the fact
that iron, although magnetic while in contact with the loadstone,
loses all its properties when it is removed; while steel, which is at
first attracted with inferior power, when it has become magnetic by
contact with that mineral, retains that condition after separation,
and thus becomes a permanent artificial magnet. A steel magnet
thus formed may in its turn be used in place of a loadstone to form,
others; and almost all the magnets we employ in experiments have
thus obtained their power, as native loadstone is not found in sufficient quantity, or sufficiently intense in action, for our purposes.
The steel bars which are magnetized are generally straight, but often
also bent in the centre, so that the halves are nearly parallel, and
are then called horseshoe magnets.
When a magnetic bar is dusted over with iron filings, it will be
found that the filings attach themselves to -      A.
the extremities of the bar, and scarcely at              p
all to the centre; the magnetic power is.:...
thus seen to exist only near the ends of the bar..' Each filing being
itself for the time a nmagnet, attracts others, so that they form strings,
which arrange themselves,' according to definite laws, in an order
which is termed the magnetic curves, and' from the disposition qf
these curves it is evident that the action of the magnet emanates'from a single point, P, near each, 
extremity; these points being the L':,
centres of action of the magnet,:
are termed its poles. Thus, in the
figure, the bar being a magnet, the
points P and P are the poles, nd i;'
the directions of attractive force.
are indicated by the diverg in:..
lines, rihich, uniting on the inner
side, form the magnetic curves.''::L-:;":-:..... " —.:.;i
The utility of the magnet in navigation is well known; it arises
firom the poles of the magnet being attracted by the earth in such a
way, that, lwhen free to move, the mnagnet rests in a direction nearly
north and south; the pole- of the magnet which is turned to the
north is termed the north pole, the otherithe south pole. If two
magnets be brought into the neighbourhood of one another, they do
not attract indifferently, as either would attract a mass of iron'; but
the north pole of one magnet attracts the south pole of the other,
and is attracted by it, while the north poles of the two, or the south
poles, if brought near each other, repel as powerfully. In magnets,
therefore, poles of the same name repel, and poles of' opposite names




144      INTIMATE  STRUCTURE  OF  MAGNETS.
attract, a condition precisely similar to that which'holds between the
electricities evolved by friction. In magnetism, also, the attractions
and repulsions follow the law of the inverse square of the distance,
and thus complete the superficial analogy which led astray for so
many years the investigators of this branch of science.
The action of the earth upon magnets at its surface can only be explained by
supposing the earth itself to possess magnetic properties. The northern portions
of the earth attract the north pole of a magnet, and must therefore possess southern polarity; the southern portions of the earth attracting the south pole of the
magnet, must possess northern polarity. The action of the earth cannot be explained, however, by supposing it to be a simple magnet with a pole at' each extremity. It possesses.at least two centres of force or poles in the north, one in
Siberia and one in North America, while the exact distribution of the centres of
magnetic force in the southern hemisphere has not been yet made out. These cen
tres themselves are, however, not fixed; the needle is continually changing in direction; at present it points to 24-1~ west of north; but in the year 1664 it pointed
to the north, and it had previously pointed in an easterly direction, towards which
it is now returning.
Prior to the discovery, by Ampere, of the true nature of magnetic
phenomena, a theory similar for the most part to thit of the two
electrical fluids was maintained;, two magnetisms were supposed to
exist, the particles of the same fluid repelling each other, but the
particles of one fluid attracting those of the other.  The assumption
of magnetic properties by a piece of iron or steel in contact with a
magnet became, therefore, a phenomenon of induction similar to
that described under the head of statical electricity, the constitution
of iron being such that the fluids recombined on the disturbing cause
being removed; the constitution of steel, on the contrary, preventing their reunion.  There existed, however, one great difference
between a' magnetic bar and a body excited by induction with maA       C       B   chine electricity.  If the bar A, C, 13, excited
Q     i _i_     I    by induction, and of which the portion A is
Ax       ii      /\   positive, and B negative, the middle C being
neutral, be cut in two at C, the portions A
~:~     m. ~        and B retain their peculiar states, one positive and the other negative.  But if the magnetic bar A, C, B be broken across at the::i.:    a         -'.: neutral portion C', then each half becomes
a perfect magnet of half the strength of the...":    entire; the points C' and C", which had...,.....:...:.   been neutral, acquire magnetic power; and
if these portions be again brokren, ezch frag~i'!      5       ment is a perfect magnet.  Mag'netism belongs, in this way, to the inmost particles of the body, and in the
general mass each magnetic molecule is still active and independent; a magnet resembles, therefore, an exceedingly bad conductor,
which has been inductively excited by common electricity, and the
particles of which retain for an indefinite length of time their state
of polar excitation.
In order to understand the real nature of magnetic action, we
must free ourselves, however, from all these analogies to machine
electricity, no matter how well grounded they may appear to be
when superficially examined.'The electricity of the magnet is
constantly circulating, and it possesses so little tension that it




,i[A  NETIC QUALITIES OF GALVANIC  CURRENT. 145
never leaves the magnetic element, or molecule of iron or steel, in
which it has its origin; in fact, every current of electricity possesses magnetic properties, and simulates the action of a magnet situated transversely to it. Thus, if a needle be held transversely on a
wire carrying an electric current, it becomes magnetic precisely as
if it had been laid parallel to a magnet; and by bending the wire
round so as to form a coil, the magnetism  which it confers being
increaued in proportion to the number of turns, may be rendered so
intense as to surpass that of the most           rig. i.
powerful steel magnets that are made.. —: ___  L
In fig, 1 a small coil is represented, by   7   
which magnetism is conferred upon the t                   -/-:
Fig. 2.    bar of steel inside. And   -//
in fig. 2, a large horseshoe of soft iron, by being covered by a helix of many
hundred turns, may become able to raise a weight of
some hundreds of pounds by the magnetism  it acquires.
X  The coil of wire carrying the current may be
shown, also, to possess magnetic properties by its
attractive and repulsive action on a magrnet. A —coil
as in fig. 3, suspended so as    Fig. 3.
to be able to move freely, is
attracted and repelled by the
poles of a magnet precisely
Fig.  4.
as if it also had a magnetic
pole at each, end. A flat coil, as in fig. 4,
is also found to be magnetic, the pole's being indefinitely near each other at the centre of the coil. A beautiful form of the exFig. 5.      periment consists
in  a  long  wire,         ('{
which is made into a close coil, and connected at the ends with a pair of little plates of
zinc and copper, as in fig. 5. On placing this
system, buoyed by a piece of cork, in a dish
of acidulated water, it settles itself at right
-=________  I  -   angles to the direction of the magnetic needle, and behaves in all respects like a mag_ _" lj~~m _ = net situated'in the centre of the coil, and
___ __ 2 gperpendicular to its plane.
It is now necessary to examine into the.... —- ---- =  relation which the' direction of the current
bears to the poles of the magnets which it forms, or which might
represent its action. If A B be a wire in which a current
is descending, as fibarked by the arrow, and a needle, N S,   WA
is placed transverse to it, the right-hand end of the needle
becomes the north, andsleft-hand end of the nee- S   N
dle the south pole; if the direction of the current   B
N be reversed, the north pole is formed at the left. In a
I:    circular current, the position of the pole may be, consequently, easily seen; the current A B, which descends in front
T




146 M AGNETIC ACTION OF A GALVANIC CURRENT.
of, and ascends behind the needle, produces in the bar, N S, a
northern polarity to the right, and a southern to the left; the action of magnetic currents upon each other supplies the explanation of these phenomena. If two wires carrying Galvanic currents
be brought near each other, there is attraction or repulsion, according to the direction of the currents; if the two currents be in the
same direction, the wires attract; if in opposite directions, the wires
the figure: the upper wires being arrows which. carry
NS (  currents in the same direction, they act on each other,
as should a pair of magnets placed transverse to their
direction; the ends of the magnets which are juxtaposed
have opposite polarities, and attract; while in the lower
arrows, where the currents are in opposite directions,, the effect is the same as would result from the magnets
of which the contiguous poles are of the same name, and hence repulsion.
A wire carrying an electric current being thus a magnet, it acts
upon permanent magnets, attracting or repelling, according to its
position, and generally, from the combination of the two forces,
generating very complex and singular motions. These actions
have been so minutely and so extensively studied as to constitute
a distinct branch of this department, termed electro-magnetism; but
being unimportant in detail except in physical relations, I shall
only notice the experiments by which (Ersted first created this
branch of science, and which have ultimately led to one of the best
u:easures of electricity, the multiplying galvanometer.
If a Galvanic current be passed over a magnet in the direction of
the arrow in the figure. and the
- -?  > needle be movable on its centre,
it endeavours to assume a position
such as will bring it parallel, and
with opposite poles presented to
the magnet which the wire represents; and hence, in the figure, the...          motion would be to bring the south
pole above the plane of the paper, and to depress the north pole
below it, until the needle'had assumed a position perpendicular to
the conducting wire. if the current had been in the opposite direction, the action would have been reversed, and the north pole
would have been turned up from the paper; but if the current be
reversed at the same time that it is brought under the needle, as in
the figure, it causes a deflection similar to that of the superior portion, and hence the angle through which the needle moves is much
increased.. If the needle were affected only by the current passing
over or under it, its ultimate position would be, In all cases, at right
angles to the current; but as the magnetic action of the earth tends
constantly to bring it back to its direction of north and south, the
position which it ultimately assumes is the resultant of the two
forces.
The deflection of the needle being thus an indication of the passage of an electric current through the wire, it is desirable in prac




ASTATIC.COlMBINATIONS OF MAGNETS.   147
tice to give the power of the current as much effect as possible,
and at the same time to diminish as much as can be done the action
of the terrestrial magnetism.  The first is effected easily by increasing to the desired degree the number of turns which the wire makes
round the needle; for the total eftect, as will easily be understood
from the description of the figure above, is proportional to the number of coils; but the diminution of the effect of the earth upon the
needle requires some more care. If the needle be made but feebly
magnetic, the power of the current to turn it diminishes just as
much as the power of the earth to prevent its turning, and there is
hence nothing gained; but the object is effected by using a combination of two, three, or four powerful needles, so arranged that
with regard to the earth they are made to represent one very feeble
needle. Thus, in the figure, the three magnets N and S, being
suspended with their opposite poles next one  
another, act on each other so powerfully that  S 
the remote and weaker opposing action of the N
earth becomes almost insensible. A current
passing in the direction of the arrows, C, E,  S
D, will tend to depress the north poles of the
upper and lower, and the south pole of the middle needle below the
plane of the paper; and when it passes under the middle needle,
its action upon it will be the same, since its direction is reversed.
The amount of deflection of such a system of needles will still be
regulated by residual terrestrial influence; but as this may be rendered as small as may be wished, the delicacy of the apparatus may
be increased without limit. It is not desirable that the system of
needles should be completely astatic, that is, indifferent to the earth,
for then the degree of deflection by a given current would be affected by trivial and accidental causes; but by leaving a small residue of terrestrial magnetic eftbet, the current acts against this, and
thus produces a deflection subject to an assignable law, by which
the strength of the current may be determined. Within a certain
limit, about 300, the angle of deflection is proportional to the quantity of electricity flowing along the wire, but beyond that it follows
a more complicated law, which, as involving mathematical relations,
I shall not admit here. To obtain a greater degree of delicacy and
uniformity of action, the system of needles is in all good instruments
hung by a thread of glass or of silk, like the beam of Coulomb's
balance (page page 13). The deflecting force then acts against the force
of torsion, and the resistance to be overcome is reduced to its sim
plest possible conditions.
The galvanometer, such as, with the thermo-pile, constitutes the
therino-multiplier, is represented in section and in perspective in
the following figures; the same letters apply to both. A, B, C is the
frame around which the copper wire is coiled, the ends T of which
terminate in the metallic tubes F, F'. This frame is fixed on a horizontal plate D, E, which can turn in its own plane around its cen
tre by means of a toothed wheel and endless screw, which are put
in motion by the button G. Q, M, N is the support of the astatic
system of two magnetic needles, suspended to a thread of cocoon
silk V, L. R, S is the glass cylinder, secured by brass rings P, S,




148  coNSTRUCTION: OFr THE  GALVYANOMETER.
Y, Z, which covers the apparatus, and rests on the base K, I. A
graduated semicircle, accurately divided, is drawn upon the card,
and by means of the supporting screws, and the movement of the
frame A, B, C, the upper needle is brought to be exactly parallel to
the coils, and to point to the commencement of the scale, being
regulated in its height by means of the screw X, with which the
silk thread is in connexion.
Whe'e the current to be measured by the galvanometer is derived from a thermo-electric combination, it is necessary that the
wire should be much thicker than for a similar current from a hydroelectric source, as the low intensity of the fluid thrown into motion
by heat might cause false indications of its quantity, unless an ample path were opened through the best conductors for it; the number of coils for a thermo-electric galvanometer should also, for the
same reason, be as few as possible. It is, therefore, not usual to
employ the same instrument for these two kinds of researches.
The position of the galvanometer in employing tlie thermo-electric
pile in the researches on radiant heat, has been described, page 98,
and its use in measuring the quantity of electricity flowing from
galvanic sources, which has been already partly noticed, will be farther described in a future place.
The passage of an electric current in the vicinity of any substance
capable of assuming magnetic properties is thus, by what has passed, shown to be sufficient for their excitation, and conversely if a
magnet, whether permanent or temporarily produced, be brought
near a substance through which an electric current may circulate,
a current is immediately formed, the direction of which is always
the same as that of a.pre-existing current, which would have conferred on the magnet the properties which it actually has. In like
manner, one current may generate another in a closed condiactoT
near it, precisely as one magnet may produce another, or that a
body statically excited may induce the electric condition on the




EARTH'    ROTATION  A  SOURCE- OF  CURR IENTS. 149
bodies in its neighbourhood; but such peculiar influences are too
removed from the proper domain of chemistry to justify any detailed description of them.
In concluding this section of the subject of electricity, it is, however, important
to prevent its being supposed that, by the omission of such considerations, they are
to be considered as of inferior interest in the phenomena of nature. It is so much
the reverse,, that perhaps one of the most active sources of the electricity which
we shall find to play a most important part in chemical combination, is derived from
the induction of the magnetic influence of the earth itself: for the earth being rendered magnetic by means of the thermo-electric currents which circulate around
it spirally fiom the equator to the poles, it is sufficient to bend a bit of copper wire
into a ring, and whirl it round the finger in the plane of the magnetic equator, to
obtain a current through the wire. A disk of copper revolving in this plane is a
source of electricity derived from the inductive influence of the earth, differing, indeed, amazingly from the brilliant excitation of the thunder-cloud, but surpassing
it far in real power of effect, and in the quantity of the electric fluid actually brought
into play. We arrive here, indeed, at the extreme modification of this active and
omnipresent force: we found it in the commencement, though existing in exceedingly small quantity, preservable only by the very best insulating means, and manifesting its tendency to escape by the attractions, the flashes, the mechanical violence which characterize machine electricity; while, in the form of magnetism, or
of a magneto-electric current, though present in.a quantity many millions of times
greater, it flows uniformly, and almost insensibly, along the perfect conductors
through which alone it is competent to pass, and it requires particular care to succeed in demonstrating its heating, its luminous, or its mechanical effects; but we.
recognise in it,. nevertheless, the untiring agent by which the inorganic superstructure of the habitable globe has been produced, by which the. depositories of the most
important metals in the clefts of rocks have been accumulated, and which being
thus the safeguard of navigation, the source of all metallurgic industry, becomes not
less important to the civilization of mankind at large, than it is found, from its paramount influence on chemical affinity, its power to separate those elements most
intimately joined, and to effect the union of those which appear most adverse to
mutual combination, as well as the facility with which its principles may be applied
to the explanation of the laws of chemical phenomena, to be available in the hands
of the philosopher for the advancement of science.
To the chemist, therefore, the most useful property of electricity is the power
which it possesses of modifying, annulling, or superseding chemical affinity. I have
hitherto avoided as much as possible involving any ideas of chemical decomposition
in the account of electricity just given, restricting myself to narrate such circumstances as Inight serve for the recognition of bodies by means of their electrical
properties, independent of their chemical constitution. But the question whether
electrical influence and affinity are identical, or what are their exact relations,
and the discussion of the theory of electro-chemical combination, still remain, and
will be examined when, first, the nature of affinity and the distinction between it
and the action of cohesive force have been described, and the general system of nom
enclature by which chemical substances are designated has been briefly noticed
CHAPTER V.
OF CHEMICAL NOMENCLATURE.
THE general properties and laws of the physical agents, cohesion,
light, heat, and electricity, having been now described so far as was
necessary, that we may avail ourselves of those properties in characterizing the substances, elementary or compound, whose more peculiarly chemical relations we shall now proceed to study, it is ne



150        P R I N C I P L E S OF N O MENCLATURE.
cessary to prefix to the description of the forces by which chemical
union is effected, and of the laws by which it is controlled, a short
statement of the principles upon which the names of the substances
to which there will be frequent occasion to refer have been constructed.
There are at present known fifty-five substances which the chemist
has not been as yet able to separate into other elements.  These are
distinguished by the following names:
Oxygen,   0.  Potassium, K. Arsenic,    As.
J.Hydrogen, H. Sodium,   Na. Antimony,  Sb.
i!Nitrogen,  N.  Lithium,   Li. Tungsten,   W.
Carbon,   C.  Barium,   Ba. Molybdenum, Mo.
Boron,    B.  Strontium, Sr. Tantalum,  Ta.; Silicon,    Si. Calcium,  Ca. Chromium,  Cr.
Sulphur,   S.  Magnesium, Mg. Vanadium,  V.
q Selenium,  Se. Aluminum, Al. Uranium,   U.
Phosphorus, P.  Glucinum, G.  G old,    Au... Chlorine,  C1. Zirconium, Zr. ridium,  r..Iodine,   I.  Thorium,  Th. Osmium,    Os.
Bromine,  Br. Yttrium,   Y.  Platinum,   P1.
Fluorin. F.  Cerium,   Ce. Tin,      Sn.
Tellu'rium,  Te. Lanthanum, Ln. Lead,    Pb.
Mercury,  Hg. Manganese, Mn. Bismuth,   Bi.
Zinc,     Zn. Iron,      Fe. Silver,    Ag.
Cadmium,  Cd. Copper,   Cu. Palladium,  Pd.
Cobalt,    Co. Titanium,  Ti. Rhodium,   R.
Nickel,    Ni.
By the combination of these bodies among each other, the various
substances which exist in nature are produced.
These simple bodies have been divided, from the earliest days of
accurate chemistry, into two classes, the metallic and the non-metallic elements. The first thirteen in the list are non-metallic; the
remaining bodies are metallic. It is found, however, that this division is only popularly correct; no matter how we may define a
metal, we cannot avoid breaking through connexions of the most intimate and important kind if we endeavour to retain the class of
metals as one founded on really existing chemical principles.  Thus,
in density and lustre, arsenic and tellurium are inUubitably metals;
and yet, if we class these bodies with copper or lead, we break through
all laws of chemical analogy, for in their combinations they assim
ilate themselves most perfectly, one to sulphur, and the other to
phosphorus. In selenium, also, the metallic characters are so feebly
marked, that even did we not know that by its properties it must be
classed with sulphur, we could not place it as a metal without great
doubt.
In describing the simple bodies, I shall retain as a division the
chemistry of the metals, for the classification, like all those which
have been long in extensive use, has in some respects much utility
and truth; but in cases where the study of certain bodies will be fa.
cilitated by departing from it, I shall not hesitate to do so. In order
to avoid confusion subsequently, I shall here describe, as succinctly
as possible, the nomenclature which has been -adopted in chemistry;
for in a science where the multiplicity of objects to be noticed is
so great, it is of the highest importance that the principles upon




NOMENCLATURE  OF LAVOISIER AND GUYTON. 151
which the names of these objects are founded should be clearly
understood.
In all conditions of science, the nomenclature has been regulated
by the prevalent theoretical ideas of the time, and it is probably vain
to look for a system of names which shall tell what the bodies really
are, and not pretend to tell more; for that would suppose that we
knew what the bodies are, whereas, in the most perfect state of
science, we only know what we believe them to be. Thus, at a time
when, by a mal-application to chemistry of the analogy of the human
body and its soul, all bodies were looked upon as having a volatile
and a fixed, an active and an inert element, the names of spirit of
wine, spirit of hartshorn, and spirit of salt were invented; at a later
period, when the theory of phlogiston prevailed in the minds of
chemists, the spirit of salt became dephlogisticated marine acid;
when the important functions of oxygen were pointed out by Lavoisier, the name was in his theory changed to oxymuriatic acid; and,
finally, when the present view was introduced by Davy, the name
hydrochloric acid became the most correct. The cause of this is,
that in a good system of chemical nomenclature, we require two conditions which it is very difficult to successfully combine; that the
name shall not only tell us that the substance is an independent substance, but that it shall give to us an idea of its most important chemical character, its composition; thus the name prussic acid is less
strictly scientific than that of hydrocyanic acid, which shows us that
its elements are hydrogen and cyanogen; and iron pyrites gives a
less perfect picture of the body it describes than the words bisulphuret
of iron. The necessity for indicating by the chemical name of"a
body its chemical composition, is thus what renders chemical nomenclature at once so variable and so complex, but it is also that which
alone enables us to connect distinct ideas with our words.
The benefit conferred upon chemistry by the nomenclature introduced by Lavoisier and Guyton was scarcely inferior in its importance to the accurate ideas of combination in which it had its origin.
The removal of the unconnected and unfounded names, which had
been invented by the older chemists, and the invention of the idea
that every name of a compound body should express its composition,
involved the increase of accuracy in the minds of those chemists by
whom science was subsequaetly to be prosecuted, which may be
looked upon as the most fertile source of the discoveries made up
to the present day.
The names most employed in chemistry are acid, base, and salt.
The word acid signifying originally sour, was applied to all bodies
which tasted like vinegar. The word base signifies any substance
which, uniting with an acid, forms a compound, of which it is the
basis or foundation; and the compound formed by their union, being
generally similar to common salt in superficial characters, is termed
a salt. Thus, oil of vitriol tasting, when mixed with water, sour, is
an acid; soda is a base, and, when combined, they form the wellknown salt called after Glauber, who discovered it. Such are the
names of those classes of bodies, the discovery of which dates from
a remote period.
Acting on the principle that, in naming a simple substance, the




152  SIM PLE BOD IES AND PRIMARY COMPOUNDS.
name should be derived from its most characteristic property, Lax
voisier formed the word " oxygen" from ofvf, acid, and yevvao, I
generate, to signify the important substance, the functions of which
he was the first to show, and which he imagined to have the peculiar
property of forming acids. In like manner, he constructed the word
"' hydrogen" from v&op, water, and yevvao, to express its most important property, of being an element of water. This principle can,
however, seldom be rigidly acted on; for example, oxygen is as
much a water former as hydrogen; and the name of oxygen itself is
not without objection, as the pre-eminence as acid former, which
Lavoisier imagined it to possess,-has been latterly overthrown. In
the case of simple bodies, names derived from quite arbitrary sources,
as tellurium from tellus, the earth; selenium from ar7a7Xp', the moon;
vanadium'and thorium from Vanadis and Thor, deities of Scandinavian mythology; chlorine from X~rpog, yellowish green (its colour); and similarly iodine from tosetdq (like a violet), have a great
superiority over those which, by attempting to teach more when
first invented, have the disadvantage of teaching falsely at a future
period.
The simple bodies, combining with each other, form compound
bodies of the first order, or binary conpounds. The names. of those
binary compounds which contain oxygen are of two kinds, according
as the compound possesses acid properties or not; if it be an acid,
the word acid is added to that of the other body to which the termination ic is joined. Thus the acid compound of sulphur and
oxygen is sulphuric acid; the'acid compound of phosphorus and
oxygen is phosphoric acid. It frequently happens that the same
body forms with oxygen two acids, in which case, that containing
most oxygen retains the terminal ic, while that in which there is
least oxygen ends in ous. Thus there is sulphurous acid, and phosphorous acid, consisting of sulphur united with less oxygen than
could form the sulphuric or the phosphoric acids. Many bodies form,
however, with oxygen more than two acids, and in this case a
new principle of nomenclature has been introduced: the words
vrro, hypo, and i,'rep, hyper, under and over, are prefixed to the degrees terminating as before stated. Thus there is an acid of sulphur containing less oxygen than the sulphurous acid, and it is called hypo-sulphurous acid; and also an'acid containing more oxygen
than the sulphurous, but less than the sulphuric acid: this might be
called either hyper-sulphurous or hypo-sulphuric acid; the latter name
has been universally adopted. Chlorine forms, with oxygen, four
acids, which are the hypo-chlbrous acid, chlorous acid, chloric acid,
and hyper-chloric acid, or, as it is often called, substituting the shorter Latin per for the Greek &vrep, perchloric acid.
In cases where the compound formed with oxygen is not an acid,
it is termed an oxide of the substance with which the oxygen is united. Thus oxide of lead, oxide of iron, oxide of copper, are re-spectively the compounds of oxygen with lead, with iron, and with
copper. In many cases, where oxygen unites with bodies in more
than one proportion, one compound may be an acid, and the other
not. Thus manganese, uniting \with oxygen,gives imanganic acid and
permanganic acid, but in a lower degree of oxidation it forms several




VARIOUS CLASSES OF PRIMARY  COMPOUNDS.:153
oxides of manganese. For as a substance uniting with oxygen may
form  many acids, so may it form many oxides also; and in such
cases it becomes necessary to distinguish them from one another
This is done by the adoption of the Greek words 7rpoTof, dEV7Epof,
rplro (first, second, third), prefixed to the Lvord oxide.  Thus we
say protoxide of lead, deutoxide of lead, tritoxide of iron; the ox;
ide which contains most oxygen is often called the peroxide, and that
which contains least the suboxide, as peroxide of manganese, suboxide of
copper. The word sesqui (one and a half) is also used for oxides intermediate between protoxides and deutoxides, but the nomenclature
then involves numerical proportions, which will require to be described herafter.
Some other simple non-metallic bodies, in combining with the metals, form compounds, of which the names are constructed on the same
plan as those of the metallic oxides. Thus,
Chlorine forms Chlorides.     Bromine forms Bromides.
Iodine    "'  Iodides.        Fluorine   "  Fluorides.
The compounds of sulphur with the metals having been popularly
named before Lavoisier's time, and it being desirable to retain, as
much as possible, the names already in common use, a different
form of termination is adopted for that body and some others.
Thus,
Sulphur  gives Sulphurets.     Nitrogen  gives Nitrurets.
Selenium   "  Seleniurets.    Phosphorus'"  Phosphurets
Tellurium  "  Tellurets.       Arsenic'"  Arseniurets.
Carbon    "' Carburets.
To distinguish between the different sulphurets or chlorides, &c.,
of the same Inetal, the Greek prefixes are adopted, as in the case of
oxides. We have thus p'oto chloride and deuto-chloride of manganese; also perchlorides and subchlorides. The Latin bis is often
substituted for the Greek deuto, as the bichloride of tin in place of
the deuto-chloride. Among Continental chemists, names which
should be translated chloruret in place of chloride, and sulphide in
place of sulphuret, are frequently employed; but as these are founded on certain theoretical ideas that have not yet been discussed, the
propriety of adopting such additional terminations cannot be considered until we have proceeded farther.
Where two non-metallic bodies are united, it is a question how
the name of the compound should be formed. Thus, in a compound
of chlorine and phosphorus, should it be calle'd chloride of phosphorus or phosphuret of chlorine? This is decided by referring to
the classification of the simple bodies which will be hereafter given,
and which is founded on a view of all their chemical properties taken
together.  Whichever element stands highest in the scale gives
the characteristic name to the compound body. Thus chlorine is
above phosphorus, and we say chloride of phosphorus. Iodine is also
above phosphorus, and we say iodide of phosphorus; but iodine is
below chlorine, and we hence call the compound which they form
chloride of iodine.
The combination of the metals with each other, except in some
U




154     N A  ES OF SECONDARY CO M POUNDS.
peculiar instances, are termed alloys.  Thus we say brass is an alloy
of copper and zinc; fusible metal is an alloy of bismuth, tin, and
lead. Where one metal is mercury, the alloy is termed an tamalgam
of the other metal; thus, an amalgam of silver is an alloy of mercury
and silver; an armalgdm of tin is an alloy of mercury and tin. Arsenic and tellurium  are so far removed from  the metals by their
chemical characters, that their compounds with'the proper metals
have the peculiar termination in uret.
By the union of two primary compounds there is formed a secondary compound. These secondary compounds are generally termed
salts.  The word salt is, however, applied to numerous classes of
primary compounds. Thus, the metallic iodides, chlorides, bromides,
and fluorides are recognised as salts. It is now also a debated question whether the bodies formed by the direct union of an acid and
an oxide are really primary or secondary compounds; but I shall
now describe only the ordinary nomenclature of those bodies, postponing the discussion of their intimate constitution to another place.
When an acid and a metallic oxide, both primary compounds, combine to form a secondary compound or a salt, the specific name of
the salt is that of the base, without any change; we thus say a salt
of soda, a salt of oxide of co?oer; the generic name is taken from the
acid, the word acid being omitted, and the final ic ueing changed into
ate, or the final ous into ite.  There is thus formed from sulphuric
acid and soda sulphate of soda. From nitric acid and oxide of lead,
nitrate of oxide of lead. From sulphurous acid and potash, sulphite
of potash.  From hypochlorous acid and lime, hypochlorite of lime.
Where the salt contains an oxide of one of the common metals, it
is usual to suppress the words of oxide in its name, and thus to say
sulphate of copper in place of sulphate of oxide of copper; nitrate
of lead in place of nitrate of oxide of lead. The strict correctness
of language is thus sacrificed; but if the idea of the composition of
the salt be held clearly in the mind, the abbreviation is not injurious; this mode of naming salts is so universal, that breaking in on
it might be productive of more injury than allowing it to remain; I
shall therefore say, for example, nitrate of lead, understanding, however, that the nitric acid is combined not with lead, but with oxide
of lead.
It frequently happens that a metal forming with oxygen two oxides, will form with acids a class of salts for each oxide. In this
case the words proto, deuto, sesqui, or per, by which the oxides are
distinguished from each other, are prefixed. to the generic name of
the salt.  We thus'say proto-sulphate of iron, persulphate of iron;
indicating that there is in one salt the protoxide, and in the other
the peroxide of iron. We have sesqui-sulphate of manganese, and
deuto-sulphate of platinum. The relative quantity of acid and base
being liable to variation, there are acid salts with an excess of acid,
and basic salts with an excess of base. In such case, the proportion
of acid is marked by the Latin bi, ter, &c., as bisulphate of potash, and
the proportion of base where it is in excess by the Greek USE, -pic,
&c., as di-sulphate of zinc, tri-sulphate of mercury; or still better
by the words hi-basic, tri-basic, &c., to indicate the quantity of base;
there is thus tribasic-sulphate of mercury, quadribasic-sulphate of
copper, and so on.




TERNARY  AND  QUATERNARY  COMPOUNDS.  155
There are many other kinds of secondary compounds than the salts
just noticed. Thus water enters into numerous compounds, which
are called hydrates. This water may act in very many different capacities, and its nomenclature must be varied accordingly, as will
be seen under its proper head; but where we wish to indicate that, body contains water, without determining more nearly the specific
function- of the water, we describe the body as being hydrated.
Oxides and chlorides combine together to form  secondary coimpounds, which are called oxychlorides, as the oxychlorides of mercury,
the oxychloride of lead.  Oxides and sulphurets combining form oxy
sulphurets, as oxysulphuret of antimony.  Chlorides and sulp/hurets
form by their union chloro-sulphurets, as chloro-sulphuret of mercury.
When two chlorides combine, the compound is termed a double
chloride, or a chloride of the metals; as the chloride of gold and sodium, the chloride of copper and potassium.  In the same way there are
double iodides and double bromides. But where two su]phurets unite,
the nomenclature has received an important change.
Berzelius has proved that, in very numerous cases, where a body
forms an acid with oxygen, which acid uniting with a metallic oxide
forms a salt, that body, uniting also with sulphur, gives a sulphur
acid, which, uniting with a sulphuret of a basic metal (a sulphur
base), forms what he terms a sulphur salt. Thus double sulphurets
are salts, consisting of a sulphur acid united to a sulphur base
Hence, as arsenic combining with oxygen forms arsenious acid, so,
uniting with sulphur, it produces sulpho-arsenious acid, which, uniting
with sulphuret of lead, forms sulpharsenite of lead, precisely as the
oxygen acid, uniting with oxide of lead, produces what should be
called oxyarsenite of lead.  The prefix oxy is, however, not used;
the ordinary salts are supposed to contain the oxygen acid, and it
is only where a salt does not contain an oxygen acid that an additional word is necessary to point out what sort of acid it does contain.  Tellurium and selenium act like sulphur; there are tellurium
acids and tellurium bases, selenium atids and selenium bases, and hence,
in place of calling the compound of seleniuret of antimony and seleniuret of sodium a double seleniuret, it is called the selenio-stibiate of sodium.
An attempt w"as made to assimilate the nomenclature of the chlorine and iodine
bodies to that of the oxygen and sulphur compounds; thus, to call chloride of mnercury a chlorine acid, and chloride of sodium a chlorine base, and the compound
which they form a chlorine salt, chlorohy drargyrate of sodium. This idea, however, has not been received into science; for, indeed, now the direction of the ideas
most popular among chemists points precisely contrary, and in place of assimilating
the double chlorides to ordinary oxygen salts, there is a general tendency to class
the ordinary salts along with the simple chlorides.
Ternary compounds are formed by the union of two secondary compotnds. Thus dry alum is a compound of sulphate of potash and sulphate of alumina.  Compounds of this order seldom  exist in more
than one proportion. Alum combining with water to produce the
crystallized alum, generates a quaternary compound; and even more
complicated stages may be attained; but they are so rare, and of so
little scientific importance, that they do not require notice here.
In organic chemistry, the principles of nomenclature are for the
most part identical with those now stated; where deviations occur,
they will be noticed under their proper heads. The progress of scl




156         SYlM BOLICAL NOMIENCLATURE.
ence has, however, introduced remarkable changes in the mode ot
representing the constitution of bodies, particularly by means of the
symbolical nomenclature now universally adopted after Berzelius.
In the list of the simple bodies in page 150, the name of each
substance is accompanied by its symbol, which is generally the initial letter of its Latin nanme; and in cases where the name of more
than one body begins with the same letter, they are distinguished
by adding to the symbols of all the bodies but one a second letter
in smaller type, which may be the second letter of the word, or
whatever letter  will best serve to characterize the name.
If there be bat one non-metallic substance in the group, it is generally selected to be denoted by the single letter, as C. and P. for
carbon and phosphorus, while the metals whose symbols have the
same letter are denoted by Ca., Co., Cd., Ce., and PI., Pb., Pd. Where
there are more than one non-metallic body commencing with the
same letter, it is a matter of indifference which is designated by
the one or by the two, but the single letter is generally attached to
the body which is of most importance in chemical phenomena.
Thus S. is sulphur, while Si. and Se. denote silicon and selenium
respectively.
The symbols of compound bodies are constructed by grouping together the symbols of their constituents; thus Pb.O. represents a
compound of oxygen and lead; C.H.N.O. a compound of carbon,
hydrogen, nitrogen, and oxygen. The algebraic sign of addition is
frequently used to connect symbols, as CI.+S., chloride of sulphur;
I +-K., iodide of potassium. But I shall use that sign only where I
wish to express that the bodies so connected are united by an inferior degree of affinity; thus Cl.Ca. is chloride of calcium dry, but
when crystallized it becomes Cl.Ca.+6H.O., in which the J- sign is
used to show that the water is united with the Ca. C1. by a power
distinct from, and inferior to, that which retains Ca. and C1. in combination. Water thus combined is often represented by the symbol
Aq., for water is capable of acting in a variety of ways in combination, and, as will be shown when we come to speak of the chemical
relations of water, it requires to be expressed sometimes as H.O. and
sometimes as Aq.
But that which requires special notice in speaking of symbolical
nomenclature is, that it involves essentially the idea of numerical
relations. Thus the symbols Pb. or Cu. do not call up to the mind
of the chemist the simple ideas of lead or copper, but of a quantity
of lead and of a quantity of copper, in the proportion of 103.6 and
31'7, which is termed an equivalent of each. Thus, also, the symbol Pb.0. signifies not merely a compound of lead and oxygen, but
specially a compound of an equivalent of lead and an equivalent
of oxygen, in the proportion by weight of 103.6 of lead and 8'0 of
oxygen. It is thus that the symbol Pb.0O, or Pb.+20., which represents also a compound of lead with oxygen, shows to the chemist
that this second body contains to the same 103-6 of lead twice as
much, or 16.0 of oxygen, as had existed in the former. Pb.O. is
therefore protoxide, and Pb.02 is the peroxide of lead.
The details of the application of those symbols involve thus the
numerical'aws of constitution, which have yet to be described; and




NATURE  OF CHEMICAL AFFINITY.                   157
hence it is unnecessary to develop their arrangement farther at
present. It was necessary to allude so far to them when speaking
of nomenclature, as I may have occasion to introduce some of them
in a general way in the next chapter.
CHAPTER VI.
OF CHEMICAL AFFINITY, AND ITS RELATIONS TO HEAT, TO LIGHT, AND TO'
COHESION.
THE peculiar power by which we suppose chemical phenomena to
be produced, is specially distinguished from cohesion, and from all
other forces in nature, by exerting in the different kinds of elementary or compound substances various degrees of energy; and by its
capability of acting: upon certain bodies'exclusively, and in preference to acting upon others, which, so far as physical circumstances
go, appear equally exposed to its effects. Thus, if to some liquid
muriatic acid there be added a mi:<ture of lime and magnesia, the
lime will all dissolve in the acid before any trace of the magnesia
will be taken. up. If a slip of iron be placed in a cup of nitric acid,
a large quantity of deep red fumes is immediately expelled from
the acid, with an appearance of boiling or effervescence; and the
iron disappears, being taken up by the liquid in place of the substances which had been expelled. If a slip of copper be dipped in
the acid, the same effect is produced; but if the iron and copper be
left together in the acid, no action takes place upon the copper until
the iron shall have been totally dissolved. The muriatic acid, therefore, presented equally to lime and magnesia, combines with the
lime in preference, and the nitric acid takes up copper, giving off,
to make room for it, a quantity of gaseous elements (nitrous acid
fumes) it had previously contained; but it will take iron in preference to copper, if the two be presented to it at the same time.
Chemical affinity is therefore elective; it chooses among a variety
of bodies which it will act upon, and is thus different from cohesion
or gravity, which will act. upon all bodies equally exposed to their
influence at the same time.
In the example of the metal and nitric acid, there is involved a
second phenomenon, which, equally with elective affinity, is characteristic of chemical force. It is decomposition. The copper cannot dissolve in the nitric acid without the expulsion of another sub
stance. By a simpler example, the decomposition may be rendered
more evident. Sulphuret of hydrogen consists of sulphur and hydrogen; if it be brought into contact with iodine, the iodine expels'the sulphur and takes the hydrogen; the sulphuret of hydrogen is
decomposed, and a new body, iodide of hydrogen, is formed. Here
the hydrogen chose between iodine and sulphur, and preferred the
former: the greater affinity for the iodine caused the decomposition.
Hydrogen has, however, a still more decided tendency to combine




158  PRINCIPLES OF ELECTIVE DECOMPOSITION.
with chlorine; and if chlorine be brought into contact with iodide
of hydrooen, the iodine is in its turn expelled, and chloride of hydrogen formed. Here is a series of decompositions depending on
the relative power of the affinities of chlorine, iodine, and sulphur
for the one body, hydrogen. Thus, by the elective affinity of an
uncombined body, choosing among a variety of other bodies all
equallIy uncombined, there is produced a new combination, containing that for which its affinity was strongest. But when an uncomn
bined body is put in contact with two substances already united, it
tends to separate them, to combine with one and to set the other
free.
If we could combine any one body, as hydrogen, for example,
with every other of the simple substances, we might, by such experiments as those described with the sulphuret of hydrogen, iodine,
and chlorine, obtain an idea of the exact order of intensity of the
affinity of each of them for hydrogen, and could easily represent,
under a tabular form, such an idea. This has accordingly been tried,
and was, indeed, the result of the first sound ideas of the nature of
chemical affinity which were obtained. It was not done completely
in any case, for even at present our knowledge is not sufficient to
enable us to form a series, including all the simple bodies. It was
particularly in the chemistry of the salts that the benefit of this
principle was found, and it was to explain and predict the result of
the decomposition of salts that tables of the elective affinity were
constructed.
It has been stated that, if lime and magnesia be placed together
in contact with muriatic acid, the acid will dissolve all the lime before it acts upon the magnesia; the affinity of lime for muriatic acid
is therefore greater than that of magnesia for the same acid, and
hence, if to a solution of magnesia there be lime added, the nmagnesia wrill be expelled and the lime will take its place. If to the
lime solution of soda be added, the lime will separate, and soda may
be in turn expelled by potash. On the other hand, there are many
metallic oxides which' enjoy a still more feeble affinity than magnesia; thus, if to a solution containing oxide of iron, magnesia be
added, the oxide of iron is thrown down and the magnesia taken in
its place. In -this manner may be arranged a series of compounds,
consisting of different bases, in union with the same acid; and by
observing the order of decomposition by each other, a view of the
relative affinities which they exercise may be fovmed. If, also, a
series of acids be combined with the same base, a similar view of
their relative affinities may be drawn up. Thus, when a solution
of potash is exposed to the air, it absorbs carbonic acid, for which,
therefore, the potash has an affinity of a certain energy; on adding
acetic acid, the carbonic acid is expelled, and acetate of potash
formed; on adding nitric acid, the acetic acid is expelled from it,
and nitrate of potash formed; and from this, by means of sulphuric
acid, the nitric acid may be recovered, the potash remaining in the
state of sulphate.
The results so described may be exhibited as follows, by writing
in a column the names of the different acids, in the order of their
affinities for a certain base (soda), which is placed at top. Similarly




ORDER OF ELECTIVE DECOMPOSITION.   159
in a column, at the top of which is placed the name of a given acid,
the various bases in the order of their affinities may be written.
Thus:
Soda.                      Mu riatic Acid.
Sulphuric acid.                Potash.
Nitric acid.                    Soda.
Muriatic acid.                  Lime.
Acetic acid.                   Magnesia.
Carbonic acid.                  Oxide of iron.
For the simple bodies similar lists might be constructed: thus, In
the same way as the series of affinities for hydrogen already noticed,
a table of affinites of the different metals for oxygen may be drawn
up from observation. If to a solution of nitrate of silver, in which
the silver is combined with oxygen, a globule of mercury be placed,
it dissolves, and the silver is set free. By dipping into the solution
of nitrate of mercury a slip of copper, the mercury is thrown down,
and the copper takes its place. From the nitrate of copper the
metal maybe thrown down by lead, and the lead again precipitated
by a plate of zinc. The affinities of the simple bodies for each other
may be therefore expressed, taking hydrogen and oxygen as illus
trations, by the following columns:
Hydrogen.                         Oxygen.
Chlorine.                         Zinc.
Iodine.                           Lead.
Sulphur.                          Copper.
Mercury.
Silver.
In which any one body in the list may expel all below it from corn
bination, and will itself be expelled by every body below which it
stands.
Such is simple elective affinity; but it often manifests itself in a
more complex form, as when it acts among a greater number of
bodies than three; and by the mutual action of two compound bodies, two new ones may be formed. Thus, when nitrate of lime is
decomposed by potash, there is simple decomposition, and the lime
is set free; but if, in place of pure potash, we employ? carbonate of
potash, the result is the formation of carbonate of lime; for when
the potash leaves the carbonic acid to go to the nitric acid, and
the nitric acid leaves the lime to go to the potash, the carbonic
acid and the lime, finding themselves in presence of one another,
unite, and precipitate as carbonate of lime. The nature of the decomposition may be more clearly shown from the figure:
Nitric acid. Potash.
Lime.        Carbonic acid.
The bodies existing before mixture being composed of those writ
ten above one another, and those formed by decomposition consisting of those which are in the same horizontal line.'Ihis action is termed double decomposition. In the example just
stated, the difference between it and simple decomposition mav




160              DOUBLE  DECOMPOSITION.
appear to have been accidental, the potash acting precisely as if It
had been free, and the lime and carbonic acid uniting only because
they came into contact, without any other ties, and hence combined together; but the peculiarity of double decomposition is,
that by means of itreactions may occur which could not have
been produced by simple affinity, and which, on the contrary, appear to have been produced in opposition to it.  Thus, ammonia
cannot decompose nitrate of lime; on the contrary, lime will take
nitric acid from ammonia; and yet, if we mix a solution of nitrate
of lime and carbonate of ammonia, they decompose each other,
and, by double elective affinity, there are formed nitrate of ammonia and carbonate of lime. As in the former diagram, the compounds, before and after mixture, are foulnd arranged in the horizontal and vertical lines of the diagram.
5 Nitric acid.  Ammonia.
Lime.         Carbonic acid.
In fact, in order to understand the cause of such double decomposition, we must take into account not merely the affimity of the
ammonia for the nitric acid, but that of the lime for the carbonic
acid.  Thus, if the affinity of lime for nitric acid be represented
by 80, and that of ammonia for nitric acid be represented by 70,
the lime will be the stronger, and can, when by itself, expel ammonia; but if the carbonic acid intervene, and the affinity of lime for
carbonic acid be 50, and of ammonia for the same acid be 30, then
decomposition must occur; for the forces preventing decomposition are the affinities of nitric acid for lime, and of carbonic acid
for ammonia; that is, 80+30- 110; while those tending to cause
decomposition are the affinities of nitric acid for ammonia, and of
carbonic acid for lime, -— 70 -150-120; the latter are the more
powerful, and the constituents of the two salts consequently exchange places.  The former affinities are termed the quiescent, the
latter the divellent affinities; and whenever the sum of the divellent is greater than that of the quiescent affinities, decomposition
must occur.
Thus the simple affinity of hydrogen for sulphur is much greater than that of
mercury for sulphur, and the affinity of mercury for chlorine is much greater than
its affinity for siLphur; and yet, on bringing chloride of mercury into contact with
sulphuret of hydrogen, complete decomposition ensues, chloride of hydrogen and
sulphuret of mercury being produced. In this case, the affinity of mercury for
chlorine being 20, and for sulphur being 10; the affinity of hydrogen being for sulphur 15, and for chlorine 30, the result may be shown as follows:
30
Chlorine.   Hydrogen. 11
QMercury.   Sulphur.
10
the Iorce producing decomposition being 30+10-40, and greater than those,
20-4-15=35, which tend to keep the elements as they were.
Such are the results of chemical affinity manifesting itself in its
simple and in its more complex form; hence there would appear
to be nothing  more easy than to determine the scale of affinities,
and to construct a series of tables in which all existing substances




CAUSES WHICI-I INFLUENCE  AFFINITY.   161.
should hrid t;ieir place, and all possible cases of chemical decomnpo 
sition migbt be iboreold with the same accuracy as the law of gravitation ailows the dlsturbing effects of a new planet to be calcl:lated;
but, ulutortunately lr tuie simplicity of expression which the laws of
chemical affinity would' thus assume, new and unexpected complications arise, and ernbarrass all cur explanations; thus, if we take
mnuriatic acid, and form a table of the affinities of bases for it, we
shail find that it is as given 1n rNo. i, aid constructing for sulphuric,xid an independent column, we shi1 21iL1 it to be as in No. 2.
No. 1.-M3ctzriaiic Acid.'         No. 2 —Sulphucric Acid.
Oxide of silver.;Barytes.
Potash.                           Strontia
Soda.                             Potash
Barytes.                          Soda.
Stroutia.                         Lime.
Linme.                            Magnesia.
kMagnesia.                        Oxide of silver.
there the order is quite reversed, for oxide of silver, the strong
est base in one column, is the weakest in the other; and barytes
and strontia, which manifest the most intense affinity for sulphuric
acid, are found but midway among the bases arranged in order of
strength for muriatic acid.  Which column must be taken as repre.
senting the true order of affinities l  What principle is there by
which these conflicting testimonies of experiments may be brought
to correspond 1 The answer is, that neither table is exclusively
correct; that these lists, although showing the order of decomposition, and thus exhibiting to the eye, most usefully, the result of a
great number of experiments, must not be supposed as strictly showing to us the order of the affinities of these bodies, unless we apply
thereto a number of corrections, arising from those numerous and
important causes which influence and disturb the simple action of
affinity, and frequently invert altogether the results, which, if unimpeded, it would have produced.
For the chemical action of two bodies does not arise simply from
their chermical affinities, but results from the combined influences of
heat, electricity, cohesion, and other physical agencies, which frequently modify the chemical forces to a remarkable extent.  By a
change of temperature, an affinity originally weak may be made to
preponderate over one previously much stronger; by electrical
conditions, the strongest and most direct chemical affinities may be
overcome; according as the cohesion of the acting bodies may prevail, decompositions, simple or compound, may be produced in opposite ways; and thus a chemical result is not the simple conse.
quence of affinity directly acting, but is the resultant of a number
of forces acting in different directions, and with variable intensities,
of which affinity is but one, although that one which, for our object, is the most important.
It is indeed fortunate for the intellectual progress of mankind that it is so; for on
the variability of the intensity with which chemical affinity may be exerted depends
the existence of the infinite variety of organized and inorganic beings which people
and beautify this earth. Had mere affinity been omnipotent; had those bodies
which attract each other most powerfully been in all cases able to combine; and,:    X




162    CAUSES WIHICH  INFLUENCE  AFFINITY.
had there been no means of dissolving their connexion when once formed, immedi-.
ately on the origin of our globe, those bodies which have the most powerful affinities
would have satisfied them by entering into eternal union; those next in power would
subsequently have satisfied their tendencyto combine, and long since all nature would
have been arranged into some few chemical combinations, the breaking up of which
could not be accomplished by any existing force. The complex changes of animal
and vegetable digestion and respiration could not go on; the working of the metals,
the chemical arts of civilized life, could not have been invented; andl the planet which
we iohabit would have revolved in space a barren and uninhabitable ball.
The action of these modifying causes may be easily exhibited by one or two examples. It has been already described how.a solution of muriate of lime is dcecomnposed by carbonate of ammonia; carbonate of lime being precipitated, and nmuriate
of ammonia remaining in the liquor; but if, in place of bringing these substances
into contact in solution, they be brought to act on each other at a high temperature,
the result is'exactly the reverse. If muriate of ammonia and carbonate of lime be
heated together without water, carbonate of ammonia is fiound to be sublimed, and
muriate of lime remains behind. If watery vapour be brought into contact with metallic iron heated to bright redness, it is decomposed, one of its constituents, oxygen,
combining with the iron, tile other, hydrogen, being set free; here evidently the affinity of iron for oxygen is greater than that of hydrogen. But if oxide of iron be
heated to redness also, and hydrogen gas be passed over it, the. oxygen is totally removed by the hydrogen in the state of water, and metallic iron is set free; here the
order of affinity is exactly the reverse, and we shall soon discover the cause to
which it must be attributed.
The philosopher who first declared that the order of decomposition was not the order of affinity, and pointed out the importance
of attending to the other forces that modify it, was led by his observations to assert that the power to which we have attached so
much importance, elective affinity, had no real existence; he said
that chemical union differed from mechanical cohesion only in being
exerted between the particles of different substances, and that in all
cases where certain bodies combined in preference to others, the
source was to be found in the accidental and external circumstances.
On his ideas, the force by which the particles of a fragment of sulphate of soda are united, differs from the force by which the sulphuric acid is united to the soda only in the fact that the cohesion
unites particles of the same kind, while affinity unites particles of
different kinds.  A salt dissolved in water is thus held in solution.
by chemical attraction.  Two pieces of lead which adhere together
are retained by mechanical cohesion; but if a piece of lead adhere
to a piece of tin, or a drop of water to a surface of glass or metal,
the union should be'attributed to chemical affinity.  It will be seen
hereafter that a great deal of this peculiarity of view arose from the
principle of indefinite chemical combination, which, although supported by the amazing talents of Berthollet, has been finally and totally given up.  We do not now consider such phenomena as solution to be produced by chemical affinity, for we require that a chemical compound should have parted with the properties of its constituents, and acquired peculiar properties of its own, in order to prove
its title to.the name.
But it is still by no means easy to fix upon the limits beyond
which the change of properties must:pass.  A change of state of aggregation is one of the most common evidences of chemical combination, as where muriatic acid and ammonia, both gases, become solid; oxygen and hydrogen, both gases, become liquid; water and
bichloride of tin, both liquid, become solid, and innumerable other




AFFINITY AND COHESION.                      163
cases. The production of heat, and often light, is one of the most
universal attributes of chemical action; and hence for many ages
the explanation of the phenomena of combustion included all that
was of importance in the philosophy of chemistry. A change of
volume is also very frequent, though not so universal; and consequent on this change of volume, a change, generally an increase, of
the specific gravity of the body from the mean specific gravity of its
constituents; thus, when oxygen and nitrogen unite to form nitrous
oxide, the volume of the compound is but 2 of that of the mixed
constituents; when nitrogen and hydrogen unite to form ammonia,
the resulting volume is but I of that of the gases mixed before combining; if 100 volumes of alcohol be mixed with 100 volumes of
water, the mixture will occupy but 196 volumes; and on mixing
similar quantities of water and oil of vitriol, the resulting volume is
but 185. Change of colour also frequently occurs; but in all These
cases, although such marked results indicate an intimacy of union
that can scarcely be explained by mere cohesion, yet other physical
forces may intervene, and in addition to the evidence of chemical
action already stated, the most important and necessary still remains,
change of chemical properties.'I have on several occasions mentioned change of properties as
characteristic of chemical combination, but it may be proper here
to enter into a few detailed examples of its nature and its source
Chemical affinity is not a single force, giving to all bodies within
its influence the same properties, though it may be in different degrees. On the contrary, the power which confers upon bodies their
chemical properties is of two kinds, antagonistic to each other, and
such that, by acting with equal energies, their effects are mutually
destroyed. Gravity, in acting upon bodies, acts upon all bodies in
the same manner; the molecular forces, which determine the hardness, the ductility, the solid, or liquid condition of bodies, may make
one body more or less hard or ductile than another, or they may
render one body solid and another gaseous; but it is not in the nature of cohesive forces to render the hardness of one body opposite
to the hardness of another, so that together they shall produce softness. Yet such is the nature of the sources of chemical activity;
thus sulphuric acid and soda are actuated by affinities for each other; the same force which gives to them their tendency to combine,
gives to one the properties of an intense acid, and to the other the
character of a powerful alkali; yet these forces are so peculiarly
related to each other, that, when the bodies have combined, the
acid and the alkaline properties disappear, and there results a substance, formed by their union (Glauber's salt), innocent, inactive,
with little tendency to combine, destitute of chemical affinity for
other bodies, yet containing in itself constituents which may be
again set free, and exhibited with all their active properties.
The force of chemical affinity is therefore exerted only between
bodies possessing opposite qualities, and by their union a substance
is produced possessing qualities which are not the mixed qualities
of its components. The forces which produce cohesion and solution are found most active where the resemblance between the
bodies is most complete. Thus metals adhere most powerfully to




164            AFFINITY AND COHESION.
other metals, and for their solution, mercury, a liquid metal, call
alone be used; salts dissolve in water always most easilyvwhen they
show their resemblance to it by already containing water of crystallization in their mass; inflammable bodies, as sulphur and phospbho
rus, do not dissolve in water, nor in acids, but in liquids,' themselves
inflammable, as ether, sulphuret of carbon, and the oils; camphor,
the resins, the fatty matters, require also,,for their solution, fluid
menstrua of analogous, oily, and spirituous natures. It is the contrary with chemical combination; the more complete the opposition
of properties may be; the more intense is the affinity by virtue of
which combination is effected: a metal comhbines with oxygen or
chlorine: ether, or a metallic oxide, combines with the acids to form
salts. In all these cases the opposition of properties is the cause
of the chemical affinity, and the neutralization or change of properties is its effect. Thus the gases, ammonia, and muriatic acid, a
caustic alkali, and an intense acid, form the solid sal ammoniac, a
neutral salt, destitute of the active properties of its constituents:
thus carbon, hydrogen, and nitrogen, elements of our daily food,
combine to generate the most active poison that has been found,
the prussic acid; and this prussic acid, by farther combination with
oxide of iron and with potash, may generate a yellow salt, which
is perfectly without action on the living body, and which, under the
name of ferro-prussiate of potash, is of daily extensive employment
in the arts.
The elements which, mixed together, constitute our atmospheric
iir, combined in one proportion, form a gas which, when breathed,
produces agreeable intoxication (nitrous oxide); in other proportions, a deep orange-coloured gas (nitrous acid), which, by intense
cold, may be obtained liquid; and in an intermediate form, a gas
colourless and transparent (nitric oxide), which, when mixed with
air, produces, by combining with its oxygen, the nitrous acid. In
all these cases new properties are assumed, the characters of the
constituent elements furnishing no means of predicting the proper
ties of the compound.
This clear distinction between chemical affinity and cohesion was
not perceived by Berthollet; and hence, misled by the supposed
existence of compounds which connected together the extremes of
chemical and mechanical force, he advanced the principle that the
differences observed between them arose solely from external circumstances. This principle has been rejected; but the discussion
to which it was subjected showed the importance of attending to
the influence which external circumstances really do exercise, and
which is frequently, in practice, more powerful than the force of affinity itself. It is therefore necessary to study in detail the influence of the external physical agents upon chemical affinity.
1st. Influence of Cohesion.-A  diminution of cohesive power
among the particles of one body, allows those of another to come
into closer approximation to them, and favours the chemical action
of the two bodies. Thus the ancient chemists expressed the influ.
ence of cohesion by the Latin proverb: Corpora non agunt nisi sint
soluta; bodies do not act unless they be dissolved. And of all
forms of matter, liquidity is that in which chemical action is most
rapid and most energetic.




INFLUENCE  oF COHESION.                    165
There are many instances of bodies acting on each other, although
in the solid form. Thus, when chlorate of potash and sulphur, or
chlorate of potash and sulphuret of antimony, are rubbed together,
the mixture explodes fromn the rapid decomposition which ensues.
When fulminate of silver, or iodide of amidogen, is even slightly
touched, detonation follows. In these cases, the original arrangement of particles mnust have been so\instable, that the imperfect approach produced by mechanical mixture, or the slight change of position arising from a sudden shock, Was sufficient to cause a new
mode of combination. But, if such cases as these be considered as
exceptions, we may look upon solid bodies in general as being without chemical action on one another.
In the gaseous form of matter, chemical affinity appears to be
controlled and weakened by the mutual mechanical repulsion of the
gaseous particles. Thus, oxygen and hydrogen, bodies whose affinities are so strong, may retmain in contact as gases for an indefinite period. Nitrogen and hydrogen have no apparent tendency to
unite when mixed. Hydrogen, in the form of a gas, is without action on carbon, or arsenic, or phosphorus, although under other
circumstances it unites with them, forming characteristic bodies.
In order to obtain the full chemical action of gaseous bodies, they
must be brought into play at the moment of their being set free or
formed; in their nascent state, as it is termed. It may well be, that,
when water is decomposed and hydrogen is liberated, there is a
moment before the hydrogen actually assumes the permanently elastic form; and being then, perhaps, liquid, and in a highly concentrated condition, its affinities are manifested with extraordinary force.
It is the samre with other gases; they act always with their full
power only in their nascent state.
The influence of cohesion in determining chemical action is,
however, of much greater importance in another way, as serving,
upon the principles of Berthollet, to explain the anomalous discordance between those experiments upon which the tables of the afinities of bodies for each other had been constructed. Thus it has
been shown, that in a table of affinities of the bases, oxide of silver
would appear to be the strongest base if we used muriatic acid:
barytes should be looked upon as the most powerful if sulphuric
acid had been employed; while, if the relation of the bases to nitric
acid were taken as the standard, potash would be found to excel the
others. In such cases, the diversity is to be ascribed to the influence of cohesion; and in-all cases of the mutual action of various
bodies in solution, the result is found to be the formation of such
compounds as are least soluble.
Let us imagine a quantity of sulphate of soda and nitrate of potash
to be dissolved in water. Each acid is attracted at the same moiment by both bases, and each base by both acids, so that there occurs a division of each acid between the two bases, and of each
base between the two acids. There are thus in solution sulphate
of soda and sulphate of potash, nitrate of soda and nitrate of potash;
and while the solution is dilute, all remain so; but if the liquor be
very. much concentrated, the sulphate of potash, being a sparingly
rsoluble salt, is deposited in crystals, and a new distribution takes




166   ARRANGEMENT OF ACIDS AND BASES.
place in the mother liquid. Supposing all sulphate of potash removed, and that there remain sulphate of soda, nitrate of soda,, and,
nitrate of potash, the remaining potash divides itself again between
the acids, and a new portion of sulphate of potash is formed, which,
by a new crystallization, may be separated. In this way, according
as the evaporation is-continued, new quantities of sulphate of potash
are consecutively formed, until there remains in solution neither
potash nor sulphuric acid, but only soda in combination with nitric
acid. Here, then, supposing the chemical affinities of potash and
soda, of sulphuric and of nitric acids, to be exactly equal, the decomposition which actually occurs, and the manner in which it really takes place, are explained perfectly by the greater cohesion of
the sulphate of potash, and its consequent sparing solubility.
In like manner, ordinary hard water contains soda, muriatic acid,
lime, and sulphuric acid. The soda is certainly the stronger base,
and the sulphuric the stronger acid; and yet, on evaporating such
water, the salt which first crystallizes is sulphate of lime; and on
continuing the evaporation, all sulphuric acid may be removed in
combination with the lime. But the acids and bases being divided
among one another in solution, there coexist sulphate of lime, sulphate of soda, muriate of lime, and muriate of soda. But when the
liquor is concentrated, the sulphate of lime is first deposited, and a
new quantity being formed, all its constituents are eliminated in
combination, precisely as the sulphate of potash was separated in
the former case.
In these instances the separation of the least soluble ingredients
took place by degrees, and, as it were, artificially; but if any one
of the substances produced be perfectly insoluble, it is at once and
in full quantity expelled. Thus, when we mix together solutions of
nitrate of barytes and sulphate of soda, there — is instant formation of
sulphate of barytes, and the solution contains only nitrate of soda.
But even here, although the formation of the sulphate of barytes appears instantaneous to the senses, it yet may, in point of fact, be
just as gradual as in other cases. Thus there may have been a moment after mixing the solutions when there were present, dissolved
together, nitrate of barytes, nitrate of soda, sulphate of soda, and
sulphate of barytes; in the next moment the latter precipitates, and
the barytes in solution, still dividing itself between the two acids,
another quantity is formed. This then precipitates, and thus, in a
space of time that is too small to be detected, the quantity of barytes in the solution is reduced to the mere trace of sulphate which
the quantity of water can dissolve, and which is too small to be detected by our ordinary tests.
The nature of double decomposition depends thus on the relative
solubility of the compounds formed. In whatever way the most in-.
soluble bodies may be generated, the decomposition occurs. It is
thus that, on mixing solutions of carbonate of ammonia and.f nitrate
of lime, there are formed carbonate of lime and nitrate of ammnonia;
not merely that the divellent affinities were more powerful than the
quiescent forces, but that the insolubility of the carbonate of lime
produced its separation from the liquid, and hence the union of the
substances which compose it




DISTRIBUTION  NOT INVARIABLE.                   167
The inversion of affinity which is produced by the influence of
cohesion is not limited to cases of double decomposition.  There
is no doubt but that acetic acid is a stronger acid than carbonic acid;
and on adding acetic acid to a solution of carbonate of potash in
water, the carbonic acid is expelled, and acetate of potash formed.
Yet, if a stream of carbonic acid gas be passed into a solution of
acetate of potash in alcohol, the salt is decomposed, acetic acid being' set free, and carbonate of potash formed. The cause of this is
the insolubility of the carbonate of potash in alcohol; for, on the
first action of the carbonic acid, the potash divides itself between
the two acids, and there is formed some carbonate, which is thrown
down; then'another quantity, which also separates, until ultimately
all is precipitated, and thus one of the feeblest acids may overcome
the affinities of another which is much stronger.
By this principle of distribution of acids and bases, we are thus
enabled to account for a variety of facts, which appear totally opposed to affinity, if it were not subject to such modifications; but,
although it is so convenient for explanation, it should not be admitted as a principle in science if there could not be adduced evidence of its actual and independent truth. That it does occur in
many cases cannot well be doubted; thus the solution of sulphate
of copper in water is of a rich blue colour, and that of muriate
(chloride) of copper of an emerald greeti. Now, on mixing. muriatic acid with a solution of sulphate of copper, the blue solution
is immediately changed to green, showing that the weaker acid. has
divided the oxide of copper with the stronger, although, so far
from precipitation occurringo, the new compound is the more soluble of the two. Also, on mixing a solution of sulphate of iron with
sulpho-cyanin acid, the liquor becomes intensely blood-red coloured, showing that a quantity of sulpho-cyanide of iron has been
formed, although the sulpho-eyanic acid is much weaker than the
sulphuric, and no precipitation occurs to favour its production.
These, and many other such examples which might be brought
forward, show that the opinion of Berthollet,,that the acids and
bases, when mixed together' in solution, arrange themselves so that
each base shall be divided amongo all the acids, and each acid among
all the bases, is in a great many cases true, and that it is one of the
most fruitful sources of the decompositions which occur in our experiments; but it remains to be decided whether it is universally
true, and whether, if all acids and bases act thus equally on one
another, we should abandon the idea of chemical affinity being
elective.'The answer to this question has been long since received in science. The principle of Berthollet does not hold always, for numerous instances may be produced where this partition of acids or
of bases does not take place. Thus boracic acid and sulphuric
acid both redden litmus, but the former colours it of a port-wine
colour, while the latter tinges it of the red of an onion-skin. If a
quantity of borax (borate of soda) be dissolved in water coloured
blue by litmus, and. some sulphuric acid added thereto, the liquor
becomes coloured wine-red from free boracic acid; but, although
the slightest trace of sulphuric acid in excess would show itself by




168  INFLUENCE OF ELASTICITY ON AF F INITY.
changing the red to that of the onion-skin, no sign of it is found
until all the boracic acid-has been expelled. Here, therefore, there
is no partition of the base between two acids; all the sulphuric acid
which is added unites with the soda, and all the boracic acid is ex
pelled. If a solution of carbonate of soda be coloured blue by
litmus, and sulphuric acid added, it may also be shown, by the ab
sence of the peculiar red which free sulphuric acid gives, that there
is no division of base between the two. The carbonic acid is totally expelled, and the sulphuric acid combines exclusively with the
soda. If the solution be dilute, the carbonic acid remains dissolved
in the liquor; if it be concentrated, it is evolved in the gaseous
form; that makes no difference.
Affinities are not, therefore, as Berthollet considered, all the same
in power. The framers of the tables of affinity were right as to
the general principle, that different bodies have different degrees
of affinity for each other; but they erred in supposing.that they
could construct a table for the absolute order of affinities.
To sum up the details that have been given of the influence of
cohesion on the affinities of bodies acting on each other in solution,
it may be said that, 1st, TIn almost all cases of precipitation, the nature of the double decomposition is determined much more by the
~fact of one of the bodies formed being insoluble, than by the resultant of the united affinities of the bodies which are engaged. 2d,
That where there is no separation of an insoluble or of a sparingly
soluble compound, the acids and bases, if they differ very much in
energy, are exclusively united, the strongest acid with the strongest base, and the weakest acid with the weakest base; and if there
be not base sufficient to neutralize all of the acids, a corresponding
quantity of the weakest acid being left out of combination altogether; but, 3d, That if the acids and bases be not very different
in energy of affinity, they arrange themselves in such a manner
that each base shall be divided between all the acids, and each acid
divided between all the bases, in proportions which depend upon
the quantities of each acid and of each base that may be present,
and on its affinitary force. Thus, if there be two acids and two
bases present, there will be four salts; if three acids and three
bases, nine different salts; and generally, the number of compounds in solution will be equal to the whole number of acids multiplied by the whole number of bases present.
2d. T/he Influence of Elasticity.-The absence of cohesion, or, still
more, the substitution for cohesion of its antagonist power repul.
sion, as shown by the property of elasticity in the form of gas or
vapour, modifies chemical affinity in a perfectly analogous manner
to that which has been already described; for, precisely as the
formation of an insoluble substance in a liquid will enable lower
decrees of affinity to preponderate by removing the body which is
formed by its insolubility, so will repulsion or elasticity determine
the production of such substances as by their volatility may be
driven off, even though the affinities of their elements may be nlmch
feebler than those of other bodies. In all such cases the same
principle of distribution, so fully described already, may be suppo.
sed to hold: thus a solution of sulphate of magnasia is perfectly




INFLUENCE OF COHESION AND ELASTICITY. 169
decomposed by ammonia, the magnesia being precipitated; but, on
mixing sulphate of ammonia with dry magnesia, and applying heat,
the ammonia is expelled, and the sulphuric acid remains, united
exclusively with the magnesia. Supposing that there is little dif
ference between the affinities of these two bases for sulphuric acid,
the acid in the mixture may be divided between the two; in each
case there is free magnesia and free ammonia, for the acid is only
able to saturate a part of each. In the solution the excess of magnesia is insoluble, and it is expelled; in the dry way the excess ot
ammonia is gaseous, and it is driven off; and thus, with the same
substances and the same affinities, precisely opposite decompositions are produced by the influence of cohesion and elasticity.
The decomposition of muriate of lime by carbonate of ammonia
in solution has been already noticed, where carbonate of lime is
formed in consequence of its insolubility. If the carbonate of
lime and the muriate of ammonia so produced be dried and heated,
the precisely reversed decomposition will take place; there are at
first produced muriate and carbonate of lime, muriate and carbonate
of ammonia; and this latter, being volatile at the high temperature
which is used, is driven off, and new portions formed until the interchange of elements is complete.
The boracic acid has been already noticed, as being one so feeble in its affinities that the law of the division of acids and bases
does not hold with it, but that sulphuric acid can deprive it of every
particle of base. This is quite true as long as these acids are in the
liquid form, but at a high temperature the reaction is reversed.
If a mixture of sulphate of soda and boracic acid be heated to redness
in a crucible, the sulphuric acid will be driven off in consequence of
its volatility, while the fixed boracic acid will remain combined with
the whole quantity of base. The white, inert, earthy substance, silica (powdered flints), the acid properties of which are so feeble
that it is only from analogy that it is recognised by chemists to be
an acid, may, at a high termperature, expel the most powerful acids
from their combinations; thus the commonest sort of pottery is
glazed by throwing over it, when at a bright red heat, handfuls of
common salt; this is instantly decomposed; the silica of the earthy
material of the vessels combines with the soda of the common salt,
and the muriatic acid is driven off in white clouds of elastic vapour.
HIere the acid, which is the feeblest when dissolved in water, may
expel the strongest when the temperature is raised; and admitting
that in the commencemenent a partition of the base between the two
took place, even to a very small extent, the final and complete expulsion of the more volatile must result.
From the great variety of compounds into which water enters, it
is easily expelled, not that it is inferior in affinity to most other
bodies, but from its greater volatility.  We shall hereafter see reason
for looking upon water as being a base of considerable force, and
entering into eormcbinatloil in forms which should possess consider
able stability; but when a compound of water is subjected to heat,
the elasticity of the water diminishes its affinity so far that it may
easily be expelled.
The elasticity which Certain elements possess when free, may be




170 INFLUENCE OF VARIOUS M1 ODIFYING CAUSES.
a cause why the compounds which they form are easily decomposed
by heat, if their actual affinity to one another be not considerable.
Thus the nitrate of barytes, which contains nitrogen and oxygen in
combination with barytes, gives, when heated, a mixture of nitrogern
and oxygen gases: nitrate of lead gives, when heated, pure oxygen
and nitrous acid fumes. Chlorate of potash, by a high temperature,
abandons all its oxygen gas; and the remaining elements, having a
powerful affinity for each other, resist the increase of heat, and remain as chloride of potassium.
When the decomposition of a body by heat is thus determined
by the elasticity of one of its constituents, it is necessary, for the
success of the process, that this constituent should be allowed fireely
to escape. If it be forced to remain enveloping the residual substance, the decomposition ceases. Thus, by heating carbonate of
lime to redness, it is resolved into lime and carbonic acid; but if the
carbonic acid be not removed, the decomposition would immediately
cease, and the carbonate of lime might be melted without being decomposed. The removal of the carbonic acid is accomplished, in
burning lime on the large scale, by the limestone being heated in a
kiln, through which there is a continuous draught, by which the carbonic acid is carried off according as it is formed. The necessity
for the removal of the carbonic acid may be shown by placing bits
of white marble in a porcelain tube, heated to redness in a furnace,
connected with a pneumatic trough, and fitted to a retort at the other
end, by which steam may be passed into the tube; at first scarcely
any carbonic acid is set free; but, by keeping up a supply of steam,
the gas is rapidly produced, and the lime becomes very soon completely cautstic.
It is in this way, also, that we may explain the contrary order of
decomposition that may be produced by oxygen, hydrogen, and iron.
If metallic' iron be in the tube, and the latter be kept full of steam,
every particle of hydrogen which is formed is carried off; and there
being then aspace provided into which the hydrogen can easily
spread itself, the steam will be decomposed, and the iron converted
into oxide. If,, on the contrary, the tube contain oxide of iron, and
be kept full by a current of hydrogen gas, there is presented to
every molecule of steam produced room for its escape; and the
formation of steam being thus favoured by its elasticity being allowed full play, the reduction of the metal is completed.
Independent of its influence on cohesion, a change of temperature is capable of modifying the affinities of bodies in a remarkable
degree. Thus charcoal is not capable of being melted or vaporized,
and yet, although at ordinary temperatures quite inert, few bodies
can resist its deoxidizingr action at a red heat. Bodies which takes
fire when heated do so in consequence of their affinity for oxygen
being augmented by the increase of temperature. The action of the
electric spark in producing the explosion of gaseous mixtures, depends on its heating very much the few particles of gas Which lie
immediately in its path, and the combustion being communicated
by them to the general mass. The affinities of bodies for each other
appear to be thus exalted by the agency of heat in many cases, but
the exaltation does not appear to be the same for all. Heat appears




B ERTHOLLET S THEORY  OF  A F FINITY.   171
often to diminish the affinity of bodies; thus the explosion of de
tonating compounds was so explained; but this appears to arise
from the heat really exalting the affinity of the more powerful constituents, so that new and more permanent bodies may be formed:
thus fulminating' silver explodes, not that its elements may separate,
but that bodies of a more permanent constitution may be formed
The iodide and chloride of azote were looked upon as being examples of mere separation of elements on the application of heat; but
Marchand and I have found that these bodies contain hydrogen, and
that they are decomposed in consequence of the formation of hydrochloric or hydriodic acid.  To produce many bodies of instable
nature, it is necessary to avoid the use of heat; not that heat diminishes the affinities of their elements in general, but that the heat.enables those elements to satisfy their affinities better, by combining
in a more stable form.
It has been mentioned that Berthollet considered affinity as being not elective, but that the combination of one body to another
was determined by the circumstances under which they were placed;
and that, in cases where nmany bodies of equal solubilities existed
together, they were divided among one another in proportion to
their masses; but he in this case introduces a term which has caused
great difficulty in the discussion of the doctrines which he advanced.
HIe says that the bodies mixed together combine, not only in proportion to their masses, but of their affinities; and hence mig'ht appear to admit that bodies had different degrees of affinity, and that
this might, therefore, be elective; but, if I conceive his opinions
rightly, the affinity of which he spoke was not the force to which
we assign the power of choice of one body over another, but he carried on the analogy to cohesion, and considered that the affinity of
one body, A, to another, B, might be greater than to a third, C, not
so as to make A unite with B in preference to C, but thtt, when it
had been united with B, it would hold it more firmly than it could
retain C.  This is like what is found with cohesion; if several
bodies be placed beside each other, they show no power of elective
cohesion; but if they be brought into actual close contact, the degree
of cohesion may be different for each.  It is in this way that Berthollet recognises a diffbrence of affinity, and hence the obscurity
that is often ascribed to his statement of his views, from the sense
which he attached to the word affinity being mistalen.
WVe owe to this philosopher an attempt at measuring this power of affinity,
which, thouigh incorrect, yet, as being one of the first steps made towards numerical laws in chemistry, deserves notice. He looked upon the neutralizing power of
a body as being the measure of its affinity for another, and considered that the deviations trom this rule arose from the influence of cohesion or of elasticity: thus
the same quantity of potash is saturated by
Sulphuric acid...  40 parts.    Muriatic acid... 36'5 parts.
Nitric acid...   54  "       Acetic acie... 51    "
Carbonic acid... 22  "       Oxalic acid... 36 
Hence, if mere affinity was allowed to act, carbonic acid should be the strongest,
and nitric acid the weakest in the list; in like manner, the same quantity of sullhuric acid neutralizes
Potash...         48 parts.    Lime....      28 parts.
S...... 32  "       Barytes.... 76 "'
Ammonia....        17  "        Magnesia...        18  "




172      INFLUENCE  OF LIGHT  ON  AFFINITY.
and ammonia and magnesia should be the strongest of all bases, were it not for
the insolibility of the one and the volatility of the other body.
These numbers, which are now known as expressing the quantities of substances that are equivalent to each other in combination, are fully recognised as totally
independent of the force of affinity exercised by each body. As yet we have no
other measure of affinity than the order of decomposition, controlled by the estimate of the influence which cohesion and elasticity may exercise. From the
electrical relations of bodies, attempts have been made to estimate the relative
affinities of chemical substances, the results of which will be -described in their
proper place.
Of the Influence of Light on Clhemical jffnity.-Although attention
has latterly been very much directed to the influence of li(ht on
chenical affinity, from  the accidental discovery of some very remarkable circumstances connected with it, yet there have not been
discovered as vet any general principles to which those results can bc
reduced; and the greater number of the investigations that have been
made are occupied by experiments of detail, which, from their want
of connexion and their multiplicity, cannot be successfully conternm
plated from any general point of view at the present moment.  So
far, however, as positive facts have been discovered, and as even
plausible explanations of those facts have been suggested, I shall endeavour to represent, briefly, the actual condition of our knowledge
of this department.
In many cases, bodies which in obscurity remain totally without
action on one another, are brought into combination by exposure to
light, and the rapidity of their reaction is proportional to the brilliancy
of the light.  Thus chlorine and hydrogen mixed remain unaltered
for any period in the dark; if exposed to the diffuse daylight, they
silently combine, but explode suddenly if a direct ray of sunshine
fall upon the mixture.  Chlorine dissolved in water, if kept in the
dark, remains a long time unaltered, but if exposed to sunshine, is
rapidly converted into chloride of hydrogen, water being decomposed, and oxygen eliminated in a gaseous form.  Chlorine unites with
carbonic oxide only under the influence of lilght, whence the name
Phosgene, a light-formed gas, was given to the compound by-its discoverer, Dr. Davy. Chlorine and sulphurous acid unite also only
when exposed to brilliant sunshine; so much so, that in Dublin but
few days in summer are found bright enough to form it.  The decomposing action of chlorine, iodine, and bromine upon organic
bodies, which consists in the separation of hydrogen, and the assumption generally of a corresponding quantity of chlorine, &c., in
its place, is regulated also in a remarkable degree by the brilliancy
of the light under which this operation is carried on.  Thus, even
in summer, in Dublin, I never could deprive acetone of more than
one third of its hydrogen, forming from C3 H;, 0., the body C3 IH  C1.
0.; but in Paris, in summer, the chlorine rernoved another equivalent of hydrogen, and Dumas and I succeeded in obtaining the body
C3 H. C12 0.  In. like manner, in bright sunshine, the action of
chlorine on pyroxylic spirit is so violent, that unless the vessel be
carefully shaded, the decomposition proceeds by a series of explo.
sions, while I have found it exceedingly difficult in gloomy weather
to produce any action whatsoever. Instances of this kind might be
very much multiplied, but those described are sufficient to point out
the general manner in which light is found to. act.




PHIOTOGRAPIIIC  DRAW ING.                  173
The action of light appears occasionally limited to the simple
separation of bodies previously combined. Thus colourless nitric
acid, when exposed to sunshine, evolves oxygen gas, and becomes
coloured yellow from nitrous acid which remains. The fading of
Prussian-blue patterns on cotton, which Chevreul found to depend
on the escape of cyanogen, and the conversion of the blue into a
white compound, containing less cyanogen, is also an example of this
principle.
Setting aside, for the present, the influence of light on the production of colouring matters in organic bodies, which will be described as a portion of the chemical history of the individual substances, I shall now only advert to the action of light upon the compounds of the easily-reducible metals, particularly silver, by the study
of which such remarkable results have latterly been obtained.
Scanlan first showed that, when nitrate of silver blackens under
the influence of light, its decomposition is produced by organic
matter, as by contact with paper, or by the organic substance, which
even distilled water contains in small quantity. Chloride of silver
also is affected by light only when in contact with organic matter or
with water, and in the latter case, also, most probably from acting on
the oroanic matter which the water held in solution.  When oil of
vitriol is poured over chloride of silver, this is not altered by the
light, the sulphuric acid combining with the water, and probably destroying the organic matter therein dissolved. I apprehend that in
most, if not all cases of the decomposition of a metallic salt and the
reduction of the metal under the influence of light, a substance con.
taining hydrogen, exclusive of the water of solution, must come into
play.
The decomposition of the salts of silver in contact with paper
under the influence of light, has become of interest to the arts as a
process of obtaining accurate outlines, and is called phottgrap, / y, or
photographic drawing. If a sheet of paper be washed with a very dilute solution of chloride, iodide, or, better, bromide of potassium,
and then with a solution of nitrate of silver, there is formed in the
substance of the paper chloride iodide, or bromide of silver, which,
being in contact with abundance'of organic matter, is blackened by
a very short exposure even to moderate light. If an opaque body
be laid between a sheet of such paper and the light, the portions to
which the light arrives become dark, while that under the object remains white, and thus the most'delicate and complicated outlines of
foliage or fibres may, by a few minutes' exposure to the solar rays,
be fixed upon the paper with a degree of accuracy inimitable by the
hand. To render such a drawing permanent, it is necessary to remove the silver compound under the pattern; for if it remained, the
blackness would gradually become uniform  over the entire surface,
and the picture would be effaced. This is effected by washing the
paper, after the image has been completely formed, by a solution of
some substance capable of dissolving out all of the undecomposed
salt of silver; for this purpose, ammonia, hypo-sulphite of soda, and
strong solution of common salt are those generally employed.
The most remarkable features connected with the chemical agencies of light result from the recent experiments of Herschel. He




1174  COLOURING EFFECTS OF THE CHEMICAL RAYS.
has shown, as was slightly noticed when describing the general characters of light, that the chemical effects are not regulated by, nor
iimnited to the luminous spectrum, but by totally distinct rays, which,
according to the substance employed to show their decomposing action, may extend far beyond the visible limits on either side, or may
stop short in the middle of the coloured space; and that the greatest
effect, which generally occurs at the violet extremity of the spectrum,
may be produced at other and widely-distant points.
A singular, and at present unaccountable, consequence of the action of the prismatic spectrum  on paper impregnated with chloride
of silver is, that the spaces' on which the coloured rays fall become
coloured, acquiring a tint corresponding to that of the light incident
upon them, so that the spectrum  fixes its own image on the paper.
Thus the colours impressed were in one experiment:
|  Speclrum Col!urs.  Colours formed or  he P.per.  -
Extreme red.    None.
Mean red.      None.
Orange.        Faint brick red.
Orange yellow.  Brick red, pretty strong.
Yellow.       Rled, passing into green.
Yellow green.    Dull bottle green.
Green.         Do., passing into bluish.
Blue green.    Very sombre blue.
Blue.          Black, passing into metallic yellow.
Violet.          Do.     Do.
Beyond the violet. Violet, or purplish black.
It is in the lavender-coloured space that the chemical effects are
generally most intense; when the light of it had been concentrated
by a lens, and received on a piece of prepared paper, the blackening was instantaneous, precisely as if a red-hot body had been applied behind, or a smoky flame directed on the paper over all the
space illum'inated, and accurately marking its outline.
In the table of impressed colours just giv en, the red rays appear
to have produced no effect; but they are by no means destitute of
action.  When a quantity of diffused light is allowed to fall upon
the paper, in addition to the more brilliant spectral colours, the
chemical image is found to acquire a pure white prolongation beyond the red space, in which the darkening action of the diffuse
light appears to have been suspended.  The opposite extremities of
the spectrum appear, therefore, to have different powers, the darkening quality of white light being due to the difference between the
two in favour of the violet end; and it is probable that by a balance
of action, a sensitive paper might be exposed to the action of united
beams of brilliant violet and red light, and remain perfectly unaltered in its colour. Herschel did not, however, succeed so far: paper
blackened by violet light has that blackness removed by the action
of red light upon it; but it was found impossible to catch the point
where the paper should be white; for, according as the black of the
violet end passed off, the red impression was substituted for it.
When, however, the different coloured rays were made to fall simultaneously on the paper, the neutralizing power of the opposite
ends of the spectrum was beautifully shown.  The blackening power of the more refrangible rays was suspended over all the space




DAGUERRE  S PROCESS  OF  TAKING  IMIAGES.  175
upon which the less refrangible rays fell, and the shades of green
and sombre blue, which the latter would have impressed upon a
white paper, were produced on that portion which, but for their
action, would have been merely blackened.
The paper with which those results were obtained derived its
sensibility to light from chloride of silver; but the action of other
salts of silver gives such anomalous and variable effects, that no
general principle whatsoever can be deduced from  them; thus,
with bromide of silver, the blackening proceeds uniformly over the
whole of the visible spectrum, and the whitening efiect is produced
beyond it to a considerable distance.  The subject has been shown
by Herschel to be one of considerable importance and great extent;
and from the popular interest it excites, some clew to a more general knowledge of its principles will probably be soon obtained.
The process lately discovered by Daguerre, of fixing the images
of external objects upon a prepared metallic plate, is one which also
deserves attention, as being founded upon the chemical agencies of
light, although hitherto there has been but little success in the attempts made to assign a theory of it.  It is not complicated in detail. A plate of silvered copper is cleaned with dilute nitric acid,
so that the surface of silver may be absolutely pure, and is then exposed to the vapour of iodine until a gold-coloured pellicle of iodine
of excessive tenuity is deposited upon it. In this state it is very
sensible to light.  The plate so prepared is placed in a camera-obscura, and the image of the object required is allowed to remain on
it for a space of time, which varies with the brightness of the light.
When it has been sufficiently exposed, it is removed, and submitted to the action of the vtpour of mercury, by which the picture is
rendered visible.  As there still remains, however, a general sensibility to the farther influence of light, this is removed by dissolving
away all the iodine and iodide of silver by a solution of hyposulphite of soda.'The shadows remain then marked by smooth anamlgamated surfaces, and the lights, by the corresponding portions being of a dull gray colour, possessing only a power of dif-fise reflection.
The explanation of this process, which, from my own observations, I am disposed
to suggest, is, that the iodine combines with the silver, and forms iodide of' silver,
which is spread in an amorphous state, forming an excessively thin layer, like varnish, over the surface of the plate. Under the influence of the light, I consider that this
crystallizes as melted sugar does, but' so minutely as to be invisible to the eye, and
the closeness and completeness of the crystalline structure being proportional to the
duration and intensity of tlie light to which it had been exposed. When, then, the
vapour of mercury attacks -the plate, the iodide of silver in both conditions is decomposed, and, the iodine being replaced by mercury, an arnalgam of silver is formed, uniform in surface, and perfectly metallic in its lustre, over the shaded portions;
but the crystalline iodide, in being decomposed, gives a crystalline amalgam, whiceh,
from the minuteness of its particles, presents only a grayish tint, and, being mixed
with interspersed points of bright, smooth amalgam where the light had been less
powerful, shades oflf' proportionally all the intermediate effects.
The application of the mercurial fumes cannot be pushed far enough to decompose all the iodide of silver, for it would injure the picture by depositing itself irregularly and in excess. It is therefore necessary, as soon as enough has been acted
on by the mercury to bring out the pIicture in a distinct manner, to remove the remainder by the washing which has been described.
The influence of colour on the production  of pictures by Daguerre's process is very marked; the images of green objects are
scarcely at all defined, so that the method is scarcely applicable to'




176      PROCESS FOR TAKING PO R-TRAITS.
taking landscapes.  Red and orange are also very feeble in their ef
feet; but blue, even so intense as to be not at all bright, is more
powerful than a brilliant white light.  In order, therefore, to produce
good effects, objects should be selected either white, or of colours
from which red and'orange should be absent. The fixation of' colours in a manner similar to that discovered by Herschel, and already
noticed, has been remarked in Daguerre's process, althougylh so irregularly that no advantage has as yet been taken of it for technic:al
uses; but I have myself seen, on more than one occasion, where a
deep blue sky was interspersed by patches of bright white clouds,
a perfect picture of the sky in its natural colours to be formed upon
the plate.  Time-worn' stains, and marks upon the surface of stone
buildings, are also occasionally represented in their natural colours.
In the majority of cases, however, where colours are produced upon
the plate, they do not correspond in position or tint to those of the
natural objects whose image had been obtained.
[Since the preceding paragraphs were written by Dr. Kane, numerous improvements have been made in this beautiful chemical
art in America and elsewhere: the theory of the process is also
much better understood.  The most important of these improvements is the application of Daguerre's process to taking portraits
from the life.  This is due to Dr. Draper, who succeeded with it
soon after the French process was known in this country.  At first
the direct or reflected rays of the sun were required; but modes of
preparation, giving the plate more sensitiveness, have been since discovered, so that the ordinary diffused light of day is now sufficient.
The best process for obtaining portraits is as follows: The plate,
having been carefully cleaned, is iodized to a pale lemon colour; it
is then exposed to the vapour of bromine for a sufficient length of
time to bring it to a golden yellow. It is a great advantage to keep
it in total darkness for three or four hours before using it.  The
person whose portrait is to be taken, having been seated in a suitable chair, with a support to keep the head perfectly steady, before a
window, so that the light shall illuminate all those portions seen in
the camera with proper strength, the plate is to be exposed to the
focal image for a time, which may be determined by previous trials.
Much of the beauty of the picture depends on the object-glass of
the camera; very good proofs may be had by an arrangement of
uncompensated convex lenses four inches in diameter and eight
inches in focus; but the most finished pictures are obtained by the
use of achromatics, which ought always to be preferred.
The process of exposing the proof to the mercurial vapour is one
of great delicacy; sometimes the object is suddenly evolved, sometimes it requires the mercury to be maintained at 175~ Fahrenheit
for a long time. Experience alone can determine when the full effect has been obtained.
After the picture has been brought out, and the coating of iodide
of silver removed, it remains only to effect the gilding. This is accomplished by pouring all over the silver surface a very weak solution of the chloride of gold in hyposulphite of potash, and warming
it gently with the flame of a spirit-lamp. At a particular temperaure, the shadows increase in depth and the lights in brillancy; the
plate is then to be thoroughly washed. The gilding serves to render




T IIEORY  OF THE PRO CESS OF DAGU ERRE. 177
the picture inmlmovable by ordinary exposure or accident, and imparts to it a beautiful satiny lustre, and chatoyant play of colour.
The great difficulty in the management of the Daguerreotype lies
in the circumstance that the iodide of silver is not affected correspondingly by lights that are of different degrees of brilliancy, if
they should be of different colours. And it is only under particular
circumstances, not easy to reproduce, that lights of the same colour,
but of different strengths, produce a corresponding degree of whiteness on the plate. Often,-whtn the light is too active, the proof
takes on an unpleasant slate-blue colour, from the exterior portions
of the iodide assuming a state of solarization before those beneath
have had time to undergo change; a phenomenon resembling what
takes place when a sheet of paper is held before a very bright fire,
the exposed surface becoming scorched, while the back has scarcely had time to become warm.
As respects the theory of this process, I do not coincide with the
views expressed by Dr. Kane. In the shadows no mercury exists;
the lights are an amalgam. When a Daguerreotype is exposed to
t'he vapour of mercury to bring out its picture, a decomposition of
all those portions of the iodide which have been exposed to the
light ensues; an amalgam is formed, and the iodine expelled unites
with the metallic silver behind, effecting, therefore, a corrosion of
the plate; no iodine is evolved, and for obvious reasons such an
event is impossible. The light therefore imparts to those portions
of iodide on which it has impinged, the quality of being decomposed
at a lower temperature by the vapour of mercury than the temperature at which an unexposed iodide can be decomposed; an amalgain therefore forms on such positions when the temperature does
not rise beyond 1750 F., though the whole surface might be decomposed and whitened if the temperature were carried high enough.
The chemical rays which affect the iodide of silver are chiefly
those of high refrangibility, and these rays manifest many habitudes
resembling those of radiant heat. They are absorbed and lost in
effecting the change, so that a ray of light which has once fallen
on a Daguerreotype plate, and is reflected by it, has lost all its activity. Whatever, therefore, will interfere with the absorption, \vill interfere with the sensitiveness of different compounds. Thus it has
long been known that there is a proper colour to which the plate
may be brought when it possesses the maximum of sensitiveness:
this is the golden yellow; when it is red, or green, or blue, it is
much less sensitive; and when of a lavender colour, hardly sensitive
at all. This arises from the circumstance that under these conditions the optical character of the plate is such that it reftects the
active rays in part or altogether.
I have already remarked that lights which vary in intensity do
not affect these plates in a corresponding way; this arises from the
circumstance that, as the iodide of silver is undergoing chancre, a
large quantity of light becomes latent, precisely as a piece of ice in
the act of melting absorbs a large quantity of heat, not discoverable
by the thermometer; this phenomenon accompanies the blueness
which the compound assumes as it changes into the condition of a
subiodide.]




178           NATURE OF COMBUSTION.
CHAPTER VII.
OF THE LIGHT AND HEAT DISENGAGED DURING CHEMICAL COBINATION,
IT has been already noticed that the union of substances having
chemical affinity for each other is accompanied by increase of temperature; and in cases where the affinity is powerful, the effect may
be so great that the bodies shall become luminous: in such instances
the chemical action is said to be accompanied by conbustion. In considering the relations of this phenomenon to affinity, it will be necessary to notice, first, the general circumstances of combustion;
secondly, the relation between the amount of affinity and the quantity of heat evolved; and, finally, the explanations that have been
offered of the origin of the light and heat.
In ordinary language, a body is said to burn when its elements
unite with the oxygen of the air, and form new products. The accompanying phenomena are in general those on which popular attention becomes fixed, and for which the process is generally car
ried on; and hence, to the world at large, combustion is of importance only as a source of heat and light. One of the bodies, as hydrogen or sulphur, is termed the burning or combustible body, and
the oxygen is said to be the supporter of combustion; but this lan
guage, although convenient for common use, is incorrect as a scientific expression; for oxygen may be burned in a vessel of hydrogen,
as well as hydrogen may be burned in a vessel of oxygen gas, the
one and the other being equally active in the process, and being related to each other in every way alike. In combustion, as, indeed,
in all cases of combination, no particle of matter becomes lost or
annihilated; it assumes new forms, in general gaseous and invisible
to the eye of popular observation, but easily collected, weighed,
and analyzed by the means that chemistry possesses. The solid
coal or wood which burns to ashes, changes but its external aspect;
mixing with the general mass of air under the form of carbonic acid
gas and watery vapour, its elements become the food of living plants,
which in their turn, cut down or fossilized, form to succeeding ages
the stores of light and warmth such as we now enjoy.
There are but few bodies endowed with so great an affinity for
oxygen as to enter into combustion at ordinary temperatures by
contact with it. If they do combine at ordinary temperatures
with oxygen, the products are not those which combustion would
tend to generate, but a distinct class of substances, containing a
smaller proportion of oxygen combined. Thus nitric oxide gas
combines with oxygen, even when quite cold, forming red fumes
of nitrous acid gas, which is an inferior degree of oxidation.
Phosphorus, when burning at common temperatures, emits but
little light, and forms phosphorous acid; if it be heated, it bursts
into brilliant flame, and forms phosphoric acid, which contains




PRODUCTS OF SLOW  C OMBUSTION.                 179
0ths more oxygen. Potassium combines at common temperature
with oxygen, forming potash; but when heated it burns with flame,
and combines with three times as much oxygen. In the complete
corbustion of organic matters, the products are always water and
carbonic acid. Thus, woody fibre, which is C.H.0O., combines with
20. to form C.0O and H.O.; and alcohol, which is CH110., combines
with 60. to form 2(C.02) and 3(H.O.). But at common temperatures the slow oxidizement of woody fibre produces the black vegetable mould, a form of ulmine, the C.H.O. taking 0. to form C.H.O,.
At common temperatures alcohol becomes acetic acid, the C2H30.
combining with 20. to form CH1120 and H.O. The pyroxylic spirit
at common temperatures becomes, by slow combustion, formic acid,
C2H,40 taking 04 to form C21104 and 2(H.O.).
This slow combustion produces heat, although so much less than
is evolved by the more rapid process that it may easily be overlooked. But if a number of sticks of phosphorus be laid together
and allowed to oxidize, they will warm each other so much as to
melt and burst into vivid flame. The oils and tallow, if there be a
large surface exposed to the air, as when cotton or linen rags im
bibed in oil lie in a heap, combine so rapidly with oxygen as to
form a sort of resin, that by the heat evolved the mass will be set
on fire; and hence the origin of those spontaneous fires, so called,
wvhich consumed the naval arsenal at St. Petersburgh, and, in many
cases, cotton-mills in England. To this cause also may be ascribed
the light which issues from points in the surface of a marsh or bog,
and the luminous appearance which fish assumes when decomposition has just commenced. The energy of this slow combustion
may be much increased by heat applied below the point which produces.rapid action: thus tallow, when heated below redness, burns
with a pale lambent flame, invisible in daylight, but still so marked
that, if it be plunged into a vessel of oxygen, the whole mass bursts
into brilliant combustion, forming then the ultimate products, water and carbonic acid.
On this fact of the increased energy in the process of slow com-'bustion produced by a heat below that at which the body is inflamed, is founded the construction of the lamp without flame, or
the aphlogistic lamp. If a wine-glass be taken, and rinsed inside
with strong alcohol or ether, and then a coil of fine platina wire,
or a ball of spongy platina heated to redness, be suspended in the
middle of the glass, it will remain red until all the alcohol or ether
has been exhausted. The glass becomes filled with a mixture of
air and inflammable vapour, which, by the influence of the heated
platina, is enabled to combine, and form acetic and formic acids.
By this combination heat is evolved, which prevents the cooling of
the wire or ball, and thus, as long as any combustible material remains, the platina is kept ignited. The platina ball or wire may
also be (and in practice generally is) fixed over the wick of a spiritlamp, and the lamp having been ignited, is blown out as soon as the
platina has become red, which then continues to glow until the lamp
has been emptied of the spirit, the latter ascending through the
capillary wick, and forming over its top a little explosive atmosphere, in which the ball of platina is immersed and works.




180  CONSTRUCTION OF THE PLATINA GAS LAMP.
This property of platina appears to depend on the power which
it possesses of attracting to its surface in a condensed form a layer
of particles of whatever gaseous mixture it is immersed in. Hence,
if its surface is in the slightest degree soiled, it ceases to exert this
action; and by increasing the surface, its energy may be augmented
in a remarkable degree. The form in which it is most powerful is
that of the slightly coherent spongy mass, obtained by reducing at
a full red heat the ammonia chloride of platinum; if a ball of the
metal so prepared be plunged into a vessel of oxygen and hydrogen,
mixed in suitable proportions to form water, the gases instantly explode;'for tih oxygen and hydrogen, being absorbed by the spongy
platina, are brought into intimate contact upon its surface, and unite,
evolving so much heat as to raise the temperature of the platina
ball to redness, and thereby inflame the remaining gas. The action
of the spongy platina may be weakened by mixing it with some pipeclay, or using, as in the aphlogistic lamp, the platina in the form- of
plate or wipre. In this way all combustible gases may be caused to
combine gradually' with oxygen, but they require different temperatures, and the action is modified by the presence of other gases
in a manner which is often taken advantage of in gaseous analysis.
The most remarkable application of this property is to procure
instantaneous light by means of the hydrogen gas
lamp. A vessel,f, contains dilute sulph uric acid, into
which the tube of the vessel g Ih dips nearly to the bottom, having attached a piece of ordinary zinc, e. The
vessels being ground air-tight iwhere they fit to one
bigly   c loanother, when the stopcock b is closed, and the acid
a acts on the zinc, the hydrogen evolved cannot escape.
and, pressing on the liquid in f, forces it up into h,
if>    - until the acid falling below the level of the zinc, the
action ceases. To the stopcock b is attached a jet,
c, in front of which is fixed a ball of spongy platina, a,
which, being in the air, has always condensed in its pores a quantity
of oxygen gas; on opening the stop-cock, the hydrogen, issuing
from the jet, strikes upon the platinum, and combining with the oxygen, heats the ball so highly that it inflames the jet of gas, and
thus affords a flame at which any other substance may be lighted.
This lamp has assumed a variety of forms, of which the above is
that which best shows its principle. All bodies possess this property to a slight extent, particularly when hot; but in none is it active enough to be usefully applied, except in platinum.
The temperatures at which bodies enter into rapid combustion
are very various; thus phosphorus inflames at a temperature of
120~ F., and sulphur at 300W F. Phosphuretted hydrogen gas inflames at all ordinary temperatures, while hydrogen requires a dull
red, and carburetted hydrogen a bright red heat before they will
take fire. The inflammability of phosphorus has been shown by
Graham to be affected by the presence of small quantities of various
substances in a very curious manner; thus phosphorus may be sublimed in air saturated with vapour of, oil of turpentine, without any
tendency to combustion, or combination with oxygen, being evinced.
Combustion occurs only at the point where the two substances




CONSTITUTION  OF FLAME.                     181
which enter into union are in contact. Thus, in an ordinary flame,
the true combustion is limited to a thin sheet, the inside of which
is totally dark, and occupied by the combustible material of the
burning body in a state of gas. This is easily shown by holding
over the flame of a candle or a spirit-lamp a piece of wire gauze:
the burning sheet is marked by a ring of light, but the interior is
dark, although full of inflammable vapour, which passes through uninflamed, and may be ignited on the opposite side of the gauze. In
the flame of an ordinary candle, a, four distinct portions may be observed, having totally distinct constitutions; at the base,
of the flame, i i, a pale, blue-coloured light is emitted, for
there the air is in excess, and the combustion is at once e
complete; higher up, from i i to c, the combustible material
is in excess, and the most brilliant light is produced by the
active combination; this portion is surrounded by a sheet  >  2
of much paler and yellower light, e e, which is observable
particularly at the sides of the flame, while the inside of
the flame, b, remains completely black, and is occupied only
by vapour incapable of burning from having no access to
the external air. The light emitted arises also from the
circumstances of the combination; the temperature of flame is in
all cases exceedingly high, although often but little luminous, for
it is found that a current of air hot enough to brilliantly ignite a
solid body, is itself not at all incandescent. Hence, in all cases
where bright light is produced in combustion, one of the bodies engaged must be solid, and the light is really derived from its becoming ignited. Thus hydrogen and suilphur give, in burning, very little
light, because the one is a gas, and the other, when burning, is in
the state of vapour, and the products of combustion are, when formed, in both cases gaseous. Phosphorus, when it, in burning, forms
a volatile body, gives but little light, but when it forms a fixed prodnet, is one of the most brilliant instances of combustion. Iron and
zinc, which form solid oxides, burn with great light, and carbon, although forming a gas, being itself solid, produces light also. In the
case of a candle, the source of light is to be found in the decomposition which the inflammable vapour inside of the flame undergoes
from the high temperature to which it is subjected; one half of its
carbon is deposited in the solid form, forming smoke, and it is this
smoke which, becoming ignited, constitutes the great source of
light. A body which could not form smoke, could not give out
much light in burning. The separation of this carbon (soot) in the
flame may easily be shown by placing over the flame of the candle
a sheet of wire gauze: below the middle of the luminous space the
flame becomes dull, and the carbon, which in burning should have
rendered it brilliant, passes as smoke through the gauze, and may
be inflamed above; when the supply of air is insufficient, this smoke
is not completely burned, and a corresponding quantity of heating
and lighting material is lost; and as it carries off with it a great
quantity of the heat already formed, it actually cools the flame.
When, therefore, a high temperature, or a clear flame without smoke
is required, all the carbon must be consumed. This is effected by
a variety of contrivances: in the burner of the Argand lamp or gas




182            HEATING   EFFECTS  OF  FLAME.
jet, a current of air is established through the centre of the flame,
and thus the combustion of the inflammable vapour much accelerated; in the flame of the blowpipe the same effect is produced by
the current of air from  the bellows or the mouth; and on a large
scale by the numerous ways of burning smoke, so necessary in factories situated in large cities.  In the employment of the blowpipe,
the constitution of the flame is of great importance; for according
as the body to be heated is placed at b, where the
oxygen of the air preponderates, or between a and
-  b, where it is immersed in an atmosphere of' inflammable material, the most opposite effects of violent
oxidation, and of reduction from the state of oxide,
may be —produced.  Thus a glass of copper becomes green at b, and red from a to b; a glass of
manganese is rendered purple at b, but colourless from a to b; there
being few bodies whose relations to the blowpipe can be completely
known without a comparison of the effect of the oxidizing and reducing flames.
During combustion, the heat evolved is at first absorbed by the body which is
then produced; but it is afterward distributed through the mass of all neighbouring bodies in proportion to their conducting powers. It is easy to calculate the
temperature to which the product of the combustion is in the first place raised.
Thus eight parts of oxygen unite with one part of hydrogen by weight to form nine
of water. If watery vapour had the same capacity for heat as water, the temperature of the vapour produced should be, since one part of oxygen heats twenty-nine
parts of water, 180 degrees -9 (29 X 180) —4640 above the freezing point; but the
capacity of watery vapour in equal weight is only 0'847, and therefore it is more easily heated in that proportion than liquid water; hence the temperature really produced is -4640 X0'847, or 5478 above the freezing point of water. If, however, in
place of pure oxygen, atmospheric air had been made use of; then 23'1 parts of
oxygen are mixed therein with 76'9 parts of nitrogen, which must be heated to the
same temperature with the watery vapour, and, of course, at its expense. The capacity of nitrogen gas for heat is 0'2865, one third that of watery vapour; but in
the air which is necessary to form nine parts of water, there are 26'8, or almost
exactly three times as much nitrogen, so that precisely one half of the quantity of
heat produced is absorbed by the nitrogen, and the temperature of the mixture rises
only to 2739~ above the freezing point.
Such being the temperatures produced by hydrogen gas in burning in oxygen and
in atmospheric air, it is easy to understand why we can by its power fuse those
substances which resist almost every other means. The melting point of cast iron
is' 27860, that is, almost exactly the same as that produced by hydrogen burning in
the open air; but the temperature of 5478~, given by hydrogen burning in oxygen,
is very nearly double that, and passes, therefore, far beyond the melting point of
platinum, and exceeds the heat of all our other artificial fires; it is only in the discharge of'th!e galvanic battery, or in the solar rays concentrated by a lens, that the
heating effects of burning hydrogen and oxygen can be equalled. If the nitrogen
had been present in a quantity ten times as great, it would have absorbed - 0- of the
amount of heat evolved, and hence the resulting temperature should be only about
5000. Such a mixture, therefore, could not explode at all, for the first little portion
w hich might be burned could not produce the necessary temperature for communicating the combustion to the mass. In this manner, the combustibility of gaseous
mixtures may be destroyed by mixing them with other gases in such quantities as
may cool them below the temperatures at which explosion can take place. One
volume of a mixture of oxygen and hydrogen- is prevented from exploding by the
presence of nine volumes of' hydrogen, six volumes of nitrogen, one of olefiant gas,
two of ammonia, three of carbonic acid; but with eight volumes of hydrogen, or
five volumes of nitrogen, explosion may occur.
The greater density of solid bodies, and the greater rapidity with
which they are capable of conducting, away the heat which they re




CONSTRUCTION  OF THE  SAFETY-LAMP.  183
ceive, enables them, in a still more remarkable degree, to reduce the
temperature of flame, and, consequently, to extinguish it. Thus, if
a piece of metallic gauze be held over a jet of ignited coal gas, the flame will be arrested at the low-  Mn\
er surface of the gauze; and although the gas and G.
air may pass through, forming an explosive mixture,..:.\\'x:
yet no inflammation can be propagated; and if the
mixture of air and gas be allowed to pass through.
the metallic gauze, and then ignited at its upper
surface, it will burn there; but, although the space
between the jet and gauze be occupied by inflammable material, the flame cannot pass down, the metallic tissue conducting away the heat sw rapidly as to prevent the
temperature from rising to the necessary degree. Another and a
very striking form  of this experiment is to lay on the metallic
gauze a piece of camphor, and to hold it over a lamp; the camphor
will melt and vaporize, but as it melts it will in part filter through
the gauze; this portion takes fire, and a sheet of smoky flame covers the lower surface; but above, the camphor in vapour mixes
with the air without inflaming.
The application of this principle to the construction of the safetylamp for mines, constitutes one of the most beautiful instances of
the advantages which mnay practically flow from what, superficially
considered, might appear a mere abstract principle in science. The
fire-damp, or light carburetted hydrogen, which, issuing from the
minute fissures in the excavations of a coal-mine, is diffused through
the air introduced for the purposes of ventilation, often forms an
explosive mixture, which, being set on fire by accident or negligence, detonates with awful violence, and destroys all living beings
which may at the time be in the mine. This gas is one of the least
easily inflammable, and hence, most fortunately for humanity, one
to which the principle of cooling orifices may be most successfully
applied. The candle or lamp, b, by
which light is to be obtained for work-     
ing in the mine, is surrounded by a cylinder of wire gauze, of about 1500 orifies in the square inch. Inside of this  X
the inflammable mixture may explode,'d'l
but the flame cannot pass out; the com-    l~i:ijii 4?
bustion cannot be communicated to the
general mass of external air, and thus     i:             r
the miner, guided by the never-failing.
indications of his safety-lamp, passes
along through galleries under ground,  
where the emission of a spark would..
cause destruction, and measures, by the
appearance of the lamp, the actual condition of the air he breathes, the phenomena of the flame indicating also its n   "
fitness for respiration. If the air be
pure, the lamp burns clear, as in tilhe
upper air; if some fire-damp be present,




184 QUANTITY OF HEAT  EVOL.VED IN  COMBUSTION.
the lamp shows much less light, the flame becomes red and smoky,
if the noxious impregnation be still increased, the flame of the lamp
itself becomes extinguished, and the cylinder of metallic gauze is
filled by a sheet of lurid flame; the miner being then enveloped by
an atmosphere fully explosive, and even fatal to life if it be long
respired.  If he proceed still farther, all flame is lost; for, as the
fire-damp then predominates, there is produced, from  deficiency of
oxygen, only a slow invisible combustion; but even this is made,
by the sublime genius of its inventor, Davy, to give the miner the
last warning to return to safer regions: a sheet of thin platina, being
coiled up and hung over the wick of the lamp, becomes ignited, as
in the aphlogistic lamp, and continues to emit a faint, but mnost use
ful beacon glow, until an atmosphere is obtained where there is oxygen enough to support a rapid combustion, or until a place is
reached so destitute of oxygen that no combustion whatsoever can
take place.
The determination of the quantity of heat produced' during the
combustion of a given quantity of combustible substance is a problem of great importance in the arts, as on it depends the economic
value of all varieties of fuel. The plan generally followed has been
to burn the substances by means of the smallest quantity of air
which is sufficient, in a vessel surrounded, as far as possible, with
water. If it be found that the burning of a pound of wood heats
37 pounds of water from 32~ to 2 t2~, no idea can be thereby formed
of the quantity of heat evolved; hut if, in another trial, it be found
that the burning of a pound of charcoal raises the temperature of
74 pounds of water through the same range, it follows that the charcoal had double the calorific power of the wood.  True relative
numbers can thus be obtained, although they have independently no
positive signification; The results obtained in this manner have
been exceedingly discordant; but, by the late researches of Des
pretz and of Bull, which appear to have been conducted with more
attention to accuracy than former ones, a very interesting rule has
been obtained: it is, that in all cases of combustion the quantity of
heat evolved is proportional to the quantity of oxygen which enters
into combination.  Thus Despretz found
1 lb, of oxygen, uniting with hydrogen, heats from 32~ to 212~, 29~ lbs. of water.
i"    i'     "       charcoal,      "       "i     29
"-     "      "      alcohol,           "  "       28  "
"t   "(.6     ether,,' "        281- "
This rule, however, must be liable to some very curious changes; for one pound
of oxygen, in combining with iron, could heat, by Despretz's experiments, 53 pounds
of water, or almost exactly twice as much as in the former list, and with tin and
zinc the same double proportion held.  With phosphorus a singular peculiarity
was observed, which, when the subject comes to be more fully studied, may throw
some light upon the former differences. When phosphorus burns slowly, so as to
form phosphorous acid, it heats, in. combining with a pound of oxygen, 28 pounds
of water; but when it burns brilliantly and forms phosphoric acid, the heat evolved
is doubled, and becomes the same as that produced with iron, tin, or zinc. As a
suggestion, I would remark, that in the cases where the smaller proportion of heat
is evolved, the products of combustion are all volatile, and where the larger proportion is produced, the products are fixed and solid; even in the case of phosphorus,
when it combines, producing least heat, it forms a volatile product, but one which
resists a full red heat in the case where the combination has been complete.
Hess has lately pointed out a relation between the amount of chemical action




LAVOISIER  S  THEORY  OF  COMBUSTION.   185
and the quantity of heat evolved, which may, when examined in a greater number
of cases, lead to very important conclusions. He has found that sulphuric acid, in
combining with any base, generates in all cases the same quantity of heat; the rise
of temperature is, of course, greatest when the acid and base are both in an uncombined condition, as where vapour of anhydrous sulphuric acid produces, by contact with dry barytes, brilliant ignition; but, although the barytes generates, by contact with dilute sulphuric acid, much less heat, yet, if the two quantities evolved,
first by mixing the strong acid with water, and then the dilute acid with the base,
be added together, the sum appears, from a great number of experiments, to be
constant; thus, diluting oil of vitriol with water, and neutralizing it, so diluted,
with ammonia, Hess found the heat in each case to be,
With Ammonia. With Water.  Sum.
Oil of vitriol... 5958.....            595'8
First dilution... 5189.. 778... 596'7
Second dilution.. 480 5. 1167... 597.2
Connecting these results with those of Despretz, just given, for the bodies which
unite with oxygen, it would appear likely that the quantity of heat evolved in chemical combination may be connected with the equivalent number and the electrical
condition of the substances by a definite law, which farther investigation may disPlose.
At all periods in the history of chemistry, the explanation of the phenomena of
combustion was that for which the general theory of the science was constructed;
and, accordingly, we find that every period of its progress has been marked by the
views adopted to account for the heat and light so evolved. The coarse and unphilosophical ideas of the existence of inflammability Mwhich prevailed before Lavoisier's time, do not require notice; but the theory which he proposed, although not
now received, is yet, like all his works, of so much interest and importance, that
it would be improper to pass it over.
When Lavoisier lived, the minds of philosophers were fixed in the opinion
that heat and light were positively existing substances, which might enter into
combination, or be disengaged  from combinations in which they had previously
been engaged, just as lead, or oxygen, or any other of the ordinary bodies we operate upon in our experiments. Gases were believed to be compounds of the true
solid body with light and heat; and hence, when oxygen gas combined with iron
or with phosphorus, and assumed the solid form, the light and heat with which the
real oxygen had previously united were set free. Hydrogen and oxygen gases, in
combining to form liquid water, underwent the greatest condensation, and by their
union, therefore, the greatest heat was evolved; and in all such cases where a gas
became a liquid or a solid, this theory was fully competent to explain the facts.
However, in very many cases it failed completely; thus, by the union of carbon
with oxygen, so far from a gas becoming solid and so evolving a heat, a solid becomes a gas, and should produce an equivalent degree of cold. Lavoisier here
brought in to his aid the relative specific heats of the gases before and after union;
thus, if the carbonic acid formed by burning carbon in oxygen gas had a much less
specific heat than oxygen, there might be evolved a quantity of heat in the same
way as it occurs with water and sulphuric acid; but thlis is not the fact; on the
contrary, the carbonic acid has a specific heat greater than that of the oxygen gas
it was formed from, in the proportion of 1195 to 808; and hence, on Lavoisier's
views, an intense degree of cold should be produced in the combustion of charcoal,
as well by the latent heat which the solid should absorb in becoming gaseous, as by
the increased specific heat of the gas so formed. This example is sufficient to
show the way in which Lavoisier's theory became inapplicable to the wants of
science.
Dr. Thompson has recently endeavoured to account for the heat evolved in chemical combination by an application of the law of Dulong regarding specific heats
(described page 66). Every molecule of a simple body being supposed provided
with the same quantity of heat, he suggests that, when a number of them combine
together, the heat of one or more is expelled, and thus produces the rise of tem.
perature. Thus, considerinlg oil of vitriol to contain seven combining equivalents,
two of hydrogen, four of oxygen, and one of sulphur, and that the specific heat of
all of these is the same, 3'1, as results from Dulong's law if it be supposed rigidly
311X7
exact, the specific heat of oil of vitriol should be  -1 04,42, 49'1 being tho
49'1




186  HEAT  OF  COM~IBINAT1ON7 WHENCE  DERIVED.
equivalent number of oil of vitriol; but the specific heat found by experiment is
only 0'352; so that exactly one fifth of the total quantity of heat has been lost by
the act of combination, and may hence be supposed to have caused the phenomena
of combustion.
In the extension of this principle a little farther than Dr. Thompson appears to
have contemplated its application, some coincidences, with results already known,
are found, which give it an aspect of considerable theoretic interest. Thus we
may consider certain metallic oxides as consisting of an equivalent of' each constituent, and hence their proper specific heat should be, if none were lost by combination, 3 1 X 2-_62; but the specific heat of the compound molecule is experimentally
found to be 54, and thus that 0-8 of heat had been lost, producing the phenomena
of combustion in combination. In this manner we can understand why Despretz
found that a certain quantity of oxygen evolves the same quantity of heat in combining with very many bodies. If we examine the sulphates noticed, p. 67, in relation to the same principle, we find that as there are in each six molecules, the
specific heat should be 186 —3-1 X6; but it is found to be but two thirds of that,
12"4. Now if here, as in the oxides, the combustible material retains its heat, and
it is from the oxygen that the portion set free is taken, the experimental result
arises from the heat of each oxygen molecule being reduced by 1-6, and hence that
when oxygen forms a salt with sulphur and a metal, the heat evolved is double that
produced in simple oxidation. The fact of the same quantity of oxygen giving
double the amount of heat when it converts phosphorus into phosphoric acid, compared with what is evolved when it forms only phosphorous acid, may have its ori
gin in an analogous condition.
In the case of the carbonates, another form of the principle becomes manifest;
but on this view it is necessary to consider carbonic acid as containing five molecules, one of carbon and four of oxygen, and as uniting with two molecules of a
metallic oxide. The carbon and metal burn each in half of the quantity of oxygen
with which they ultimately unite, and, like phosphorus, separate from that oxygen
only the smaller quantity which it can lose when entering into combination; the
carbonic acid and suboxide then unite with the residue of oxygen, and from it
separate the larger portion of heat as occurs when phosphoric acid is produced.
The resulting specific heat for a carbonate is therefore 93+609+5-=20.7,; or, reduced to the equivalent number used in p. 67, it is 10'35, the experimental number
being 10-4.
The results in these three cases may be shown in the form of the following table,
in which the first column contains the equivalent molecule of the body, M. denoting
the equivalent of a metal; the second column contains the specific heats calculated
on the supposition that there is none lost in combining; the third, the calculation
by which the fourth column of true calculated specific heats is obtained; and the
fifth, the specific heats that have been found by experiment.
1.   2.            3.             4.  5.
MI. O.   6 2      3.1 —2.3            5.4 5-4
M. 04S. 18-6   (2X3 1) —(4 X 15)    12 2 124
MA/206c  27 9 (3 x 31)+(3 X 2'3)+3 x 1'5)120.7 20-8
The coincidences refer only to the bodies already selected, p. 67, as exanl
ples of simplicity in the relation of their specific heats, and certainly do not exist in
a great number of other cases in which I have sought for them; they may therefore be accidental; but there is yet so much likelihood of some physical law of the
kind being to be discovered, that everything that may assist in its detection is of
importance.
Laying aside altogether the attempt at deducing the phenomena of combustion
from any change in the amount of latent or of specific heat in the bodies which
enter into combination, it remains only to be admitted as a general and independent
principle that chemical combination is a source of heat and light. It is, however,
impossible to arrest inquiry at that point, and, accordingly, the speculations of philosophers have been directed in seeking a cause for the phenomena of combustion to the disengagement of electricity, which accompanies all manifestations of
chemical action, and have endeavoured to identify the light and heat emanating
from a burning body with that which is produced by the separation or combination
of the electric fluids. The evidence in favour of this view will be best described
among the relations of electricity to affinity.




INFLUENCE  OF ELECTRICITY  ON  AFFINITY. 187
CHAPTER VIII.
OF THE INlFLUENCE OF ELECTRICITY ON CHEMICAL AFFINITY.
IT has been already shown, that in the production of galvanic or
hydro-electric currents, there always occurs between the liquid and
solid elements of the circle a degree of chemical action, to which
the quantity of electricity generated is exactly proportional in
amount, and that no current, such as was there described, can be generated without, by the chemical action of the more oxidizable metal, the liquid being decomposed, and some one element of it expelled, in place of which a corresponding quantity of zinc may be substituted. I did not then attempt to discuss the question of whether
the chemical action in the battery be the cause or the effect of the
current of electricity which arises, as that can be best done when
the action of the current, no matter from what source it may have
been derived, upon chemical substances, similar to those that are
used as exciting liquids in the galvanic battery, has been described.
If the wires belonging to the plates Z C, of the simple circuit in
the figure, be brought into communication by means
of a cup of water, the current passes, and it is found    X - 
that at the terminations of the wires bubbles of gas
form in considerable number, which, when collected,
are found to be, from the wire in connexion with the
copper plate, oxygen gas, and hydrogen gas from
the wire which is attached to the plate of zinc. If
the conducting liquid had been muriatic acid, hydrogen would have been evolved as gas at the zinc extremity, and chlorine liberated upon the wire of the copper plate, though from its
solubility in the liquid it would not be disengaged as gas.
If a solution of iodide of potassium had been employed, iodine
would appear upon the copper side, and potassium should be set
free upon the zinc wire; but by the action of the water, the metal
is instantly converted into potash, and hydrogen set free.
It is not necessary that such bodies should be in solution, for this
only serves to give to their particles the freedom of motion, which
may allow their elements to separate. If chloride of lead melted in
a cup be used to complete the voltaic circuit, chlorine is evolved
upon the +, and lead upon the - wire; with oxide of lead (litharge),
the evolution of lead at the -, and of oxygen upon the + extremity of the wires, occurs similarly; protochloride of tin, iodide of
lead, chloride of silver, all act in the same way.
In place of bodies consisting of two elements, such as those above
described, we may employ in solution, or in a fused state, secondary
compounds, consisting of an acid and a base. If the current of electricity pass through a solution of sulphate of soda, the sulphuric
acid appears upon the +, and the alkali upon the -  wire. With
sulphate of magnesia, the earth passes to the negative, and the acid
to the positive extremity of the liquid circuit; in these cases water




188 CIE MIC AL AFF IN ITY ELECTRICAL AT TRAC TION.
is also decomposed, of which the hydrogen accompanies the base,
and the oxygen the acid; but, on using a salt of lead, of silver, or
of copper, the metallic oxide is reduced by the action of the nascent
hydrogen, or, at least, it may be so expressed, and the metal is deposited in crystals upon the - wire, while the acid and the oxygen
are evolved together upon the extremity of the positive conductor.
The affinity which held together these bodies in combination is
superseded during the passage of the electric current. The elements
previously united appear to repel each other, and to be at the same
time attracted by the excited terminations of the metallic wires, by
which the battery is placed in connexion with the substance to be
decomposed.
The simplest mode of accounting for these phenomena is to say
that water is decomposed, because the oxygen is attracted more
powerfully by the positive pole of the galvanic battery than by the
hydrogen with which it had previously been associated, while this
last. is more powerfully attracted by the negative pole than by the oxygen. The elementary bodies separate, therefore, from each other;
but, not being capable of entering into combination with the substance
of the poles, they are evolved as gas. This explanation may be applied to all such cases. Oxygen, chlorine, iodine, sulphur, as well
as the various acids, are attracted by the positively electric pole,
while hydrogen, potassium, sodium, copper, silver, lead, and the
various bases, are attracted to the negative pole of the battery. But
one force cannot completely supersede another, as electricity here
supersedes affinity, unless it be of the same kind, or, at least, closely
resembling it in nature. What, then, is the relation between the
chemical force which had kept the elements united, and the electrical force which makes them  separate l The cause was easily
found: they are. identical. The oxygen and hydrogen united originally from being in opposite electrical states, and they are forced
to separate from being subjected to the action of still more powerful attractions; the decomposition of water by the voltaic current
becoming thus a case of double decomposition, in which the original
electricities of the two simple bodies were the quiescent, and the
excitation of the opposite poles of the battery were the divellent
forces.
Chemical substances were thus considered to have affinities for
each other, from being in opposite electric states, and the peculiar
play of affinity of each body depended on which electricity it was
naturally excited by when in combination; those bodies which are
attracted by the positive pole of the battery being necessarily in the
negative condition, and vice versa. Thus, all substances may be divided into two classes, those being termed electro-negative which
are evolved at the copper pole of a simple, or at the zinc pole of a
compound circle, and those which appear at the opposite pole being
termed electro-positive. The simple bodies thus classified are ranged as in the following list:




ELECTRO-C H EMI C A L  CLASSIFICATION.    189
Electro-negative.,            Electro-posllive.
Oxygen.      Mercury.       Palladium.   Potassium.
Fluorine.    Chrome.      A Silver.      Sodium.
Chlorine.    Vanadium.    Copper         Lithium.
Bromine.    Iridium.   X  Lead.          Barium.
Iodine.      Rhodium.       Tin.         Strontium.
Sulphur.     Uranium.       Bismuth.     Calcium.
Selenium.    Osmiumn.       Cobalt.      Magnesium.
Tellurium.   Platinumn.     Nickel.       Glucinum.
Nitrogen.    Titanium.      Iron.        Yttrium.
Phosphorus.  Gold.         iManganese. I Thoriunm.
Arsenic.     Molybdenum.  Cadmium.   Aluminum.
Antimony.   Tungsten.       Zinc.         Zirconium.
Silicon.     Columbium.   Hydrogen.   Lanthanum.
Boron.                      Carbon.      Cerium.
Tht most powerfully negative bodies are placed in the first, and
those most powerfully positive in the fourth column, these being
connected by the intermediate columns in the order marked by the'
brackets and arrows. Any substance in the list is positive with regard to any other towards which the arrow points, and negative in
relation to any from which the arrow  is directed.  Thus hydrogen
is negative to all in the fourth, but positive to all in the three preceding columns, and so on. These positions should also indicate
the relative affinities of the simple bodies towards each other; but,
in interpreting such arrangements, it must be recollected that the
order of affinities may be totally changed by heat or by cohesion,
and that the electrical order may be completely different, according
to the nature of the exciting liquid, as in the table, p. 129.
Two bodies in combination are therefore like two pith balls which
mutually adhere, but of which the attraction is permanent from their
electricities not being discharged. How do these bodies acquire
those oppositely excited states l and why, if their condition resembles that of ordinary electricity, do they remain combined, when
their opposite fluids might unite, and neutralization being produced,
all combination cease 
These two questions have not yet been answered. Several times their explana
tion has been attempted; and thus the electro-chemnical theories of Davy, Ampere,
and Berzelius have been proposed. I shall briefly notice the leading features of
these before proceeding to discuss tgc remarkable advance recently made in our
ideas of the electro-chemical relations of bodies by Faraday and Graham.
The theory of Davy was based upon the principle that bodies in their ordinary
uncombined condition do not contain free electricity, but that by contact they become excited. Thus a disk of sulphur touched to a disk of copper becomes negative, and the copper positive; its charge increases in intensity on applying heat,
until, at a certain temperature, the tension of the electricities becomes so great that
they suddenly recombine, carrying with them the molecules of the sulphur and copper which thus enter into union, and producing the evolution of light and heat by
which the chemical action is accompanied. The sulphuret of copper, when formed,
is no longer electric; it remains permanent in virtue of a force which Davy does
not strictly define, but which he appears to have considered an intimate cohesion
between the particles which had been closely approximated by their electrical attractions; and when, by an electric current, the molecules of copper and sulphur are
brought into the reverse state to that which favoured their combination, they separate. This view supposes, therefore, the electrical excitation to be only moment
ary, during the act of combination and during the moment of disunion; before and
after, all is neutral. To all phenomena of decomposition this theory suffices. but
it is vitally deficient in the principle upon which it is basecd. It has been since




1.90  THE OR. I ES OF DAVY  AMPERE  AND BERZEL I US.
completely proved that it is not the contact which evolves electricity, but the
chemical action; and( also, on Davy's views, the electrical disturbance only suffices to account for the secondary phenomena of union, the light and heat, leaving
the act of combination to be ascribed to a different and independent force of affinity or cohesion.
A more complete theory was proposed by Ampere, whose philosophical views in
magnetism and other sciences have been found so singularly in accordance with
experiment.. He proposed to consider that each substance in nature is endowed
with a definite amount of one or of the other electricity, and is thus naturally and
invariably electro-positive or electro-negative, and stands higher or lower in the
list of bodies, according to the intensity of the charge. Such an excited body he
considered to attract round its mass an atmosphere of electricity of the opposite
kind, and corresponding in intensity.  Now, on bringing into contact an electropositive and an electro-negative body, their atmospheres unite, and produce the heat
and light resulting from their chemical action on each other; but the bodies themselves must remain permanently combined, as each retains its own excitement,
and they hence attract without cessation. When one body is exactly as negative
as the other is positive, the resulting compound cannot manifest any signs of electro-chemical activity; but if the charge of the negative body be more powerful than
that of the positive element, the resulting compound will be negatively excited to
the amount of the difference between the two; if the I)roportions be reversed, the
new body formed will be positive in the same degree; and such compound electronegative and electro-positive bodies, being acids and bases, attract each other, and
unite to form neutral salts.
All that was difficult to comprehend upon the theory of DIvy is here beautifully
explained. The light and heat of combination are produced by the atmospheres
of electricity; the permanence of combination by the invariable excitation of the
molecules. The gradually diminishing intensity of charge, according as the bodies
formed become more complex, necessarily follows; but the assumption that any
one body is naturallyand invariably positive or negative, is contradicted by the
history of almost all the simple substances.
Thus, if sulphur or arsenic be heated in oxygen gas, they burn, and the combination is effected with all the phenomena of intense action, the resulting compounds
being acid and electro-negative.  The sulphur and arsenic are thus shown to have
been feebly positive bodies. But if sulphur or arsenic be heated with potassium,
there is similarly combustion, showing that chemical combination has taken place;
and as potassium is the most positive body in the series, the sulphur and arsenic:
must be the negative elements of the compounds. Sulphur and arsenic are therefore at one time positive, and at another negative. There is, indeed, no substance
known which, can be said to be invariably negative or positive. Nor can the
amount of negative or positive excitement be in any case looked lupon as constant,
for oxygen is often found to be less negative than chlorine, and potassiumn to be
less positive than iron or than carbon; -and hence, if electrical forces be considered
as representing affinitary power, they must be capable of the same fluctuations in
intensity.
It was for the purpose of bringing Ampere's theory into harmony with the
changes of chemical decomposition, that Berzelius proposed the modification of it
which now remains to be described. Hie suggested that each body should be
looked upon as containing the two electricities, but that the one might be more
powerfully developed than the other, as in a magnet one pole may be stronger than
the other; also, from the analogy of certain bodies, which were supposed to admit
the passage of one electricity rather than the other, he imagined that a body thus
excited with the two fluids might discharge the one and yet retain the other. Thus
oxygen possesses high negative and feeble positive excitation; hydrogen an intense
positive, bhut a feeble negative charge. When these bodies combine, the phenomena
of combustion follow from the union of the positive fluid of the oxygen with the
negative of the hydrogen, and the more intense and more permanent charges retain
the bodies in combination. To account in this way for certain bodies being at one
time electro-negative and at another electro-positive, Berzelius considers that, Xwhen
potassium is brought into contact with sulphur, the naturally feeble negativity of
the latter is heightened by induction, while, if the sulphur be acted on by oxygen, it
is its positive charge that is increased; and thus any substance near the middle of
the electro-chemical series may become positive or negative, according as it combines with a body situated nearer to the negative or positive extremity.




DISE NGAGEM ENT OCCURS AT LIMITING  SURFACES. 191
This view might explain most chemical phenomena; but it is, like Davy's theory,
founded on physical principles which cannot be considered sound. Thus, although
the effect of one pole of a magnet may be weaker than another, that only happens
where the action is complicated by the existence of more poles than two; and in all
cases the amount of north and south magnetism present is exactly equal. Also, the
fact of the existence of bodies which conduct the one better than the other electricity,
is now abandoned by all sound reasoners, and cannot be looked upon as even in any
degree probable in theory. Indeed, all views'like those of Berzelius and Ampere,
which are founded on the existence of' different degrees of electrical excitement,
which represent the different powers of affinity by which chemical substances corn.
bine, must be now abandoned; Ibr it has been proved by Faraday that a molecule of
oxygen, in uniting with hydrogen to form water, or with zinc to form its oxide, a
molecule of iodine or chlorine uniting with lead, with tin, with silver, or with potassium, bodies so far separated in the electro-chemical scale founded on their reactions,
evolve in uniting the same quantity of electricity, and require for their separation,
when combined, the same amount of current derived from another source.
Before more definite and correct ideas of the electrical relations
of chemical substances can be obtained, it is necessary to study
somewhat more in detail the chemical phenomena which occur in
the galvanic battery, which, for simplicity, shall be considered as a
simple circle, and in the liquid through which the circuit is completed; the former is generally termed the generating, and the latter
the decomposing cell.
The decompositions hitherto described have been considered as
resulting from the attractive and repulsive forces of the extremities
of the wires, on which the charge of the battery was supposed to be
collected.  But, when the circuit is completed, no such accumulation can exist; once the current passes, it is everywhere present
in equal quantity and of uniform tension; and such forces of attraction and repulsion, acting upon molecules already electrically excited, were only imagined for the foundation of the imperfect theories
already noticed, and, when impartially exami-ned, are found to have
no real existence.  It is also fatal to the idea of attractive forces exercised by the poles, that the substances evolved upon their surface
do not necessarily combine Gwith them; thus, if one platina pole have
such attraction for oxygen as to separate from the hydrogen it had
been united with, it is unreasonable that it should lose, suddenly and
completely, this power, and allow the oxygen totally to escape; the
other platina pole behaving similarly to the hydrogen.
Faraday has definitely shown that the disengagement of the substances, which are separated from each other by the current, takes
place in all cases at the bounding surfaces of the body decomposed;
and that where they are evolved on the metallic
conducting wires, it is only because those are the
limits of the decomposing fluid.  The proofs of
this principle are numerous and simple: thus, in
a glass basin, a partition of mica, a, is cemented so      L
as to be completely water tight, and extending half
way to the bottom; a strong solution of sulphate
of magnesia is poured in until it rises a little above
the edge of the partition, and then distilled water
poured in on the side c, d, with such precaution
that it shall not mix with the saline solution, but
shall float on it, the surface separating the two
liquids remaining perfect at c.  The solution of sulphate of magne




192     ELEAMENTS NOT EVOLVED ON  POLES.
sia is now to be connected with the negative pole of a battery by
means of the platina plate b, and the water with the other pole. of
the battery by the plate e, which dips slightly inclined below the
surface.  When the circuit is completed, the sulphate of magnesia
and the water are simultaneously decomposed, the oxygen appears
upon the plate b, the hydrogen gas upon the plate e; but, although
the sulphuric acid is liberated freely upon Ihe plate b, no magnesia
travels farther than the limiting surface of the saline liquor c. Here
the metal e serves as a pole to the hydrogen, but not to the magnesia; and the water on which the magnesia has evolved has no power
to prevent the farther passage of the hydrogen.
If A, C, B be filled with solution of sulphate of soda, and by means
of the plates P and N, a current from a battery
_ _ a      _=be passed through it, the acid will collect upon
the one and the alkali upon the other plate:
AjN  IP   1  but if, by means of pieces of bladder, a and b,
the vessel be divided into three compartments
-    A, C, and B, and the central one being filled
with a solution of sulphate of soda, dilute. nitric acid is poured
into those at the side in order to afford a conducting medium,
the acid and alkali do not appear at the metallic poles when the current passes, but are evolved upon the inner surfaces of the partitions
a and b: it is only when, by mechanical filtration, some of the liquor
of C passes into A and B, that the slightest trace of sulphuric acid
or of soda can be found upon the metallic plates.
By the electricity of the machine the same principle can be demonstrated: if a slip of paper moistened with solution of iodide of
potassium. be held near the insulated prime conductor of the electrical machine while iii action, and the rubber be connected with the
ground so as to ensure a continuous discharge of positive electricity
into the air, iodine will be evolved in quantity upon the point of the
gaper nearest tne prime conductor, while hydrogen and potash may
)e traced as tar an any liquid conductor admitting of th,.ir passage
goes. Here ihere is nothing that can be termed a pole; the iodine
is discharged upou the limiting surface, which is here that of the
atmospheric air.
Hence the idea of poles which produce attractions and repulsions
in a closed circuit must be abandoned, and some other Way of explaining The decomposition of the liquid elements of the circuit must
be obtained. The word poles must first be laid aside, and the expressions proposed by Faraday in their place deserve universal adoption.  The surfaces, whether of metal, of water, of acid, or of air,
by which the current passes from one kind of conductor to another,
he terms electrodes (1l8eIC-xpov, odoc), they being the routes through
which the electricity makes its way. I shall therefore, in future,
speak of the positive and negative electrodes in relation to the surfaces, generally of metal, by which the battery is brought to act upon
the substance which is to be decomposed.
Since there are thus no attractive forces by which the chemical
affinities of the substances in the decomposing cell can be overcome,
to whlat mechanism  can we attribute the separation of elements
which occurs 1 Concerning this, as yet, there is only speculation to




E LECT R O-CHEMICAL DECO MPO SITION.   193
be presented. The decomposition is certainly propagated from
particle to particle, that is to say, at the moment that the molecule
of water loses oxygen at the positive electrode, a different molecule gives off its hydrogen upon the negative electrode; neither
the hydrogen of the former nor the oxygen of the latter become
free, but the decomposition is transferred from one particle to another along the line, all particles of oxygen advancing a step against
the current, and the molecules of hydrogen moving in a corresponding manner in the direction of it. Thus, if a line of particles of
water in a decomposing cell be represented 
before the current passes, the electrodes be- +0.11.O.1.  O.H.5ing represented by the plus and minus signs,
on the current passing, a molecule of oxygen
will be evolved upon the positive, and one of — I. H. H.+
hydrogen upon the negative side, as in the. H.
second line; and as this motion is participated
in by every molecule of oxygen and hydrogen   + O.H. O.H.in the circuit, they will come into the final position of the third line. The current still pass-    O
ing, another molecule of each will be evolv-  - e.       0. +
ed, as in the fourth; and, ultimately, all the
intervening water may be decomposed; the
it                                      + O.H. —
separation of the elements being thus accompanied by a continual rotation on each other of the intermediate
molecules, each molecule of oxygen being successively united with
every molecule of hydrogen in the series, and each molecule of hydrogen combining in turn with every particle of oxygen as it passes
along. In Faraday's words, the current is an axis of power, equal,
and exerted in opposite directions, by which, in every case of a
true binary compound, the molecules of one element are carried in
one direction, while those of the other constituent move in the reverse course.
From this idea, the evolution of the iodine, the soda, the magnesia on surfaces of air, of bladder, or of water, is easily understood.
The sulphates of magnesia and soda are decomposed, because there
exists in the solution a chain of particles of sulphuric acid capable
of conveying their bases along, and thlese are evolved where that
chain of acid particles is broken, although there may be other conductors to complete the circuit.  The iodine is evolved where the
air touches the surface of the paper, because the air has no potassium by which it could be carried farther.  The decomposition appears thus to be effected, not by annulling chemical affinity, but
with its assistance, for it is exactly with those conducting bodies
whose elements have the strongest affinities for each other that decomposition is most easily effected. Thus iodide of potassium is
decomposed much more easily than iodide of lead, yet the affinity
of potassium for iodine is certainly greater than that of lead for the
same element.
It is in this manner that arise the remarkable phenomena of transfer observed first
by Humphrey Davy.
If a solution of sulphate of soda be placed in the glass a, dilute sulphuric acid in
the glass b, and water in the glass c, and they be connected together with slips of
amianthus, moistened to allow the passage of the current, and the positive electrode
B B




194-      ELECTROLYSIS AND  ELECTROLYTES.
of a battery be immersed in a, and the negahit                  il;,   /  tive in c, the sulphate of soda will be decomposed, and its alkali will appear in c, although
the acid in b, through which it must have
a   _' bad         ca_      passed, retains all its power. Here, then, was
~ the affinity of the acid in b for soda completely annulled by the superior attraction of the
negatively electric pole in c, and this was considered to be farther proved by the
acid preventing the passage of barytes, for which its affinity was so much stronger 
when a contained nitrate of barytes, the earth, on entering into b, combined with
the sulphvric acid, and went no farther. But in these experiments, considered at
the time so decidedly in favour of Davy's theory, that which was believed to be the
obstacle,o the passage of the soda is in reality the cause of it. Had there been no
acid in bd, no alkali could have passed across it, and the barytes remained combined.
only because, becoming insoluble, it no longer formed any portion of the liquid-conducting medium.
It has been, indeed, found, that although a feeble current may
be transmitted through liquid conductors without any sign of de
composition, yet, in general, the passage of a more powerful current can only be accomplished by means of bodies which are at the
same time decomposed by its influence. Faraday proposes to term
the decomposition by the current electrolysis [y2etC-rpov, XvW], and
such bodies as undergo electrolysis electrolytes.  It is, therefore,
only electrolytes that are capable of conducting, and they do so by
the opposite directions in which the chains of liberated particles
move. That electrolysis may occur, it is necessary that the substance be in the liquid state, and hence all conducting power is lost
when the body becomes solid; ice is a non-conductor, and it is only
by being melted that the chlorides and iodides of lead and silver,
and sulch bodies, become capable of conduction, and of being hence
decomposed. But there are many bodies which insulate when cold,
and yet, when heated, allow the current to pass even before they
fuse, its passage being unattended by any electrolysis, even though
the current be very powerful. Sulphuret of silver, iodide and chloride of mercury, and fluoride of lead, are remarkable examples of
this anomaly.
Faraday, considering that the words electro-positive and electronegative involve too much those ideas of attractive and repulsive
forces emanating from the poles, which have been proved to be incorrect, proposed some changes of nomenclature, which, if not
adopted, deserve to be at least described. If we consider a voltaic
battery lying on the ground, with the positive end to the east, and
the wire connecting the ends bent into an arch, similar to that
which the sun describes in his daily rotation, the current will flow
up from the point of the sun's rising, and pass down into the battery
opposite the point at which he sets. If the wire be now interrupted by a decomposing cell, the surface at which the current enters
the liquid may be termed the anode (ava, upward), and the other the
cathode (Ica-rd, downward); oxygen, chlorine, and such bodies are
evolved upon the surface of the anode, wvhle from the cathode hydrogen and the metals are liberated. The elements which, by their
combination, form electrolytes, Faraday proposes to term ions, IytLt,
and to distinguish them into anions which pass to the anode, and
cations which pass to the cathode. Electro-negative bodies are
therefore anions, and electro-positive substances are cations in Far



THE  CHEMIICAL VOLTAMETER.                      195
aday's nomenclature.  These names are shorter, and involve less
theory than the older terms, and hence deserve adoption.
The most important principle that has been as yet discovered,
connecting the agencies of electricity and affinity, is the law of definite electro-chemical decomposition.  If the same current of electricity pass through a series of electrolytes, it will decompose a
quantity of each which is proportional to its chemical equivalent.
Thus, at the same time and by the same force, there are obtained
8 grains of Oxygen and  I of Hydrogen from  9 parts of water.
35'4   "   Chlorine and  1 "Hydrogen "  36-4  "  muriatic acid.
354-  "   Chlorine and 108' " Silver    "143'4  "  chloride of silver.
126-3   "   Iodine and  103-6 " Lead  " 2299  "  iodide of lead.
The principle of definite electro-chemical action may be applied
to measure the quantity of electricity which is circulating in the
current, for by collecting the substances evolved in the decomposing
cell, we may obtain a standard to which all other effects may be reduced.  In such case the decomposing cell becomes a voltanmeter, or
measurer of voltaic electricity.  One    3
of its most convenient forms consists
in a conical vessel, A, terminated by a
tube, B, in the neck of which are soldered the platina electrodes in connexion with the battery; the vessel and                           C
tube being filled with water, which is A, 
rendered easily decomposible by the  
addition of sulphuric acid, the circuit
is completed; a quantity of oxygen and hydrogen, proportional to
the amount of electricity which passes, is evolved, and, issuing from
the aperture at C, may be collected in an inverted glass and measured.  A variety of other forms, not differing in principle, have been
proposed and are in use.
If the absolute identity of electrical and chemical agency be insisted on, then, in all electrolytes, the elements must be held together by the same force, since they require the same amount of electricity to produce decomposition; and we should return nearly to
the principles of Berthollet, that chemical affinity was equally powerful for all bodies, and merely appeared to vary from external influences; but this would be a rash and unphilosophical conclusion;
the electrolytes are but one class of chemical bodies, those which
are primary compounds, of an equivalent of each element; the current does not act upon dentoxides or bichlorides, and on double
salts its agency is exceedingly complicated. All that can be inferred from this very beautiful result is, that the elements of bodies
combine, in separating from each other under the influence of a current,, all with the same quantity of' electricity, and that, as the specific heats of the ultimate particles of bodies have been already
found to bear a simple relation to each other, the specific electricities may follow an equally, or still more simple law.
Having thus examined the important phenomena produced in the
decomposing cell, the current being considered as originating in
any sufficient source, we shall pass to the discussion of what occurs in the gemnerating cell, where the current which passes through




196     ACTION IN  THE GENERA'TING CELL.
the other is evolved by the mutual action of the liquid and solid
elements of the voltaic battery.
For the generation of the current, it has been already shown to
be necessary that the liquid excitant should be an electrolyte, and
that the solid elements should occupy positions in the electrochemical scale as remote as possible from each other in relation to
the liquid which is employed. That the solid elements also should
be conductors, by which the selection is limited to the metals and
to some forms of carbon. Now, when a slip of zinc is immersed in
an electrolyte, which we shall, for simplicity, consider for the future
to be muriatic acid, the particles of the acid are brought
-Z    into a state of excitation, the molecules of hydrogen be-. coming positively excited, and those of chlorine becoming negative. This condition has been already described
(page 132) as being that of the acid particles; but it is
now necessary to indicate more nearly the immediate
manner in which it is produced. The mass of zinc itself, which
we before considered as having, like a magnet, its positive excitation referrible to one, and its negative to the other extremity, must
also, like the magnet, be looked upon as consisting of a great number of excited elements, each of which has its positive and negative extremities; or, for greater definiteness, they may be considered as grouped in pairs, of which one molecule is positively and
the other negatively excited. The condition of the slip of zinc of
the last figure may therefore be represented as in the figure at the
A             side, the particles of zinc being conq.~~iq3E  ~~~oo         tained in the shaded bar, and those,+.AU~C2Kt}of the liquid, consisting of chlorine
Zn. Zn. Zn. Zn. C1. H. Cl. H. and hydrogen, represented outside
of it. The terminal particle of zinc becoming positive, and the
nearest particle of chlorine becoming negative, there would result
immediate union if no other action interfered; but the chlorine is.
held back by the positive molecule of hydrogen with which it is
united, and so the action continues balanced, no matter how far the
series may extend on either side. If. now, the plate of copper be
introduced so yq;.o complete the circuit, and to allow the passage of
the galvan:.arrent, it is easy to see how the decomposition of the
exciting nuid follows; for although, in the arrangement above described, the inductive excitement is most active at A, and diminish
es from thence as it extends along the zinc upon the one hand, and
through the fluid upon the other, yet when, as in
the figure, the circuit is completed, the action becomes equally powerful all through; the particles
of copper assume a condition similar to those of
the zinc, but in the reverse order, the molecule
next the acid being negative, and that becoming
positive which is in contact with the zinc, and hence
a complete chain of inductively polarized particles
B- 4\'5 kbeing established, precisely such as are represented
by cuttings of silk thread which convey a current
from an electric machine throulgh oil of turpentine; the molecular
arrangement being represented in the following figure. Such be



ORIGIN  OF TIHE GALVANIC CURRENT.    197
ing the position of the mutually-excited
molecules, the electricities of the particles
of zinc and chlorine nearest to each other
combine, and their neutralization is follow- Zn             u.
ed by that of the entire chain; the adjacent    /
particles of zinc and
chlorine then  unite,
Zinc E         Cop. and the hydrogen, dis-       A d
i;    ellnnaoed  is  thrown    Acid.
upon the second particle of chlorine, its hydrogen upon the third chlorine molecule, by
which the hydrogen it had previously been
d united with, being thrown off, is emitted under
Acid.
the form of gas.
The three distinct stages in this reaction are, therefore, 1st, The
mutual excitation, by inductive polarization of the zinc and muriatic
acid.  This is the fundamental fact due to the chemical relations of
these bodies. 2d, The completion of the chain of inductively polarized particles, by the intervention of the copper plate and connecting wire. 3d, The passage of the current, and the consequent decomposition of the liquid electrolyte in the cell, the chlorine being
evolved upon the zinc, with which it enters into combination, and
the hydrogen being eliminated upon the surface of the copper plate.
The- source of the current is therefore not to be found in the decomposition of the acid, for it precedes it; but the quantity of chemical action in the generating cell is proportional to the quantity of
electricity which passes, for it is produced entirely by its agency.
There is, therefore, no difference in reality between the generating
and the decomposing cell; the action in each is equally produced
by the passage of the electric current; but in the generating cell,
one element at least, the chlorine, is absorbed by the electrode (the
zinc) on which it is evolved, and the amount of obstacle presented
to the passage of the current is proportionally less.
Such is the theory of galvanism which I believe to be most consistent with all the results hitherto obtained. The current cannot
have its origin in the contact of solid bodies, for it remains the same,
no matter how much the circumstances of contact may be changed;
and by every alteration of the conditions of chemical action, it varies in direction and in power, although the relations of the solid
bodies which are in contact are not affected. Neither does the current arise from the transfer of elements which occurs in the generating cell, for, on the contrary, the transfer of elements results from
the passage of the current, indicating its direction and measuring
its amount; but the current arises fromn the continuous restoration
through the copper, or positive element, of the excitation produced
by the tendency of the zinc to combine with the chlorine of, the muriatic acid. In fact, although I have hitherto considered the zinc as
only influencing the acid by means of a disposition to unite with one
of its constituents, yet such expressions, being rather abstract and
indefinite, may in the present case be laid aside. The zinc does,
on immersion, decompose a certain quantity of acid, of which the
hydrogen is evolved in the form of gas, constituting upon the sur



198  COMPOUND  BODIES FOR MED  BY  T II E  CURRENT.
face of the zinc an exceedingly thin layer. The chlorine is then in
a state of combination, which is not without analogy in other cases;
that is, in presence of two substances for which its affinity is equally intense, it is disposed to unite with either, according as external
forces intervene, and is determined to the zinc by the establishment
of the current.
The proofs that hydrogen must be thus nascently liberated upon
the surface of the zinc are to be found in a phenomenon already
noticed under the head of affinity-the precipitation of one metal
from  its salts by means of another having, a greater affinity for oxygen than it. If we immerse in a solution of sulphate of copper a
slip of pure zinc, there is instantly a deposition of copper, which
we must ascribe to the superior affinity of zinc for oxygen and sulphuric acid; but when the zinc has become thus sheathed in metallic copper, the decomposition would cease, by the access of the acid
being prevented, were it not that the copper deposited acts as the
copper element of a galvanic circuit, and the subsequent decomposition proceeds, each new portion of copper being deposited on the
outside, farthest from  the zinc, the action of which becomes thus
at every moment more intense. If hydrogen had a physical constitution, such as would enable it to act as the positive element of a
simple galvanic circle, then, no doubt, the purest zinc would decom*pose the muriatic acid, the circuit being completed by the hydrogen
evolved; but such is not the case, owing to its gaseous form; but it
being that alone which is the obstacle, the previous step, which depends simply on the chemical affinity of hydrogen and chlorine, may
reasonably be considered to have occurred.
The action of electricity in separating the elements of bodies is scarcely of greater
interest or importance fiom the ideas it suggests of the nature of chemical affinity,
than it becomes as a means of presenting to each other, under the most favourable
circumstances for union, the different elements of the voltaic circuit, and thus
causing the formation of bodies for whose construction the ordinary processes of
the laboratory are much too violent and abrupt. In this way some of the most remarkable substances of the mineral kingdom may be artificially produced, the secretion of the metalliferous ores into the veins and cavities of rocks accurately represented, and bodies, whose affinities for each other rank as the most intense, completely, though silently and gradually, separated from each other. It is to Becque-.rel that we owe almost all our knowledge of this importa.nt function of electricity;
from him we have also received the important lesson, that it is not in the brilliant
effects of the great batteries of Davy or of Daniell that we must seek a clew to the
history of the electrical processes of chemical affinity, but in the slow but unintermitting action of currents of such low intensity that a drop of pure water would be
an insuperable obstacle in their path. The electricity to be employed in the artificial formation of compound bodies must be such as is generated by a single pair,
and these generally of metals whose similarity prevents that current from being of
great amount.
These phenomena, into the examination of which I cannot enter with much detail, are best observed by means of a tube bent into a U shape, and at the bottom
of which is interposed a porous partition of clay or plaster of
Paris; the liquids, whose mutual reaction is to generate the new
substance, are placed in the legs of the tube, one at each side of
the partition, through the pores of which they gradually mix with
each other. The voltaic current is then supplied either by connecting the liquids with the poles of a feeble battery, or by im\I'.H:.1: mersing in one leg a zinc, and in the other a copper or platina
plate, connected by a wire with each other. If a solution of carbonate of soda and of sulphate of copper be thus brought to act
on one another, a double carbonate of copper and soda —crystallizes on the plate immersed in the copper liquor; and if then




SYNTHETIC ACTION OF ELECTRICITY.  199
the solution of soda be replaced by ordinary water, a new current is generated
which decomposes the first product, and forms a new crystallization of carbonate of
copper. If the zinc leg be filled with a solution of oxide of zinc in potash water,
and a solution of nitrate of copper be placed on the copper slde, a crystallization of
oxide of zinc is produced upon the zinc plat$ and a deposition of crystallized copper upon the metallic surface in the other tube.
By using two liquids which have unequal chemical actions on a
strip of metal, this may be made to precipitate itself, being reduced at
one extremity according as it is dissolved at the other. Thus, if the
glass A be filled with solution of nitrate of copper to a, and then water,
rendered slightly acid by nitric acid, be gently added, up to the level  ti
of B, a slip of copper, introduced so as to present equal surfaces to    
the two liquids, generates a current which passes up through its mass, 
and down from  the lighter to the denser fluid: the copper dissolves, a:
therefore, above, and the salt formed being electrolyzed by the current,  li!
its metal is deposited on the lowest surface under the form of crystals,
and this is continued until the free acid, and hence the electromotive
force in the liquid, becomes equal, when, of course, no current passes., [, 
Dr. Bird, who has extended considerably the results obtained by Becquerel, has
constructed an apparatus for such reactions, with which he has obtained, in an isolated form, those simple bodies, as boron, silicon, potassium, &c., whose compounds
resist ordinary means most obstinately.  It consists of a generating and of a decom
posing cell. This last is a glass cylinder, a, within another glass cylinder,       c    \
h. The inner one, a, is four inches
long, and an inch and a half in diameter, and is closed at the lower end by!
a plug of plaster of Paris, 0'7 inch in
thickness. This cylinder is supported G
within the other, b, which is an ordi-        li
nary jar, about eight inches deep and         il
two inches diameter, by means of i  I          li(lal      n..
wedges of cork.  A piece of sheet copper, c, four inches long and three inch-   \   lif
es wide, having a copper conducting
wire soldered to it, is loosely coiled up
and placed in the inner cylinder, while
a piece of sheet zinc, of equal size, is also coiled up and laid on the bottom of the
outer cylinder, it being also furnished with a conducting wire. The outer cylinder
is then to be nearly filled with a weak brine, and the smaller with a saturated solution of sulphate of copper; the two fluids being prevented firom mixing by the
plaster of Paris diaphragm.  After it has been in action for some weeks, chloride of
zinc is found in the external cylinder, and beautiful crystals of metallic copper, frequently mixed with the riuby protoxide (closely resembling the native ruby copper
ore), and large crystals of sulphate of soda, are found adhering to the copper plate
in the smaller cylinder, especially on that part where it touches the plaster diaphragm.
The apparatus is completed by the decomposing cell, which is, in fact, a counterpart
of the battery itself, consisting, like it, of two glass cylinders, one within the other,
the smaller one having a bottom or floor of plaster of Paris fixed into it; this
smaller tube may be about half an inch wide and three inches in length, and is intended to hold the metallic solution submitted to experiment, the external tube, b,
into which it is immersed being filled with a weak solution of common salt.  Into
the latter solution, a slip of amalgamated zinc (for the positive electrode), soldered
to the wire coming from the copper plate of the battery, is immersed, while for the
negative electrode, a slip of platina foil, fixed to the wire from the zinc plate of the
battery, passes through a cork, c, fixed in the mouth of the smaller tube, and dips
into the metallic solution it contains.
The influence which electricity thus exercises upon affinity, and the modifications
in its results producible by its means, although proving a most intimate connexion.
do not go, as I believe, so far as to demonstrate a complete identity of cause. It
is possible that, hereafter, some sublime generalization may embrace the phenomena of heat, of light, and of electricity, of cohesion and gravity, as well as of chemical affinity, within one law, and indicate how, by varied manifestations of a single
agent, their separate peculiarities may arise; but, though we may look forward to




200   ELECTRO-CHE MICAL  THEORY  PROPOSED.
such a state of science, we dare not rashly seek to anticipate its approach; and I
look upon electricity as producing and being produced by chemical phenomena,
precisely as we find heat to influence as well as to be evolved by chemical combination.
Where electricity is brought into. —play so powerfully by the action of a simple
body upon a compound fluid, it is, I consider, unreasonable to imagine that, in the
combination of simple bodies, or of compound bodies with each other, no electricity
should be set free, particularly when it is proved that in such cases some electricity does appear, although in quantity bearing no proportion to that of the feeblest
galvanic battery. If I were to suggest an electro-chemical theory, such as might
agree with the facts that have hitherto been discovered, I should consider that bodies in their free state are perfectly destitute of excitation; but that chemical
union, or the degree of intimate approximation which precedes union, may be a
source of electrical disturbance, and is that which, in all ordinary cases, gives origin to the electricity employed in our experiments.  When united, bodies are likewise destitute of electrical properties; in iodide of potassium, the bond is the affinity of iodine and potassium for each other, and not that the iodine is in a permaiient state of negative excitation while the potassium remains positive.
If hydrogen gas be burned in oxygen, there is evolution of electricity, of which
only a trace escapes immediate recombination under the form of light and heat, but
the existence of which, in a highly intense form, has been demonstrated by Pouillet. The oxygen and the vapour of water produced assume the positive condition;
the residual hydrogen becomes negative.  If carbon be burned in oxygen, there is
likewise combustion and evolution of electricity, of which the positive passes off
with the carbonic acid, and the negative rests upon the carbon. The evolution of
heat may be in these cases an independent effect of combination, but I would look
upon it as being more probably the Tesult of the union of the electricities evolved.
If the bodies which act upon each other are dissolved in water, there is no comlbustion, but heat is still evolved, and the electricities unite with one another without
the necessity for any intermediate circuit. It is only where the replacement of
one body by another occurs, that the establishment of the chain of inductively polarized molecules becomes necessary; for the particles of zinc and hydrogen, which
become oppositely united, have no power to conmbine, and hence cannot be restored
to neutrality unless by the medium of a third body, to which both may impart their
excitations.  That the zinc and hydrogen upon the one hand, and the copper and
hydrogen upon the other, do not unite, is, I conceive, fatal to those views which
assume the identity of chemical and electrical, or, as they call it, current or induetive affinity; for if a molecule of copper in the acid stood in the place of, and acted
as a molecule of chlorine, it should unite with the hydrogen in place of allowing it
to pass off free.
The act of chemical union being such as to produce electrical excitation and discharge before it is completed, and the permanent combination of the elements
being the result of the return to the neutral state, it is easy to understand that,
when these conditions are reversed, the chemical affinity should be superseded, and
the bodies brought into the state in which they had been at the moment of excitation, and while their elements, oppositely excited, were yet separate firom each
other. A  compound body is therefore, as I apprehend, decomposed by the battery, from having this electrical state given to it by the current; and the transfer
of its elements across the liquid is accomplished by a series of neutralizations and
excitations, accompanying the unions and decompositions by which they pass to the
electrodes, on which they yield up their ultimate excitation, and appear isolated
and completely neutral. The quantity of electricity necessary to decompose a
body is therefore the same' as it had evolved when its elements entered into
union, and it should hence follow that the current of electricity evolved in the
union of chemical equivalents of the simple bodies with each other should be the
same. That this actually occurs appears probable from the analogy of heat; an
equivalent of oxygen, in combining with various nletals, evolves the same quantity
of heat, and if the heat be a consequence of the neutralization of electricity, the quart.
tity of this evolved should be the same also. It appears, likewise, that an equiva.
lent of sulphuric acid, in combining with different bases, evolves the same quantity
of heat, and to decompose the various salts thus formed, the same quantity of
electricity should be required; and hence, that the two actions, so completely equiv.
alent to each other, may satisfactorily be referred to the same source.
Such is the interpretation I put upon the phenomena of electro-chemical decore




BECQUEREL S  E LECTRO-C H E M ICA L  THEO R Y. 201
position, and. the relations of electrical forces to affinity. In the molecular condition
of polar excitation which accompanies the passage of a current, I adopt fully the
peculiarly explicit mode of representing hle actions of the bodies on each other
proposed by Graham, but I consider it too hypothetical to assume that such molecular state naturally exists in bodies; it may or it may not; but in the absence of
evidence that it does, I am not inclined to presuppose it unnecessarily. I look upon
the current as being produced by the union of opposite polarities, which are themselves not the cause, but the consequence, of the chemical affinities of bodies.
Graham is not disposed to admit that the union of simple bodies may be accompanied by an electrical plhenomena, and to exclude also from the application of an
electro-chemical theory the combination of acids and of bases with each other, as
not capable of generating currents; but the reason of this is, as I imagine, that the
currents so generated are necessarily closed.
In concluding the admirable treatise on electricity with which he has enriched
scientific literature, M. Becquerel details the views which he has adopted regarding
the electro-chemical relations of bodies; and although they are not expressed with
the definiteness which might be wished fiom so admirable a philosopher, I shall
endeavour, in concluding this section, to give a short description of them. In the
main, they do not differ much from the principles of electro-chemical combination
which I have long since adopted, and which have been already noticed.
*M. Becquerel considers that in all bodies there is distributed a quantity of electricity indefinitely great, which is so intimately connected with their molecular
constitution, that it is disturbed, and excitation produced in all cases where molecular disarrangement is produced; hence pressure, friction, an unequal distribution
of heat, &c., are sources of electricity.
Chemical affinity is also a source of electrical disturbance. When an acid combines with an alkali, the first sets free positive electricity, and the second an equal
quantity of negative electricity; these two combine immediately in the liquor, forming neutral fluid, and produce as many currents as there had been particles in action; now this multitude of little currents ought to determine the production of a
quantity of heat, depending on the energy with which the affinity was manifested,
and the conducting power of the liquid. In decompositions, the electrical effects
are inverse, that is, the acid takes the negative, and the alkali the positive electricity; hence it may be concluded, as M. Becquerel had already stated with regard
to aggregation, that if electricity does not constitute affinity, it is at least indispensable to its manifestation, since it is always subjected to the same laws every time
that simple or compound atoms unite or separate. From all considerations, it appears that the electricity produced by chemical action is only an effect resulting
from the action of the affinities brought into play; and this effect being brought into
inverse action in decomposition, announces at the same time a molecular electric
state, indispensable to the permanent union of the elements of compound bodies.
To explain decomposition by a current of electricity, M. Becquerel adopts Ampere's idea of electrical atmospheres, although he denies that any bodies are naturally or permanently in a positive or negative condition; but he supposes that the
neutral condition of a body consists in the molecule being either positive or negative, and being surrounded by an atmosphere in an opposite state. When bodies
unite, the union of their atmospheres produces light and heat, and the molecules remain excited while in union, although the union is the cause of the electrical disturbance, and not its effect. Now, when zinc is put in contact with water, this last
is decomposed, and there is hence a disturbance of electricity; the particle of zinc
abandons its negative atmosphere, and unites in a positive condition with the negative and nascent oxygen; the hydrogen is liberated nascent also, and highly positive; in this state the oxygen would be balanced between the two equally positive
particles of zinc and hydrogen, and the decomposition could not proceed; but, if a
slip of copper be introdutced, this supplies a negative atmosphere to the hydrogen,
which, becoming neutral, is evolved as gas, and, transferring its positive electricity
to the point of contact with the zinc, neutralizes its excess of negative excitement,
and generates the current. M. M. ecquerel refers the chemical action of the current
in the decomposing cell to each electricity setting the same electricity of the compound in motion in tle same direction with which the particles are transferred by
a series of combinations and decompositions, as has been already described, until
the limits of the substance are attained, and then the elements are evolved in the
neutral state.
M. 1)eequorel haIs endoavouoed to apply the agency of electricity to determine the
Cc




202                LAWS  oF  COMrBINATION.
relative affinities which bodies have for each other. His principle is as follows: it
nitrate of copper and nitrate of silver be dissolved together in equal quantities, and
decomposed by a galvanic current, the nitrate of silver alone is at first affectel, because the affinity of the silver for the oxygen and acid is so much less than. that
of the copper for the same. But, when the quantity of nitrate of copper is gradually
increased. a term is arrived at when the electric current is exactly equally divided
between the two metals, the greater quantity of copper making up for the greater
resistance it offers to the decomposing power. His results are, that when the solution contains twenty parts of copper to one of silver, the current acts equally on
both; when the copper is 25 to 1, the current acts as if it divided itself 2 to the
copper and ~ to the silver; and when the quantity of copper is thirty times that
of the silver, there are three equivalents of the copper salt decomposed for one of
the salt of silver. M.-E. Becquerel has essayed the same important problem in a
difierent way, by testing the power of solutions of chlorine, iodine, and bromine, to
absorb nascent hydrogen and nascent oxygen, evolved in their mass by means of a
galvanic current. His results appear to show that the affinities are expressed by
the numbers; for
Hydrogen.                              Oxygen.
For Chlorine..        922         For Chlorine...   169
Bromine....   712             Bromine.... 380
Iodine...... 212                  Iodine......         469'Ihese two series are, however, independent of each other, and afford no mutual
term of comparison whatsoever.
It is to be trusted that such investigations, conducted with the ingenuity and accuracy which the Becqueirels can so well apply, may lead to results of the highest
interest to science. The reduction to numerical laws of the influence of quantity
on affinity, and the determination in numbers of the tendencies of the simple bodies
to unite, would certainly advance the condition of chemistry, as an exact science,
in a remarkable degree.
CHAPTER IX.
ON THE LAWS OF COMBINATION.
THE general nature of affinity, and the modifications which it undergoes from  the influence of the physical agents, having been now
stated, I shall proceed to discuss the numerical laws to which its results are subjected, the discovery of which was the first step in conferring upon chemistry the character of an exact science.
It is characteristic of chemical affinity, that the proportions in
which bodies are brought to unite by its agency are limited upon
both sides, whereas, in those cases where molecular forces alone
prevail, the proportions, although perhaps limited in one direction,
are indefinite in the other.  Thus a saturated solution of chloride
of sodium cannot take up any more salt, but it may be mixed with any
quantity of water, whereas the chloride and the sodium, which constitute the salt, form  it only in certain proportions which are invariable, 100 parts containing always 39'66 of sodium and 60'34 of
chlorine.  If it were not for this constancy of proportion, the science
of chemistry could never have advanced beyond its merest elements;
for, had chlorine and sodium been capable of combining in all indeterminate proportions, or had the properties which "'ve recognise in
chloride of sodium been ascribable to compo'inds of those elements




CHE M ICAL EQUIVALENTS.                  203
in. every possible proportion, no accurate ideas regarding the conlt
stitution or properties of bodies could have been acquired, and none
of the benefits derivable from experience or experiment could have
been attained.  The first law of constitution is, therefore, that the
composition and properties of any given substance are always the
same.
WVhen, by the intervention of superior affinities or by double decomposition, a compound body is decomposed and a new comnpound
f'ormed, the proportions by weight of the various substances brought
into action have a constant relation to one another, and, as they represent the quantities of the bodies which exercise equal, or, at least,
equivalent combining powers, they are'terlned, when reduced to
numbers, the combining proportions or equivalents of these bodies.
Thus, if 100 parts of oxide of copper be heated in a current of hydrogen gas, it is reduced, and the hydrogen, uniting with the oxygen
which it contained, forms water. In the 100 of oxide there were 79'83
of metallic copper and 20'17 of oxygen, which last, taking 2'52 of
hydrogen, forms 22'69 of water. Now, in this case, the 2'52 of hy
drogen produce the same result of satisfying the combining po wer of
the 20'17 of oxygen as the 79'83 of copper; and hence these quantities of hydrogen and copper are equivalent to each other. This example may be, however, brought much farther. If, in place of treating the oxide of copper by hydrogen gas, it had been acted on by
chloride of hydrogen, the oxygen should have been carried off by the
hydrogen, which would abandon its chlorine for that purpose; but
the chlorine should not be set free; it, on the contrary, would unite
with the copper from which the oxygen had been taken, and the reaction would be so proportioned that the quantity of copper reduced
by the hydrogen of the chloride of hydrogen would be exactly sufficient td unite with all the chlorine which was therein contained, and
form with it chloride of copper. In this case the 100 parts of oxide
of copper would require for its decomposition 91'73 of chloride of
hydrogen, and there would be formed 169.04( of chloride- of copper
and 22'69 of water. Here, as before, the 20'17 of oxygen uniting
with 79'83 of copper and 2'52 of hydrogen, show their equivalency;
but we learn in addition, that 79'83 of copper and 2'52 of hydrogen
unite'equally with 89'21 of chlorine, and hence that that quantity of
chlorine corresponds, and is equivalent in combination, to 20'17 of
oxygen.
Starting from this point, we may proceed to a still more extended range of instances. If we treat sulphuretted hydrogen gas with.
iodine, we find that it is totally decomposed, sulphur being precipitated, and iodide of hydrogen being formed. Now, taking the
quantity of the sulphuret of hydrogen, containing the weight obtained in the former example, 2'52 of hydrogen, we find it to be 43'09,
and hence to contain 40'57 of sulphur, which separates by the action
of the iodine, of which 318'28 parts, uniting with the 2'52 of hydrogen, form 320'79 of iodide of hydrogen. If this iodide of hydrogen
be next treated with chlorine, it abandons its iodine, and forms 91'73
of chloride of hydrogen.
Setting out, therefore, from 100 parts of oxide of copper, and
tracing its elements through a variety of decompositions, in all of




204    scALES OF CHE M ICAL EQUIVALENTS.o
which' the quantities engaged effect the same purpose of satisfying the
tendency to combine, we found for the numbers which express the
equivalent quantities of the simple bodies employed the following:
Copper......7983          Chlorine.. 89'21
Hydrogen.....  2' 52           Sulphur..... 4057
Oxygen......2017               Iodine......318 28
and as the compound bodies formed are also equivalent, from their
being produced by the same, or equivalent combining actions, we
may express also in numbers their combining proportions thus:
Oxide of copper... 100'00    Sulphuret of hydrogen. 43'09
Oxide of hydrogen.. 22'69     Iodide of hydrogen.. 320'79
Chloride of hydrogen. 91'73     Chloride of copper.. 169'04
It is evident that if, in place of oxide of copper, any other metallie oxide reducible by hydrogen had been employed, its equivalent should have been obtained, and in this way the equivalents of
the majority of metals have been determined.
These numbers are quite arbitrary; and any other body in the
list might as well have been taken for the origin as oxide of copper.
In practice such numbers are reduced to a standard, which is taken
as 1 or 100, and for this purpose, oxygen or hydrogen, the most
important bodies, are selected.
Any number experimentally obtained, as the above, may be reduced to the standard scale by the rule of simple proportions: thus,
the equivalent of copper being 79'83, oxygen being 20'17, and hydrogen 2'52, it is
20'17: 7983:: 100-395'7  Oxygen =100
and 252: 7983::   1-31'71  Hydrogen =-1
It is difficult to decide which of the two scales thus formed deserves preference: the hydrogen scale has been, by the authority
of Davy, so long prevalent in these countries, that it is difficult to
supersede it; and it possesses the advantage that hydrogen has the
smallest equivalent of all bodies. The standard of oxygen is, however, for use, the more convenient, as, in consequence of the greal
preponderance of bodies in which oxygen exists, the calculations
are much simplified by its number being 100; and there are but
two or three bodies which, on that scale, require to be expressed
in a fractional form.
When the study of these equivalent proportions first occupied the
minds of chemists, Doctors Prout and Thompson were led, from
speculations regarding the physical constitution of gaseous bodies,
to suggest that the equivalent numbers of all substances were sime
ple multiples of that of hydrogen; and as, representing hydrogen
by 1, the other numbers therefore became all whoie numbers, the
scale acquired thereby considerable simplicity.  The researches of
Berzelius appeared, however, to controvert that hypothesis; and in
his numbers, which are, for the most part, those given in the following list, no trace of such a law can be detected: later researches
have also, in the hands of Turner and of Penny, afforded additional
support to this opinion; but Phillips has lately reopened the dis.
cussion, and Dumas is inclined to consider the original views of
Prout as being probably correct.  In any case, the numbers given




SCALES  OF  CHEMICAL  EQUIVALENTS.    205
In the list must be looked upon as being, in a slioht degree, still
open to revision.
In the following table, the equivalents of all the simple bodies are
expressed on each of these scales; and throughout this work the
two equivalent numbers will be given for each compound body, ex
cept where it is otherwise remarked.
Names of Elements.              Names of Substances..1i0  et...
0      I.= 100  I.= I            0.=100  H.= I
Aluminum.    1712  1:37  Mercury....         12658  10143
Antimony..  16129 129'2. Molybdenumrn..  595  47.96
Arsenic....  9401  7534 Nickel....  3697   29'62
Barium....  856         669 G6866 Nitrogen...  1750   14'00
Bismuth..  8869 71'10 Osmium... 1244'5  99'72
Boron..       1362  10'91 Oxygen....  1000    801
Bromine..    9783 7839 Palladium...  665'9  53'36
Cadmium...  696 8 5583 Phosphorus               3923   31P44
Calcium....  2560 20'52 Platinum... 1335  9884
Carbon...         760  6'08 Potassium...  489'9  39'26
Cerium....  574 7 4605 Rhodium..    651'4  52 2
Chlorine...  442.6 35'47 Selenium..   4946  3963
Chromium...  351 8 2819 Silicon....  277'3  22'22
Cobalt...   3690 29'57 Silver.... 1351'6 108'3
Columbium.. 2307 4 184'90 Sodium....  290'9  23'31
Copper...  3957 31'71 Strontium...  547'3  43'85
Fluorine...'.  2338  18 74 Sulphur....  201'17 16'12
Glucinum...  331 3 26'54 Tellurium...  801-76 64'25
Gold..      24860 199'21 Thorium...   449   59.83
Hydrogen...   12.5  1'00 Tin..73529 5892
Iodine.... 15795 126'6  Titanium...  303'66 24'33
Iridium.... 1233 5 9884 Tungsten... 1183 0  94'80
Iron.....  3392 27-18 Vanadium...  856'9  68'66
Lanthanum..              Uranium... 27114  21726
Lead... 1294 5 103'73 Yttriumrn...  4025  32'25
Lithium...   80-3  6'44 Zinc...   403'2  32 31
Magnesium..   1583  1269 Zirconiurn...  420 2  33 67
Manganese...  3459 27'72
The determination of the equivalents of compound bodies is an
equally remarkable application of the principles that have been laid
down.  The equivalent number of a compound is the sum  of the
equivalent numbers of its constituents, as has been already seen in
the numbers obtained for the oxides and chlorides of copper and of
hydrogen. In this way may be constructed lists of the equivalents
of compound bodies; thus, reducing the substances already noticed to the scales, there are:
Equivalents.                       Equivalents.
Substuncas.                      Substances.....
0.=__100)._ _                     0.=100i H.=- 
Oxide of copper.. 4957 3972 Chloride of copper.  838 3 67 18
Oxide of hydrogen. 1125 901 Iodide of hydrogen       1592-0 127 57
Chloride of hydrogen. 4451 13647 Sulphuret of hydrogen   2137 17'12
It is in relation, however, to the mutual decomposition of saline
bodies that the principle of equivalent proportion becomes of most
interest, and by which it is best illustrated.  If to a solution of nitrate of barytes we add a solution of sulphate of soda, there is immediate decomposition, by the mutual interchange of acids and ba
ses, and the neutrality of the solution remains completely undisturb
ed; the salts which exist after mixture are equally neutral with




206    EQUIVALENTS  OF  COMPOUND  BODIES.
those which had existed previously, and the quantities of acids and
bases which are involved in the decomposition are hence equivalent to each other.  Thus, if we take 130.7 parts of nitrate of barytes, we find that they require for their decomposition exactly 71'3
parts of dry sulphate of soda, and that there are formed 116'7 parts
of sulphate of barytes and 85'3 parts of nitrate of soda.  The composition of these four salts is:
Sulphate of Barytes.                Nitrlate of Soda.
Sulphluric acid..  40           Nitric acid...  54
Barytes....  76'7             Soda.....  31-3
116' -153
Nitrate of Barytes.                Sulphate of Soda.
Nitric acid...  54             Sulphuric acid.. 40
Barytes....  76'7               Soda...... 31 3
130'7                                71'3
All four are neutral; the acids and bases are in all equally neutralized, and hence the 40 of sulphuric acid and 54 of nitric acid, being
capable of saturating the same quantity of base, whether it be soda
or barytes, are equivalent quantities, and represent the combining
proportions of these acids; and the 76'7 of barytes and the 31 3 of
soda being likewise shown to possess equal powers of neutralizing
the acid, whether nitric or sulphuric, are the numerical equivalents of
those bases.  If there had been a larger quantity of either salt present, it would have remained unaffected, the interchange of elements
taking place only in equivalent proportions. Had nitrate of lead been
employed in place of nitrate of barytes, the proportion necessary
-would have been different, and a different quantity of sulphate of lead
would have been, produced from the same sulphate of soda.  Thus,
to the 71'3 of sulphate of soda, there should be,
Nitric acid..  540, producing Sulphuric acid..  401
Oxide of lead    111-7,   CC   Oxide of lead... 111'7
Nitrate of lead   165 7       Sulphate of lead     151.8
If, in place of sulphate of soda, we take oxalate of soda, we shall
find that 67'3 of it will exactly fulfil the functions of 71'3 of sulphate
of soda, and these, consisting of 31.3 of soda and 36'0 of oxalic acid,
will, by decomposing 130'7 of nitrate of barytes or 165'7 of nitrate
of lead, produce 147.7 of oxalate of lead or 112.7 of oxalate of barytes.  36 of oxalic acid are therefore equivalent to 40'1 of sulphuric
acid and 54'0 of nitric acid.
A table of equivalents of acids and bases might thus be drawn up:
there should be,
Substances.             Substances..
__- _100_ _  _~o='0.  i,. 1.
Nitric acid..         S 77(0]54-0 Soda....   3901 31-3
Sulphuric acid. 5011 -1401 Barvtes...  9569 76i 7
Oxalic acid  1. 52'9 36'0 1Oxide of lead. 1394.51111-7
It was in this form  that the equivalency of different quantities of
chemical substances was first recognised, and numbers assigned with
extraordinary skill, by W enzel, whose labours, although overlooked
at the time, must be considered as the first and greatest step towards
assigning the numerical conditions of chemical action.




LAW  OF MULTIPLE  PROPORTIONS.                    2~
The mode of determining the equivalent number of a new substance can now be easily understood. If it be an acid, it is to be
combined with some base of which the equivalent is known; if it be
a base, it must be united with an acid. If it be a metal, it may be
united with chlorine or oxygen.  If it be a simple non-metallic body,
it may be united with a metal. In any case, a well-defined compound of the new body with one whose equivalent number is already
known must be obtained and accurately analyzed.  The equivalent
numbers of the two bodies are proportional to the quantities in
which they were combined, provided we have reason to consider
that the compound examined contained an equivalent of each.
Thus, if the new body form with sulphuric acid a perfectly neutral and soluble salt, and, on analysis, this yields 37-3 of sulphuric
acid and 62-7 of the new base in 100, the equivalent is found by the
proportion, as, 373: 62-7:: 40-1: x=67'4, which is the equivalent of the body, 40-1 being that of sulphuric acid, and hydrogen
beinog = 1.
A calculation of this kind requires, however, to be checked by a
knowledge of the next law of combination, that of multiple proportions; for, as has been stated, we presume, in the example, the salt
analyzed to be composed of an equivalent of each constituent. It
may be, however, that it contained two equivalents of acid to one
of base, in which case the number for the latter would become
134-8; or two equivalents of base to one of acid, which would make
the number 33-7.  The proportions might be even still more conmplex; and hence, before attempting to decide on the equivalent number of a body, its general history must be studied..
The third law of combination is, that where one body unites with
another in more proportions than one, there exists a simple relation
between the quantities of the second, which, in the different compounds, unite with the same quantity of the first. Thus, talcing- manganese and nitrogen, which are remarkable for the number of' compounds which they form with oxygen, there are,
345'9 of manganese unite with 100 of oxygen, forming protoxide.
345'9        "          150       "        sesquliioxide.
345 9        "          200       "        peroxide.
345'9                   250       "         anganous acid.
345'9        "          300       "        ranganic acid.
345.9        "          350        "       permanganic acid.
And with nitrogen,
175 of nitrogen unite withI 100 of oxygen, forming nitrous oxide.
175        "        200        "       nitric oxide.
175        "        300       "        hyponitrous acid.
175        "         400       "       nitrous acid.
175        "         500       "       nitric acid.
Here the successive quantities of oxygen talren by the manganese
are as the numbers 2, 3, 4, 5, 6, 7, and those which combine with the
nitrogen are as 1, 2, 3, 4, 5. In the last case they are all simple
multiples of the first proportion, but in the case of manganese they
are multiples of one half of the quantity contained in the protoxide.
The analogy of some other similar bodies, however, renders it extremnely probable that, though it has not been yet discovered, there




208        LAW  OF  MULTIPLE  PROPORTIONS.
exists a compound of 348'9 of manganese with 50 of oxygen. and
this should then be the first term of the series.
This law of multiple proportions holds not only with regard to the
simple bodies already stated, but also with compound bodies of every
class. Thus chromic acid combines with potash in three diif/rent
mroportions, forming by
52'2 chromic acid +47.3 potash, neutral chromate of potash.
104'4    "    +-47'3   "  hichromate of potash.
1566     "    -4-47'3   "  terchromiate of potash.
Sulphuric acid combines with potash in two proportions,
40'1 sulphuric acid +47.3 potash, neutral sulphate.
80'2            4 -+47-3   "  bisulphate.
It was, indeed, by the verification of it in the carbonates and ox.
alates of potash by Wollaston, that this law obtained in the first
instance general acceptation.
22 of carbonic acid +-47'3 potash, form carbonate of potash.
44              4 -+47'3  "     bicarbonate of potash.
36 of oxalic acid -+-473 potash, form oxalate of potash.
72     i"       +47. 3    "     binoxalate of potash.
144     9"      +47' 3     "     quadroxalate of potash.
In salts with excess of base, the same principle holds.  Thus, in
the sulphates of copper, I have shown that
39.7 oxide of copper +40'1 sulphuric acid, form neutral sulphate.
79.4        +' -40-1                   h bibasic sulphate.
158'8    +" 401 1                       quadribasic sulphate.
317'6     "       +t-40 1       "       octobasic sulphate.
In other cases the series, though not so complete, evidently follows
the same law.
The great use of the symbolical nomenclature, noticed already in
page 156, consists in its supplying an exact expression of this law
of multiple proportions.  The ordinary symbol of a simple body indicating an equivalent of it, the number by which that symbol is
multiplied, in the formula of each compound body, represents the
number of equivalents therein contained. Thus, for manganese and
nitrogen, already used as instances, the symbolical expression of the
law is given in
N.O. Nitrous oxide.          Mn.O. Protoxide of manganese.
N.0, Nitric oxide.            Mn2O3 Sesquioxide.
N.03 Hyponitrous acid.    IMn.02 Peroxide.
N.O4 Nitrous acid.           Il\n.03 Manganic acid.
N.05 Nitric acid.             Mn,207 Permanganic acid.
The numerical coefficient is sometimes placed, as here, below
and to the right of the letter symbol; by other chemists it is placed
to the left and on the same line, as Pb.+20. Cr.+ 30., and sometimes
to the right and above the letter, as Pb.02 Cr.03.  This makes no
difference in chemistry; but the student must be careful not to
confound chemical with mathematical symbols, in which the position of the number might alter its power and meaning altogether.
It must be noticed, however, that numbers written as the above affect only the immediate symbol to which they are attached; but




RESEARCHES  OF  PROUST.                             209
sometimes a number affects a group of symbols: thus, 3MAIn.0. is
three equivalents of protoxide of manganese = —Mn303: thus, also,
S.03 K.O.+A1203. 3S.03, the formula of dry alum, contains four figures of 3, of which the first, second, and fourth only affect the 0.,
to which they are subjoined, but the third affects the S.O,, to which
it is prefixed.  A little practice will enable the student to become
quite familiar with the arrangement of the symbols, or formulae, as
they are termed, of bodies, even of the most complicated nature.
This is the principle of multiple proportions: that the successive
quantities in which one body may unite with another are multiples
of the first by a whole number; and the cause of this is at once
seen, and a simple and positive meaning given to this law, by saying that the first body contains an equivalent of each element; the
second, one equivalent of one and two equivalents of the other, and
so on; the successive steps being formed by the number of combining proportions of the second body which unite with one combining proportion of the first.
This principle, which establishes a remarkable distinction between the action of
chemical affinity and of cohesion, was, at the moment of its first being traced, attacked by Berthollet, to whose exclusive doctrines it was quite fatal. Berthollet,
in fact, considered that the affinity of bodies should make them unite in all possible
proportions, and that it was only by the influence of cohesion and elasticity that the
formation of the bodies actually produced resulted. Thus he asserted that sulphuric acid and barytes actually unite in all proportions; but those of 40'1 of acid to
76'7 of base forming the body of the least solubility, the whole quantity of acid i,
determined to unite with the barytes in those proportions, and in none others.
Thus he imagined, also, that mercury and oxygen should unite in all proportions
and that it wnas only by the intervention of external causes that their union was determined in preference to occur in the proportions of 101-4 of mercury to 4 of oxygen, and 101'4 of metal to eight of oxygen. We owe to Proust the complete refutation of Berthollet's views in this respect; he cleared away a heap of incorrect
ideas which had prevailed regarding compounldbodies, showing that numerous degrees of oxidation, which had been looked upon as intermediate, and connecting
the extreme limits, as Berthollet thought they ought to be connected, were impure
and badly prepared mixtures of the true compounds, and that, when pure, the transition from one state to the other is sudden and definite, as has been shown to be
the consequence of the law of multiple proportion. It is interesting to notice, however, as an example of how easily a great discovery in science may be lost, that, although Proust had in his hand all materials necessary for establishing the laws ot
combination, such as they have been described, they escaped his notice, from his
having contemplated his results only in one point of view; thus he found that in
1 00 parts,
1st Oxide of copper contained        2d Oxide of copper contained
Oxygen..... 1122               Oxygen..... 2017
Copper...... 8878               Copper..... 7983
1st Oxide of mercury                 2d Oxide of mercury
Oxygen.....         380           Oxygen..... 732
Mercury.....        96-20           Mercury..... 9268
1st Sulphuret of iron                2d Sulphuret of iron
Sulphur..           37'23          Sulphur.....54-26
Iron...... 6277             Iron.....   45'74
He proved that no indefinite intermediate degree of combination could be traced,
and that the influence of cohesion could not be supposed to be the only cause of the
definiteness of constitution; but, had he made a trifling change in his way of calculation; had he taken a certain weight of one element as the standard, and not 100
parts of the compound body, his numbers would have become,
1st Oxide of copper                   2d Oxide of copper
Oxygen.....   100-0                 Oxygen.....200'0
Copper....7914                    Copper..... 7914




210        METHODS  OF  DETER MINING THE
1st Oxide of mercury              2d Oxide of mercury
Oxygen..... 100'0            Oxygen.....        2000
Mercury..... 2531'6          Mercury.... 2531-6
1st Sulphuret of iron             2d Sulphuret of iron
Sulphur.            2012          Sulphur.....   4024
Iron...... 3392            Iron...... 339'2
And thus the fact of the quantity of oxygen or sulphur in the second range of
compounds, being exactly double that in each of the first, would have been evident
and the law of multiple proportions been discovered twenty years before its existence was suspected.
We are now in a condition to examine more in detail the method
of determining the equivalent number of a body, which, as was before noticed, is rendered difficult, sometimes, when the substances
in question unite in more proportions than one. Thus it is evident
that the manganese series might be represented as
100 of oxygen -345'9 of manganese, bforming protoxide.
100    "     230'5     "       "     sesquioxide.
100    "     172'9     "       "      peroxide.
100    "     138'3      "   "        manganous acid.
100    "      115'3     "      "      manganic acid.
100    "      98.8      "      "      permanganic acid.
And the metallic oxides and su]phurets above described might be
written, and express still the law of multiple proportion; as,
1st Oxide of copper               2d Oxide of copper
Oxygen.. 1000                    Oxygen....   100-0
Copper.7914                      Copper.             395.7
ist Oxide of mercury              2d Oxide of mercury
Oxygen..... 1000            Oxygen.....  1000
Mercury..         2531-6         Mercury.1265'8
Ist Sulphuret of iron             2d Sulphuret of iron
Sulphur...   201'2            Sulphur... 2012
Iron...... 3392            Iron...... 169'6
There might thus be deduced from each kind of compound a different equivalent for each simple body, and it is therefore necessary to lay down some general principles by which one must be
guided in their choice.
First. Whenever there exists but one proportion in which two
bodies are capable of combining, it may be concluded, unless there
are good reasons to the contrary, derived from  other sources, that
the proportion is one equivalent of each element. Thus lime and
magnesia are the only compounds formed by the metals calcium
and magnesium  uniting with oxygen, and are hence looked upon
as protoxides.
Second. Whenever one body combines with another in two pro
portions, as a metal with oxygen, and the quantities of oxygen are
as 2: 1, it may be concluded, unless there are other reasons for an
opposite decision, that the bodies consist either of one equivalent
of metal united respectively with one and two of oxygen, or of one
equivalent of oxygen united respectively with one and two of metal.
To decide between these views, it must be considered, that as the
tendency of the metal and of oxygen to unite is pretty well satiated
by the combination of an equivalent of each, if the protoxide so
formed unite with another equivalent of either metal or of oxygen,,this will be retained with inferior power, and when the substance
so produced is exposed to decomposing agencies, it may be resolved




EQUIVALENT CONSTITUTION  OF BOD IES. 211
into protoxide and metal in the one case, and protoxide and free
oxygen in the other. Thus copper, lead, and mercury unite each
with oxygen in two proportions; and if black oxide of mercury
be heated, it resolves itself easily into metallic mercury and red
oxide, while the red oxide undergoes no change except total decomposition into mercury and free oxygen. Red oxide of copper
decomposes itself easily into metallic copper and black oxide of
copper; but this last does not admit of any decomposition which
is not total. If we take yellow oxide of lead, we cannot change it
by the application of heat; but if we heat brown oxide of lead, it
gives off one half of its oxygen, and yellow oxide remains; similarly,
when peroxide of manganese is heated by deoxidizing agents, it
abandons one half of its oxygen, but the oxide so formed cannot be
farther reduced. In th'is way, therefore, we conclude that
Red oxide of copper is suboxide. Cu20.
Black oxide of copper is protoxide. Cu.O.
Black oxide of mercury is suboxide. Hg20.
Red oxide of mercury is protoxide. Hg.O.
Yellow oxide of lead is protoxide. Pb.O.
Brown oxide of lead is deutoxide. Pb.O,.
Olive oxide of manganese is protoxide. Mn.O.
Black oxide of manganese is deutoxide. Mn.02.
Thus, also, hydrogen and oxygen unite in two proportions, to form, in
one, water, a body remarkably neutral in properties and permanent in
constitution) and in the other oxygenated water, of which half of
the oxygen is so loosely combined that its decomposition is provoked by the slightest causes, and is explosively violent. It is hence
concluded that
Water is protoxide of hydrogen. H.O.
Oxygenated water is deutoxide. H.O,2.
If there be still more degrees of combination of the two bodies,
these principles apply still more determinately to their characteristic
properties.
Third. The constitution of an acid may be frequently determined by the consideration that an equivalent of it is the quantity
which neutralizes an equivalent of a well-characterized base. Thus
the equivalent number of potash on the hydrogen scale is 47'3, and
this combining with 40'1 of sulphuric acid to form neutral sulphate
of potash, this number is determined to be the equivalent of the
acid; and as it is made up of 16'1 of sulphur and 241 of oxygen, the
acid is considered to be composed of one equivalent of sulphur
16'1, and three equivalents of oxygen 8x3 24. Its formula is
therefore S.03. In the same way, on analyzing hyposulphate of
potash, it is found to consist of 47'3 of potash, united to 72'-2 of the
acid, which is, therefore, its equivalent number. But this number
is made up of 32'2, or two equivalents of sulphur, and 40, or five
equivalents of oxygen, and the formula expressing its constitution
is S20,.
Where an acid forms several classes of salts, it is difficult to determine which is that containing an equivalent of each element, and




212        METHODS OF DETERMINING  THE
hence this mode of ascertaining the constitution of the acid may be
occasionally at fault. This happens particularly with the acids of
phosphorus and arsenic; and in these cases it is necessary to recur
to considerations regarding the constitution of their salts, which
will be described when we come to speak of salts in general.
Fourth. In cases where the ratio between the quantities in which
the bodies combine does not follow the simple proportion of 1: 2: 3,
&c., but assumes the more complex form  of 2:3, or 3:4, or
3: 5: 7, it is necessary to seek for analogies between the members
of the series and certain other bodies with regard to which there is
not the same uncertainty. Thus there are two oxides of iron
which may be looked upon as consisting, either
the 1st of 27'9 of iron +  8 oxygen.
the 2'd   27'9   "         - 12 "
or the 2d    18'6   "   1- 8
the 1st  27'9   "   +-8 8 
In the first mode of view the oxygen varies as 2: 3, but in the second it is the metal which changes in proportion. Here we obtain a
guide in the study of the salts formed by these bodies. It is found
that the oxide which contains~27'9 of iron to 8 of oxygen agrees in
its laws and properties with magnesia, with black oxide of copper,
and with olive oxide of manganese, which are all protoxides, and
that it differs totally in its relations from such bodies as are very
fully known to be suboxides. This oxide of iron contains, therefore,
an equivalent of each element, and its formula is Fe.O. The peroxide of iron then becomes Fe.O 1i; but as the equivalent of oxygen
cannot be considered to be divided, we look upon it as being rather
FeO,, and having its equivalent number twice as large. This view
is confirmed by finding that when sulphate of peroxide of iron unites
with sulphate of potash to form iron alum, it does so in the proportion of FeO3, dry iron alum being S.O0, K.O.+Fe203, 3S.0,; and as
this is the only proportion in which these two salts unite, it is reasonable to suppose that it contains an atom of each element.
This mode of controlling the equivalent numbers is beautifully
shown in the instance of the compounds of chrome with oxygen.
There are two; the
Green oxide of chrome consists of 18.79 chrome + 8 oxygen.
Chromic acid         "          1879   "   +16   "
Here the quantity of oxygen is doubled in the second compound;
and as this yields half of its oxygen readily, either by heat, or to any
substance having an affinity for it, it would appear highly probable
that the 18'79 is the equivalent of chrome, and that the oxide of
chrome should be looked upon as a protoxide; but such is not the
case. Sulphate of chrome combines with sulphate of potash to form
a chrome alum, resembling in all characters and constitution the iron
alum already noticed, and hence oxide of chrome corresponds to
peroxide of iron, and its formula is Cr,20. This is farther proved
by the relations of chromic acid to bases. The chromates resemble
perfectly the sulphates with which they are isomorphous, and to
saturate 47'3 of potash 52'2 of chromic acid are required, consisting




EQUIVALENT CONSTITUTION  OF BODIES.  213
of 28'2 of chrome and 24 of oxygen; and hence the formula of
chromic acid is Cr.O, resembling that of sulphuric acid S.03.
Fifth. In cases where there is only one compound of a body with
oxygen, we may be induced to consider it not to be composed of an
equivalent of each element from analogical grounds, such as those
now described. Thus aluminum and oxygen form only one compound, alumina; but this resembles, in all its laws of combination
and crystalline form, oxide of chrome and peroxide of iron, and
hence it is considered to be a compound of two equivalents of metal
and three of oxygen, and its formula to be Al203.
Sixth. When bodies are found combined in proportions expressed
by high numbers, they are generally looked upon as secondary compounds, formed by the reunion of others, the ratio of whose elements
are simple. Thus lead forms with oxygen compounds intermediate
to the two true oxides already described, the one containing three
equivalents of lead and four of oxygen, the other four of lead and
five of oxygen; these consist really of the protoxide and peroxide
united in the proportions shown by the equations:
Pb4O,=3Pb.O.+Pb.Q,, and Pb304=-Pb.Oo+Pb.O.
In like manner, between the two proper oxides of iron there intervene the two magnetic oxides, the formule of which are FeO,5 and
Fe3,O,, being compounds of protoxide and peroxide, as,
Fe40= —g Fe.. -F Fe20,, and FeO,4=Fe.O.  - +Fe2O3.
By this means the constitution of an extensive class of complex bodies is reduced to very simple forms.
If we take oxygen, hydrogen, chlorine, and nitrogen in the pro
portions by weight which correspond to their equivalent numbers,
and measure the volumes which, as gases, they occupy, an exceedingly striking relation will be found between them, the volume of
oxygen being exactly one half that of each of the other gases. If,
also, we heat iodine and bromine in quantities proportional to their
equivalents by weight, we shall find that, when converted into vapour, they occupy precisely the same volume as the equivalent of
hydrogen gas at the same temperature and pressure. On converting into gas equivalent weights of arsenic and phosphorus, they occupy precisely the same volume, which is equal to that of the equivalent of oxygen gas; and by similarly treating an equivalent of sulphur, its volume becomes one third that of the oxygen. Finally,
when a quantity of mercury, representing its equivalent number, is
converted into vapour, its volume, reduced to the same standard of
temperature and pressure, is four times that of oxygen, and double
that of hydrogen or chlorine gases.~ It hence results, that although
the equivalent weights of the simple bodies may be totally unconnected, and may range within very extensive limits, yet the volumes
which these equivalent quantities occupy when in the state of gas
or vapour, have a very simple relation to one another; thus, taking
the equivalent weight of oxygen as 100, and its equivalent volume
as 1, the proportion of the other bodies mentioned are:




214 EQUIVALENT VOLU M ES OF COMPOUND BODIES.
Equivalent [Sp. Gr. of Vapour.
Name of SubStance.   Equivalent Weight. Euivalen  p. Gr. of Vapour.
aelae.j   Air=lOO.
Oxygen..      100' 0     1: 1102'6
Hydrogen.        12'5     2        68'8
Chlorine..    442'6      2      2470'0
Iodine..    1579'5     2      8701.0
Bromine..    978'3         2      5393.0
Nitrogen..     1750      2       976 0
Sulphur.      201 2            6648-0
Phosphorus        392'3     1      4327.0
Arsenic..    940-1   1    10362'0
Mercury..   1265'8       4      6969 0
Not merely does this simple proportion of equivahlt,,t volumes
hold among the simple bodies, but it determines in the compounds
which they form an equally regular constitution.
The volumes of the gases which unite are necessari'y in simple
equivalent proportion to each other, and when the same gases unite
in more than one proportion, the second is a multiple of the first. In
all cases, also, where, after union, a condensation of volume occurs,
the resulting volume is simply related to the volumes which the
constituents had occupied before combination. Thus, in the formation of water, one volume of oxygen unites with exactly two of hydrogen, and the volume of watery vapour which is formed is equal
to that of the hydrogen employed.  To fohn ammonia, one volume
of nitrogen unites with three of hydrogen, and the four volumes are
condensed into two by the combination. There may, tlherefore, be
arranged for the various bodies which assume the gadeus form, a
series of equivalents in volume, which will not be totally unconnected numbers, like those of the equivalents by weight, but are found
to be, as the weights should become if the suggestion of Proust were
verified, simple multiples'of the equivalent of some standard body
which may be selected, as oxygen in the table....Name of the Compound Vapour. Formula.  Equivalean   Eqcale uiva ewl; sup. Gr. of
N ame of the Compound Vapour.  Formula, qWuighlent. Volume of Volume of the Vapour.
Weight' C..onsitilueots. Cormpoud. Air=1000.0.
Water.....            H. O. -  1125    3       2      620'2
Nitrous oxide...... N.O.   275.0    3          2    1527'3
Nitric oxide......  N.02   375.0    4            4    1039'3
Sulphurous acid.        S.02  401.2    7         6    2210.6
Sulphuric acid......   S.O    501'2   10      6    2761'9
Sulphuretted hydrogen... S.H.    2137    7        6    1177'0
Muriatic acid.. C1.H.   455'1    4                 4.   1269'5
Hydriodic acid...... I.H.   1592'0    4        4    4385'0
Hydrobromic acid...   Br.H.   990'8    4        4    2731'0
Ammonia.... N.H3 214'5  4   4   591'5
Arseniuretted hydrogen.. As.I-3  952 6    7       4    2694'0
Terchloride of arsenic...As.Cla 2268'0    7       4    6295.0
Calomel.......Hg2C1. 2974-3    6      4    8204'0
Corrosive sublimate... Hg.Cl. 1708'5    8       4    9439'0
Arsenious acid.. -. s.   A.03 1240'1    4     1   13670.0
Sulphuret of mercury... Hg.S. 1467'0    7        9    5384'0
Chloride of sulphur.... S2CI.  8450    4         3    4686'0
Protochloride of phosphorus    P. C13  1720'1    7   4    4741'1
Perchloride of phosphorus. P.C15  25053   11      6    4788'1'I'he simplicity thus shown to exist between the volumes of the
constituent and compound vapour enables us very often to calculate
beforehand what the specific gravity of a vapour should be, and thus




SPECIFIC GRAVITIES OF COM POUND VAPOURS. 215
to ascertain how closely the numbers found experimentally by the
methods described in the first chapter may approach to absolute
correctness. Thus, to calculate the specific gravity of ammonia:
it is formed by the union of three volumes of hydrogen and one of
nitrogen, and the weights of these volumes being as their specific
gravities, the weight of the ammonia formed should be 976+(3 x
69)=1183 if the four volumes of constituents were condensed into.
one; but as the condensation is into two, the specific gravity of
the ammonia is 1183-=2-5915, as given in the table. Sulphur
and hydrogen unite in the proportion of one volume of sulphur to
six of hydrogen, and hence, if there were but one volume of resulting gas, the specific gravity should be 6648+(6 x 69)-7062; but as
there are six volumes of gas formed, the true specific gravity of sulphuretted hydrogen is 7062  6 —1177. The general rule being to
multiply the specific gravities of the simple, gases or vapours respectively by the volumes in which they combine, to add those
products together, and then to divide the sum by the number of volumes of the compound gas produced.
By the application of this principle, we may often decide with
great probability on the specific gravity which certain bodies should
have in the state of vapour, although it has not been as yet possible to weigh their vapours experimentally. Thus the temperature
at which antimony is volatile is so high that the specific gravity of
its vapour may possibly never be determined by experiment; but
the chloride of antimony resembles, in all its chemical relations,
chloride of arsenic, and there is the greatest probability that the
constitution of the two are alike in the state of vapour. Now we
know that chloride of arsenic consists of six volumes of chlorine
and one volume of arsenic vapour condensed into four volumes;
and hence, if we multiply the specific gravity of the vapour of chloride of antimony, which is S106'5, by four, we obtain 32426'0, and
subtracting from it the weight of six volumes of chlorine =14820,
there remains 17606, which, if the analogy between the arsenic ahd
antimony be correct, must be the specific gravity of the vapour of
antimony reduced to the standard of air =1000.
Similar principles have been applied to the determination of the
specific gravity which carbon should possess if it were converted
into vapour. This number would be of great importance in all calculations of the specific gravities of the vapours of organic bodies,
most of which contain carbon as an element; but, unfortunately,
there is no volatile body so similar to carbon as that its analogies
can be taken as a guide, and hence the bases of the calculated
density of gaseous carbon are purely hypothetical. Indeed, chemists are not agreed upon the precise number, s'me making it the
double of what it is estimated at by others. If we look upon carbonic acid as consisting of equal volumes of vapour of carbon and
oxygen, the two condensed into one, the specific gravity of carbon
is 1524'1-1102 6: —421'5; but if the carbonic acid consist of two
volumes of oxygen and one of carbon, the three volumes condensed
into two, the calculated specific gravity of the latter vapour is
3048 2-22052=-843'0. On the first idea, the carbonic oxide consists of two volumes of carbon vapour and one of oxygen, the three




216  CIIEMICAL AND MOLECULAR  CONSTITUTION.
condensed to two (2 x 421'5 + 1102'6) - 2-972'8; and on the latter,
of equal volumes united without condensation (843'0 + 1102'6)-. 2=
972'8. It is this latter view which I adopt, and in any calculations
that may occur hereafter, I shall consider the specific gravity of
gaseous carbon as 843. It does not at all necessarily follow that
the true specific gravity is either of these numbers, as it may be
that the relations by volume of carbonic acid and carbonic oxide
are much more complex. Before the specific gravity of the vapour
of sulphur had been experimentally determined, it was considered,
front similar theoretic grounds, to be 2216, but it is actually three
times as great, 6648, and we must hence not reckon too implicitly
on the relations by volume at present given for the gaseous compounds of carbon.
In the combination by volume, the same laws of multiple proportion hold as in combination by equivalents; thus the compounds of
chlorine and oxygen, which are by weight Cl. O., C1.04, C1. 05, and
Cl. 07, are by volume two of chlorine to one, to four, to five, and to
seven volumes of o. ygen respectively, and so in all other instances; and, consequently, all remarks that have been made regarding the law of multiple proportions in equivalents by weight, apply
to combinations: of equivalents-by volume also..
CHAPTER X.
OF TIE RELATIONS OF CHEI\IICAL CONSTITUTION TO THIE MOLECULAR
STRUCTURE OF BODIES.
IT has been abundantly shown, throughout the preceding portions
of this work, that even the most purely physical properties of a
body are closely connected with its chemical constitution; and that
thus the density, the crystalline structure, or the electrical relations
of a substance, or the manner in which it is acted on by heat, may,
by affording distinctive characters, or by influencing its affinities,
become necessary to its chemical history. The numerical laws of
constitution last described yield additional evidence of the intimate
relation of chemical to molecular constitution; and in the present
chapter I purpose to conclude the description of the general history of chemical action, by an account of such principles as have
been advanced, and such facts as have been discovered illustrative
of this connexion. They are as follow:.:1st. The connexion between the molecular constitution and the:equivalent numbers of bodies. Tlie atomic theory..2d. The connexion between the crystalline form and the chemical
equivalency of bodies. Isomorphism.
3d,' The relation of constitution to composition. Of Dimorphism
and Isomerism. The theory of types.
4th. Of chemical action independent of affinity. Catalysis.




THE ATOMIC THEORY.                      217
SECTION I.
OF THE ATOMIC THEORY.
It was natural that, as soon as the remarkable laws of combination
discussed in the last chapter had been discovered, philosophers
should be anxious to ascend to the causes in which they had their
rise, and to trace, in the operation of some one general principle,
the three determinate numerical conditions to which experiment
proved chemical action to be subjected; accordingly, such theoretical views were promulgated even before the laws of combination
were fully understood; and it has been since one of the most difficult
tasks of the philosophic chemist to disentangle the real and practi
cal from the merely speculative portions of atomic chemistry.
For Dalton, in promulgating the law of multiple combination, the
most beautiful, as well as the most extensive principle that had been
conferred on chemistry since the epoch of Lavoisier, announced it
as the result of speculations which, though in their general nature
true, and constituting still the essential basis of all theories of chemical action, were yet overlaid by a tissue of hypotheses so irregular
and so unnecessary, that for a long time the real dignity and excellence of the experimental laws were underrated and misunderstood.
These accessory speculations have now, however, passed away, and
the theory of combination laid down by Dalton may, in all its essential conditions, be very briefly expressed as follows:
All substances are supposed to be constituted of particles perfectly indivisible, and hence truly atoms. In different kinds of matter, these atoms are of different weights, and probably of different
magnitudes; but this latter quality is of no material interest. When
bodies combine chemically, their combination must be so effected
that one atom of one unites with one atorn of another; or one of the
first with two, or three, or four of the second; or two of the first
with three, or five, or seven of the second; but no intermediate degrees can possibly occur, for the atom being absolutely indivisible,
no intermediate degree of union can take place. The relative
weights of these atoms are the equivalent numbers of the bodies
combined; eight parts of oxygen unite with one part of hydrogen,
by weight, to form water, because the simplest proportions in which
they can unite are one atom of each, and the atom of oxygen is
eight times as heavy as the atom of hydrogen; eight parts of oxygen
are equivalent to 35 4 parts of chlorine, because, when an atom of
hydrogen leaves the atom of oxygen, it combines with an atom of
chlorine in its place, which is heavier than that of oxygen in the
proportion of 35'4 to 8, and the quantity Inust be consequently so
determined. When a second atom of oxygen combines with hydrogen, it being equally heavy with the first, doubles the quantity
of oxygen which the equivalent of hydrogen has taken up, and, as
might be illustrated by any series of examples, introduces as a necessary consequence the law of multiple combination.
Such is the atomic theory of Dalton. It expresses faithfully the
laws of combination; lst, the law- of definite constitution; 2d, the
principle of equivalent proportion; and, 3d, the law of multiple comE: 




218       PHYSICAL AND CHEMICAL ATOMS.
bination. It is therefore, even in this form, the most embracing and
perfect generalization that has ever been proposed in chemistry; but,
before committing ourselves implicitly to its adoption, it is necessary to examine into its bases with some detail.
Dalton assumes that matter is constituted of indefinitely small
particles, atoms, but he advances no proof that it is so; he adopts,
unreservedly, that side of the discussion which, from the earliest
ages, has divided the opinions of philosophers, and shows' that on
that hypothesis all the most remarkable phenomena of chemistry can
be explained. But I have already, in the first chapter of this work,
pointed out, that the question of the ultimate constitution of matter
is now no nearer its solution than it was twenty centuries ago; and
I will now proceed to show, that for the explanation of the laws of
combination, the atomic theory of Dalton is unnecessary, or, at least,
that it becomes only one out of a variety of molecular conditions
which matter may assume. In the first place, it is necessary to ascertain in what manner the relative weights of the atoms of bodies,
if they really exist, are to be determined.
I pointed out in the last chapter the number of circumstances
which should be taken into account for the determination of the
equivalent number of a body; it is by such considerations that in
similar cases the atomic weight of a body is determined; and where
the idea of the existence of such ultimate combining molecules is
adopted, the atom is the equivalent, and the number is its weight.
if, therefore, the theory of molecular constitution involved chemical
results alone, no difficulty would occur; but when we consider these
atoms as building up the mass, and conferring upon it its physical
properties at the same time that they produce its chemical constitution, inconsistencies are found which must prevent our coming
too hastily to a conclusion.
When Gay Lussac first determined the existence of those simple
relations which have been described as existing between the volumes
of gases which combine together, it was considered certain that
all gases contained in the same volume the same number of atoms.
The gases are remarkable for all possessing the same physical constitution. Their relations to pressure and to heat are governed by
the same lawT in all cases, which can be best explained by supposing
that in the same space they contain the same number of ponderable
atoms, set at equal distances from each other, and whose material
repulsion is expressed by the same law. Hence, when one volume
of chlorine unites with one of hydrogen, an equal number of atoms
of each element come into play, and an atom of the compound consists of an atom of each constituent. But here a difficulty occurs;
the chloride of hydrogen which results occupies two volumes, and
yet it is in physical properties identical with the hydrogen or chlorine; all physical evidence would lead us to believe that muriatic
acid gas contained in the same volume the same number of atoms
as its constituents, but the most positive chemical evidence shows
that it contains but half so many. In like manner, on physical
grounds, there should be the same number of atoms in the same
volume of oxygen and hydrogen; and as water is formed by the
union of one volume of oxygen with two of hydrogen, it should




PHYSICAL AND CHEMICAL ATOMS.                   219
consist of one atom of oxygen and two atoms of hydrogen; but the
most perfect chemical evidence we possess proves that water is
composed of an equivalent of each element. The number of chemical molecules in gases is different, therefore, for each gas; it is the
combining or equivalent volume which contains equal numbers of
chemically equivalent molecules or atoms, and, as has been shown
in the tables in the last chapter, those volumes differ remarkably from
one gas to another.
Another physical condition, which is intimately connected with
the molecular constitution and the chemical relations of bodies, is
their specific heats, on the remarkable law of which, regarding the
simple bodies, as discovered by Dulong and Petit, and extended to
many compound bodies by Nauman and Avogadro, I have already
fixed attention (page 67). If we look upon the specific heats of all
the ultimate particles of simple bodies as being the same, we should
at once have a mode of determining their atomic weights, and these
should coincide with the equivalents deduced from chemical considerations.
In the great majority of cases, the atomic weights of the solid simple bodies, deduced from their specific heats, coincide with those
adopted from chemical considerations; and in some of the exceptional instances, as bismuth and silver, there is doubt as to the
true number, which may be fairly interpreted as so far remaining
neutral. But in other cases we find that it completely fails; thus,
the atomic weight of iodine, deduced from its specific heat, is 63 1,
while there is no doubt but that its chemical equivalent is 126'3,
twice as much. Also, the history of arsenic and phosphorus is so
complete, that there is no doubt that their equivalents are 75'4 and
31'4; but when we calculate the atomic weights front their specific
heats, we find as the result for arsenic 37.7, and for phosphorus
15'7, that is, in each case but the half of the real number. In the
gases, also, there is complete discordance between the specific heats
and the chemical equivalents, no matter whether we consider their
purely molecular constitution, by which they should have an equal
number of atoms and equal specific heats in equal volumes, or
whether we compare their combining volumes with their specific
heats. The specific heats of equal volumes (p. 69) of oxygen and
of hydrogen have been proved by Apjohn to be as 808.to 1459,
while on chemical grounds that of oxygen should be double, and
on molecular considerations the same as that of the hydrogen.
It follows, from what has been said, that it is totally impossible
to adopt completely the opinion of Dalton, that bodies are composed
of ultimate and indivisible particles, which, aggregating together,
give origin to sensible masses of the same nature when similar particles unite, and to the phenomena of chemical combination wvhen
the union is between particles of different kinds; I adopt fully the
idea of Dumas, that it is possible, and, indeed, more consonant to
experiment, to explain all the laws of chemical combination quite
independent of all considerations as to whether the masses which
combine are indivisible or the reverse. The word atom, if interpret
ed in its strict and proper sense, is unnecessary, and may be inju
rious if employed with any vague or undefined meaning.




220  VARIOUS ORDERS OF MOLECULAR GROUPS.
I consider, as I have already stated (page 17), that sensible masses
of matter are constituted of a number of lesser masses, which again
may be made up of similar constituent groups, proceeding downward to any extent, but still without involving the question of a limit
to the degree of possible division. One class of these groups of
particles I consider to be represented by the equivalent numbers;
and it is possible that these numbers may indicate the manner in
which the chemically combining groups may be supposed to subdivide themselves, in order to generate a set of groups of an inferior
class. The specific heats of bodies may be considered'to have reference to an order of groups of particles often, but not necessarily,
coincident with those which combine to produce chemical compounds; and the third, probably the most remote, engaged in the ordinary properties of matter, may be such as, being uniformly distributed in the gaseous form,.confers upon those bodies the properties
which characterize mechanically that condition, and are independent
alike of the chemical properties and specific heats which appertain
to, and are exhibited by, groups of a more complex structure and
superior order.
From this point of view I contemplate the atomic theory; for
these groups, engaged in chemical combination, and indivisible by
chemical means, are, in all chemical relations, atoms. Their relative
weights are our equivalent numnbers. From their union the laws of
definite and multiple combination directly follow. But, when we
remove them from their proper sphere, when we subject them to
physical forces, we may dissect them, and separate them into other
groups; or we may unite many of them together to form a larger
group, characterized by the relations to heat and to pressure that
have been already stated, but no longer the group or atom engaged
in chemical operations. Thus the group which-is acted on by the
heat when a gas expands, occupies only half the space in muriatic
acid that the chemical group takes up; but in gaseous sulphur it
occupies three times the space of the chemical atom. In gaseous
oxygen, arsenic, and phosphorus, the mechanical atom is of the
same volume, but the chemical atom only of half the volume that
they respectively occupy in hydrogen, chlorine, and iodine. In
most of the simple bodies the same groups produce chemical combination,.and determine the specific heat; but in iodine, inarsenic,
and in phosphorus, the group which enters into chemical combina
tion contains two of the groups which are pointed out from the
specific heats of these bodies.
I shall frequently employ the word atom in the course of the following page>, but I do so only as an abbreviation for the terms
equivalent quantity or combining masses. Of the ultimate particles of
matter, or true atoms, we know nothing; and all of the discussions
that have taken place, from the earliest and vaguest speculations of
Democritus or Leucippus, to the modern experiments of Wollaston
and Faraday, must be considered as absolutely without influence on
the positive decision of the question.




RELATION OF CONSTITUTION  TO  FORM.  221
SECTION II.
OF ISOMORPHISIM.
The general principles of the isomorphism of crystallized substances have been already noticed, with relation to the fact of their
substitution for each other (page 31), and of the advantage with
which this property may be applied to determine equivalent numbers (pagoe 212); it now remains to study this character, as indicative of the molecular constitution of the body.
It must, in the first place, be carefully observed, that identity of
crystalline form does not imply similar chemical constitution, unless under limiting circumstances, which require to be studied with
great care. The principle upon which all subsequent reasoning
must rest is, that in proportion as the structure of the crystal becomes more complex, and the conditions necessary for its formation, consequently, more varied, the greater probability is there
that two bodies shall not assume exactly the same form, unless their
chemical constitution and the molecular arrangement belonging to
it be the same, or, at least, similar in both. Hence, in the regular system, there can be no inference whatsoever drawn with regard to
constitution from the crystalline form alone. Bodies the most contrasted possible in their properties and composition have identical
external figures, as fluor spar, bismuth, alum, sulphuret of lead, common salt. The conditions of molecular arrangement for the forms
belonging to this system being the easiest possible to fulfil, the
greatest variety in the number and grouping of the chemical constituents- is allowable.
In the other systems of crystallization, where the double refraction and the rings produced by polarized light, transmitted along
their principal axis, indicate a much greater complexity of struc
ture, it becomes highly improbable that the molecules of two bodies shall be so similar to each other as to produce identity of crystalline form, unless there is, if the body be compound, a similarity of
composition, or, if the body be simple, such similarity of properties
as brings the two into the same group in a natural classification.
This probability increases with the complexity of molecular struc
ture of the crystals.
The isomorphism of compound bodies has been explained upon
the supposition that, in such cases, the replacing elements were
themselves isomorphous, and hence might change places without
disturbing the mechanical arrangement of the other components of
the crystal. Thus, in the sulphuric, chromic, selenic, telluric, and
manganic acids, which contain each three equivalents of oxygen,
the molecules of sulphur, chrome, tellurium, selenium, and manganese have all the same form. The perfect determination of whether those elements are really thus isomorphous, is very difficult, from
the fact of comparatively very few being crystallizable. Thus tellurium and sulphur are those of which, alone, we know the crystalline form, for the only crystals of selenium that have been observed are microscopic and imperfect, and neither chrome nor manganese can be had crystallized at all. We must, therefore, be guided




222    ISO)IORPHIS M OF COMPOUND BODIES.
by analogy in such cases; and if we examine another group of comrn.
pounds into which chrome and manganese enter, we find that Cr2
03 and  n2,O,3 are isomorphous with Fe203, and MIn.0. and Fe.O. are
isomorphous with Cu.0. Now we here arrive, by a chain of isomorphous conditions, at a metal which may be obtained crystallized,
but the crystalline form of copper is always one of the regular system, as the cube, octohedron, rhombohedron, dodecahedron, &c.;
while sulphur, with which it should be isomorphous, if this principle were absolutely true, crystallizes in two forms, of which one belongs to the oblique prismatic, and the other to the right prismatic
system; while tellurium belongs to the rhombohedral system, affecting a totally different form altogether. Numerous other instances might be taken; thus the periodic, perchloric, and permanga.
nic acids are isomorphous (I.07, CI.0,, and Mn207), while the elements themselves are certainly not necessarily isomorphous, as
iodine belongs to the right prismatic system. Also the isomorphism of the phosphoric and arsenic acids (P.O5 and As.Os) is one
of the best examples that has been found; but phosphorus and arsenic are so far from being isomorphous, that phosphorus crystallizes
in the regular, and arsenic in the rhombohedral system. The principle that compound bodies are isomorphous, because their replacing elements have necessarily the same figure, is therefore one
which cannot be received in science.
Another idea suggested for the explanation of the phenomena of
isomorphism is, that the crystalline form of a body is completely
independent of its chemical composition, and is produced only by
the number of ultimate particles or atoms by which it is made up.
Thus alum has the same form, whether it contains aluminum or iron,
or manganese or chrome, not because their particles have the same
figure, but because, in all these cases, the molecule of alum is made
up of.the same number (71) of simple atoms. This idea is, however,
even less tenable than the former; for it supposes that we have arrived at the ultimately simple bodies, the true elements, which is a
very unphilosophical assumption; and according to it, bodies could
replace each other only when they were all simple or all of the same
degree of composition, which is not the case; and also among the
simple bodies, that the replacement should be always by an equal
number of ultimate molecules, which is also negatived by experiment. Thus we find that an equivalent of a simple body, K., is replaced by a group of five equivalents, N.H4, and that the simple atom,
Cl., is replaced by the two atoms lMn,. This suggestion cannot, therefore, be considered as satisfactory, and we must examine farther
into the conditions of isomorphous replacement before we attempt
the farther discussion of the source from whence it has its rise.
It is necessary first to study the crystalline relations of the unde
composed bodies, both so far as they have been really observed, and
as they generate similar compounds which are isomorphous. The
simple. bodies which are known to crystallize are:




ISOM OR PHO US  G ROUPS.                          223
Regular System.                      R/iombohedral.
Carbon.                               Carbon.
Phosphorus.                            Tellurium.
Selenium.                             Arsenic.
Copper.                               Antimony.
Silver.
Gold.                              Right Priematic.
Platinum.                             Sulphur.
Mercury.                              Iodine.
Bismuth.
Titanium.                           Oblique Prismatic.
Lead.                                 Sulphur.
It is thus seen that, of the simple bodies which may be obtained
crystallized, two thirds crystallize in the regular system, which, as
already noticed, prevents our resting upon their forms any chemical
reasoning; and the bodies whose isomorphous equivalency is best
established, are not found to belongT even to the same systemn.  Carbon and sulphur are known also to have each two forms of different
systems, and to be thus diniorphous.  It must be observed, however,
that the assumption of the forms of the regular system by so many
of the simple bodies, particularly among the metals, may arise from
circumstances such as confer the external cubical figure on analcime
or boracite, and that their internal structure may be, in reality, more
complex, and their arrangement different; for the metals do not reflect
light as other bodies of the regular system  do; they change it into
the state of elliptical polarization; and in the only case whllere light
can be examined, after having been refracted throuogh a metal, that
of gold leaf, it is found to be elliptically polarized also.  The diamond resembles the metals in this property, and is found sometimes
to possess double refraction, which should belong also to the metals,
probably, if their nature allowed it to be tried.  The cubic crystals
of gold, copper, and bismuth, the octohedrons of lead, silver, and
zinc, may therefore belong to the square or right prismatic: systems,
the three axes being equal among each other, and hence the isomorphism  of the simple bodies be rendered still less probable.
The examples of isomorphism in compound bodies, 1which are most deserving of
attention, are the following:
GROUP I.
Sulphuric acid...... S. 0       These acids, the composition of which
Telluric acid b..        TOe0'3 Iis similar in all, form salts, which, when
elluenric acid...            t e. h S  o tey contain the same base, and the
Selenic acid........
Chromic acid......     e..Cr~03  same proportion of base and of water of
Chromic  acid.0   crysta
Mananic acid  3  crystallization, have the same clystalline
Manganic acid  *..........orl.
GROUP II.
Magnesia.........g.O.
Magnesia. -.      These protoxides combine with acids
Protoxide of iron. Fe.   and form salts whh, when n the same
Protoxide of manganese..   lMn.O.rm salts, which, when in ite same
1 degree of saturation vwith base and water
Oxide of copper...... u. 
Protoxide of cobalt           C.O. of crystallization, have the same form.
Protoxide of nickel            Ni.O. The sulphates of these oxides combine
Oxide of zinc....... ZniO. with sulphate of potash to form isomorphOxide of cadmium....  C,    ois double salts.




224                  ISOMORPH OUS GROUPS.
GROUP III.
Sesquioxide of ihon.... Fe203    These  sesquioxides, combined with
Sesquioxide of manganese.. Mn03  sullphuric acid, with sulphate of potash,
Oxide of chrome... Cr203 and with water, ibrm the different speAlhimina........ A1203 cies of alum, which have all the octohedral form. They are themselves also isomorphous.
GROUP IV.
Potash........             0.    These fixed alkalies may be substituSoda.....           Na.O. ted for each other in the different speHydrated ammonia... N.H3H.O.  cies of alum. The hydrated ammonia,
Hydrate of lime....  Ca.O.H.O. H.O.N.H13 (often called oxide of ammonium, N.H40.), is truly isomorphous with potash in all its compounds; but it. is only
rarely that the compounds containing soda appear to have the same form. In min
erals, and in some forms of alums, potash is replaced by an atom of any oxide in
Group II., united with an atom of water, as hydrate of' lime, or by two atoms of
such compound without water.
GROUP V.
Phosphoric acid...... P.O        These acids combine with bases in
Arsenic acid.......As.05   different proportions to form each three
classes of salts, between which respectively the isomorphism is complete. It was
by the study of the forms of the corresponding arseniates and phosphates that Mitscherlich first established the principle of isomorphism, although the true laws of
their constitution escaped his notice, and were only brought into view by the later
excellent researches of Graham. Even now there is no example of isomorphism
between two complete series of compounds so well established as that of the arseniates and phosphates.
GROUP VI.
Perchloric acid...... C1.07    The corresponding salts of these acids
Permanganic acid..   Mn07 are truly isomorphous, and this group afPeriodic acid.......    07 fords an example of a form to which I
shall recur, that of one equivalent of one body being replaced by two of another, as
C1. by Mn2.
GROUP VII.
Sulphuret of antimony.... Sb.S3    These bodies, which are found crystalSulphoret of arsenic...  As. SS3lized in nature, have the same form.
Sulphuret of bismuth.... Bi2S3  The oxide of antimony and the arsenious
acid, Sb.03 and As.03, though they are not found crystallized in the same form, appear to replace each other in some salts without changing its figure, and may,
therefore, be sometimes isomorphous.
GROUP VIII.
Stannic acid.......  Sn.02  These are found native crystallized in
Titanic acid....... Ti.02 J the same form.
There are many other cases in which similarity of crystalline form has been observed between bodies of more or less analogous constitution; but as here I wish
to bring forward only a sufficient number of the most remarkable examples of the
principle, I shall postpone for the present the consideration of the remainder.
The principle of isomorphism, as thus described, has been supposed to require that the angles of the crystals of the isomorphous
bodies should be truly equal, which they are not found really to be,
for even in the best examples taken slight differences appear.  Thus,
in the carbonates of lime and magnesia, the angles of the rhombs
differ -by 2~ 36'; in the sulphates of zinc and magnesia they differ
by 38'; in the sulphates of barytes and strontia the difference is 2~
48'. To express this, the word plesiomorphism, indicating that such
crystals are not exactly, but nearly, of the same form, has been
proposed; but it is totally useless, as absolutely isomorphous forms
would then be extremely rare.  It is easy to understand that slight




ISOMO EPHISIM  IMPORTAN-T TO THE CHE M IST. 225
changes in external circumstances might prevent the absolute isomorphism of two bodies, particularly as it is found that the value
of the angles in different specimens of even the same substance is
liable to fluctuation even to nearly a degree.  I apprehend that we
must seek the cause of these plesiomorphic differences in the peculiar circumstances under which the body forms, particularly with
regard to temperature; for when a crystallized body, not of the regular system, is heated or cooled, it expands in different degrees,according to the direction of its axis, and may even contract in one
direction while it is expanding in another; thus, when carbonate of
lime is heated from 32~ to 212', the linear expansion in the direction
of the principal axis is 0,001961, while in the direction of each horizontal axis a contraction of 0'00056 occurs; in consequence of this,
the obtuse angle of the rhomb, which at 50' Fah. is equal to 105~
4', becomes more acute by 8I', and the acute angles, which are 74;~
54' 15', become more obtuse in a corresponding degree.  Hence, if
we heated or cooled, through a certain range of temperature, the
various crystallized bodies of that group, they might be brought to
coincide absolutely in form, and possibly, when at first generated,
they were thus coincident; but by change of figure, when brought
to ordinary temperatures, the small plesiomorphic differences may
have occurred.
Isomorphism, considered as thus sketched, affords to the chemist
the most valuable criterion at present at his disposal for determining those substances which replace each other most truly in combination; and where a number of bodies are so connected by external form, very important conclusions may be obtained as to the internal arrangement of their constituents. In this manner it has
been satisfactorily established, that bodies may replace each other
in proportions quite different from  their ordinary equivalents, and
thus pass, as it were, by a doubling or trebling of their atomic
weights, into a different natural group; and that even two bodies,
combined in an equivalent of each, may form a complex group, capable of being substituted for one of simpler structure.  Tius ani
equivalent of chlorine is replaced by two equivalents of manganese;
an equivalent of silver is replaced by two equivalents of copper; an
equivalent of soda or of potash is replaced by two equivalents of
lime, or of one of lime and one of water, or by one of lime and one
of oxide of manganese or of iron, or by ammonia and water united
to each other, or to an equivalent of a protoxide of the magnesian
group.  By such observations we obtain the foundations of a philosophical classification of bodies, with which the analogies drawn
from  purely chemical characters are found remarkably to corre.
spond.
But it is important to ascertain whether the isomorphism of various bodies establishes necessarily, or even probably, in the absence of other reasons, grounds lar
assimilating the formulae of the bodies, or imagining that their chemical constituents are equivalent and are arranged in the same way. This is a point which has
been, as I consider, much misunderstood, and has led to some error and confusion.
Thus anhydrous sulphate of soda crystallizes in the same form as perchlorate of
barytes and permanganate of barytes; and if it be necessary, as a consequence of
isomorphism, that these bodies should have similar constitutions, we must change,
the formula, S.Og. Na.O. into S207. Na2O., in order to make it resemble Mn207..
Ba.O. This requires us to compare the sulphates whose elements are most powF F




226 PRINCIPLES OF ISOMORPHOUS REPLACE M ENT.
erfully united, with some of the most easily decomposed salts that we know; it re,
quires us to consider the alkalies as being suboxides, which is opposed by every
circumstance in their history; and it requires us to consider two equivalents of so
dium as being equivalent to one of barium, for which no other evidence can be had
from other examples. But, again, the anhydrous sulphate of soda is isomorphous
with sulphate of silver, and hence the formula of this last should be S207. Ag20.,
which is so totally unsupported by other evidence that it has been proposed to subdivide the atomic weight of silver and sodium, for the purpose of explaining the isomnorphism of (Cu2 and Ag. These examples are sufficient to show how unphilosophical is the attempt at rashly inverting the principle of isomorphism, and seeking to
deduce, as a necessary consequence of the mere similarity of form, similarity of
chemical constitution. Bodies of similar chemical constitution affect the same
crystalline form; but bodies of the most diverse natures may have the same crystalline form also. Even without speaking of the regular system, where fluor spar
and alum, Ca.F. and K.O.. S.03+A1203. 3S.0s+124H.O., have the same form, we
find numerous examples, of this fact;, nitrate of soda and carbonate of lime are isomorphous in the rhombohedral system, and nitrate of potash and carbonate of lead
in the right prismatic system; the chemical constitution of the formulae N.O5. Na.O.,
and C.02. Ca.O., and that of the formulae N.05. 1.O., and C.O2. Pb.O., are
widely different, but the forces by which the assumption of crystalline form is governed are alike. Even in these instances the attemptsat generalizing the chemical
formulae have been tried, and the nitrates of soda and potash have been written
N.06 K. and N.06. Na., with which the formulae of the carbonates, when doubled,
C2O6Ca2 and C206Ba2, have been compared. In this way one equivalent of soda is
made isomorphous with two of barytes, while by a former and similar reasoning,
one of barytes was made isomorphous with two of soda. Bisulphate of potash,
K.O. S.O03+-H.O.. S.O3, crystallizes in two forms, one of which is that of sulphur, a simple body, and the other of which is that of feldspar, K.O. S3+A-AI203.
3So3. Here, in neither case is there the slightest similarity of constitution.
The circumstances of isomorphous replacement may be reduced
to the following simple propositions; with which I shall terminate
the subject:
1st. Similarity of crystalline form requires that the moleculal
structure of the bodies shall be alike, but has no necessary reference
to the chemical nature or composition of these molecules. Exam
ples.-Nitrate of soda and carbonate of lime, sulphate of soda and
perchlorate of barytes, bisulphate of potash and sulphur.
2d. WVhen the physical molecules consist of chemical elements
which rollow the same laws of combination, and which belong to
the same chemical family, the similarity of molecular structure i-s
most completely and most easily produced, and such crystals are
isomorphous. Examples.-Sulphate of zinc and sulphate of magnesia,
carbonate of lime and carbonate of zinc, sulphate of barytes and sulphate of strontia.
3d. But identity of molecular structure may result from the aggregation of substances the most different in their chemical relations,
and hence isomorphous bodies are not necessarily of similar chemical constitutions.
4th. As the influence of the chemical constitution does not extend
to the absolute determination of the molecular structure, a body,
chemically the same, may assume incompatible crystalline forms,
and so become dimorphous; but as the chemical structure influences
the molecular arrangement in some degree, dimorphous bodies,
which are isomorphous in one form, are generally so in the other,
they are isodimorphous.  Examples.-Sulphur, bisulphate of potash,
nitrate of potash and carbonate of lime, garnet and idocrase, arsenious acid and oxide of antimony.
5th. We cannot assert that the similarity of folnm of truly isomorph



O F DIM ORPHISM AND ISOMERIS M.                227
ous bodies results from the isomorphism of their elements; for,
so far as our observation goes, their simple constituents are not
necessarily, or even usually isomorphous. Examples.-Arseniates
and phosphates, sulphates and seleniates.
6th. We cannot assert that isomorphism results from the aggregation of the same number of simple molecules; for we do not
know what bodies are truly simple, nor do we know, without doubt,
that we canl value the relative number of atoms present; but, evenin the existing state of our knowledge,' we have numerous examples of bodies truly isomorphous which contain an unlike number
of atoms according to our-present ideas. Examples.-Potash and
ammonia, natrolite and mesotype, sulphur, feldspar, and bisulphate
of potash.
Finally. Isomorphism does result from the aggregation, according
to the same laws, of similar molecular groups, which are most generally formed by the reunion of similar -chemical substances in the
same state of combination.
SECTION III.
OF DIMORFPHISM AND ISOMERISM, AND OF THE THEORY OF TYPES.
The fact of the same body being capable of crystallizing in forms
belonging to two different systems has been already frequently referred to, but, for convenience of reference, a more detailed list of
such cases is here inserted, taken from -Professor Johnston's excellent report on the subject made to the British Association.




223                 LIST OF BDIMO1 HOPO   BODIF'8
Symbol or Forn.   |           CrY;!alne Forno.
Sulerek:p,. bodI                                    l Rt. Rh. Pr., M. on M. 109,  id.
|              S. Sulphur....13. A t l   S.Oblique Rh. Pr. of 990 32', 11.
SulpCarbon          A..:                            Reg. Octohedron.
Carbon             BA               C.               Rhombohedral.
II. Bi-elementary Compounds:                          Cube.
IDioxidre of Copp8  * A t I       c.Cu O.         th. of 99~ 15', 6 sid. Pr. Rhomb
cleav.? Sle    Rohomb, P. oi PP  
Disulphut. of CoppeTA)        Cu.8. or Au2S~        Do., Primary a Rhonb., P. on
DulPhufofOpper A   Cu.. or Cu2S.  Reg. Octohedrons.
I)                       t ( Cube in Silver glanee
Rhomboid.
Sulphuret of Silver   t        AgS. or AgaS.         Chbmboid. 
Sulph. of Manganese A             Me.S.             C homboid.
B                                 Rbes.
Bisulpluret of Iron               Fe.S2. AbRKh  R. on'. M             lqf2'.l
_____.     B               l               Octb.O ed. h with square base. 
Biniodidef Mercury A                g12.            Rt. R. Pr., M. M.- 114
Bichlor of Mercury_.                              it Rt. Rh Pr., M.M.-71'55.
OctoheA. with rect. base.
| _. B          s              Reg. Octohedrons.
Arsenious acid      A             As~O               Keg. A  ct Aedrons.. —--  8   l ~.... on 7'Rt. Ro. Pt.
Oxide of Antimony. A             Sb20               Do., M.  on Mc'. 360 55t'
B              heg.-Octohedrons.
III. Coinpounds of 3 Elements:                           Rhomb. of 1050 4', M.
lB S                            Rt. IRhomb.  of 106~ 15',.
Carbon. of Magnesi A  Mg.O.+C.02                  1  homb of 10h. 0 15'.Pr.
I B              l                t ( Rhorb.O Of 07 0.,   I
(tarbonate of A~~~ ur. tRh. Pr., 1D08 260, 118, 0'?
Carbonat of Iron               Fes AFeO+C.02.
Carbonate of Lea   r AO                              Rhomboid, 010 53'?
BCarbonateofLead   A  Pb.O.+C.02.  Rt. lh. Pr. of 1170 14', K'.
B  homb. of 106R 15'.
N|itrate of Potash.A          K.0.+N.O.            Rtphomboid of 10636, 5FM-?
B                               OOh. h. Pr.
Chromate of Lead     A        Pb.O.+Cr.O.  Square Pris
IV. Compounds of 4 or more
Sulphate of Nlementsickel P:i.O.+S.O 7.             Rt. Rh. Pr., M. on M'.. 910 t', Bk.
Bisulphate of Potash                                 Rbombe   ctoh form of sulphur),
B   K.O.S.3                     Ob. Rh. Pr. (frm of feldspa), 
\    Biphosphate of Soda A) N2 \ a.O.+-I-P205+4H.'O | Rt. Rh. Pr. of M. on M'. 930 54'. 
B       or. a, 1s.H2P.+2H.      Do.        of         780 30.
Garnet....A'1  -         Reg. Dodecahedron.
I    G a rne                t.  Square PrisMn.
Idocrase..... B)                 Fe.)          \OblSquare  h. Prism.
Baryto-Calcite.A   Ca. C         Ba.0           Oblique Rh. Prisym.
~Baryto-Ca~cito ~  t     C O +Sa     O. (02e.   Right 1h. Prism (form of arragoB~phatAcute rhomhoid of 720 30'.;' r.O Sr.O.         7 nite) 
ulphate o- Tricar on-                                Rt. Rhomb. Prism,N M. on.Ms 120.
ate of Lead                   bs.opa Prb),. C    S
Ilaidiger sayS an,blique rhombic prism which according to the subsequent measurement of Brook   in
correct. il.,Broosa    Kt., lpfer; Lit., Levy; liT., MIitscheidiclri,S., SurlniV




VARIOUS STRUCTURE OF DIMORPHOUS BODIE S. 229
The molecular arrangements which produce this diversity of form
arb not in general of equal stability; on the contrary, one figure appears to be in general forced upon the body, and is abandoned by
it upon very slight disturbance. Thus, when a prism of arragonite
is heated in the flame of a spirit-lamp, it breaks up into a congeries
of little rhombs of common calc spar at a temperature far below
that at which the carbonate of lime commences to be decomposed;
but no alteration of temperature can convert cale spar back again
into arragonite. Indeed, arragonite appears to be formed only be
tween very narrow limits of temperature. When chalk is melted,
-it forms, on cooling, marble, whose fracture shows it to have the
rhombohedral structure; and when carbonate of lime is precipitated
at ordinary temperatures, the microscopic crystals produced are
rhombohedrons; but when it is precipitated from a boiling solution,
it deposites minute crystals of arragonite, which a hi her or a lower
temperature would have prevented.
When sulphur has been crystallized by fusion in oblique rhombic
prisms, these lose their transparency after a day or two, and change
into a mass of very minute right rhombic octohedrons. When the
arsenious acid is crystallized in rhombic prisms, it alters slowly,
and eventually becomes a dull white mass, which is a congeries of
regular oetohedrons; but if the rhombic form of the acid be dissolved
in muriatic acid, and the solution set to crystallize, it is deposited
in the octohedral form, and the formation of each crystal is accompanied by a brilliant flash of light, indicating probably the moment
of the change of molecular condition. One form is therefore the
stable condition of arrangement, the other being produced by the
sudden fixation of the molecules in a form which is naturally oily
transitive, and from which they free themselves as soon as the external circumstances admit of their suitable motion among each
other.
Independent of the change in external figure, dimorphous bodies
present remarkable differences in physical properties; thus the density is generally different; in one form the substance is more soluble than in the other; they differ also in hardness, and, generally
speaking, in all characters derived from the physical arrangement
of molecules.
A body in its dimorphous conditions presents frequently a difference of chemical properties deserving of particular notice. The
bisulphuret of iron, in its cubical form, is remarkably permanent,
not being acted on either by air or water; but in its right rhoimbic
form, when exposed to moist air, it absorbs oxygen with avidity,
and is converted into a crys tlline mass of copperas. On this printiple depends, most probably, the change of molecular condition
which takes place in oxide of chrome, peroxide of tin, zirconia, and
alumina, when exposed to a temperature just below redness. These
substances, which had been easily soluble in acids, become almost
totally insoluble, except in boiling oil of vitriol, and this change is
generally accompanied by the spontaneous ignition of the body,
which the temperature applied would be quite insufficient to produce.
Independent of crystalline form, we must refer to circumstances




230    CHANGE.S APPROACHING D IMORPHISM.
similar to those which produce dimorphism, a variety of differences
in physical constitution observable in certain bodies.; thus melted
sulphur is, at 230~ F., perfectly liquid; on being heated to 430 it
becomes thick, and so tenacious that the vessel containing it may
be' inverted without it running out; when heated farther to 480', it
ecomes again liquid, and continues so till it begins to boil. When
the red oxide of mercury is heated nearly to redness, it becomes
almost quite black. J,f the red iodide of mercury, formed by precipitation, be sublimed, it becomes yellow; but if the sublimed mass
be scratched with a pin, the edges of the scratch turn red, and.the
redness spreads from thence until the whole mass is converted into
its original condition. Even in liquids and gases, this difference in
molecular -condition, whether produced by temperature or by other
caupses, appears frequently to occur. Thus the liquid hyponitrous'i-i'd (N.03) is deep green at 60~, but at 4' it is quite colourless;
and the deep red gas of nitrous acid (N.O4) becomes, when heated
to 212', absolutely black and opaque. The compound of starch and
iodine, so beautifully blue-coloured at ordinary; temperatures, becomes colourless when heated to 2003, but acquires its original tint
in proportion as it again cools. In all such cases, there is scarcely
room to doubt but that, if we had as perfect methods of determining
the molecular structure as is afforded by the measure of the angles
and the optical properties of the bodies when crystallized, we should
find these phenomena to depend upon causes of the same kind.
In solid bodies, a difference of molecular structure, fully equivalent to that. to which dimorphism may be referred, is capable of being
produced by very simple means. Thus, when a plate of glass is compressed by means of a screw, it assumes a doubly refracting structure,
and gives with polarized light a cross and rings, variously disposed
according to the direction of the pressure. In this case, the change
of structure arises necessarily from an increase of density in the
compressed portions; but the same effect may be produced by the
converse process; a plate of glass which has been suddenly cooled
from having been red-hot, assumes a similar doubly refracting and
polarizing structure, although here the density is diminished in place
of being increased. I have found the sp. gr. of glass suddenly
chilled to be about _,, less than that of glass of the same kind
which had cooled slowly, indicating that the volume was the same
that it had; occupied at a dull red heat, and that hence the internal
molecules, were arranged so as to occupy a greater space than in the
usual condition.
The differences of chemical properties may, however, proceed
much farther, so that in place of econsih4ering that there is one chem-e
ical substance which may exist in two molecular conditions, we are
obliged to consider that the individuality of the body is lost, and
that in its two forms it. constitutes two distinct and independent
chemical substances. - Thus, by the action of sulphuric acid on alcohol, we obtain a gas consisting of carbon and hydrogen, in the
proportion of an equivalent of each. In the destructive distillation ol
wood, a solid substance is obtained, fusible like wax, and volatile only
at a high temperature; this consists also of carbon and hydrogen,
and in the same proportions. These elements, so combined, present,




PRINCIPLE  OF ISOMERISM.                     231
therefore, a difference in molecular arrangement still greater than
those which have been observed among merely dimorphous bodies,
and when we examine their chemical relations, the diversity becomes
still more marked. The gas (olefiant gas) is remarkable for the number of compounds to which it gives rise, and has been, from the variety of its reactions, of great influence on the existing theories of
organic chemistry.  The solid is inattackable even by the strongest
agents, and, from its total indifference to combination, has been called
paraffine (parum affinis.) In this case, the difference of properties
indicates a difference of structure much more profound than that by
which change of density, colour, or even crystalline arrangement
could have its source; it is not merely that the molecules are differently placed, but that the molecules are different; the carbon and
hydrogen which unite to constitute the chemical equivalent of the
body are themselves differently arranged, and thus give rise to difference of properties; and the physical molecules formed by their
reunion being again grouped according to dissimilar laws, produce
the diversity of physical properties and states of aggregation; the
bodies being thus in every property unlike, are to be looked upon
as independent substances; they are said to be isomeric (from twos
iepot) because they have the same ultimate composition, but in all
their chemical relations they may differ as widely as bodies which
have no element in common.
W.hen, therefore, the groups of chemical molecules are differently
arranged, the various differences in colour, density, solubility, and
figure which belong to dimorphous bodies are produced; but when
the difference of arrangement extends to the chemical constituents
of these molecular groups, independent, but isomeric bodies are
produced.
It is generally found that this difference in the constitution of the
chemical molecule has the effect of changing, in a simple manner,
the equivalent number of the body. Thus oil of turpentine and oil
of citron are isomeric, each having the composition C0H4; but when
we combine these oils with muriatic acid, we find that the equivalent group of oil of turpentine contains C,,0,,, while that of oil of
citron is only C,,H,; it is remarkable that, though the chemical
group of oil of citron is only one half the weight of that of oil of
turpentine, it exercises the same power of circular polarization, but
in the opposite direction. Another example of this simplicity of
proportion in weight between the equivalents of isomeric bodies, is
met with in common alcoho'l and methylic ether, that of the former
being C4H602, that of the latter being CH1130.
The difference of the chemical constitution in isomerie bodies is
not limited to magnitude, as determined by the weight of their
equivalent, but extends to internal structure. Thus alcohol is composed of ether and water, CH.H,O.+H.O., while methylic ether cannot
be resolved into those substances. Formiate of methylene and glacial
acetic acid are each CHO44, not differing even in the weight of their
equivalent; but all the properties of these bodies show that glacial
acetic acid is CHO,+H.O., while formiate of methylene is C,11H.0 
2H30O. Instances of this kind might be multiplied to any extent,
hut these will be sufficient to illustrate the principle.




232 CONNEXION OF DIMIOIR 1.. ISM AND ISO.IMERISM.
It is necessary, however, in study'i such cases of isomerism, to
bear in mind what has been so beaut.,'ully shown by Graham, that
the presence of foreign bodies, in quantities so small as to be totally unappreciable, except in the most rigidly accurate analysis, may
change so completely the properties of bodies that they will simulate isomerism. Thus phosphuretted hydrogen may exist in two
conditions, in one of which it is spontaneously inflammable, and in
the other not. They both give, on analysis, the same formula,
P.H3; but the first nmay be changed into the second by mere admixture with a very small quantity of the vapour of ether, and the second may be converted into the first by the most minute bubble of
nitrous acid gas. Such bodies, therefore, which owe their diversity
of properties to accidental circumstances, are not isomeric, and
must be carefully distinguished from those before described.
As we have thus traced a gradual transition from the feeblest indications of dimorphism, to the complete difference of structure and
properties constituting isomerism, it becomes an interesting question whether wve may not have occasion to retrace our steps, and
to seek in those bodies which we have hitherto considered as only
differing in physical properties, for evidence of difference in chemical arrangement. May not a simple substance, as sulphur or antimony, enter into combination with equivalents of different weights,
and so resemble oil of turpentine and oil of citron; and may not
this difference in equivalents be the source of diversity in form'?
When sulphur crystallizes in the form of bisulphate of votash, may
we not reasonably suppose that its molecules are grouped into a
complex figure, like that of the compound salt, and that its equivalent is, in proportion, greater than when it crystallizes as a simple
body l We say that two ordinary equivalents of manganese replace
one of chlorine, bet is it not really that when manganese replaces
chlorine, its equivalent is double what it is when it replaces hydro.
gen or copper'l Manganese replacing chlorine, is to manganese replacing copper, what oil of turpentine is to oil of citron; and hence
it may be isomeric with itself, for the functions it performs in its
two modes of combination are the most widely different possible.
The bisu]phuret of iron, in its cubical form, is Fe.S2, and, like Mn.O,2,
is decomposed only by a red heat, when it parts with one third of
its volatile constituent; but in its rhombic form, may not its equivalent be Fe2S4, resembling C1.04, and, like it, be decomposed by the
slightest causes?
The circumstance that isomeric bodies are almost universally con.
nected by simple relations between their atomic weights, coupled
with the idea that even among the simple bodies a kind of isomerism may be the cause of their dinorphous conditions, acquires remarkable interest from the fact that the equivalent numbers of many
of the simple bodies are closely related to ore another, as is shown
in the following table:




NATURE  OF COM1POUND RADICALS.                      233
i  equivalent of bismuth  -10665 1 equivalent of zinc         3231
2  " s    palladium..   10672 1        "     yttrium... 32'25
((    antimony..   32'4.0
2 equivalent of osmium... 1992 1           antimony.. 
1      "     gold...  19921 2            tellurium... 32 13
1 equivalent of platina...  9884 2   "     sulphur... 32
1      44   iridium... 9884 1 equivalent of cobalt...   29'57
I equivalent of molybdenul.   4796 1'  nickel.... 29'62
~ ";    tungsten..  4740 g-   "     tin...   2946
aMay it not be possible that science shall hereafter find the metals
so connected to be truly isomeric'1 In no case are their properties
more different; and we find in the racemic and tartaric acids an
example of the general similarity of properties in the compounds
of isomeric bodies, which is so remarkable in the combinations of
sulphur and tellurium, or of cobalt and nickel, among the simple
substances.
Considerable probability is given to the idea of the compound nature of bodies at present considered simple, by the existence of
certain compound bodies which simulate the properties of, and
enter into combination subject to the same laws as the undecompounded substances.  Thus carbon and hydrogen unite to form a
gas, cyanogen, which combines with the metals, with oxygen, with
hydrogen, &c., precisely as chlorine does; it is the origin or root
of a series of cyanides, as chlorine is of a series of chlorides, and
it is hence called a compound radical. The discovery of this principle by Gay Lussac was the foundation of all that is exact and
philosophical in our views of organic chemistry.  Bodies which
contain the same ultimate elements may be different, because they
contain different radicals, precisely as the salts of nickel and the
salts of cobalt vill remain quite distinct, even should nickel and cobalt be hereafter shown to be isomeric bodies.  This principle of
compound radicals is so beautiful and so easily applied, that its use
has been, as I conceive, somewhat too extensively adopted; and
hence, wherever simplicity of expression was sought for, or a difference of properties was to be explained, the formule of organic
bodies were perhaps too hastily grouped, by the assumption of a
hypothetic radical, of which the different bodies of the series were
supposed to be combinations. It is certain that, in many cases, this
plan has been of great use to science, as in the benzyle theory of
Liebig, and in the ether and ammonia theories proposed by Berzelius and myself; but I consider the degree to which it has latterly
been extended, by which the existence of a great variety of bodies
has been assumed, for which there is scarcely any reason, except
some additional simplicity of formuk], which often served toconceal the truth, to have been productive of much disadvantage to
true science and a misdirection of thought, which we should seek
as much as possible to avoid.
In all that has been described of the arrangement of the elements
of compound bodies, their union has been considered as resulting
from  their antagonistic and mutually neutralizing properties, and
the successive stages of composition being  effected in binary
groups: thus crystallized alum is a compound of water and dry
alum; this last, a compound of sulphato of potash and sulphate of
G~G




234     CO NSTITU 1ION OF ORGANIC BODIES.
alumina; these respectively, compounds of sulphuric acid and a base
which consists of oxygen united to a metal; the sulphuric acid it
self being formed by the union of oxygen and sulphur. This view
results necessarily from what has been said of tile nature of chemical affinity, and expresses faithfully the principle upon which the
electro-chemlical theory has been formed; there is no doubt but that
the constitution of inorganic bodies is regulated in this way, but we
meet with considerable difficulty in applying its principles to or-'ganic chemistry.'thus I myself suggested a few years ago, that
the formic and acetic acids should be looked upon as oxides of compound radicals, formyle and acetyle, CH.03 —Fo.03 and C,4H303
Ac.03, by which  means a variety of bodies of analogous constitution
were simply connected together, as the formyle or acetyle, which
combine with oxygen to form those vegetable acids, combine with
iodine, chlorine, sulphur, and cyanogen to form binary compounds,
precisely as manoanese (a simple radical) combines with oxygen to
form manganic acid, and with chlorine, &c., to form an analogous
series of bodies. I am far firom abandoning this view: the question
of its full applicability will be discussed among the general laws of
organic chemistry, but at present we will attend to only one circumstance connected with it. Hydrated acetic acid is formed from alcohol, by the latter losing twTo equivalents of hydrogen, and gaining
two of oxygen in their place; and in like manner, hydrated formic
acid is produced from pyroxylic spirit, by losing Ha and gaining 02,
thus:
Alcohol....   C4HG02          Pyroxylic spirit.  C2H-402. gives by    -H.. -02         gives by.   -. H2+02
H-Iydrated acetic acid. C04-I1404.  Hydrated acetic acid. C2H204.
Now, if acetic acid contains acetyle, does it exist in alcohol; or
must we consider that, by the gradual process of oxidation, the
molecular structure of the alcohol is totally broken up, and that the
acetic acid formed has no natural or necessary connexion with it 
We owe to Dumas the introduction of a principle into organic
chemistry, which, applied to changes such as those described above,
promises to shed considerable light upon the reactions and const4i
tution of organic bodies; but it yet involves conditions so opposed
to our present ideas of chemical affinity, that we can only look on
it as a proposition which merits profound attention. He considers
that the elements of organic bodies are not united by affinity arising
from opposition of properties, but that they represent a group of
molecules connected by a single force, precisely as the planetary
masses are by gravitation, and just as any of the planets might be
replaced in the solar system by a ball of matter of totally different
chemical properties, provided its gravitating mass remained the
same, without disturbing in the least the conditions of mechanical
equilibrium; so, in an organic substance, elements of the most diverse characters may be substituted for each other, and yet the
molecular group remain unaltered in structure and physical constitution. Thus the molecular group of alcohol (C4H,02) contains
twelve chemical atoms. When it is changed into acetic acid (C4H404),
the numbei of chemical atoms is the same; the mechanical type of




OF ACTIONS BY CONTACT.                      235
the body is unaltered, although its chemical properties are completely changed and a new substance formed. Bodies, therefore, are
classified by Dumas according to certain types or models. When
the number of molecules in the equivalents of the bod:es remains
the same while the nature of the elements changes, the bodies have
the same mechanical type; but if the substitution of elements is accompanied by a change of properties, the chemical type of the original body is destroyed. Thus alcohol and acetic acid have not the
same chemical type.
When acetic acid is treated with chlorine, it loses three equivalents of hydrogen and gains three of chlorine (C4H04-H3-+Cl3=
C4ClIH.O0), forming chloroacetic acid. The sum of the molecules
is here twelve, and this substance has the same mechanical type as
alcohol and common acetic acid; bLit in changing to this body, common acetic acid scarcely changes its properties, and hence is said
to retain its chemical type. When ether (C4H,O.) is treated with
chlorine, its hydrogen is totally replaced by chlorine, and the body
(C4C15O.), chlorine ether, is produced; the number of molecules being
the same, the mechanical type is preserved; but more, the chlorine
ether combines with acids forming salts like those of common ether,
which it resembles in all essential chemical characters, and hence,
in this case, the chemical type is undisturbed, notwithstanding the
total substitution of chlorine for hydrogen, a body differing finom it
so much in general characters.
The question how far this theory of types should be adopted, and
how far the law of substitution on which it rests is verified by experiment, will be hereafter examined. The theory is here only noticed as involving important relations between the mechanical structure and the chemical constitution of organic bodies.
SECTION IV.
OF CATALYSIS.
The decomposition of compound bodies is frequently effected by
the intervention of causes which cannot be referred to ordinary affinity; and in many cases, bodies which have but little tendency to
unite, enter into combination when brought into contact with a substance for which neither has affinity, and which remains, after the
action is completed, perfectly unaltered. Thus, when hydrogen and
oxygen, mixed together in a gaseous form, are brought into contact
with a clean slip of platinum, they gradually unite, and so much
heat may be evolved by their rapid combination as to ignite the
platinum, and explode the remainder of the gas. In this case we
seek to explain the phenomenon by supposing that the platinum
condenses powerfully on its surface a layer of mixed gaseous particles, and thus brings them within the sphere of their mutual attraction. But this explanation does not apply to other cases. If we
boil starch (C,,H,,O,,) with diluted sulphuric acid, it is converted successively into dextrine, gum, starch-sugar, and, finally, crystallizable
grape-sugar (C,,H120O,), having associated to itself the constituents
of two equivalents of water. At the termination of the process, the
sulphuric acid i-s found unaltered in properties and in quantity, so




236           ANALY:IS AND CATALYSIS.
that the smallest portion of sulphuric acid is sufficient to convert
into sugrar an indefinitely great quantity of starch. If oxamide
oC)O2N.H2) be diffused through water, in contact with the smallest
possible quantity of oxalic acid, it gradually disappears, and, appropriating to itself the elements of an equivalent of water, is converted
into neutral oxalate of ammonia, (C203+N.H3), the small quantity of
oxalic acid originally added remaining unaltered and in excess.
Among instances of decomposition by forces of this kind, the ox*
vgenated water (H.O2) may be taken as an example. This substance,
when pure, separates spontaneously, after some time, into water and
oxygen gas, but its decomposition may be rendered violent and intantaneous by putting it into contact with finely-divided metallic
liatinum, or metallic silver, or black oxide of manganese, or fibrine,
or a variety of other bodies. In all these cases, the body added remains quite unaltered; no affinity can be traced between it and the
oxygenated water, the mere presence of the foreign body appearing
to cause the decomposition.
Berzelius, wrho first directed general attention to these phenomena,
proposed to attribute them to a peculiar force, differing from ordinary affinity. When one body is decomposed by another, in virtue
of a superior affinitary power, the decomposing body combines with
one element of the body which is decomposed, and the other is then
expelled. It is in this way that we obtain the constituents of bodies
by ordinary analysis; and for distinction, he proposes to term such
decompositions as those just described, operations of catalysis, and
to name the power which these bodies have of acting by mere contact, a catalytic force.
It is evident, certainly, that by giving a name to this class of phenomena, we are enabled usefully to contemplate them as a group,
and to examine more easily their relations to each other and to
ordinary action; yet the word catalysis really teaches us nothing of
the phenomena, and it is, indeed, improbable that such varied cases
of union and separation should be derivable from one single force. It
is hence necessary, before concluding on the nature of this action,
to trace it through a greater variety of cases, and to revert briefly
to the conditions of affinity by which the elements of compound
bodies are held together.
The elements of a compound substance are retained together in
a certain molecular arrangement, because the affinities are then sat-.sfied; but it is natural to suppose that, while the elements remain
the same, their affinities for each other might be just as completely
satisfied by a different molecular arrangement. The original body
might therefore be changed into another, by a change in the action
of its own particles, independent of any substance acting chemically
on it from without; and hence the principle of catalytic decompo.
sition resolves itself into a means of disturbing the molecular equilibrium of a compound body, so that it can be only restored when
the particles are differently arranged. Catalysis may, therefore, be
produced not merely by the presence of various bodies, but still
more remarkably by the action of physical agents, among which
heat is the most powerful; thus, when acetate of lime (C4H3O4Ca.)
is strongly heated, the equilibrium of its miolecular group is over




COMMUNICATION  OF MOTION.                    237
turned, and when the affinities again satisfy themselves, two new
bodies result, acetone and carbonate of lime (C3H30. and C.OCa.).
Destructive distillation is therefore a catalytic process, and the origin of all pyrogenic products is to be traced to the new conditions
under which the affinities are satisfied, which had originally united
the elements of the body exposed to heat. The sudden decomposition of explosive bodies by an elevation of temperature or by a
slight blow, is traceable to the same disturbance of the old equilibrium, and establishment of the new. A most important means of
thus setting into motion the particles of bodies, and enabling them
to rearrange themselves under new forms, consists in bringing them
into contact with a substance already in a state of decomposition;
thus, if oxygenated water be brought into contact with oxide of silver, the decomposition is propagated to the latter, which is completely resolved into oxygen and metallic silver; if peroxide of lead
be used, it is converted into protoxide by the escape of half its oxygen, and even the black oxide of manganese may be reduced to
the state of protoxide if the solution contain an acid; in all these
cases, the decomposition, which commenced with the oxygenated
water, extends to the metallic oxide, in virtue of the motion communicated to their particles, enabling the new arrangement to be,effected. In some instances, in organic chemistry, this principle is
still more beautifully shown. If a solution of sugar (C,,H,,O,,) be
brought into contact with a little decomposing gluten or yeast, it
unites with the elements of an equivalent of water, and divides itself into two equivalents of alcohol, 2 (C4H,O,2), and four of carbonic
acid, 4 (C.O2). If a solution of urea (C.O.N.H2) be put in contact
with yeast, it unites also with an atom of water, and is then decomposed into an equivalent of ammonia (N.H1) and one of carbonic
acid. The conversion of starch into sugar in the processes of gerrnination and of malting, is effected by a substance which accompanies the starch in the grain. This substance is called diastase, and
is analogous in most of its properties to vegetable gluten. The
slow decomposition of the diastase communicates to the molecules
of many thousand times its weight of starch the degree of motion
necessary for their rearrangement, and the appropriation of the
elements of water requisite for the formation of starch-sugar.
If platinum, which is, by itself, totally unacted on by nitric acid,
be alloyed with silver, the alloy dissolves in dilute nitric acid without leaving any residue. Pure copper is not acted upon by dilute
sulphuric acid; but when it is alloyed with nickel and zinc, as in
the argentine, or German silver of commerce, it dissolves complete-.y. In these cases, the molecular action which produces the combination with the acid was not possessed by the platina or copper
when alone, but is acquired by them, being transmitted from the
other metals with which they are alloyed.
It may not be easy to reduce to the action of this principle all
phenomena of catalysis; for, in the imperfect light by which we
contemplate therm, it is possible that we may rank together circumstances whose real nature is very different; but, at all events, we
must recognise in this principle, the definite introduction of which
into science is due to Liebig, a cause of chemical decomposition




238          CLASSIFICATION  -OF BODIES.
peculiarly important in explaining the complex reactions of organic
bodies. It is remarkable, also, that this law, of which the simplest
expression is, that where two chemical substances are in contact,
any motion occurring among the particles of the one may be communicated to the particles of the other, is of a more purely mechanical nature than any other principle as yet received in chemistry;
and when more definitely established by succeeding research, it
may be the basis of a dynamical theory in chemistry, as the law of
equivalents and of multiple combination expresses the statical condition of bodies which unite by chemical force.
Wie must, at least, look upon these actions of catalysis, the con
ditions of molecular arrangement which give rise to isomerism and
dimorphism, and the introduction of the principle of types in oppo
sition to that of mere binary combination, as tending towards a
change in our ideas of the nature of chemical affinity, which may,
before long, remodel the -whole constitution of the science.
CHAPTER XI.
ON TIHE CLASSIFICATION OF TIIE ELEMIENTARY BODIES.
THE principal classifications of the simple bodies that have been
proposed are those of Berzelius, founded on their electro-chemical
relations, and of Thompson, who divided them into supporters and
on-supporters of combustion. It has, however, been fully shown,
that in combustion each body is mutually a supporter and a cornbustible: oxygen burns in hydrogen or in the vapour of sulphur, just
as much as hydrogen or sulphur burn in oxygen; Thompson's principle is therefore radically defective; and theelectro-chemical theory, although far superior as a principle, is liable to weighty objections of a somewhat similar kind. These have been already, however, so far noticed, and the arrangement of the simple bodies in that
series so fully given, p. 188, that it is unnecessary to recur farther
to the subject.
The kind of classification that is suited to the present wants of
chemistry must be founded upon the general analogy of properties
between substances belonging to the same class, and on their isomorphous replacement of one another. This last character is not
absolute; for, from the dimorphism of many of the simple bodies,
it is often difficult to assign their true crystalline relations to each
other, and in many cases we do not possess any positive information
of their forms.
Graham has recently proposed a classification which expresses,
more completely than any other, the natural relations of the simple
bodies. The first class consists of oxygen, sulphur, selenium, and
tellurium. The parallelism in properties of the last three is complete, and their compounds are strictly isomorphous;.their similarity to oxygen is not so perfect, but they resemble it in their method
of comlibination and in the characters of the substances which they
form in uniting with hydrogen and the metals.




CLASSIFICATION  OF ELEMENT.-S.                 239
The second class comprises magnesium, calcium, manganese, iron,
cobalt, nickel, zinc, cadmium, copper, hydrogen, bismuth, chromium, aluminum, glucinum, vanadium, zirconium, yttriumn, thorium.
The similar salts of the protoxides of this class are isomorphous;
and, as has been already shown under the head of Isomorphism, two
equivalents of a protoxide of this class replace one equivalent of an
alkali. Chromium, aluminum, glucinum, vanadium, and zirconium
do not form protoxides, but sesquioxides, the salts of which are isomorphous with those of the sesquioxides of iron and manganese. A
remarkable connexion is established between this class and the preceding by the ismorphism of the manganic acid (Aln.O3) and chromic
acid (Cr.03) with sulphuric acid (S.O,), indicating that under cer
tain circumstances these metals may change from one natural family to another.
The third class contains barium, strontium, and lead. Their salts
are strictly isomorphous, and they are connected together by great
similarity of chemical properties. Thus the sulphates of the metals
of the second class are soluble in water, while the sulphates of this
class are almost insoluble. Calcium approximates to this condition
by the sparing solubility of sulphate of lime; and the connexion between the two families is still more fully shown by the dimorphism
of carbonate of lime, it having in one form the figure of the carbonates of magnesia and of iron, and in the other that of the carbonates
of barytes and of lead.
The fourth class consists of potassium, sodium, and silver. The
similarity of chemical properties of potassium and sodium is sufficiently evident; and although their compounds are not frequently
isomnorphous, yet there is good reason for attributing that to the dimorphism of each. Silver differs remarkably in its chemical relations from potassium and sodium, and the only grounds for inserting
it in this class is the isomorphism of sulphate of silver with anhydrous sulphate of soda.
The salts of potash are perfectly isomorphous with the salts of
ammonia which contain an atom of water; and hence, if the base
of the ammoniacal salts (N.H,+H.O.) be written N..I1. 0., it may
be considered as an oxide of a compound radical which is isomorphous with potassium, and would rank, did we not know its composition, in the present group. This view of the composition of the
ammoniacal salts was suggested by Berzelius, who gave to that compound radical the name ammonium; but I have since showvn that
the replacement is really by two equivalents of a hydrogen compound, as already noticed in speaking of the second class.
Fifth class, chlorine, iodine, bromine, and fluorine.  Trhis group
is best characterized by similarity of chemical properties; and, so
far as observation, extends, their isomorphism appears to be complete. It is connected with the first and second classes by means
of manganese, of which two equivalents replace, in truly isomorphous compounds, one of chlorine.
Sixth class, nitrogen, phosphorus, arsenic, and antimony. In their
chemical history these compounds exhibit considerable, the ugh not
complete similarity. The corresponding compounds of arsenic, antimony, and phosphorus are generally isomorphous, but in no case




240        CLASSIFICATION  O F ELEMIE NTS.
has isomorphism been observed between their compounds and those
of nitrogen. A certain analogy appears to exist between nitrogen
and the substances of the fifth class, as the nitric acid corresponds
remarkably in properties to the chloric and iodic acids, with which,
however, it is not isomorphous. Nitrogen appears also to replace
oxygen in many cases in the proportion of one third of its equivalent weight.
Seventh class, tin and titanium, connectedf by the isomorphism of
titanic acid and peroxide of tin.
Eighth class, silver and gold, from their isomorphism in the metallic state.
Ninth class, platinum, palladium. iridium, and osmium, from the
isomorphism of their double chlorides, by which also Graham consiers this class to be connected with the seventh.
Tenth class, tungsten and molybdenum; the tungstates and molybdates being isomorphous. These metals will probably be found
to be of the same family with chrome, as chromate of lead has been
found crystallized in the same form as the molybdate.
Eleventh class, carbon, boron, and silicon: of these substances
no isomorphous relations are known; they are brought together by
a general, though imperfect analogy of properties.
Graham makes no attempt at classifying mercury, cerium, columbium, lithium, rhodium, or uranium.
I agree completely with the general principles of this classification, but, in a few cases, researches made since it was drawn up by
Graham render some alterations necessary; thus the similarity of
constitution between the compounds of bismuth and copper, which
had induced him to insert bismuth in the second class, has no real
existence, and I would transfer it to the same class with antimony;
their sulphurets being isomorphous, and their chemical properties
br-ing, generally speaking, very similar. Indeed, it is almost certain
that the oxide of bismuth is not a protoxide, but a sesquioxide, and
hence corresponds to the oxide of antimony.
I do not consider the isomorphism of sulphate of soda and sulphate of silver as being a sufficient ground for ranking the latter
metal in the fourth class. We have already seen numerous examples
of isomorphism among substances of totally different chemical constitution, and the properties of the compounds of silver resemble so
completely those of lead, as to demonstrate positively that it belongs to the same natural group. When copper enters into combination in a double equivalent Cu2, it becomes likewise a member of
the lead and barytes group, as is shown by the sparing solubility of
its sulphate and chloride; and its being isomorphous with silver furnishes additional evidence of its true position.
Silver and gold being isomorphous only in the regular system,
and their compounds being totally dissimilar in constitution, I do
not retain the eighth class of Grahanm.
I have satisfied myself of the perfect analogy of palladium with
copper; it therefore must be separated from platinum, and removed
to the second class. When mercury enters into combination with
the equivalent 101,4 (Hg.), it coincides in the nature of its compounds with palladium and copper, and attaches itself to the seconld




NON-METALLIC BODIE S. —OXYGEN.                     241
class; but when its equivalent is 202,8 (Hg2), its compounds resemble those of lead and silver, and, like copper, it then becomes a member of the third class..
A classification such as this, although necessary for the philosophical study of the relations of the simple bodies, could not, without
considerable inconvenience, be strictly adhered to in an elementary
work like this; I shall, therefore, having thus laid down these general principles, place it for a time aside, and commence the study
of the non-metallic bodies, and their compounds with each other,
without reference to any arrangement, except that of treating first
those subjects that may be useful towards understanding or illustrating those that follow.
CHAPTER XII.
O0 THE SIMPLE NON-oMIETALLIC BODIES, AND THEIR COMPOUNDS WITH EACIT
OTHER.
Of Oxygen.
FROMI the great quantity in which it exists in nature, the numerous processes into which it enters as an agent, and the influence
which its discovery exercised upon the progress of chemical theory,
oxygen may be looked upon as the most important of the simple
bodies. It constitutes more than a fifth of the atmosphere by which
our planet is invested, eight ninths of the whole quantity of water
which exists upon its surface, and, besides existing in great quantity in most animal and vegetable bodies, it forms at least a third of
the total weight of the mineral crust of the globe. On it the proeesses of combustion and of respiration are dependant, and the
functions of organized existence, in both its forms, are essentially
connected and sustained through its agency.
Oxygen exists only under the form of gas; it is colourless and
transparent; its specific gravity is 11026; 100 cubic inches of it
weigh 34'2 grains; its refractive index is 0'8616, that of air being
1.0000. It is very sparingly dissolved by water, 100 cubic inches of
water taking up only between three and four of
the gas. It is, consequently, in most cases,
collected over water, by
forms of apparatus that
shall be now described.
For the collection and preservation of gases, such as oxygen, the instruments generally employed are the pneumatic trough and the gasometer, The former is any vesH. R




.i42 GASOMETERS. —PREPARATION   OF  OXYGEN.
sel, g, containing water, for such gases as are not absorbed by it, in which is
inverted a glass vessel full of water, which is sustained in it by the pressure of the
external air, as is the mercury in the tube of the barometer. The orifice of the
tube c, from which the gas issues, being brought under the edge of the jar, which
is generally sustained upon a shelf, the water descends according as the bubbles
of gas ascend; and when the jar in the water has been all replaced by the gas, the
jar may be, removed on a tray, containing as much water as serves to prevent all
communication from the interior with the external air.
The gasometer, or gas-holder, consists of a cylindri:al
copper vessel, on which another is secured by five props of
copper, of which two are hollow tubes, in connexion with
the cylinder below. The tube m passes down nearly to the
bottom of the cylinder, but the. other, n, only extends to
the upper surface; both are provided with stopcocks, so
Iz    that the communication between the cylinder and the!::    upper vessel may be opened or cut off at pleasure. At I
there is also a small tube with a stopcock, and below there
is a large orifice at i, which can be tightly closed by means
of a screw-plug.
To fill the cylinder with water, the orifice z is to be
-losed, and all the stopcocks, mn, n, 1, left open. Water
being then poured into the upper vessel, it flows in through
the tubes mnz and n, while the air issues at 1. When water
begins to flow out at 1, that stopcock is to be closed, and
then the air which still remains escapes by the tube n, bubbling through the water in the upper vessel.  When this
also ceases, the stopcocks m and n are to be closed, and
the orifice i being then opened, the cylinder remains full of water by the external
pressure. The tube from which the gas issues is inserted at i, and a quantity of
water escapes by that aperture equal in volume to the gas which passes in.
A great variety of processes may be put in practice for the purpose of obtaining oxygen gas; one, which is very simple in theory,
and of great interest in history, from being that by which the important agencies of oxygen in chemistry were first recognised, although it is not at present practicably useful, is the following:
Some red oxide of mercury (Hg.O.) is to be introduced into a
retort, a, of hard glass, to which is then attached a receiver, b, with
a tube, c, passing to the pneumatic trough.  On applying the heat of
the argand spirit-lamp to the oxide of mercury, it is decomposed;
the oxygen is given off in the state of gas, and may be collected in
the bell glass e, and the mercury distils over, and, condensing in
the neck of the retort, collects in drops which flow into the receiver.  The substance used is thus resolved into mercury and oxygen;
from  109-4 grains, there would have been obtained 101'4 grains of
metallic mercury, and 8 grains of oxygen gas, occupying at the
standard temperature and pressure 23'4 cubic inches.  It was by an




PREPARATION  OF OXYGEN.                     243
experiment of this kind that Lavoisier demonstrated the true constitution of the metallic oxides.
Although there are few metallic oxides which, as that of mercury,
admit of being resolved by heat completely into free metal and oxygen, yet many, when heated, give off a portion of their oxygen,
the metal remaining in a lower degree of oxidation. Of this kind
are the peroxides of lead and of manganese; and it is generally from
the latter that oxygen is obtained for experimental purposes, when
it is not required to be absolutely pure. The peroxide of manganese (lan.O,) abandons, when at a red heat, one third of its oxygen,
and a complex oxide, tMfn3O4, remains, analogous to the black magnetic oxide of iron, and formed by the union of equivalents of pro
___~ —~ —~~  C~C  d'\
toxide and of sesquioxide (AiMn.O.+Mn2IQ3). For this purpose the
manganese is introduced in an iron bottle, a, to the neck of which
is attached a piece of gun-barrel, b, and this connected by a cork, c,
with a smaller tube, d. For sake of freedom of motion, the tubef,
which passes to the pneumatic trough or the gasometer, is attached
to d by a caoutchouc connector, e. The bottle having been filled
abotut two thirds with oxide of manganese, may be placed either in
a common fire or in a furnace, its parts being all arranged as in the
figure. When first heated some water passes off, and frequently,
from the occurrence of carbonate of lime and of ammonia in the
substance, the first portions of gas are mixed tvith carbonic acid or
with nitrogen; these should be allowed to pass away, and the oxygen collected only when a small tube full of it is capable of relighling a taper four or five times. The pure dry oxide of manganese
consists of 27'7 of manganese, united to sixteen of oxygen, of which
5'3 are given off, and hence 1 lb. troy of it is capable of furnishing
about 700 grains, or nearly 2000 cubic inches, equal to seven impe




244           PREPARATION  OF OXYGEN.
rial gallons of gas. The oxide of manganese found in commerce is,
however, not pure; in general it does not contain more than 65 per
cent. of pure oxide, and hence the quantity of oxygen furnished by
a pound of it is about two thirds only of that just stated.
Peroxide of manganese yields more of its oxygen when treated
with oil of vitriol than when simply ignited, one half becoming
free,-while the manganese, with the remainder, forms protoxide,
which combines with the sulphuric acid thus: H.O.. S.03+Mn.O, —
H.O.. S.03. Mn.O.+O.
This operation is conducted by placing the manganese in a flask,
a, supported in a little
cup of sand, b, over a
lamp, and mixing it with
twice its weight of oil of
vitriol; atube, c, bent, as
in the figure, passes to
the pneumatic trough,
and dips under the edge
of the jar in which the
gas is to be collected..
When the flask is heated, oxygen gas is rapidly disengaged, but care
must be taken that, towards the close, the water of the trough may not pass back into the flask, where, mixing
with the hot oil of vitriol, it might produce an unpleasant explosion.
The decomposition which here occurs has been supposed to consist simply in the expulsion of the second atom of oxygen by the
sulphuric acid which takes its place. This, however, is not the case.
By a very gentle heat, the sulphuric acid decomposes the peroxide,
Mn.O,, into protoxide, Mn.O., and permanganic acid, MnO7 (5Mn.02
=3Mn.O.+Mn207). This last is decomposed, when the temperature
rises, into 2(Mn.03),manganic acid, giving out one equivalent of oxygen; but the temperature must be raised very much to complete
the separation of the Mn.03 into 02 and Man.0. Hence, in this process, as ordinarily conducted, the residue in the flask is found to be
green, from manganic acid; and, although in theory a more abundant source of oxygen than that by simple ignition, in the proportion of 3 to 2, it is not so useful in practice.
When oxygen is required completely pure, it is generally prepared
by heating in a glass tube or flask, to which a
bent tube is attached, as in the figure, a small
quantity of chlorate of potash. This salt consists of chloric acid united to potash Cl.O+IK.0.,
and when heated somewhat above its melting
point, it is decomposed, all the oxygen it contains being evolved in the state of gas, and the
Z    other elements remaining combined as chloride
of potassium. The constituents of this salt are
by weight 35'4 chlorine, 39'7 potassium, and 48
of oxygen. Hence 100 parts of it give 39 of
oxygen by weight, or an ounce troy, 187 grains,




PROPERTIES  OF  OXYGEN.                        245
or 543 cubic inches.  An ounce of it is therefore equivalent' in effect to six ounces of ordinary peroxide of manganese.
The most remarkable property of oxygen is the energy with which
it supports combustion.  If a lighted taper be blown out, so that a
point of the wick shall continue red, it will be brilliantly relighted
on being plunged into a vessel of oxygen gas, and this may be repeated several times in succession. A bit of charcoal, heated to
redness at a single point, burns, when immersed in oxygen, with
rapid scintillations of exceeding brilliancy; and when phosphorus
is inflamed in oxygen, the splendour of the combustion is insupportable to the eye. Even bodies which are not combustible under ordinary circumstances, may be made to burn in oxygen.  Thus, if an
iron wire be tipped at its extremity with sulphur, or have attached
to it a small bit of waxed cotton wick, on lighting this, and plunging
the whole into the gas, the combustion extends from the sulphur or
wick to the iron, which is converted into oxide, with the disengagement of most brilliant light. The heat evolved by the combination
of the oxygen and iron is so great, that the oxide formed is melted,
and flows down in drops from the extremity of the burning wire,
which, even after having passed through a layer of water, fuse themselves into the substance of the earthenware plate, upon which the
gas jar generally stands.  If, at the moment when a drop of oxide
is about to fall, it be projected by a little jerk against the side of the
glass, it will melt its way into its substance, or even, if it be not
thick, pass completely through.
The heat evolved when the body burns in pure oxygen may be readily shown by
simple methods. If a jet, u, be attached to the lateral stopcock, i, of the gasometer, and the flame of a   111
spirit-lamp, h, be urged by the issuing stream of gas,
as by a blowpipe, the most refractory substances
may be fused by it. If the tube be curved downward, the jet may be brought to bear on a little cup  -
of red-hot charcoal, in which the body to be fused
may be laid, and thus, upon a small scale, the construction and effect of the most powerful wind fur-'
naces may be imitated.
Oxygen gas is necessary to the support
of animal life. It is the oxygen which exists in the atmospheric air that fits it for    
its uses in the economy of nature.  The
blood which returns dark and venous into the lungs is there changed
into the bright arterial state, by absorbing oxygen and evolving carbonic acid, in a manner of which the exact details will be hereafter
studied.  This change occurs even with blood which has been removed from the body.  If a quantity of dark blood, drawn from  a
vein, be agitated in a vessel of oxygen gas, it is immediately changed
into the vermilion-coloured arterial blood. An animal can live longer in a vessel of pure oxygen than in the same volume of atmospheric air; but still, pure oxygen is not fitted for the support of life. It
is too stimulating; the animal lives too fast, and ultimately dies with
symptoms of general inflammatory fever, even though there may remain still a quantity of oxygen gas capable of supporting the life of
another animal for a considerable time.
The name of oxygen was given to this body from the idea of its




246          PREPARATION  OF  HYDROGEN.
peculiar power of conferring acid properties on its compounds; and,
in reality, most of the, bodies recognised by chemists among the
class of acids contain oxygen. But this is not invariable; other
simple bodies-possess the same power, as has been already noticed
on more than one occasion, and I shall have opportunities of recurring to it when describing the properties of those bodies.
Of Hydrogen.
Hydrogen exists abundantly in nature as a constituent of animal
and vegetable substances, and is particularly of interest by forming
a constituent of water. From this fact it derives its name, vda)p
yevvaw (I form water), and it is by the decomposition of water that
hydrogen is almost always obtained for experimental purposes.
If a small quantity of the metal potassium be placed in contact
with water, it immediately abstracts the oxygen, forming potash,
which is an oxide of potassium. The hydrogen is set free, and appears as a gas. If the experiment be performed under a bell glass,
inverted in a basin of mercury or water, the gas may be collected;
but if the decomposition takes place in contact with the atmospheric
air, so much heat is evolved by the rapidity and intensity of the
action, that the hydrogen tales fire, and burns according as it is
produced. This is the simplest form under which the decomposition of water can be exhibited, the reaction being K.+H.O.=IK.O.
+H.
If the circuit of the electrical current from a'voltaic battery be
completed through water, which has been rendered a good conductor by the addition of sulphuric acid, or cornmon or Glauber salt,
the two constituents of the water are evolved at the opposite electrodes, or terminating surfaces of the liquid, and the two gases may
be collected either separately or mixed together, and will be then
found to have been evolved in such proportions that the hydrogen
will be double the volume of the oxyoen. The theory of this mode
of obtaining hydrogen has been described, so far as we are competent to explain it, in a former chapter.
These methods, although the simplest, are yet not applicable to
ordinary purposes, from their expense; those usually employed are
the following. There are many metals which, although having a
powerful affinity for oxygen, are yet not able to abstract it from hydrogen, and so to decompose water at ordinary temperatures; but
at a red heat the decomposition rapidly takes place. For this purpose iron is generally employed. A gun-barrel, or an iron tube, c c,
is taken, and the interior having been loosely filled with iron turnings or coils of iron wire, it is placed horizontally in a furnace, by
means of which it can be brought to a full red heat. To one extrem
ity of the tube is connected a small glass retort, a, containing water;
to the other, a flexible metal tube,f, which passes under the shelf of
the pneumatic trough. The iron tube being red hot, the water in
the retort is made to boil; the vapour passes into the tube, and
comes into contact with the red-hot iron; decomposition immediately occurs, and the iron is oxidized, while the hydrogen gas is
disengaged in large quantity. The state of combination into which'the iron is found to have passed is that of the black oxide, such as the




PREPARATION OF HYDROGEN.                     247
scales that are formed at the smith's forge by the action of the atmospheric air on iron, and which is also formed when iron is burned in oxygen gas. The action may, however, be simply represented as follows:
Fe.+ H.O.- H.r+Fe.O. Protoxide of iron.
2Fe.+-3H1.0.-3H.+Fe,03 Peroxide of iron.
3Fe.+4H.O.-4H.+FeO4 Black oxide of iron.
The action of the iron in thus decomposing water might appear
paradoxical, as it will be seen hereafter that by means of a current of
hydrogen gas, acting at a red heat, oxide of iron may be decomposed,
the iron separating in the metallic state, and water being produced;
and thus, at the same temperature, two decompositions, precisely the
reverse of each other, may go on. It would appear that this is one
of those cases in which affinities, nearly equal otherwise, are directed to one or the other object, according as one or the other substance is in excess. When the iron is kept in a stream of watery
vapour, this latter is decomposed, and the hydrogen being carried
away, according as it is formed, by the current, it cannot interfere
by its presence in any opposing manner. On the other hand, when
oxide of iron is heated in a stream of hydrogen gas, it is decomposed, and the water being removed as rapidly as it is produced, the
tendency to reaction is prevented.
By the agency of a dilUte acid we may also increase the tendency of a metal to combine
with water, so that the decomposition of water can
be effected rapidly even at _
common temperatures. If
a few slips of zinc or iron
be placed in a flask, to
which a bent tube, f, is
adapted, as in the apparatus represented in the fig-              I
ure, and then oil of vitri



248 PREPARATION AND PROPERTIES OF HYDROGEN,
ol, diluted with eight times its weight of water, be poured upon it
through the funnel, an abundant effervescence occurs, arising from
the escape of hydrogen gas, and the zinc or iron rapidly dissolves.
The action continues until the acid has been all neutralized by the
zinc, or the zinc all dissolved by the acid; or, finally, until so much
of the compound formed during the reaction has been produced,
that the water present cannot dissolve any more. This compound
consists of oxide of zinc or of iron united to the sulphuric acid, the
oxygen of the decomposed water uniting with the metal, while the
hydrogen is set free. The process may be thus represented, zinc
being used, Zn.+-S.03+-H.O.=H.+(S.03+Zn.O.)
To account for the circumstances of this reaction, a peculiar
power was at one time supposed to exist, termed disposing affinity;
and it was said that the presence of the sulphuric acid disposed the
zinc to decompose the water, because the oxide of zinc, when formed
by the decomposition, might unite with the acid. This theory is
quite futile. There can be no oxide of zinc to influence the acid
until the water has been decomposed, and the effect, the source of
which was to be sought for, had consequently passed away. It ap
pears to me that the explanation is of a much simpler form. Zinc
and iron decompose water at ordinary temperatures, even without
the presence of any acid, but with excessive slowness, so that the
effect is almost imperceptible. In fact, the first minute trace of oxide which is formed, being insoluble in water, coats over the metallic
surface with a varnish impermeable to the fluid, and thus prevents
its farther action. This coating of metallic oxide is soluble in acids;
and thus, by the presence of an acid, a fresh surface of bright metal
is kept constantly exposed, and the dec6mposing action is allowed
to proceed without hinderance. It is possible, however, that this
simple view may require some alteration, and that this mode of obtaining hydrogen gas may be found to involve voltaic conditions
which at present are not well understood. Pure zinc is but very
feebly acted on even by a diluted acid; and the rapid action which
occurs with.commercial zinc or iron may be referred to decomposition by the electric currents which circulate from one portion of
the impure metal to the other, through the liquid. See page 135.
Hydrogen gas, when it has been prepared by any of these processes, is seldom pure. The iron and zinc of commerce contain generally traces of carbon, of sulphur, and sometimes of arsenic, which,
combining with some hydrogen, form gaseous or volatile products,
which give to the hydrogen a peculiar disagreeable odour, and colour its flame. Occasionally, also, traces of potassium and zinc, in
very minute division, are carried up with the hydrogen by the mechanical force of the effervescence, but by repose these latter impurities are found completely to separate. To get rid of the former
class of impurities, the gas may be made to bubble very slowly
through solutions of potash and of corrosive sublimate, by which
the arsenic and sulphur would be absorbed, and through alcohol,
which would for the most part dissolve the carburetted hydrogen.
It is, however, better, when pure hydrogen is required, to prepare
it by acting upon water with metallic sodium mixed with quicksilver,
so as to moderate the rapidity of the decomposition. Zinc, which




PROPERTIES  OF  HYDROGEN.                           249
has been refined by distillation, gives also, with sulphuric acid and
water, a gas almost completely pure.
When free from foreign matters, hydrogen gas burns with a very
pale white flame, almost invisible in bright day. In burning, it combines with the oxygen of the air, and forms water. If a jar of hydrogen gas be suddenly turned with the orifice upward, and inflamed, the whole mass of gas rushes out, and gives a sheet of pale
white or yellowish flame. If it be mixed with air previous to being
set on fire, the combustion of the mixture is instantaneous, and accompanied with an explosive report. The proper proportions are two
volumes of hydrogen gas to five of air.  If a lighted taper be plunged
into a jar of hydrogen, it is immediately extinguished, the gas not
being able to support combustion.
Hydrogen gas is colourless and transparent; it is absorbed by wa
ter in very small quantity, and hence, for ordinary purposes, is always collected over that liquid. It refracts light strongly, its re
fractive index being 6'61, air being 1'00.  In its capacity for heat
it exceeds all other gases, being 21'9 by Apjohn's experiments, air
being 1'00 for equal weights, or 146 for equal volumes.  It is the
lightest substance known, being only one fifteenth of the specific
gravity of air; or, more accurately, its specific gravity is 68'8, air
being 1000'0.
It is hence used for filling balloons; as the balloon full of hydrogen weighs less
than the same volume of air, it ascends with a force equal to the diffberence of
weight. For the purpose of illustrating this property of hydrogen, a small balloon
made of gold-beater's skin, or of the serous membrane of the turkey's craw, may
be made use of. On this minute scale, however, the gas should be used dry, as,
when prepared and collected over water, its specific gravity may be so much increased by the watery vapour it may contain, that, although good enough foI a
larger balloon, it could not carry up a small one, the small balloon being really
much heavier in proportion to the quantity of gas it can contain; consequently, the
hydrogen should be dried, which may be effected by causing it to stream from the
gasometer through a tube filled with fragments of fused chloride of calcium, which
absorbs water with great avidity, and from thence to enter the balloon. At present,
hydrogen gas is but seldom employed, it being found cheaper to make the balloon
very large, and to use coal gas, which, although much heavier than hydrogen, is
considerably lighter than atmospheric air under the same volume.
By the same experiment, the three most remarkable properties of hydrogen may
be exhibited in an interesting form. If a jar of hydrogen be held vertically, with
the orifice downward and open, it will remain filled by the hydrogen for a certain
time, as the air, being so much heavier, mixes itself with the lighter gas but very
slowly. If a lighted taper be now applied, the gas will inflame at the surface
where it is in contact with the atmosphere, but, on plunging the taper upward into
the pure gas, it will be extinguished; being then lowered, it can be relighted at the
sheet of flame which marks the surface of contact of the gas and the atmosphere,
and when' again raised into the pure gas, it will again be extinguished; this can be
repeated very often: the horizontal sheet of flame having been gradually rising into
the jar according as the hydrogen consumed, if then the jar be suddenly turned
with the orifice directed upward, the residual gas will at once rush out, and, mixing
with the air, will burn explosively with a single flash.
The same experiments on the combustion of hydrogen may be made with pure
oxygen gas in place of atmospheric air, but then the results are at least five times
more brilliant. The proportions for burning hydrogen with oxygen gas are two
volumes of hydrogen and one of oxygen; then, if the gases were pure, nothing but
pure water should remain.
If a bladder be filled with the two gases mixed in these proportions, and being
punctured, the flame of a taper be applied to the orifice, the whole explodes with a
flash of brilliant light and deafening explosion, the strongest bladder being torn to
shreds by the expai.aive force of the ignited gases. In this experiment the bladder
I 




250             PROPERTI.ES OF HYDROGEN.
must, of course, be secured, which is easily done by tying the stopcock by which
the gas has been passed into the bladder between two nails, with some stout cord
or copper wire.
A mixture of hydrogen and oxygen may also be exploded by means of the electric spark; for this purpose a strong tube, closed at the top, and graduated into
parts of a cubic inch, is taken, and two brass or platina wires are inserted through
the opposite sides near the top, their extremities being kept about one eighth of an
inch asunder. This tube is termed a eudiometer,
~,2 e....-b   as it is frequently used to measure the quantity of
_  oxygen in the atmosphere, and generally for the
]_rwg=] ~ Yanalysis of gaseous mixtures. The oxygen and
l-,1-l =f    \j          hydrogen gases being confined in this tube over
water or mercury, an electric spark is passed
through the mixture by means of the wires; the
n          gases explode, and, if the proportions had been
accurately observed, no residue is found; if one
or the other gas had been in excess, the excess
_-_ -              remains behind, one third of the volume which
disappears being oxygen, and the other two thirds
being hydrogen. In order to explode a bladder
full of the mixed gases by means of electricity, a
yery simple plan is to fasten the bladder upon a
large cork, having in the centre an opening, into
which a stopcock is screwed foir the passage of
the gas, and through which, near the edges, pass
12; =1   C  i     two stout brass wires, terminating inside the
bladder in small knobs; these ends being brought
near each other, and the external ends being connected by long wires with the
coatings of a charged Leyden jar, the spark passes between the terminal knobs in
the bladder, and the explosion immediately occurs.
Hydrogen and oxygen are capable of entering into combination,
and forming water without any explosion or visible combustion.
If the mixed gases be transmitted through a tube heated to scarcely
visible redness, they quietly combine, and this effect occurs at a
still lower temperature, if the  tube contains coarsely-powdered
glass or sand. Slips of gold and silver are still more favourable;
but the most rapid union is effected, even at ordinary temperatures,
by platinum.  This effect appears to be due to the metallic surface
retaining a thin layer of gas by so strong a force as by condensation
to bring the molecules within the sphere of their mutual chemical
attraction; they, combining, form water, and a new quantity of the
gaseous mixture comes into contact with the platinum, and follows
the same course. If, the platinum be in the form of a sponge, in
which the acting surfaces are very great, the union takes place so
rapidly, that the heat evolved raises the temperature of the platinum
ball to bright redness, and then the remaining gas explodes.  Platinum in form of sponge always contains a quantity of air in this condensed condition, and hence, when a jet of hydrogen gas is caused
to play upon a morsel of spongy platina, it is absorbed, and water being formed, the ball of platinum becomes red hot, and inflames the
jet of gas. This constitutes a sort of lamp for instantaneous light,
equally pretty and ingenious, the jet of hydrogen in its turn being
contrived to fall upon and light a little lamp. See p. 179 and 235.
Spongy platinum introduced into a mixture of oxygen and hydrogen explodes them instantly, but it can be usefully diluted, as it
were, by being made into balls with a little pipe-clay, and then it
can only produce their union in the slow and silent way. This mode
is accordingly often used in the analysis of mixtures of gases, and




IIYDRO-OXYGEN BLOWPIPE.                     251
tne energy of the platinum balls can be graduated by the proportions
of metal and of pipe-clay which are employed. Hydrogen and oxygen, however, are not the only gases which can be made to unite by
the agency of platinum surfaces, as will be elsewhere shown.
The heat produced by the combustion of oxygen and hydrogen
gases is the most intense that can be obtained by any artificial
means. It is hence, at present, much used in an instrument termed
the hydro-oxygen blowpipe. The apparatus employed must be of
such a nature as to prevent any risk of injury from explosion, which,
with any large quantity of the gases, might produce most serious
accidents. The safest form for experiment on a large scale consists in having the gases separate, in two gasometers connected by
tubes, and of such a size and pressure as that in the same time
there will be delivered two volumes of hydrogen to one of oxygen
gas. The hydrogen gas tube terminates in a hollow cylindrical jet,
inside of which passes the jet of oxygoen gas; the flame thus produced resembling that of a candle, into the interior of which is injected a stream of air by the blowpipe in common use. Another form
consists of a metallic. box, made so exceedingly strong that, even
were the gases to explode within, it, there could be no danger of its
being burst. The gases, previously mixed in a bladder, are forced,
by means of a condensing syringe, into the box,'and a sufficient
quantity having been introduced, the condensing syringe is removed,
and a stopcock connected with a jet opened. The pressure of the
condensed gas inside forces out a stream, which is ignited, and, if
the flame be not allowed to burn too long, the rapidity of the current is sufficient to prevent  the passage backward of the flame.
This form is now, however, almost totally superseded by the very
ingenious safety cylinder and jet of Mr. Hemming. It consists of
a brass cylinder of about five or six inches long, by three fourths
of an inch in diameter, which is filled as closely as possible by a
bundle of fine brass wires, into the centre of which a wedge-shaped
brass rod is introduced and driven very hard, so as to pack the
wires closely. The interstices between the wires form thus a collection of exceedingly minute tubes, through which the gas must
pass. To one end of this cylinder is connected a bladder containing the mixed gases; the other end terminates in a jet from which
the gas issues; the flame, in passing backward from the jet, must,
in its way to the bladder, stream through the metallic cylinder, and
then comes into contact with so great a surface, and so large a mass
of material which conducts heat rapidly, that the gases are cooled
far below the temperature at which their union can occur, and their
farther combustion is, of course, prevented.
For experiments upon a small scale, this little apparatus combines
the highest qualifications of convenience, security, and simplicity.
In the flame of the hydro-oxygen blowpipe, the most infusible substances are melted; flint, pipe-clay, the most refractory metals, as
platinum, not merely fuse, but even appear to evaporate: a rod of
iron takes fire, and burns with a brilliancy surpassing that of its
combustion in oxygen gas. Some of the earths alone, are capable
of resisting its highest power. These, as lime and magnesia, particularly the former, become, in the flame of the mixed gases, so




252      CHIEMICAL  RELATIONS  OF  HYDROGEN.
brightly luminous as to rival in intensity the noonday sun, and
hence furnish one of the most important uses of the blowpipe, by
serving for optical purposes as a substitute for the solar ray, which,
in our climate, is so uncertain in its supply. The solar microscope
fitted up with a ball of lime, ignited by a jet of the mixed gases in
place of the solar rays, constitutes the hydro,oxygen microscope,
now a common exhibition in our large towns; and the same light has
been proposed for use in lighthouses, and has been actually employed for signals in connecting the trigonometrical surveys of the British islands.  In one case the light emitted by the ball of lime was
distinctly visible at a distance of seventy miles.
A singular phenomenon, which is best produced by the flame of hydrogen, although not peculiar to it, is the production of musical sounds, if an open tube be
held over the flame. The flame, in fact, although unilbrm to the eye, consists of a
succession of little explosions of mixed air and gas, which recur too rapidly to be
individually distinguishable. If the tube be now held over the flame, it will be seen
to flicker, and after a few irregular, interrupted, explosive sounds, a distinct musical note is heard. The explosions set the air in the tube to vibrate, at first irregularly, but at last with such a velocity of vibration as corresponds to the length of
the tube, and to the rapidity with which the explosive mixtures of air and gas can
be formed; and thus, by any of the known methods of determining the number of
vibrations corresponding to a given note, the frequency of the little explosions may
be found. Occasionally, also, a distinct beat, or alternations of sound and silence,
may be heard, as in two organs, which being nearly, but not completely in unison,
sound together; this arises from a current of hot air ascending in the centre of the
tube, while a current of cold air is formed next the side. These do not, for a time,
vibrate completely as one mass; and hence, at certain periods, alternately redouble
and destroy the sounds which they produce.
In its relation to other bodies, hydrogen plays' a very remarkable
and peculiar part.  It was at one time supposed that it shared with
oxygen the power of generating acids; and as sulphur, chlorine, cyanogen, iodine, &c., form one class of acids by combining with oxygen, so they formed a second class, called hydracids, by entering
into union with hydrogen; and hydrogen was believed to be related
to hydrochloric acid, as oxygen was to the sulphuric or the phosphoric acids. In the year 1832, I proved that this view was totally incorrect, and that all the properties of the compounds of hydrogen combined to show that it was an eminently electro-positive body; that it
took a place along with iron, manganese, and zinc; and that the compounds of hydrogen with chlorine, oxygen, iodine, and sulphur were
almost universally electro-positive in combination, and possessed basic characters derived from the pre-eminent positive energies of the
hydrogen itself. These views have, since that period, been still farther corroborated by the researches of Graham, and by additional
investigations of my own; and although the old familiar nomenclature will still retain its place to a great extent, yet there rests now
no doubt upon the minds of philosophical chemists, that hydrogen
is most closely allied to the metals, particularly to zinc and copper;
that the chlorides, iodides, and fluorides of hydrogen, although they
simulate some of the characters which we assign to acids, resemble,
in all important points, the chlorides, iodides, &c., of the metals
above mentioned; that, in fact, hydrogen is a metal enormously
volatile, standing probably in the same relation to mercury that
mercury does to platinum in that respect, but still possessed of all
truly chemical peculiarities of the metallic state, and no more de.




CONSTITUTION  OF NVATER.                   253
prived of the commonplace qualities of lustre, hardness, or blilliancy, than is the mercurial atmosphere ivhich fills the apparently empty
top of the tube of a barometer, or the salivating atmosphere of a
quicksilver mine or of a gilder's workshop.
Of Water-Oxide of Hydrogen.
H.O.
It has been already shown that water consists of hydrogen andi
oxygen combined, in the proportions of two volumes of the former
gas to one volume of the latter, and by weight of one part of hydrogen united to eight of oxygen, or of 11'1 hydrogen and 88'9 of
oxygen in 100 parts.
The exact determination of the composition of water is one of the
most important investigations in the domain of chemistry, as from
the great range of affinities which oxygen and hydrogen exercise,
and the variety of compounds into which they respectively enter,
the numbers adopted for the combining proportions of almost all
other bodies hinge upon those which are employed for the constituents of water. It has, consequently, attracted the attention of many
distinguished chemists. But, although the determination of the respective volumes in which the oxygen and hydrogen unite, as deternlined by Gay Lussac, gave a-very accurate result, yet the most
positive determination was obtained by Berzelius, with the method
now to be described.
A known weight of black oxide of copper is introduced into a
glass tube, on which a bulb is blown, and to the extremity of which
a flask, containing the materials for generating pure hydrogen gas,
is connected. As, however, the hydrogen gas passes off in a damp
condition, and thus introducing water might falsify the result, there
is interposed a tube containing fragments of fused chloride of calcium, by which the hydrogen gas is completely dried before it
comes into contact with the oxide of copper. When the apparatus
has been filled with pure dry hydrogen, heat is applied to the bulb
containing the black oxide of copper, and, as soon as its temperature
has been raised to dull redness, decomposition commences. The
oxide of copper becomes glowing red, and then, even if the heat of
the lamp be much reduced, the reaction still goes on; the glowing
gradually pervades the whole mass, water is formed and condensed
on the colder parts of the tube in considerable quantity, and when
the reaction is completed, there remains in the bulb a porous mass
of pure metallic copper. It is necessary, however, to determine
exactly the quantity of water formed: for this purpose, a small tube
filled with fragments of fused chloride of calcium is attached to the
bulb tube by means of a caoutchouc connector, and the stream of
hydrogen gas is allowed to continue through the apparatus until
the residual copper has become quite cold, and all traces of water
have been carried into the chloride of calcium tube, where it is completely absorbed and retained. The oxide of copper tube having
been weighed before and after the experiment, the loss found is the
oxygen which has been carried off: the chloride of calcium tube
having been also weighed before and after, the gain gives the weight
of water formed, and hence the composition of water may easily
be calculated, thus:




254         CONSTITUTION  OF WATER.
100 parts of black oxide of copper give
79'S5 of metallic copper, and lose
20-15 of oxygen, which form
22067 of water;
consequently, 22'67 of water consist of
00.15 of oxygen,
2'52 of hydrogen;
or in 100 parts,
88'9 of oxygen,
11.1 of hydrogen.
To determine the combining equivalents of these substances, or,
in theoretical language, their atomic weights, it is first necessary to
ascertain what grounds there are for deciding on the atomic constitution of water.
It has been already mentioned that at one time equal volumes of
all gases were considered to contain the same numtber of atoms;
and hence, as water is formed by the union of one volume of oxygen and two of hydrogen, it was considered by some chemists to
consist of one atom of oxygen united to two of hydrogen; therefore, if we take oxygen as the standard of atomic weights, and call its
equivalent number 100, the result would be that 8S'9 ~ 111:: 100:
12'48=  weight of two atoms of hydrogen; and hence the atomic
weight of hydrogen should be 6'24. To the adoption of this number
there are very many objections: Ist, The ground upon which it was
first adopted has been proved to be false, as the same volumes of all
gases certainly do not contain the same number of chemical atoms;
and, although hydrogen enters so much into combination, it is but
very rarely that it does so in the proportion of 6'24. Likewise water, in all the modes in which it is capable of combining, does so in
a quantity containing 12'48 and not 6'24; and, finally, water in combination allies itself to a variety of metallic oxides, all of which
there is the strongest reason for supposing to be composed of one
equivalent or atom of the metal united with one of oxygen.
Water is therefore assumed to be composed of an equivalent of
each of its constituents; and according as the standard of oxygen or
of hydrogen is taken, its atomic weight is
One atom of oxygen....   100.00        8
One atom of hydrogen...  1224         1
112.24      9
Water is colourless, transparent, destitute of taste and smell. If
agitated, it solidifies at a temperature of 32~ F. (0 Centigrade), but
if preserved quiescent, it may be cooled much lower without freezing; if it be then touched or shaken, a portion is immediately converted into ice, and the temperature of the whole is raised to 32~.
In freezing, water expands very much, and exerts therein so great
a force as to burst the strongest vessels in which it is contained.
It is thus that the surfaces of the hardest rocks are gradually crumbled into soil fit for the support of vegetable life; the water perco



SOLUTION  OF  GASES IN  WATER,                   255
latlng into minute crevices and fissures during the warmer months,
and, when frozen in winter, breaking down, by repeated and increasing expansive efforts during successive years, the substance
of masses which would appear, from compactness and hardness, fitted to withstand the severest effects of time and climate.
The specific gravity of steam, such as it Would be at the standlard
temperature and pressure, is found to be 620'1, atmospheric air being 1000'0. Two volumes of steam contain two of hydrogen and
one of oxygen; hence there is a condensation of three volumes to
two produced by the union of the gases. The calculated result is
thus found:
Two volumes of hydrogen. 68 8x2=  137'6
One volume of oxygen.. — 1102'6
give two volumes of vapour of water -1240 2
hence one volume of vapour of water =  620.1
In forming steam at 212', and a pressure of 30 inches mercury,
water expands to 1696 times its volume according to the determination of Gay Lussac, which gives almost exactly the proportion of a
cubic inch of water formino a cubic foot of steam, which contains
1728 cubic inches.
The solution of gases in water appears to be governed by prin
ciples similar to those'Which -regulate the solvent action of water
upon solid bodies. In some instances there certainly takes place
chemical union, as in the case of muriatic acid gas and ammonia; and
in these cases the condensation of the gases by the water is accompanied by the evolution of considerable heat. But in other cases,
particularly where the quantity of gas is small, the result appears
to be merely a mechanical distribution of the molecules of the gas
throughout the mass of the liquid. The following is a table of the
quantity of these gases absorbed by water without combination'100 volumes of water at 600 Fahr. and 30 inches bar. absorb of
Sulphuretted hydrogen.........   253 vollmes.
Sulphurous acid...........   438   "
Chlorine......   206"
Carbonic acid...                 100   "
Nitrous oxide.........  76   "
Olefiant gas.............              12' 5  "
Oxygen...........     37 
Nitrogen 
Hydrogen..1.6.16
The mixture of nitrogen and oxygen, which constitutes the air
we breathe, is absorbed by water, and it is to the air thus dissolved
that water, in great part, owes its refreshing taste. If water be
boiled this air is expelled, and this should be done if it be wished
to saturate the water with any other gas, as the power of water to
absorb any other gas is remarkably diminished by the presence of
even a small quantity of air. If water already saturated with one
gas be exposed to the action of a second,- it lets a portion of the
first escape, and absorbs a corresponding quantity of the second.
In this way, a very small quantity of a sparingly soluble gas may
expel a large quantity of one much more soluble. A familiar example of this fact consists in taking a glass half full of Champagne, and




256       C II EMICAL RELATIONS OF    ATER.
having formed the palm of the hand into a hollow cup, to strike the
top of the glass, closing the glass and flattening the hand at the same
time; the air above the wine is thus forcibly compressed, and a portion is then absorbed, under pressure, by the fluid, from, which a
quantity of carbonic acid is expelled, greater than that of air absorbed in the proportion of 1060 to 16, and thus the effervescent character of the wine restored.
Notwithstanding this character of neutrality, which renders water so useful as a vehicle or solvent for more energetic bodies, water is actively engaged in a great variety of chemical reactions, in
which its elements, separating from one another, appear in an isolated state, or, by combining with other substances which may be
present, generate new compounds. Even, however, independent of
decomposition, water plays a most important part in chemical theory,
from the numerous classes of compounds of which it forms a constituent. The generality of saline bodies, in crystallizing, retain a
quantity of water, often more than one half their weight; this is
termed water of crystallization.  On the application of a moderate
heat this water separates, and frequently the salt dissolves in its
own water of crystallization on being heated, undergoing what is
termed watery fusion.
Salts containing water of crystallization often attract still more
if surrounded by damp air, and fall into a liquid state: such are
termed deliquescent salts; others, on the contrary, give off their
water of crystallization even at ordinary temperatures, if the air be
moderately dry; some, such as the carbonate and sulphate of soda,
losing all; others, as the phosphate of soda, only a portion of that
constituent: these are termed efflorescent salts; when the efflorescence is complete, they lose their crystalline arrangement and fall
to powder.
Graham has shown, that in many classes of salts, particularly in
the sulphates, one portion of the water is much more intimately
united than the remainder; that, in fact, in addition to the mere
water of crystallization, which may be removed without injury, there
is water essential to the constitution of the salt, and replaced by
other bodies when the. salt enters into combination. Thus, in the
common crystallized sulphate of copped there are five atoms of water, of which four are removable by a temperature of 1500, but the
fifth withstands a temperature of 3000. The formula of this salt is,
therefore, not Cu.O.. So3+5H.0., but Cu.O..S.3 H.O.+4H.O.,the
four atoms being water of crystallization; now if this salt be combined with sulphate of potash, this fifth atom of water disappears,
and the double salt is (Cu.O.. S.O3) (K.O.. S.03) +4H.O.; the K.O.
S.O0 having entered into the place of the water which had been expelled; water thus circumstanced is termed constitutional water,
as being necessary to the complete constitution of the substance.
Water, in combination with the stronger acids, is capable of acting as a base, and, indeed, we know of the existence of many acids
only in the form of their compounds with water.  Thus the nitric,
the chloric, the oxalic, the acetic acids, have never been obtained
in a separate form; what we generally term those acids being, in
reality,compounds of these acids with water-salts of water.  Oil




WATER IN  CHEMICAL COM BINATION.                   252
of vitriol is a compound of sulphuric acid and water, sulphate of
water, and it combines with more water, producing great heat, to
form a sulphate of water with excess of base, precisely as the sulphate of copper combines with more oxide of copper to produce a
corresponding basic salt. The salts of water possess the most corn.
plete similarity with those of zinc and copper, and it is from their
comparative study that the evidence in favour of the view inculcated already, of hydrogen being a volatile metal, has been in greatest
part derived.
WNater combines also with bases: the majority of metallic oxidez
combine with water, often with the evolution of considerable heat.
Theslacking of lime, which is the act of combination of dry lime
with water, produces so much heat as to ignite gunpowder, and,
when in large quantity, to become red hot. Ships laden with lime
have often been burned at sea, from water getting into the hold
among the lime, and so much heat being evolved as to set the ship
on fire. Barytes and strontia produce, in slacidng, still more heat.
Potash retains water so strongly that it can only be obtained free
from it by the direct combustion of the metal, potassium, in dry
oxygen gas or air. In relation to these powerful bases, water appears, therefore, to act the part of a feeble acid.
The compounds of water have been generally termed by chemists
hydrates; thus, hydrate of lime, hydrated oxide of copper, hydrated
sulphuric acid, hydrated sulphate of zinc. The very different functions performed by water, in the various modes of combination it
affects, render it necessary to adopt a definite principle of nomenclature in this respect.  In the subsequent pages I shall employ the
word hydrate only where the water is combined with a base, such
as a metallic oxide; thus, hydrate of lime, hydrate of potash, hydrated oxide of lead. Where the water is united to an acid, I shall,
in all cases in which the true chemical nature of the compound
comes into play, term it a salt; as sulphate of water, oxalate of
water, &c.; but where no strict theoretical explanation is involved,
I shall continue to use the common name, as oil of vitriol, strong
sulphuric acid, oxalic acid, aquafortis, &c. There is no name peculiarly applicable to the form of compounds which contains constitutional water, but it will serve as well to characterize the absence or
deprivation of this water by the word anhydrous, the ordinary
name of the substance being supposed to include the combined water; thus, common sulphate of zinc, freed from water of crystallization, is Zn1.0.. S.03. H.O.; anhydrous sulphate of zinc is Zn.0.. S.03.
W'hen there exists water of crystallization in a salt, it is of course
included when the salt is spoken of as crystallized. In formula,
for the purpose of distinguishing between water of crystallization
and water more closely united, the latter will always be marked by
the symbols of its constituents, the former by the two initial letters
of the Latin word aqua, aq.; thus the crystallized oxalic acid is
C203. H.O. + 2Aq. The phosphate of'soda is P20- + 2Na.0.. H.O:. 
24Aq.,
Water does not exist in nature in a perfectly pure condition. It
contains dissolved a small portion of atmospheric air and of carbonic
acid, and also certain quantities of solid impurities, of which com
K I




258 MINERAL WATERS. —PEROXIDE OF HYDROGEN.
mon salt, sulphates and carbonates of lime, and chloride of magnesium, are the most important. In particular, localities, the water issuing from the earth contains iron, and often sulphuretted hydrogen;
also traces of iodine and bromine; and occasionally the quantity of
these foreign matters present is so great as to confer upon the water medicinal properties, and to make such springs, under the name
of mineral springs, spas, be resorted to for the purpose of preserving
or recovering health. These impurities arise from the water, in
percolating through the porous rocky strata, of wvhich the mountains and general crust of the earth are composed, dissolving in small
quantity almost all the substances it mneets. Hence rain-water or
snow-water, collected at a distance from houses, is the purest water
which can be obtained in nature. It contains only some carbonic
acid and air dissolved. The sea being' the general reservoir into
which all the  rivers of the earth discharge their waters, contains
in a concentrated form all the materials which the river waters had
carried down. Although not of absolutely the same constitution all
over the globe, yet it- varies so little that the deviation may be explained by local circumstances.  It is in many countries the source
friomn which common salt and sulphate of magnesia are. derived.
When sea-water freezes, the ice contains scarcely a trace of saline
matter, so that, when melted, it forms a sweet, drinkable anater.
Hence, in voyages in the Northern Seas, supplies of fresh water are
obtained by chopping blocks of ice from the frozen surface of the
ocean. To obtain water pure for chemical purposes, it: i necessary
to distil it.  The saline and fixed impurities remain behind, the pure
water passes over. Its purity may be ascertained by means of the
reagents fitted to detect the most important impurities.  Thus, if
free from common salt, it will give no precipitate With a solution of
nitrate of silver; if free from lime, it will not be affected by oxalic
acid; and if it be not rendered, turbid by nitrate of barytes, it can
not contain sulphuric acid.
From the inactivity of water, and the facility with which it may
be obtained pure, as well as the important part which it plays in the
economy of nature, it is taken as the standard with which the prop-,erties of other bodies, when numerically determined, are compared.
Thus the specific heats of solids and. liquids are reduced to a scale,
water being taken as 1'000. The specific gravities of liquids and
solids are also taken in numbers, that of water being the standard.'If, however, the specific gravities, and heats of gases and vapours
were reduced to the standard of water, the fractions by which they
should be expressed wo:uld be inconveniently small; and hence, for
this class of bodies, a better suited standard substance is found in
atmospheric air.
Of Oxygenated Water. Peroxide of Hydrogen.
H.O.-+O., or H.02.
This singular substance was first discovered by Thenard; its,
preparation is somewhat circuitous and indirect, oxygen and hydrogen not combining with each other directly in any other proportions
but those which form.,water.
For its preparation, peroxide of barium must be first procured; this is prepared




PEROXIDE  f01?TYDtOGEN,  PREPARA'TION  ETC. 259
by placing pure barytes (oxide of barium) in a porcelain tube, which is heated to
redness in a charcoal furnace, and then a stream of pure oxygen gas passed- over it
as long as it is absorbed; the barytes absorbs as much more oxygen as it already
contained, and from Ba.O. becomes Ba.02
This substance may be still more easily prepared by mixing pure barytes with
its weight of chlorate of potash, and heating it nearly to redness; when the disengagement of oxygen fromn the chlorate of potash has set in, the mass becomes
glow ing red at onepoint, and this appearance spreads over the whole mass like tinder.'lie barytes burns, as it were, in the atmosphere of oxygen, and forms the deutoxide of barium.  If, then, the residual mass be washed with water, the chloride of
potassium, which remains from the chlorate of potash, is dissolved, and the deutoxide of barium, combining with an equivalent of water to form a bulky, white, insoluble hydrate, remains behind, and may be collected on a filter.'rhe best mode of obtaining peroxide of hydrogen from this substance is that proposed by Pelouze. To dilute hydrofluoric, acid (fluoride of hydrogen), the peroxide
of barium is added until the acidity of the liquor is completely neutralized. The
reaction is very simple; the fluorine combines with-the barium, while all the oxygen is transferred to the hydrogen, which the filuoric acid abandons; thus,
lI.F.+Ba.0.2- Ba.F.+H.O2.
The fluoride of barium is insoluble, and may be collected on a filter along with
the excess of peroxide of barium; the liquor contains only pure oxygenated water.
Fluosilicic acid, which is cheaper, and more convenient than the fluoric acid, may
also be used in this decomposition. The fluosilicate of barium separates as an insoluble white powder, and the peroxide of hydrogen remains dissolved.
Thenard's plan consisted in dissolving the peroxide of barium in dilute muriatic
acid, and then precipitating the barytes by sulphuric acid. The muriatic acid
which became free was then neutralized by another portion of peroxide of barium,
and this again precipitated by sulphuric acid. When the liquor had become strong
enough, the free muriatic acid was removed by the cautious addition of sulphate of
silver, and the sulphuric acid then evolved was precipitated by the addition of pure
barytes, carefully avoiding an excess.
The weak solution of peroxide of hydrogen thus obtained must be placed, along
with a capsule of sulphuric acid, under the exhausted receiver of the air-pump.
The water being more volatile, evaporates first, and the liquor gradually becomncs
more concentrated, until, finally, the peroxide of hydrogen remains pure behind. If
left too long in the exhausted vessel, it evaporates itself without alteration.
Peroxide of hydrogen is a thick, colourless liquid. Its specific gravity is 1!452.
It has a nauseous taste, and irritates the skin. It bleaches and destroys all vegetable colours. Its reactions are generally so violent that it mustl be diluted with
many times its volume of water before they can be accurately observed.
Its most curious property is, that by being put in contact with any one of a great
number of solid substances, it is decomposed with great rapidity, being resolved
into oxygen and water. Black oxide of manganese is one of the most active. If a
little of this substance, in powder, be introduced into strong peroxide of hydrogen, in
a graduated tube, over mercury, the latter is decomposed almost explosively, disengaging 475 times its volume of oxygen, the oxide of manganese remaining perfectly
unaltered.  Platinum, gold, silver, quicksilver, particularly if the metal be in the
form of leaf or sponge, produce the same effect; and if the peroxide of hydrogen
be put into contact with an oxide of these metals, as oxide of silver, it is not merely decomposed itself, but the oxide is also decomposed, the oxygen and metal both
becoming free. In the (lark, and with strong peroxide of hydrogen, a flash of light is
seen to accompany its decomposition, and the tube becomes red hot. The decomposition of the oxide of silver cannot, however, be referred to the great heat produced,
as, even if the peroxide of hydrogen be diluted with fifty times its volume of water,
oxide of silver produces complete decomposition, evolution of oxygen, and separation of metallic silver; yet the effervescence is not very energetic, and the liquor
does not become sensibly warm to the hand.
With other metals, the oxygen, in place of becoming free, enters into combination,
forming an oxide of a higher degree; thus, with the oxides of lead and bismuth
there are formed peroxides of those metals; with arsenic there is formed arsenic
acid. The aninmal substances fibrine and albumen, which are so similar in- most
respects, are distinguished from each other by their action on this body, fibrine de'
composing it with rapidity, while albumen is without effect. It is highly probable,
that in the decomposition of water by the voltaic pile, some of this compound may




260        PREP.ARATION' OF  NITROGEEN  GAS.
be formed, as the quantity of oxygen collected is frequently smaller than it should
be; and a portion of the process of bleaching, by exposing the wetted cloth to the
action of light and air, may possibly be carried on by the formation and subsequent
decomposition of this substance.
Peroxide of hydrogen, when kept for any length of time, even in a dlilute condition, gradually decomposes, oxygen being given off, and water remaining behind.
The presence of an acid in the liquor retards this action very much, while the presence of an alkali accelerates it. It was in great part from the remarkable characters of this body that Berzelius derived his evidence in favour of the existence of a,'atalytic force influencing chemical action, which has been described already.
Of.Jitrogen.
N.
It has been already noticed, that the substance by which the oxygen is diluted in atmospheric air, so as to render it suitable to the
respiration of animals, is called nitrogen, from its being the basis
of nitric acid and nitre (the nitre former).  It is also called by some
chemists azote, from its incapability of supporting life; but, as a
great number of gases resemble it in that respect, the former name
is the more, characteristic, and it alone will be hereafter used.
As nitrogen exists in great quantity in the air we breathe, it is
most easily obtained by acting upon a confined portion of the air so as to abstract the
oxygen, when the residual gais is found to
be nitrogen almost completely pure.  Thus,
if a small piece of phosphorus, laid in a cup
d, floating on water, be set on fire, and a bell
i   glass, a, be inverted over it, the phosphorus,
d     i     I ~~~8~ in burning, unites with the oxygen of the
air, and forms white fumes of phosphoric
acid.  At first, from the great expansion of
the air caused by the high temperature of the flame, some bubbles
escape from under the edge of the glass; but soon, even before the
phosphorus has ceased to burn, the water begins to rise in the bell,
and, finally, the clouds of phosphoric acid gradually dissolving in the
water, the residual gas will be found to occupy about four fifths of
the original volume of the air, and to be colourless as the air had
been before.  Any other burning body would answer the same purpose, although not so perfectly as the phosphorus. Thus, if spirit
of wine, or pyroxylic spirit, or ether, which burn without smoke, be
placed in the little cup, and set on fivre under the bell glass, as in
the former instance, the inflammable constituents, carbon and hydrogen, combine with the oxygen of the air, forming carbonic oxide
and water, the nitrogen remaining behind.  The gas thus obtained
nust be washed well with water, or, better, a little solution of potash, to remove the carbonic acid, and even then the nitrogen contains some oxygen unconsumed; for in every case where carbonic
acid is formed by a burning body, the combustion ceases before all
the oxygen present has been consumed, the carbonic acid exercising
on combustion a positively impeding power, similar to that which it
has on respiration.  The purest' nitrogen is consequently obtained
by means of phosphorus.
Independent of this source of nitrogen in atmospheric air, it may




PREPARATION  OF NITROGEN. GAS.                  261.
be obtained indirectly from a great number of substances. Thus
most animal substances contain nitrogen in large quantity, united to
carbon, hydrogen, and oxygen. If, therefore, some pieces of muscle,
or albumen, or gelatine, be boiled in a retort with some nitric acid,
the oxygen of the nitric acid combines with the carbon and hydrogen
of the animal substance, forming different compounds according to
the temperature and the proportions, while the nitrogen of both is
disengaged.
If a gas, termed nitrous oxide, which will be described in a subsequent section, be put into contact with a slip of metallic zinc, at
the moment of its formation the zinc deprives it of its oxygen, forming oxide of zinc, and the nitrogen is set free. The apparatus used
for this purpose consists of a tubulated retort, into which is introduced the salt (nitrate of ammonia), which, when heated, yields nitrous oxide. Into the tubulure ismfitted a cork, through which passes
a copper wire, to the end of which a slip of zinc is fastened. To
the neck of the retort a belnt tube is adapted, passing to the pneumatic. trough. Heat being applied to the retort by means of a lamp,
the salt melts, and then begins to emit gas. At this moment the
copper wire is depressed, so that the slip of zinc may touch the surface of the melted mass. The effervescence immediately becomes
muchl more violent, white-clouds of oxide of zinc are formed, and
the gas, which passes over, is nitrogen quite pure. The theory of
the formation of the nitrous oxide will be noticed under the proper
head. Its decomposition by the zinc is simple: nitrous oxide is N.
0., and acted on by Zn. their products are N. and Zn.O.
If ammonia dissolved in water be exposed to the action of a current of chlorine, it is decomposed, sal ammoniac is formed, and nitrogen gas is disengaaged. The solution of ammonia may be contained in b \
a bottle with a wide neck, g, to which
a cork is fitted, perforated to admit   I:f
two tubes, the one, f, conveying the
chlorine from the vessel a, in which
it is disengaged, and opening under
the surface of the liquid near the bottom, the other projecting but little
under the cork, and leading to the
pneumatic trough.  The action of the
chlorine upon the ammonia is accompanied by the formation of white
fumes and the evolution of much heat. If the solution be strong, a
flash of light is seen at the entrance of each bubble of chlorine. gas;
but these are not attended with any danger. The ammonia, however, must, all through the process, be kept in excess, as, were the
chlorine in excess, it might produce a body, chloride of amidogene,
possessed of the most eminently dangerous explosive properties.
The reaction which here takes place may be simply shown. Ammonia consists of one equivalent of nitrogen and three of hydrogen;
by the action of three equivalents of chlorine there are formed three
of chloride of hydrogen (muriatic acid), which unite then with three
equivalents of ammonia to form three of sal ammoniac (muriate of
ammlonia). Thus (N.-+3H.) and 3C1. give N. and (3C1.H.), which




262 PROPERTIES OF NITROGEN.-ATMOSPHERIC AIR.
combine with 3N.H3 to form  3(CI.I.. N.H3), one equivalent of niitrogen becoming free.
Nitrogen, when obtained by any of these processes, is a permanent gas, colourless and transparent; it is absorbed by water only
in very small quantity. It is lighter than atmospheric air, its specific
gravity being 976, air being 1000. It is characterized by the complete absence of the positive properties which distinguish other
gases. Thus, it does not support combustion or respiration; it extinguishes a taper, and animals are suffocated in it; but these effects appear to be due only to the absence of oxygen.
Although nitrogen is thus incapable of combining directly with
oxygen, yet by indirect methods they may be made to unite, and
the compounds formed of these elements are surpassed in number
and importance by few series of binary combinations.'When oxygen and nitrogen combine, their xesult is almost universally that
which contains most oxygen, nitric acid; their union may be efiected by the electric spark, provided water, or a solution of an alkali
be present; hence rain-water often contains traces of nitric acid,
particularly if its deposition has been preceded by discharges of
lightning between the clouds; and lime or potash contained in old
walls are found, after a certain time, to be neutralized by nitric acid.
A mixture of ammonia and oxygen may be converted into, nitric
acid and water, likewise, by spongy platinum at a temperature of
572'.
The combining proportion of nitrogen is, on the hydrogen scale,
14'0, and on the oxygen scale, 175. In a great number of instances,
however, it appears to enter into combination with one third of its
ordinary equivalent, and I have found this peculiarity to extend to
arsenic and phosphorus, which are so closely assimilated to it,
throughout their chemical relations.
Before entering upon the history of the compounds of nitrogen
with oxygen, I shall describe more particularly the properties and
composition of atmospheric air, which, being of so much importance
in the majority of chemical reactions which occur on a large scale,
and being assumed as the standard of properties for gaseous and
vaporous bodies, deserves minute attention.
Of thle.tmosphere.
The analysis of atmospheric air was the first important problem
in the chemistry of gaseous bodies with which chemists occupied
themselves, and hence the names of instruments originally devised
for examining atmospheric air became generally used to indicate
those employed in the analysis of gaseous mixtures or compounds
of any kind. The word eudiometer signifies a measurer of the goodness of the air; and from the interest which the problem presented,
numerous methods were early invented, although it is only recently
that very great precision has been obtained. It was at first believed
that the relative salubrities of districts, and even of different localSties in the same neighbourhood, could be dtermined by the proportions of oxygen and nitrogen which the air of these places might
contain; and that the admixture of pernicious substances, exhaling
from a marsh, or generated within the ill-ventilated apartments of




ANAL Y SIS OF AIR.                    263
an hospital or of a jail, might be recognised, and means discovered of removing them, or of destroying their activity, when their
nature had become determined by the analysis of the air in which
they had been contained. The differences between the results of
various chemists, on which these expectations had been sounded,
have gradually disappeared by the use of better methods, and the
constitution of atmospheric air is now recognised as being almost
absolutely the same throughout its entire mass; but from other
sources, the very results which had been originally sought after
now appear to form a legitimate and promising subject of inquiry.
In addition to oxygen and nitrogen, its principal constituents, at
mospheric air contains some carbonic acid and watery vapour; the
quantity of the latter is determined by methods almost entirely
physical, and forms a practical department in the theory of vapours,
termed hygromnetry. I shall, therefore, not touch upon it here, referring to what has been already noticed of it in the sections upon
water and upon heat.
The determination of the quantity of carbonic acid present in atmospheric air has been made accurately by Saussure, who found
that, in general, 10,000 volumes of air contain 4' 15 of carbonic acid;
the maximum of carbonic acid he found to be 5'74, and the minimum
3415. Over the surface of lakes, as that of Geneva, the quantity of
carbonic acid is smaller, but in cities greater, amounting to 446 in
the average: the quantity is somewhat greater by night than by day,
and in the higher regions of the air than on the surface of the low
fground; it is diminished also during, and for some time after rain.
To determine the quantity of the carbonic acid, a large globe or
bottle containing air is taken, and a solution of barytes is introduced,
until, after having been well agitated with the air, it is found, by
Browning turmeric paper, to be present in excess. The carbonic
acid combines with barytes to form a white powder, carbonate of
barytes, which, being collected on a filter and weighed, gives, by a
simple calculation, the volume of the carbonic acid in the air.
The experiments of Saussure and of Boussingault have made it
probable that carbon combined with hydrogen (probably as the gas
of marshes) exists in very small quantity in atmospheric air. Thus,
when Saussure, after having removed all carbonic acid by barytes,
detonated the residual air with pure hydrogen, he obtained a quantity of carbonic acid equal to nearly one part in 2000 of the air employed; and, although employing other methods, the results of Boussingault strongly corroborate the same idea:: he found sulphuric acid
to be blackened when exposed to air, although all access of dust or
accidental impurities was removed, and that when air, previously
freed from carbonic acid, was passed over red-hot oxide of copper,
a perceptible quantity of water and of carbonic acid was produced.
But the most important portion of the analysis of atmospheric air
is to ascertain the proportions of the oxygen and nitrogen. To effeet this, any one of a great variety of bodies which are capable of
uniting with oxygen may be used; thus, if a solution of sulphuret
of potassium be exposed to air, it absorbs oxygen, and gradually
passes to the state of hyposulphite of potash, and by the amount of
absorption the quantity of oxygen may be ascertained. This is the




264      COMI POSITION OP  THE ATMOSPHERE.
method of Scheele. One proposed by Sir Humphrey Davy consisted
in agitating the deep olive liquor formed by passing nitric oxide
gas into a solution of green sulphate of iron, with a measured quantity of atmospheric air; but it is now abandoned. An excellent
mode of using these bodies as eudiometers is to fill with the liquid
a small caoutchouc bottle, holding about two fluid ounces, and then
tie it securely on the tube of air which passes pretty closely in at
the neck; the mass of air and fluid can thus be brought extensively
into contact, and the absorption is shown by the gradual rise of the
liquid in the tube, the soft parietes of the bottle yielding to the pressure of the external air.
Nitric oxide gas possesses the property of combining with the
oxygen of the air, and forming deep red fumes of nitrous acid, which
dissolve in water. By this mleans, using an excess of the nitric oxide, all oxygen may easily be removed from atmospheric air, but
the composition of the nitrous acid fumes is not always the same,
and hence the quantity of oxygen which the air contained is liable
to be mistaken. This mode, therefore, from the great precaution
necessary in its use, has been quite laid aside.
The use of the hydrogen gas eudiometer, whether the combination
of that substance with the oxygen be accomplished by the agency
of the electric spark, or by means of spongy platina, has been already
noticed. It is one of the most accurate and easy methods that can
be used, and. hence has been most generally employed. The risk
of accident from the violence of the explosion by the electric spark
is much diminished by using the form proposed by Ure. The tube,
which need not be at all so stout as in. the common form, is taken
about twice as long, and bent into the form of a U. Having been
filled with mercury, the mixture of air and hydrogen is transferred
to the sealed leg, and then, the open leg being about half occupied
by air, it is to be firmly closed by the thumb or by a cork. When
the explosion follows, the air in the open leg yields to the pressure
and graduates the shock; no portion of the exploded mixture can
be projected.
Slips of copper foil, moistened with muriatic acid, absorb oxygen
with great avidity, and have been proposed by Gay Lussac for the
analysis of atmospheric air. Saussure has used in his accurate researches thin filings or turnings of lead, which combine with oxygen
very rapidly, and remove it totally from the air.
Phosphorus, which burns in oxygen and in air so brightly, may
also be employed to form a eudiometer. It may be used either by
slow or by rapid combustion. In the former mode, a stick of moistened phosphorus, placed in a graduated tube of air, deprives it completely of its oxygen in about twenty hours; the residue is nitrogen, which has the smell. of phosphorus, and requires a correction
for a small quantity of vapour of that substance which is diffused
through it. The rapid combustion of phosphorus is too violent, and
exposes the vessels to too much risk of breaking, to be made use of
for accurate experiment.
All of these methods are,'however, liable to error to the amount
of nearly 1 per cent., which is to be in great part attributed to the
small quantity of air which the apparatus allows to be experimented




CONSTITUENTS.OF ATMOSPHERIC AIR.   265
on. This disadvantage has been obviated by the mode proposed by
Brunner, and used by him in some determinations lately made, in
which the liability to error has. been reduced to 0"20 per cent.  In
the figure, a, b, c is a tube, consisting of a wide portion, b, and a narrower, c; the wider part being - 
drawn in a to a capillary opening. Into it is intro-    b
duced a quantity of loose cotton and some bits of
phosphorus, and being then warmed, the melted
phosphorus is allowed to spread over the fibres of
the cotton so as to expose a very great surface.
The tube at c fits air-tight to the orifice of the vessel d, which is graduated and filled with mercury;
a cock at e allows the mercury to flow out on oc- 
casion. To use this apparatus, the tube a, b, c is
weighted, and then attached to the vessel d; the  X      1W
cock e is then slightly opened; the mercury issues
out in a properly graduated stream, and its place is supplied by air,
which, entering at the capillary orifice a, streams over the surface
of the phosphorus, by which all its oxygen is removed, and the residual nitrogen passing into the graduated vessel, its volume can be
easily read off; or the mercury wvhich flows off being caught in a
graduated glass, its volume is equal to that of the nitrogen which
has passed in. Besides extending the surface of the phosphorus,
and thus quickening the absorption of the oxygen, the mass of cotton serves as a filter to collect the white fumes or flakes of phosphorous acid formed. When a sufficient quantity of air has passed
~through the apparatus, the tube a, b, c is to be weighed again; the
increase of weight is the quantity of oxygen absorbed, from which
the volume may be known, and the mercury measured is the volume
of the nitrogen, from whence its weight may be calculated.  The
air must be of course dry. This is effected by securing to the tube
a, b, c, by means of a caoutchouc connector, a small tube containing fragments of fused chloride of calciunm, through which the air
streaming deposites the moisture it may contain.
The result of all these methods indicates that atmospheric air contains from 20-79 to 21'08 of oxygen gas in 100 volumes; and from
experiments of Gay Lussac on air brought down by him from a
height of 21,735 feet, to which he had ascended in a balloon, and
those of Brunner for the air on the summit of the Faulhorn, 8020
feet above the level of the sea, the constitution appears to be identical at all heights. By weight, the constituents of the atmospheric
lr in 100 parts are, omitting carbonic acid and water,
Oxygen gas....  =2304
Nitrogen gas....   =e7696
100.00
This permanency of constitution of atmospheric air, together
with many other circumstances which I shall briefly notice, led to
the opinion among many chemists of its being a compound, and not
a mere mixture of its constituents. The analysis not being then so
accurately made, it was supposed to consist of one volume of oxygen united to four volumes of nitrogen, a simplicity of proportion
L  L




266     VELOCITY  OF DIFFUSION  OF GASES.
whichb characterizes chemical union among gases. It was also re
mariked, that if the nitrogen and oxygen were merely mixed, their
different densities should cause them to separate; t;he heavier oxygen accumulating near the earth, while the lighter -nitrogen should
occupy the higher regions of -the air. The former ground has been
completely disproved by later research, and the elements of air are
separated from one another by such feeble means, thus, by nitriu
oxide, by metallic lead, by agitation with water, &c., as would be
unexampled in chemistry among substances of a constitution such
as it, if a true compound, should be supposed to have. Besides,
its density, its refractive power, its specific heat, are the mean
qualities of the oxygen and nitrogen whrichl form it; circumstances
which necessarily occur if it be a mixture, but which do not take
place in any case of chemical combination. An artificial mixture,
also, of oxygen and nitrogen possesses all the properties of atmospheric air.
It is also not the fact that gases of different densities tend, when
mixed together, to separate, and form different layers, in
a  accordance with their specific gravities.  On the contrary,
if two bottles, containing, the one, a, a li(rhter, and the other,
e, a heavier gas, be connected by stopcocks, b, c, d, and allowed to stand for a few hours, the bottle containing the
b     heavy gas being lowest, they will be found to mix, the lightd03  er gas finding its way to the lower bottle, and the heavy
gas ascending to the bottle which is above. In this process
the gases evince a positively active power of penetrating
into the spaces occupied by each other; and this occurs
— e   even when they are separated by membranes, or by masses
of porous earthy substances. This peculiar property of
gases was first recognised by Dibereiner, and then studied
by Mitchell, but finally examined, and its laws accurately assigned,
by Graham.  When gases of unequal densities are placed in contact with each other, they tend to mix ultimately in a uniform
manner; but the rapidity with which they penetrate each other's
volume, or, as it is termed by Graham, the velocity of diffusion of'the gases, is unequal, and depends upon their densities; the lighter
gases diffusing themselves most rapidlyr, the heavier more slowly.
Thus, if a tube be closed at the top by a plug of plaster of Paris,
which, when dry, is very porous, and filled with hydrogen gas, the
plug being kept dry, the hydrogen and the external air tend to mix
across the porous plug; but the hydrogen comes out more rapidly
than the air gets in, and hence the water rises considerably in the
tube. In a similar way, if a glass be filled with hydrogen gas, and,
the top being closed by a sheet of India rubber, a bell glass of air
be inverted over it, the hydrogen passing out of the glass more rapidly than air enters to supply its place, the sheet of India rubber
is gradually bent into the glass, and ultimately burst by the external
pressure. On the contrary, if the small glass contain air and the
bell glass hydrogen, the membranous cover is gradually forced upward by means of the excess of hydrogen which passes in, and
which finally breaks through it by the elasticity thus produced inside.




LAW   OF  DIFFUSION:OF  GASES.                           267
The exact law of the diffusion of gases is, that the velocity of diffusion is inversely proportional to the square roots of the specific gravities of the gases.  This is exhibited in the following table.
Specific Gravities.  Square Roots ot S. G.  Diffusion Volump
Hydrogen.... 00688.... 0'2623...  457
Ammonia.. 0-5898.. 076S1..  130
Air......  1  0 000..00.. 100
Carbonic acid... 1.5239... 12345.. 81
Chlorine.... 24700.... 15716.... 64
By this table it will be seen, that in the same time in which 100 volumes of atmospheric air escape fiom a vessel through a membranous or porous plug, 457
volaines of hydrogen pass in; and if the vessel were previously full of hydrogen,
457 volumes will escape from it during the entrance of 100 volumes of atmospheric
air. If the vessel contained carbonic acid, the result would be the passage of 81
volumes in the same' time, and so of the other gases.
[This law is, however, entirely departed from when the gases are separated
fiom one another by a plug or barrier which exerts upon them a condensing action,
and the diffusion volumes are found to be other than those indicated in the foregoing table.  A plug of stucco exerts but little condensing effect upon the gases, and
hence their diffusion takes place into one another with a velocity inversely proportional to the square roots of their densities; but a thin lamina of India rubber, ef
fecting a powerful condensation, presents the two gases to each other with densi
ties that are abnormal, and hence disturbs their rate of diffuision.
Phenomena of this kind may be very beautifully shown by means of soap-bub
bles. If a vial that has had a film of soap-water spread over its mouth be exposed
under a jar to an atmosphere of ammonia or protoxide of nitrogen, its horizontality
is instantly disturbed, and it begins to assume a spherical convexity, and continues
expanding until, after passing through a series of brilliant colours, it may become
so thin as to be almost invisible.  To show the great rapidity with which a gas or
vapour will pass through such barriers, if a soap-bubble be expanded in a vial containing a little aqua ammonite, and the air from its interior be immediately withdrawn into the mouth, the strong caustic taste of the ammonia will be immediately
perceived.
Through thin pieces of India rubber gases will diffuse into each other, though
resisted by any given pressure. I have found that sulphuretted hydrogen will thus
pass into atmospheric air against a pressure of more than fifty atmospheres.]
This law of the passage of gases through each other is the same as that for the
passage of a gas into a perfectly empty space.  If the different gases be allowed to
strain through a porous plug into a vessel from which the air has been removed by
the air-pump, they will enter with different velocities, regulated by their specific
gravities, precisely as in the former instance; and hence it is experimentally demonstrated that different gases are ultimately permeable to each other, precisely as
the spaces they occupy would be if entirely empty; that the gases, in fact, form
vacua to each other, but that so far as the law of mixture and the final effect are
concerned, the mixture taking place more slowly, in consequence of the mechanical obstruction.
This general principle had, however, beemi laid hold of by the keen intellect of
Dalton, and announced long before its truth had been accurately proved in the manner that has been now described; to him we are indebted for the first philosophical
view of the molecular constitution of the atmosphere; he proposed to consider the
different gases which exist in the atmosphere as being in all points independent of
each other, mixed uniformly in virtue of the diffusive power which he had been
the first to recognise, and exercising pressures upon the suriface of the earth proportional to their quantities.  Thus, if we suppose 1-00 parts of' atmospheric air to
consist by weight of,
Nitrogen gas...... 788'
Oxygen gas                      23' 04   1 ( 00
Watery vapour... 103 (
Carbonic acid..05 J
the pressure of the air being taken at thirty inches of mer,' lry, the respective
pressures of the independent atmospheres tvill be as follows:




268 CONSTITUTION OF THE ATMOSPHERE PERMANENT.
Pressure of the nitrogen gas.......   22 764 inches.
"4    oxygen gas....... 6912  "
c"     watery vapour......   0'309  "
c"    carbonic acid gas.....  0'015  "
30000oo
The different constituents of air are thus in the state best suited
to the purposes for which the atmosphere is destined; no one gas
can interfere with, or retard the others' action; there are no affinities to be overcome, or existing combinations to be broken up, before
the agency of watery vapour, of carbonic acid, and of oxygen can
be brought into the extended alternations on which the continiued and happy existence of animal and vegetable life depends, from
which arises the diversity of aspect of our ever varying sky, and
the gradual detrition of the solid rocky materials of the earth's surface giving a fruitful soil.
By the processes of combustion and of respiration which are in action on the surface of the earth, the oxygen of the atmosphere is
continually removed, and an equal volume of carbonic acid generally substituted for it. This carbonic acid is absolutely a narcotic
poison, and the air becomes unfitted for the support of life before
one half of the quantity of oxygen it contains has been consumed.
A healthy man spoils in twenty-four hours, by respiration, 720 cubic
feet of atmospheric air, that is, a mass of air eleven feet square and
six feet thick.  The burning of three ounces of charcoal produces
the same effect. In many factories there are burned daily ten tons
of coal, which deteriorate at least as much air as the same weight
of charcoal, and hence each day, by such a factory, there is rendered unfit for respiration 3,185,760 cubic yards of air, which would
cover to the depth of six feet a space a quarter of a mile square.
Nevertheless, it has been already mentioned, that even in cities, the
relative proportions of oxygen, nitrogen, and carbonic acid in the
air are but little altered, and it becomes an object of great interest
to ascertain in what manner that permanency, on which the stability, in truth, of all organized nature seems ultimately to depend, has
been secured.
In the first place, from the frequent occurrence of storms and violent currents, which agitate vast tracts of air, accumulation of noxious gases or corrupted portions cannot take place, except in some
rare and limited localities, which do not affect the condition of the
atmosphere even near at hand; and although the numbers which
have been shown as indicating the amount of air destroyed become
enormous when multiplied by the number of breathing beings and
the quantity of fuel burned on the earth's surface, they yet bear but
a triflinac proportion to the immensity of the aerial ocean in which
we live. The atmosphere may be considered as being, if brought
throughout to its usual density at the surface of the earth, about
five miles deep; and Prevost has calculated that the loss of all the
oxygen employed in respiration and combustion for 100 years could
not diminish its quantity by v7-2  part, a quantity too trifling to be
detected by our methods, even' had the exact sciences flourished
~for such a. period as to allow a comparison to be made.
But, ind-ependent of this negative proof of permanence of com



ATM.OSPHERIC  PRESSUR E.                     269
position, science has pointed out, in the peculiar relations of the
lunctions of vegetable and animal beings, a provision of adaptation
to each other's wants, which retains the atmosphere in a condition
practically of eternal identity of constitution. A healthy growing
plant, exposed to sunlight, is found to absorb carbonic acid, and to
emit oxygen from the surfaces of its green leaves. In the dark, an
inverse effect takes place, oxygen being absorbed, and carbonic
acid formed. The coloured parts of plants, as flowers and fruits,
absorb likewise oxygen, and emit carbonic acid; but as the green
surfaces preponderate so much throughout the vegetable world, and
the stimulus of light is active throughout the greater portion of the
twenty-four hours, the ultimate effect is, that an action the opposite
of that which animals exercise upon the atmosphere is constantly
going on. That which the plant rejects is to the animal the source
of energy and of all vital powers, while the same element which the
plant absorbs, and from wvhich it forms its tissues, has been thrown
out as useless by the animal, and would, if not removed, accumulate
in the end, and destroy all animal existence.
The most accurate experiments have determined that 100 cubic
inches of atmospheric air, freed from moisture and carbonic acid,
weigh 31,0117 grains; the barometer being at 30 inches, and the
thermometer at 60~. Its specific gravity is taken as the standard
for gases and vapours, and is hence 1000. It is about 780 times
lighter than water at 40'5~ Fahrenheit, when water is at its greatest
density, and is'then also 10,600 times lighter'than quicksilver.
The weight of the atmosphere pressing upon the surface of the
earth is equivalent to about fifteen pounds on each square inch of
surface. The existence of this pressure may be shown in many
ways: a bladder or a thin plate of glass may be burst if the pressure
of the air be removed from one side by the air-pump while it is allowed to act against the other; a pair of brass hemispheres, which
are easily separated while filled by air, are pressed most firmly together if the air be removed from their interior.  This pressure is
equivalent to that exercised by a column of mercury in a tube about
thirty inches high, and, accordingly, an instrument, the common barometer, or pressure measurer, is thus constructed, to register, at every moment, the pressure which the atmosphere exercises. A tube
closed at one end, and about thirty-two inches long, is to be carefully filled with pure mercury; it is then inverted in a basin of mercury, and being placed in a vertical position, the column of mercury
sinks to a certain height in the tube, generally between twenty-nine
and thirty inches, leaving above it a space which is, at low temperatures, the most perfectly empty that can be experimentally procured. From the name of the inventor of this instrument, it is called
the Torricellian vacuum. If the external pressure varies, the height
of the column of mercury alters likewise, rising when the pressure
increases, descending when it is diminished; and as considerable
changes in the amount of pressure generally depend on violent mo
tions in the air, which produce changes in the weather also, the
barometer is popularly regarded as a weather-glass, although no accurate indications of approaching changes can be at all reckoned on
from its use.




270 PRESSURE AND EXTENT'OF THE AT MIOSPHERE.
If the atmosphere preserved throughout its entire mass the same
density and elasticity which it possesses at the surface of the earth,
its height would be about five miles.  But such is not the case;
the lower portions of the air, which press upon the earth, are pressed
upon by the portions next over them, these again by those still
higher up, so that the amount of pressure, and, consequently, the
dtensity of the air, decreases continually as we ascend through its
niass.  The rate of diminution is even very rapid, forming a geometrical proportion when the heights are taken in an arithmetic
series; and on this principle is founded one of the most accurate
modes of estimating heights that has been yet discovered.  If a
barometer be carried to the summit of a mountain, the column of
quicksilver will be observed to be shorter than it had been upon the
plain, and the dfferene bein  marked' tihe heht corresponding to
it is determined, from a knowledge of the law just stated.  In practice there are corrections depending on temperatures and other
causes, to which it is not necessary to allude.  So rapid is this diminution of density, that one half of the whole mass of the atmosphere
lies within three miles of the surface of the earth, and four fifths of
it within eight miles.  Hence, in those elevated regions, the luangs
receive, even in a deep inspiration, but little oxygen, and the blood
not being well arterialized; causes the headaches, lassitude, and
faintness which those wvho ascend high mountains or in balloons feel
so severely. The lakes in the mountainous valleys of Switzerland
and the Andes are, for the like reason, destitute of fish; the water
holds no air dissolved to fit it for their respiration, precisely as
one may kill a fish in water by placing it under the receiver of an
air-pump and abstracting the atmospheric air.
The question of how far the atmosphere really extends in space,
possesses, in relation to the views of the ultimate constitution of
matter, already noticed, considerable interest.  If the particles of
atmospheric air wvere capable of division to an infinite degree, then
the attenuation which occurs in the higher regions of the air should
have no limit, and Nwe should look upon all space as occupied by the
elemnents which form our atmosphere, rarefied to an inconceivably
great degree, and our earth as having provided itself, in its course
through space, with as much of this circumambient imatter as, from
its attractive power, it was able to keep round it. If, on the other
hand, the oxygen and nitrogen of the air consist of molecules of definite form and size, these, being in the gaseous form, are subjected to
the simultaneous action of twvo forces: one, the mutual repulsion
~which characterizes the gaseous condition, and which causes their
elasticity, buit which, diminishing with this elasticity, must become
very small in the upper strata of our atmosphere; the other, the
general attraction of the earth, which, though much inferior at the
surface, must, since it di~minishes but very little in ascending so far,
at a certain point become equal to the former, and then all farther
expanding tendency' being overcome, the atmosphere should be terminated by a definite surface, similar iin form to that of the solid earth,
having its tides and currents like those of our great oceans, and
from  these variotis fluctuations in its depth, produce the regular
variations in the height of the barometer, which, though involved
by the irregular motions of much larger amount, have been detected




POISSON'  S ATMOSPHERIC  THEORY.    271
The amount of refraction proves that the sensible atmosphere
does not extend beyond 45 miles; at least, if it exist higher up, it
must be so rare as to have no effect in deflecting  a ray  of light.
But other considerations prove that the air does not extend through
space. If we had obtained our atmosphere by gathering up, in virtue of our attracting force, the thin air which pervades all space, the
other bodies of our system  should also possess atmospheres whose
densities should represent the masses of the bodies they include.
However, exact observation has shown that even the largest bodies
of our system  possess no atmospheres.  A  ray of light sufflers no
bending in its course, although it passes by the edge of Jupiter;
yet, from  the imunense size of that planet, it should have collected
round it an atmosphere so dense, that by its refraction a star should
become visible to us upon one side of it before it had disappeared
at the other.  The sun, likewise, the gravitatinc centre of our system, does not possess a trace of atmosphere sufficient to cause a
sensible refraction.
Poisson has recently suggested a view of the constitution of our atmosphere,
upon grounds, however, so little connected with experiment that it wouldl not be
a subject  br notice here, had it not been introduced to the notice of chemists
under the sanction of Dumas's eloquent discourses.  I will, therefore, briefly describe
the theory he has put forward.
The atmosphere, as we ascend, grows colder.  The source from which the atmosphere derives its heat is not the sun, but the solid earth; the solar rays passing
through the air as they pass through glass and all transparent bodies, without communicating mnuch of their heat.  These heating rays are absorbed by the dark and
rugged surface of the earth.  From this the layer of air next to it derives its warmth,
and hence, the farther from the earth the air is taken, the colder it is found to be.
Hence, even under the glare of a tropical sun, there exists an elevation where the
temperature never rises above 320, tile mlelting point of ice; above that heighlt all is
eternal snow.  Farthest from the level of the sea at the equator, being 15,000 ftet,
this line of perpetual congelation gradually descends, until at the poles it sinks below
the surface of the earth.  In these countries we have nd mountains with pwrpetual
snow, the line of congelation being 6000 feet above the surface.
From this source, also, are derived the various phenomena of fog. and cloud, the
production of snow, of hail and rainri. The vapour forming at the sur:ace of a pond
is generated with an elasticity proportional to its temperature;  anti when the air,
thus mixed with vapour, rises to a higher and colder stratum, the elastticity of the
vapour is diminished, and a portion separates either as cloud or rain.  Thus, if air
becomes loaded with vapour at the surface having a tetpl)eratulre of 60~, annd, on
ascendling, it becomes cooled to 40~, the quantity of water separated is thus found'
The elasticity at 600 is 0'524 inch of mercury.
";      40~ is 0.263   "
the difference is.. 0.261       "
But 52,I: 261:: 100: 49 8, or nearly 50, and hence almost exactly one half of the
quantity of vapour carried up is deposited under the form of clotud; in addition to
this, another portion of vapour is deposited as liquid water, froml the circumstance
of the dimtinution in volume of the mixture of gas and vapour produced by the lowering of its temperature; this is equal to about four per cent., so that there remains
as invisible vapour only about forty-six, while fifty-four per cent. are engage-d in the
production of the cloudy masses. The farther properties of clouds, the cirlcullstances which determine the production of rain, snow, or hail. are of so little reference to chemistry that I shall pass from them without remark.
Reasoning from the principle that all gases may, by suitable reduction of their
temperature, be reduced to the solid form, Poisson proposes to consider the atmo.
sphere as being extended above the earth, gradually becorning more attenuated and
more cold, until it arrives at a point at which it freezes; there then should be a
shell of transparent colourless air-ice, lined on its concave surPacre with a sea of




272                     NITROUS OXIDE,
liquid oxygen and nitrogen mixed or combined together. From such assumptlon,
Poisson proposes to render the theory of astronomical refractions more definite and
exact than it had before been, but those grounds can scarcely be deemed sufficient
to justify the adoption of that idea as a physical reality. So far, in fact, as collateral evidence can be found, the fundamental idea of Poisson's theory is disproved;
for it results from Fourier's researches on the distribution of Heat, that the temperature of the planetary spaces cannot be below -57~ of Fahrenheit, a degree of
cold which is met with in Melville Island during winter, and which has been far
exceeded by artificial means. At this temperature air shows no sign of even becoming liquid, far less solid; and hence the supposition of such a hollow sphere
of frozen air cannot be granted.
Compounds of XJitrogen and Oxygen.
Nitrous oxide              N. —14,0+  O.=  8.-N.O =22'0
Nitric oxide...     14'0 1- 0.-16-N.O2=30.0
Hyponitrous acid           N. -14 0+ 30. - 24-N.OQ3-   38'  0
Nitrous acid...        N.= 14'0+40.=32 —N. O4=460
Nitric acid.....         N.- 14 0+5 0.=40 -N.O=554 0.Nitrous Oxide.  Protoxide of Xitrogen.
This substance, which exists, under ordinary pressure, in the gab
eons form, is best and most easily prepared by henting to about 350~
Fah. the crystallized nitrate of ammonia.  This salt melts at 3000
Fah. into a colourless liquid, without being at all decomposed or
losing water; but when the temperature is raised to 350', a lively
effervescence occurs, and the salt is totally resolved into vapour of
water and nitrous oxide gas, an equivalent of nitrate of ammonia
producing two equivalents of the gas and four of water, thus:
N.03,+N.H40O.  2(N.0.)+4(H.0.)
The nitrate of ammonia may be placed in the flask a, imbedded.
in the little cup of sand.
A bent tube conducts the
gas evolved to the pneulmatic trough, as in the
figure, or to the gasometer, if the quantity be
g64nl                 A             large. In this process
the temperature should
not be allowed to rise beyond the point at which
l.! 0 >   _the effervescence is moderately brisk; for when
the salt becomes much
hotter, the decomposi- tion is tumultuously rapid, and the gas obtained may not be at all pure.
The nitrous oxide gas so obtained is perfectly colourless -and
transparent; it is absorbed by water in moderate quantity, and hence
the water over which it is collected should always be heated to about
90: in order to diminish the loss of gas thus suffered. It is heavier
than air, its specific gravity being 1'527.
A lighted taper burns with increased brilliancy in this gas; and if




IT'S  PROPERTIES  AND COMPOSITION.                      273
blown out, may be relighted, provided a pretty large portion of the
wick remains bright red.  If the gas be mixed with its own volume
of hydrogen, it may be inflamed by a taper or by an electric spark,
and then burns with a loud explosion. If phosphorus be heated in
this gas, it inflames and burns with almost as much brilliancy as in
pure oxygen.
In none of these instances does the nitrous oxide enter into corn
bination. It is decomposed by the high temperature of the burning
body and the affinity of this last for oxygen, and the combustion is
maintained by means of the oxygen which is thus disengaged.  After
the process is completed, the nitrogen of the nitrous oxide remains
free.
In this manner' nitrous oxide may be analyzed. If a little bit of potassium or of
phosphorus be heated in a measured quantity of the gas until the decomposition is
complete, and then the apparatus be cooled to its original temperature, it will be
found that a quantity of nitrogen remains exactly equal in volume to the nitrous
oxide used, and the quantity of oxygen absorbed is such, that in its gaseous form
it had exactly half that volume.. The nitrous oxide consists, therefore, of two volumes of nitrogen and one.of oxygen condensed to two volumes, and hence its specific gravity may be calculated thus:
Two volumes of nitrogen 976 X 2=1952'0
One volume of oxygen... 1102'6
give two volumes of nitrous oxide 3054.6
and one volume weighs, therefore 1527.3
By weight, the composition of nitrous oxide and its equivalent
number on each scale are expressed as follows:
Nitrogen, 639.       One equivalent, 140.or 175
Oxygen, 361                  "         8'0 " 100
100'0                        22'0   275
and its formula is N.O.
The most singular property of this gas is, that when breathed
pure for a few minutes it produces a lively and agreeable intoxication, which does not leave any lassitude or disagreeable sensation
when it goes off. To prepare gas for being breathed, it is necessary to attend to the purity of the nitrate of ammonia used, as very
frequently the salt found in commerce contains muriate of ammonia, in which case the gas obtained may be contaminated by nitrous
acid and chlorine, and prove very irritating to the lungs. To obtain the full effects of the gas upon the system, four or five quarts
must be introduced into an air-tight bag or bladder, and inspired
through a pretty wide glass tube. About two ounces of nitrate of
ammonia yield sufficient gas to intoxicate one person.
N Vitric Oxide.  Deutoxide of Jitrogen.
This substance exists naturally under the form  of a gas, which
chemists have not, as yet, been able to reduce to the liquid form.  It
is very easily prepared, being almost always the principal product
of the decomposition of nitric acid by the metals.
If a small quantity of quicksilver, or of copper cut into small bits,
be placed in the gas bottle in the figure, and diluted nitric acid, prepared by mixing equal volumes of the aquafortis of commerce and of
water, be poured in by the funnel a, effervescence is immediately proM M




274   PREPARATION,  ETC., OF NITRIC  OXIDE.
duced, even without the
application  of heat, and
the metal dissolves in the
acid, which becomes pale
l 9 ac  Hgreen-coloured if quicksilver had been employed,
/-\_fH    _   but of a rich blue if cop-  per had been used. From
greater economy, the latter metal is almost always
that employed. For some
time after the action commences, the space in the bottle over the
liquid is occupied by reddish fumes; but these gradually pass away,
and the gas may be collected when the upper part of the. generating
flask is occupied by it completely colourless.
The theory of this process is very simple: a quantity of nitric
acid gives off three fifths of its oxygen to the copper, and the nitrogen is evolved in combination with the remaining two fifths,
forming nitric oxide. The copper, being thus oxidized, combines
with another portion of nitric acid to form a fine blue salt, nitrate
of copper, which exists in the blue liquor, and may be obtained crystallized.  For complete decomposition, four equivalents of nitric
acid and three of copper are required, and the action may be then
expressed as follows: 4N.05 and 3Cu. give 3(N.O,5. Cu.O.) and
(N.02).
By the action of organic substances, such as starch or sugar, upon
nitric acid, nitric oxide may also be formed in abundance, but it is
not then so uniformly pure as when obtained by means of mercury
or copper.
This gas is colourless and transparent; it is scarcely absorbed by
water, and may hence be, on all occasions, collected over it.  It is
a little heavier than air, its sp. gr. being 1039; its refractive index
is 0'8761. A lighted taper plunged into this gas is extinguished, and
a red-hot wire may be applied to phosphorus in it without inflaming
it; but if the phosphorus be already set on fire, it not only continues
to burn when plunged into the nitric oxide gas, but the combustion
is almost as brilliant as in pure oxygen. In this case, it is indeed in
oxygen, and not in nitric oxide, that the combustion actually occurs;
for the gas is decomposed by the high temperature of the burning
phosphorus, and, being resolved into its constituents, the oxygen is
tlwh body with which the phosphorus combines, and the nitrogen remains untouched.
In this way nitric oxide may be analyzed. and is found to consist of equal volumes of nitrogen and oxygen united without any condensation. From this its specific gravity may be calculated:
One volume of nitrogen... = 976'0
One volume of oxygen... =11026
give two volumes of nitric oxide  2078.6
of which one is found to weigh.  1039.3
Its equivalent volume is therefore 4, and its composition by weight
and it.s equivalent number on each scale are as follows:




IIYPON'ITROUS ACID.                          275
Nitrogen, 46'95      One equivalent,  -175 or 14'0
Oxygen, 53'05        Two equivalents, =200 or 16'0
100'00                          375    30'0
and its formula is N.O,.
Nitric oxide may be deprived of one half of its oxygen, and so be
reduced to the state of nitrous oxide, by remaining in contact for
some days with moist iron or zinc filings; in this case its volume
is reduced to one half.
The most remarkable property of nitric oxide is its tendency to
unite with oxygen when this last is uncombined.  Nitric  oxide
cannot take oxygen from any other substance; but when it is mixed
with air, or with any mixture of gases, of which oxygen is one, it
unites with this, forming deep red fumes.  It is this which causes
the red fumes in the flask in which the nitric oxide is generated.
The oxygen, in combining with the nitric oxide, may form either
hyponitrous acid (N.O,) or nitrous acid (N.04), and they are both
generally formed in uncertain proportions.  Hence we cannot exactly calculate the quantity of oxygen that had been present; and
this process does not answer well for gaseous analysis, but it is
useful for removing oxygen from a gaseous mixture, which it effects
completely if the nitric oxide be added in excess. The red fumes
so formed are soluble in water, and, by washing the mixed gases
with water, may therefore be completely removed.
Nitric oxide combines with a grreat number of salts and with some
acids to form compounds, which in some respects possess considerable interest: these shall be noticed under those heads to which
their history more particularly belongs.
If[yponitrous v.cid.
The red fumes which are formed when nitric oxide is mixed with
atmospheric air or oxygen, consist in great part of hyponitrous acid,
particularly when the nitric oxide is in excess. To obtain it pure,
four volumes of nitric oxide should be mixed with one volume of
oxygen, and the vessel containing the hyponitrous acid vapour formed, exposed to a cold of about 40 degrees below the freezing point
of water. The acid then condenses into a deep green-coloured
liquid, which is excessively vo4atile.
When hyponitrous acid, either in the state of liquid or of vapour, is brought into
contact with water, it is in great part decomposed, being resolved into nitric oxide
and nitric acid, three equivalents of hyponitrous acid (3N.O,) giving 2(N.O2) and
N.05. The same occurs when it is acted on by bases dissolved in water, and
hence the salts of this acid can only be prepared by indirect means.
When nitre has been kept melted for some time, so as to have parted with a portion
of its oxygen, it is reduced to the state of hyponitrite of potash, N.O. K.O. giving off
20., and leaving N.03. K.O. This is known by the hyponitrite being decomposed
by acetic acid, and giving off copious red fumes, while the nitrate of potash is unalterable by acetic acid. The hyponitrite of potash cannot be crystallized so as to
free it from the excess of unaltered nitre, but it may be converted into sparingly
soluble salts, as those of silver and of lead, and so pure salts of hyponitrous acid
formed.
The specific gravity of the vapour of this acid has not been experimentally determined. It consists of two volumes of nitrogen united to three of oxygen, but of
their condensation we know nothing.
Its composition by weight and its equivalent constitution are,




276   PREPARAT.ION,- E T'C;-.  OF- NTR'OUS ACID.
Nitrogen, 37.11. One equivalent, -        175 or 14'0
Oxygen, 62'89.    Three equivalents,  300 or 24-0
1-0000                            475   38.0.JVitrous.Acid.  Jitroso-nitric.cid.
This substance presents itself, like the last, under the form of deep
red fumes, and is produced when the oxygen is in excess with regard
to the nitric oxide.  By a cold of about 0' on Fahrenheit's scale, it
may be rendered liquid, To form it directly, four volumes of nitric
oxide are to be mixed with two volumes of oxygen, and the mixture
exposed to a great cold; but it is more conveniently prepared by
means of the decomposition of nitrate of lead by heat.
A quantity of finely-powdered and dry nitrate of lead is to be placed in an earthenware or hard glass retort, and heated to full red.
ness. The red vapours that are produced are to be conducted into
a receiver, carefully cooled by a mixture of snow and salt.  They
then condense into a liquid, while a quantity of oxygen gas escapes,
and oxide of lead remains behind in the retort. The nitric acid of
the nitrate of lead is decomposed into nitrous acid and oxygen, as
follows: N.05. Pb.O. gives Pb.O., free N.04 and O.
The liquid nitrous acid is nearly colourless at zero, at 60~ it is
orange yellow, and at -40' it solidifies into a white crystalline
mass.  It boils at 820, and its vapour, which is ruddy red at that
temperature, is almost perfectly black at 212 I. In these various
coloured states, it exercises remarkable absorbing power on light.
The specific gravity of the liquid acid is 1'451.
Nitrous acid is the most stable compound of nitrogen and oxygen; it is not decomposed by a red heat; it is decomposed in great
part by water, nitric acid being formed, and nitric oxide being given
off as gas.  Thus, 3(N.04) give N.O0  and 2(N.0C).  The nitric acid
formed always protects a portion of the nitrous acid from this reacm
tion.
When the nitrous acid is formed by the direct union of nitric oxide and oxygen,
it is found that the six volumes of gas are condensed by combination into two;
hence the specific gravity of nitrous acid vapour should be 3181'2; thus,
One volume of nitrogen.....  976'0
Two volumes of oxygen....    22052
One volume of nitrous aci.... 3181.2
Its composition by weight and the constitution of its equivalent
are as follows:
Nitrogen, =30'33       One equivalent, =175 or 14'0
Oxygen,  =69.67        Four equivalents, =400 or 32'0
100'00                          575    46'0
Considerable doubt has been thrown upon the nature of this substance, for many
chemists regard it as incapable of uniting with bases, and hence look upon it as a
kind of acid salt, consisting of nitric and hyponitrous acids combined together,
2(N.04)=N.05sN.O0. But late researches have shown that it does produce true
salts, and that even many saline compounds which had been supposed to be salts
of hyponitrous acid really contain this substance; thus, the yellow basic salt, formed
by boiling a solution of nitrate of lead on metallic lead, is a true nitrite.  I retain,
therefore, for this body the old name of nitrous acid, the more as that of peroxide
of nitrogen, proposed for it by Graham, is frequently applied to nitric oxide.




N I TR IC A C I D.                 277
JVitric.Icid.
N.03O
it Is found that when nitric oxide is brought into contact with a
great excess of oxygen over water, they combine in the proportion
of four volumes of the- first to three of the second; and when the
red funmes which are produced. have dissolved in the water, that is
found to be a solution of pure nitric acid. Looking to the composition of nitric oxide, we find in this manner that the nitric acid
consists of two volumes of nitrogen gas:united with five volumes
of oxygen.
Although nitrogen and oxygen do not unite at once when directly
brought into contact with each other, yet they are capable of combining under certain circumstances; and there is no doubt but that
the great, if not the only source of nitric acid in nature, is the union
of the nitrogen and oxygen of the atmosphere.'Although nitrogen
is not strictly inflammable, yet, if some of it be mixed with hydrogen, and this mixture be set on fire, the flame is coloured green,
and the water formed is found to contain nitric acid; if a series of
electric sparks be passed through a quantity of air confined over a
strong solution of potash., this gradually loses its alkaline reaction,
and after a time crystals of saltpetre (nitrate of potash) form in it.
This may be shown, also, by simply moistening some litmus paper
with a solution of an alkali, and taking, by means of it, a succession
of sparks' from a strong electrical machine; at the point where the
spark passes, the paper becomes reddened, and that nitric acid has
been formed is shown by its burning like touch paper when dried
and set on fire. Rain-water, particularly that which falls after a
thunder storm, contains a certain quantity of nitrate of ammonia;
the lightning forming, -as the electric spark does, nitric acid in passing through the air, and this uniting with the ammonia which is always present in our atmosphere from decomposing animal remains.
In warm climates, where the abundance of organic matter and its
rapid decomposition pour into the atmosphere a copious supply of
ammonia, the formation of nitric acid proceeds with extraordinary
energy, and the nitrate of ammonia being washed down by the rains
into the porous limestone soils, the ammonia is again given off, while
the ground becomes coated with an efflorescence of earthy nitrates
when it dries on the cessation of the rain,; a small quantity of nitrate of potash is also thus formed, but the nitrate of lime, of which
the crude produce of nitre principally consists, is converted into
saltpetre by means of carbonate of potash.. In this way there is
formed in the East Indies a quantity of nitrate of potash sufficient
to supply the wants of Europe. On the Continent, this process is
imitated in artificial nitre-beds, and large quantities of horne-made
saltpetre are used in France and Germany for the manufacture of
gunpowder. In South America, particularly in Chili and Peru, there
are found immense deposites of nitrate of soda upon the surface of
the soil, and it is now extensively imported into these countries;
the source of the nitric acid is, in this case also, the union of the
elements of the atmosphere, although'the circumstances which supplied the alkali cannot be distinctly seen.




278        PREPARATION  OF NITRIC  ACID.
It is from the nitrates of soda or potash so produced that the
nitric acid is always obtained. True nitric acid has never been isolated; that substance which is generally spoken of as nitric acid,
and which I shall, unless especially remarked otherwise, be understood to mean in the following account of its properties and preparation, is a compound of it with water; it is a nitrate of water, or, as
it is popularly termed, liquid nitric acid, or aquafortis.
To prepare liquid nitric acid from nitrate of potash, equal weights
of this salt and of oil of vitriol are mixed in a glass retort, A, which is placed in
a furnace, supported in a
sand bath, as in the figure.
_//__i           The oil of vitriol consists
of sulphuric acid and water, and by the reaction
which ensues, the sulphuric acid combines with the
potash of the nitre, while
the water of the oil of vitriol uniting with the nitric
acid, forms the liquid nitric acid, which distils over, and is condensed in the receiver, B. To render the condensation more complete,
this is surrounded by a net, and placed in a trough, c c; a stream of
cold water flows continually on it from the pipe i, and being distributed evenly over the surface by the network, flows out by the
exit pipe of the trough, 1, and escapes into d e. Using the proportions just noticed (equal weights), the quantity of sulphuric acid
present is double that necessary to neutralize the potash of the nitre, and completely expel the nitric acid; for
The nitre consists of        Oil of vitriol consists of
One atom nitric acid, 54'0    One atom sulph. acid, 40'1
aOne atom potash. 47'3    One atom water. 90
101'3                         49.1
These, reacting upon each other, should produce,
Sulphate of potash consisting of  Liquid nitric acid formed of
One atom sulph. acid, 40'1      One atom nitric acid, 54'0
One atom potash. 47'3         One atom water        9.0
87'4                           63.0
And hence nitre might be decomposed by half its' weight of oil of
vitriol; but the following reasons prevent those proportions being
employed in practice.
WVhen oil of vitriol acts upon nitre, there is at first but one half of
the sulphuric acid taken by the potash, and the sulphate of potash
so produced unites with the remaining oil of vitriol (sulphate of
water) to form bisulphate of potash, thus, 2(S.O. H.O.) and K.O.
N.O5 give
(S.O3. H.O.+K.O.. S.O,) and H.O. N.05.
If there be oil of vitriol enough, the nitre is thus perfectly decom



PREPARATION  OF  NITRIC  ACID.                          279
posed at a temperature not exceeding 260~ F., and the bisulphate of
potash which remains is very easily soluble and fusible, and may
hence be removed from  the retort without inconvenience.  But if
the nitre and oil of vitriol be used in the proportion of an equiva.
lent of each, or by weight in round numbers of two parts of nitre
to one of oil of vitriol, then one half of the nitre remains at first
totally unacted on, aril the retort contains, when the process is half
finished, a pasty mass of bisulphafe of potash and of nitre, which
do not fully act on each other until the temperature rises to 400~.
The nitre is then decomposed; the nitric acid distils over, and
there remains in the retort a mass of neutral sulphate of potash,
which can seldom be removed from glass vessels with success.  The
high temperature necessary also increases very much the risk of
the apparatus breaking.
The scientific chemist and the apothecary, however, do not prepare nitric acid; it
is made on the large scale for the purposes of the arts, and the processes of purifying the acid of commerce is so simple that no other source is required. On the
great scale the nitric acid is prepared, not in glass retorts, but in iron cylinders,
connected with condensers, as represented in the figures, one being a section perpendicular to the axes of the cylinders, and the other a section parallel to the axes:
the same letters apply to both.
a is the grate, and d the ashpit of the fiurnace, b. In each fiurnace two cast iron
cylinders, c, c, are set, of such capacity that about 1-. cwt. of the nitrate used may
be decomposed at once. The ends of the cylinders are closed by covers, e, e, in
one of which is fixed a tube, f, for introducing the oil of vitriol, and to the other is
adapted a tube of glazed earthenware, g, h, by which the vapours of the nitric acid
are conducted to the range of condensing jars of earthenware, fitted with safety
tubes, of which the first is seen in the figure, as h, 1, k. The flues, m, m, m, pass
from the furnaces to the chimney, n. As in this apparatus the temperature can be
raised to dull redness without injury, and as the residuum can be removed in the
solid form, a smaller quantity of oil of vitriol may suffice, and is generally used.
Since the introduction of nitrate of soda into commerce, it has almost completely
superseded nitrate of potash for making nitric acid. It is much cheaper, and it
yields a larger product. It does not require, either, so much sulphuric acid nor so
high a temperature. The nitrate of soda consists of
One equivalent of nitric acid...... 54'0
One equivalent of soda........ 31-3
85'3
and hence 100 parts of it yield about 74 parts of liquid nitric acid, while 100 parts
of nitrate of potash yield but 62.
In making nitric acid, there always occurs at the commencement
of the process a disengagement of red fumes, which dissolve in the
liquid acid  which comes next, and tinge it yellow.  This arises from
the oil of vitriol in excess abstracting the water from  some of the
nitric acid, which then is decomposed into nitrous acid, and some
oxygen becomes free.  At the termination of the process if the tern



280 PROPERTIE S  E T -C.  OF  LIQUID  NITRIC  ACID.
perature pass much beyond 300~, there is a new evolution of red
fumes, for the nitric acid is then similarly decomposed into N.O4,and 0.
The strongest nitric acid that can be thus made is of specific gravity 1'521, and
consists of N.05+H.O.
One equivalent of nitric acid... 540 qor per cent. 85-71
One equivalent of water...... 90  I "    14'29
63'0         100-00
It boils at 187~ F., but cannot be distilled without partial decomposition. The
acid is very seldom obtained of this strength. In general, the specific gravity of
the strong liquid acid is 1-500, and it consists of 2N.05+3-3H.O.
Two equivalents of nitric acid.. 1080 or per cent. 80'00
Three equivalents of water... 27'0     "    20'00
1.35 0'  100000
When the nitric acid is gradually mixed with water, the'boiling point rises until
when the specific gravity is 1-420, it boils at 248~. If it be farther diluted, the
boiling point is again lowered. At this point the acid has a definite chemical constitution; it consists of N.Os+-4H 0.
One equivalent of nitric acid..  54"0 or per cent. 60'22
Four equivalents of water....  36'0     "    3978i
90 0          100-00
The liquid nitric acid is, when pure, completely colourless; it
fumes when exposed to the air, and if exposed to the direct solar
light, very soon becomes- deep yellow, while oxygen gas is disengaged; the same decomposition into nitrous acid and oxygen gas
may be instantly effected by passing the vapours of the acid through
a red-hot pprcelain tube.  In a great variety of processes where
substances are to be oxidized, nitric acid is employed. It acts with
remarkable rapidity on the generality of the metals and of organic
bodies, supplying oxygen for the constitution of a variety of new
compounds, and being itself reduced to the state of nitric or nitrous
oxide, or even pure nitrogen.
If the organic body do not contain nitrogen, it is generally ultimately converted into the oxalic and carbonic acids; with animal
substances, new  bodies are formed of a deep yellow colour, and
hence the stains produced upon the nails and fingers where nitric
acid touches, and it is hence used for stamping the yellow patterns
on woollen table covers. The decomposition of the acid is generally accompanied by the production of red fumes.
In its action on the metals, nitric acid presents some remarkable
anomalies; when of the specific gravity of 1-48, it may be put into
contact with tin or' iron without acting on those metals, although,
if a little stronger or weaker, its action is very great; and this inac
tive acid may be brought into activity by various means, as by touching the immersed metal with another different one.  These phenomena appear to involve conditions probably electrical, which are not,
as yet, completely understood.
The nitric acid prepared by decomposing nitre by half its weight
of oil of vitriol, is always of a deep red or orange colour,' owing to
a quantity of the acid having been decomposed into nitrous acid,
which remains dissolved.  This deep-coloured acid is frequently




DETECTION  OF  NITRI.C  A.CID.                  281
useful, as it gives off oxygen still more easily than the pure acid,
and is hence sometimes applicable as an oxidixing agent where the
colourless acid fails. A deep red fuming acid may be prepared by
passing a stream of nitric oxide gas through the colourless acid; it
is absorbed in great quantity, and the liquor assumes successively
various shades of yellow, green, and red, according to its state of
dilution. The nitric oxide (N.O2) decomposes the nitric acid (N.05),
and forms nitrous acid (N.04), which dissolves in the excess of liquid
acid. If it be required to obtain a colourless acid, it is sufficient'that the coloured acid should be boiled for a few minutes; all the
nitrous acid fumes pass off, and the nitric acid remains colourless,
though somewhat weaker. 
I have mentioned that the nitric acid is not prepared on the small
scale, as the commercial aquafortis is easily purified. The impurities of it are, generally, chlorine, arising from the nitre employed
having contained common salt; sulphuric acid, from some having
been distilled over by too great heat; and some iron, arising from,the cylinders or, stoneware bottles in which the acid is preserved.
These may be easily detected; on mixing a few drops of the cornmercial acid with half an ounce. of distilled water, a drop of solution
of nitrate of barytes will give a-precipitate if sulphuric acid be present; nitrate of silver will indicate, by a precipitate, the presence of
chlorine; while a little'solution of yellow prussiate of potash will
form Prussian blue if the acid contained any iron. From these impurities the acid may be freed by being redistilled; the chlorine
passes off along with the portions which first come over, and by
thus testing from time to time the acid which is thus obtained, it
will be found no longer to precipitate the'nitrate of silver, and may
then be considered pure; the iron and sulphuric acid remain behind
in the retort, provided the distillation be not pushed too far. I have;found that from twelve pounds of commercial aquafortis there can
be obtained eight quite pure, three being allowed to come over first
to carry off the chlorine, and one being left in the retort with the
fixed impurities.
The detection of nitric adid is not difficult; it cannot be recognised by forming precipitates, as all its neutral salts are soluble, but
its properties are very marked.  1st, The production of red fumes.by nitric oxide when it is brought into contact with a metal, is characteristic of it.  2d, When a drop of nitric acid is added to water
tinged blue by sulphate of indigo, and the mixture boiled, it is
bleached by the oxidizement of the indigo by the acid. 3d, When
a small crystal of protosulphate of'iron is placed in contact with
water containing nitric acid, a ring of deep olive-coloured liquid
forms round it, according as it dissolves; from one portion of the
protosulphate reducing'the acid to the state'of nitric oxide, which
then combines with the remaining protosulphate. 4th, Nitric acid
confers upon muriatic acid the power of dissolving gold leaf, but
this test is not of such distinctness as the others, from the same
effect being produced by the chloric and some other acids.  5th,
Nitric acid may also be distinguished by the deep red colour it produces with a crystal of morphia,
For the detection of a small quantity of nitric acid, the best plan
I      Li   11~d b




282            SOURCES,  PROPERTIES,  AND
is to neutralize the liquor, if it be acid, by a solution of potash, and
to evaporate to dryness.  The salt so obtained crystallizes in sharp
needles, and deflagrates when placed on ignited charcoal; heated with
a little bisulphate of potash and some copper filings, it evolves copious
red fumes, and with a drop of sulplhuric acid and a crystal of protosulphate of iron, produces the olive-coloured liquor already noticed.
All solid compounds of nitric acid, such as the basic nitrates, may
be recognised in this way.
The nitric acid not being isolable, we do not know the state of
condensation of its elements, which are united in the proportion of
two volumes of nitrogen to five of oxygen. Its composition by
weight and its equivalent numbers are as follows:
Nitrogen, 26'15       One equivalent,  -175 or 14,'0
Oxygen, 73'85         Five equivalents, -500 or 40 0
100.00                           675   54'0
The specific gravity of the vapour of the liquid nitric acid, 11.O. 0.. NO. 0., is not known;
but Bineau has found the sp. gr. of the vapour of the liquid acid, which boils at 2480,
H.O.. N.O+-S3H.O., to be 1243, which might result from
Two volumes of nitrogen......   976 X 2_19520
Five volumes of oxygen.......  11026 X55513'0
Eight volumes of watery vapour....  6201 X 8:-4960:8
condensed into ten volumes........... 12425 8
of which one, therefore, should weigh........ 12426
T'his result requires confirmation.
Sulphur.
This substance exists in large quantity in nature in combination
The most important ores of copper, lead, silver, mercury, antimony,
and many other metals, are their sulphurets; and a great quantity
of the sulphur at present used in commerce is derived from the iron
pyrites, bisulphuret of iron. Sulphur is exhaled in large quantity
also from volcanoes, partly uncombined, partly in the state of sulphuret of hydrogen, arising probably from the decomposition of metallic sulphurets by the high temperature in the interior of the earth.
The native sulphur so produced, condensing in fissures, constitutes
the great deposites of volcanic sulphur of Sicily and other places,
which supply a large proportion of that employed in commerce.  It
exists also native, combined with oxygen and various metallic oxides,
forming native sulphates, of which those of lime and of barytes are
the most abundant. In many organic bodies, also, sulphur exists as
a constituent, as in the white, and particularly the yolk of egg, the
hair, the horns, and hoofs of animals, and in the black mustard-seed
it exists in considerable quantity.
At ordinary temperatures sulphur exists generally as an opaque
solid, sp. gr. 1'98.  When heated, it melts at'26~ into an ambercoloured thin liquid; if the temperature be then raised to about
400~, it becomes dark brown, opaque, and so thick that the vessel
containing it may be inverted without its pouring out; but when heated farther it becomes thinner, until at 601~, its boiling point, it is as
thin and limpid as when first it began to melt. If the sulphur, when
just melted, be allowed to cool slowly, and the internal liquid be




PREPARAT'ION  OF  SULPHUR.                           283
poured out when the outer crust has solidified, the
interior will be found lined with crystals, as in the
figure, which have the form of the oblique rhombic
prism, of which a common modification with secondary faces, and the surfaces of the octohedron, which
determines the heigh.t of
the principal axis of the
crystal, is given.  These crystals, when
first obtained, are transparent and ambercoloured, but after a few  days they be
come opaque, sulphur yellow, and friable,
being then changed' into the dimorphous
state.
If the thick tenacious sulphur at 4000 be suddenly cooled by immersion in a large quantity of water, it forms a soft and transparent
mass of considerable elasticity, and may be drawn out into long
threads like India rubber; after some time, however, it changes
into the ordinary state.
Sulphur is used in pharmacy under two forms, that of roll and
flowers; the former is made by melting the rough native sulphur,
and pouring it into slightly conical moulds, in which it solidifies.
The flowers of sulphur are formed by the condensation of the vapour of sulphur so rapidly that the molecules have not time to form
crystals of any perceptible size, so that the condensed sulphur, although really crystalline, appears to the sight and touch as an impalpable soft powder.
For the manufacture of flowers of sulphur, the apparatus is arranged as in
the subjoined figures, in which A is a vertical and B a horizontal section, to which
XA g;           A.
the same letters refer. In an apartment and shed, M, MI, a chamber, A, is con
structed, which must have at least 2000 cubic feet capacity. Outside of this chamber is an iron pan, c, in which, by a fire at o, the sulphur is kept gently boiling. The
boiler and fireplace must be completely surrounded by brickolrk, so that as little
heat as possible may be communicated to the vaulted chambers A; the draught
from the fire passes to the chimney, g; the pan is supplied with sulphur by the
door, n, which can be closed air-tight; the vapour of sulphur mixes with the air in
the wide space, d, over the boiler, and, passing through the aperture b, rises into
the chamber, where, mixing with the large mass of cold air, the sulphur is condensed, and falls like a fine snow shower upon tl.e floor underneath. When a sufficient quantity of the flowers of sulphur have been thus formed, they are removed
by the door at p. If, at the commencement of ihe process, the mixture of sulphurvapour and air should inflame, the explosion c,pens the valve at e, the gases escape
at t, and all danger is avoided.
The form of crystal of sublimed sulphur is the right rhombic octohedron, of which a common modification is represented in the




,.24     RELATIONS  OF  SULPH-UR  TO  OXYGEN.
mnarcrin.  Sulphur is found crystallized in this form  on
the edges of the craters of most volcanoes, the crystals being transparent, and sometimes of considerable
size.  When sulphur is deposited from its solution in
chloride of sulphur or in sulphuret of carbon, it is in
this form also that its particles arrange themselves.
NiX //   Sulphur may be obtained, however, in a state of
mnuch more minute division, and  destitute of all cryslalline structure, by precipitation from  solution.  Thus, if the per.
jsulphuret of potassium, K.S5, be decomposed by muriatic acid, four
equivalents of sulphur are set free, and separate as a milk-white
powder.  This constitutes the Sulphur Precipitatuni of pharmacy.
In all cases where sulphur is precipitated from a cold solution, it is
pure white.
Sulphur is not soluble in water or in alcohol; it dissolves in the
oils,- still more in those liquids mentioned above.  It dissolves in
alkaline solu.tions, or' in milk of lime; but there then occur complex
reactions, which will be studied hereafter.
When sulphur is boiled it forms a deep yellow vapour, the specific
gravity of which is 6648.  Sulphur evaporates, however, very rapidly long before it boils, and even forms some vapour below  its
melting point.  At a temperature of about 300' it takes fire, burning
with a bluish violet flame, and forming sulphurous acid (S.O2).
The resemblance of sulphur to oxygen in its chemical relations is very striking,
by combining with the same bodies, according to the same proportions, they gener
ate completely parallel classes of acids, bases, and salts. Thus, with carbon and
potassium, there are formed
C.02 Carbonic acid.                  C.S2 Sulpho-carbonic acid.
K.O. Oxide of potassium.             K.S. Sulphuret of potassium.
K.O.. C.O2 Carbonate of potassium.    K.S.. C.S2 Sulpho-carbonate of potassium.
and with arsenic and potassium,
As.05 Arsenic acid.                  As.S5 Sulpharsenic acid.
K.O. Oxide of potassium.             K.S. Sulphuret of potassium.
K.O.. As.05 Arseniate of potassium.    K.S.. As.S5 Sulpharseniate of pota,sium.
In like manner, the similar compounds Fe304 and Fe3S4 are not altered by heat,
but are magnetic, while Fe.S2 and Mn.O  give out oxygen and sulphur, and are redluced to Fe3S4 and Mn3O4. I shall have frequent occasion to revert to these considerations, which have already been noticed under another point of view (p. 238).:The equivalent number of sulphur is 16.1 or 201.2, and its cormbining volume one third that of oxygen.
Sulphur combines with oxygen, forming
Sulphurous acid.                   S.02.
Sulphuric acid....  S.0, or  S.02. O.
HEyposulphurous acid                  S,20, or  S.02. S.
Hyposulphuric acid.... SO   or 2S.O2. 0.
Sulphurous,Icid.
Sulphurous acid exists at ordinary temperature and pressure in
the gaseous form; it is one, however, of the most easily liquefied
gases.'It is produced always when sulphur burns either in air or;n pure oxygen, sulphur not being capable of passing directly to a




P REPARATIO N  ETC.,; OF. SULPHUROUS ACIID. 285
higher degree of oxidation. In the burning of sulphur, the volume
of sulphurous acid gas formed is exactly equal to that of the oxygen
consumed.
When required pure, it is prepared generally by decomposing
sulphuric acid by means of a metal not very easily oxidized, as
mercury or copper. The metal combines with one atom of the oxygen of the sulphuric acid, and the sulphur, with the remaining two
atoms of oxygen, pass off as sulphurous acid gas; the oxide formed
unites with the remaining sulphuric acid to form a salt. Thus, if
mercury be used, S.03 and Hg. give S.O and Hg.O., and Hg.O. unites
with S.O, to form sulphate of mercury. If the heat be not raised
beyond 200~ in this process, it is black oxide of mercury which is
produced (Hg20.), but above that degree the red oxide (Hg.O.) alone
is formed.
Sulphurous acid gas may also be very simply prepared by he-ating
three parts of flowers of sulphur with four of peroxide of manganese. The reaction is very simple; one part of the sulphur uniting
with the metal, and another with the oxygen, form sulphuret of manganese and sulphurous acid; thus, Mn.O2 and 2S. give Mn.S. and
S.O2. The apparatus used in these processes may be that figured
under the heads of oxygen (p. 244) or nitrous oxide (p. 272).
Sulphurous acid gas is absorbed by water; and hence, in order
to examine its properties in that state, it must be collected over
mercury. It is colourless and transparent, possessing an odour peculiarly irritating (the smell of burning sulphur), and cannot be
breathed. It is not combustible, nor- does it support combustion.
[t bleaches a variety of vegetable and animal bodies, and is hence
used in the arts to whiten straw bonnets, corn, silk, sponges, and
other substances. The bleaching is produced by the sulphurous
acid combining with the coloured substance, and forming a white
compound, from which the gas gradually escapes on exposure to
air, and hence such bleaching is not permanent. The sulphurous
acid may be expelled, also, from this kind of compound by a stronger
acid, and the colour generally restored; thus, if a red rose be exposed to the fumes of burning sulphur, it becomes completely white;
but if washed in dilute sulphuric acid, its red colour is perfectly
renewed.
The specific gravity of sulphurous acid gas is 2210'6, and it is
formed by
One volume of sulphur-vapour.           6648'0
Six volumes of oxygen.                6615'6
The seven volumes condensed to six, give.'  13263.6
Weight of one volume of S.O,.22106
When'this gas is exposed to a cold of 0~ F., it condenses into
liquid heavier than water, which boils at 14~, and produces by its
evaporation a very intense cold; it
is easily obtained in the liquid form, _
by putting a quantity of mercury and
oil of vitriol into a tube, and sealing
up the ends, as in the figure; on applying heat to the extremity a,




286  PROPERTIES,  ETC., OF  SULPHUROUS ACID.
containing those materials, and cooling the other end by means of
ether, the gas evolved is liquefied by its own pressure, and collects
in quantity at b.
When a large quantity of sulphurous acid is required dissolved in water, or when
it is to be employed to form compounds with bases. it may be produced in a much cheaper way than
i   those descrlbed above. Into a matrass. a, placed in a furnace, is introduced a quantity of well-burned
charcoal, in bits about the size of a
hazel-nut, and by means of the safety-funnel 1, as much oil of vitriol is
poured in as that the mixture shall
_ i-~ ii                            half fill the vessel; a tube passes to
( {|~If  1       a bottle, i, containing some water to
XF - - - _'_    wash the gas from any adhering sul-'1          _____    phuric acid, and it is then conduct
ed by the tube f, which passes to
the bottom of the vessel h, containing the liquor in which the gas is to.11 Il Igllllli91 1g 1   be dissolved. On applying heat, the
carbon of the charcoal abstracts
from the sulphuric acid one third of its oxygen, so that with C. and 2S.O.. there are
formed C.O2 and 2S.02; there is produced a mixture of two volumes of sulphurous acid and one of carbonic acid, which last cannot enter into combination, and
passes off froiom the apparatus without change.
Water dissolves about thirty-seven times its volume of sulphurous
acid; the solution possesses the properties of the gas in a very high
degree, and bleaches vegetable colours with great power; when
kept for some time, it gradually absorbs oxygen, and the sulphurous
becomes changed into sulphuric acid.
The sulphurous acid is one of the feeblest acids, and is expelled
from  its combinations by almost all btat- the carbonic acid.  Of its
salts, those which are soluble, all possess alkaline reaction.
The sulphurous acid passes into the state of sulphuric acid by
absorbing oxygen from many bodies; thus, when it is heated with a
solution of gold or silver, or of mercury, these metals are reduced
to the metallic state; others yield but a part of their oxygen; thus
the peroxide of iron abandons a third, and the black oxide of capper
one half of that constituent.
The salts of sulphurous acid possess the same deoxidizing power.
The composition and equivalent of sulphurous acid are as follows:
Sulphur, 50'14,       One equivalent,  =201'2 or 16'1
Oxygcen, 49'86        Two equivalents, =200 0 or 16'0
100-00                             401'2    32 1
Sulyhuric.lcid.
S.03.
Sulphuric acid, one of the most important compound bodies, from
the energy of its action, and the variety of combinations which it
forms, is not produced by the direct union of oxygen and sulphur
in any case, but arises from the combination of sulphurous acid Awith
another quantity of oxygen.  Thus, by the action of sulphurous acid
on the easily reducible metallic oxides, sulphuric acid is produced.
This principle is beautifully shown by passing a mixture of sulphur.




PREPARATION   OF  SULPHURIC  ACID.                         287
ous acid gas and air through a tube filled with spongy platinum,
and heated to dull redness, when there issues from the extremity a
mixture of vapour of sulphuric acid, mixed with the residual nitro
gen of the air; by such processes, however, it could not be formed
in quantities suited to the purposes of commerce.
The preparation of sulphuric acid is effected upon the large scale
by bringing sulphurous acid, produced by the burning of sulphur,
into contact with watery vapour and nitrous acid fumes; these unite
to form  a white crystalline solid, which appears to be a compound
of sulphurous acid and nitrous acid (S.-0,2N.04), united with a quantity of sulphuric acid and water which is not constant. The formation of this substance may be shown by the arrangement in the
figure.  The central vessel, the inner surface of which is slightly
moistened, contains atmospheric                            
air; by means of the tubes, sul- r             m.p
phurous acid gas generated in the  [1
flask a, and nitric oxide formed in   4                                 1
b, are introduced, to the latter of
which the oxygen is supplied by
the air to form  nitrous acid fumes;                   t
the interior of the vessel becomes
gradually covered with a deposite
like hoar-frost, consisting of this   
substance; and, in order that its                              i
production  may proceed without                      -.interruption, the vessel may be filled with fresh atmospheric air by
blowing through one of the tubes c, d, while the residual gases are
expelled through the other.
This crystalline substance is decomposed by a larger quantity of
water; hence, if the bottom of the central vessel be covered by a layer
of water, the crystalline substance falling into it according  as it is
generated, is resolved into sulphuric and hyponitric acids; thus S.
02t-N.04 gives S.03 and N.03, which last is decomposed  by the
water into nitric acid and nitric oxide, 3N.O  givint' N.O;, and 2
N.02; the nitric acid remains combined with the water along with
the sulphuric acid, while the nitric oxide escaping with effervescence,
generates, on arriving at the air, a new quantity of' red fumnes, and
oxidizes a new quantity of sulphurous acid.
It was supposed that a certain quantity of water wras necessary to the existence
of this solid body, although a larger quantity decomposed it; but it has been found
that a similar substance may be formed which contains no water. Sulphurous and
nitlrous acids do not act on each other when in the gaseous form, unless water be
present; but they combine if placed in contact under considerable pressure, and
liquid, even when completely dry. A portion of the nitrous acid converts an equivalent of the sulphurous acid into sulphuric acid, it being itself reduced to lhe state
of hyponitrous acid, while another quantity of nitrous and sulphurous acid unites
directly; there are thus formed fiom 2S.0,2 and 2N.04 a white crystalline solid
S.02. N.O,+S.O3, and a quantity of N.O,, which is given off on the tube in
which the combination is produced being opened.
It may be questioned, however, wlhether this substance, for the discovery and
analysis of which rwe are indebted to M. de lPrevostaye, interferes in the formation
of sulphuric acid on the large scale, where the nitrous and sulphurous acids act on
one another in the gaseous forms.
In the manufacture of sulphuric acid, the apparatus consists of a long leaden
clhanber consisting of two portions; the lower a tray of about 1~ feet deep, the




289       MANU FACTURE  OF  OIL  OF  VITRIOL.
other a quadrangular bell, which, being suspended on a wooden framework, b, b,
rests with its edges immersed in the li(quid, with which the tray is filled, like the
cylinder of a bell gasometer. The bottom of the chamber, which is supported at a
certain distance from the ground on pillars, a, a, a, slants froim before, so that the
b                                         b.a,                 i
@.,., _ - t I~~~~~ ~I!:
liquid which occupies it increases in depth towards the end. Under the front is
placed a furnace, da oii the floor of which e the sulphur is buined and the sulphur
oHs acid passes into the chamber by the chimneyf; the heat necessary is supplied
by the fireplace under e; the nitrous acid is obtained by placing over the buning
sulphur in e a   pan containing a quantity of nitrate of soda and oil of vitriol the nitrio acid evolved from which directly oxidizes a portion of sulphurous acid and
then, being brought to the state of N.04 acts on the mass of sulphurous acid as has
been just described g is a boiler, by which  steam is driven into the chamber at h,
and thus, in the intevior are provided the conditions for the reunion of steam  sulphurous acid gas and nitrous acid fumes, which produce, as in the apparatus figured
already the white crystalline solid, by which, wahen decomposed by the water at
the  bottom of the chamber, the sulphurous acid is produced, and nitric oxide gas
evolved.  This nitric oxide, mixing with the atmospheric air, which is always
present in large excess in the interior of the chamber, is reconverted into nitrous
acid, which combines with a new quantity of sulphurous  acid, generating another
proportion of the solid body, from whose decomposition by the water the nitric oxide
is again evolved with little loss; and thus the oxygen of the air is gradually transferred to the sulphurous acid byhe supo cite intermediate agiency of the nitrous acid fumes.
Were thereno nitric acid formed, the same quantity of nitric oxide might convert
an infinite quantity of sulphurous acid into sulphuric acid; but as the oil of vitriol
produced always retains  a certain proportion of the nitric acid, it is necessary to
supply its loss, and to send into the chamber a continued current of nitrous acid fiumes.
This is secured by the construction already described, about one part of nitrate of soda
being decomposed for every eight or nine parts of sulphur burned in the furnace d
e. The draught is regulated by the chimney c, whicl is fitted with a valve by the
position of which a current of air is established through the chamber sufficient to
bring the gases into complete mixture inside, and in due proportions, but which
does not carry them away until their action is completed.
The inclination given to the bottom of the chamber is for the purpose of allowing the water, which, having dissolved most of the sulphuric acid, and become
hleavy, to flow down to the falthest end; and thus there is, on the surface has next
the front, a layer of the weakest acid, ready to absorb and decompose the great




MANUFACTURE  OF  OIL  OF -V I T R IO L.                     289
Iuantity of the crystalline body formed when the mixed sulphurous and nitrous
acid gases meet the damp atmosphere of the chamber.
The water in the chamber is allowed to remain unchanged until it has attained
a specific gravity of about 1'600; it is then removed by leaden pipes, and concen
trated by evaporation in leaden cisterns, until its specific gravity is increased to
about 1'76. At this strength it begins to act upon the lead, and must be transferred
to vessels of glass, or, still better, of platinum, in which the concentration may be
finished. In the strongest form in which it can be so obtained, its specific gravity
is 1'847, and it contains 81'54 of real acid in 100.
Thus is the oil of vitriol of commerce manufactured. At present, a modification
of the process has been introduced, in consequence of the extensive use of the iron
pyrites (bisulphuret of iron, Fe.S2) in place of sulphur, as the source of the sulphurous acid. Instead of the furnace e, f, there is built in front of the chamber a
kiln, somewhat like a limekiln, except that it is narrowed at top into a chimney
passing into the chamber. At the bottom of the kiln is placed a layer of coal or
wood, on it the pyrites ip small pieces. The fire is lighted, and the ignition being
communicated to the pyrites, the sulphur burns, forming sulphurous acid, which is
conducted into the chamber, while the iron remains behind as peroxide. The pan
with nitre and oil of vitriol is supported in the kiln at such a height above the mass
of burning pyrites as that the temperature may not be too great. As the combustion proceeds, newquantities of pyrites are introduced by apertures high up in the
kiln, while the residue of adherent rock and oxide of iron is raked out from the
ashpits at the bottom.
A  form  of sulphuric acid is prepared upon the Continent, and
known as German oil of vitriol, or fuming sulphuric acid, which is
much stronger than can be made by the combustion of sulphur, as
has been described.
It is obtained by exposing sulphate of iron to a red heat, in earthen retorts. If
the sulphate of iron, perfectly dry, be strongly heated, the sulphuric acid is driven
off, and oxide of iron remains behind; but the acid is mostly resolved into sulphurous acid and oxygen, and consequently lost. But if the sulphate of iron be not
completely dried, the sulphuric acid combines with the water, and, distilling over in
combination with it, forms a dark-coloured liquid of a thick, oily consistence, specific gravity about 1 9, and consisting generally of about 90 of real acid and 10 of
water in 100, approaching closely to the formula 2S.O-3+H.O. At the same time,
a quantity (one half) of the acid is decomposed, the iron becoming peroxidized,
and sulphurous acid gas being evolved. Thus 4(S.03,+Fe.O.) and H.O. give
2S.O,4-H.O. and 2S.02, leaving behind 2Fe203, known in commerce as colcothar
of vitriol.
This process is carried on in a long furnace, in which are ranged about 120
earthen retorts, as I, in rows of 20, containing the
partially-dried sulphate of iron. They are gradually heated until the fumes of sulphuric acid begin
to appear, and the receiver A is then attached, in which the acid is condensed by
means of cold applied externally.
When this fuming sulphuric acid is heated, it is resolved into ordinary oil of vitriol and real sulphuric acid. This last, being very
volatile, distils over in colourless vapours, which, on coming into
contact with moist air, form dense white fumes of liquid acid. If
the colourless vapour be received in a dry vessel, cooled by a freezing mixture, it condenses in beautiful white satiny fibres, constituting the dry sulphuric acid. This acid melts at 770, and very
little above that temperature it boils.  The specific gravity of its
vapour is 2762, formed by
One volume of vapour of sulphur......     66480
Nine volumes of oxygen...    11026X 9= 99234
The ten volumes forming six......... -16571'4
Of which one weighs, therefore........             2761'9
When this dry sulphuric acid in vapour is brought into contact
O o




290  SULPHURIC ACID.-HYPOSUL P H UROUS ACID.
with dry barytes, lime, or magnesia, they combine with brilliant
combustion, forming sulphates of those earths. When a mass of
the crystals is thrown into water, it hisses as on the immersion of
red-hot iron, and ordinary liquid sulphuric acid is produced.
There exist several definite compounds of sulphuric acid with
water, of which the most remarkable are two: the first is the strongest oil of vitriol made in this country, and contains an equivalent
of acid united to one of water; its formula is S.03 + H.O.; its most
important properties have been already described. The other cone
tains twice as much water; its formula being S.03,+ 2H. 0.; its spe
cific gravity is 1780. When exposed to the temperature of melting
ice, this acid forms large and regular crystals, while the stronger
or weaker acids require very intense cold to solidify them. When
oil of vitriol is mixed with water, the great heat which is produced
results from the formation of definite compounds; and it has been
already shown (page 185) that, no matter what combination a certain quantity of sulphuric acid forms, it evolves the same quantity
of heat on entering into union.
Sulphuric acid, formed by the combustion of sulphur, as described,
in leaden chambers, is liable to be contaminated by the presence of
some nitric acid and lead; from these it may freed by redistillation, which should, however, be conducted with great care, as the
vapour of the acid forms interruptedly and by sudden bursts, which
might endanger the apparatus.  On diluting common oil of vitriol,
a white powder is generally seen to form, which is sulphate of lead,
that had been held in solution by the strong acid, but which precipitates from the diluted acid.  The acid now formed from the iron
pyrites is found to contain frequently arsenic and selenium: the
presence of the former may become of great importance in medicolegal investigations, and the detection of it twill be fully described
in its proper place.
Sulphuric acid is very easily detected by means of a solution of
nitrate of barytes. If the smallest quantity of sulphuric acid be
present, a white precipitate is formed, which is insoluble in muriatic
acid, even when boiled.
Sulphuric acid appears to dissolve certain bodies in small quantity,
which are not soluble without alteration in any other medium.
These are sulphur, carbon, tellurium, and selenium.  These solutions are not, however, of any independent interest.
HyposulpAhurous dIcid.
SO2, or S.0, +-S.
When a stream of sulphurous acid gas (S.02) is passed into a solution of sulphuret of calcium, it is absorbed, a quantity of sulphur is precipitated, and the liquor;
when filtered, is found to be a solution of hyposulphite of lime. The reaction
which occurs is simple. Half of the oxygen of the sulphurous acid passes to the
calcium to form lime, reducing the sulphurous to the state of hyposulphurous acid,
and, at the same time, the sulphur which had been combined with the calcium is
set free, 2Ca.S. and 2S.0, giving 2Ca.O.+S,O,, while 2S. is precipitated.
This acid is also formed when sulphur is boiled with an alkaline liquor or with
milk of lime. Thus, when soda and sulphur are boiled in water, the liquor contains
hyposulphite of soda and sulphuret of sodium, produced by 3Na.0. and 4S. giving
Na.O.-F-S20, and 2Na.S.
TIis acid itself is very easily decomposed; it may, however, be obtained, at




HYPOSULPHURIC  ACID.                              291
least for a time, in a free state, by adding to any of its salts a stronger acid, or, better, by bringing sulphurous acid and sulphuretted hydrogen gas to meet in water;
the reaction which occurs is that 4S.02 and 2S.H. give 3S20,, and 20.H. The
water gradually becomes intensely sour, but after some time this acid resolves itself
into sulphur and sulphurous acid.
The most remarkable character which the compounds of hyposulphurous acid
possess is, that they dissolve those compounds of silver which are insoluble in
water, as the chloride and iodide, and form a solution possessing an intensely sweet
taste; upon this property is founded their use in Daguerreotype and photogenic drawing. This acid is also recognised by its silver salt being decomposed, when boiled,
into black sulphuret of silver and free sulphuric acid, S,0,+Ag.0. giving S.0, and
Ag.S. It is an important fact, also, in the history of the hyposulphuric acid, thlat
its salts do not always contain metallic oxides, but that it may form salts with metallic sulphurets; thus there are two hyposulphites of sodium, of which one contains oxide of sodium (soda), the other sulphuret of sodium. Their formulae are
S2 02+Na.O., and S,02,+Na.S  Each of these. in crystallizing, combines with ten
atoms of water, like common sulphate of soda; they possess, like it, a point of maximum solubility, and the crystals of all three appear to be isomorphous. There
are, therefore, three salts,
S.O,. S.+Na.S.+-lO.O.,
S.O,. S.+Na.O.+lOH.O.,
S.O,.-O.+Na.O.+lOH.O.,
the similar constitution of which evidences the relation of sulphur and oxygen in a
remarkable degree, and will furnish the ground of speculations of great interest, to
which I shall again recur.
IIyposulphuric dcid.
S205, or S204 O.
When sulphurous acid gas is passed through water in which pure peroxide of
manganese is diffised, this dissolves, and the solution contains neutral hyposulphate of manganese. The reaction by which it is produced is simply that the second atom of oxygen of the peroxide of manganese converts two equivalents of sulphurous acid into hyposulphuric acid, which is exactly neutralized by the protoxide
of manganese that is evolved, Mn.O, and 2S.0, giving Mn.O.+S,205.
When a salt of hyposulphuric acid is heated, it is resolved into sulphurous acid,
which passes off as gas, and a neutral sulphate which remains behind, SOs+-It.O.
giving S.02 and S.O,3-+R.0. The acid may be obtained free by decomposing its
barytes salt by sulphuric acid, but it cannot be kept long. When heated, it gives
off sulphurous acid, and sulphuric acid remains; and even when cold it rapidly
forms sulphuric acid by absorbing oxygen.
Remarks on the Constitution of the Compounds of Oxygen and Sulphur.
The progress of science has gradually brought into view a number of facts, by which it is now very nearly fully established, that
of the bodies just now described, we must look upon the sulphurous
acid as the only direct compound of sulphur and oxygen, and that
in the others, sulphurous acid must be considered as pre-existing.
The reasons for this are very numerous. By the direct union of
sulphur and oxygen we can never obtain any other compound than
sulphurous acid; the others being always formed from  it, prepared
either perfectly distinctly, or at the moment of the reaction, and
then presented to other elements with which it may unite.
On this view the necessity of the indirect process of manufacture
of sulphuric acid becomes evident.  The sulphur, when it forms sulphurous acid, is fully saturated with oxygen, and cannot combine
with any more; but the sulphurous acid (S.O,) acts as a compound
radical, like cyanogen, as described in p. 233, and may unite with




292       PREPARATION  AND PROPERTIES
any of the simple and compound bodies. It does not unite directly
with oxygen, but it does so with nitrous acid, and the body so formed is decomposed by water, producing sulphuric acid, as has been
fully described. In like manner, to form hyposulphurous acid, the
radical, sulphurous acid, combines with sulphur; the compound is
a sulphur acid, S.O,2+S., and combines with sulphur bases to form a
distinct class of salts. The hyposulphuric acid contains also sulphurous acid as its basis; but there are two equivalents of the radical to one of oxygen: it is 2S.02+0.  This hypothesis is rendered still stronger by the fact that sulphurous acid combines with
chlorine and with iodine to form the chloro-sulphurous acid S.0,
+C1., and the iodo-sulphurous acid S.O,+-I.  It combines also
with nitric oxide to form the nitro-sulphurous acid S.O,+N.02.
The chloro-sulphurous acid is produced by the direct combination
of chlorine and sulphurous acid, when exposed to strong sunlight.
The iodo-sulphurous acid is formed by passing sulphurous acid gas
through a solution of iodine in pyroxylic spirit, and the nitro-sulphuric acid, which exists only combined with bases, by placing a
solution of sulphite of potash in contact with nitric oxide, which it
gradually absorbs. The sulphurous acid forms, therefore, an extensive range of combinations, in which it serves as a compound radical., and of which the formulm are as follows:
Sulphuric acid...........   S.O2+0.
Byposulphuric acid......... 2S  +0.
Hyposulphurous acid......... S.O2-S.
Chloro-sulphurous acid........ S.02+C1.
Iodo-sulphurous acid.........   S. 02 I.
Nitro-sulphurous acid..           S.02+N.02.
The ordinary salts of sulphurous acid, the Sulpphites, I rank along
with the compounds of chlorine with the metallic oxides and with
peroxide of hydrogen, which bodies they resemble also in their
bleaching powers.
Compounds of Sulphur and Hydrogen.
Sulphur unites with hydrogen in two proportions, forming a gas,
Sulphluretted Hydrogen, by an equivalent of each element, and a heavy
liquid when in the proportion of one equivalent of hydrogen to two
of sulphur.
To prepare sulphuretted hydrogen, the protosulphuret of iron
(Fe.S.) is acted on by dilute sulphuric acid, in the apparatus figured
in p. 247. A lively effervescence occurs from the escape of sulphuretted hydrogen gas, and the solution contains sulphate of protoxide of iron; a gentle heat may be applied to favour the reaction
of the materials. In this process water is decomposed, its oxygen'
being transferred to the iron, and its hydrogen to the sulphur; the
result may be expressed as follows: Fe.S. and S.03+1H.O. give
H.S. and S.03+Fe.0. This gas may also be obtained by acting on
sulphuret of potassium by dilute sulphuric or muriatic acid, in which
case the theory is the same as that already given. Sulphuret of
antimony and liquid muriatic acid produce, when heated, very pure
sulphuretted hydrogen, the reaction being that Sb,2S and 3(H.CI.)
give Sb2Cl3 and 3(H,.S.).




OF SULPHURETTED' HYDROGEN.'293
The sulphuretted hydrogen gas, being absorbed by water, cannot
be well collected over it, except it be saturated with common salt,
or be leated to above 90~, in which case its solvent power is very
much diminished.  It cannot be kept long over the mercurial pneumatic trough, for the lead and tin always present in the mercury of
commerce gradually decompose it, combining with the sulphur, and
leaving the hydrogen free; the volume of the gas remains the same
during this decomposition.
This gas is colourless and transparent: it is characterized by its
fetid odour, that of rotten eggs, which, indeed, owe their. peculiar
odour to the formation of this gas during their putrefaction. Its
specific gravity is 1177. It consists, therefore, of
One volume of vapour of sulphur...... 66480
Six volumes of hydrogen...... 688 X6-  412 8
the seven volumes are condensed to six..  70608
of which one weighs, therefore........  1176'8
The sulphuretted hydrogen gas dissolves in water, forming a solution which is extensively used as a reagent for the metals, from
the solutions of most of wvhich it precipitates metallic sulphurets of
various colours, by which many metals may be recognised.  Thus
antimony'gives an orange, manganese a flesh red, arsenic and cadmiuma a canary yellow, and several, as lead, mercury, and bismuth,
black or brown precipitates.
Sulphuretted hydrogen is highly inflammable; if burned in a limited quantity of air, the hydrogen is consumed, while most of the
sulphur is deposited. By means of nitric acid or chlorine it may be
completely decomposed; hence chlorine acts as a disinfectant and
purifier of sewers or rooms impregnated with the odour of sulphuretted hydrogen. This gas is very poisonous; air being capable of
producing death to large animals, if respired, though it may not contain more than 8v- of this gas.  Many of the metals decompose sulphuretted hydrogen, particularly when heated in this gas, combining
with the sulphur, and setting the hydrogen free.  This occurs slowly, even at common temperatures; and hence metals, as gold and
silver, which are not oxidized by the air, are gradually tarnished by
the sulphuretted hydrogen, which, exhaled from decomposing animal
matter, is always present in the atmosphere. This gas, evolved
probably by the action of water on the native sulphurets of iron, at
high temperatures, is a frequent constituent of mineral springs, and
forms the class of spas termed sulphureous, such as those of Hiarrowgate, Lucan, and Golden-bridge. They are easily recognised
by the fetid odour, by blackening a silver spoon, or by giving a black
or brown precipitate with a solution of acetate of lead.
In its chemical relations, sulphuretted hydrogen assimilates itself closely to water; its composition and equivalent numbers are
as follows:
Sulphur,  94118      One equivalent, =2-01'2 or 16'1
Hydrogen, 5'82       One equivalent, =  12'5 or 1'0
10000 0213'7   17'1
Bisulphuret of Hydrog'en.-To prepare this substance, bisulphuret of potassium
is to be dissolved in water, and the solution gently poured into dilute muriatic acid;




294 SELENIU MI ITS COMPOUNDS  WV ITH OXYGENo ETC.
the potassium combines with the chlorine, and the hydrogen unites with the sulphur, K.S2 and H.C1. giving K.C1. and H.S2; the latter sinks to the bottom of the
vessel as a heavy yellow liquid, insoluble in water, but decomposed rapidly by contact with it, unless free acid be present. It is not easily obtained pure, as the sulphuret of potassium, formed by melting salt of tartar and sulphur together, or by
dissolving sulphur in a solution of caustic potash, always contains an excess of sulphur beyond two atoms, which, precipitating along with this true compound, dissolves in it, and modifies its properties and composition.
This oily liquid is characterized by separating, with great ease, into sulphuretted
hydrogen gas and solid sulphur; indeed, the best way of obtaining sulphuretted hydrogen condensed into a liquid, is to seal up, in a strong tube, a quantity of this bisulphuretted hydrogen, which, after a short time, is decomposed; the gas, not being
able to escape, is liquefied by the pressure it exercises, while the sulphur separates
in octohedral crystals.
This body is decomposed by all substances which decompose deutoxide of hydrogen. Black oxide of manganese, or oxide of silver put in contact with it, evolve
sulphuretted hydrogen gas, and often with the appearance of light and heat; it
corrodes the skin. and appears to possess bleaching properties..
Sulphurets of Nztrogen have been discovered and described; they are solid and
crystallizable, but are of no importance.
Of Selenium.
Selenium was discovered by Berzelius, and accompanies, although
in exceedingly small quantity, the native metallic sulphurets, existing
as seleniurets of the same metals. It remains even still a very rare
substance: it has not been introduced into the arts or into medicine,
and it will hence be necessary to touch upon its history but very
slightly.
When extracted from  its native combinations, selenium  is a solid
of a dark brown colour, and when smooth, with metallic lustre.  Its
density is 4.32; its fracture is crystalline; it melts a little above
the boiling point of water, and boils at 650'; its vapour is of a deep
yellow colour, like that of sulphur. In its manner of combination
it resembles, almost completely, sulphur.
In one respect, however, they differ; when selenium is burned in air, it combines
with but one equivalent of oxygen, forming oxide of selenium (Se.O.), a colourless
gas, which is remarkable for its pungent odour of horseradish. By this means
selenium may be recognised, even when present in exceedingly small quantity.
Sulphur does not appear to form a similar compound.
When selenium is boiled with nitric acid, it unites with two equivalents of oxygen, and forms selenious acid, Se.02. This may be also produced by burning selenium in oxygen gas at a high temperature. It is solid, white, volatile, and may
be obtained crystallized by sublimation, or from its watery solution. Selenious
acid may be deprived of its oxygen by contact with zinc or iron filings, or by sulphurous acid: selenium is set free as a crimson precipitate. When selenite of anmmonia is heated, it gives water, nitrogen, and free selenium.
If a current of chlorine gas be passed through a solution of selenious acid, or if
selenium be melted with nitre, the selenic acid is formed (Se.O,), which has the
most remarkable analogy with sulphuric acid. All their similar salts are isomorphous, and almost identical in properties. Indeed, to distinguish them, it is necessary
to boil the salt'with muriatic acid, which has no action on the sulphate, but gives
with the seleniate, chlorine, and selenious acid.
Seleniuretted Hydrogen is formed by the action of acids upon metallic seleniurets,
in precisely the same manner as that described under the head of sulphuretted hydrogen. It is a colourless gas, of an extremely fetid odour, irrespirable, soluble
in water, and precipitating, from the solutions of many of the metals, metallic seleniurets; these are generally black or brown; but the seleniuret of manganese is,
like the sulphuret, flesh-red, and that of zinc is white.
When sulphuret of hydrogen is passed into a solution of selenious acid, water is
formed, and a sulphuret of selenium is produced analogous to selenious acid, its
formula being Se. —S2. It is a canary yellow powder, insoluble in water.




PUOSPHORUS,  ITS  PREPARATION, ETC.    295
Of Phosphorus.
Phosphorus exists in nature, principally in the animal kingdom,
in the bones of the vertebrated animals, in the fluids of the body,
and also in the pulpy material of the brain and nerves. It is found
in small quantity in many vegetables, and is a constituent of some
minerals.  It is prepared as an article of manufacture in large quantity in London and Paris. In the latter city it is computed that
about 200,000 lbs. of phosphorus are annually obtained.
The principal source of phosphorus is the earthy material of bones (phosphate of
lime). The bones are first burned until they become completely white, and then
ground to powder. To three parts of' this powder are added thirty parts of water
and two of oil of vitriol. The sulphuric acid unites with a portion of the lime of
the bone ashes, while the remainder forms, with the whole of the phosphoric acid,
a soluble salt, which is obtained in the liquor, when the insoluble sulphate of lime is
separated by straining through a cloth. The
liquor is evaporated to the consistence of a sirup,
and gradually mixed with a quantity of powdered
charcoal, about one fourth the weight of the
bones that had been used, and the whole completely dried at a temperature just below redness.
The mass is introduced, in powder, into an
earthen retort, a, which is placed in a furnace,
as in the figure. To the neck of the retort is.          
adapted a copper tube, b, the other extremity of
which dips a little into the water in the bottle
which serves as a receiver. The retort being
gradually heated, the excess of the phosphoric
acid is decomposed by the charcoal, the carbon
of which combines with the oxygen to form car-_
bonic acid, while the phosphorus becomes free; i-1
this being volatilized by the high temperature,
passes in the state of vapour into the copper Si
tube, where it is condensed, and, flowing down
in the liquid fobrm into the bottle, collects under the surface of the water. The cop
per tube must dip so little under the water, that by no condensation could this be
forced back into the retort.
The phosphorus so obtained is again melted under the surface of the water,
and poured into glass tubes, where it is allowed to solidify. It thus gets the cylin,
dlrical form in which it is found in commerce.
Phosphorus, when pure, is transparent and colourless; but, as
generally found, it is of a pale yellow, or even of a reddish colour. At ordinary temperatures it is soft, so that it may be bent or
cut with a knife; but at 32' it becomes quite brittle and crystalline
in its fracture.  It is insoluble in water, but it dissolves in the volatile oils, in ether, and in sulphuret of carbon, from which last it
may be obtained in crystals of considerable size,
which are regular dodecahedrons, as in the figure.
It has also been obtained crystallized by fusion,
under the form  of octohedrons.  At 108~ phosphorus melts into a colourless liquid, and at 550O
it boils, forming a colourless vapour, the sp. gr.                   /
of which is 4307.  Phosphorus appears to assume
an anomalous condition like that of sulphur; when
strongly heated  and  suddenly cooled, it becomes jet black and
opaque, but gradually returns to its ordinary aspect.
Phosphorus is exceedingly inflammable.  Even at ordinary temperatures, when exposed to the air, it burns slowly, forming phos



296  CO.MPOUND S  OF  PHOSPHORUS AN'D  OXYGEN.
phorous acid, and emitting light visible in the dark, from whence
its name (Pwi 05spwo, I bring light).  It, at the same time, emits a
remarkable and penetrating garlic smell. It is hence that phosphor
rus is used to analyze atmospheric air, and that it must always be
preserved under water.  When heated to  120' phosphorus bursts
into brilliant flame, and unites with oxygen to form  phosphoric acid.
The combustibility of phosphorus is influenced by the presence of
various gaseous bodies in a very remarkable degree.  Thus, in
pure oxygen, phosphorus does not burn nor give any light until the
temperature is raised to 80'; and if the oxygen or air be mixed
with small quantities of olefiant gas, or the vapours of ether or of
oil of turpentine, its slow combustion may be totally prevented.
This influence even extends, under some circumstances, to much
higher temperatures..
The atomic weight of phosphorus had been formerly taken as
15'7 (H.-1) in consequence of some views of the constitution of
its compounds, which are now generally abandoned, and I consider
the true equivalent number to be 31'4, double the former.
Phosphorus combines with oxygen in four proportions, forming an -oxide and
three acid compounds, the constitution of which follows:
Oxide of phosphorus... -2P.+-O.-628-8+ 8'0 —70 8
Hypophosphorous acid... -  P.+-0.=31-4+ 80 —39-4
Phosphorous acid....  P.+03-31t4-+.24 0-55.4
Phosphoric acid....  -- P.-+O5-314+40'0=714
Oxido of Phosphorus.-When phosphorus is exposed to light, in water containing
air dissolved, it gradually becomes covered with a white powder, vWhich is a compound of phosphorus with water; but there forms, at the same time, a reddish substance, which is oxide of phosphorus. It is generated, also, whenever phosphorus
is incompletely burned, and may be formed in large quantity by melting phosphorus
under water, and bringing a stream of oxygen gas to act upon it by means of a tube
passing to the bottom of the vessel; the phosphorus burns brilliantly, but, being
present in great excess, it passes principally only to the lowest degree of combination that it can form. It may be obtained purer by other processes, which are, however, too complicated to be introduced in this place.
The oxide of phosphorus so formed is a red or yellow powder, insoluble in water;:it is exceedingly inflammable in some forms, but in others does not take fire until
heated to near the boiling point of mercury. It is not probable that the red and
yellow substances which are called oxide of phosphorus are really identical, as they
differ:in their most striking characters besides in colour. The formula P20. is that
obtained from the yellow matter; Pelouze considers the reddish matter to be expressed by P,0,.
Hypophosphorous Acid.-This acid is very little known; it is formed when phos
phorus is heated in a solution of an alkali or earth: water is decomposed; one portion of phosphorus combining with the hydrogen, and another with the oxygen,
produce phosphuretted hydrogen gas, which passes off, and hypophosphorous acid,
which remains combined with the alkali or earth employed; the reaction may be
shown thus with phosphorus and solution of barytes: 4P., 3H.O., and 3Ba.O., give
3(P.O.+Ba.O.) and P.H3.
The hypophosphite of barytes, so obtained, may be decomposed by sulphuric acid,
and the sulphate of barytes being removed by filtration, the hypophosphorous acid
remains uncombined; its solution may be evaporated to the consistence of a sirup,
but it cannot be obtained solid; it is decomposed, by continuing the heat, into
phosphuretted hydrogen, phosphoric'acid, and some phosphorus is set free.
Its salts are all soluble in water, and most of them crystallize and contain water
of crystallization; when heated strongly, they give phosphuretted hydrogen and a
phosphate of the base.
Phosphorous Acid.-This acid is the principal product of the slow combustion of
phosphorus, but, to obtain it pure, it is necessary to avoid carefully an excess of
oxygen; for this purpose, a glass tube of ten inches long and half an inch bore is




PHOSPHORIC  ACID, ITS PREPARATIO N  ETC. 297
drawn out at one end to a point, with an aperture large enough to admit a pin, and
bent at an obtuse angle about two inches from the point; at the bend is laid a piece
of phosphorus, which is heated until it takes fire, but the temperature must not rise
so high as to sublime any of it. As there is a great excess of phosphorus present,
the principal product of the combustion is phosphorous acid, which, being formed in
exceedingly light flakes, is carried by the current of air to the upper part of the
tube, where it is deposited. These flakes are volatile, and may be sublimed from
one part of the tube to another; they attract water so powerfully, that the heat
evolved is sometimes great enough to inflame the phosphorous acid, which then
combines with more oxygen, and forms phosphoric acid.
Phosphorous acid is more easily prepared in the liquid form; for this purpose, a
quantity of phosphorus is placed in a thin glass vessel, covered with water to the
depth of some inches; a current of chlorine is then conducted by a tube to the
phosphorus, which inflames and forms protochloride of phosphorus; this substance
is immediately decomposed by the water, phosphorous acid and muriatic acid being
produced; the P.C13 and 3H.0. giving P.0,3 and 3H.C1l; both acids dissolve in the
water, but by evaporating the solution to the consistence of a sirup, the muriatic
acid passes off as gas, and the hydrate of phosphorous acid, P.03-,31-.0., remains
behind. This hydrated acid cannot be freed from water by farther heat. it being
then decomposed into phosphoric acid, and the variety of phosphuretted hydrogen
which is not spontaneously inflammable. Thus 4(P.03-+-3H.O.) give 3P.05 —3H.O.)
and P.H,3.
The solution of phosphorous acid absorbs oxygen rapidly from the air, and, with
the assistance of heat, reduces to the metallic state the salts of mercury, silver,
gold, and platina. It is hence occasionally used as a deoxidizing agent.
Phosphoric  dcid.
When this acid is required in laroge quantity, it is generally prepared from the earth of bones, which are acted on by sulphuric acid,
as was described for the preparation of phosphorus.  The acid solution of superphosphate of lime is decomposed by carbonate of ammonia, by which the lime is thrown down in combination with carbonic acid, and the phosphoric acid remains in solution as phosphate
of ammonia. This salt may be crystallized, but it is generally
evaporated to dryness, and ignited; the ammonia passes off, and
the phosphoric acid remains behind melted, and solidifies on cooling into a colourless glass, the glacial phosphoric acid.
It may also be obtained by acting on phosphorus with dilute nitric
acid. This supplies oxygen to the phosphorus, and nitric oxide is
evolved. When the action has terminated, the solution is to be
evaporated to dryness, and the residual phosphoric acid ignited, to
expel all traces of nitric acid.  This process is somewhat dangerous, as sometimes fragments of phosphorus are projected by the
effervescence out of the liquid, and burning in the nitric oxide gas,
may burst the retort.  The phosphoric acid may also be prepared
very simply, and in a pure and dry state, by setting fire to some
phosphorus in a little cup, and covering it with a large bell glass.
The oxygen of the contained air forms phosphoric acid, which is
deposited in white flakes on the inside of the glass and on the supportilig plate.  In all these cases, the acid so obtained is destitute
of water; it is aniLydrous.
The phosphoric acid has a great affinity for water, combining
with it almost explosively. It may form three distinct compounds,
phosphates of water, the constitution of which is as follows:
Monobasic phosphate of water.      P.O,+  H.O.
Bibasic phosphate of water                 P.,O+-2H.OO.
Tribasic phosphate of water.  P.O +3H O.
P p




298             POS P H A T ES OF WATE a.
This relation was first established by the researches of Graham,
whose admirable memoir on the arseniates and phosphates formed
an important epoch in science. The phosphoric acid combines not
only with water in these three proportions, but each of them is a
type of& a series of salts which the phosphoric acid is capable of
forming.  Thus there is a class of mnonobasic phosphates, another
class of bibasic phosphates, and a third, which is the most common, of
tribasic phosphates; the water contained in the phosphates of water
being replaced to a greater or less extent by means of equivalent
proportions of ammonia or metallic oxides.
A solution of phosphoric acid in water may contain any one of
the three phosphates of water that have been described, and, when
neutralized by bases, may hence produce totally different salts.
The properties of a solution of phosphoric acid may therefore be
totally different, according to the manner in which it had been prepared, and hence this acid was at one time ranked as a remarkable
instance of isomerism; but Graham has beautifully shown that the
difference of properties is only the result of the existence of the
different states of combination in which the phosphoric acid actually
exists. It will consequently be necessary to study separately the
properties of the three compounds of phosphoric acid with water..Monobasic Phosphate of Water. —A solution of this body reacts powerfully acid; it precipitates albumen (white of egg) in white curds;
when neutralized by a base, it gives salts which contain but one
atom of base, their formula being P.O,+ R.O., and a soluble salt of it
produces, in solutions of silver, a white, soft precipitate, P.05,Ag.0. This is the least stable of the phosphates of water; it gradually passes into the other forms, particularly when its solution is
boiled.
Bibasic Phosphate of Water. —This form of the acid may be prepared by decomposing bibasic phosphate of lead by sulphuretted
hydrogen~  it is characterized by combining always with two equivalents of base, formingo salts, whose formula is P.O~+2R.O.; its
salts give, with nitrate of silver, a white precipitate, P.O,-2Ag. O.,
which is not pasty like the monobasic phosphate.  The salts of this
acid may contain only one equivalent of fixed base, the other being
water, and may hence, at first sight, appear to be constituted like
the monobasic salts; the basic water is, however, easily known to be
pyesent, by its not being expelled by a moderate heat with the water
of crystallization, but requiring a temperature approaching to ignition for its expulsion.
Tribasic Phosphate of Water.-This is the form of phosphoric acid
which represents the class of salts most generally known; it is
characterized by not precipitating albumen, and by combining with
three equivalents of base when fully neutralized. In the majority
of cases, of the three equivalents of base, one is water; thus the comlnon phosphate of soda is a tribasic phosphate, its formula being
(P.0+-t2Na. 0.H.O.)+-24Aq.; when moderately heated, or even by
lons exposure to dry air, it loses the 24Aq., but it requires to be
melted at a red heat in order to drive off the twenty-fifth atom of
water; and, if this be done, on redissolving the fused mass in water,
it crystallizes in a totally different form, and is found to have been




P IO SPHURETTED HYDROGEN..299
changed into bibasic phosphate of soda, the formula. of which is
(P. 0-{ —2Na.0.)+ 10Aq.  The difference is remarkably shown by
the action of these salts on solution of silver; common phosphate
of soda precipitates nitrate of silver of a canary yellow, and the solution becomes acid; one equivalent of tribasic phosphate of soda
decomposing three equivalents of nitrate of silver, producing one
equivalent of tribasic phosphate of silver, two of nitrate of soda,
and one of nitrate of water; this last b.eing liquid nitric acid, of
course, renders the liquor acid. The reaction may be simply expressed:
P.O,+-2Na.O.H.O. and 3(N.O0  LAg.O.)
give P.05+3Ag.O... 2(N.O,+Na.O.) and N.O5+H.O.
If, on the other hand, bibasic phosphate of soda be used, the liquor
remains neutral, for P.O5 + 2Na. O. and 2(N.0, + Ag.O.) give P.O, +
2Ag.O. and 02(N.O + Na.O.).
In the tribasic phosphates it frequently occurs that there is but
one equivalent of fixed base, the other two being water; such salts
have frequently an acid reaction, and were formerly termed biphosphates. Thus one tribasic phosphate of soda is P.O5 +Na.O..  2H.
0.; the biphosphate of ammonia is tribasic, its formula being P.O,
+ N.H40.. 2H.0.
These salts of phosphoric acid were originally designated by
Graham metaphosphates, pyrophosphates, and common phosphates,
but the systematic names which he has since proposed should be
universally adopted.
In the general remarks on the constitution of salts, and on some
other occasions, I shall have opportunities to return to the consideration of this subject.
Compounds of Phosphorus and Hydroggen.
Although it is probable that there exist at least two compounds
of phosphorus and hydrogen, yet I shall describe only that which
is gaseous (P.H,), as of it alone do we possess accurate knowledge.
The modes of preparing this gas have been already noticed. It
may be formed, 1st, when phosphorus is heated in a solution of
potash or barytes, or with milk of lime; the water being decomposed, gives its oxygen to one portion of the phosphorus to form
hypophosphorous acid, and its hydrogen to another, forming phosphuretted hydrogen gas: 2d, when the hydrated phosphorous acid
is heated, the water is decomposed, and phosphoric acid and phosphuretted hydrogen are produced. The gas, prepared in these ways,
possesses very different properties; I shall term that obtained by
the first process the
A., and that by the
second the B variety.
If the A gas, evolved                              C D  
from  the retort a,                                Q 
be allowed to bubble through the wa-                 = —: —-!
ter of the pneumatic    I!
trough, each bubble,   X          - -
of gas, as it bursts in.




300           PHOSP HU RETTED HYDROGEN,
the air, takes fire spontaneously, and, burning with a beautiful white
flame, forms a ring of phosphoric acid smoke, which, widening as
it rises, may ascend to a considerable height, if the air of the apartrment be still, without its form being broken up. The structure of
this ring is exceedingly curious and pretty; it consists of an amazing number of small rings, which revolve with great rapidity on
their axis, and whose plane is perpendicular to that of the general
ring which they produce. This is spontaneously inflammable phosphuretted hydrogen: if the gas bubbles be received in a jar of pure
oxygen, the combustion is excessively brilliant and explosive. The
B variety of the gas is not spontaneously inflammable, but if set on
fire it burns with the same appearance as the other.
On analysis, the two varieties give exactly the same result; they
are colourless and transparent, and of a very disagreeable garlic
smell; but slightly absorbed by water, and precipitating the generality of metallic salts, giving insoluble phosphurets.  The specific gravity is the same for both, being 1185, which arises from
One volume of phosphorus-vapour....... =43270
and six volumes of hydrogen...... 688 X 6= 412'8
being condensed to four............         4739'8
of which one weighs, therefore.........   1184'9
Their constituents by weight, and equivalent numbers, are as follows:
Phosphorus, =91'29       One equivalent,    =392'3 or 31.4
Hydrogen,       8'71     Three equivalents,- 37'5 or 3'0
100'00                          429'8  3' 4
These two varieties were naturally looked upon as isomeric, but
Graham has shown that the difference of properties may arise from
the presence of a small quantity of foreign substance, as such may
change the one variety into the other.  Thus a very small quantity
of the vapour of ether removes altogether the power of spontaneous
inflammability from the A variety; the vapour of the essential oils,
and even carbon, phosphoric acid, and potassium, produce the same
effect. On the other hand, an exceedingly small quantity of vapour
of nitrous acid or nitric oxide converts the variety B into A, and
makes it spontaneously inflammable.  Graham  considers that, in
obtaining the gas from phosphorus and milk of lime, &c., it is accomnpanied by a very minute trace of some compound of phosphorus and
oxygen, probably the same as is formed by nitrous acid with the B
variety, which is really spontaneously inflammable, and, acting as a
match, inflames the general mass of gas (see p. 296.)
Phosphuret of Nitrogen.-This compound has been discovered and described by
Rose, but possesses no important properties.
Sulph-uret of Phosphorus is formed by melting together sulphur -and phosphorus in
equivalent weights. It appears that these elements unite in more proportions than
one. The compound is much more inflammable than phosphorus, and is the material used in the phosphorus match-boxes.
Of Chlorine.
Chlorine exists in large quantity in nature, principally combined
with sodium, forming immense deposites of rock-salt (chloride of




CH L O RINE, ITS PREPARATION.                         301
sodllm) in England, in Poland, and elsewhere; and in the same
state it communicates the saltness, and constitutes the chief ingre
dient of sea-water. It is found also combined with calcium, mercury,
lead, silver, and some other metals; but these compounds are rare,
and exist only in small quantity. The only source of chlorine
practically useful in chemistry and in the arts is from common salt,
To obtain chlorine in large quantity, the common salt is mixed with peroxide of
manganese. and then decomposed by sulphuric acid; the half of the oxygen of thll
peroxide of manganese passes to the sodium, the chlorine being expelled, and tlie
soda and protoxide of manganese both unite with the sulphuric acid. Thus Mn.O0
and Na.CL., treated with 28.0,, produce S.03. Na.O.+S.O,. Mn.O., and C1. is
evolved. By weight, about six parts of oxide of manganese and eight of chloride of sodium are employed
with thirteen of oil of vitriol; and as the manufactu-     7
rers of chloride of lime are generally makers of oil of
vitriol also, a proportionate quantity of acid of 1'600
from the chamber (p. 289) is generally used in place
of strong oil of vitriol, the expense of concentration   
being thus saved. Into a leaden still, h, h, such as is
represented in the figure, the mixed salt and manga-,/
nese are introduced at the aperture i, which is then      -7;
tightly closed; the sulphuric acid enters by the bent  L 
funnel b, and these materials are well mixed by means  e v   X       t
of the agitator, turned by the cross handle n; the gas
evolved escapes by the tube a, which conducts it to its
destination. At first the operation does not require
heat, but the still sits in an iron jacket, e, e, into which steam is conducted by the
tube 1, and thus the heat necessary for the decomposition is kept up; a waste-pipe,
g, serves for running out the residue of one process, in order to clear the still for
another.
When chlorine is required in small quantity in the laboratory, it
may be more conveniently prepared from the muriatic acid of cornmerce, which is a solution of chloride of hydrogen gas in water.
This is completely decomposed by peroxide of manganese at very
moderate temperatures, the hydrogen of the muriatic acid combining
with the oxygen of the peroxide of manganese to form  a deutochloride of manganese, which is completely resolved by a very
moderate heat into protochloride and free chlorine. Thus, at first,
Mn.02 and 2CI.H. give Mn.C1 and 2H.O., and then Mn.Cl2 separates into Mn.C1. and Cl., which is evolved as gas.  For this it is
only necessary to introduce about one part of peroxide and three of
muriatic acid into an apparatus, such as those already often figured,
and the gas may be obtained.
The collection of the chlorine
requires some remark.  It iA absorbed rapidly by cold water,
and it cannot be collected over
mercury, as it combines rapidly with it, forming calomel; water heated to above 90' should
therefore be used; but it is still
better to take advantage of the
great density of chlorine for its
collection.
If the tube conducting the
chlorine  from  the  flask a, in




-302      BLEACHING  POWER OF CHLORINE.
which it is generated, be brought to the bottom of a dry glass, c, the
chlorine issues there, and, being much heavier than the air, pushes
the air up out of its way, and gradually fills the jar completely, precisely as, by conducting a stream of water to the bottom of a vessel
containing oil, this might be perfectly expelled, and the vessel filled
with water. The colour of the chlorine allows the gradual filling of
the bottle to be seen, and by stopping its aperture with a greased
stopple, the gas may be preserved unaltered for a long time.
The chlorine, when thus prepared, is a greenish yellow gas,
whence its name (Xoapoc); of an extremely suffocating odour, irritating the air passages when respired, even very much diluted, in
an intolerable degree. Its specific gravity is!2;70. On plunging
a lighted taper into chlorine, it burns for a moment with a red, smoky
flame, but is soon extinguished. Many bodies burn, however, inore
readily in chlorine than in air, or even in oxygen gas. If some
powdered antimony or arsenic be thrown into a bottle of chlorine,
they take fire, with bright scintillations.  Tin or brass foil burns
spontaneously, as also phosphorus, although with little light. A
paper dipped in oil of turpentine takes fire spontaneously, the hydrogen burning, and the carbon being deposited as a thick black
smoke.  The affinity of chlorine for hydrogen is very great: when
mixed, these gases gradually unite, even at common temperatures,
and suddenly, with explosion if set on fire by a taper or by the
electric spark. In consequence of this affinity for hydrogen, chlorine decomposes most organic substances, one half of the chlorine
removing an equivalent quantity of hydrogen, and the other half
going in its place; thus ether and chlorine give chloride of hydrogen and chlorine ether, C.H,50. and lOC1. giving CCI,O0. and 5H.Cl.
Very often, however, the action of chlorine is much more complex.
Perhaps the most important character of chlorine, and certainly
that upon which its value in the arts depends, is its power of removing the colour of organic substances; its bleaching properties.
Formerly it was considered that water was necessary for this bleaching, and that the chlorine combined with the hydrogen, while the
oxygen of the water, being thus thrown upon the organic substance,
oxidized it, and formed a new body, which was colourless. I have
shown, however, that this is not the case, but that the chlorine enters
into the constitution of the new substance formed, sometimes replacing hydrogen, at others simply combining with the coloured body,
and in some, the reaction being so complex that its immediate stages
cannot be completely traced. I shall notice this agency of chlorine
again when describing the chloride of lime, and also when discussing its relations to organic chemistry.
From this action on organic bodies, chlorine is extensively employed as a disinfectant, to remove the miasmata and infectious impurities by which the atmosphere of an hospital may be contaminated.
For this purpose, it is desirable to evolve the gas slowly, but continuously; in order to do so, some chloride of lime, diffused through
water, may be placed in a capsule or teacup, and by a funnel, the
throat of which is partly stopped, dilute sulphuric acid be allowed
to drop down on it. The acid takes the lime, and the chlorine is
set free.




OXIDIZING  POWER- OF  CHLORINE.                 303
When chlorine is brought into contact with water at 32~, they
combine, forming a hydrate which crystallizes in plates, and which,
when heated to about 450, is decomposed. If a quantity of these
crystals be sealed up in a strong glass tube, the chlorine, when liberated, exercises so much pressure as to condense itself into a liquid.
This was the first instance in which the liquefaction of the gases
was successful. Water holding chlorine in solution possesses the
colour, odour, taste, and bleaching properties of the gas itself, and
may hence be used for the purposes of the arts, although not so
manageable or convenient as many other forms. When chlorine
water is exposed to the light, it is gradually decomposed, chloride
of hydrogen being formed, and oxygen set free; the solution becomes colourless, loses its bleaching powers, and acquires an acid
reaction. In contact with other bodies, chlorine may decompose
water much more rapidly, and is hence frequently employed as an
oxidizing agent, substances being frequently oxidized by chlorine
to a higher degree than by nitric acid. This results, probably, from
the chlorine first combining with the body, and the compound then
decomposing water; thus, when chlorine converts selenious acid
into selenic acid, it is probable that it is not that the chlorine decomposes water, but that it unites with the selenious acid, forming chlo
ro-selenious acid, Se.02. Cl., which, in contact with water, is resolved into Se.02. 0. and C1.H. Very frequently chlorine oxidizes a
metal to a higher degree by combining with one portion of it, and
hence throwing all of the oxygen upon the remainder; thus protoxide of iron is converted into peroxide by chlorine, because 6Fe.
0., acted on by 3C1., produce Fe2Cl3 and 2Fe,03. The direct decomposition of water by chlorine 1 consider to occur very seldom.
The combinations of chlorine form, perhaps, next to those of oxygen, the most complete series which exists in chemistry. Its affinities are so varied that it unites with almost all the simple bodies,
metallic and non-metallic, and in most cases it forms more than one
compound with the other body. Its metallic compounds are generally constituted like the oxides of the same metals, but in its union
with the non-metallic bodies it does not appear to follow so closely
the analogies of oxygen.
Chlorine possesses also the property of combining with metallic
oxides, apparently without decomposition in many cases, and forming compounds resembling peroxides, in which a portion of the oxygen is replaced by chlorine. Thus, with lime it forms Ca.O.. Cl.,
with protoxide of lead Pb.O.. CI., with barytes Ba.O.. Cl., which correspond probably to Pb.O2 and Ba.O,. In the hydrate of chlorine,
which is Cl.+10H.O., it is likely that a compound corresponding to
peroxide of hydrogen may exist, and that the constitution of the
crystals may be H.O.. Cl.+ 9H.O., and that bleaching compounds in
general may have that type.
Chlorine is easily recognised, when free, by its peculiar odour, by
its bleaching powers, and by producing with a solution of nitrate of
silver a white curdy precipitate, which is insoluble in acids, soluble
in water of ammonia, and is rapidly blackened by exposure to the sun's
rays.  When in combination with a metal, its solution gives the
same kind of precipitate of chloride of silver, but the bleaching properties and smell are absent. 




304    HYPOCHLOROUS ACIID.- -CIILORIC ACID.
Compounds of Chlorine with Oxygen.
These are four, constituted as follows:
Hypochlorous acid....  =C1.-  0. —354+8 =43.4
Chlorous acid......   =C1l.+40. 35'4 — 32=67'4
Chloric acid.....   =C1.50.-35 4+L40-75 4
Perchloric acid...=Cl.-I-70. —35 4+56 —914
Hypochlorous d1cid.
If red oxide of mercury, diffused through a small quantity of water, be introduced into bottles containing chlorine, and the whole
be agitated, the gas is rapidly absorbed, and, combining with both
constituents of the oxide, forms chloride of mercury and hypochlorous acid. Thus Hg.O. and 2C1. give Hg.Cl. and Cl.O. As there is
always an excess of oxide of mercury employed, the chloride of
mercury combines with it, forming the insoluble brown oxychloride
of mercury Hg.Cl. + 13Hg.O., which separates, and the hypochlorous
acid remains nearly pure in solutibon in the water. By a very moderate heat it may be distilled in a dilute form, and so obtained quite
pure from sublimate, but at 212' the acid is rapidly decomposed
into chlorine and oxygen.
A solution of hypochlorous acid is yellow; its odour is like that
of chlorine; it bleaches powerfully; it decomposes spontaneously
even in the cold, forming chlorine and chloric acid; it oxidizes most
bodies with extreme energy.  To obtain it in the gaseous form, it
is sufficient to introduce a small quantity of the solution into a tube
over, mercury, and to add pieces of dry nitrate of lime; the water is
absorbed by this deliquescent salt, and the acid remains as a greenish yellow gas, very similar to chlorine in all respects; water absorbs 100 volumes of it; by raising its temperature even slightly, it
explodes, and its volume is increased by one half: 100 volumes of
it produce 100 of chlorine and fifty of oxygen, Its specific gravity
is by theory 3021'3, and its equivalent numbers 542'6 or 43.4: its
formula is CI.O.
The hypochlorous acid combines with bases to form salts, hypochlorites, which possess the bleaching properties of the acid in a
great degree; but their nature is involved so much in the general
history of the bleaching compounds of chlorine, that I shall not enter
upon any notice of them here.
Chloric.cid.
When chlorine is brought into contact with an alkaline solution,
it is absorbed with great avidity, and the liquor acquires powerful
bleaching properties. Concerning the nature of the reaction, the
opinions of chemists are not completely settled; it may be supposed, on the one hand, that the chlorine unites directly with the
alkali, forming simply, if potash be employed, chloride of potassa,
K.O.. Cl. But, on the other hand, it is possible that a quantity of
alkali may be decomposed, as certainly occurs with oxide of mercury, and that chloride of potassium and hypochlorite of potash may
coexist in the liquor; thus, that 2K.O. and 2C1. should produce K.
Cl. and C1.O.+K.O.  The majority of chemists incline to the latter
view, but the subject will hereafter receive: detailed consideration.




CHLORIC ACID.- C-HLOROUS ACID.                 305
In any case, this bleaching alkaline liquor is completely decomposed
by boiling, particularly if it be very concentrated. Oxygen is then
evolved in considerable quantity, while chloride of potassium and
chlorate of potash are produced: thus 9(K.O.+Cl.O) evolve 120.,
and form 8K.CI. and K.O.+-C].O. It is in this way that the chlorate
of potash of commerce is obtained, and from it the chemist prepares
chloric acid.
A solution of this acid is readily prepared by decomposing a so
lution of chlorate of barytes by sulphuric acid. It cannot be obtained
solid, as, when a concentrated solution of it is heated, it is resolved
into chlorine, oxygen, and perchloric acid. It does not bleach; it does
not precipitate a solution of nitrate of silver: when in its strongest
form, of a thick, oily consistence, it sets fire to many organic bodies,
and is a powerful oxidizing agent.
The compounds of chloiic acid are easily recognised, by yielding,
when heated, oxygen and a metallic chloride; thus the chlorate of
potash is used in the preparation of oxygen (p. 244), Cl.04 —K.O.
giving C1.K. and 60. When mixed with sulphur and rubbed in a
warm mortar, they explode, and if thrown upon an ignited coal, they
deflagrate with violence.
The chlorate of potash is of very great commercial importance,
from its utility in making matches, and is the source from whence
the chemist obtains the remaining compounds of chlorine and oxygen.
The constitution and equivalent numbers of chloric acid are as
follows: by weight,
Chlorine, 46'95    One equivalent, =442'6 or 35'4
Oxygen, 53'05    Five equivalents, =500'0 or 40'0
100'00                     942'6   75'4
Its formula is C1.05, and, like the nitric acid, which it resembles in
so many other properties, it consists of five volumes of oxygen united to two of the other element.
Chlorous dcid. —W hen chlorate of potash in fine powder is decomposed by moderately strong sulphuric acid, the chloric acid, at the
moment of being set free, breaks up into two other compounds, one
containing more, and the other less oxygen, the former being the
chlorous, and the latter the perchloric acid, 3C1.05 giving 2(C1.
04) and C.O7.' This process must be conducted very cautiously, and
the retort warmed very gently in a water bath. The chlorous acid
may be collected over mercury, or, from its great density, like chlorine, in a dry jar; there remains in the retort a mixture of bisulphate and of perchlorate of potash.
This acid gas is of a rich yellowish-green colour, and an aromatic
odour; it is rapidly absorbed by water; it bleaches strongly, and is
a powerful oxidizing agent, its elements separating from the slightest
causes. If it be heated above 212~, it explodes with a flash of light;
phosphorus immersed in it takes fire spontaneously, and burns brilliantly in the mixture of chlorine and oxygen which results from its
decomposition. This may be very well shown by placing some
crystals of chlorate of potash and some phosphorus together, at
O.a




:306                PERCIILORIC ACID.
the -bottom of a tall glass filled with water, and conducting to. the
mixture, by means of a long glass funnel, some. oil of vitriol; the
phosphorus burns in each: bubble of chlorous acid gas which forms,
and a brilliant combustion under water results..
When this gas is decomposed, 100 volumes produce 1:50, of which
50 are chlorine and 100 oxygen; its specific gravity may therefore
be calculated to be 2337'5.
The chlorous acid combines with.bases to form salts, chlorites
which possess bleaching properties, -but are not of much importance,
as they do not enter into practical use.
Peirchloric AJcid.-.-This acid is formed in the process for obtaining
chlorous. acid,. as already described, and is obtained by washing the
saline.residue with cold water. The bisulphate of potash readily
dissolves, leaving behind the perchlorate of potash, which is but
sparingly soluble therein; this may. then be dissolved in boiling
water, from which it crystallizes as the'solution cools. When' the
object:is only the preparation of perchloric acid, and not of chlorous
acid,. the process becomes easier by.heating chlorate of potash with
dilute nitric acid; the elements of the chlorous acid are then separated, merely mixed together, and the explosions and sputtering
which occur with sulphuric acid are avoided.
In the process of obtaining oxygen from chlorate of potash, there
occurs.a period.at.which it is, necessary to elevate the temperature
very much in order to keep up the evolution of gas; this arises
from the salt being at first decomposed into oxygen, chloride of
potassium, and perchlorate of potash, 3(K.O.C1.O,) giving 2(Cl.K.)
and Ki.O.Cl.0, while 80. are evolved as gas. This is exactly half
of the oxygen which the salt contains. If the saline mass then remaining be washed with' a small quantity of water, the chloride of
potassium dissolves,. and the perchlorate of potash. remains behind.
Perchloric acid may be prepared from t1lis-potash salt by mixing
it in a retort with half its weight of oil of vitriol, and as much water, and distilling; the acid passes over with the water. If it be
distilled with an excess of oil of vitriol, it may be obtained free from
water, and is then a white crystalline mass, very deliquescent, and
evolving great heat when mixed with water. In this process, however, a great part of the acid is decomposed.
The perchloric acid is the most stable compound of chlorine and
oxygen. It is not decomposed by muriatic acid, by which the chloric acid is immediately decomposed, a mixture of chlorous acid and
chlorine being evolved; C1.O, and Cl.H. giving H.O. and a mixture
of Cl.QO with CL.,  which was described by Sir Humphrey Davy as a
peculiar gas, Euchlorine. By this means the salts of perchloric and
of chloric acid may be distinguished. It is not decomposed by alcohol, nor has it any spontaneous action on organic bodies. It is
well. icharacterized'by the very sparing solubility of its potash salt,
whence it has been employed as a reagent to detect that allkali.
The-constitution and equivalent numbers of perchloric acid are as
follows:
Chlorine, 38'741    One equivalent,  =44026 or 35'4
Oxygen, 61,26    Seven equivalents,  70~0 or 56'0
100.00                      1142 6   91.4




CHLOR 1 DE  OF iiHYDROGE'N.                 307
Compound of Chlorine anld 4l yd'iogen.
This compound exists naturally as a gas,.-of which a solution in
water has been known since a very early period in chemistry under
the names of spirit' of salt, marine acid, muriatic acid;:hydrochloric
acid, and, more properly, chloride —of: hydrogen.'. In speaking of it
under ordinary circumstances, I shall use the common names of liquid or gaseous muriatic acid, according as it is' free or combined
with water; but in cases where its functionfs in combination are disciussed, I shall term it chloride of- hydrogen.'  - 
To prepare the gaseous muriatic acids a small quantity of'-tle corn:mercial spirit of salt may be placed in a flask or retort. connected
with the mercurial pneumatic'trough, and the gas,. which passes off
on the application of heat,' collected. It may also be prepared; by
the action of oil of vitriol on common salt; -`water being decomposed,
its oxygen unites with the sodium, forming soda, which combines
with the'sulphuric:acid, while its hydrogen, uniting- with the c-hlo
rine, produces the chloride of hydrogen, which is given off as a gas;
the reaction may be thus expressed-: S.0H.O. and Na.Cl. give S.
O0Na.0. and H.CI.
This gas may also be formed by putting together chlorine and hydrogen in equal volumes. Even in diffuse light they combine
completely in some hours, but in the direct sunshine the union
is instant and explosive. The mixture may also be fired by the taper or by the electric spark; the colour of the chlorine disappears,
and the resulting muriatic acid gas occupies the same volume as
its ingredients.. In almost all cases of the action of chlorine on organic matters, this substance is also formed; indeed, the agency of
chlorine in bleaching, and. in decomposing organic compounds, appears generally to resu-lt from its disposition to unite with hydrogen.
The chloride of hydrogen is a colourless and invisible gas. When
completely dry it' has no action on vegetable colours, but if a trace
of moisture be present it reddens litmus paper, and restores the
colour of turmeric paper that has been browned by an alkali; hence
it is generally looked uponi as a powerful acid. When mixed with
damp air it forms heavy white fumes by uniting with the watery vapour, and condensing in minute drops of liquid acid: It may
be liquefied by great pressure.' It cannot'be breathed, but does not
produce anything like' the suffocating effects of chlorine.
When muriatic acid gas is put in contact with a metallic oxide,
both are deco mposed, a metallic chloride and water being produiced;thus Cu.O. and H.C0. give Cu.Cl. and H.-. If any of the more oxi-;
dable:metals, as iron, zinc, or potassium, be heated in a current of
the gas, it is decomposed, a metallic chloride being formed and hy-!
drogen gas. evolved. This occurs, also, when these metals, are, immersed::in the liquid acid;- a copiou:s effervescenece i'prodtced by
the escape of hydrogen, -and:the vwater holds.a chloride:of the ofthe metal
in. solution. In this way muriatic acid may be proved to consist of;
equal volumes of hydrogen and  chlorine united without condensa
tion., -Its specifie.gravity is, by theorTy,'!




308    PREPARATION AND PROPERTIES OF
One volume of chlorine...... -2-170O0
One volume of hydrogen.......  =   68'8
give two volumes of muriatic acid....   =2538 8
of which one weighs, therefore......   1269'4
Its constitution and equivalent numbers are therefore,
Chlorine,  97'26    One equivalent,  -442.6 or 35-4
Hydrogen, 2'74    One equivalent,  -  12'5 or  1'0
100'00.                         455'1    36'4
This gas is distinguished by its great affinity for water. If a jar
of it be opened under water, this fluid rushes in, as if it were into a
vacuum. If a fragment of ice be introduced into a bell glass of the
gas, over mercury, the ice instantly melts, and the mercury rises
in the tube, the gas being totally absorbed. The solution of the
gas in water is one of the most valuable agents in chemical research.
To prepare liquid muriatic acid in the laboratory, chloride of sodium is to be introduced into a glass globe, placed in a sand-bath on the fuirnace, and then an equal
weight of sulphuric acid and water, mixed together, are to be introduced by the iunnel: the decomposition proceeds as already explained, and the gas evolved passes
Bei!(n l                                 ___
Xl I!, if                       ii
-.y the tube into the first of a range of three-necked bottles, as in the figure. Eace
bottle is about half full of water. When that in the first has become completely saturated with the gas, this passes into the second, and when it has been saturated,
into the third. The vertical tube in the central neck of each bottle is a safety-tube,
the action of which is as follows. If a sudden condensation occurred in the first
bottle, the acid in the second might, by the greater pressure on its surface, be
forced back into it; but, before it can rise so high as to pass through the connecting
tube, the external air enters by the safety-tube, being driven in by the difference of
pressure inside and outside, and thus restores the equilibrium. Pure muriatic acid
may be much more conveniently prepared for laboratory use by rectifying the spirits of salt of commerce. When this is placed in a distilling apparatus, arranged as
that figured in p. 278, and about one fourth as much water is introduced into the
receiver to condense the quantity of gas which is first expelled, the distillatioh may
be carried on until the retort is nearly empty, and an acid so obtained completely
pure, and of a very convenient strength for the general range of applications.
The manufacture of this acid is carried on on a very large scale more generally
with a view to the extraction of the alkali fromthe residual sulphate of soda than fol
the sake of the muriatic acid, the great difficulty in a soda factory being how to get rid
of the muriatic acid which is produced. When the object is, however, to prepare the




MIURIATIC ACID.                              309
liquid acid, precisely the same apparatus is employed as for the manufacture of nitric
acid, which has been already figured and described (p. 278), the cylinders being
somewhat larger, as from four to five cwts. of common salt are generally decomposed in each cylinder at a charge; the upper part of the cylinder is generally, both
in this operation and in the making of nitric acid, protected from the too corrosive
action of the acid vapours by being lined internally with thin fire-tiles, and the
heads e e in the figure are very frequently constructed, not of metal, but of freestone or of granite. In the decomposition of the salt upon this large scale, the oil
of vitriol is employed of the strength to which it is brought in the chambers, without
concentration, and in such quantity that for each equivalent of chloride of sodium
an equivalent of real sulphuric acid is employed. The strongest liquid muriatic
acid, thus prepared, possesses a specific gravity of 1-211. In order to obtain water
fully saturated with the gas, it must be kept near the freezing point by artificial
cold; it then absorbs 480 times its volume, and increases in bulk by about one fifth.
Its constitution is quite definite, for in this state it consists of H.Cl.+6-H.O., or in
numbers,
Muriatic acid. 40'27    One equivalent.  455-1 or 36'4
Water..  59 73    Six equivalents. =675'0 or 540
100'00                      1130'1   904
When this concentrated acid is heated, it evolves a large quantity of gas, and
the boiling point gradually rises to 230~, at which temperature the residual acid
distils over unchanged; it then has a specific gravity of 1.094, and consists of
H.CL+16H.O.. or in numbers,
Muriatic acid. 20'13    One equivalent... = 455'1 or 36'4
Water... 79 87    Sixteen equivalents.. =1800'0 or 144.0
100l00                             2255.1   180-4
Graham has found that the strong acid, when evaporated in the open air, abandons a quantity of gas, while the remaining liquid becomes H.C1 +12H.O.
The metallic character of hydrogen, and the analogy of its combinations with
those of zinc, are completely shown by comparing the formulra of the compounds
of oxide and chloride of hydrogen with the compounds of oxide and chloride of zinc,
and their combinations with water. Thus I have shown that the hydrates of oxychloride of zinc are as follows:
Zn.Cl.+6Zn.O.
Zn.Cl.+6Zn.O.+ 6Aq.
Zn. C1.-+6Zn.O.- 10Aq.
and the definite states of liquid muriatic acid are
II.Cl.+6H.O.'H.C1.-+6H.O.+ 6Aq.
H. Cl.+-6H.0.+-10Aq.
As we proceed, other similar proofs of the electro-positive and metallic character
of hydrogen will be found.
The other degrees of strength of the liquid muriatic acid are solutions in water
of one or other of these definite compounds; a table of them will be found in the
appendix.
The muriatic acid of commerce frequently contains sulphuric acid,
and always a trace of iron, derived from the metal cylinders in
which it is fabricated. Occasionally, suiphurous acid is formed in
it in small quantity. These impurities are detected thus: by diluting the muriatic acid with water, and adding nitrate of barytes, a
white precipitate is formed if sulphuric acid be present; yellow
ferroprussiate of potash indicates the existence of iron; while solution of protochloride of tin produces a brown precipitate of sulphuret
of tin if sulphurous acid had been present.
Muriatic acid is easily recognised, as a gas, by its action on moist
litmus paper, its fumning in the air, its forming with ammonia dense




,310                N I T 1-.:0 "MR U RI A T IC  A C I D.:w;~hite cl~ouds of sal -mmnoniac, and in solution, by giving: with nitrate
oSf ilver a curdy white precipitate, which blackens on exposure to
light, is- totally insol0ble in nitric acid, but dissolves easily in water
of. amtmonia.;i JVitromu:iattic:ciJ; dqua- Regia. —When  nitric, and  mruriatic
acids, both:colourless, are mixed together, the mixture becomes;deep yellow, and exhales a strong smell of chlorine and of nitrous
acid-,'H.Cl.a and'No0  giving Cl. and N.04, with formation of H.O.
Thi s decomposition, however, proceeds only so far as to saturate
the liquid, with chlorine; but' if a metal beplaced in the liquid it:unites with the chlorine, and new quantities of the acid are decomposed.: Thus' the nitromuriatic acid is a source of chlorine'in a
very concentrated state, and is hence employed to dissolve gold
and platina,, which are not soluble in -nitric acid, and to oxidize some
bodies (metallic. sulplhurets) which resist the action of nitric acid.
The name aqua regza was given to it from  its power of dissolving,gold, the ancient rex metallorum.
Chloride of Sulphur.-In order to obtain this body, a quantity of sulphur is placed
in a tubulated retort, into which a current of chlorine gas is conducted by means
of the bent tube e, in: the figure.
The chlorine and sulphur unite to
_form a volatile reddish yellow li-,  quid, which distils over, and condensos in the receiver f, which
/!e -::'  ~, \must ae kept very cool; any unconLdensed gas, is conducted,away by
the tube 1. The chloride of sulphur, thus obtained, has always
an excess of sulphur dissolved in
it, from which it may be freed by
a asecond distillation. Its specific
gravity is 1'687.'When exposed to the air it gives off' very acrid fumes-: it, boils
at 2800; the specific gravity of its vapour is 4686. It consists of one equivalent of
chlorine united to two of sulphur, S2Cl., and in contact with water, muriatic acid,
sulphur, and hyposulphurous acid' are formed by mutual decomposition.
It is probable that there is another chloride of sulphur consisting of one equivalent of each, S.C1.
Chlorides of Phosphorus.-Chlorine unites with phosphorus in two proportions,
forming a liquid protochloride, P.C13,, and a solid perchloride, P. C1. These may
be prepared in a simple apparatus,' like that used for chloride of sulphur; but as a.~~ ~~~~~~~~~~~~~~'a.W.
more complex arrangement is.necessary for examining the action of chlorine upon
mnany substances  that will be described hereafter, I will introduce the description




C H LORIDES  OF  PHOSPHOR US.-IODINE.   311
of it here. The chlorine is generated by liquid muriatic acid and peroxide of manganese, in the flask a, supported on a sand-bath over the lamp; from it a bent tube
passes to the receiver b, in which a quantity of watery vapour is condensed, and.
serves to absorb any muriatic'acid gas that might escape decomposition. The pure
chlorine passes then through the tube c, which is filled with fragments of fused
evhloride of calcium, which, from its great affinity for water, dries the gas completely.
In the bulb e is contained the substance to be acted on by the chlorine, and the
product of the reaction, if volatile, distils over into the receiver k, in which it condenses; the excess of chlorine escapes by the tube 1, and a stream of water from the
reservoir i h retains the receiver k at the tempeiature proper for condensation.
The phosphorus being placed in the bull e, takes fire on the arrival of the chlorine'
gas, and continues burning until it is all converted into the liquid chloride which
collects in k. While there is an excess of phosphorus, the protochloride is principally formed; but after all the phosphorus has been consumed, if the current of
chlorine be continued, it is absorbed by the liquid in k, which changes into the solid
perchloride.
The Protochloride of Phosphorus is obtained pure by stopping the process before
all the phosphorus has been consumed, and rectifying the colourless liquid by distilling it in a retort containing some bits of phosphorus, which bring back any perchloride it might contain dissolved, to the state of protochloride. This body is
heavier than water, by which it is completely decomposed, P.C13 and 311.O. giving
P.O0  and 3H.C1. It is thus that the liquid phosphorous acid is obtained, as described in p. 297.                           volatile under 10
The Perchloride of Phosphorus is awhite solid, volatile under 212~, and condensing in a crystalline form. In contact with water, it is decomposed with the evolution of great heat, producing phosphoric acid and muriatie acid, P.CI5 and 5H.O.
giving P.O5 and 5H.O.; ~the sp. gr. of its vapour is 4788, consisting of ten volumes
of chlorine and one of vapour of phosphorus, the eleven being condensed to six.
There is a Cdloride of Selenium analogous in general properties to the chloridA
of sulphur.
Iodine.
Iodine is found principally in sea-water, associated  J.ith chlorine,
combined with sodium  and magnesium.  It has beei, also discovered in the mineral kingdom, united with silver.  For the purposes of
commerce  it is always extracted from  kelp, which is a sernifused
mass of saline ashes remainingafter the burning of various species
of fuci (sea-weed).
For this purpose, the powdered kelp is lixiviated in water, to
which it yields about half its weight of salts.  The solution is evaporated down in an open pan, and when concentrated to a certain
point, begins to deposite its soda-salts, namely, common salt,. car-.bonate and sulphate of soda, which are removed from  the boiling
fiquid by means of a shovel pierced with holes like a colander.
The liquid is afterward run into a shallow pan to cool, in which
tt deposites a crop of crystals of chloride of potassium; the same
operations are repeated on the mother-ley of these crystals until it
is exhausted.  A dense, dark-coloured liquid remains, which'contains the iodine, in the form, it is believed, of iodide of sodium, but
mixed with a large quantity of other salts, and this is called the
iodine ley.
To this ley, sulphuric acid is gradually added in such quantity
as to leave the liquid very sour, which causes an evolution of carbonic acid, sulphuretted hydrogen, and sulphurous acid gases, with
a considerable deposition of sulphur.  After standing for a day or
two, the ley so prepared is heated with peroxide of manganese, to
separate the iodine.  This operation is conducted in a leaden retort,




312            PREPARATION  OF IODINE.
a, of a cylindrical form,
supported in a sand-bath,
which is heated by a
small fire below. The
retort has a large open
ing, to which a capital,
b, c, resembling the head
D                 ~~~c cZ   of an alembic, is adapted, and luted with pipe-.__ D,- of clay. In the capital itI eL->              a --    < self there are two openings, a larger and a smallo  0 Bo 1il 0  0\   |//\er, at b and c, closed by
v  f $ iIA\\        Illit leaden stoppers. A seo        0.  / 11 \ \\        I /1 \ i\ ries of bottles, d, having
each two openings, con(-o- i    Wt                      nected together, as represented in the figure,
and with their joinings luted, are used as condensers. The prepared ley being heated to about 1400 in the retort, the manganese is
then introduced, and b c luted to a. Iodine immediately begins to
come off, and proceeds on to the condensers, in which it is collected; the progress of its evolution is watched by occasionally removing the stopper at c; and additions of sulphuric acid or marqganese are made by b, if deemed necessary.  This description of
the manufacture of iodine upon the large scale at Glasgow is due
to Professor Graham.
In this operation, the peroxide, of manganese will be in contact
at once with hydriodic, hydrochloric, and sulphuric acids; but for
success, the quantity of sulphuric acid must be sufficient only to de.
compose the iodides, but not the chlorides. If both were decomposed, the chlorine and iodine simultaneously evolve d would unite
to form chloride of iodine, by which the iodis.e would be lost; but
as the chlorine remains combined, the action becomes simply, that
the metal of the iodide present is oxidized by the oxide of manganese, and the iodine set free; thus, with iodide of sodium, S.O,+
Mn.0, and Na.I. give Mn.O.. S.0,. Na.O. and I.
Another mode of preparing iodine consists in adding to the selution containing iodide of sodium, a solution of sulphate of coprFer.
in which the copper is reduced to the state of sub-oxide (Cu2O.) bv
means of protosulphate of iron dissolved along with it. By the ilterchange of elements, sulphate of soda is formed, and a sub-iodido
of copper of a very pale yellow colour, and quite insoluble
in water, is produced, S.03+Cu2O. and Na.I. giving S.O,+
Na.O. and Cu2I. This last is then decomposed by peroxide
of manganese and sulphuric acid, as in the former processin this way the various crystallizations described above
\  may be avoided.
Iodine exists generally in crystalline sca.es of a bluish
black colour and metallic lustre. It may also be obtained
from solution, in the form of oblique octohedrons with a
rhomboidal base, as in the figure, or in prisms. The density of




PROPERTIES  OF  IODINE.-IODIC  ACID.   313
iodine is 4'948; it fuses at 225~, and boils at 3470; but it evaporates
at the usual temperature, and more rapidly when damp than when
dry, diffusing an odour having considerable resemblance to chlorine7
but easily distinguished from it. Iodine stains the skin of a yellow
colour, which,, however, disappears in a few hours. Its vapour is of
a splendid violet colour, which is seen to great advantage when a
scruple or two of iodine is thrown at once upon a hot brick. Hence
its name, from Ioetdq?, violet-coloured. The vapour of iodine is
one of the heaviest of gaseous bodies, its density being 8707'7, according to calculation from its atomic weight.
Pure water dissolves about 1-7000th of its weight of iodine, and
acquires a brown colour. In general, iodine cornmports itself like
chlorine, but its affinities are much less powerful. Iodine is soluble
in alcohol and ether, with which it forms dark reddish-brown liquors;
solutions of iodides, too, all dissolve much iodine.
A solution of starch forms an insoluble compound with iodine, of
a deep blue colour, the production of which is an exceedingly delicate test of iodine. If the iodine be free, starch produces at once
the blue precipitate; but if it be in combination as a soluble iodide,
no change takes place till chlorine is added to liberate the iodine.
If more chlorine, however, be added than is necessary for that purpose, the iodine is withdrawn from the starch, chloride of iodine
formed, and the blue compound destroyed. The iodide of starch, in
water, becomes colourless when heated, but recovers its blue colour
if immediately cooled. The soluble iodides give, with nitrate of
silver, an insoluble iodide of silver, of a pale yellow colour, insoluble
in ammonia; with salts of lead, an iodide of a rich yellow colour;
and with corrosive sublimate, a fine scarlet iodide of mercury.
Iodine combines with most of the non-metallic bodies, and with
all the metals, forming compounds which possess the closest similarity to the analogous compounds of chlorine. It is employed in
the laboratory for many chemical preparations, and as a test of starch
and for several metals.
Compounds of Iodine and Oxyg'en.
Iodine appears to combine with oxygen in three proportions, form
ing the iodous acid, the iodic acid, and the periodic acid. Of the constitution of the first there is nothing positively known; it has not
been isolated, and the substances that have been supposed to contain
it may also be considered as compounds of an iodide with an iodate.
The description of these compounds will be found in the chapter
on the salts; and I shall, therefore, at present, only. notice the other
two acids.
lodic./lcid.-This acid may be very easily prepared by boiling
iodine in fuming nitric acid until it is all dissolved, and then distil
ling off the excess of acid; the iodic acid remains as a white crys
talline mass, which deliquesces in the air. If the quantity of iodine
be large, this process would occupy a very long time; and a much
shorter, though more complex method is the following: The iodine
being diffused through water, a current of chlorine is passed through
it until all iodine is dissolved; the acid liquor so obtained is to be
neutralized by carbonate of soda, by which a quantity of iodine is
R it 




314  PR OPE.RTIL'S OF  IODIC ACID.-PERIODIC  ACID.
precipitated; the chlorine is then passed through until this iodine
disappears,- and then more carbonate of soda added, and this alternation continued until the addition of the carbonate of soda piroduces
no deposite of iodine; the solution contains'then iodate of soda and
chloride of sodium, generated by the decomposition of the soda by
the chloride of iodine first formed.  Thus 5C(1. and I. produce I.C15,
which, with 6Na.O., give 5Na.CI. and Na.O.,+I.O,.  This solution is
then mixed with a solution of a salt of barytes, and iodate of barytes
precipitates, which may be decomiposed'by boiling, it for some time
with one fourth its weight of oil of vitriol and 1~ times its weight
of water; the sulphate of barytes may be then separated by the filter, and the solution of iodic acid evaporated gently to dryness.
Iodic acid is very soluble in water; from a strong solution it crys
tallizes in rhombic plates and octohedrons.  When heated strongly,
it separates into iodine and oxygen. It first reddens, and then
bleaches litmus paper. It acts as powerfully as nitric acid in oxidizing the metals.  When mixed with solution of sulphurous acid,
water and sulphufic acid are formed, and iodine is set free; with
sulphuretted hydrogen it gives water and iodide of sulphur.  By an
excess of these agents, the iodine is finally converted into iodide of
hydrogen.  By these means the iodic acid may be recognised, and
also by its peculiar action upon morphia, which it decomposes, iodine being set free.  This is more valuable as a character of morphia than of iodic acid.
The salts of iodic acid resemble the chlorates in most respects,
and,- like them, when heated, separate into oxygen and a metallic
iodide.  One mode of preparing the iodide of potassium  of commerce is founded on this property. Iodine is dissolved in a solution
of potash, and, when dried down, gives a mixture of 5K.I. and I.05.
K.O. When this mass is fused, oxygen is given off in abundance,
and ultimately pure K.I. remains.  The commercial salt prepared in
this way has been shown by Mr. Scanlan frequently to contain iodate
of potash, either fradulently or accidentally, left undecomposed.
The composition and equivalent numbers of the iodic acid are as
follows, its formula being I.O:
Iodine,  75'96       One equivalent,  -1579.5 or 126.6
Oxygen, 24 04        Five equivalents, -  500'0 or 40'0
100'00        -20795    166'6
Its elements are united in the proportion, by volume, of two volumes of vapour of iodine to five voluimes of oxygen.
Periodic Acid, 1.07.-If a solution of iodate of soda be mixed with a great excess
of caustic soda, and acted upon by a current of chlorine, a quantity of the soda is
decomposed; its sodium combining with the chlorine, while its oxygen, being added
to the iodic acid, converts it into the periodic acid, which combines with two equivalents of soda. Thfis, 2C1. acting on 3Na.O. and I.05+Na.O., produce 2Na:.Cl. and
I.-0+2Na.O. On adding to the solution of this salt nitrate of silver, a, baSiC periodate of silver: is produced, which, being dissolved in nitric acid, gives yellow crystals of neutral periodate of silver. - When put in contact with water, these crystals
are decomposed, half of the periodic acid precipitating with the whole of the oxide
of silver as the insoluble salt, I.07+2Ag.O.;'while the other half of the acid remains
in- solution quite pure, and by evaporation may be obtained as a white crystallized
mass..: This acid is more stable than the iodic acid; it resists a higher temperature




HYDRIODIC ACID, ITS PRE.PARATION.'
ewthlout decomrpsition. All its important  characters~ may be inferred from the
m        rethod 0fipeparation.   
Its composition and equivalent numbers are,
Iodine,  69'31      One equivalent,  =15795 or i26-6
Oxygen, 30 69       Seven equivalents,- 7000 or 56' 0
o10000                        - 22795  s182'6;.Compound of Iodine and Hydrogen.  IHydriodic dcid.
There is but one compound of iodine with hydrogen: this exists
under ordinary temperatures and pressure as a colourless gas, which
may~ be best generated in the folloiwing manner: Some iodine and
small fragments of phosphorus are to be put together at the: bottom
of a glas:s tube, then cqvered with pounded glass, and gently heated,
so as to produce combination.  Iodide of phosphorus is thus formed.
If a little water be now poured on tlie poundeed
glass, it filters through to the bottom, and there,
acting violently on the iodide, of phosphorus, is
decomposed; from P.I. and H.O. there are produced P.O. and H.I.  To the mouth. of the tube
may be adapted, by a cork, a smaller tube, bent
as in the. figure, and the hydriodic acid gas issuing from it may be collected-:.  This gas is obtained by the method of displacement, as has been
described for chlorine (p. 302); and as it fumes
like mnuriatic 4tcid in contact with'the air, lit can
easily be recognised when the bottle.is full.
The specific gravity of this gas is 4385, produced by
One volume of vapour of iodine.... =8701.0
One volume. of hydrogen......... =  68 8
united without condensation..8769'8
and one volume weighing, therefore...... 4384-9
To obtain hydriodic acid dissolved in water, the simplest process
is to act.on iodine, diffused through wvater, by sulphuretted hydrogen
gas. -The iodine combines with the bydrogen, and'the sulphur is
set free.-  When the iodine has all disappeared, the liquor should be
well: boiled, to drive off the excess of sulphuretted hydrogen, and
then filtered; the liquid, hydriodic acid may be. evaprated to' a sp.
gr. of 1.70'0: it is' then'in' its' Strongest form, and may be dist:illed
unaltered.  Liquid hydriodic acid reddens litmus paper strongly;
it dissolves iodine in large quantity; it is decomposed by all the
oxidable metals -and even by mercury; and hence the gaseous-acid
cannot be collected over mercury.  Exposed -to the air, it-'rapidly
absorbs oxygen, water being formed,'and iodine being. set free.  It is
decomposed by sulphurie.. acid, suiphurous acid and iodine being pro.
ducedu; also by nitricd   anci d by chlorine.
Hydriodic acid may also be obtained by acting on iodide of barium
witlil dilute sulphuric acid.
Its composition and equivalent numbers.are as.follows:
Iodine,   99'22        One equivalent, -15795 or.126.6
Hydrogen,: 0'78        One equivalent,'.: 1-25 or'  1.0
100.00                         1592.0   - 127.6



316         IODO-PHOSPHURET  OF  HYDROGE N.
A solution of hydriodic acid or of a metal produces, with nitrate
of silver, a curdy pale yellow precipitate, which is insoluble in acids
and in water of ammonia; by this character the iodides are distinguished from the chlorides, even without the action of starch upon
the iodine when set free.
Iodine and sulphur may be melted together in equivalent proportions, and, on
cooling, form a steel-gray crystalline mass, iodide of sulphur, which is decomposed
gradually by exposure to the air, and appears to be rather a mixture than a true
compound of its elements.
When iodine and phosphorus are warmed together very gently, they combine,
evolving considerable heat, and forming iodides of phosphorus, the constitution of
which depends on the proportions used; there appears to be at least three: the
first fuses at 2120, is orange coloured, and-gives, when decomposed by water, hydriodic and hypophosphorous acids; its composition is therefore P.I.: the second is
gray; it fuses at 84~, and gives, with water, hydriodic and phosphorous acids; its
formula is hence P.13. The third, which produces, when decomposed by water,
hydriodic acid and phosphoric acid, consists of P.15, is black, and melts at 1140~.
Hydriodic acid combines with phosphuretted hydrogen, forming a white solid
compound, the constitution of which is of considerable interest. It cannot be prepared directly, as the gases are without action on each other except when in their
nascent form. It is best.prepared by introducing eight parts of iodine, two of phosphorus, and one of water, into a retort, mixed with some coarsely-powdered glass;
to the neck of the retort is adapted a wide glass tube with a cork, through which a
small tube passes and dips into some water. On applying heat, the phosphorus
and iodine unite, and the iodide of phosphorus being instantly decomposed by the
water, hydriodic acid and hypophosphorous acid are produced, which last is resolved, by contact with the water at that temperature, into phosphorous acid and
phosphuretted hydrogen. This last immediately unites with the hy riodic acid, and
the compound formed condenses in the neck of the retort in well haped crystals,
which, by a proper management of the heat, may be driven into the wide glass tube
to be preserved. The excess of hydriodic acid gas is conducted off by the small
tube, and condensed in the wvater.
This body was supposed to crystallize in cubes, and to be isomorphous with hydriodate of ammonia, to which this formula, in one way, might assimilate it,
H.I.+-P.H3 corresponding to H.I.+N.H3, the difference being only that phosphorus
replaced nitrogen. It will, however, be shown fully, in the division on organic
chemistry, that ammonia is not mere nitruret of hydrogen, N.H3, but that it contains amidogene (N.H2), being amidide of hydrogen, Ad.H. It has been also shown
that the crystals of the body H.I.+P.H3 are not cubes, but belong to a rhombic
system. When I come to describe the compounds of mercury, I shall show that
there exist similar bodies containing phosphuret of mercury and nitruret of mercury,
and that the constitution of phosphuretted hydrogen may, with great reason, be
supposed to be, not P.H3, but that a quantity of phosphorus equal to one third of
its ordinary atomic weight unites with an equivalent of hydrogen, its formula being
-.H., and the commonly received equivalent of phosphuretted hydrogen being in
reality three equivalents, =3.-.H. I therefore consider the compound which I have
just described as having for its true constitution H.I.+-3.[H., as there will be hereafter described the bodies Hg.C,1.+3.p.,Hg., and 2Hg.Cl.+3.-.Hg.: the equivalent of nitrogen being capable of the same subdivision by three.
This Hydriodate of Phosphuretted Hydrogen is decomposed by water, hydriodia
acid and phosphuretted hydrogen being given off, the last in the B variety. But if
a little oxide of silver be sprinkled on the salt, the gas is evolved in its spontaneously inflammable condition. It burns when heated in air, but, in a dry tube containing no oxygen, it may be sublimed from place to place unaltered.
Chlorides of Iodine.-I have shown that chlorine and iodine unite in three proportions, forming bodies having the formulae I.+-Cl., I.+3C1., and I.+-5C. By
much water the first and second are decomposed, producing muriatic and iodic
acids, and iodine becoming free. The third, which was long ago discovered by
Humphrey Davy, gives muriatic and iodic acids without separation of iodine.
These bodies are interesting only as being employed to obtain the iodic and periodic
acids, as already noticed.




PROPERTIES  OF BROMINE.                     317
Of Bromine.
This subst ance, which is intermediate in almost all chemical properties to chlorine and iodine, exists associated with those bodies in
sea-water, in many varieties of sea-weeds, and in some of the brinesprings belonging to the deposites of rock-salt in the earth. In these
cases it is generally combined with sodium or with magnesium,
forming very soluble salts, which remain behind when the common
salt crystallizes out by evaporation from sea-water. When a current of chlorine gas is passed through the mother liquor so obtained,
which is called bittern, the bromine is set free, and tinges the solution
yellow. On agitating this liquor with some ether, the bromine is
completely taken up by it, and an ethereal solution of bromine, of a
fine hyacinth-red colour, is produced; when this is acted on by potash, there is formed a mixture of bromide of potassium and bromate
of potash, which by fusion gives off oxygen, and pure bromide of
potassium remains; this is mixed with peroxide of manganese and
sulphuric acid, and precisely as in the preparation of chlorine or of
iodine, the bromine is set free and may be distilled over. It is necessary to condense the bromine with great care, and to receive it,
in water, to the bottom of which it sinks; the reaction that occurs
is that 2S.O,, Mn.O2, and K.Br. produce (S.O03. Mil.O- +K.O..    S.03)
and Br.
Bromine is a liquid at ordinary temperatures, but at 4~ it solidifies; it is deep red by transmitted, but black by reflected light; it is
much heavier than water, its specific gravity being 2-97; its odour
is like that of chlorine, but much more disagreeable, whence its
name (from Bpwfowo). It is very volatile, boiling at 116~; but even
at common temperatures it forms copious fumes, which have the
same orange-red colour-as those of nitrous acid; the specific grav
ity of its vapour is 5'393; it does not conduct electricity; it must
be preserved under water, as otherwise the quantity of vapour it
would form might burst the vessel containing it. It dissolves sparingly in water, but copiously in alcohol and ether. A taper is extinguished by its vapour, but not immediately, burning for a moment
with a green flame and much smoke. Some of the metals in fine
powder or leaf burn spontaneously in its vapour, as in chlorine; a
drop of liquid bromine, put in contact with a globule of potassium,
unites with it explosively and with brilliant ignition. It bleaches
vegetable colours, but leaves itself a yellowish stain, less intense
than that of iodine; it is poisornous.
Bromine unites with water, forming a crystalline hydrate like that
of chlorine.
With starch, bromine produces a fine yellow colour, which is not
intense if the solution be very much diluted.
Bromine is easily recognised by the peculiar colour and odour
of its vapour, which can only be confounded with that of nitrous
and hyponitrous acid, from which its other characters completely
separate it. A solution containing bromine or a metallic bromide
gives, with nitrate of silver, a white, curdy precipitate, insoluble in
nitric acid, but dissolved by ammonia. This precipitate is distinguished from the chloride of silver by giving vapours of bromine
when heated with a little- chlorine water




31       B3RO MICa  A CID. —HYDROBR OMI: C  ACID.
The equivalent numbers of bromine are 978'2 on the oxygen
scale, and 78'4, hydrogen being unity.
Bromic./cid.-There' is known only one compound of bromine
and oxygen, the bromic acid, the history -of whi/h is still" very imperfect.  When bromine i:s dissolved in a solution of potash, bromide of potassium  and brom'ate of potash are formed, 613r.: and
6K.O. giving 5K.Br.' and Br.0,-~ K.O.  On adding a solution of a
salt of barytes to the liquor so obtained, bromate of barytes is precipitated, and this may be decompose:d by sulphuric acid,; Which;
forms sulphate of barytes, leaving'the bromic acid in solution.
The bromic acid has not been obtained'solid; it is still more
easily decomposed by deoxidizing agent's than'the chiloric acid; thus
the sulphiirous acid and the plosphorous'acid liberate bromine.' The
same effect is produced by sulphuretted hydrogen.:Its salts have
not been'much examined, but appear to resemble the chlilorates and
iodatfes.:Its formula is B'r.O,, its composition by iweight and equivalent.
numbers being,
Bromine, 66'18'One equivalent, =978'2 or 78'40
Oxygen, 33'82        Five equivalents, — 500'0 or 40'00
100:00                          1478'2  118'40
These elements are united by volume in the ratio of two volumes of bromine vapour to five volumes of oxygen.
Hyd?robromic./cid.-The processes for obtaining the bromide of
hydrogen are precisely the same as those described for preparing
hydriodic acid in the liquid or in' the gaseous form, to which I shall
therefore refer (p. 3'15), bromine being substituted fo'r iodine  in
every case.  This gas is colourless; it is rapidly'absorbed by wva
ter, the solution reacting acid; it is not decomposedby oxygen,
nor does'bromine decompose Water, so that it stands between' iodine
and chlorine in that respect'.  It resembles- muriatic acid'in almost
all its reactions, but is at once distinguished from  it' by evolving
bromine on contact with chlorine or nitric acid.  If bromide of potassium be acted on by oil of vitriol, the result is partly as occurs
with a chloride, water being decomposed and'hydrobromie acid
evolved, and partly as occurs with an iodide, bromine and- sulphurous acid being evolved together; hence lydi'obromic acid cannot
be prepared pure in that way.
The sp. gr. of hydrobrornic acid gas is 2731, being produced by
Onevolume of bromine-vapour... 5393'0
One voluime of hydrogen'...      68. 68'
united without condensation.... 5418
and hence one volume weighs.... 2730'9
The Bromide of Sulphur is a heavy reddish liquid, like chloride of sulphur, probably SaB3r.
There are two Bromides of Phosphoru.,s one liquid, P.Br3, and'the other solid,
P.Br.i which present' complete analogy with the chilorides of'phosphorus. Neither
of these bodies presents particular interest.
The bromide of hydrogen unites with phosphuretted hydrogen,' forming a compound sinmilar to that already noticed, containing hydriodic acid. It is sufficient to
mix.the two gases together over mercury; a dense whiteeloud forms, which condenses on the sides of the glass in small crystals,' hich appear to be' cubes, but are




OF FLUORINE.                            319
not so really. This substance can also be formed in the indirect manner describea
for the-iodine compound. It consists of an. equivalent.of each element., its formula being H.Br.+-P.H3, or, as I prefer to write it, for the reasons already stated,
H.Br.+3 1. H.
This body is volatile, and may be sublimed, provided neither oxygen nor water
be present; heated in oxygen, it takes fire, and with water it is instantly decomposed.
The Chloride of Bromine and the Bromides of Iodine resemble in general charac
ters the compounds of chlorine and iodine. The first, when decomposed by water,
produces hydrochloric and bromic acids; the latter, on the contrary, gives hydrdbromic and iodic acids. These bodies aretot otherwise of interest.
Of Fluorine.
Although the existence of this body is rendered exceedingly probable by analogical reasoning, and recent experiments have gone
very far in  establishing its distinctive characters, yet it cannot
be prepared in an isolated form, or exhibited like all the simple
bodies as yet described; for such is the intensity and variety of its
affinities, that no sooner is it liberated from  combination with one
substance, than it enters into union with some other, attacking the
materials of which the apparatus used may be constructed.  The
most successful experiments made for examining it in its isolated
form are due to two talented Irish chemists, the Messrs. Knox.
The only substances on which fluorine is incapable of actingf being su ch as already are fully saturated with it, Messrs. Knox had
vessels constructed of fluor spar (fluoride of calcium), which were
filled with pure dry chlorine gas.  Into these vessels was then introduced fluoride of mercury, and the whole carefully warmed. The
chlorine decomposed the fluoride of mercury, forming chloride of
mercury, and the fluorine was disengaged, Hg.F. and C1. giving
Hg.CI. and F.  There was in this way obtained a colourless gas,
which acted with violence on the fragments of metallic foils, that
by means of a very ingenious arrangement were submitted to its
action.  The small quantity of material on which the experiments
were conducted did not allow of the metallic compounds so formed
being analyzed; and the. only doubt that can exist of the isolation
of fluorine in this process is that, as it was liberated, it might have
combined with the excess of chlorine present, and that the colourless gas may have been chloride of fluorine, and not the mere fiuto
rine itself.
The specific gravity of gaseous fluorine,  calculated from  the
analogy of its compounds to those of chlorine, is 1289; its equivalent
number is 233'8, or 18.7.
Fluorine does not combine with oxygen.
The most important compound of fluorine that' is known is the
Fluoride of IHydrogen, or Hydrofluoric./cid.  To prepare it, pure
fluor spar, which consists of fluorine and calcium, is reduced to
powder, and distilled in a leaden retort with twice its weight of the
strongest oil of vitriol.  The receiver must also be of lead, and be
kept cool by ice.  An acid liquor distils over, of an excessively suffocating odour, and so intensely corrosive, that a drop let fall upon
the hand produces a sore very difficult to heal.  This liquid is hydrofluoric acid, the reaction be':ng that H.O.. SO,3 and Ca.F. give
Ca.O.. S.O3 and 1H.F.  Sulphat(  f lime remains in the retort.




320               HYDROFLUORIC ACID.
The hydrofluoric acid, which is thus obtained in an anhyldrous
form, is very volatile, boiling at 60'. It is heavier than water, and
becomes still more so when diluted to a certain degree. It dissolves
the more oxid able metals rapidly with the escape of hydrogen gas,
and the formation of a metallic fluoride. The only metals which it
does not act upon are gold, platina, silver, and lead. There lnust
be no solder about the leaden vessels in which the acid is kept, as
it is acted on very violently. It is dangerous to have much to do
with the anhydrous acid, from i4s corrosive power; and as a dilute
acid answers for all practical purposes, a quantity of water is generally put into the receiver, into which the acid is distilled.
The most remarkable property of hydrofluoric acid is its action
upon glass, which it corrodes and dissolves. The glass contains
silica, which the hydrofluoric decomposes, Si.0, and 3H.F. producing
3H.O. and Si.F3. This fluoride of silicon is a gas, decomposed by
water in a way that will be soon described. Patterns or desiglns
may therefore be etched upon glass by means of this hydrofluctic
acid. There are two modes in which this operation may be conducted: 1st, by the liquid acid; 2d, by the acid in vapour. For the
first, the glass plate being covered with a uniform coating of wax,
the design is traced on it with the point of a needle or gravincg tool,
taking care that the surface of the glass shall be laid bare throughout the whole extent of each line; a rim of wax being then formed
round the edge of the plate, the liquid acid, the strength of which
must be regulated by the depth of engraving required, is poured on
the plate to the depth of two or three lines, and left for a time dependant on the judgment of the operator. When it has remained
long enough, the remaining acid is poured off and the wax cleared
away. The etched portions of the glass are equally transparent
with the others, and the design is therefore indistinct except in certain incidences of the light.  A glass plate so prepared may be used
as a copper plate to print from, but the risk of breaking is too great
to allow of its introduction into practice.
To etch by the second mode, the plate of glass is prepared exactly
as described for the first, except that there need not be any raised
edge. A flat leaden basin, of the size of the plate, is used to hold
the mixture of powdered fluor spar and oil of vitriol, and the glass
plate is laid upon it, with the waxed side down; the basin is then
heated so gently as not to melt the wax or injure the accuracy of
the design; the hydrofluoric acid, which rises in vapour, acts upon
the surface of glass exposed, and decomposes the silica, forming
fluoride of silicon; but a sufficient quantity of watery vapour rises
to decompose this substance, and a quantity of silica is regenerated
and deposited upon the corroded surface, giving it a rough and white
appearance, so as to be easily visible in every direction. When the
action has continued long enough, the plate is removed from the
basin, and the wax cleared off by means of some spirits of turpentine.
Other uses of the hydrofluoric acid, such as in mineral analysis, will
be described hereafter.
The composition and equivalent numbers of the hydrofluoric acid
tre as follows:




OF  SILICON.                        321
Fluorine,  94.93     One equivalent, =233'8 or 18-7
Hydrogen,  5'07      One equivalent, -  12'5 or 1-0
100'00                       246'3   19'7
There are no other combinations known of fluorine with any of the simple bodies
as yet described, except sulphur and phosphorus: these are dense volatile liquids.
The Fluoride of Phosphorus, when decomposed by water, produces hydrotluoric acid
and phosphorous acid; it is, therefore, P.F3. When heated in the air, it burns, but
the product of the combustion has not been examined.
Of Silicon,
This substance is one of the most extensively distributed of the
undecomposed bodies, constituting, probably, a sixth of the total
weight of the mineral crust of the globe. It never exists free, but
always in nature combined with oxygen, forming silicic acid, or, as
it is termed in popular language, the earth silica.  Quartz, in the
state of rock and crystallized, flints, agate, sand, and many other
mineral substances, are silica completely or nearly pure, and when
combined with various metallic oxides, it forms the great family of
silicates, which includes the majority of earthy minerals.
It is exceedingly difficult to deprive silicic acid of its oxygen;
even by ignition with potassium it is but imperfectly decomposed.
To prepare silicon, therefore, a somewhat complex body is selected
to be acted on, the'double fluoride of silicon and potassium (2Si.F3
w-3K.F.), which is a white powder like starch, very sparingly soluble
in "water; a quantity of this substance is to be mixed with nearly
its own weight of potassium, cut into little bits,
and placed in an iron cylinder, or in a tube of
hard glass, which may be held, as in the figure,
over the flame of a spirit-lamp.  As soon as the'
bottom of the tube has been heated to redness,
vivid ignition occurs by the decomposition, which
spreads, with little need of external heat, throughout the entire mass; when cool, the residual
brown matter is to be washed carefully with water: fluoride of potassium dissolves, and the siicon remains behind;
the 2Si.F3+ 3K.F., acted on by 6K., give 9K.F. and 2Si.  To have the
silicon quite pure, numerous precautions are necessary, which need
not be detailed here.
The silicon so obtained is a dull brown powder, which, when
heated in air or in oxygen, takes fire and burns, forming silicie
acid. If it be ignited in a closely covered vessel, it shrinks in volume, increases very much in density, and becomes insoluble in
acids or alkalies, which,in its original form, it would dissolve in,
with evolution of hydrogen gas; it then also cannot be made to
burn in oxygen gas; it burns in the vapour of sulphur and in chlorine, combining with these bodies.  When ignited with carbonate
of potash, the silicon burns brilliantly, setting carbon free, and form.
ing, with the oxyg-en of the carbonic acid, silicic acid, which combines with the potash.  The equivalent number of silicon is 277'31
or 22.22, according as the oxygen or the hydrogen standard may be
adopted.
*~~~~~~ cM




322                    SILICIC  ACiD.
Silicic aTcid. Silica.-This, the only compound of silicon and
oxygen, exists in nature completely pure, in masses constituting
quartz rock, and in crystals which belong to the rhombohedral system; their ordinary form is represented in the margin. It is exceedingly hard, and, in order to be reduced to powder, requires to be heated first to redness, and then thrown into a large mass of cold water.
The piece of quartz cracks in every direction by being so suddenly cooled, and is then easily reduced
i     I   to powder in an agate niortar. It may be obtained
in a state of much more minute division, by melting,;..       in a platinum crucible, a mixture of equal weights of
carbonate of potash and of carbonate of soda, and adding thereto powdered flint, by small quantities at a
time; the silica dissolves in the melted alkali, while carbonic acid
gas is given off. When the alkaline silicates, so formed, are dissolved in water, and a stronger acid added, the silicic acid is precipitated as a gelatinous hydrate, which, when completely dried,
forms a white powder, still somewhat gritty to the feel.  When the
gaseous fluoride of silicon comes into contact with water, a portion
of it is decomposed, fluoride of hydrogen and silicic acid being
produced; this last separates in the gelatinous form, but, on drying,
becomes an exceedingly fine light powder.
Silica, even when prepared by precipitation, feels gritty between
the teeth; when in mass, it is exceedingly hard, scratching glass
and the generality of minerals. Its specific gravity is 2'66; it is
fusible only by the oxyhydrogen blowpipe, in the flame of which
it melts into a colourless glass; when once dried it is totally insoluble in water, but in its gelatinous form it is soluble to a small extent; hence many mineral waters contain silica, which, being gradually precipitated in the substance of decomposed organic matter,
produces the silicious petrifactions in which the most delicate vegetable tissues are so beautifully preserved.  The differences between
silica in its dry and in its hydrated condition are so great, that we
can scarcely suppose them to be satisfactorily accounted for by the
presence of a substance for which the silica appears to have so little affinity.  When a dilute alkaline solution of silica is decomposed
by an acid, there is no precipitation, the silica remaining dissolved;
but on evaporating the liquor to dryness, the silica assumes the insoluble condition, and remains behind when the saline constituent
is dissolved. On the other hand, by the presence of an alkali, the
insoluble silica is made to assume the soluble state.
There is some difference of opinion as to whether the compounds
of silica and water are truly definite, but I look upon the existence
of at least one, having the formula 2Si.0, + H.O., as being certain;
I have- found the light spongy masses of silica deposited from volcanic springs, and on the edges of volcanic craters from Iceland and
Teneriffe, to have accurately that constitution.
It is probable that a great deal of the silica which exists in nature
has been originally deposited in the soluble condition. The struc
ture of the agates, chalcedony, and many other minerals, proves
that they were formed by a solution of silica havink penetrated




CHLORIDE OF SILICON.                              323
into a cavity in the surrounding rock, and having then gradually
dried down or crystallized.  It is even pretty certain that the crystallized quartz is also of this aqueous origin.
In the arts, silica is of exceeding importance, being an essential
constituent of glass, porcelain, and every kind of delft and earthenware.  For purely chemical purposes, it is only of interest from
the compound which silicon forms with fluorine; the hydrofluoric
acid being the only acid capable of dissolving silica.
The composition of silica and its equivalent numbers are as fol.
lows, its formula being Si.,03.
Silicon, 48O04     One equivalent,    -277'3 or 22'22
Oxygen, 51-96        Three equivalents, =300'0 or 24'00
100'00                             577:3   46'22
Silicon does not combine with hydrogen nor with nitrogen: there
exists a sulphuret of silicon, which is probably Si.S,, as when acted
on by water it produces soluble silica and sulphuretted hydrogen.
Chloride of Silicon.-This substance, although not itself important, is yet interesting from the fact that the method of preparing it is one by which a number of
remarkable compounds of chlorine have been discovered, and hence it deserves to
be described. Chlorine has no action on silica at any ternperature;  but if finelydivided silica be mixed with powdered charcoal, and heated to redness in a porcelain
tube, a, c, inserted in the filrnace, as in the figure, and by means of a glass tube at.
tached at b, a current of dry chlorine be made to stream over the ignited mixture,
decomposition ensues, the oxygen of the silica combining with the carbon to firm
carbonic oxide gas, while the chlorine and silicon unite, producing the chloride of
silicon, which, being a very volatile liquid, requires to be carefully condensed; for
this purpose, the tube c f is wrapped up in a cloth, or a paper kept constantly wetted
by a stream of water from the reservoir e, and the liquid produced then collects
in the bottle f, while the oxide
of carbon and the excess of
chlorine pass off by the tube
m. In this process the reaction is such, that 3C1. acting
C           on Si.03 and 3C., give rise to
t f6 - \    E3' i _'~'~I~==zft~,  - 3C.O. and Si.CI3.
The stream of dry chlorine
].             d ii       may be very conveniently obtained by the apparatus here
figured; the muriatic acid and
peroxide of manganese are
I~i~i                     placed in the flask a, ai d the
gas evolved, depositing the accompanying liquid in the receiver b, passes through the
-ilriia       tube c, which, being filled with




324:FLUORIDE  OF  SILICON.
fragments of recently-fused chloride of calcium, absorbs all the watery vapour
The gas issues dry from the extremity, where it is connected with the end b of the
porcelain tube in the preceding figure.
The chloride of silicon is a colourless liquid, denser than water; it boils at 1240;
in contact with water, it is resolved into silica and hydrochloric acid, from whence
its formula must be Si.C13.
Fluoride of Silicon.-This is the most remarkable compound of
silicon after silicic acid; it is a gas colourless and transparent; to
prepare it, fluor spar and sand, or glass in powder, are mixed together,
and heated in contact with oil of vitriol; the mass swells up very
much, so that a large vessel must be employed. In this reaction
we may look upon water as being decomposed or not, as the results
may be explained in either way. Thus the oxygen of the silica may
combine with the calcium, forming lime, and this with the sulphuric
acid, while the silicon unites with the fluorine of the fluor spar. Or,
water being decomposed, hydrofluoric acid and lime may be first
produced, and the former, reacting on the silica, may reproduce water, and form fluoride of silicon. I prefer to omit here, as I did
when describing the formation of chlorine, all the unnecessary theoretic agency of the water, and to express the decomposition as
3(S.03. H.O.) with Si.03 and 3(Ca.F.) give 3(S.03. Ca.O.. H.O.) and
Si.F3.
This gas must be collected over mercury, and in vessels dried
with the greatest care.  When it mixes with air, it forms dense
white fumes, which arise from the foimation of silica by the watery
vapour present being decomposed.
It is colourless and transparent; its specific gravity is 3600. Its
composition and equivalent numbers are as follows, its formula being
Si.F3.
Silicon, 28'32     One equivalent,   = —277'3 or 22'22
Fluorine, 71'68     Three equivalents, =701'4 or.56'22
100'00                          978'7   78'44
The hydrofluosilicic acid, or the double fluoride of hydrogen and
silicon, cannot be obtained free from water, but its solution is of
considerable importance as a chemical reagent, and hence its preparation requires to be described.
The mixture of powdered fluor spar and sand is introduced into
the matrass a, which is imbedded in a sandbath, as in the figure. By means of the
siphon funnel 1, the oil of vitriol is then
poured in, and the gas evolved is conducted by the tube to the water in the vesii    sel d e. If the tube opened into the water directly, so much silica would be deposited at its orifice as to stop it up every
l_  moment; and hence a quantity of mercury, e, is placed at the bottom, and the
e        _I  _   end of the tube dips into it. The gas bubble, therefore, does not touch the water
until completely separated from the tube:
it escapes from the surface of the mercury, and then it becomes invested with a




OF BORON.                          325
coating of silica, like a bag of tissue paper, of which many preserve
their form for a certain time.  The passage of the gas is to be continued until the water becomes thick from the quantity of silica separated; it is then to be poured on a fine linen cloth, and the silica
removed by straining and pressure. In this process, one third of
the fluoride of silicon is decomposed by the water forming silica
and hydrofluoric acid, which last unites with the remaining fluoride
of silicon to form the hydrofluosilicic acid, the formula of which is
2(Si.F,) +- 3H.F.
When a solution of this acid is heated, fluoride of silicon is given
off, and hydrofluoric acid remains. Hence, although the hydrofluosilicic acid is without action upon glass, glass vessels in which it is
evaporated are corroded.
The property of this acid which is of most interest to the chemist
is, that it forms, by acting on the salts of potassium  and barium,
compounds, fluosilicates, or double fluorides of those metals which
are very sparingly soluble in water; and hence it is used to detect
the presence of these substances in solution. The precipitate so
obtained is remarkable for beinc at first so gelatinous and transparent that it can be recognised in the liquor only by the play of colours
in the light reflected from its upper surface. When collected on a
filter and dried, these compounds appear like powdered starch. The
constitution of the salts of the hydrofluosilicic acid resembles that
of the acid itself, the hydrogen being replaced by a metal; thus
the fluosilicate of potassium, already described as used for preparing
silicon, is expressed by the formula 2Si.F,+-3K.F.
The composition of hydrofluosilicic acid is easily known from that
of the hydrofluoric acid and fluoride of silicon. Its equivalent number is 2696%4 or 21.62.
Of Boron.
The history of this substance presents a very close analogy with
that of silicon. It was first obtained by decomposing boracic acid by
galvanism, but is best prepared by acting on the fluoborate of potash by metallic potassium, exactly as has been described under the
head of silicon. That salt consists of fluoride of boron united to
fluoride of potassium; by the reaction, all the fluorine passes to the
potassium, and the boron is set free.
Boron is a dark olive substance, which does not conduct electricity. It is insoluble in water and all other neutral fluids.  When
heated to 6003 in the air or oxygen, it takes fire, and burning, forms
boracic acid; the same effect is produced by boiling with nitric acid,
or by ignition with nitrate or with carbonate of potash.
This element's not extensively distributed in nature, and only
found combined with oxygen, forming boracic acid.  This exists in
certain springs in India, combined with soda, and, being crystallized
in an imperfect way, was brought into commerce under the name
of tinkal, or crude borax. The boracic acid is also found, and in
much larger quantity, free, or combined only with a small quantity
of ammonia, in the small volcanic lakes or lagoons of Tuscany. It
accompanies the watery vapour which gushes out of fissures in the
earth, and which contains also nmuriatic acid. The water of these




326    B O RACIC  ACID. —'CHILORIDE  OF  BOROIN.
lakes is evaporated, and the boracic acid being crystallized, is imported into these countries for the manufacture of borax (borate of
soda) and other salts.
The boracic acid is the only compound of boron and oxygen; it
may be obtained quite pure from the native acid by boiling this
with eight parts of water and a little white of egg, and filtering the
solution. On cooling slowly, the boracic acid crystallizes in large
brilliant plates, soft and unctuous to the feel, and of an irregular
crystalline form. It may be also produced from borax by dissolving
it in four times its weight of boiling water, and adding  sulphuric
acid until the liquor becomes sour to the taste.  On cooling, the
boracic acid crystallizes; but as it retains a little sulphuric acid and
sulphate of soda, a second solution and crystallization is necessary
to'have it pure.
The crystals of boracic acid, so prepared, contain water, the oxygen of which is equal to the oxygen of the acid; when heated, this
water passes off, and the acid melts; on cooling, it forms a colourless
glass; when completely dry it is fixed, but in the presence of water it is carried off by the vapour in great quantity.  The glacial
acid, when exposed to the air, absorbs water, swells, and becomes
opaque.  The boracic acid is much more soluble in hot than in cold
water, the crystals requiring twenty-six parts of water at 60', and
only three at 212' for their solution.  Alcohol dissolves boracic acid
copiously; and the solution, when set on fire, burns with a beautiful green flame, by which this body may easily be recognised. The
boracic acid possesses but very feeble acid properties; many of its
soluble salts possess alkaline reaction, and all are decomposed by
the weakest acids.  It does not redden litmus, but gives it a portwine colour, and a strong solution of it browns turmeric paper like
an alkali.  At high temperatures, however, boracic acid may decompose the salts of the nitric, or even of the sulphuric acids, from the
principles that have been already explained in the chapter on Affinity (p. 169).
The composition and equivalent numbers of boracic acid are as
follows, its formula being B.03:
Boron,  31'22    One equivalent,   -136'2 or 10'9
Oxygen, 68'78    Three equivalents, =-300'0 or 241'0
100.00                          436.2    34-9
Boron does not combine with hydrogen or nitrogen; its compounds with sulphur and selenium are not important.
Chloride of Boron.-Boron burns spontaneously in chlorine gas, but the best lway
to prepare the compound of chlorine and boron is to proceed as described for making chloride of silicon, substituting boracic acid for the silica. The product is a gas,
colourless and transparent, but producing dense white fumes in contact with damp
air, owing to its decomposition, and the formation of boracic and hydrochloric acids.
The presence of this last in the volcanic lagoons would render it probable that by
some subterraneous action chloride of boron is generated, and is decomposed when
mixed with the watery vapour simultaneously exhaled. The chloride of boron is
rapidly absorbed and decomposed by water; its specific gravity is 4079; it contains
1' times its volume of chlorine; its formula is B.C13.
Fluoride of Boron.-This substance is prepared in exactly the
same way as fluoride of silicon, substituting the boracic acid for
the silicic acid. It is a gas, rapidly absorbed and decomposed by




GENERAL  CHARAC TERS  OF  THE  METALS.  327
water, and generating hydrofluoboric acid, which is perfectly analogous to the hydrofluosilicic acid.  It hence forms dense white
fumes when mixed with damp air.  Its specific gravity is 2362.
The hydrofluoboric acid is obtained by precisely the same plan
as that described for the hydrofluosilicic acid. The boracic acid is
deposited in crystals according as the gas is absorbed.  If the liquol be evaporated without the acid deposited being removed, it is
all again taken up and carried off as gaseous fluoride of boron.
The liquid hydrofluoboric acid resembles, in the combinations that
it forms, the hydrofluosilicic acid, and is similar to it also in constitution, its formula being 2(B,F3)+ 3H.F.
No other compound of boron of any interest is known.
The history of carbon involves so many considerations regarding the constitution
and properties of organic substances, that I shall postpone entering upon it until
after the description of the metals and their salts, and other compounds with the
non-metallic bodies. I will then commence the study of the chemistry of organic
substances with that of their most constant ingredient, carbon.
The compound of nitrogen with hydrogen (ammonia) has not been introduced
among those of the non-metallic bodies with each other, because all the details of
its history attach it to organic chemistry, under whicli head it will consequently be
found. The hypothetical compounds of nitrogen and hydrogen (amidogene and ammoniurm) will be associated with it.
The substances hitherto described as chloride and iodide of nitrogen having been
found to contain hydrogen, and to range themselves in an important series of organic combinations, have not been noticed in the chapter now closed, but will be
fbund in their true position hereafter.
CHAPTER  XII.*
OF THE GENERAL CHARACTERS OF THE MIETALS, AND OF THEIR COMPOUNDS
WITH THE NON-METALLIC BODIES.
ALTHOUGH, as has been already noticed, the metals cannot be considered as forming a class of bodies, united by such analogies of
chemical properties andlaws of combination as would constitute a
natural family, yet in their physical characters, and the most prom.
inent facts of their technical history, they have so much in common
as to render a notice of the conditions in which they exist in nature, the methods by which they are extracted upon the large scale,
and the physical and chemical properties by which they are distinguished as a great division of the elementary bodies, necessary, be,
fore proceeding to the detailed history of the individual metals.
The metals are forty-two in number; their names have been already given in more than one place (p. 150 and 189). They reflect
light powerfully, and hence possess what is termed metallic lustre.
If the incident light be plane polarized, it undergoes a remarkable
change, produced only by the metals and by diamond, becoming
elliptically polarized on reflection. The metals are characterized
very completely by their power of conducting heat and electricity,
in which, although they differ among each other, yet the worst
excels all non-metallic bodies. Lists of their relative conducting




328  GENERAL  CHARACTERS  OF THE  IMETALS.
powers in these respects have been already given (p. 92, 109, and
137). By the combination of these characters, the lustre and conducting power, tie metallic or non-metallic nature of a body is always determined.
In the other properties of the metals there is found remarkable
diversity; thus in colour, although silver is purely white, the majority of the metals are of various shades of bluish-white or gray,
while copper and titanium are reddish coloured, and gold is yellow.
In specific gravity, the metals include some of the lightest along
with the heaviest solids that we knowv; the density of platinum being
21 times, of gold 19 times, and of potassium only -r9t that of water.
Some of the most important applications of the metals in the arts
depend on their malleability and ductility. Those metals are malleable which admit of being rolled or beaten out into thin leaves;
those being ductile which can be drawn into wire.  Gold is the
most malleable of metals; gold leaf may be obtained of 8'   of
an inch in thickness, and is hence the only metal in which any trace
of transparency has been found; silver, copper, tin, rank next in
malleability. The most malleable metals are not at all the most
ductile; platinum, and even iron, can be obtained in finer wire than
gold; platinum wire was made by Wollaston of,( inch diameter; but a metal which is not malleable cannot be ductile, and vice
versa; thus antimony, arsenic. and bismuth, the brittle metals, may
be powdered in a mortar, but give neither leaves nor wire. The
texture of the metals which produces the malleable and ductile conditions, depends closely upon temperature.  Thus zinc is malleable
and ductile at 300~; it loses this power, but remains tough, at 60~,
while at 600~ it becomes so brittle that it powders as easily as bismuth. In the drawing of lead pipe, and in making most of the metallic wires, there is a peculiar temperature required for the most
perfect execution, by which is regulated the rapidity with which the
process is carried on.
In strength and tenacity the metals differ also; iron is the strongest metal; an iron wire of a given thickness will support a greater
weight than a similar wire of any other metal; copper is next to iron.
but only about one half so strong; then platinum, silver, and gold;
tin and lead are the weakest of the metals. The tenacity depends
also on the molecular structure; if the wires had been annealed, so
as to allow of an approach to internal crystallization, the tenacity
is often found to be reduced to one half.
In their relations to heat the metals exhibit remarkable variety.
but one metal is liquid at ordinary temperatures. All the metals
are fusible, but they require for their liquefaction the greatest rango
of temperature which can be produced; thus mercury melts at — 39~.
potassium and sodium below the heat of boiling water; tin, lead.
zinc, antimony, and tellurium below a red heat, and many metals
as platinum, are infusible in the most intense heat of a blast furnace
and yield only to the flame of the oxyhydrogen blowpipe. in tho
history of each individual metal, its point of fusion will be given, so
far as it is known.
The majority of the metals are fixed at the greatest heat of our
furnaces; but mercury, zinc, cadmium, arsenic, tellurium, potassium,
and sodium may be volatilized.




CL.ASSIFICATION   OF  THE  METALS.                         329
The generality of metals, when exposed to the air, particularly
when damp, absorb oxygen and form oxides; some becoming merely tarnished upon the surface, others becoming thoroughly oxidized.
Some metals, however, as gold, silver, platinum, palladium, and
mercury, are not liable to this action.  Those metals which oxidize
when exposed to air, unite with oxygen at a higher temperature
with great rapidity, many with actual combustion. Thus zinc, when
heated to full redness, takes fire and burns brilliantly with a white
flame, and the combustion of iron wire in oxygen is one of the prettiest lecture experiments.  Mercury also, which does not tarnish
when exposed to oxygen at common temperatures, becomes oxidized when heated to near its boiling point, but the oxide is resolved again at a red heat into oxygen and metallic mercury.
It is owing to their affinity for oxygen that many of the metals
decompose water, and one of the most convenient classifications
that have been proposed for ordinary use is fouhded on the fact of
the different degrees of facility with which this decomposition proceeds. Thus,
Potassium,
Sodium,
~itlhium,    t  The first class consists of metals which decompose water witht
tBarium,      lively effetrvescence, even at 32~.
Strontium,
Calcium,
Magnesium,
Aluminum, 
Glucinum,
Thorium,        The second class consists of metals which do not decompose water
Yttrium,      with lively effervescence, except at about 2120, but very far below a
Zirconium,    rd eat.
Lanthanurn,
Cerium,
Manganese,
Iron,
Nickel,
Cobalt,         The third class consists of metals which do not decompose water
Zinc,         except at a red heat, or at common temperatures in contact with
Cadmium,    strong acids.
Tin,
Chromium,
Vanadium,
Tungsten,   A
Molybdenum,
Osmium,
Columbium,      The fourth class consists of metals which decompose vapour of
Titanium,     water energetically at a red heat, but which do not decompose it at
Arsenic,      common temperature, even in contact with strong acids.
Antimony,
Tellurium,'
Uranium,
Copper,         The fifth class consists of metals which decompose water at a red
Lead,         heat but very feebly, but whose oxides are not reducible to the meBismuth,    J tallic state by heat alone.
Silver,
Mercury,
Gold,           The sixth class consists of metals whose oxides are decomposes
Palladium,    alone at a high temperature, and which do not decompose water
Platinum,    under any circumstances.
Rhodium,
Iridium,                          T 




330      CLASSIFICATION  OF TIlE METALS.
This kind of classification was first proposed by Thenard, and has
been adopted by Graham in a form differing very slightly from that
now given.
The following classification, although old, and founded solely on
popular considerations, is yet so far consonant with the simplest
characters of the metals as to be frequently referred to, and hence
to be worthy of notice.
Those metals which do not tarnish on exposure to the air, and
the oxides of which are reduced by heat alone, were termed the
noble or peifect metals; at the head of this list stood gold, and at the
bottom mercury.
All the other metals known to the older chemists were termed
ordinary or imperfect metals. Of the metals of the first and second
class, none had been then discovered; and of their oxides, only
potash, soda, barytes, lime, magnesia, and alumina were known.
From the old name of potash, Kali, with the Arabic prefix al, potash
and soda, at one time confounded together, were termed alkalies,
and ammonia, resembling them very much when dissolved in water
or combined with acids, was also called an alkali; it was the volatile alkali, potash and soda being fixed alkalies; it was also termed
the animal alkali, while soda was the mineral alkali, being derived
from rock-salt or from the ocean; and potash received the name of
the vegetable alkali, from its source being the ashes of plants growing upon land. The alkalies are characterized by being very soluble
in water, and by neutralizing the strongest acids. They hence restore the blue colour of reddened litmus paper, and change the
vegetable colours in general: the yellows to brown, the reds and
blues to green.
Paper tinged yellow by turmeric is a delicate test of the presence
of an alkali, by which it is browned.
Magnesia and alumina were termed earths, and silica was classed
with them; these bodies, the earths proper, are insoluble in water,
and have no action on turmeric paper.
Barytes, lime, and strontia were termed alkaline earths; they are
soluble in water, but much less so than the alkalies; these solutions
brown turmeric paper, and neutralize acids; but they are completely distinguished from the alkalies by their combinations with carbonic acid, which are insoluble in water, while the alkaline carbonates are very soluble in that liquid. These.phrases of alkalies and
earths are of constant recurrence in descriptions of chemical processes and results, and are thus seen to be founded on, and expressive of, some of the most important characters in those bodies.
Most of the metals combine with oxygen in more than one proportion, and the characters of the oxides are found to be regulated;in a great degree by their composition. All protoxides (R.O.) (R.
representing an equivalent of any metal) appear capable of combining with acids to form neutral salts; they constitute, properly, the
metallic basis, but in many cases suboxides, (R,20.), such as those
of copper and mercury, form well-characterized salts, and sesqui.
oxides, (RO,), as those of iron, manganese, aluminum, and chrome,
produce well-defined classes of salts also, which, however, in solution always possess an acid reaction. Peroxides, (R.O2), as those




AFFINITY  OF METALS FOR  CHLORINE, ETC. 331'
of manganese, tin, titanium, and lead, are either indifferent or feebly
acid, and the higher degrees of oxidation lose all basic character,
and become true acids, as the manganic acid, Mn.O,, and the chromic acid (Cr.O,).
The different oxides of the same metal frequently unite w-%ith each
other, producing compounds which have great similarity to salts.
Examples of this will be found under the heads of manganese, of
iron, and of lead.
The affinity of the metals for chlorine is, in many cases, even
more remarkable than that which they manifest for oxygen; thus
gold and platinum, which resist even nitric acid, at once combine
with chlorine; and tin, copper, mercury, antimony, arsenic, and
bismuth, which require a high temperature to effect their rapid
combination with oxygen, burn spontaneously when introduced into
chlorine gas in a state of minute division. MIost metallic oxides
are decomposed by chlorine also at a high temperature; thus, if' a
stream of chlorine gas be passed over lime heated to redness in a
porcelain tube, oxygen gas is expelled, and the calcium remains
combined with chlorine. On this account, the chlorides are gene'ally, after the oxides, the most important metallic compounds.
Towards iodine, bromine, and fluorine, the metals are related nearly as to chlorine, the affinities being, however, much weaker towards
bromine, and still more sjo towards iodine: of fluorine wie do not
as yet possess much positive knowledge, but its affinities appear to
be at least as intense of those of chlorine.
The compounds of sulphur with the metals constitute a very extensive and important series, which, as has been more fully noticed
in p. 284, resembles in a very striking manner the series of oxides
of the same metal. M[any metals, at a high temperature, combine
with sulphur with brilliant combustion; and even at common temperatures, if iron filings and sulphur be mixed together with a little
water, they will, in uniting, produce so much heat as to burst into
flame, if the mass be moderately large. The metallic sulphurets,
like the metallic oxides, are some acids and some bases, and these,
by uniting, form the extensive classes of sulphur-salts. The metals
combine with selenium and with phosphorus, subject to nearly the
some conditions as in forming sulphurets, but the history of those
compounds is not nearly so complete. As yet but very little has
been done towards the history of the compounds of the metals with
nitrogen, silicium, or boron.
Some of the metals, tellurium, arsenic, and antimony, combine
with hydrogen, forming gaseous compounds, which resemble very
closely the sulphurets and phosphurets of hydrogen in properties
and constitution. In these bodies the hydrogen is the positive ele.
ment, the metal playing the part of the sulphur or of oxygen.
The circumstances under which the metals are found in nature
are exceedingly diverse. Some are found native, or only alloyed
with other metals, as gold, silver, tellurium, bismuth, and some others. Many exist combined with arsenic, the sources of cobalt and,
nickel being almost exclusively their native arseniurets. Some metallic chlorides and iodides exist also native, but the most abundant
forms in which the metals are to be found are combinations with




332        GENERAL PRINCIPLES OF THE
oxygen and sulphur. There are few of the metals that do not exist
naturally in the state of oxides, which are either free or else combined with acids, forming salts. Thus lead, copper, iron, zinc, tin,
manganese, antimony, are all found in abundance as native oxides,
or as native sulphates, carbonates, arseniates, phosphates, silicates,
&c. The majority of the metals exist also in nature combined with
sulphur. The sulphurets of lead, of zinc, and of copper are the
sources from whence the supplies of those metals are obtained; and
the sulphuret of iron exists in great abundance, and, although not
used for the extraction of the metal, is of great importance in the
manufacture of green vitriol, of alum, and of sulphuric acid. These
native compounds of the metals are termed ores; and the metal is
said to be mineralized by the substance with which it is united.
The\processes followed in the extraction of the metals must be, of
course, regulated by the composition of the ores in which it is contained; and as it will save the necessity of frequent repetition hereafter, I shall describe the general manner of treating each kind of
ore, so far as may serve the purpose of an elementary work like the
present, in which the introduction of minute and technical details
would be useless and improper. In cases where the plan followed
for any particular metal deviates essentially from that now about
to be described, I shall notice the circumstance in its special history.
Where the metal exists in a simply oxidized condition, it is only
necessary to heat the ore strongly in contact with the fuel, by wvhich
carbon is supplied in abundance for its reduction. The carbon combines with the oxygen, and the metal is set free. It is not often that
the ores have this simple constitution, but in many cases the metal
exists as a carbonate, and then the carbonic acid being expelled by
the first application of the heat, the oxide which remains is reduced
by the deoxidizing action of the ignited fuel. Thus the native carbonates of lead, of copper, of zinc, and especially of iron, are simply
reduced in this way: the last mentioned is the ore which consti.
tutes the great iron deposite of the neighbourhood -of Glasgow.
If the mineralizing substance, however, be any other than oxygen,
carbon, no matter how intensely heated, cannot produce any effect
upon the ore. Thus the native sulphurets and arseniurets are not
acted upon by carbon. Nor can the metals be obtained in a pure
form from any of their salts, except the carbonates, by means of carbon, for the oxygen of the acid and base being simultaneously removed by its agency, the radical of the acid remains united with the
metal, which is thus only changed into a new kind of ore. Thus,
if sulphate of lead be heated with any of the forms of carbon, it is
converted into sulphuret of lead, S.0, —Pb O. and 4C. giving S.+Pb
and 4C.O. And if arseniate of iron be ignited with carbon, all the
oxygen is removed, and the arsenic and iron remain in combination.
In such cases, it is necessary to adopt somewhat more circuitous
methods, suited to the constitution of the individual ores.
In the case of certain metallic sulphurets, the metal may be very
simply separated by melting the ore with a proportional quantity of
a metal having a greater affinity for sulphur. Thus metallic antimony is very generally obtained by the fusion of the native sulphu-.
ret with iron; Sb2S3 and 3Fe. giving 3Fe.S. and Sb2. On the large




REDUCTION OF THE METALS.                      333
scale, however, this method would not be economically available.
In order to extract the metal from its sulphuret, as in the generality
of the ores of lead, of copper, and of zinc, the ore, first reduced to
fine powder, is heated to redness in a current of air, by the oxygen
of which the sulphur is converted into sulphurous and sulphuric acid,
while the metal is oxidized. This process is termed calcination. A
great part of the sulphuric acid formed is carried off with the current of air, and the remainihg product is a sulphate of the metal,
with excess of base. When the salt so formed is deoxidized by
contact with the ignited fuel, the excess of oxide abandoning its ox
ygen, yields an equivalent quantity of metal, which, however, would
be impure and of inferior quality, by having dissolved a portion of
the sulphuret reproduced by the reduction of the sulphur from the
sulphuric acid. It is therefore necessary to get rid of that residual
portion of the sulphuric acid before the deoxidizing process.commences, and this is effected by mixing up a proper quantity of lime
with the calcined mass. The lime decomposes the metallic sulphate,
combines with the sulphuric acid, and sets the oxide free; and when
the deoxidizing flames of the furnace pass over the calcined mass,
the metallic oxide being reduced, yields a pure metal, while the sulphate of lime, by losing its oxygen, is brought to the state of sulphuret of calcium, and remains as glassy scoria upon the surface
without injury. This kind of operation is generally carried on in a
sort of furnace termed reverberatory, from its office of beating down
the flames from the fireplace upon the materials strewed upon its
hearth. The adjoining figures will
give an idea of its construction. The
upper is a vertical, and the lower a, 
horizontal section, to which the same'..              iletters apply. a is the fireplace, and               c.'
b the ash-pit; at c a low wall is rais-l   C
ed, termed the bridge, and the flames  VI/,*
and heated air ascending from the
fire are reflected downward by the
low, vaulted roof, and, impinging up-.......
on the hearth, or sole of the furnace, n    /.
d, produce the greatest heating ef-1 )
feet upon the materials laid thereon. 
The openings i and g serve for the
introduction of the materials, and for
giving them the arrangement, agitation, and mixture most condi-.
cive to the success of the operation. The damper, p, in the flue,
regulates the draught, and hence the intensity of the fire.
In this furnac  the calcining or oxidizing, and the reducing or
Aeoxidizing effect is produced, according as the supply of fuel and
of air is regulated; and thus the two stages just described, in the
extraction of a metal from its native sulphuret, are carried on. The
hearth, d, is generally dished or concave towards the centre, so that
the reduced metal, in its melted condition, may flow there, and be
run out by an aperture in the side of the furnace when the operation is concluded.
In the case of sulphuret of lead, a very simple and beautiful pro




334         GENERAL PRINCIPLES OF THE
cess of reduction consists in roasting the ore at a moderate temper.
ature, so that about one half of it shall be converted into sulphate
of lead by oxidizernert, without any of the sulphuric acid being driven off; and then, having mixed this up well with the unaltered portion of the ore, increasing the temperature very rapidly, so that the
two shall be fluxed together. The result is the complete conversion
of the mixture into suiphurous acid gas, which passes of, and pure
metallic lead, which remains, the sulphur of the unaltered ore coinbining with the sulphur and oxygen of' that portion which had been
oxidized. Thus S.03- Pb 0. and S. tPb. produce exactly 2S2O, and
2Pb.
One of the most interesting processes of reduction is that by which
iron is obtained from its most abundant ore, the clay iron stone.
This substance consists of oxide of iron of greater or less purity,
combined with alutnina and silica. Nowv, as carbon cannot deprive
silica of oxygen except under very peculiar circumstances, such as
those described in page 323, so the metal cannot be obtained by
mere deoxidation; and even if the oxygen were removed, the result
would not be pure iron, but a compound of silicon and iron, which,
indeed, is formed in small quantity, and is found generally in cast
iron. It is necessary, therefore, to decompose the silicate of iron
of which the ore is constituted, and this is effected by means of lime.
The coal or coke and the ore are introduced into the furnace, mixed
with a proportion of limestone, which, being calcined by the heat,
yields lime, which seizes upon the silicic acid, and the oxide of iron
being set free, is immediately reduced by the carbon of the fuel with
which it is in contact, and produces metallic iron. The lime, the
silica, and the alumina being melted together, forin a substance of
a nature somewhat between glass and porcelain, which floats upon
the mass of melted metal. and constitutes the slags or scorine of the
iron furnaces.
In the case of ores containing arsenic, of which only the arseniurets of cobalt and nickel are of technical importance, the method
followed is to roast the ore in a furnace so constructed that a powerful oxidizing action shall be produced by a current of air streaming over the ignited ore; both metals being thus oxidized, arsenious
acid, and oxide of cobalt or of nickel are produced; the greater
part of the former is expelled by the heat, and, being carried oft' by
the draught, is conducted into large chambers, where it is gradually
deposited under the form of a fine white powder upon the walls and
floor. The metal with which the arsenic had been combined remains in the state of oxide united with a little arsenious acid, and
is subsequently extracted or employed in other processes.'the reduction of a metal from the state of sulphuret is frequently
effected upon the small scale by fusion with a mixture of lime and
charcoal, or of carbonate of potash and charcoal, which last is familiarly termed black flux.  The theory of this process is very simple. T'hus, if sulphuret of antimony, lime, and charcoal be melted
together, the sulphur *ombines with the calcium  of the lime, the
oxygen of which unites with the antimony, Sb2S3 and 3Ca.O. giving
3Cia.S. and Sb,O. This last is then decomposed by the charcoal,
the oxygen combining with the carbon, and the metallic antimony
separates.




REDUCTION  OF THE METALS.:335
The black flux used in such operations is prepared by deflagrating
together equal parts of nitre and cream of tartar; the nitrogen and
oxygen of the former unite with the carbon and hydrogen of the
latter, forming carbonic acid, nitrogen, and water: the potash of
both remains behind as carbonate, mixed with the excess of carbon
which had escaped combustion. If two parts of nitre be used with
one of cream of tartar, there remains after deflagration a white
mass of carbonate of potash, which is known as white flux, and used in
processes where the deoxidizing effect of the carbon is not required.
Thus, for the reduction of chloride of silver, it is sufficient to fuse
it with half its weight of white flux; the chlorine combines with the
potassium, and the silver, which at a lower temperature would have
united with the oxygen and carbonic acid, is separated, those two
bodies escaping in the gaseous form; the formula of the reaction
being that K.O.. C.O and Cl.Ag. give K.C1. and free Ag., while O.
and C.O are driven off.
Hydrogen, although inapplicable to the reduction of the metal.
upon the large scale, and for the purposes of the arts, is yet to the
chemnist a most valuable agent for this office, as it acts upon all varieties of metallic combinations, whether oxides, chlorides, or sulphurets; and that the results it gives are so accurate as to serve as
bases for some of the most fundamental propositions of the science.
Thus we have already seen that the composition of water is best
determined by the action of hydrogen gas upon oxide of copper,
and in analytical investigations, the isolation of a metal, by decomposing its chloride or sulphuret in a stream  c.f hydrogen gas, is
frequently employed. The deoxidizing action of hydrogen is occasionally used in an indirect manner. Thus a very convenient
mode of obtaining silver from the chloride consists in flising it
with sorne common resin: this consists of carbon, hydrogen, and
oxygen, of which only the hydrogen is active; it combinin1g with
the chlorine carries it off as muriatic acid gas, while the metallic
silver is separated.  If the chloride of silver be diffused through
water rendered slightly acid, and a slip of zinc be introduced, an
evolution of hydrogen commences, and the silver separates as a fine
metallic powder as the zinc dissolves.. But the action is here more
properly galvanic; an equivalent (32-3) of zinc combiningi with the
chlorine in place of each equivalent (108) of silver whlich is set
free. The precipitation of copper from the water of copper mines,
which holds sulphate of copper dissolved, by dipping therein pieces
of iron, and, indeed, all cases of tile precipitation of one metal by
another, are referrible to the samle source.
The physical agent, electricity, which has been already fouind to
influence chemical action to so remarkable a degree, has been employed with considerable success in the reduction of certain metals. It was first applied by Davy, who thereby made his wonderful
discoveries of the composition of the alkalies and eartlis. It has
been totally superseded in that point of view by simpler processes,
but has recently been applied by Becquerel, upon the large scale, to
the extraction of the precious metals from their ores.
There are many other methods of reduction, which, however,
being limited in their application to individual metals, will form
more properly a part of their special history.




336                     PO TASS I U M.
CHAPTER XIII.
OF TIE INDIVIDU.AL METALS, AND OF THEIR COMPOUNDS WITH OXTuiEN,
SULPHUR, SELENIUM, AND PHOSPHORUS.
SECTION I.
DIETALS OF THE FIRST CLASS.
Of Potassium.
POTASSIUM is the metallic basis of the alkali potash. It was origi
nally discovered by Sir Humphrey Davy, whlo obtained it by submitting a piece of caustic potash, slightly moistened, so as to be a
conductor of electricity, to the action of a powerful galvanic battery; the water and the potash were simultaneously decomposed,
oxygen being evolved at the positive electrode, while hydrogen and
potassium were separated at the negative wire. From the heat
generated by the intense power used, the metallic globules generally burned as soon as they came into contact with the air, and it
was with difficulty that a quantity was obtained sufficient for the
important researches in which it was employed by its illustrious
discoverer. By using mercury as the- negative electrode, the decomposition can be effected by a much weaker force, and even
with a single pair of plates, as in the arrangement of Dr. Bird, described in p. 199.
The decomposition of potash by truly chemical means is due to
Gay Lussac, but it is by the process of Brunner that the metal is
now universally obtained. As it is carried on only, however, in the
most extensive and best-appointed laboratories, a very short sketch
of it will suffice here.
Cream of tartar, which consists of tartaric acid united to potash,
is to be ignited in a covered crucible, until there remains a mass of
carbonate of potash mixed with carbon in a state of very minute
division, and this mass is to be intimately mixed, while still hot,
with a quantity of coarsely-powdered wood charcoal, which serves
to render the whole porous, so as to allow of the escape of the
gases generated in its interior without its swelling up. The material so prepared- is introduced into an iron bottle, such as those in
which quicksilver is imported; to the mouth of the bottle, which is
laid horizontally in a wind furnace, is adapted a short iron tube,
passing to a copper condenser partly filled with rectified naptha,
and so constructed with partitions as to exclude the air, while there
passes through it a stout iron wire, terminated by a screw, with
which the iron tube can be cleared of any solid material that might
be deposited in it. The apparatus being so arranged, and the receiver surrounded by ice, a fire is lighted in the furnace, and when
the iron bottle has become white hot, the decomposition of the
potash begins, the metal distils over, and condenses in the receiver




PREPARATION AND PROPE RTIES OF POTASSIUMJ. 337
In globules, which are protected by the napthan, in which they sink,
while the oxygen of the potash and of the carbonic acid combines
with carbon, forming carbonic acid, which, escaping under the partitions in the receiver, passes away; K.O.+C.02 and'2C. producing
K. and 3C.O. The great difficulty and loss in this process arise,
however, from a cause which is not at first apparent; it is, that
carbonic oxide and potassium  unite to form a dark gray mass,
which sublimes, and, condensing in the short iron tube, renders the
screw necessary to keep the passage clear, and frequently causes
the failure of the process. Even in the most successful results,
one half of the metal actually reduced is lost by combining with
the carbonic oxide.
The potassium thus obtained is very impure, containing much
carbon, and a quantity of that compound of carbonic oxide which
passes over into the receiver. To purify it, it is redistilled in cast
iron retorts, from which the air has been previously excluded by
vapour of naptha, and it is thus obtained in globules like peas, in
which state it may be preserved under naptha perfectly free frolr
oxygen.
At common temperatures, potassium is soft, and may be moulded
in the fingers like wax. At 32~ it is quite brittle, and crystallizes
in cubes; at 70: it is pasty, and at 150' perfectly liquid. At a dull
red heat it boils, forming a green vapour, and may, as described
above, be easily distilled. It is specifically lighter than water, its
specific gravity being 0'865.
The colour of potassium is of a bluish white, but its surface in
stantly becomes gray when exposed to the air, owling to the absorption of oxygen and the formation of a crust of potash. If' it be.
heated, it burns with a vivid violet flame. So great is its affinity
for oxygen that it decomposes water, and even ice, with great violence, so much heat being evolved that, if the experiment be made
in the air, the hydrogen gas evolved and the metal both inflame
and burn with a fine violet colour. When the metal has been all
consumed, a globule of fused dry potash remains, which, when it
has cooled to a certain degree, combines with water with a loud report, and instantly then dissolves.
Potassium is remarkably characterized by its great affinity for oxygen, which it abstracts from alnost all bodies; thus its use in the
preparation of boron and silicon has been already noticed; and although, at very high temperatures, iron and carbon take oxygen from
potassium, yet at a lower degree of heat, oxide of iron and carbonic
acid are both decomposed by potassium, carbon being deposited
from the one, and metallic iron separated from the other.
The symbol of potassium is K., the initial of the word Kalium,
by which the metal is designated by most of the Continental chemists; the old name kali being still retained in preference to the word
potash, which has been adopted only in Great Britain and in France.
The equivalent is 490 or 39'3, according to the scale.
Oxides of Potassium.-Potassium  combines with oxygen in two
proportions, forming a protoxide K.O., and a peroxide K O,.
The protoxide of potassium constitutes the important alkali potash; it can only be obtained free from water by exposing potassium
Uu




333  PIR'EPARATION' AND  PAiOPERTI.ES  OF POTASH.
to the' action of dry air,-'when it is converted into a white powder,
wbhich is fusible at a red, and volatile at a white heat; if this substance, be once united with water, it cannot be separated from it,except hby combination with an acid.  The potash of commerce,
and that used. in the laboratory, is, therefore, always hydrate of
p9tash; the dry potash, in.uniting with water, becomes icnited.
Befbre the discovery of carbonic acid, the alkalies and their carbonates -Were distinguished from each other by the epithets of mild
ardd-caustic, and hence'for medicinal purposes, and in some phar
kpxacopmias, the hydrate of potash is still termied caustic potash.
To prepare a solution of potash, the carbonate of potash of com-,meece, derived ff om the sources to be detailed in its description, is
to he dissolved i'n ten parts of water, and the solution being made
to boil smartly, is to be decomposed by one part of slacked lime in
fine ppwider, which is to be gradually added, the boiling being briskly
kept up; the lime abstracts the carbonic acid from the potash, and
carbonate of lime is formed, which at that temperature, constituting
minute crystals of arragonite, is rapidly and completely deposited.
The clear liquor is to be tested occasionally by adding to a small
q.uantitty of it an excess of muriatic acid; as soon as the absence of
effervescence shows that all the alkaline carbonate has been decomnposed, the pan is to be removed, and being laid aside, carefully covnered, until the carbonate of lime has been well settled, the clear liqu'or may be siphoned off. The decomposition of the carbonate of
potash by the lime would take place also at ordinary temperatures,
but the precipitate would be in the rhombohedral form, and being
specifically lighter and more finely divided, would occupy much
jnore room, and would not separate so well. If the carbonate of
potash be dissolved in less than six parts of water, it is not decomposed by lime; on the contrary, when a strong solution of caustic
potash is boiled with carbonate of lime, carbonate of potash is produced, and lime set free.
When the solution of caustic potash is evaporated in a basin of
iron, or silver, or platina, there remains a liquid which solidifies on
coolinog into the hydrate of potash, K.0.. 1.O.  This liquid is generally run into cylindrical moulds, in which form the caustic potash
or fused potash of the shops is generally found.  In this state it is,
however, impure, and it requires to be freed from the admixed sulphate and carbonate of potash, chloride and peroxide of potassium,
and oxide of iron, which it generally contains, by being dissolved
in absolute alcohol, the solution evaporated to dryness, and the remaininmg potash fused a second tinle.
Hydrate of potash is a pure white solid, of a crystalline fracture;
it fuses belowv redness.  In the fingers it has a peculiar soapy feel,
owing to its dissolving the cuticle, with which it forms a kind of
soap; it acts powerfully on all organic tissues, dissolving and decomposing them, and hence its use in surgery, and its name of caustic
potash.  It dissolves in water, with the evolution of conside'rable
heat; a concentrated solution of it crystallizes when exposed to
cold, in rhombic octohedrons, whose composition is K.O. +SH.O.
The solution of potash is pre-eminently allkaline; it neutralizes the
strongest acids, browns turineric paper, and restores the blue colour




SULPHILURETS  OF  POTASSIUM.                        339
of litmus paper reddened by an acid.  It absorbs carbonic acid rapidly from the air, and must hence be preserved in close vessels.  It
acts rapidly on glass containing much alkali or lead, and hence should
be preserved in bottles of common green glass.
The uses of potash in chemistry are too numerous to mention; it
being the strongest base, is employed in almost all cases of saline
decomposition, and its various compounds are of great importance
in the chemical arts, of which many swill be noticed hereafter in detail.
Potash is distinguished, when free, first, by its general alkaline
characters,  and by its not being precipitated by carbonate of soda,
which separates it from  everything but soda and ammonia.  From
the latter it is known by the browvn stain produced on turmeric paper
being permanent, whereas the brown colour produced by ammonia
disappears when the paper is warmed; and frohm soda it is known
by giving with an excess of the perchloric, tartaric, and hydrofluosilicic acids, sparingly soluble salts, whereas the soda salts of these
acids are all easily soluble.  A solution of potash, if neutralized by
muriatie  acid, gives, on the addition of chloride of platinum, a fine
yellow precipitate, vhereas, with a solution of soda, no precipitation
occurs.
The salts of potash act in all respects similarly, except that, as
there is no alkali in excess, the action on vegetable colours is not
that of an alliali.  The salts of ammonia resemble precisely the salts
of potash in their action on those precipitants described above, but
they are at once disting uished by the application of heat.  The salts
of ammonia are all volatilized, either with or without decomposition,
by a red heat, while those of potash are fixed, and give to the flame
of the blowpipe a distinct and characteristic violet tinge.
Potash consisting of an equivalent of each element, its formula is
K.O., and its composition,
Potassium, 83'05       One equivalent =490 or 39'3
Oxygen,   16o95        One equivalent =100 or  8'0
100.00                         590    47.3
Pcroxide of Potassium. K.03.-This substance, which is of very little importance,
is formed by burning potassium in an excess of oxygen gas;!t is a yellow powder,
decomposed by water, potash dissolving, and oxygen being given off: When hydrate'of potash is heated to redness in air, some peroxide is always formed, and
hence the fused potash of the shops generally gives off minute bubbles of oxygen
gas when dissolved in fwater.
Sulp/tzurets of Potassium.-When potassium  is gently heated in
contact with sulphur, they unite with brilliant combustion, and, according to the proportions in which they are employed, form  the
sulphurets of potassium, of which there are altogether four.  These
bodies are, however, always prepared in practice by more economical processes.
If sulphate of potash be ignited in a glass tube, and a current of dry hydrogen gas
be passed over it, all the oxygen, both of acid and base, is removed in the state of
water, and protosulphuret of potassium remains. Thus K.O.. S.0, and 4H. produce
411 O. and K.S. The same result follows from igniting strongly, in a crucible, a
mixture of charcoal and sulphate of potash; all the oxygen is removed as cart)onic
oxide, and thle sulphur and the potassium remain in combinationi, K.O.. S.0. and 40.
giving 4C.0. and K.S.




340    S u LP H URETS  OF  POTASSIUM.-SOD IUM.
This protosulphuret is of a brown colour, fusible below a red heat, easily solu.
ble, and its solution is yellow, and reacts highly alkaline and caustic. When exposed to the air, it absorbs oxygen rapidly; and in preparing it from sulphate of potash, by carbon, if lampblack be used, so that the product shall be in a state r.f very
minute division, it takes fire spontaneously on coming into contact with the air,
constituting a pyrophorus.  If the protosulphuret of potassium be acted upon by
acids, water is decomposed, K.S. and H.O. giving K.0. and H.S.; the potash remains, united with the acid, and the sulphuret of hydrogen is given off.  Yo solidl
sulphur is deposited, and the liquor remains clear.
A solution of the protosulphuret dissolves sulphur in large quantity, the higher
sulphurets being formed. It absorbs sulphuretted hydrogen in such proportion that
a compound is produced, K.S.+H.S., exactly similar to the hydrate of potash,
K.O.+tI.O.
The tersulphuret of potassium corresponds to the peroxide, its formula being K.S3.
It constitutes the mass of the hepar sulphuris, liver of sulphur, of the pharmacopreias. It may be prepared by fiusing, at a low red heat, one part of sulphur and
two of carbonate of potash, the mass being kept liquid as long as it effervesces, from
carbonic acid gas being evolved. In this reaction, a quantity of oxygen from the
potash combines with one portion of the sulphur, forming hyposulphurous or sulphuric acid, according to the temperature, while the remainder of the sulphur combines with the potassium, producing a sulphuret, the composition of which is determined by the quantity of sulphur present. With the above proportions the reaction may be considered thus: 4(K O.+C 02) and 10S. give 3K.S3 and K.O.. S.03,
which constitute the fused mass, while 4C.02 is driven off with effervescence. If,
however, equal weights of carbonate of potash and of sulphur be employed, the
sulphuret formed contains five equivalents of sulphur: it is the pentasulphuret.
These sulphurets resemble each other completely in external appearance; they
are liver-brown; they deliquesce in the air, and absorb oxygen rapidly. Their solutions, which are at first deep yellow, become colourless by uniting with oxygen,
hyposuiphite of potash being formed, and sulphur precipitated. If a solution of the
tersulphuret or pentasulphuret be treated with an acid, water is decomposed, and
potash being formed, sulphuret of hydrogen is produced; the remaining sulphur
then separates in a state of very minute division, and of a milk-white colour, constituting the lac sulphuris, or the sulphur precipitaotun of pharmacy. If the acid employed be strong and in great excess, a quantity of bisulphnret of hydrogen is formed, as explained in page 293.
Rose is of opinion that the whiteness of precipitated sulphur depends not merely
upon its minute division, but that it is owing to the presence of a trace of bisulphuret of hydrogen. When the hepar sulphzLris is decomposed by an acid, it is not
merely that the excess of sulphur is set free, but in addition, as there is always hyposulphurous acid present; this, when evolved, acts on the sulphuretted hydrogen,
and the sulphur of both is precipitated, water being formed; S.02 and 21H.S. giving
2H.O. and 2S.
The Pentasulplhuret of Potassium is prepared perfectly pure by decomposing sulphate of potash by sulphuret of hydrogen, at a red heat. Thus K.O.  S.03 and
4H..S. give K.S5 and 4H.O. This reaction supports very much the view that this
pentasulphuret is really sulphate of potash, in which the oxygen, both of acid and
base, is replaced by sulphur, for K.S5 may be constituted of K.S. and S.S3.
The seleniurets of potassium are similar in constitution to the sulphurets.  They
evolve seleniuret of hydrogen when treated 5y acids, with precipitation of selenium when it is present in greater proportion than one equivalent.
Of Sodium.
Sodium  exists in great quantities in the mineral kingdom, especially combined with chlorine, as common salt, of which enormous deposites are found inEngland, Poland, and elsewhere, besides
forming the leading saline ingredient of the waters of salt lakes and
of the ocean.  It is found in many minerals, and is remarkably
prevalent in the animal fluids, all of which contain common salt.
It is, indeed, from  the chloride of sodium  that we derive, whether
directly or indirectly, all the supplies of the various compounds of
this metal.




SODIUM  AXND  SODA.                    341
The discovery of sodium was made in the same manner, and im
mediately subsequent to that of potassium, by Humphrey Davy,
and it is now prepared in exactly the same manner as that metal.
It is, however, much more easily prepared; its reduction does not
require so high a temperature, and it does not unite with carbonic
oxide, so that the formation of the black sublimate, which is the
principal source of loss and failure in preparing potassium, does not
occur.
Sodium is lighter than water, its sp. gr. being 0'972; it consequen tly floats upon that liquid; and when a globule of the metal is
thrown into a basin of water, this is decomposed with great rapidity,
hydrogen being evolved; but the action is not so energetic as with
potassium; the gas does trot take fire spontaneously. But if the
globule be prevented from moving about, the water becomes heated, and the action increases so much as to set fire to the gas; this
occurs when there is so little water that the globule does not swim,
or when it is fastened to the edge of the vessel, or if the water be
thickened by gum or starch. If some oil of vitriol be added to the
water, the action is so much more active, that combustion occurs
even when the metallic globule moves rapidly about.
The symbol of sodium is Na., derived from the word Natrium, as
soda still retains in many countries the name Natron. Its equivalent numbers are 291 or 23'3.
Sodium unites with oxygen in two proportions, forming the protoxide, or soda, Na.O., and the peroxide, of which the constitution
is not exactly known. This last is prepared just as the peroxide of
potassium, which it resembles completely in its properties. The
former only requires detailed notice.
The preparation of dry soda is effected like that of potash, by
heating the metal in dry air or oxygen. It is grayish white, and
absorbs water with excessive power. From the hydrate of soda
the water can be expelled only by an acid. The caustic soda is,
therefore, always like caustic potash, a hydrate of the alkali. For
the preparation of caustic soda, the same process is to be followed
as for that of potash. The carbonate of soda of commerce, dissolved in boiling water, is decomposed by slacked lime, it being necessary, however, to use one third more lime, from the smaller equivalent number of soda. The solution of caustic soda resembles that
of caustic potash in all its alkaline characters, but its action is not
so intense. It is a weaker alkali, its salts being decomposed in
all cases by potash.
The soda consists of an equivalent of each element; its formula
is Na.O., and its composition,
Sodium, 74'42    One equivalent =291 or 23'3
Oxygen, 25'58    One equivalent =100. or 8.0
100'00                    391 1   31'3
The detection of soda is very simple. On adding to a solution ot
the substance to be examined a solution of carbonate of soda, if there
be no precipitate produced, the base of the salt present must be an
alkali. On then applying the various tests for potash and for ammonia detailed in the last section, if no evidence of their presence




342                    L ITHIUM.-B A RI U M.
be obtained, the alkali must be soda; and even where potash also
is present, a small quantity of soda may be recognised, by its tin.
ging the flame of the blowpipe-of a fine yellow colour.
The compounds of soda are very numerous and important, antd
will be described in their proper place, among the salts.
The sulphurets of sodium resemble so completely the sulphurets of potassium as
not to require more than a reference to their description. To the seleniurets of
sodium the same remark applies.
Lithium.
This metal is found only in a few  minerals, of which one of the
most common, spodumene, occurs at Killiney, near Dublin.  This
mineral is a double silicate of the alkali lithia (oxide of lithium) and
alumina.  The metal has been obtained by voltaic decomposition,
but only in very small quantity.  It is white, like sodium, and becomes oxidized immediately on exposure to the air. Its symbol is
L., and its equivalent number 80'3 or 6.4.
To obtain lithia, the simplest process is to mix the mineral containing it (generally lepidolite or spodumene), previously reduced to very fine powder, with fluor
spar, and digest the mass with oil of vitriol, until it is completely decomposed; the
silica is carried off by the hydrofluoric acid (see page 324), and the lime, the alumina,
and the lithia remain combined with the sulphuric acid. By the action of a small
quantity of water, the sulphates of lithia and alumina are dissolved out, and the last
then precipitated by ammonia. The sulphates of lithia and ammonia being then ignited, the sulphate of ammonia is decomposed, and the sulphate of lithia obtained
pure. This is but a general outline of the process, which requires many additional
operations for a fully successful result.
Lithia is distinguished from the other alkalies by the sparing solubility of its carbonate, in which character it approximates to the
property of the earths, thus connecting the two classes of metals.
Being so rarely found, and of no application in the arts, its history
is not of much importance.
Lithia is recognised by the sparing solubility of its carbonate, and
by tinging the flame of the blowpipe of a brilliant red colour.  This
last character easily distinguishes it from soda. Lithia is a protoxide, its formula being L.O.; its equivalents 180'3 or 14'4.
The sulphurets and seleniurets of lithium do not possess any interest.
The alkali ammonia might, on one hypothesis of its nature, be described here.
When combined with hydrogen, it is considered by Berzelius and many other chemists to form a remarkable compound metal, amnlonimum, N.I-I4, whose relations to
potassium are of an exceedingly intimate kind; and the salts of ammonia, which
contain ammonia and water, N.H3+H.O., are looked upon as consisting of an oxide
of that metal, N.H4. O. in combination with an acid. I prefer, however, to study the
history of ammonia, and all the classes of compounds into which it enters, among
the bodies of organic origin.
Barium,
Barium  is found'exclusively in the mineral kingdom, where its
oxide, barytes, is the basis of several minerals, as the sulphate and
carbonate, which are the usual sources from which it is obtained
for use.
The metal barium was discovered by Sir Humphrey Davy immediately after the discovery of the basis of the alkalies. It may be
prepared by voltaic action, as described under the head of potassium,




PREPARATION  OF BARYTES.                        343
or much better by passing the vapour of potassium  over barytes
heated to redness; the potassium takes the oxygen of the barytes,
and the barium is set free. By washing the residue with mercury,
the metallic barium is dissolved out, and the mercury being then
distilled off in a retort of hard glass, the barium remains behind; it
is a white metal like silver; it fuses below a red heat; it is denster
than oil of vitriol: it decomposes water with great rapidity, evolving hydrogen gas and forming barytes (oxide of barium).
The name barium is derived from hfapvs, heavy; the native sulphate of barytes having been called formerly terra ponderosa, or heavy
spar. Its symbol is Ba.; its equivalent numbers 856'9 or 68'7.
Barium combines with oxygen in two proportions, forming a protoxide, which is the earth barytes, Ba.O., and a deutoxide, Ba.O0
The preparation of this last has been described so fully when explaining its only important use, the formation of deutoxide of hydrogen (p. 258), that it need not be farther noticed here. The
protoxide, barytes, is, however, one of the most important earths.
To procure pure barytes, the nitrate of barytes is to be gently
heated to redness in a porcelain crucible.  It fuses at a dull red,
and boils briskly from the rapid escape of oxygen; when this has
terminated, there remains a gray loosely Coherent powder, which
is barytes. The melted salt is in this process very apt to froth up,
so much as to overflow, unless the vessel be of considerable size;
this is very simply avoided by mixing the nitrate of barytes, beforehand; with twice its weight of sulphate of barytes in fine powder.
When the nitrate melts, the sulphate gives the mass a degree of
consistence which prevents its frothing up, and on boiling the residual mass with water, all the pure barytes dissolves, the sulphate
remaining totally unacted on.
If the native carbonate of barytes, Ba.O.. C.02, be strongly heated with carbon, the
carbonic acid is converted into carbonic oxide, which passes off, and pure barytes
remains behind, Ba.0.  C.02 and C. giving Ba.O. and 2C0.O.; the former process is,
however, so much easier, that it alone is now usually employed. Graham has suggested the employment of iodate of barytes as a substitute for the nitrate: other
processes will be described under the head of sulphuret of barium.
Pure barytes is a heavy gray powder; when exposed to the air,
it absorbs water rapidly, giving out much heat, and falling into a fine
white powder, hydrate of barytes, Ba.O.+-H.O.  Another hydrate may
be obtained crystallized, by dissolving barytes in three parts of boiling water, and allowing the solution to cool slowly; it contains nine
equivalents of water. The solution of baryies is very caustic and
alkaline; exposed to the air, it absorbs carbonic acid, and a white
precipitate of carbonate of barytes is formed; it is hence used to
determine the quantity of carbonic acid present in the air (p. 263),
and in some other cases.
The detection of barytes is very simple; its soluble compounds
give white precipitates with carbonate of soda, with sulphuric acid,
and with hydrofluosilicic acid, and none of these are affected by a
solution of sulphuretted hydrogen gas in water.  The sulphate of
barytes is not merely insoluble in water, but also in nitric and muriatic acids, which is a farther characteristic of this earth.
The formula of barytes is Ba.O., and its composition,




344    SULPHURET OF BARIUM.-STRONTIUM.
Barium, 89'55    One equivalent =856'9 or 68'7
Oxygen, 10'45    One equivalent =100.0 or 80
100.00                    956i9  7.67
The soluble compounds of barytes are all poisonous, and the car.
bonate, although insoluble in water, is yet dissolved by the free
acids of the stomach, and becomes poisonous. The antidote to all
barytic preparations is sulphate of soda, or sulphate of magnesia,
administered in excess; the sulphate of barytes then produced is
absolutely inert.
Sulphuret of Barium. Ba.S.-This body is of considerable interest, as the source of barytes and of most of its ordinary compounds;
to prepare it, sulphate of barytes in fine powder is to be mixed with
one fourth of its -weight of lampblack, and exposed to a very strong
heat for two hours; the carbon removes all the oxygen from  the
salt; carbonic oxide is evolved, and sulphuret of barium remains;
Ba.O.. S.0, and 4C. giving 4C.O. and Ba.S. The mass thus obtained is to be boiled in water; a deep yellow solution is then produced, from which the sulphuret of barium crystallizes on cooling;
it is then a hydrate, but its water of crystallization may be removed
by a moderate heat. The sulphuret of barium is decomposed by
acids, sulphuret of hydrogen being evolved, and a salt of barytes
formed: it is thus that the salts of barytes are obtained for laboratory use.
A simple mode of obtaining caustic barytes directly from the sulphuret of barium has been recently given by M[ohr. It consists inl
adding to a boiling solution of the sulphuret, black oxide of copper,
until the whole of the sulphuret of barium is decomposed, as is easily
ascertained, by adding a drop of the solution to a solution of acetate
of lead; the copper combines with the sulphur, while the barium
and the oxygen unite, Ba.S. and Cu.O. producing Ba.0. and Cu.S.
This is probably the simplest and cheapest meanrs of obtaining pure
barytes.
Of Strontium.
This metal is the basis of the earth strontia, protoxide of strontium, which exists native combined with sulphuric and carbonic
acids. The native carbonate of strontia was first found at Strontian
in Scotland, and proved to contain an earth different from barytes
by Dr. Hope. The similarity of these two earths is very great, so
Ihat the general outline of the history of strontia is the same as that
of barytes.
The metal strontium is obtained precisely as barium, with which
it perfectly agrees in character so far as its properties have been
ascertained. Its symbol is Sr., and its equivalent number 547'3 or
43.8. To obtain strontia, the same processes may be employed which
were described for the preparation of barytes, substituting the native
carbonate or sulphate of strontia for the compounds of barytes. The
strontia is gray, slacks on exposure to the air, forming a hydrate,
Sr.O.. H,0., and by crystallization from its watery solution, another
hydrate, Sr.O. + 9H.O. Strontian is less soluble than barytes, its taste
is not so caustic, nor is it so poisonous




COIM POUNDS OF CALCIU M.                    345
Strontia is distinguished from barytes by tinging the flame of the
blowpipe a rich crimson. The red lights used in fireworks owe
their colour to nitrate of strontia, which is used in the preparation.
Like barytes, the soluble salts of strontia are precipitated by sulphuric acid, but the sulphate of strontia is not so very insoluble as
sulphate of barytes; a solution of strontia is also precipitated by
carbonate of soda. The hvdrofluosilicic and the hyposulphurous
acids, which precipitate barytes, do not precipitate strontia, and thus
these earths may be distinguished and separated from each other;
the chromic acid acts in a similar manner.
The sulphuret and seleniuret of strontium resemble perfectly those
of barium, and are prepared in the same way.
Of Calcium.
The existence of this metal was first recognised by Sir Humphrey
Davy, it being obtained from lime by the same method as that described under the head of barium; it is white like silver; it sinks in
water, which it decomposes rapidly, evolving hydrogen,and uniting
with oxygen, forms lime (protoxide of calcium). The symbol of
calcium is Ca., and its equivalent number 256 or 20'5.
Calcium combines with oxygen only in one proportion, forming
lime, the most important of the earths. It is found very extensively
~ distributed in the mineral kingdom, principally combined with sulphuric and carbonic acids, forming sulphate of lime (gypsum, plaster of Paris) and carbonate of lime (marble, limestone, chalk). These
substances exist as rocks or crystallized, the last constituting the
mineral species, arragonite and calc spar, often referred to under
the heads of crystalline systems, isomorphism, and dimorphism.
Lime is found also combined with phosphoric and arsenic acids in
several minerals, and the native fluoride of calcium is the fluor spa',
used for the preparation of the hydrofluoric acid and other compounds of fluorine.
Notwithstanding the immense quantities of carbonate of lime
which are found constituting a great portion of the surface of the
globe, as, for instance, the whole centre of Ireland is one vast plain
of limestone, and in that as well as other forms, chalk, marble, &c.,
it is equally extensive in most other countries, it is questionable
whether lime should not be looked upon as rather a characteristic
of the animal than of the mineral kingdom of nature. The bony or
testaceous skeleton, by which the softer portions of the animal frame.are attached, is always found to consist of lime united either with
carbonic or phosphoric acids, and the diversity of chemical composition in this respect is found to coincide in a remarkable degree
with the most natural physiological classification. The skeletons of
the vertebrated animals consist principally of phosphate of lime,
while in the shells of the invertebrate animals, the carbonate of lime
is the prevalent component. The teeth also consist of phosphate
of lime; in all these cases, the phosphate of lime is associated with
fluoride of calcium, just as occurs in the native phosphate, the mineral apatite.
Now it is remarkable that all the great geological formations
which contain carbonate of limne are found to consist of the aggo-re
Xx




346               PROPERT IE S OF LIME.
gated skeletons (shells) of myriads of the tribes of invertebrated an
imals, which had existed in some former period of the world's history.  From the densest and hardest limestone to the softest chalk,
the entire mass resolves itself ultimately into a congeries of animal
remains, and hence the great supply of lime in the mineral state
arises from the destruction of its animal sources. Even those crystalline marbles in which no organic remains can be traced, appear
destitute of them only from having been subjected, by volcanic heat
or otherwise, to the influence of causes which have gradually rendered the texture of the mnass completely uniform.  The lime which
exists in nature must therefore be looked upon as being continually
in a state of passage between the organized and the inorganic kingdoms.  The plants which grow upon the soil take up, by dissolution
in their juices, salts of lime, which pass into the substance of the
animal which feeds upon them, and, accumulating in its system, afford materials for the proper development of the skeleton.  When
the animal dies, the materials of its tissues either serve for the nutrition of some other animal, or, being totally decomposed, its elements return to the mineral kingdom, to be, in after ages, the subject of similar alternations.
Lime is always obtained, for the purposes of chemistry and of
the arts, by the decomposition of the native carbonate.  To obtain
lime perfectly pure, crystals of calc spar or pieces of Carrara marble should be strongly heated in a crucible loosely covered, so that
the carbonic acid can readily escape. In the presence of carbonic
acid. carbonate of lime is not decomposed by heat, as was explained
already in p. 170.  On the large scale, lime is obtained by burning
the ordinary limestone in kilns. At the bottom is a grate on which
fuel'is laid, and the kiln then filled with limestone and fuel (calm or
small coal), mixed in suitable proportions; when the fire is lighted
on the grate, the combustion extends throughout the mass, and as
the perfectly burned lime is extracted at the bottom by the orifice
of the grate, new quantities of fuel and limestone are introduced
above, so that the combustion is continuous; the carbonic acid
evolved is completely removed by the rapid draught through the
fire.
Lime is a pure white earth.  When exposed to the air, it rapidly
absorbs water, and falls into a white powder (slacked lime), which
is a iydrate,Ca.O.. H.O. If a little water be poured on a piece of
well-burned lime, it is absorbed instantly, and the lime appears quite
dry, but after a few moments cracks, and falls into the powder of
hydrate, evolving so rmuch heat as to char wood and inflame gunpowder when in large quantities. It is thus that vessels laden with
lime have been burned at sea, by water penetrating to the hold.
Lime is soluble in water, though but sparingly, and still less soluble
in boiling than in cold water; one part of lime requiring 778 of water at 60', and 1270 at 212' for its solution; hence, when lime-water
is boiled, it becomes turbid. The solution of lime has an acrid, slightly caustic taste; it reacts alkaline; exposed to the air, it absorbs
carbonic acid, becoming covered with a crystalline pellicle of carbonate of lime.  On breathing into lime-water through a glass tube,
it is immediately rendered turbid by the carbonate of lime produced




SULPHURETS  OF  CALCIUM.                           347
by respiration; an excess of the carbonic acid, however, dissolves
tihe precipitate.  It is in this way that carbonate of lime is held dissolved in almost all ordinary spring and river waters. If lime be
perfectly dry, it has little or no tendency to absorb carbonic acid;
it requires to be first slacked, and then the hydrate is decomposed,
the water being expelled by the carbonic acid; the absorption is
very rapid until the limne becomes one half saturated, a compound
of Ca.O.. C.O,+Ca.O.. 1H.O. being probably formed, but after that
point it advances very slowly.
Lime being a protoxide, its formula is Ca.O., and its composition
and equivalent numbers are as follows:
Calcium, 71'91         One equivalent =256'0 or 20'5
Oxygen, 28'09          One equivalent =100'0 or  8'0
100'00                           356'0    28'5
Lime is easily distinguished by its dilute solutions not being precipitated by sulphuric acid or sulphate of soda, but giving a white
precipitate of oxalate of lime on the addition of a solution of oxalic
acid; an excess of oxalic acid does not redissolve this precipitate.
The nitrate of lime is deliquescent and soluble in alcohol, in which
it also differs fiom the preceding earths.  The compounds of lime,
when ignited before the blowpipe, tinge the flame of a brick-red
colour.
Lime is of great importance in the arts, from  its use in makingmortar, and in agriculture from  its application as a manure.  T'he
lime in mortar is not as carbonate, and its coherent property appears to depend only on the gradual drying of the hydrate by which
the stones are retained together, as boards are by the drying of the
glue between their surfaces.  The use of lime as a manure arises
from  its decomposing the insoluble  organic matters of the soil,
woody fibres, ulmhnine, &c., and producing other products more read.
ily taken up by the radicles of the growing plants.  It is hence on
such soils as possess a large quantity of organic matter, but are
still barren from its not being in the suitable condition, that the beneficial effects of lime are peculiarly marked.
There is a deutoxide of calcium, Ca.02, prepared by adding a solution of deutoxide
of hydrogen to lime-water; it resembles deutoxide of barium, but is of no importance.
There are three compounds of sulphur and calcium known; the first, or proton
sulphul ret of calcium, Ca.S., may be prepared by heating sulphlate of lime to redness
in a stream of hydrogen gas, or, more simply, by igniting sulphate of lime with on6
third of its weight of lampblack; all the oxygen of the salt is carried off as water
in the one, or as carbonic oxide in the other case, and the sulhur and calcium remain united. It is a white powder, but very sparingly soluble in water. It plays
an important part in the manufacture of carbonate of soda, as will be hereafter explained. When flowers of sulphur and slacked lime are boiled together in water, a
deep yellow solution is obtained, which is said to be a sulphuret of lime, but which
really consists of a mixture of' hyposulphite of lime and bisulphuret of calcium, 6S.
and 3Ca.O. producing S2021-+Ca.O. and 2Ca.S2. If the solution be concentrated, this
last separates in yellow prisms with water of crystallization. It is from this yellow
liquor that the precipitated sulphur is prepared; for, on adding to it an acid, sulphu.
ret of hydrogen is evolved from the sulphuret of calcium in such proportion as to
decompose the hydrosulphurous acid, and all the sulphur is precipitated, while the
lime remains in combination with the acid which is employed. If the sulphur be
in great excess in proportion to the lime, a pentasulphuret of calcium may be fbrmed.
The seleniuret of calcium is not important. If phosphorus in vapour be passed




348           PREP ARA TIO N" OF  M AGNE S IUM.
through a red-hot tube loosely filled with lime, a brown substance is produced, popularly termed phosphuret of lime, but which is a mixture of phosphate of' lime and
phosphmi'et of calcium; the temperature must not be raised too high, or else the
phospborus may be expelled again. When this phosphuret of calcium is brought
into contact with water, it is decomposed, phosphite of lime and phosphuretted hydrogen being produced; this last being evolved in its spontaneously inflammable
condition, it is an interesting experiment to throw a fragment of the brown substance into a glass of water; numerous gas. bubbles are immediately formed, which
explode when they reach the air, as described in p. 300.
Of J.Magnesium.
This metal, like the bases of the other earths, was first recognised by Humphrey Davy, but the process by which it is best prepared is that given by Bussy. A few pieces of potassium are to be
placed at the bottom of a tube of hard glass, and then a quantity of
anhydrous chloride of magnesium in small fragments to be laid upon
them; the part of the tube containing the earthy chloride is to be
heated to near its point of fusion, and the metal converted into vapour by the application of the lamp, as in the figure, p. 321; as
soon as the vapour of the potassium  comes into contact with the
heated salt, vivid ignition ensues, and chloride of potassium  being
formed, the magnesium  is liberated in the metallic state, Mg. Cl.
and K. giving K.C1. and Mg.  When the action has ceased and the
tube is completely cool, the mass is to be washed with warm water; the chloride of potassium dissolves, and leaves the magnesium,
with perfect metallic properties, behind.  It is white like silver, malleable and fusible at a red heat; it is not changed by dry. air, and
but slowly oxidized by damp air; it may be boiled in water without
this being decomposed.  If magnesium  be heated to redness in air
or oxygen, it burns with brilliancy, forming -magnesia,  and it inflames spontaneously in chlorine; it dissolves in dilute acids with
the evolution of hydrogen gas, and the formation of a salt of magnesia.  The symbol of magnesium  is MOg., and its equivalent number
is 158-3 or 12'7 according to the standard.
Magnesia, the only known compound of magnesium  and oxygen,
is a protoxide. It exists in considerable quantity in nature, being
a constituent of a great variety of minerals; it is found as hydrate,
as carbonate, sulphate, and silicate, but its most abundant source is
the magnesian limestone, common both in Ireland and in England,
which consists of an equivalent of each carbonate, its formula being
Ca.O..C.O2 +M.O.. C.O0.  The pure magnesia is always prepared
by exposing the carbonate of magnesia of commerce, the preparation
of which will be described among  the salts, to a full red heat; the
carbonic acid is expelled, and the earth remains pure.  Magnesia is
a very light white powder, without taste or smell; it is almost perfectly infusible; but it and lime are remarkable for becoming beautifully phosphorescent when strongly heated, and it -is hence that
lime is used as a source of the most brilliant light when it is heated
in the jet of the oxyhydrogen blowpipe. It is very sparingly solluble in water, and still less so in hot than in cold water; its solution
browns turmeric paper very slightly.  It is remarkably inferior to
lime in basic power, but still neutralizes the strongest acids perfectly, forming excellently characterized classes of salts.
The formula of magnesia is Mg.O., and its composition and equivalent numbers are,




PREPARATION  OF ALUMINUM.                    249
Magnesium, 61"29    One equivalent = 158.3 or 12'7
Oxygen,    38'81    One equivalent =100'0 or 8'0
100o00                    258'3   20)7
Magnesia is recognised by its sulphate being very soluble in water, and a solution containing it being precipitated by the alkalies
and their carbonates. The precipitate so obtained is redissolved
on adding to the liquor a strong solution of sal ammoniac. The
most delicate test for magnesia consists in rendering the liquor suspected to contain it alkaline by ammonia, and then adding a solution
of phosphate of soda; after a short time the phosphate of ammonia
and magnesia crystallizes on the side of the glass, particularly if it
be scratched by a glass rod: this double salt is almost.completely
insoluble in an alkaline liquor. A solid substance containing magnesia possesses the property, that, if it be moistened by a very small
quantity of nitrate of cobalt, and ignited strongly by the blowpipe,
it becomes a fine pink or rose colour: the presence of other bodies
may, however, interfere with this result.
The sulphurets and seleniurets of mafgnesium are of no importance; they resemble, almost perfectly, those of calcium already
noticed.
SECTION II.
METArLS OF THE SECOND CLASS.
Of Xlznminum.
This metal is prepared by the action of potassium upon its chlo.
ride, exactly as described for magnesium in the last division, but the
operation must be performed in vessels of platinum or porcelain,
as the heat spontaneously evolved during the reaction is so intense
as to fuse the most refractory glass; the quantity operated on
should likewise be small. A gray melted mass of chloride of potassium and metallic aluminum remains, which is to be washed fwith
cold water, and the metal is thus obtained in minute but brilliant
scales.
Aluminum does not decompose water at ordinary temperatures,
and only slowly even at a boiling heat, but it dissolves rapidly in
dilute acids, and also in solutions of the caustic alkalies, with the
evolution of hydrogen gas, from the water being decomposed. The.
synbol of aluminum is Al., and its equivalent numbers are 171'~ or
137, according to the scale.
There is but one compound known of aluminum and oxygen: it
is alumina. This earth exists in very large quantity in nature, being
even still more abundant than lime; it is a principal ingredient of
almost all rocks, except the purest kinds of limestone; it constitutes
the great mass of the ordinary clays and soils, these deposites being
produced by the gradual decomposition and detrition of various kinds
of rocks. In all these forms the alumina is generally combined with
silica, and sometimes with sulphuric or phosphoric acids; it is also
met with pure, or at least contaminated by the presence of only a
trace of foreign matter; thus the ruby and the sapphire, two of the
most highly prized precious stones, are alumina, combined with small




350  IPREPARATION AND P ROPERTIES OF  ALUMINA.
quantities of colouring matter. The importance of alumina in the
arts is very great; it is a necessary ingredient in the formation of all
kinds of earthenware, from tiles or bricks to the finest kinds of porcelain, and is extensively used as the basis or mordant for some of
the most brilliant and durable colours that can be fixed upon cotton
or woollen cloth. The alumina derives its name from the salt which
it forms with potash and sulphuric acid, the alum of commerce, from
whic h it is always prepared for the purposes of the chemist.
To prepare pure alumina, a solution of alum is to be decomposed by carbonate of potash, and the precipitate separated by the
filter.  This precipitate is alumina, the sulphuric acid being taken
by the potash, and the carbonic acid, which cannot combine with
the alumina, being evolved as gas. The alumina thus produced is,
however, not quite pure; it always carries dowzn with it a little sulphate of potash, from which it must be separated by being dissolved
in dilute muriatic acid, and again precipitated by carbonate of aminonia; being then well washed, until the water passes from the filter completely free from sal amnmoniac, it may be looked upon as
pure. The alumina so obtained, when dried at common temperatures, constitutes a bulky gummy mass, which is a hydrate, the earth
and the water containing equal quantities of oxygen.'o expel this
water completely, it must be exposed to a white heat; in drying it
contracts very much. It was on the measurement of this contraction that Wedgewood founded his pyreomleter, now gone out of use,
and to allow for it, all vessels of earthenware and china are made
much larger than they are intended to be when completely balled.
In consequence of the great power with which alumina absorbs
and retains moisture, it adheres strongly to the tongue, producing a
very peculiar sensation when applied to it. The more or less retentive quality of soils results fromn the sarne property, and is generally
proportional to the quantity of pure clay which they contain.
Alumina is white; if dried at moderate temperatures, it dissolves
freely in acids and in solutions of the fixed caustic alkalies, but if
it be very strongly heated, particularly if fused by the oxyhydrogen
blowpipe, it dissolves much more slowly. It is particularly remarkable for its tendency to unite with organic matters. If a cotton cloth
be immersed in a solution of acetate of alumina, the earth will deposite itself completely on the fibres of the cotton, and leave the acetic
ncid free. The most important processes in calico printing repose
upon this principle.
Although alumina is the only compound of aluminum and oxygen,
it is yet not to be considered as a protoxide' I have already deseribed, pages 213 and 223, the isomorphotus and other relations which
establish its constitution to be similar to that of peroxide of iron.
It is hence a sesquioxide, and its formula is A1,Q0. Its composition
and equivalent numbers are,
Alumina, 53-3     Two equivalents,  =34,2'4 or 27'4
Oxygen, 46-7      Three equivalents, = 300'0 or 24'0
100 0                        640'4    51%1
A.lumina is easily recognised. Its solution is precipitated by the
alkaline carbonates, and the precipitate is dissolved by the caustic




GLUCINUIM,    YTTRIUMU, THORIUM, ETC.                            351
fixed alkalies, but not by ammonia.  It is also precipitated white by
hydrosulphuret of ammonia.  If a solid substan-e containitg alumina
be moistened with a trace of nitrate of cobalt, and ignited by the
blowpipe, it becomes of a beautiful blue colour.
If alumninum be heated in tile vapour of sullphur, it takes fire, and forms a gray
mass of stulphuret of aluminium.  This is decomlposed by water, producing alumnlina
and sulphuretted hydrogen, showing that its formula was A12S3, wlic;h with 3tI.0.
give A1203 and 3-H.S.  This suIphuret, therefore, cannot be formed in solution; and
when a solution of alumina is precipitated by hydrosulphuret of ammlo.nia, as already
noticed, the precipitate is pure alumina, and the liquor contains sulphuret of hydrogen.
The seleniuret and phosphuret of aluminum are known, but are of no importance.
Of Glucinum.
The earth of which this metal is the basis has been found but in a few rare minerals, and as it exercises no influence on science from the nature of its conlpounds,
and is of no application in medicine or in the arts, a very brief notice of it will suffice.  It exists in the emerald, beryl, and euclase.  To obtain it fromn hervl, the
mineral is fused with carbonate of potash, the mass treated with dilute muriatic
acid, and evaporated to dryness to separate the silica. The portion which dissolves
then in water is to be decoinposed by ammonia, whifch precipitates the alumina and
glucina together, and the moist precipitate digested in a strong cold solution of carbonate of' ammonia, in which the glucina dissolves.  On boiling the filtered liquor
so obtained, the glucina separates in combination with carbonic acid, fiom which it
is freed by ignition, and so obtained pure.
This eartlh is tasteless and inodorous; it is insoluble in water, and has no action
on vegetable colours.  Its salts taste remarkably sweet, whence its name (y2avvv).
It is easily recognised by its relation to pure and carbonated ammonia, described in
the details of its preparation.  The metal glecirnuen is prepared from  its chlori'de
precisely as aluminum  and magnesium, which it resembles very closely in all its
properties.  Its symb-lol is G., and its eciuivalent numbers are 331-4 or 26-5.
Glucina is considered to be, like alumina, a sesquioxide, and its forrnula being
G203, its composition and equivalents may easily be calculateld.
Of Yttrium, Thorium, anrd Zirconiunz.
These metals are the bases of earths, concerning which, from the rarity of lthe
sources from which they have hitherto been derived, but little is known, and fromn
their being destitute of scientific importance as well as of practical application, short
notice of their characters only need be given.
Yttri.m. —The earthl yttria, oxide of yttrium, exists in some rare Swedish minerals, which were its only sources until the very remarkable discovery, by Apjohn,
of its presence in the ordinary Bohemian garnet or pyrope.  The methl(od of its extraction is too complicated for description here.  It is insoluble in the fixed caustic
alkalies, and is precipitated by the yellow prussiate of potasl, by which it is completely distinguished from  the other earths.  It is a protoxide.  Its formula is
ihence Y.O.
T/horiiem.-The earth thloia, oxide of thoriutm, Th.O., has been found but in two
very rare minerals.  It is the heaviest of all the earths, its sp. gr. being 9 4. It reserhbles yttria closely in its properties.
Zirconium.-The earth zirconia, scsquioxide of zirronium, Zr203, is found in two
rare minerals, tile hyacinth and zircon.  It resembles alumina very closely in all its
properties, and in some respects assimilates itself to silica, and appiears to iirmn the
link by which the metallic andl non-metallic bodies are connected in this direction.
Thus the double fluoride of zirconium  and potassium is a sparingly soluble salt, like
the fluoride of silicon and potassium, and it is fromin this double fluoride that zirconium is oibtained, by a process identical with that which is described in page 321,
for the preparation of silicon.
Cerium. Lanthanum.
These metals are found in a few rather rare minerals, antl have been buit very
recently distinguished from one another.  They are always associated together ia




352      MANG ANESE, ITS PREPARATION) FTC.
nature. Their history does not possess any particular interest, and need hence be
noticed but very briefly.
The metallic cerium is obtained by igniting the protochloride of cerium with potassium, as has been already described for other metals. It is a slightly coherent
brown powder, cwhich decomposes water slowly, evolving hydrogen, particularly if
the water be hot, and forming oxide of cerium. It combines with oxygen in two
proportions, forming a protoxide and a sesquioxide, Ce.O. and Ce203. But all the
results obtained with it now require revision, as the discovery of lanthanum has
thrown much doubt on the purity of the substances that have been hitherto analyzed
as compounds of cerium, and -on its received atomic weilght. The protoxide of
cerium is of a pale fawn colour. If it be heated in the open air, it absorbs oxygen,
and changes into the dark brown peroxide; and if this be reduced by hydrogen
gas, at a red heat, it forms a yellow complex oxide, probably Ce304.
Lanthanum.-It was found by Mosander, that by calcining protoxide of cerium
so as to convert it into peroxide, only a portion of. it became insoluble in dilute nitric acid, and that which dissolved was found, on accurate examination, to be really
an oxide of a new metal, which, not forming an insoluble peroxide, may be thus
separated fiom oxide of cerium. From its having been so long hidden in the oxide
of cerium usually made, he named it lanthanum (alvOavw), but its detailed history remains yet undeveloped.
Of Jl~anganese.
This metal exists very extensively diffused through nature, although not in very great quantity.  Traces of it are found in the animal and vegetable kingdoms, but its great sources are the numerous
combinations which it forms with oxygen, and which are employed
for the purposes of the arts and of research. Its name is a modification of magnesia, for the native peroxide was once termed magnesia nigrac; but when the peculiar metal which it contained was recognised, the present appellation was given to it.
lManganese is one of the metals most difficult to reduce, from  its
great affinity for oxygen, and the high temperature necessary for
its fusion.  To obtain it, the oxide must be taken in a state of very
fine division, and for that object it is best to use an oxide artificially
prepared,. as described farther on.  This is to be mixed with an
equal weight of lampblack, and made into a dough with oil, and this
mass fixed into a crucible, previously coated with a mixture of clay
and charcoal powder.  The crucible, so filled, being covered, is to
be exposed to the most violent heat of a smith's forge for a couple
of hours. On then examining it, a button of metallic manganese
will be found occupying its lowest portion.
The metallic manganese is grayish white, granular, and brittle;
its sp. gr. 8'013. It is exceedingly infusible. It very soon tarnishes
in the air, absorbing oxygen, and falling into a black powder after
some time. It decomposes pure water, but very slowly; but rapidly
dissolves in dilute sulphuric acid, with the evolution of hydrogen
gas, sulphate of the protoxide of manganese being formed.
The symbol of manganese is Mn., and its atomic weight is 346 or
27'7, according to the standard.
It is remarkable for the number of compounds which it forms with
oxygen, which are as follows:
Protoxide of manganese..  Mn.O.
Sesquioxide of manganese    -       MnO,.
Peroxide of manganese...          Mn.02.
Manganic acid.              Mn.O3.
Permanganic acid.....    Mn,07.




OXIDES OF MANGANESE.                    353
In addition, there are two complex oxides:
The red oxide..n..   Mn3O4, or Mn.O.+Mn2O3.
Varvicite...... Mn40,, or 1In203+-2Mn.O02.
The metallic manganese being of such difficult preparation, the
various compounds of it are usually obtained from its most abundant
source, the native peroxide, which is sent into commerce in large
quantities, to be employed in the arts for the fabrication of chlorine,
and in chemistry to prepare oxygen, and many other purposes.
The simplest way of preparing the salts of manganese from this native peroxide, which is usually associated with a large quantity of
oxide of iron, consists in dissolving it in an excess of muriatic acid,
and evaporating the liquor so obtained to dryness. The resulting
mass consists of chloride of manganese mixed with perchloride of
iron. When this mass is heated to redness, the perchloride of iron
is partly decomposed and partly volatilized, and on digesting the
residual mass in water, oxide of iron remains undissolved, and a
colourless or faintly amethystine solution of protochloride. of manganese is obtained. From this the various other preparations may
be easily formed.
Protoxide of.Manganese —Mn.O.; equivalent 446 or 357 —may
be prepared in many ways. If to a solution of protoch]oride of
manganese an excess of a caustic alkali be added, a bulky white
precipitate is produced, which is hydrated protoxide of manganese.
In this state it rapidly absorbs oxygen from the air, becoming reddish
brown, being converted into red oxide, which is the most permanent
of the oxygen compounds of manganese. If any of the higher oxides of manganese, in a state of fine division, such as the red oxide
or peroxide artificially prepared, be heated to redness in a tube of
hard glass, in a stream of hydrogen gas, oxygen is removed in such
proportion as to leave protoxide of manganese behind. The oxide
so obtained is of a greenish gray colour; it does not absorb oxygen
at all so rapidly as the hydrated oxide; but if it be exposed to the
air while hot, it rapidly becomes brown, or even burns. But it is
best obtained by mixing together chloride of manganese, carbonate
of soda, and sal ammoniac, and exposing them in a kind of platinum
crucible to a full red heat. The chloride of manganese is decomposed by the carbonate of soda, chloride of sodium and carbonate
of manganese being formed; Mn.Cl. and Na.O.. C.02 giving Na.
C1. and Mn.O.. C.O,0 The carbonic acid is, however, driven off by
the high temperature, and the protoxide of manganese set free, being
evolved in presence of the sal ammoniac, which readily yields hydrogen, is prevented from passing to a higher degree of oxidation.
The oxide obtained at this high temperature has no tendency to
combine farther with oxygen under ordinary circumstances, and
may hence be easily preserved.
The oxide is of various shades of grayish green, according to the
method of preparation. It is without action on vegetable colours,
but it combines with all the acids, evolving in some cases, as with
oil of vitriol, intense heat, and forms salts remarkable for their definiteness and neutrality. These salts are generally colourless, but
often of a peculiar rose colour, which is not due to the presence of
v i




3;00-  SESQ U IOXIDE AND PEROXIDE OF MIANGANESL.
any higher degree of oxidation, but to a peculiar (isomeric) condition of the salt itself.
Sesquioxide of AJianganese. —Mn203. Equivalent 992 or 79'4. This
oxide is found in nature in considerable quantity, either pure, as in
the mineral braunite, or combined with water, as in the mineral manganite. It may be prepared artificially by exposing the peroxide for
a short time to a dull red heat, but it is difficult to manage the decomposition of that substance so that it shall not proceed too.ar.
The sesquioxide is of a dark browna colour; exposed to a strong
heat it is partly decomposed, evolving oxygen, and being reduced
to the state of red oxide. It combines with acids, forming salts
which are of a deep red colour, and which are isomorphous nwith
those of alumina. Its salts are immediately decolorized by sulphurous acid and by sulphuretted hydrogen. This oxide possesses the
property of staining glass purple or violet, and by this character an
exceedingly small trace of manganese can be detected by fusing the
substance with borax in the oxidating flame of the blowpipe.
Peroxide of JManganese, 07' Black Oxide. —TMn.02. Equivalent 546
or 443.7. This substance, which is the most abundant source of
manganese, and that from which all its technical applications are
derived, exists in nature in a variety of forms. Crystallized and pure,
it forms the mineralpyrolusite; combined with water, 2iMn.02-~-H.
0., it constitutes the mineral Wadd, which,in an impure form, contaminated with variable quantities of peroxide of iron, carbonate of
lime, and carbonate of barytes, forms the earthy varieties, which are
those usually found in commerce. This oxide may be prepared artificially by decomposing the protochloride of manganese by a solution of chloride of lime, Mn.Cl. and 2Ca.O.:+C1. producing 2Ca.Cl.
and Mn.02. It is also produced when permanganate of potash is decomposed by any organic substance. In these cases it is precipitated in combination with one equivalent of water, Mn.O2+ H.O., from
which it may be freed by a temperature below redness.
This peroxide of manganese is black; exposed to heat, it abandons
oxygen, being reduced first to the state of sesquioxide, and finally
to that of red oxide. It does not unite with either acids or alkalies;
but, when heated with strong sulphuric acid, it is decomposed in the
manner fully described under the head of oxygen, in page 244. Its
use in the preparation of chlorine has been also noticed, page 301.
An important object to which it is applied is to peroxidize the iron
contained in the ordinary materials used in the manufacture of glass.
If the iron were as protoxide, it would colour the glass green; but the
red oxide produces only a very faint yellowish tinge; and as the
protoxide of manganese is itself destitute of colouring power, by the
action of Mn.0, on 2Fe.O. there are formed Mn.O. and Fe2O3, two
substances which have no injurious effect upon the glass; if, however, the peroxide of manganese be added in excess, a purple colour
is produced.
Of the complex oxides, the red oxide is alone of interest. It is
the most stable of the compounds of manganese; and whenever the
quantity of this metal present in a substance is to be determined by
analysis, -it is always as the red oxide that it is obtained. A solution
of any salt of manganese, being precipitated by an excess of a caus.




ANALYSJS  OF  PEROXIDE  OF  MANGANESE.  355
tie alkali, the precipitate, cautiously washed and ignited in an open
crucible, gives the quantity of red oxide corresponding to the quantity of manganese present. The varvacite, the other complex oxide,
is a mineral of rare occurrence, and only of interest as it may be
mistaken for the peroxide, to which it is inferior in technical value.
The peroxide of manganese found in commerce is never quite pure; and as its
use in the arts, and, consequently, its price, are, generally speaking, due exclusively
to the quantity of oxygen it is capable of yielding, a ready mode of effecting its analysis becomes of great importance.  There are two modes in which this may be accomplished upon very simple principles, and in a short time, with sufficient accuracy for all practical purposes. The first consists in converting oxalic acid into
carbonic acid, by means of the second atom of oxygen which the peroxide of manganese contains; for MIu.02 and C203 produce Mn.O. and 20..02. For this purpose
100 grains of the manganese are to be introduced into a weighed flask, and 150
grains of oxalic acid, dissolved in 500 grains of water, are to be then poured upon
it; to this 350 grains of oil of vitriol are to be added, and the orifice of the flask
closed by a cork, through which passes a tube containing fragments of recently-fused
chloride of calcium. The weight of this cork and tube are to be included in the tare
of the flask. On the addition of the oil of vitriol, a brisk effervescence takes place,
owing to the escape of carbonic acid gas, which, passing over the fragments of
chloride of calcium in the tube, are dried, so that the gas alone passes off. When
the action slackens, a gentle heat may be applied until all the oxide of manganese
has dissolved; a small quantity of a light brownish sediment, which generally forms,
is easily distinguished from the particles of black oxide: as soon as the action is
quite over, the flask is suffered to cool, and as it contains still a quantity of carbonic
acid gas, this is removed by taking out the cork, and blowing air into the flask
gently by a glass tube; the cork is then to be replaced, and the flask, wvith its contents, weighed. It is found to be lighter than it and the materials together had
been, and the loss is the carbonic acid. The quantity of carbonic acid formed is
thus found, and the quantity of oxygen it contained calculated; one fourth of
this had been derived from the peroxide of manganese by its conversion into protoxide, which remains combined with sulphuric acid in the liquor, and the quantity
of peroxide in the 100 grains of the ore is thus directly found. Thus, talking as
an example an actual determination, the flask and materials weighed altogether
1876 grainls; after the action had terminated it weighed 1816'5 grains; the loss
was, therefore, 59 5. This consisted of 16 3 of carbon and 43'2 of oxygen. The
oxygen derived from  the mineral was, therefore, 4i3-210'8, which represent 59
grains of pure peroxide of manganese in the 100 of the substance used.
The second mode of analysis consists in treating a certain quantity of the native
oxide with an excess of muriatic acid. and passing the chlorine so evolved through
-water in which lime is diffused; chloride of lime is formed. A certain quantity of
protosulpliate of iron (green copperas) is to be dissolved in water, and the solution
of chloride of lime added thereto, until the iron liquor ceases to strike a blue colour
with a drop of solution of red prussiate of potash; then comparing the quantity of
the solution of chloride of lime required with the quantity that was produced, the
total quantity of chlorine generated, and, hence, the total quantity of oxygen available in the mineral, are known. The theory of the process may be still more simrply
expressed by the formulm of the bodies engaged, as follows: Mn.02 and 2H.C1.,
acting together, produce Mn. C1. and 2H.O., while C1. is given off as gas;* this combines
with Ca.O. When the compound Ca.O.CI. is brought in contact with 2(Fe.O.. S.O3),
the oxygen passing from the lime to the iron, we have Ca.CI. and Fe2 03. 2S.O3 produced. As long as any protosulphate of iron exists, the solution gives Prussian
blue with the red prussiate of potash; but iwhen all the iron is changed to peroxide,
the blue colour is no longer produced. The following example of an actual operation will complete this explanation. 100 grains of commercial oxide of manganese
were placed in a flask with about one ounce of strong spirits of salt, and the chlorine evolved was conducted by a bent tube to the bottom of a deep jar containing!600 grains of walter with 100 grains of slacked lime; when the oxide of manga.
nese had been completely decomposed by the muriatic acid, and all evolution of
chlorine had ceased, a quantity of the solution of chloride of lime was filtered for
use; this being very strong, 500 grains of it were diluted with 1000 of water. On
the other hand, 100 of crystallized protosulphate of iron were dissolved in 1000
grains of water, and the dilute solution of chloride of lime added thereto by drons




356   MANGANIC AND PERMANGANIC ACIDS.
from an accurately graduated tube, until, by the test of red prussiate of potash, ace
the iron was peroxidized. It required 1300 grains of the dilute solution, and hence
433 of the strong solution. Now, as 100 grains of the mineral had given 1600
grains of this strong solution, the 433 grains corresponded to 27 grains; the available oxygen of which was exactly equivalent to transfer the iron of the protosulphate to the state of peroxide. Now the 100 grains contain 45'6 of water, 28'9 of
acid, and 25'5 of protoxide of iron, consisting of 19'7 of iron and 5 8 of oxygen, and
it requires one half more, that is, 2'9, to form peroxide. The result is, that in the
27 grains of commercial oxide of manganese, the available oxygen is 2'9, and the
quantity of pure peroxide consequently 15'8 grains, or 58-7 per cent. This whole
process, although, when thus described in detail, it may appear complex, is exceedingly simple in execution., and does not occupy much time. In accuracy, the two
methods are about equal, giving results which may be depended on to one per cent.
A mode has been recommended, which consists in simply adding the green sulphate of iron directly to the muriatic acid and oxide of manganese in the flask, until
the salt is found to be slightly in excess by the filtered liquor giving Prussian blue
with red prussiate of potash; the quantity of green copperas added is known by
having previously weighed out a quantity, and then weighing what may remain
after the process has been completed. If no chlorine could escape the action of the
iron salt, this method would be much the shortest and simplest that could be employed; but it is exceedingly difficult so to manage the decomposition as to avoid
its partial loss. On this account, I look upon this method as inferior in accuracy,
and really not much simpler of execution, than those previously described.
The composition of the commercial oxide is very variable, but the general limits
may be considered as being between 60 and 70 per cent. of pure peroxide in 100.
Frequently, the commercial substance contains sesquioxide, or one of the complex
oxides; but in all these cases, the methods given, as they determine the quantity of
available oxygen, show the true value of the specimen, rio matter what the state of
combination of the metal may be.
Mangananic  dcid. —I  n.O.  Equivalent 646 or 51,7.  If peroxide
of manganese be mixed with caustic potash, or carbonate or nitrate
of potash, in a crucible, and ignited strongly, a green fused mass is
obtained, which dissolves in a small quantity of water with a fine
grass-green colour.  After some time, particularly if the solution
be  diluted, it gradually changes colour, a brown precipitate separates, and the liquor becomes of a splendid red colour.  This substance first got the name of mineral chameleon, from  these changes,
but their production is now known to depend on the formation of
two distinct acids of manganese.  The peroxide of manganese in
these cases combines with another atom  of oxygen to form  manganic acid, which unites with the potash.  If potash, caustic or carbonated, be used, the oxygen is derived from the air; if nitre, it supplies oxygen; but the best source consists in mixing four parts of
peroxide of manganese in fine powder with 3~ parts of chlorate of
potash, and adding thereto five parts of caustic potash dissolved in
a small quantity of water.  This mixture is to be evaporated to dryness, powdered, and afterward ignited in a platinum  crucible, at a
low red heat insufficient for fusion. By digestion of this mass in
cold water, a deep green solution is obtained, from  which, by evaporation in vacuo, the manganate of potash is obtained in crystals.
The salts of this acid are isomorphous with those of the sulphuric
and chromic acids. They are decomposed very easily, particularly
if organic matter be present, and the acid itself is hence incapable
of being exhibited in an isolated form.
Permanganic dcid. —MnO7.  Equivalent 1392 or 111.4.  When a
solution of manganate of potash is diluted with boiling water, a copious precipitate of hydrated peroxide of manganese forms, and a




DETEC!TION OF MANGANESE.- IRON.                  357
fine crimson solution of permanganate of potash is obtained.
3Mn.03 produces Mn.02 and Mn20,. By rapidly evaporating this
solution until a pellicle forms, an abundant crop of crystals of permanganate of potash is obtained on cooling: these are isomorphous
with the perchlorate of potash, and are almost completely black,
but with a very peculiar bronze lustre. The salts of this acid are
very stable, and by treating the permanganate of barytes with a
proper quantity of dilute sulphuric acid, a deep crimson solution of
permanganic acid is obtained. This acid cannot be had solid, according to Mitscherlich, its solution when heated to 1000 F. being
decomposed into peroxide of manganese and oxygen gas.  It is
very probable that the solid substance described as dry permanganic acid by some chemists contained some other matter combined
with it.
The formation of these acids by the action of sulphuric acid on
peroxide of manganese has been already noticed, and the most
delicate test of the presence of manganese in minerals consists in
fusing a fragment.of the substance with a little carbonate of soda
on a slip of platina foil, by means of the oxidizing flame of the blowpip,  A'!.lc tmass, on cooling, becomes apple-green, from the formation i:; -i":: nate of soda, if there be the smallest trace of manganese in the i:t'stance used.
There ji but one sulpiluret of manganese. It is found as a mineral, and ti':rned also by heating oxide of manganese and sulphur
(page 285). It is precipitated in a hydrated state, when a solution
of manganese is decomposed by hydrosulphuret of ammonia. Its
colour is then ficsh red. Its formula is Mn.S.
The detection of ranganese is very simple. When in a solid
form, its compounds are recognised by giving before the blowpipe a
purple glass with borax, and a green bead with carbonate of soda.
In solution, if the manganese be as protoxide, the solution is colb
ourless, and yields with the caustic alkalies a white precipitate (Min.
O.), rapidly becoming brown (Mn304): with the alkaline carbonates,
a white precipitate, Mn.0.. C.O0; and with hydrosulphuret of ammonia, a flesh red hydrated sulphuret. The yellow prussiate of potash precipitates the salts of manganese pure white, if there be no
trace of iron present. When the manganese is not in the state of
protoxide, the solution is always coloured red or green. These solations are decolorized by sulphurous acid and by sulphuretted hydrogen, which absorbs oxygen from all the higher degrees of oxidation, and a colourless solution of protoxide is then obtained, which
gives the reactions already described.
SECTION III.
DIETALS OF THE TIIRD CLASS.
Of Iron.
this is the most extensively distributed, and also the most important of the metals; it may, indeed, be considered as being, after
those elements necessary to the functions of animal existence, that
which is most indispensable to man for the wants of ordinary life.
")n its employment and applications is founded every important




358          STATE  OF iRON  IN NATURE.
step which marks the gradual progress of the human race friom bar
barism to civilization. The difficulties which its reduction from the
state of ore present, the variety of conditions necessary for its being
successfully wrought into useful forms, and the pre-eminent advantage it possesses over every other metal for the construction equally
of the simplest tool and the most complex machine, for the implements of war as well as peace, all combine to excite the energies
of a people to its acquisition, whether by their own labour or by
commerce; and thus impel them to mental activity and civilization,
either of native and independent growth, or borrowed from more
advanced neighbours. As gold and jewels hence become the type
of ignorant and barbaric pomp, so iron may be regarded as the greatest material source of national intelligence and industry.
Iron exists in nature under a variety of forms; it is found native;
for, in addition to loose blocks of metallic iron found on the surface
in various countries, and to which a different nature may be assigned,
it is found in veins, in mines, in Russia and America. Its most
abundant form is that of oxide, either pure, forming the various
black and magnetic oxides, the hibematite, or red oxide, &c., or combined with carbonic acid, constituting the clay iron stone from which
the iron of commerce is principally extracted. Its sulphurets are
also found in abundance, and native arseniates, phosphates, sulphates,
and other salts have been found.
A most remarkable source of iron is one not truly terrestrial, but
that, occasionally, masses appear in our atmosphere at great heights
above the surface, and presenting all the appearances of vivid ignition and combustion; they move generally with great velocity obliquely towards the ground, and generally, before touching, or at the
moment of contact with the surface, burst with an explosion, scattering their fragments to considerable distances. These masses are
termed cerolithes; they consist, in general, of an alloy of iron, with
some nickel and chrome, with traces of other metals, and are generally
invested with a vitreous glaze of earthy matter, which is constituted
of minerals (olivine and pyroxene) found native in volcanic rocks.
The only theory which can explain the origin of these meteors is,
that they are expelled violently from the active volcanoes which
telescopic research has proved to exist in great numbers on the surface of the moon, and that, passing beyond the limits of the attraction of our satellite, they come under the influence of this earth, and
fall towards its surface. No such substances are ever found pro.
jected from terrestrial volcanoes.
The general principles of the smelting of the clay iron stone
have been already noticed (p. 334), both considering it as a mere carbonate of iron, and where it contains clay, silica, and alumina, so
as to render lime necessary as a flux. It is, however, a remarlrable
property of iron-one on which rests, perhaps, its most useful applications-that the metal so obtained is not pure. The iron, when
reduced, combines with a quantity of carbon, generally about five
per cent.:, approximating to the formula C.+4Fe., and forming cast
iron, which is easily ftusible, while the pure metal is almost quite
infusible.'The cast iron is, however, not by any means a pure carburet of iron; it contains small quantities of silicon and phosphorus,




PREPARATION  OF MALLEABLE  IRON.    359
according to the proportions of which it varies in properties, so as
to constitute a number of varieties, known in the arts by their colour and texture, but of which it would be superfluous to speak here.
When cast iron remains under water for a considerable time, it becomes gradually oxidized,,magnetic oxide of iron being formed,
and the carbon remaining under the form of a spongy mass, preserving, even in minute details, the figure of the original mass.
Cast iron has a great tendency to crystallize in becoming solid,
and then expands powerfully; hence its property of filling up the
most minute crevices of moulds into which it is poured in the liquid state, and its multifarious uses for making castings, from
whence it derives its name.
Pure or malleable iron is made from cast iron by taking advantage
of the fact that, though iron and carbon are both combustible, yet
carbon is the more so of the two. Hence, if cast iron be melted in
a reverberatory furnace (see p. 333), and exposed to a current of
air, the carbon is gradually burned out, the metal becomes less and
less fusible, and ultimately bieaks up into an incoherent granular
mass like sand; by then increasing the heat, these grains agglutinate, and are wvorked up into a ball about the size of a large loaf,
which is taken out of the furnace on a shovel, and subjected to
great pressure by machinery. The soft, pasty particles of malleable
iron are thus welded to each other, and any portions of liquid, unaltered cast iron that might remain are squirted out, as water
would be by pressure from the pores of a sponge; this lump of
malleable iron is then passed through a succession of rollers, driven
by powerful steam engines; each pair of rollers having a smaller interval than the preceding, the mass is gradually elongated into a
bar, and finally is delivered, at the end farthest from the furnace, in
the form of the soft bar iron of commerce. The heat evolved by
the enormous pressure to which the metal is subjected in this process is so great, that the bar remains soft enough to be moulded
by the rollers all through its passage.
This process by the reverberatory furnace is termed _pudling, and
has been very much improved lately by burning out the carbon by
means of a certain quantity of oxide of iron or oxide of manganese.
Thus, by heating together two parts of cast iron and one of scales
of black oxide of iron from a forge, all the carbon and oxygen pass
off as carbonic acid, and the iron of both remains pure. Fe3O4 and
FeC2, produce Fe,, and CO,.
The bar iron thus obtained differs remarkably from the cast iron
in all characters: it is soft, flexible, ductile, and malleable, none of
which properties cast iron possesses. It fuses only at the very
highest temperatures, and then becomes only semifluid. It is, consequently, quite impossible to run it into moulds. It possesses,
however, the important character of welding at a white heat; that
is to say, it assumes a doughy consistence, so that several pieces
of it, laid together, may be kneaded into one by blows of a hammer
or by pressure between rollers, so as to form a single mass, the
points of junction being totally undistinguishable. It is thus that
soft iron is always worked at a white heat. Its strength is much
increased by several pieces being thus welded together, and'hence




360            MAN'UFACTURE  OF  STEEL.
all parts which require to possess peculiar tenacity, such as anchors,
&c., are always made, not in a single piece, but by thus welding to
gether a bundle of small bars.
-A third and equally important form in which iron exists in the
arts, is that of steel. Steel is intermediate to cast iron and bar iron
in constitution, containing generally about 1-5 per cent. of carbon.
Steel may be formed directly from the ore or from cast iron by proportioning the action of the fuel and of the air in the furnaces so as
to leave combined with the iron as much carbon as constitutes steel.
But the most important and curious mode of making steel is by what
is termed cementation. Bars of iron are laid in boxes, imbedded in
powdered charcoal, and exposed for some hours to a full red heat;
the carbon gradually penetrates through the whole substance of the
iron, changing it into a bar of steel of pretty uniform structure.
The bar becomes frequently blistered from gas bubbles forming in
its substance. This process can be effected even though the carbon may not directly touch the iron, provided oxygen be present;
carbonic oxide being formed, which is decomposed by the iron, half
the carbon being absorbed, and carbonic acid given off. It is the escape of this last gas under the form of bubbles that produces the
blistering of steel. The decomposition of the carbonic oxide takes
place at the surface of the bar in great part, but the carbon is transferred from particle to particle of the iron until the entire mass assumnes the same constitution.  Steel is harder and more fusible than
pure iron, but its peculiar hardness is given to it only when it has
been heated to redness and suddenly cocled; it is then exceedingly
brittle, hard, and elastic, and is thus fitted for its extensive use in
cutting instruments, pivots, files, &c. The steel, when it has cooled
slowly, is -so soft that it is easily engraved upon, cut, and may be
welded with soft iron; the instrument being so constructed, it is
heated to redness and suddenly cooled; it is thus hardened, but is
still unfit for being employed until it is tempered to the particular
use for which it is destined by being heated in oil to a certain degree, and then allowed to cool slowly. By this means the excess
of hardness is got rid of, and the steel remains of the quality required.
The peculiar property of iron and steel of becoming magnetic,
has been described in page 143. Not only is iron in the pure
state, and when combined with carbon, attracted by the magnet,
but several of its oxides and sulphurets possess the same character; of these, one constitutes, indeed, the natural magnet, the native
loadstone.
Pure iron is bluish white, exceedingly brilliant, very malleable
and ductile; it is the strongest of all the metals. Its specific grav.
ity is 7-8. It becomes pasty when intensely heated, whence its re.
markable power of welding, which belongs, besides, to platinum and
sodium.
When iron in mass is exposed to dry air, it does not become ox.
idized; but when in a state of very minute division, it takes fire
when gently warmed, and burns, forming peroxide of iron; when
strongly heated in oxygen gas, as by attaching a little sulphur or a
bit offtaper wick to a wire, and plunging it into a vessel of oxygen,




PASSIVE  CONDITION  OF IRON.                  3G61
it burns with exceeding brilliancy, and forms globules of black ox.
ide of iron, FcO,. The true product of the combustion is peroxide,
FecO3, but this loses one ninth of its oxygen by the intense temperature, and forms the black magnetic oxide. It is hence that, when
iron is burned in oxygen gas, the oxide, which is thrown off in minute grains, collects on the inside of the jar as peroxide, but the larger globules, which are intensely heated for some time before they
melt off the wire, are reduced to the state of black oxide. It is not
quite certain whether iron decomposes water in the absence of an
acid, but the presence of a small quantity even of carbonic acid produces decided action, and hence the rapid corrosion of iron in damp
air, forming carbonate of iron (rust). In dilute sulphuric acid iron
dissolves with great rapidity, evolving hydrogen, which, however,
is very impure, for even the softest iron contains traces of carbon,
which combines with some of the hydrogen, forming compounds,
which give the gas a peculiar odour, and colour its flame yellow
At a red heat water is decomposed rapidly by iron, as fully described in p.'4,6. If iron be immersed in water holding potash, lime,
or soda in solution, or if the iron be covered up in quicklime, all
rusting is prevented, probably from any carbonic acid present being
totally taken up by the base.
A remarkable property of iron, though not absolutely peculiar to
it alone, is, that when placed in contact with the hydrated nitric acid,
sp. gr. 1i35, it may remain unacted on, becoming )assive; although,
under ordinary circumstances, it is rapidly dissolved by that acid
with evolution of nitric oxide. This passive condition may be produced in many ways.  1st. If one end of a long iron wire be ignited, and then, when cool, the wire be immersed in the acid, the ignited end being dipped first, it remains unaltered. 12d. If a piece
of platina wire be fastened to a piece of iron wire, and then immersed in the acid, the platina first.  3d. By placing a platina wire in
the acid, then immersing an iron wire in contact with it, the platina
wire may be withdrawn, and the iron wire remain passive. 4th. By
making the iron wire the positive pole of a galvanic battery. 5th.
By contact with a wire already passive; thus, an iron wire being
immersed in the acid, as-in No. 3, another wire may be put in contact with it, and the first then withdrawn, and so on for an unlimited
succession of wires. These are not the only methods, but merely
the most remarkable.
The properties of iron thus rendered passive are curious. It ap.
pears to have lost all tendency to unite with oxygen; it does not
dissolve in acids; it does not precipitate copper from its solutions;
and when used as a positive electrode for a voltaic battery, oxygen
is evolved from it precisely as if the electrode had been platinum.
We do not as yet know the true theory of these effects.  The most
available explanation is, that the iron, by an alteration of molecular
structure, assumes a condition by which it becomes similar in its
electrical relations to the noble metals. It is possible that this
property may be connected with the equivalency of two equivalents
of tlhe iron and manganese group of metals to one of chlorine, and
that when, by a change of molecular arrangement, like isomerism,
Zz




362            VARIOUS. OXIDES OF  IRON.
the particle becomes Fe2 in place of Fe., it is incapable of acting as
the positive element in galvanic or chemical combinations.
The equivalent of iron is not so accurately known as those of
metals much less important and less common. The best determinations make it about 339 upon the oxygen, and 27'2 upon the hydrogen scale. Its symbol is Fe., from its Latin name.
Oxides of Iron.-Iron- combines with oxygen in two proportions,
forming a protoxide and a sesquioxide, and these, again, unite to form
complex oxides, the black or magnetic oxides of iron.
Protoxide of Iron.-Fe.O.  Equivalent 4139 or 35'2. This oxide
cannot be obtained pure in a dry state, from the rapidity waith which
it absorbs oxygen~ It exists as the basis of a very extensive class
of salts, the green or protosalts of iron. From their solutions, it is
precipitated by an alkali as a white hydrate, which rapidly becomes
green, and finally brown-red, from absorption of oxygen. If we attempt to form the protoxide by processes similar to those described
for obtaining protoxide of manganese, the iron is reduced either to
black oxide or to the metallic state. This oxide exists native, combined with carbonic acid, in the common carbonate of iron, and is the
form in which the metal exists, dissolved in all chalybeate springs.
Peroxide of Iron.-Fe203. Equivalent 978 or 78'4. This substance
exists in very great abundance in nature, crystallized in rhombohedrons, being isomorphous with the crystallized alumina, corundum.
This, the ologist iron, constitutes the celebrated Elba iron ore. It
forms, in a more or less hydrated condition, the hemnatite, of various
shades of red and brown, from which a great deal of the best iron
and steel is made. It exists in a variety of minerals, and forms the
red or yellow colouring matter of clay. and of the different kinds of
o chres. I have noticed that when iron is burned in a full supply of
oxygen, this red oxide is formed, and it is produced also when iron
rusts, for the protocarbonate which first forms is gradually decomposed, abandoning its acid, and absorbing oxygen. It is thus that
the margins of chalybeate springs become coated with an ochrey
deposite; the carbonate of iron originally dissolved being gradually
converted into red oxide, while the carbonic acid passes off.
The peroxide of iron may be artificially prepared by precipitating
a solution of any of its salts with an alkali caustic or carbonated.
In the latter case, the carbonic acid is given off, as the peroxide of
iron does not combine with it. The hydrated peroxide which is
precipitated is of a light reddish-brown colour, but when dried it
becomes dark brown. Strongly ignited, it becomes nearly black;
and, indeed, by an intense heat it loses some of its oxygen, 3(Fe,0,)
giving 2(Fe3O4), and 0. escaping, being decomposed just as the sesquioxide of manganese, but requiring much greater heat. The peroxide of iron combines with acids to form salts, which are all acid,
and easily decomposed.  They will be described hereafter. Its
chemical combinations resemble those of alumina and sesquioxide
of manganese, with which they are isomorphous.
When a solution of a protosalt of iron is exposed to the air, it
gradually absorbs oxygen until two thirds of the iron become peroxidized, and then the decomposition ceases. The liquor then contains a compound oxide, Fe.O0. +-FeO,, and on the addition of a caus



S-U L P IUETS OF IRON.                     363
tic alkali this is precipitated as a black powder, which, when dry, is
powerfully attracted by the magnet. This is the artificial magnetic
oxide of iron. It may be prepared at will by ta,:ing three equal
portions of protosulphate of iron, and peroxidizing two of them by
mneans of a little boiling nitric acid, then mixing the solutions, and
precipitating the whole by water of caustic ammonia.  The precipitate is a hydrate, but may be deprived of the water without alteration.
This magnetic oxide of iron exists native in great abundance; it
constitutes the common loadstone, and is that produced when iron
is oxidized at high temperatures.  It thus constitutes the scales of
iron which form in smithies and forges during the successive heatings and hammerings to which the metal is subjected.  These scales
of iron are, however, not uniform in constitution, and are hence inferior as a steady medicinal agent to the oxide artificially prepared
by precipitation.
Sulphurets of Iron.-Sulphur combines with iron in three proportions, forming the protosulphuret, the sesquisulphuret, and the bisulphuret.  These again combine, so as to produce complex (magnetic) sulphurets.  Other degrees (subsulphurets) are problematical.
Protosulphuuret of Iron.-Fe.S.  Equivalent 54104 or 4.3'3. The affinity of iron for sulphur is very remarkable.  If a rod of iron be
heated to whiteness, and then touched to a stick of sulphur, they
combine with energy, and the sulphuret of iron flows down in copious drops. If vapour of sulphur be made to gush from a jet, and
an iron wire heated to bright redness be placed in it, it takes fire,
and burns with scintillations as brilliantly as if it had been immersed
in oxygen gas. In these cases, where the iron is in excess, the protosulphuret is formed. It is most conveniently prepared by heating
together to bright redness, in a crucible, three parts of iron filings
or turnings, and two of sulphur; at a high temperature the resulting
mass may be fused.  This compound is black, its fracture yellowish.
It dissolves in dilute acids, evolving sulphuret of hydrogen, and forming a salt of protoxide.of iron.'This is almost its only use in the.
laboratory.  The manner of obtaining sulphuret of hydrogen from
it has been described in page 292. This protosulphuret of iron exists sometimes, though rarely, in nature, and is- dangerous, particularly in coal mines, from the avidity with which, when moist, it absorbs oxygen, forming protosulphate of iron, Fe.S. and 40. giving
Fe.O.. S.0,; during which process it occasionally becomes so heated as to set fire to the beds of coal near it, and thus cause considerable loss.
This sulphuret may be prepared in the moist way by adding hydrosulphuret of ammonia to a protcsalt of iron.  Thus Fe.C]. and
8.H.+N.H3 produce Fe.S. and C!.H.+N.H3.  It is a jet black powder, which dissolves readily in acids, and when exposed moist to
the air, rapidly absorbs oxygen, forming green copperas.
Sesquisulphuret of Iron.-Fe,S3. Equivalent 1282 or 102'7. This
compound, which corresponds to the peroxide, is very instable in
constitution.  It may be prepared in the moist way by adding to a
persalt of iron in solution, hydrosulphuret of ammonia. A black
precipitate forms, which may be dried in vacuo. It may be also




364              SULPHURETS OF IRON.
produced by heating peroxide of iron in a current of sulphur6otted
hydrogen gas, water being formed. It is not attracted by the magnet. It dissolves in acids, but-one third of the sulphur is precipita.
ted, two thirds only combining with hydrogen, and the iron existing
in solution as a protosalt. Thus Fe2S3 and 2H.Cl. give 2(Fe.CI.)
and 2H.S. with deposition of S. This arises from the circumstance
that peroxide of iron is reduced by sulphuretted hydrogen to protoxide, water being formed, and sulphur set free.
Bisulyhuret of Iron. - Fe.S2.  Equivalent 741'5 or 59'4. This
substance is met with in very large quantity in nature, constituting
the iron pyrites used in the manufacture of sulphuric acid'and of
copperas. It is dimorphous (pages 229-232), and in its two forms
possesses very different properties. It may be prepared artificially
by heating together the protosulphuret in a state of minute division,
with half its weight of sulphur. When the excess of sulphur has
been distilled off, there remains a voluminous yellow powder, not
acted on by the magnet, and insoluble in acids, which is the bisulphuret of iron. This bisulphuret of iron is found in a variety of
forms, which belong properly to the different kinds of native oxides
of iron, which being probably acted on by vapour of sulphur from
volcanic sources, have lost their oxygen, and, without being melted,
have changed into bisulphuret. It is also found simulating the figures of a variety of organic remains, as nautili, &c., where, probably, the animal having perished in w-ater holding traces of sulphate
of iron in solution, the hydrogen compounds evolved by its decomposition have reacted on the sulphate of iron, abstracting its oxygen
and producing a deposite of pyrites..MJlagnetic Sulphurets of Iron.-Of these the most remarkable is that
which corresponds to the magnetic oxide, having the formula Fe3
04-zFe.S.+Fe2S3. It is found native at Barege, and may be formed
by exposing to a red heat, in close vessels, the bisulphuret or sesquisulphuret: the pyrites 3(Fe.S2) producing FeS4 and S,, precisely
as peroxide of manganese 3(MIn 0,) produces 02 and MnO04. If,
however, the heat be raised too high, more sulphur is expelled, and
another kind of magnetic sulphuret, Fe,S= 5lFe.S.+Fe2S2, formed,
which is also found native, and which corresponds to the black
scales of oxide of iron, which are 5Fe.O.+Fe203.  This compound
is always formed in making the protosulphuret, if there be an excess
of sulphur above the proper proportion used.
The seleniuret and phosphurets of iron resemble very closely the
sulphurets. Phosphuret of iron exists generally in cast iron in small
quantity.
The detection of iron is very simple. It may exist in solution in
the state either of protoxide, black oxide, or peroxide; and as the
application of reagents becomes much simpler in the last case, it is
best, when the object is only to ascertain the presence or absence
of iron, to boil the solution with a few drops of nitric acid, by which
any iron that may be present is peroxidized.
A solution containing peroxide of iron produces with water of
ammonia a reddish-brown precipitate of hydrated peroxide; with
yellow prussiate of potash, a fine Prussian blue; with sulphocyan.
ide of potassium, a deep blood-red colour, but no precipitate; with




1'RE P.ARATION  OF  NICKEL.                        3G6
a solution of tannin or tincture of galls, a deep violet or black.
With sulphuret of hydrogen there is no effect except the separation
of a deposite of pure sulphur, but with hydrosulphuret of ammonia
a black precipitate of sesquisulphuret of iron.
If the solution contain the iron only as protoxide, ammonia pro
duces a precipitate, at first whitish, but rapidly becoming bluish.
green.  The yellow prussiate of potash, a precipitate, at first white,
but rapidly becoming blue.  The sulphocyanide of potassium, the
tannin, and the sulphuret of hydrogen are without effect, but the hydrosulphuret of ammonia forms the black protosulphuret.  The characteristic reagent for protoxide of iron is the red prussiate of potash, which gives Prussian blue, but does not act upon the solution
of peroxide.
If the solution contain at the same time both oxides, the precipitate by ammonia is, from the commencement, green or black, and
all the other reagents concur in the demonstration of the presence
of the two states of oxidation of the metal.
Of JVickel.
An ore which, from its external characters, was supposed by the
German miners to contain copper, but resisted all endeavours to
extract that metal from it, received the name of kupfer-nickel, or deceitful copper.  Subsequently it was found to consist of a peculiar
metal united to arsenic, and this metal retained the name nickel, its
meaning being forgotten or lost sight of.  A  substance found in
commerce, termed sjpeiss, a residue from the manufacture of smalts,
is also an arseniuret of nickel, and from either of these sources the
metal is generally extracted.
The mass containing nickel and arsenic is dissolved by a mixture of nitric acid
and sulphuric acid, diluted with water. By this means the nickel is converted into
sulphate of its oxide, and the arsenic into arsenious acid. On concentrating the liquor, most of the latter is got rid of by crystallization. Carbonate of potash is then
to be added to the liquor, until the green precipitate which first forms ceases to be
redissolved. On then evaporating and cooling, a double sulphate of nickel and potash is obtained, which, by two or three recrystallizations, is freed from all traces
of arsenic. This double salt may, however, be contaminated by iron and copper;
from the first it is separated by sulphuretted hydrogen, and from the last by the
solubility of the oxide of nickel in water of ammonia. From the ammoniacal solution, the oxide of nickel may be precipitated by oxalic acid, as an insoluble oxalate, which, when dried and heated, gives off carbonic acid, and leaves metallic
nickel, Ni.O.+C,03, producing 2C.0, and Ni. The metallic nickel is then in the
form of a very light sponge.
It is somewhat more fusible than cast iron; of a silvery white
colour. It does not rust when exposed even to damp air. Its sp.
gr. is about 8'5. it is nearly as magnetic as iron, and retains its magnetism, resembling in that respect steel rather than pure iron. In
its permanency of lustre, nickel resembles the precious metals, and
its alloys are of singular brilliancy and whiteness.  It is hence that,
added to brass in the proportion of one to five, it is employed as a
substitute for silver, constituting the German silver, nickel silver,
argentine, and British plate of commerce, as well as. the packfong
long used in China.
The symbol of nickel is Ni.; its equivalent 369'7 or 29'6.
Oxides of NJic/el.-This metal combines with oxygen in two pro.
portions, forming a protoxide and a sesqyioxide.




3G6               COBALT  AND  ITS OXIDES.
The protoxide, Ni.O., is prepared by precipitating a salt of nickel by caustic potasl;
a grass-green hydrated oxide of nickel separates, Ni.O.+H.0., which, when dry, gives
the pure ash-gray oxide. This is the only oxide of nickel which forms salts. It is
not, by itself; soluble in water of ammonia;  but if a salt of nickel be decomposed
by ammonia, the precipitate which first forms is dissolved on adding an excess of
the alkali, forming a blue solution, in a great degree characteristic of this metal.
The Peroxide of Nickel, Ni203, is a black powder, prepared by boiling the protoxide in a solution of chloride of lime; the oxygen of the lime changes tile protoxide into peroxide, 2Ni.0. and Ca.O.Cl. producing Ni. 03 and Ca.Cl. When ignited, this oxide gives oxygen and protoxide; with muriatic acid it forms protochloride
and chlorine. It does not form any true salts.
Nickel is easily recognised by its solutions giving with ammonia
a green precipitate, which dissolves in an excess, forming a blue
solution, and by giving with yellow prussiate of potash a white
precipitate.  The solutions of nickel are not precipitated by sul.
phuretted hydrogen, but give a black sulphuret of nickel with hydrosulphuret of ammonia.
The sulphuret, seleniuret, and phosphuret of nickel do not present
any point of interest.
Of Cobalt.
The name of this metal has its origin in a still more singular cir
curnstance than that of the preceding; from  the bright metallic appearance of its ores, the miners of the Middle Ages were led to expect an abundant produce, but the modes of reduction then in use
were employed without avail; it was hence imagined that these
ores were especially protected by the guardian spirits of the mines,
or Kobolds, and these minerals were termed Die Kobold's erze, the
Kobold's ores.  At a later period a peculiar metal vnas extracted from
them, and as the older name had been corrupted into kobalt ore, the
metal was called cobalt.
Cobalt exists ina-nature, combined with arsenic and with sulphur;
it is universally associated with nickel, which it resembles so closely
in its properties that the perfect separation of these two metals is
one of the most difficult operations in analysis.
To obtain the cobalt., the native arseniuret is roasted in a current of air, so as to
oxidize both metals, as described, p. 334. The residual impure oxide of cobalt is
sold in commerce under the name of Zaffre.'his zaffre is dissolved in muriatic
acid, and treated with sulphuretted hydrogen, by which the copper and arsenic are
separated. From the filtered liquor, the cobalt is thrown down by carbonate of
potash, and then, to free it from oxide. of iron, it is digested with oxalic acid, which
dissolves the peroxide of iron, and leaves an insoluble oxalate of cobalt; this may
still be contaminated with nickel, but for the details of the separation of these metals, I must refer to more extended works.
The oxalate of cobalt, when ignited, yields carbonic acid and
metallic cobalt in a spongy form.  Cobalt melts into a button more
easily than cast ir'on; it is reddish-gray; specific gravity 8'5;' when
perfectly pure, it is not susceptible of becoming magnetic.  It acts
upon water and acids more rapidly than nickel, but much less ac
tively than iron or zinc.  The symbol of cobalt is Co., and its equiv
alent 369 or 09.6.
Oxides of Cobalt.-Cobalt combines with oxygen to form two well
defined oxides, a protoxide and sesquioxide; there are also a complex oxide, and a compound of Which the constitution is not well
known, but which is probably a deutoxide.
Protoxide of Cobalt, Co.O., is prepared by adding caustic potash to a solution of a




USES OF  COBALT  IN  THE  ARTS. —ZINC.    367
salt of colbalt; a fine blue powder falls, which is a hydrate, Co.O.. I1.0.; when de.
prived of its water, it becomes ash-gray: it is the only oxide of cobalt which forms
salts with acids.
Sesquioxide of Cobalt, Co02 03, is prepared as the sesquioxide of nickel; it is a black
powder, which, with hydrochloric acid, gives chlorine and protochloride: it does
not form salts.
The complex oxide is Co304-Co.0. —-Co03, similar to the magnetic oxide of
iron and' red oxide of manganese.
Cobalt is recognised in solution by producing with water of analmonia a blue precipitate, which redissolves in an excess of the alkali, forming a liquor which is of a fine rose colour if the cobalt
be pure, but brownish red if nickel be present; it is not precipitated
by sulphuretted hydrogen, but is thrown down black by hydrosulphuret of ammonia.  The most remarkable test for cobalt is its
power of colouring glass blue.  The most minute trace of this metal
may be thus recognised before the blowpipe.  It is, indeed, on this,
character that is founded the most important uses of cobalt in the
arts; glass coloured deep blue by cobalt, and ground to an impalpable powder, constitutes the smalts used to give to writing, paper
and to linen a delicate shade of blue.  The blue colours upon porcelain and delft are also produced by cobalt; when speaking of
magnesia (p. 319) and alumina (p. 351), I have noticed the assistance
given by cobalt in the detection of these earths before the blowpipe;
alumina, coloured strongly blue by cobalt, is used in commerce as
a pigment, cobalt blue, in place of ultramarine.'The blue colours of cobalt are spoiled if brought into contact with chlorine or oxygen, the black sesquioxide of cobalt being formed. If paper be blued lry smalts
without the bleaching liquor having been well washed out of the pulp, it is injured
by acquiring a brown tinge; and by melting together cobalt-glass and black oxide
of manganese, a deep black glass is formned, 2(Co.0.) and Mn 02 giving Co00203 and
Mn.O.
The sulphuret and seleniuret of cobalt consist of an equivalent of each element,
but do not require notice.
Of Zinc.
This metal is found in nature in considerable quantity, combined
with sulphlur, forming sulphuret of zinc, zinc blende;  also as oxide
of zinc, which, united with carbonic acid or with silicic acid, forms
the two varieties of calamine.  The reduction of the metal is etfected
from these ores respectively on the principles already described in
Chapter XII., but, from the volatility of the metallic zinc, the process
is carried on in crucibles or large earthen retorts in place of the
open reverberatory furnace. In England the crucibles are closed
above, but perforated at the bottom, so as to admit an iron tube tc
be fitted in, the top of which rises a little above the surface of the
materials, and the bottom  of which, passinfg through the floor of the
furnace, opens just over the suirace of a reservoir of water   The
zinc, when reduced, is converted into vapour,y which escapes through
the tube, condensing when it gets below the fire into a liquid metal,
which, dropping into the water, solidified.  In Silesia very large
earthen retorts are employed, not unlike th6se figured in page 289
for the preparation of German oil of vitriol.
The zinc of commerce, as thus obtained, is impure; it contains
traces of carbon, iron, cadmium, and often arsenic. It may be freed
from the fixed impurities by redistillation in an iron retort; and bN




68                    OXIDE  OF'  ZINC.
rejecting the portions which distil over first, and which contain the
cadmium and arsenic, it may be obtained quite pure.  It is owing
to the presence of these foreign bodies that ordinary zinc dissolves
so rapidly in dilute sulphuric acid, as explained in page 135. It is
a brilliant bluish-white metal, of a very crystalline texture; its singular variations of tenacity are described in page 328. At 773) it
melts, and at a full red heat is volatilized, its vapour burningain air
with a splendid white flame, and forming clouds of oxide of zinc, so
light as to have been called by the older chemists lana philosophica
and nihil album.  When exposed;o the air, even in presence of wvater, zinc is not continuously oxidized. It becomes covered with a
varnish of a gray substance, probably a definite suboxide, which is
not farther altered by exposure, and hence this metal is admirably
fitted for the various purposes of domestic and technical use to
which it has recently been applied.  In a galvanic circuit of two
metals, zinc is almost always positive, and hence it preserves the
other metal, even if it be iron, from oxidation. The actual corrosion is, however, in this case, not diminished, but rather augmented
in amount; but, being concentrated solely upon the zinc, it is easy
to arrange it so as to prevent injury.  If zinc be quite pure, it is
little acted upon by acids; all that is known of its relations in this
respect has been already described in pages 19S and 248.
The symbol for zinc is Zn. Its equivalent number 4,03'2 or 32'3.
Oxide of Zinc. - Zn.O. Equivalent 503'2 or 40'3. Although
there is some reason to suppose the existence of other oxides of
zinc, yet at present we possess accurate knowledge only of the
protoxide. This is formed when the metal is burned in air or oxygen. It is produced, also, when the zinc is oxidized by the decomposition of water, either at a red heat or assisted by an acid.  To
form the oxide by.cornbustion, it is sufficient to project a small fragment of zinc into a crucible heated to bright redness, and slightly
inclined, so that a current of air may pass through it.  When the
metal takes fire, another crucible is to be placed inverted over the
first, but still allowing a certain access of air.  The oxide of zinc
being not really volatile, but only mechanically carried up by the
current of air, is deposited on the inside of the upper crucible as
a loose cottony mass, which, while very hot, is of a fine canary colour, but becomes pure white when completely cold.
Such is the tendency of oxide of zinc to enter into combination,
that the precipitates given by the caustic alkalies in a solution of
a salt of zinc are basic salts, and not the mere oxide. To prepare
the oxide, a solution of sulphate of zinc is to be decomposed by
carbonate of soda; the precipitate is carbonate of zinc; and by
heating this to redness in a crucible, the carbonic acid passes off,
and the oxide of zinc remains pure. This oxide is a powerful base;
it neutralizes the strongest acids, and its salts are some of the most
definite and characteristic that exist: they are easily recognised.
In their solutions, the caustic alkalies all produce voluminous white
precipitates, which are redissolved by an excess of the alkali. An
alkaline carbonate gives a similar precipitate, which, however, is
not redissolved by an excess, except it be carbonate of ammonia.
Hydrosulphuret of ammonia produces a white precipitate of hydra




CA D M I U M.-T Ir.                     369
ted sulphuret of zinc, if the solution be not very acid.  Sulphuretted hydrogen does so only if the solution be completely neutral
A solution of zinc with much free acid is not affected by sulphuretted hydrogen, either free or combined.
The native S'ulphuret of Zinc, Zn.S., is found in crystals of a variety of colours; it is a protosulphuret, and may be artificially
formed by melting zinc and sulphur together.  It is decomposed by
acids, sulphuretted hydrogen being given off, and a salt of zinc pro
duced.
Of Cadmium.
This metal exists but in small quantities in nature; the only ore
of it is its sulphuret, a mineral but lately found, and still very rare;
it accompanies almost universally, though in small quantities only,
the ores of zinc, and is obtained in the working of zinc ores by ta
kling advantage of its greater volatility. -The details of its purification need not be inserted.  It is white like tin; it is more fusible
and more volatile than zinc; its specific gravity is 8'69; it dissolves
very slowly in dilute sulphuric acid, but rapidly in dilute nitric acid;
it combines with oxygen only in one proportion. Its symbol is Cd.,
and its equivalent 696'8 or 55'8.
The Oxide of Cadmium, Cd.O., equivalent 796'8 or 63'8, is obtained by processes
exactly such as described for oxide of zinc. When anhydrous, it is an orange pow
der; its salts, which are very stable, resemble closely those of zinc, from which
they are distinguished by giving with sulphuretted hydrogen a fine yellow precipitate, and with carbonate of ammonia a white precipitate, insoluble in an excess:
its salts, like those of zinc, are all colourless.
Sulpliuret of Cadminum, Cd.O., is found native near Greenock; it is yellow like
orpiment, but is not volatile; it does not dissolve in water of ammonia nor of potr
ash.
Of Tin.
This metal, from the ease with which it is extracted from its ores,
has been known from the earliest ages, and in all countries, both of
the East and West.  Before the working of iron was discovered,
cutting instruments of all kinds were made of an alloy of tin and
copper (bronze), which in hardness was little inferior to steel; but,
from  its incapability of being tempered with the same exactness,
was only an imperfect substitute for it. It was from the tin mines
of Cornwall that England first became known to the then more civilized nation of Phconicia.  A great quantity of the tin of commerce
is still obtained from that county; but, in addition, it is imported
from Mexico and the East Indies.  The tin ore has been found in
Ireland (county Wicklow), but not as yet sought for with a view
of extracting the metal from it.
The usual ore of tin is the native peroxide, which is found in
veins, and also in fragments in the soil formed by the disintegration
of the rocks.  The process of reduction is the simplest possible,
the ore being smelted with the fuel, as described p. 332. The metal thus obtained is still farther purified from any admixture of foreign metals by the process of liquation, which is founded on the
easy fusibility of pure tin.  The ingots, or pigs of tin, are gently
heated until they begin to melt, and then the heat being prevented
A A A




370                     OXIDES  OF  TIN.
from  rising higher, the pure metal melts completely out, leaving
behind the impurities combined with a proportion of tin, forming a
-mass of less commercial value.  The tin thus purified is termed
grain tin.; the residual mass is called block tin. The former is
known by presenting the appearance of a mass of irregular columns, like. those formed by starch, or by basalt, as in the Giant's
Causeway, and emitting, when bent, a peculiar creaking sound.
The block tin possesses these characters in a very small degree, or
not at all.
Tin, when pure, is white like silver, brilliant, and after gold, silver, and copper, the most malleable of the metals.  It is very soft,
may be bent easily, and has but little tenacity. Its specific gravity
is 7'3.  It is one of the most fusible of the metals, melting at 442'
Fah.  Tin oxidizes but very slowly in contact with air and water,
and is hence used to protect the surface of the more easily oxidable metals, particularly copper, in household use. It dissolves but
slowly in dilute muriatic acid, but rapidly if the acid be strong and
boiling. Nitric acid acts with great energy on it when concentrated, forming the peroxide.
The symbol of tin is Sn., derived from  its Latin name stannum.
Its equivalent numbers are 735'3 or 58'9.
There are three oxides of tin, of which the first acts as a base,
the second appears indifferent, and the third possesses acid properties.
Protoxide of Tin.-Sn.O.  Equivalent 835'3 or 66-9.  On adding
water of ammonia to a solution of protochloride of tin, a copious
white precipitate is obtained, which does not contain ammonia, but
is the hydrated oxide, Sn.O.. H.O. The same precipitate is produced by an alkaline carbonate, the carbonic acid becoming free.
When this white hydrate is heated in a retort filled with carbonic
acid gas, it gives off its water, and the true protoxide of tin remains as a dense black powder.
If the'hydrate be heated in the open air, it absorbs oxygen, and becomes peroxide; and if the black protoxide be touched when cold with a red-hot coal or wire,
it inflames andburns like tinder, forming peroxide. The salts of tin may be formed
by digesting the hydrated oxide in acids. It also dissolves in solutions of the caustic fixed alkalies, but after some time metallic tin is deposited, and a compound of
the alkali with peroxide of tin remains dissolved, 2Sn.O. producing Sn. and Sn.02.
This protoxide of tin is remarkable for its tendency to unite with more oxygen.
Hence, by a solution of a protosalt of tin, the less oxidable metalsare reduced from
their solutions. In this way mercury, silver, gold, platina, may be thrown down in
the metallic state, and iron and copper reduced from the higher to the lower degrees
of oxidation.
The Sesquioxide of Tin, Sn2O,, is prepared by boiling peroxide of
iron in a neutral solution of protochloride of tin.  The sesquioxide
of tin precipitates, and protochloride of iron dissolves, 2Sn CI. and
Fe03, producingf Sn,3O and 2Fe.Cl. It is a gray powder; it absorbs
oxygen readily, and appearsto form salts, which have been, as yet,
little examined.
Peroxide of Tin. Stannic scid. -Sn.O,. Equivalent 935'3 or'74.9.
This substance is produced in all cases where tin is allowed to
combine with oxygen freely.  It-exists in nature, constituting the
common ore of tin (tin stone).  It is mostreadily prepared artificially by pouring the liquid nitric acid,. sp. gr. 1'42, on metallic tin, in




SULP  UR ETS OF. TIN.-CHROME.                           371.
Cfoil or powder;  the action is very violent, and the metal is totally
converted  into  a white powder, which is the hydrated peroxide.:By ignition the water is given oft; and the anhydrous oxide remains'of a pale yellow colour.
If the perchloride of tin be decomposed by an alkali, a white precipitate of hydrated oxide is obtained, in appearance identical with that prepared by nitric acid,
but so different in properties that Berzelius, and after him many chemists, look
upon them as isomeric bodies. He calls that by nitric acid, a peroxide, and that
from the perchloride; fP peroxide, and their properties may be contrasted as follows:
The a mlodification is totally insoluble in nitric acid and in sulphuric acid, wheth
er strong or dilute. It is insoluble in muriatic acid, but is changed by it into an in
soluble basic salt.
The fi modification dissolves while yet moist in dilute nitric and sulphuric acids
very copiously, and the solution is permanent if some salt of ammonia be added to
it. In muriatic acid it dissolves rapidly and copiously.
The two modifications of oxide of tin dissolve in solution of caustic potash, and,.when again precipitated from it by an acid, retain their original properties. These
modifications are also capable of being transformed into each other; the a into /
by distillation with strong muriatic acid, and the P into a by boiling with nitric acid.
The hydrated peroxide of tin reddens litmus, and combines with alkalies to form
salts, but not with acids, except in the i f1orm. It is used in the arts as a polishing
material under the name of paity, and in glass and enamelling, in order to give the
milk whiteness used for dials of watches and other purposes.
There are three sulphurets of tin corresponding to  the oxides
The Protosulp/huret, Sn.S, is precipitated as a brown powder from a solution of
protochloride of tin on the addition of sulphuret of hydrogen. It thus serves for
the detection of tin in that condition. The Sesquisulphuret, Sn2S3, is of no importance.
The Bisulphu ret of Tiz, Sn.Sz, equivalent 1137'6 or 91:1, may be prepared by
decomposing a solution of perchloride of tin by sulphuretted hydrogen; which it
precipitates of a golden yellow colour. This is a strong sulphur acid. It dissolves
readlily in solutions of the sulphurets of the alkaline metals, forming sulphur salts.
If it be strongly heated, it abandons an atom of sulphur, and is converted into the
protosulphuret. It may be also prepared in the dry way, and then possesses considerable interest, as being one of those substances which, being obtained from the
common metals, and simulating the appearance and some of the properties of gold,
led the ancient alchemists to the belief of probable success in their attempts at
transmutation. The bisulphuret of tin may be prepared in the dry way according
to several processes, but to give it the peculiar lustre which obtained for it its name
of mosaic gold, the following is the best though not the most simple: twelve parts
of pure tin are to be melted with six parts of mercury, and rubbed up in a glass
mortar with seven of flowers of sulphur and six of sal ammoniac. This mixture is
to be placed in a glass flask, and heated in a sand-bath until no more fetid white.
vapours are given off. The heat is to be then raised to dull redness, sulphuret of
mercury and chloride of tin sublime, and the mosaic gold remains in the bottom of
the vessel in metallic-looking scales of a brilliant gold colour. The use of the mercury in this process is to facilitate the combination of the tin and sulphur, and the
sal ammoniac seems by its evaporation to prevent the temperature becoming so
high as to decompose the bisulphuret.
The seleniurets and phosphurets of tin are not known.
Tin is easily recognised in solution by the action of hydrosulphuret of ammonia, which produces with solutions of the peroxide a
golden yellow,-and in solutions of the protoxide a brown.precipitate.
These both dissolve in an excess of the precipitant. The protoxide
of tin is also known by its power of reducing the salts of gold, silver,
and mercuryto the metallic state.
Of Chromium, or Chrome.
This metal derives its name from  the variety and brilliancy of the
colouirs of its compounds (XpwjtoC).  It exists as chromic acid combined with lead or with copper in some rare minerals, but abundant.




372           OXIDE  AND  ACID  OF  CHROMEI.
ly as chromic oxide in the chrome-iron ore (Fe.O.+Cr203).  It
is from this source that all the preparations of chrome are obtained
indirectly, but that ore being treated upon the large scale for the
manufacture of chromate of potash, it is this salt, as found in commerce, that may be looked upon as the source of chrome for all
other purposes.  The metal is obtained by mixing the oxide with
lampblack and oil, and exposing it to an intense heat in a crucible
lined with charcoal.  It is a grayish-white metal, very infusible,
brittle, not magnetic, and sp. gr. 5-9 or 6'0. It is not attacked by
dilute sulphuric or muriatic acids, but dissolves in hydrofluoric acid
with evolution of hydrogen gas.
Chrome combines with oxygen in two proportions, forming an ox
ide and an acid. Its symbol is Cr., and its equivalent numbers are
351-8 or 28-19.
Oxide of Chrome, CrO,3, equivalent 1003-6 or 80-4, may be obtained by a great variety of processes.  Thus, if chromate of mercury be heated to redness, the oxide of mercury and half the oxygen of the chromic acid are expelled, and the chromic oxide remains
of a beautiful green colour.
If bichromate of potash be mixed with sal ammoniac and heated to redness, chloride of potassium, water, nitrogen, and oxide of chrome result, and the latter is
obtained pure by washing the residual miass with boiling water. In this process,
2Cr.O,+K.O. and C1.N.H4 produce K.CI.,.N., 4H.O., and Cr,03. The oxide so
obtained is pulverulent, but it may be obtained crystallized as follows: the vapour
of a compound which will be hereafter described, chlorochromic acid, is to be passed through a tube of hard glass, kept at a full red heat, oxygen and chlorine gases
are given off, and oxide of chrome is deposited on the inside of the tube in rhombic
octohedrons, isomorphous with those found native of alumina (corundum) and peroxide of iron; the chlorochromic acid, 2(Cr.O0C1.) giving off 2C1. and 0., and
Cr20, remaining.
This oxide of chrome is the basis of an extensive class of salts,
and it may also be obtained by precipitation from any solution containing it. Its salts are generally made from the bichromate of potash of commerce, by the addition of some deoxidating agent and the
necessary acid. Thus, to form sulphate of chrome, a solution of
bichromate of potash is warmed, and treated successively with sulphuric acid and alcohol, until its orange colour is changed into deep
green.  The liquor then contains the double sulphate of chrome and
potash (chrome alum), and from it the oxide may be precipitated on
the addition of an alkali, as a pale green hydrate. In this condition,
the oxide of chrome dissolves readily in acids, and also in solutions
of the fixed caustic alkalies, but scarcely in ammonia, resembling
very closely, in all these characters, alumina. Its solutions are
either green or purple, and it is probable that this difference is due
to more than a mere difference in the degree of concentration.
When the hydrated oxide is heated nearly to redness, it suddenly
begins to glow like tinder, giving off its water, and losing its solubility in acids, except they be hot and concentrated. It is remarkable that sulphate of chrome, made from the ignited oxide, will not
combine with sulphate of potash to form a chrome alum.
Chromic acid. —Cr.O,.  Equivalent 651'8 or 52-2.  To prepare
this acid, a solution of bichromate of potash is to be treated by hydrofluosilicic acid gas, until the potash has been precipitated completely. The resulting liquor is to be cautiously evaporated to dry



V A N A D I U M.-T U N G S T E N.                  373
ness, and then'redissolved in a small quantity of water. The solu.
tion is of a dark brownish-red, and when evaporated again gives the
dry chromic acid. It may be obtained in a beautiful form, though
not in quantity, by decomposing the vapour of the perfluoride of
chrome by a moistened slip of paper.  Cr.F3 and 3H.O. produce 3
H.F. and Cr.O,, which last is deposited on the surface of the paper
in crimson scales and needles of great brilliancy.  This acid, when
heated strongly, gives up half its oxygen, being reduced to the state
of oxide.  It combines with bases, forming several important classes
of salts, in which it is isomorphous with the sulphuric and manganic
acids.  Its salts are all coloured, generally yellow, orange, or red.
They will be described in another chapter.
Chromium  is characterized by the remarkable colours of its corn
pounds when dissolved, and by giving, when in the state of oxide,
a green precipitate with the alkalies.  In the state of acid, it is known
by producing, with the salts of lead, a yellow, and with the salts of
the black oxide of mercury, an orange precipitate. It is at once
recognised by the beautiful green colour which it communicates to
glass.  It is, on this account, extensively used in staining glass and
painting on porcelain, and a number of its salts are employed as pigmnents and as dyes.
By the action of dleoxidizing agents, or sulphurous acid or sugar, upon bichromato
of potash, a brown substance is generated, concerning the nature of which opinion
is very much unsettled. There is reason to suspect the existence of a peroxide
of chrome, Cr.02, which this matter may possibly be. When it is washed with
much water, or digested in alkaline liquors, chromic acid is dissolved out and oxide
of chrome remains, Cr203+Cr.03=3Cr. O2.
The sulphurets, seleniurets, and phosphurets of chrome are not important.
Of Vanadium.
This metal, of recent discovery, derives its name from Vanadis, a deity of Scandinavian mythology. It is found native as vanadic acid, in a very rare mineral,
vanadiate of lead, but is of so little importance that a slight notice of it will suffice, although it forms a great variety of combinations, which resemble very remarkably those of manganese and chrome. The metal itself has been obtained, but of
its properties nothing positive is known. Its symbol is V.; its equivalent numbers.are 856'9 or 68'7.
The Protoxide of Vanadium, V.O., is a black powder, formed by acting on vanadic
acid at a red heat with hydrogen gas. It combines with acids, forming salts which
resemble probably those of the protoxide of manganese. When heated in the air,
it absorbs oxygen and becomes vanadic oxide, V.02, which is a base combining with
acids and forming salts which are generally blue. It acts also as an acid, forming
crystallizable salts with the fixed alkalies.
The Vanadic Acid, V.03, resembles very much the chromic and manganic acids.
It is a red powder, which may be melted at a red heat without losing oxygen. It
is very slightly soluble in water. It forms various classes of salts, of which some
are white, some yellow, and others orange red. In these characters it resembles
the chromic acid, but it is distinguished from chrome by producing, when deoxidized,
a blue solution, while that from chrome is green.
SECTION IV.
METALS OF THE FOURTH CLASS.
Tungsten and JMolybdenum.
Tu.ngsten.-This metal exists, combined with oxygen, as tungstic acid, in the
native tungstates of lime and iron; by boiling the tungstate of lime in strong muriatic acid, the lime is dissolved out, and tungstic acid remains as a yellow powder,
which may be farther purified by solution in water of ammonia, and igniting the




3:74       T U N G S  E N. —M OLYBDE N U M.-O SMI UM.
tungstate of ammonia. It is a deep yellow powder, which forms well-defined crys.
tallizable salts with the alkalies. The symbol of tingsten is WV., from its German
name TVolJ~Iam, and its equivalents 1183 or 94'8. The tungstic acid resembles the
chromic acid, being W.03., When this acid is exposed to a current of hydrogen
gas at a temperature about dull redness, it loses one third of its oxygen, and forms
tm~ng'stic oxide, WT.O, of a copper-red colour. This may be also formed by diffusing
tungstic acid through dilute muriatic acid in which a slip of zinc is immersed; the
nascent nydrogen then effects the deoxidation. At a fill red heat, hydrogen reduces
tungsten to-the metallic state, removing all the oxygen. The metal is like iron in
appearance, and very heavy, its sp. gr. being about 17'5.
The most curious fact in the history of tungsten is its producing a substance havirig an extraorclinary similarity to gold. It is prepared by adding to fused tungstate
of soda as:much~ tungstic acid as it will'dissolve, and exposing the product at a full
red heat to a current of hydrogen gas; the residual tungstate of soda is then to be
dissolved out. The new compound, which consists of tungstic oxide united to soda,
Na.O.+2W.02, remains in scales and cubes of a splendid gold colour. It resists the
action of acids and alkalies, even of aqua regia, in which gold dissolves, and only
yields to strong hydrofluoric acid. - Had it been discovered at an earlier period in
science, it might have lent exceedingly plausible support to the belief in transmutation. It is the more curious, as it cannot be formed by directly combining soda with
tungstic oxide, which, indeed, appears unable to unite either with alkalies or acids.
There exist two sulphurets of tungsten, W.S2 and W.Sa, of which the latter is the
most interesting. It is formed by dissolving tungstic acid in hydrosulphuret of ammonia, and precipitatingby an acid. It is a blackish-brown powder, and one of the
strongest sulphur acids. Many of its compounds with the sulphurets of the alkaline metals may be crystallized.
Molyb'enum.-This metal exists combined with sulphur, and also with oxygen, as
molybdic acid, in some minerals. It is not of any considerable interest. When obtained in the metallic state it is white, sp. gr. 8'6, acted on only by concentrated nitric and sulphuric acids, and by aqua regia. Its symbol is Mo. Its equivalent
5985 or 47'9. - It combines with oxygen in three proportions.
Molybdic Acid, Mo.03,:i easily prepared by roasting the native sulphuret of
molybdenum; the sulphur burns out as sulphurous acid gas, and the molybdenum,
absorbing oxygen, remains as molybdic acid. This may be purified as described for
tungstic acid. Molybdic acid prepared at a low temperature is white, but becomes
yellow when fused at a red heat. It is sparingly soluble in water. It dissolves in
alkaline liquors, forming salts which are neutral and crystallizable.
Molybdic Oxide, Mo.02, is best prepared by mixing together molybdate of soda
and sal ammoniac in a crucible, and igniting the mass rapidly. When the product
is washed' with water, a dark brown powder is obtained, which is molybdic oxide.
This oxide appears to form salts with both acids or alkalies, of which some may be
crystallized.  A molybdate of molybdenum, or, rather, a complex oxide, also exists,
Mo.0z+2lMo.03 —-MoO8. It is a blue powder.
When a solution of molybdate is decomposed by as much muriatic acid as redissolves the molybdic acid, which is at first thrown down, and a slip of zinc is immer
sed in the liquor, the hydrogen evolved deoxidizes the molybdic acid, and a precipi
tate is formed upon the zinc, at first blue, then brown, and finally black; thus passing
through all the intermediate degrees to the last, the Molybdoss Oxide, Mo.O. This
is a very feeble base, forming with acids salts which do not crystallize.
Sulphur combines with molybdenum in three proportions, forming Mo.S2, Mo.S3,
and Mo.S4. Of these the bisulphuret, Mo.S2, is important, as being the native ore
from which the metal and its compounds are generally prepared. It is a soft gray
substance, so like black lead as to have been mistaken for it until its nature was
pointed out: by- Scheele.- All: these sulphurets are sulphur acids, and form salts.
Of Osmium.
This metal existS in nature alloyed with iridium, and accompanies the ores of
platinum. The methods of its extraction from these ores are so complex and circuitous that I shall not introduce them here. In the systematic works, a complete account of the processes pursued will be found.
The most interesting property of osmium is its forming a highly volatile oxide of
an exceedingly penetrating odour, whence the name (oap/u). When this is dissolved
in muriatic acid, and placed in contact with mercury, the osmium is reduced, and by
distilling off the mercury it is obtained as a black powder; but by heat and compression it may be rendered coherent, and of a brilliant white colour. In the state of
powder, osmium burns when heated to redness in the air, and is oxidized by nitric




COLUiMIBIUM  AND  TITANIUM.                             375
acid, but loses both these characters when ignited.. The symbol of osmium is Os.
Its equivalent is 1244'5 or 99'7. It combines with oxygen in three proportions.
The Osmic Acid, or. Peroxide of Osmium, Os.04, is always formed when osmiumn is burned in air or in oxygen gas. It condenses in long white needles. Its
odour is remarkably acid and pungent. It melts at 2120, and boils at a heat little
higher. It is soluble in water.  The solution has no action on vegetable colours,
but it combines with the alkalies, forming osiuiates.
The Osatic Oxide, Desuto.xide of Osniiwu1z, Os.02, is produced by the decomposition of a solution of osmiate of ammonia, by a temperature of 150~; nitrogen gas is
given off; and a brown powder is deposited.
The Protoxide of OsoiiUsm is produced by decomposing a solution of protochloride
of osmium by potash; a deep green, almost black, powder is thrown down, in which.the oxide is combined with water and traces of the alkali.
The sulphurets of osmium are not known.
Columbium, or Tantalum.
This metal was discovered first in an American mineral, from whence its name;
it was subsequently, but independently, discovered in some very rare Swedish minerals, and from the difficulty of its extraction, the name tantalum was given to it,
which it still bears upon the Continent, and from whence its symbol is Ta. The
process required to prepare it need not be described, as it is similar to that for obtaining silicon.
Metallic Columbium, or Tantalum, is a black powder, which, when burnished,
appears iron gray. No acid but the hydrofluoric appears to have any action on it.
It takes fire when heated in the air, and burns vividly. Its equivalent numbers are
230'7 or 185. It combines with oxygen in two proportions.
Tantalic, or Coluembic Acid, Ta.03; exists native in all the minerals containing
the metal. To procure it, the mineral is fused with carbonate of potash, and the
tantalate of potash, which is soluble, is to be decomposed by muriatic acid. The
tantalic acid precipitates as a white powder, which contains water, and reddens litmus paper. -When tantalic acid is heated strongly in a crucible with charcoal, but
a slight film of it is reduced to the metallic state, the great mass being brought only
to the state of tantalic oxide, Ta.O2. This substance is gray. It is insoluble in all
acids.
The similarity of tantalum to silicon is very great; it resembles it in forming, with
fluorine and potassium, a double fluoride, from which the metal is obtained.
Titanium.
This metal, although not met with in large quantities, is yet found in a great variety of minerals. It is not found native in a metallic state, but combined with oxygen, forming titantic acid. To obtain metallic titanium, the volatile perchloride
is employed. This body absorbs ammonia, forming a white substance, Ti.C12+2
N.H3, which, when heated to redness, gives metallic titanium, withisal ammoniac
and nitrogen, the hydrogen carrying off the chlorine. It is of a bright copper colour,
almost perfectly infusible. Titanium exists in most of the clay iron stone, and
hence, being reduced during the smelting of the iron, is found in the slags, crystallized in cubes of excessive hardness and brilliancy, sp. gr. 5'3. This metal is not
acted upon by any acid except a mixture of nitric acid with hydrofluoric acid, and
is oxidized, but very slowly, by melted nitre. It is perfectly unalterable by air or
water. Its symbol is Ti. Its equivalent numbers are 303'7 or 24'3, and it combines with oxygen in two proportions.
-Titanic Acid, Ti.02, exists native, constituting the mineral rietile, isomorphous
with tin stone (Sn.02), and also in the mineral anat ase. More abundantly it is found
in the titan'ic iron, ilmenite, the formula of which is Fe.O.. Ti.02, and, which is
very remarkable, from having the same crystalline form as peroxide of iron, Fe2O3,
so that the titanium would:appear to replace the second atom of iron, and the formula to be Fe.Ti.+03. This is merely speculative, however, as iron is never isomorphous with tin, and in no other case with titanium, and I hence consider this
instance as one of the coincidences of' form described in pages 221 and 226.
Titanic acid is artificially prepared from the titanate of iron byigniting it with
sulphur. The oxide of iron and sulphur form sulphurous acid and sulphuret of iron,
and when this last is dissolved out by muriatic acid, the titanic acid remains behind. It requires other processes to render it absolutely pure,which need not be described here. It is a pure white powder, resembling silica very remarkably in its
propelties, and, like it, having a soluble and an insoluble i4;dification.  It is remark



-376      ARSENIC, ITS PREPARATION, ETC.
ably characterized by its solution in muriatic acid, giving with tincture of galls
an orange precipitate, and by the immersion of a slip of zinc a fine purple powder..which is Oxide of Titanizxn, Ti.O.; the second atom of oxygen being removed from;tee acid by the nascent hydrogen. This oxide of titanium may also be procured by,igniting titanic acid with charcoal; it is then a black powder, insoluble in all acids.
The Bisudplphret of Tita'inuqm, Ti.S2, is a strong sulphur acid, but not otherwise
important.
Of.1rsenic.
This metal exists in nature in a great variety of forms, and in
considerable quantity. It is found native, but more generally combined with other metals, as nickel, cobalt, iron; being considered,
like oxygen and sulphur, as a mineralizer of other metals.  Combined
with sulphur, it constitutes the native orpiment and realgar; and
with oxygen, as arsenic acid, it is united with metallic oxides in the
native arseniates of lime, of iron, of lead, &c. The great proportion
of the arsenic of commerce is obtained in the roasting of the cobalt
and nickel ores, as described in p. 334. The current of hot air
which has passed over the ignited ore carries with it, into a series
of large chambers, the volatile arsenious acid, which is deposited
under the form  of a fine grayish powder on the walls and floor.
This is discoloured by some of the oxide of the fixed metals, which
is carried over mechanically by the draught, and it is, therefore,
resublimed in iron vessels, the covers of which are allowed to become so hot that the arsenious acid, in condensingr, shall aggregate
itself into a vitreous mass, in which state it is sent into commerce.
The metallic arsenic may be prepared from the arsenious acid in
many ways, but best by mixture with three times its weight of black
flux (p. 334) in a crucible or earthenware retort, which is then to
be heated to redness. If a crucible be used, another cold crucible,
somewhat larger, must be inverted over it, on the inside of which
the metal condenses, but with a retort it is deposited in the neck as
an irregular mass of rhombohedrons, variously modified. It is very
brittle; its sp. gr. 5'96. It sublimes at 3563 F. without previously
melting. The sp. gr. of its vapour is 10362. Its vapour, if in contact with the. air, has a very characteristic garlic odour; which,
however, belongs not to the pure metal, but to an oxide produced
by a low degree of combustion which occurs.  In the air it gradually absorbs oxygen, and falls into gray powder (suboxide, fly powder).
By nitric acid it is rapidly oxidized, and deflagrates violently in
melted nitre. In fine powder it burns spontaneously in chlorine
gas, with a brilliant white flame, and burns similarly when heated
in oxygen gas. The symbol of arsenic is As., and its equivalent
numbers are 940'1 or 75'34.
Arsenic combines with oxygen in three proportions, forming a
suboxide, of which the composition is not known.  Many chemists
look upon it as a mere mixture of metal and arsenious acid, for
when it is heated it separates into these bodies.  The other degrees
of oxidation, the arsenious acid and arsenic acid, are of great importance.
Jrsenious sdcid. White.Irsenic.  Oxide of Arsenic-As.03, equiv.
alent 1240e1 or 99.34-is found in commerce in masses, which, if
recently sublimed,4.re perfectly colourless and transparent, but




ARSENIOUS ACID.-ARSENIC  ACID.                     377
gradually become milk-white and opaque. In general, the outer
portions of the commercial masses have thus changed, while the interior retains its original transparency. This alteration is probably
connected with the dimorphism of arsenious acid (p. 228), for the
acid ill these conditions differs in density and in solubility.  The
transparent is sp. gr. 3'74, and 100 parts of boiling water dissolve
9'68 parts of it; but the opaque acid is of sp. gr. 3'69, and 11'4'7 of
it are soluble in 100 parts of boiling water. A solution of the vitreous acid reddens litmus paper, but that of the opaque acid restores,
though feebly, the blue colour of litmus paper already reddened by
an acid.  The taste of arsenious acid is not narked, but ratherslightly sweet: it leaves upon the palate, however, an acrid sensa
tion.
The arsenious acid sublimes at 380' F. without previously melting. Its vapour is of sp. gr. 13670, being produced by
One volume of vapour of arsenic =10362'0
Three volumes of oxygen  -.   3307 8
the four volumes forming one..  =13669'8
If it be very slowly sublimed, it condenses in regular octohedrons
of exceeding brilliancy.  It is, however, sometimes found, in the
roasting of its ores, in crystals belonging to a different system (the
rhombohedral). Arsenious acid is dissolved by liquid muriatic acid
in large quantity, but crystallizes from that solution in octohedrons.
If the opaque acid had been employed, the crystallization is not peculiar; but if it had been the transparent variety, the deposition of
every crystal is accompanied by a sudden flash of light, very brilliant in the dark. The crystals so produced belong to the opaque
kind, so that it would appear as if, at the moment of deposition, the
particles changed their mode of arrangement, so as to pass from
the transparent to the opaque dimnorphous form, and that the alteration in molecular constitution occasioned the evolution of light,
and probably of heat and electricity.
The arsenious acid combines with bases to form salts, which are,
however, of such unstable constitution that they are but little
known. It is particularly of importance from its highly poisonous
properties, and from its being, more frequently than any other substance, administered to produce death. Its recognition is, therefore, to the medical chemist, one of the most important problems
in analysis, and will be fully discussed when the other combinations
of arsenic have been described..qrsenic.qcid.-As.O..  Equivalent 1440.1 or 115'34.  To obtain
this acid, eight parts of arsenious acid are to be placed in a retort
with two parts of strong muriatic acid, and boiled, while twentyfour parts of dilute nitric acid, of sp. gr. 1'25, are to be added, in
small quantities at a time. The mixture is to be distilled in a retort to the consistence of a sirup, and then transferred to a platina
dish, in which it is to be evaporated to perfect dryness, and heated
until all traces of nitric acid are expelled. The residual mass is
milk-white, but anhydrous arsenic acid.  The heat should not be
raised to near redness, for then the arsenic acid is decomposed into
arsenious acid and free oxygen.  The mass thus obtained dissolves
_B 3_




378           ARSENIUR E r OF  HYDRO GEN.
but slowly in:water,:but ultimately the solution -is complete; the
arsenic acid has even so much affinity for water as to deliquesce
rapidly in vessels which are not kept carefully closed.
The arsenic acid reddens litmus paper strongly, and forms with
the alkalies perfectly neutral salts.  At a high temperature it is capable of expelling all the volatile acids, even the sulphuric acid,
from their combinations. In its compounds it resembles very closely the phosphoric acid; but it appears capable of forming only one
of the three classes of salts which phosphoric acid produces.  The
arseniates are all tribasic, but as the quantity of fixed base varies,
there are some neutral and others acid arseniates; the latter were
formerly -called binarseniates.  Thus there are,
3Na.0.+-As.0,+241 aq.       called stubarseniate of soda,
2Na.0.. H.O.+As.Oj-0  14 aq. "   neutral arseniate of soda,
Na.O.. 2H.O.+As.0,+-2 aq.   "   binarseniate of soda;
but the quantity of base is really constant, being in each three atoms,
made up partly of water and partly of soda.
The arsenic acid'is recognised by being precipitated golden yellow by sulphuretted hydrogen.4 The precipitate dissolves instantly
in ammonia, and even in an excess of sulphuret of hydrogen; so
that it may not be visibly produced, if the quantity of arsenic be
small, until the liquid shall have been well boiled. A solution of
any arseniate gives with nitrate of silver a brick-red powder, arseniate of silver, 3Ag.O. + As.O,, the formation of which is easily explained.  An insoluble arseniate heated in a glass tube with charcoal powder gives a sublimate of metallic arsenic..AIrseniuret of Hydrogen. —It has been supposed, that when metallic arsenic is used as the negative electrode of a voltaic battery,
the: hydrogen evolved combines with it, and forms a brown powder,
hydruret of arsenic.  The same body was supposed to be generated
in other ways; but it is now known that this substance is only metallic arsenic finely divided, and that there is but one compound of
arsenic and hydrogen, the gaseous arseniuret of hydrogen. As.H3.
This compound is easily obtained whenever nascent hydrogen
comes into contact with metallic arsenic: thus, when an alloy of
equal parts of zinc and arsenic is dissolved in dilute sulphuric acid,
the hydrogen evolved combines with the arsenic, 3(S.03+H.O.)
and Zn3As. producing 3(S.03+Zn.O.) and H As. It is still more
easily prepared by adding muriatic acid to a solution of arsenious
acid in water, and immersing therein a piece of zinc; the hydrogen
first evolved reduces the arsenious acid, and the metal is then separated as a fine brown powder, with which the hydrogen next
evolved combines. This gas is generally stated to have a very disagreeable odour, which, however, I have not found it to possess.
It is excessively poisonous; it burns with a brilliant white flame,
water being formed, and arsenious acid or metallic arsenic being
deposited according to the supply of oxygen to the gas; it is not
absorbed by water; its specific gravity is 2694, formed by
One volume of arsenic vapour.-. =10362 0
Six volumes of hydrogen 68'8X6.  -  412'8
The seven being condensed.to four. 10774'8
Of which one weighs.....    2693'7




SULPHURE TS: OF  ARSENIC.                      379
Arseniuret of hydrogen decomposes most metallic solutions, precipitating metallic arseniurets of corresponding constitution (R,,As.).
If a current of it be passed over chloride of copper, heated to abo  ut
400', it is decomposed, H3As. and 3Cu.CIl. giving CuAs. and,3H.Cl.
This gas is absorbed by dry sulphate of copper, which it.decomposes, water being evolved, and a blackish compound of sulphuric:
acid and arseniuret of copper being produced.  This property is
made available in the medico-legal examination of substances containing arsenic. If a fragment of chloride of mercury beb heated
in this gas, it is rapidly decomposed, muriatic acid l'gas and arseniuret of mercury being formed.  At a full red heat the gas is decomposed completely by itself, so that if a single point of a tube,
through which it streams, be ifnited, all the arsenic is deposited a
little beyond that point, in the metallic state, and only pure hydrogen passes on.
Sulphur and arsenic combine in several proportions: the.Bisulpiu-.
ret of.Arsenic, As.S2, exists native, forming the mineral re'algar. It is
prepared by fusing the following sulphuret with metallic arsenic,
and subliming the product.  It is a ruby-red crystalline mass; when
it is digesfed in solution of caustic potash, a blackish powder remains, which may be looked upon as a subsulphuret; its definite
nature is problematical.  The Tersulphuret of drsenic,As.S3, yellow
arsenic, orpiment, is found native, and may be easily prepared by decomposing a solution of arsenious acid with suilphuret of hydrogen,
As.03 and 3H.S. giving As.Sjand 3H.O.  It is a rich yellow powder;
when heated, it melts; and in close vessels sublimes unaltered, but
otherwise it burns, partly forming arsenious and sulphurous acids;
it is not quite insoluble in water.  It is insoluble in acids, and best
precipitated from an acid liquor.  It is a strong sulphur acid, combining -with the sulphur bases to form  salts, sulphAo-arsenites.  It
hence dissolves readily in hydrosulphuret of ammonia, and also in
the caustic alkalies.  In the last case there exists in solution an
ordinary arsenite besides the sulphur salt; for, using potash, 2As.
S3 and 6K.O. produce (As.S3+3K.S.) and (As.O,+3K.O.).  When
sulphuret of arsenic is ignited with black flux, metallic arsenic sublimes; and the separation of the metal is still. more elegantly effected by heating the sulphuret, mixed with carbonate of potash, in a
current of dry hydrogen gas.
The Persulphuret of drsenic, As.S5, corresponds to the arsenic acid,
and is prepared by decomposing a solution of it, or of any ofits salts,
by sulphuretted hydrogen.  It is yellow, paler than orpiment; sublimes without alteration in close vessels; is a strong sulphuric acid,
and hence dissolves in solutions of the alkaline hydrosulphurets,
forming sulpho-arseniates; the metal may be eliminated from it by 
the same means as those described for orpiment.
A substance sold in this country for killing flies, under the name
of king's yellow, is, or ought to be, orpiment.  The best- sort is made;
by  boiling together lime,. sulphur, and white arsenic; but much of
it consists merely of white arsenic coloured by some sulphur mixed
with it. From the facility with which it may be obtained, and the
manner in which it -is left exposed, it is very frequently the source
of fatal accidents.




380             DETECTION  O F ARSENIC.
Notwithstanding the scientific importance which arsenic possesses
from the number and variety of its compounds, it is of much higher
interest in consequence of the frequent necessity for the detection
of excessively minute traces of it in cases of suspected poisoning,
where a responsibility, involving the life of a fellow-creature, rests
on the skill and accuracy of the medical chemist. The detection
of arsenic under all possible circumstances is anl object, therefore,
to which all the powers of analysis should be brought to bear, and
the methods at our disposal appear, if properly applied, to be satisfactory and complete. In a question so grave as this, no colours
of precipitates, however so marked-no arrangement of mere results
by test, no matter how corroborative, should be considered as by
themselves decisive; the object of the chemist should be, the isolation and production of the metallic arsenic; and where this has not
been done, it-is certain that either there is no arsenic present, or
that the skill of the operator cannot be absolutely relied on.
In poisoning by arsenic, the substance used is almost universally
arsenious acid. To this, therefore, I shall confine my remarks at
present; I shall afterward notice the peculiarities of its other preparations.
The arsenious acid being a very heavy powder, and but sparingly
soluble, it is very rapidly deposited from any liquid through which
it might have been diffused, and hence the vessels in which food
had been contained should be carefully examined for any traces of
it which might remain. This should riot be omitted, even though
they might appear to have been subsequently rinsed. Any substances vomited by the person suspected to be poisoned should be carefully examined for the same object; and in case of death, the materials in the stomach and its mucous surface must be similarly searched. The little grains of arsenious acid adherent to the surface of
the stomach are frequently tinged yellow at the surface by sulphuretted hydrogen, if the examination be deferred until some time after death.
In case of such traces of white powder being found, the examina
tion is very simple. Their porperties are:
lst.. Heated alone in a glass tube, the powder sublimes and condenses in minute brilliant octohedrons.
2d. Mixed, in a tube closed at one end, with a little black flux,
and ignited, metallic arsenic sublimes, forming a steel-gray crust,
brilliant on the side next the tube, but dull and crystalline on the
inside. On applying the nose to the open end of the tube and inspiring, a garlic odour is perceived.
3d. On cutting off the sealed end of the tube, and then heating
the part containing the metallic crust, the tube being slightly inclined, the metal disappears, and a crust of white arsenic condenses a
little higher up. A current of air passes through the tube, with the
oxygen of which the metal combines. In this process the garlic
smell becomes more marked than in No. 2.
4th. The white powder dissolves in water. It yields precipitates
with the following reagents:
A. Sulplhuretted Hydrogen.-A rich yellow: soluble in ammonia,
and precipitated on the addition of an acid. This precipitate is orpiment.




LIQUID TESTS FOR  ARSENIC.                    381
B. lmmnonia-nitrate of Silver.-A canary yellow; arsenite of silver.
This reagent is very delicate, but the precipitate is soluble both in
acids and ammonia, so that an excess of either must be avoided.
C.. inLmonia-sulp/late of Copper.-A fine apple-green. This is redissolved also by an excess of acid or of ammonia.
Each of these liquid reagents is liable to fallacy, which must be
guarded against.
A. Suliphuretted Itydrogen gives precipitates more or less resembling that from arsenic with the following metals:
Cadmium.                   Antimony.
Tin (persalts).            Iron (persalts).
The precipitate from cadmium is not soluble in water of ammonia.
The precipitate from tin, when dried and ignited with black flux,
gives no sublimate of metal.
The precipitate of antimony acts in the same way as tin, but also
it dissolves in strong muriatic acid, and the solution, diluted with
much water, gives a white precipitate. The sulphuret of antimony
is much more orange-coloured than that of arsenic.
The precipitate from a persalt of iron is pure sulphur; heated, it
melts and burns completely away, without forming any solid product.
B..lmmonia-nitrate of Silver.-Phosphate of soda produces a yel-'ow precipitate of tribasic phosphate of silver, exactly resembling
the arsenite. It is, however, much more soluble in ammonia. They
are at once distinguished by beinog collected and ignited. The arsenite gives off oxygen and arsenious acid, while metallic silver remains; but the phosphate gives no volatile product.
C. The  mnmonia-sulph/ate of Copper is uncertain, unless it be dried
and reduced; for there are numerous basic compounds of copper,
which resemble it very much in colour.
None of these liquid reagents are, therefore, in themselves positive, unless by extraction of the metal; and this is the more important when the operator has to work, not with the clear solutions
prepared intentionally for illustration, but with the complex and
discoloured liquids obtained from the stomach and intestines.
The process to be then followed may be either of two kinds; the
first consists in converting the arsenic into sulphuret, the second
into arseniuret of hydrogen. I will describe each in their turn.
The contents of the stomach and small intestines, or the matter
ejected by vomiting during life, are to be boiled in distilled water
for half an hour, and then the liquor strained through a linen cloth.
If it be too thick or coloured to allow of a small quantity of precipitate being observed and separated, a current of chlorine gas is to
be passed through it, by which most of the animal matter dissolved
is coagulated, and a more convenient solution obtained. This being strained or filtered, is to be well boiled to expel the excess of
chlorine, and then submitted to the action of a current of sulphuretted hydrogen gas. The animal matters may also be removed from
the solution by rendering it acid by nitric acid, and then adding an
excess of nitrate of silver. When the precipitate which forms has
been separated, the excess of silver is to be thrown down by some




382          MARSHE S TEST  FOR ARSENIC.
common salt, and the liquor being then filtered, is fit for the action
of the' sulphuretted hydrogen.
When the liquor smells strongly of this gas, there has been
enough passed through, and it is then to be boiled briskly for a few
minutes to expel the excess, and favour the deposition of the precipitate produced.  This is to be then collected on a filter, washed
carefully with water acidulated by muriatic acid, and dried at a
moderate heat.
When completely dry, it is to be mixed with about twice its bulk
of black flux, and ignited in a small tube of hard glass closed at one
end.  In introducing the materials, care must be taken not to soil
the sides of the tube; metallic arsenic sublimes, which is recognised by the characters given already in pages 376, 380.
The process by arseniuretted hydrogen was first proposed by Mr
MIarsh, and has been found of surprising delicacy and exactness;
the liquid having been freed from animal matters, and obtained as
thin a fluid as possible by either of the processes, by chlorine or
nitrate of silver, already described, it is rendered moderately acid
by muriatic or sulphuric acid, and introduced into a flask or bottle,
to the neck of which is adapted a narrow tube of hard glass, which,
after passing horizontally for a few inches, turns up and forms a
jet; a piece of zinc being introduced into the acid liquor, hydrogen
is evolved, which combines with any arsenic that may be present,
and, forming the gaseous arseniuret of hydrogen, passes off.  When
the gas issuing from the jet is set on fire,, if the hydrogen be pure,
no other product is generated but water  but if a slight trace of
arsenic be present, the flame is whitish, and on holding over the jet
a fragment of glass or porcelain, or a filmn of mica, a deposite is produced, which may be white from arsenious acid, or brown from metallic arsenic, according to the height at which the plate. is held,
and the consequent completenesslof the combustion, or the reverse.
If the quantity of arsenic be too small to produce this effect in a certain time, it may be better detected by igniting a portion of the hori
zontal arm of the tube. All the arseniuretted hydrogen, in, passing
that point, deposites its arsenic, which is carried a little beyond the
heated portion, by the current, and condenses there as a distinct
metallic film; as the tube may be kept thus red-hot for some hours,
the smallest trace of arsenic may be thus concentrated on a single
point, and its properties' accurately verified.
WVhere the liquor is still thickish from dissolved organic matter,
the gas bubbles would not break rapidly, but form a froth, which,
passing into the tube, would prevent altogether the successful employment of the methods just described. In this case.the liquid
should be: made so feebly acid as that the gas shall be generated but
very slowly, and that there shall be but little hy.drogen in excess.
The tube, in place of terminating in a jet, is to be bent down so
that it shall pass under the edge of a jar in, the pneumatic:tro-ugh,
and, the apparatus beingo so  left for any length'of.time,;the gas
evolved may be collected and subsequently examined.... Or, what'is
perhaps still better, the. tube may dip under the surface. of a dilute
solution of nitrate of'silver or of sulphate of copper, and all the arseniuretted hydrogen being then absorbed and decomposed, metallic




SOURCES OF ERROR.                       383
arseniurets are produced, which easily yield, by the application of
heat, the arsenic in the metallic form.
In this mode of detecting the presence of arsenic, it is necessary
to avoid some sources of error, into which, without previous knowledge of their existence, an operator might easily. fall. If the effervescence be rapid, it frequently happens that very minute portions
of zinc, or of the salt of zinc generated, may be carried up by the
stream of gas, and, being deposited upon the plate, form a crust,
which might lead to suspicion, or perhaps wrong conclusions. This
may be avoided by either moderating the effervescence, or by passing the gas, before using it, through a tube filled loosely with cotton,
by which it is filtered, as it were, and all mechanically diffu se4d
particles separated. Much more important sources of error arise,
however, from the existence of arsenic in most of the zinc and some
of the sulphuric acid of commerce. The ores of zinc occasionally
contain orpiment, which being reduced along with the other sulphuret, it is necessary to distil the zinc in order to have it pure,
and to reject it as long as it contains arsenic. The iron pyrites
also occasionally contains traces of orpimrient, and this passes into
the oil of vitriol. In employing this mnethod, it is necessary, therefore, to test the purity of the zinc and sulphuric acid by the method
itself. A jet of the hydrogen, evolved from the zinc and dilute
sulphuric acid simply, should be burned, or the gas passed throu gh
a solution of ammonia-nitrate of silver for a quarter of an hour. Ir
no trace of deposition of arsenic occur, the materials may be considered as pure, and the suspected liquor may then be employed
with confidence in the result.
A more remarkable source of error arises from the fact that the
compounds of antimony yield, under similar circumstances, a precisely similar gas, antimoniuret of hydrogen. It would anticipate too
much the history of that metal to enter into the details of the means
of distinguishing that gas from the arseniurettedl hydrogen, but they
will be fully described in their proper place.
Arsenious acid possesses the power of preventing the putrefaction of animal substances, and hence the bodies of persons that have
been poisoned by it do not readily putrefy.  The arsenious acid
combines with the fatty and albuminous tissues to form solid compounds, which are not susceptible of alteration under ordinary circumstances. It hence has frequently occurred, that the bodies of
persons poisoned by arsenic have been found, long after death,
scarcely at all decomposed, and even where the general mass of the
body had completely disappeared, the stomach and'intestines had
remained preserved by the arsenious acid-which had combined with'
them, and by its detection the crimes committed-many years before
were brought to light and punished. In the cases where the whole
body has been found fresh, it resulted from the person havinag survi'
ved for a length of time sufficient for the complete permeation of the
tissues by the absorption of the poison.; in the others, death had
occurred while it was yet only in the intestinal tube. The absorption of the arsenious acid in cases where death has not been rapid,
renders its detection possible in all the various organs, particularly
where the poisoning has been produced, not by the admnistration




384 ANTIDOTE  TO  ARSENIOUS ACID.-A NTIMONY.
of a single dose, but by frequently repeated doses, each insufficient
to produce rapid poisoning. The decision in such cases is rendered,
however, extremely difficult by the fact, recently established, that
the resemblance of function, so often alluded to, between arsenic
and phosphorus, is such, that the latter element, which character
izes the animal tissues by its almost constant presence, may be
replaced as a constituent of our organs by arsenic.  Thus, the
bones may contain arseniate of lime as a substitute for some of
their proper phosphate of lime, and in the phosphoric salts, which
are found in the blood, a similar replacement may occurs It is
certain that the quantity of arsenic thus found naturally replacing
phosphorus in the body is very small. but there is no necessary
limit to its extent; and although, in cases of suspected chronic poisoning, the analysis of the organs might lead to useful evidence,
yet the discovery of arsenic out of the alimentary canal should, as
I conceive, not without great caution. be considered as necessarily
involving its having been administered.
The sulphuret of arsenic of commerce, king,'s yellow, when taken
as a poison, is recognised by its solubility in ammonia, from which
it is again thrown down by an excess of any acid. Its reduction to
the metallic state has been already fully described.
An antidote has been recently discovered to the poisonous effects
of arsenious acid, which is founded on a very remarkable reaction
When hydrated peroxide of iron is made into a thin paste with solution of arsenious acid, this disappears, being changed into arsenic.
acid, and the iron into protoxide, 2Fe2,0, and As.03 producing 4Fe.O.
+As.O,. This arseniate of iron has no action on the system; and
hence, in cases of poisoning by arsenic, this hydrated peroxide
should be administered as largely and as rapidly as possible. It
may be made in a few moments by adding carbonate of soda to any
salt of red oxide of iron (permuriate, muriate, or acetate tincture).
It need not be washed, as the liquor contains only a salt of soda,
which would be, if not beneficial, certainly not injurious.
The preparations of arsenic are of very extensive use in the arts.
The metal is used to alloy the lead of which shot is made. White
arsenic is employed in glass-making, to prevent the deoxidation of
the oxide of lead, and the orpiment is employed to render indigo
soluble in some processes of dyeing. It has many other less extensive uses.
Of Antimony.
This metal was first discovered, and its preparations introduced
into medicine by Basil Valentine, from the unpleasant results of
whose experiments upon his fellow monks it got the name of antimoine; its proper Latin name is stibium, and hence its symbol, Sb.
Antimony exists in nature, principally as sulphuret, sometimes as
oxide, and also these two combined, forming the oxysulphuret, red
antimonial ore. It is from the native sulphuret that the metal is
prepared. The process for obtaining it by means of iron is noticed p. 332, but it is had purer by fusing the sulphuret at a bright
red heat with black flux. Sulphuret of potassium and oxide of antimony are first formed, and this last being decomposed by the car



OXIDES OF ANTIMONY.                       385
bon, carbonic oxide is evolved, and metallic antimony separates;
this process is farther detailed in p. 334.
The antimony thus obtained is a brilliant white metal, of a highly
crystalline fracture, and may be obtained crystallized in rhombohedrons, like those of arsenic, by fusion, as described in p. 23; its
specific gravity is 6'8; it melts at about 800', just below redness,
and may be volatilized by a white heat. If heated violently in contact with air, it takes fire, burning with a brilliant white flame, and
forming antimonious acid, which, though not volatile, is carried up
by the current of air, and is deposited on the neighbouring bodies
as a white powder,flowers of antimony. Antimony in powder takes
fire spontaneously in chlorine, burning with a yellowish flame; the
antimony is not oxidized by exposure to the air nor by water; it
is not acted on by sulphuric nor muriatic acids, but is rapidly oxidized by nitric acid, The symbol of antimony is Sb.; its equivalent numbers are 1613 or 129'2; it combines with oxygen in three
proportions.
Oxide of.fnti-mony-Sb.03; equivalent 1913 or 153'2-may be
prepared by adding to an acid and boiling solution of chloride of
antimony in water, carbonate of soda in excess. The carbonic acid
does not combine with oxide of antimony, which therefore precipitates pure; it is a white powder, not quite insoluble in water, and
becomes yellowish when heated. If metallic antimony be burned
in a limited supply of air, this oxide forms, and has been obtainedl
crystallized both in the prismatic and octohedral forms of arsenious
acid, with which it is, therefore, isodimorphous; both the metal and
this oxide, when ignited in a full supply of air, produce antimonious
acid.
This oxide of antimony combines with acids to form salts of very
little stability, but it produces with the acid potash salts of the vegetable acids, double salts of remarkable constitution; of these the
potash tartrate of antimony (tartar emetic) is the most important; it
also acts as a feeble acid; thus, if in its preparation caustic potash
be used to decompose the chloride, a granular white powder is obtained, in which the oxide of antimony is combined with potash;
it is on this account called hypo-antimonious acid by many chemists.
Oxysulpzhuret of.Yntimony. —Sb.03+- 2Sb.S,. This substance constitutes the red ore of antimony, and may be artificially produced
by roasting the native sulphuret in contact with the air; the sulphur
burns out as sulphurous acid, and the antimony becomes oxidized;
the product generally contains an excess of oxide, which may be dissolved out by tartaric acid, and it is thus that the basis for tartar
emetic is sometimes prepared; by continued roasting, the whole of
the sulphur may be expelled, and an impure oxide of antimony produced; this, when melted, constitutes the glass of antimony, and
the oxysulphuret is thp crocus of antimony of the older pharmnacopoeias..Antimonious./cid. Peroxide of.Antimony.-Sb.04.  Equivalent
2013 or 161 2. This is the most stable compound of oxygen and an.
timony; it is formed when antimony is oxidized freely, either by
combustion or by the action of nitric acid, and igniting the resulting
powder. It is a white powder, insoluble in water; it is not volatile i
C cc




386           S UL'PHURE TS OF ANTIM ONY.
it combines with alkalies, forming salts insoluble in water, and from
which, by a stronger acid, it is separated as a hydrate, Sb.O,4+H.O.
This hydrate dissolves in strong muriatic acid.
sintimonic Aqcid.-Sb.0O. Equivalent 2113 or 169'2. This substance is first formed when metallic antimony is oxidized by an excess of nitric acid, and remains as a pale yellow powder, which,
when exposed to a dull red. heat, abandons one atom of oxygen,
leaving antimonious acid, as just described; it is, however, more
stable in combination, and may hence be prepared by defiAlrating
antimony with nitre; when the resulting mass is digested in cold
water, nitrate and nitrite of potash dissolve out, and leave the antimoniate of potash as a white powder; this is decomposed by boiling
water, which dissolves a basic salt, and leaves one with an excess of
acid behind. In its hydrated condition, this acid dissolves in hydrochloric acid.
Antimony and sulphur combine in three proportions, forming sulphurets, which resemble completely, in constitution, the oxygen
compounds; they are sulphur acids, dissolving in a solution of the
alkaline sulphurets, and forming sulphur salts.
S~tlphuret of.lnztimony. —Sb.S3. Equivalent 2216'6 or 177'5. This
substance constitutes the common gray ore of antimony, and crystallizes in the same form as orpiment, with which it is frequently
contaminated; in its native state it is dark gray, with highly metallic
lustre, crystalline in structure, and very easily reduced to powder;
it may be prepared also by precipitation from a solution of any salt
of oxide of antimony, as the chloride, or tartar emetic, by sulphunretted hydrogen; it is then an orange powder, which becomes darker
on being dried, and has the samne composition as the native sulplhuret, with which it becomes identical in appearance by fusion. This
sulphuret dissolves in alkaline solutions, on which circumstance are
founded the various pharmacopmial processes for its formation. It
has been used in medicine'ever since the first discovery of antimony,
and in all countries; the methods of preparation, and the purity of
the products obtainable, are, therefore, exceedingly variable.
When finely powdered sulphuret of antimony is boiled in a strong
solution of caustic potash, it dissolves, and the liquor contains two
salts perfectly similar to one another, but containing, the one sul
phur and the other oxygen, united to antimony and potassium. Foi
one half of each substance is decomposed, the oxygen passing to
the antimony, and the sulphur to the potassium, so that oxide of an
timony and sulphuret of potassium result, and these respectively
combine with the quantities of potash and sulphuret of antimony
that had not been altered; in this way,
I Fb.S3   3K.O.            Sb.S3+ 3K.S.
and       produce        and'
Sb.S3   3K.O.            Sb.03+3K.O. )
When the solution cools, both compounds are partly decomposed,
so that a quantity of sulphuret and of oxide of antimony precipitate
mixed together; and hence an opinion has generally prevailed, and,
indeed, been supported by the high authorities of Leibig and Gay
Lussac, that these bodies are chemically united in the precipitate




PREPARATION OF KER M E S M INERAL.    387
so obtained, and that it is an oxysulphuret, identical in constitution:with that already described. It is, however, quite established, particularly by the experiments of Berzelius and H. Rose, that the oxide and the sulphuret are but mechanically mixed; under the microscope, the former is seen as brilliant white crystals, mixed iwith
the fine amorphous brown powder of the latter; and, besides, the
quantity of oxide is completely variable, and in no case so great as
the composition of the true oxysulphuret should require.
The precipitate thus obtained by cooling is generally of a fine
orange brown colour, the exact shade of which varies very much
with the temperature, and the degree of concentration of the liquor.
It is termed in pharmacy kermes mineral, from a very remote analogy
of its colour to that afforded by the insect kermes (coccus ilicis),
which is used as a cheap substitute for cochineal.
After the separation of the kermes, the liquor, containing still the
sulphur and oxygen salts above described, but with a greater proportion of base, is precipitated by adding an acid in excess. The
sulphuret of potassium is decomposed, and the sulphuret of antiniony, with which it had been combined, separates; at the. same
time, the sulphuretted hydrogen, evolved from the sulphuret of potassiurn, reacts on the oxide of antimony, converting it into sulphuret. This precipitate is much lighter-coloured generally than
the kermes, and is sometimes called the golden sulphuret of antimony, although that name properly belongs to a different substance,
to be described farther on. In many cases, in place of collecting
the hermes and the portion precipitated by the acid separately as
now described, the hot filtered liquor is added to the acid before
the kermes has had time to separate, and the whole being then
mixed, assumes an intermediate shade of colour, and constitutes the
brown sulphuret, or orange suzlpturet of antimony of the British pharmacopmias.
In place of caustic potash, the native sulphuret of antimony is
frequently boiled with carbonate of soda. In this case the whole
of the carbonic acid unites with one half of the soda, forming bicarbonate, and the other half of the soda acts with the sulphuret of
antimony precisely as if it had been used in the caustic state.
An important mode of preparing these pharmaceutical substances
consists in fusing the materials together instead of boiling their solutions. Thus an excellent kermes is prepared by fusing together
three parts of native sulphuret and one of carbonate of potash. The
general reaction is the same as described when the materials were
dissolved; the melted mass is boiled in water, and the solution so
obtained treated as already noticed. Rose has, however, directed
attention to a circumstance which, though occurring in all cases, is
more marked in this process than the others.  It is, that some antimony separates in the metallic state, while another portion is
changed into persulphuret; thus 5Sb.S3 produces 3Sb.S, and 2Sb. is
set free. The solution contains, therefore, not only the ordinary
sulphuret, but some persulphuret of antimony, the colour of which
is much brighter than that of the other, and it hence modifies the
tint of the preparation in a variable manner. The persulphuret carries down with it also some sulphuret of potassium, and hence the




:388        ANTIMONIURET  OF HYDROGEN.
ordinary kermes mineral appears always to contain traces of potash.
The quantity of persulphuret of antimony present seldom exceeds
two or three per cent.
Sulpho-antirnonious Acid.-Sb.S4. This substance is produced as
a yellow powder when the solution of antimonious acid is decom.
posed by sulphuretted hydrogen.
Sulpho-antimonic.Icid —Persulphuret of antimony, Sb.S5 —is obtained when a solution of antimonic acid in muriatic acid is treated
with sulphuretted hydrogen. It is of a fine golden orange colour.
Its formation in the process for kermes mineral has been already
explained. This is the true golden sulyhluet. To obtain it in large
quantity, as is given in many pharmacoporias, three parts of sul
phuret of antimony and one of carbonate of.potash are to be fused
with one half part of sulphur; this last converts the antimony into
the persuiphuret. The fused mass is to be dissolved in water, and
decomposed by muriatic acid.'.ntimoniuret of Hydrogen.-Sb. Ha. When hydrogen is evolved
in contact with antimony in a nascent or finely divided state, they
combine and form a gas, which, in properties and constitution, has
a remarkable similarity to arseniuret of hydrogen. The easiest mode
of effecting this is to dissolve zinc in dilute sulphuric acid to which
tartar emetic has been added. The gas so evolved is colourless, insoluble in water, has neither acid nor alkaline reaction. It precipitates the salts of mercury and most metals, but not copper, by
which it is distinguished from the arseniuret of hydrogen. Its
specific gravity has not been experimentallydetermined; but if it be
composed, like arseniuretted hydrogen, of one volume of metallic
vapour and six of hydrogen condensed to four, it should be 4504'7.
When this gas burns, water is formed, and antimony deposited,
either as metal or as oxide, according to the supply of oxygen. It
hence superficially resembles in its combustion the gas containing
axrsenic, but it is distinguished readily by the following characters.
1st. The antimoniuret of hydrogen, wheni it is decomposed by
heating a point of the tube through which it passes to redness,
deposites the metal at the heated part, while arsenic settles at a
certain distance beyond, where the tube is colder.
2d. The metallic crust is not volatilized at any temperature which
can be applied to glass.
3d. If the metallic scale be deposited on a porcelain plate, and oxidized by the outer flame of the blowpipe, it forms a powder yellow while hot, but white when cold, which is not volatilized by
any farther application of the flame. Arsenic, on the contrary, becomes oxidized only in the act of being vaporized.
In certain cases of compound poisoning, and where tartar emetic
has been given as an emetic in cases of poisoning by arsenic, it is
possible that the two metals may coexist in solution. In these
cases they may be separated by converting both into the hydrogen
compounds, and decomposing the mixed gases by igniting the tube
through which they pass. The antimony is deposited close to the
heated part, and the arsenic at a little distance.
The detection of antimony is generally simple; in all its combinations it is immediately recognised by the formation of its corn



TELLURIUMi  AND IrS COM[POUNDS.                               389
pound with hydrogen just described. In solution, in the state of
oxide, it gives with sulphuretted hydrogen the orange precipitate
of sulphuret.  In the other states of oxtdation the precipitates by
sulphuret of hydrogen are more yellow, but are all easily distinguished from  orpiment by not being volatile, and froln the bisulphuret
of tin by yielding the antimoniuret of hydrogen.  From  tihe slphuret of cadmium  they are known by their solubility in hydrosulphuret of ammonia.
Of Tellur'ium.
This is one of the rarest of the metals, and, although classified with them, from its
lustre and power of conducting electricity and heat, in which it is, however, far inferior to tnhe others, it ranks naturally with sulphur and seleniuln, to which last it
assimilates completely in its properties.  It exists in nature, native, and combined
with a variety of,metals, gold, silver, antimony, lead, &c., forming ores of very indefinite constitution. Its extraction, which is still farther complicated by the presence of sulphur and selenium, would require too detailed description, and is too seldom an object with chemists to require description here. Its properties and principal compounds alone deserve attention.
Pure tellurium is silver white and very brilliant.  It crystallizes easily in rhombohedrons. It is brittle and easily powdered. Its sp. gr. is 6t14. It is about as f'usible as antimony, and at a very high temperature may be volatilized. Its vapour
smells like selenium; when heated in the air it burns with a bluish flame, forming
tellurous acid. It is rapidly oxidized by nitric acid.
The analogy of tellurium to sulphur is very close. When tellurium is boiled in
a strong solution of potash, there is formed tellurite of potash and telluret of potassium; but if this solution be diluted, the potassium reduces the tellurous acid, and
the metal is precipitated, potash being regenerated. The symbol of tellurium is Te.
Its equivalent numbers are 801'8 and 642S.
Tellurium combines with oxygen in two proportions, forming tellurous and telluric acids. The former, telltaoas acid, Te.02, is prepared by decomposing the bichloride of tellurium  by water, Te.Clz and 2H.O. producing 2I-I.1l. and Te.02.
This last precipitates as a bulky white powder containing combined water.  In this
state it is sensibly soluble in water, and reddens litmus. It dissolves readily both
in acid and alkaline solutions, forming compounds of' a very instable character.
When its solution in water is heated to about 1100, it deposites the tellurous acid in
an anhydrous form. The water is also expelled by a moderate heat friom the hydrated acid in powder.  The anhydrous acid thus obtained differs essentially from
the hydrated form., It is insoluble in water, in acids, and in alkalies, and has no
acid reaction whatsoever. No salts of it can be formed in the humid way; but if it
be fused at a red heat with carbonate of potash, the carbonic acid is expelled, and
tellurite of potash formed, which dissolves in water; from this solution the hydrated tellurous acid is thrown down on the addition of an acid.
Berzelius considers these remarkable differences of properties as indicating an
isomeric distinction betwveen the two acids. In a subsequent chapter I shall point
out the manner in which I believe such compounds should be viewed.
Telluo'ic Acid, Te.03. is prepared by dellagrating teliurous acid with nitre; a soluble tellurate of potash is thus obtained, which, when mixed with nitrate of barytes, gives an insoluble tellurate of barytes, and this, acted on by sulphuric acid,
yields sulphate of barytes, and in solution telluric acid, which crystallizes in large
prisms containing three atoms of water. Of these, two are given off at 212~ jF.
It does not taste acid, but reddens litmus slightly. It combines readily with bases,
forming classes of salts containing one, two, and four equivalents of acid. When.
the crystallized telluric acid is heated to redness, all its water passes off, it becomes
orange, and undergoes a change of properties like stannic acid.  It becomes insoluble in water, in acids, and alkaline solutions; when very strongly heated, it gives
off oxygen, and tellurous acid remains; but if this anhydrous acid be fused with
potash, the tellurate of potash which dissolves contains the acid in its hydrated
state.  These forms are considered as being isomeric, and not identical bodies;
their real nature will be noticed hereafter.
Tellurium and hydrogen combine to form a gas, telluret of hydrogen, H.Te., which
resembles in its characters sulphuret of hydrogen, particularly in its odour; it red.




0390  u RAN: U M  AND  ITS  COMPOUN D S.-CO P E R.
dons litmus, is soluble in water, decomposes the alkalies and earths, fbrming soluble
tellurets, and precipitates insoluble tellurets from solutions of the other metals..Tellurium  combines with sulphur in two proportions, forming sulphurets, which
do not require detailed notice. Its compounds with the metals resemble so completely the metallic sulphurets as to render a separate account unnecessary. IThus,
in every case where a metallic sulphuret evolves sulphuretted hydrogen gas with an.acid, the telluret of the metal produces telluretted hydrogen, and the metallic tellurets are soluble or insoluble in water, precisely as the sulphurets of the same metals
are.
Of Uranium.
This metal exists in some rather rare minerals, particularly in pchblende, combined
with oxygen; the processes for its extraction are rendered very complex by the
presence of a great number of other metals, and I shall refer, therefore, to the sys-.tematic works for the details of its extraction; the metal itself is easily obtained
pure by the action of hydrogen gas on either of its oxides at a red heat. It is of a
dark gray colour, difficultly fusible, specific gravity 9'0. Its symbol is U., its equivalents are 2711 or 217:3, being the largest numbers for any of the simple bodies; it
combines with oxygen in. two proportions.
Protoxide of Uranium, U.O., is obtained by decomposing any salt of uranium by.a caustic alkali; it precipitates as a greenish hydrate, which rapidly becomes yellow, forming the peroxide by absorbing oxygen: the protoxide of uranium is dissolved by an excess of ammonia. PeToxziae (f ur-'nima, UO3, is iormed when the
protoxide is heated in air; it is yellow, and possesses some of the characters of an
acid, uranic acid; it reddens litmus; it enters into combination as well with alkalies as with acids; the alkaline and earthy uranates are insoluble, yellow or orange
coloured. This oxide is used to colour glass of a fine lemon yellow.
The sulphurets, &c., of uranium are unimportant.
SECTION V.
MIETALS OF THE FIFTH CLASS.
Of Copper.
Copper is one of the most important of the metals, and one, also,
of the most extensively diffused through nature.  It exists native in
veins, and frequently crystallized, in forms belonging to the regular
system; in the state of oxide it is found, both uncombined and forming arseniates, phosphates, carbonates, and other salts, but its most
abundant source is the native sulphuret. The ordinary copper ore,
copper 2yrites, is a double sulphuret of copper and iron, Cu2S.+Fe2S3,
and from this the metal is extracted for the purposes of commerce.
The general processes for the reduction of a metallic sulphuret
have been already described (p. 333), but, from  the composition of
the copper ore, some additional management is required; there are
two metals present in the ore, and as neither is volatile, the product
after complete reduction should be, if the process was simply managed as for a simple sulphuret, not pure copper, but an alloy of one
equivalent of copper and two of iron; this is avoided by arresting
the process of reduction at a certain stage; the copper, having less
affinity for oxygen than the  iron, assumes the metallic state first,
and, if it were possible to work so accurately, the whole of the copper might be reduced before any iron, and this last metal left altogether in the scori.a as oxide or silicate; but this not being feasible,
the copper first obtained is rendered impure by the presence.of a
quantity of iron, and also of sulphur; this impure copper is then
calcined; the iron and sulphur, being the more combustible bodies,
are first oxidized, and then again, by other reductions and calcinations, the copper is ultimately brought to a state of complete purity




PROP ERTIES OF COPPER.                     391
The separation of the iron is facilitated by adding a small quantity
of sand to the calcined mass before the process of reduction; the
silicic acid unites exclusively with the oxide of iron, and the silicate
of iron not being reducible under ordinary circumstances, the purification of the copper is more rapidly effected.
Though the copper is thus rendered quite pure from iron, great
care is still required in these, operations, in order to secure the
proper softness, ductility, and tenacity necessary in the employment of this metal in the arts; thus, if it has been too long in contact with the fuel, it combines with a small quantity of carbon; if, on
the other hand, the deoxidizing action of the fuel be not applied long
enough, some suboxide remains undecomposed, which dissolves in
the metallic copper. In both these cases the metal is brittle and
of a bad grain, so as to be unfit for many of its uses.
Copper is obtained also in the metallic state by precipitation from
the water which collects in the galleries and shafts of copper mines,
and which, from the oxidation of the sulphuret of copper, contains
sulphate of copper dissolved. Fragments of old iron are thrown
into the reservoirs in which the drainage water of the mine is collected, and by electro-chemical action, as described p. 193, 195,
and 335, the iron is dissolved and the copper precipitated in irregularly crystallized masses.
Pure copper is of a peculiar well-known reddish colour. It is
very malleable and ductile; after iron, it is the strongest of the metals. It crystallizes by fusion in a form which is not the same as
that found native, or produced when the metal is precipitated from
its solutions. Its sp. gr. is 8'9. It is fusible at 1996'. It is not
volatile. In dry air it is not tarnished, but in damp air it gradually
becomes covered with a greenish coating of basic carbonate of copper. When heated in contact with air, copper combines rapidly.,
with oxygen, and passes through a variety of rainbow colours, but
is at last converted into black oxide, which forms as scales upon its
surface. The series of colours arises first from the action of light
upon the thin coating of 6xide, as also happens in the oxidation of
iron. The generality of acids do not act on copper at ordinary
temperatures, unless in contact with air, for the copper is incapable
of decomposing water; but at the point of contact with air, oxygen
is directly absorbed, and the acid combines with the oxide so generated. In this way the feeblest acids may act upon copper, as the
acetic acid and the acids contained in the various fatty bodies, and
the metal be thus introduced into culinary preparations, and so produce poisonous effects. The acids which give off oxygen directly
dissolve copper, as nitric acid, with evolution of nitric oxide. Strong
oil of vitriol, also, when boiled on copper, gives sulphate of copper
and sulphurous acid gas.
The symbol of copper is Cu., from its Latin name; its equivalent
395"7 or 31'7.
Copper combines with oxygen in two proportions, forming a suboxide and a protoxide.
Protoxide of Copper.-Cu.O. Equivalent 495'7 or 39'7. This oxide is formed by exposing copper, at a red heat, to a current of air.
It may also be obtained by igniting the nitrate of copper. It is a




392                OXIDES OF COPPER.
dull black poxwder, which, by a very high temperature, muy be melt.
ed, and crystallizes on cooling. it dissolves but slowly in acids,
forming the ordinary blue or green salts of copper. When heated,
even below redness, in a stream of hydrogen gas, it is perfectly reduced, water being formed. It is thus that, as described in p. 253,
the composition of water is best determined. At a dull red heat,
this oxide is reduced completely by carbon and all its compounds,
carbonic acid beihig produced. For this reason it is extensively
employed in the ultimate analysis of organic substances, of which it
converts the carbon into carbonic acid, and the hydrogen into water
The metallic copper thus obtained by the reduction from the oxide
is a fine pinkish-red powder, which has a remarkable affinity for
oxygen, and is hence used in the analysis of organic substances containing nitrogen, to prevent the formation of nitrous or nitric oxides.
When a solution of caustic potash is added in excess to a solution of a salt of copper, the protoxide is thrown down as a hydrate,
Cu.O.. H.O. It is a fine blue powder, which is decomposed by a
very gentle heat, so that even if a liquor containing it be boiled, it
becomes brown and anhydrous, though in the midst of water. It is
hence that, if the solution of copper be added to a boiling solution
of potash, the precipitate is the dark brown anhydrous oxide, which,
however, obstinately retains a little potash.
Suboxide of Cop1per — Cu2O. Equivalent 891 4 or 71'4. This body
exists native, constituting the ruby copper ore, and may be prepared
artificially by igniting a mixture of five parts of black oxide of copper and four of copper filings; half of the oxygen of the former
passes to the latter, and the whole becomes suboxide. It is likewvise made by fusing together three parts of subchloride of copper
and two of dry carbonate of soda; chloride of sodium and suboxide
of copper result, Cu2CI. and Na.O. giving Cu20. and Na.Cl., while
the carbonic acid is given off. This suboxide of copper is a reddish-brown powder, which is much less acted on by moist air than
pure copper; and hence, under ordinary, circumstances, when copper becomes brown by being, coated with this oxide, the action
ceases. Articles of copper are thus coated intentionally, for the
purpose of preserving their surface, by covering them with a paste
of red oxide of iron, which, when heated, is thus reduced to the
state of protoxide, 2Cu. and FeO, giving Cu20O. and 2Fe.0.; this
last is then removed by digestion in a boiling solution of acetate
of copper.
The generality of acids decompose the suboxide of copper into
metallic copper, and the black oxide with which the acid combines;
but, besides the subchloride of copper, several of its salts may be
formed by the action of deoxidizing agents on the salts of the black
oxide; thus sulphurous acid converts the hydrate of the black oxide
into sulphate of the suboxide, S.O, and 2Cu.O. producing S.O0+
Cu,O. From the solution of this salt, a fine orange hydrate of the
red oxide is thrown. down by the caustic alkalies. Protochloride
of tin and protosulphate of iron also reduce the salts of copper to
this state of oxidation.
Sulphur combines zwith copper in two proportions, forming sulphurets equivalent to the oxides just described; they are both found




DETECTION  OF COPPER.                      393
native, and constitute, particularly the subsulphuret, important ores
of' copper. They may be prepared artificially by fusing together
sulphur and metallic copper; the union takes place with brilliant
combustion. If some sulphur be placed in a flask, and beat be applied so as to fill the flask with the vapour of sulphur, a thin copper'wire dipped in it burns, as iron does in oxygen, forming the subsulphuret; these bodies are not of importance, except as the great
sources of metallic copper..
The sulphurets of copper may also be formed by precipitating the
salts of copper with sulphuretted hydrogen; a deep brown powder is
produced, which is Cu2S. or Cu.S., according as the solution contained the suboxide or the protoxide of the metal.
The detection of copper in solution is very simple; the salts of
the black oxide are generally green or blue; on the addition of ammonia, a precipitate is produced, bluish or green, according to the
acid with which the oxide had been combined, but in all cases producing with an excess of the ammonia a deep violct-coloured solution. The only metal which resembles copper in this respect is
nickel, and from it, it is distinguished by all its other properties,
particularly by the yellow prussiate of potash, which produces a fine
chocolate brown precipitate of ferrocyanide of copper. With sullphuret of hydrogen, the salts of copper give a dark brown sulphuret,:insoluble in hydrosulphuret of ammonia; and when a slip of clean
iron or zinc is introduced into a liquor containing copper, this is reduced, and deposited upon the surface of the zinc or iron as a bright
coating of metallic copper.
VWhen the copper exists as suboxide, its reactions are very differ
ent; it gives, with ammonia, a white precipitate, which redissolves
in an excess, forming a colourless liquor; if there be no excess of
acid, chloride of sodium gives a white precipitate of subchloride of
copper. But in practice it is never necessary to look for copper by
these reactions, the salts of the suboxide absorbing oxygen with
such avidity, that by a few minutes' exposure to the air their constitution changes.  The colourless solution of suboxide of copper in
ammonia becomes violet blue in the act of pouring it from one bottle to another; and hence, for the mere detection of copper, the
properties of the protoxide alone need be taken into account.
Like the oxides of cobalt and nickel, the oxides of copper are not,
by themselves, soluble in water of ammonia. The solutions of these
metallic compounds in water of ammonia are basic salts, to the constitution of vwhich the acid, with which the metallic oxide had been
originally combined, is necessary.;The detailed nature of these
bodies will be noticed among the compounds of ammonia.
The detection of copper by the blowpipe is very simple and distinct. Fused with borax, a substance containing the most minute
trace of copper gives a glass, which, when heated in the oxidizing
flame, becomes green, being coloured by the protoxide; but when
ignited in the reducing flame and suddenly cooled, is deep ruby
red, generally opaque. This change of colour arises from the copper being reduced to the state of suboxide  The colour given to
glass by this suboxide is a pure prismatic red, so homogeneous that
ied light may be obtained for optical experiments by transmitting
0~~~~~~~ D   r. 




3941     USEFUL ALLOYS OF  COPPER.  LEAD.
white light through this coloured glass, and the tint is so fine that
this ruby glass is the most valuable that can be used for ornamental
purposes.
The salts of copper generally tinge the flame of the blowpipe
blue or green, according to the other bodies that may be present.
Independent of the direct employment of copper in the arts, for
which its properties eminently qualify it, it enters into the composition of a great number of alloys of great importance.  Thus bronze,
formerly used as a substitute for steel, and still employed in the
casting of statues and monuments, from the accuracy with which it
adapts itself to the mould, and its durability, consists of ninety parts
of copper and ten of tin in 100. It is curious, that from the very
earliest ages, this, which is still the best proportion, should have been
employed; the bronze swords from ancient Egypt, from Scandinavia, and those found in Ireland, having all this-constitution.  Gun
metal, or that of which cannons are, cast, is an inferior kind of bronze,
containing somewhat less tin.
The elasticity and sonorousness of these alloys are very remarkable.  That used for bells, bell metal, consists of 80 parts of copper
and 20 of tin.  The Indian gongs have this composition, but common bells contain less tin, and, in place of it, some lead and zinc.
In the proportion of two parts of copper to one of tin, or, more
accurately, of four atoms of copper to one of tin, 127 to 59, an
alloy is formed of exceeding brittleness and hardness, and so brilliant, when truly polished, as to be used for the mirror surface in
reflecting telescopes; it is hence called speculumn metal.  The quality
of this alloy is remarkably deteriorated by a slight deviation to either side of the true atomic proportions.
The alloys of zinc and copper are very numerous and important,
constituting the different varieties of brass.  The best brass consists
of four atom.s of copper to one of zinc; but, by changing the proportions of the metals, a variety of shades of gold lustre, used in
counterfeit jewelry, are obtained. In the proportion of equal parts
of copper and zinc, hard solder is produced; this is used in solder-.ing together surfaces of brass and copper.
Of Lead.
This metal exists in nature, very extensively diffused, and in a
great variety of forms.  The sulphate, phosphate, arseniate, carbonate, and chloride of lead are found native; but it is exclusively
from the sulphuret of lead, galena, that the metal is extracted for
the purposes of commerce.  The methods used in its reduction
have been very fully described in the preceding chapter, p. 334.
Lead is one of the softest and least tenacious of the metals; it is
bluish white, and very brilliant, but rapidly tarnishes in the air, becoming covered with a grayish coating, beyond which the action
does not appear to extend; its specific gravity is 11'44; it melts at
6123, and in solidifying diminishes in volume, so that it is unfit for
accurate castings; it may, however, be obtained, by fusion, crystallized in octohedrons; it is not volatile; it is not sensibly acted on
by muriatic nor sulphuric acids, except at very high temperatures,
but by nitric acid it is rapidly oxidized and dissolved.




OXIDES OF LEAD.                         395
When lead is exposed at the same time to air and-moisture, its
oxidation proceedrs with great rapidity, so as to be used to analyze
atmospheric air (p. 2;64.). The oxide so formed is not quite insoluble, so that when pure water, rain, or even common soft water is
preserved in leaden cisterns, an impregnation with lead may occur
in such:amount as to produce dangerous conseqtiences, if employed
habitually as a drink. Fortunately, this is obviated, in general, by
the small quantities of saline matters, particularly sulphates, wvhich
all ordinary spring and river waters contain.  These react on the
oxide of lead, and, forming compounds totally insoluble in water, remove all traces of it from solution. A whitish cru.st gradually forms
on the interior of the cistern, and assists, subsequently, in protecting
it from the oxidizing action of the air; no danger is therefore to
be apprehended from the supply of water to a city being conveyed
through leaden pipes, and preserved in leaden cisterns; for all water
of mineral origin dissolves, in filtering through the layers of rocks
in its passage to the surface, a sufficiency of saline matters to serve
for its protection.
The symbol of lead is Pb., from its Latin name; its equivalent is
1294 5 or 103'7. It combines with oxygen in two proportions,
forming oxides, which, again uniting, form an intermediate complex
oxide.
Protoxide of Lead.-Pb.O.  Equivalent 1394'5 or 111'7. This
may be prepared by exposing metallic lead at a red heat to a current, of air; the lead rapidly combines with oxygen, and the oxide
so produced fuses. It forms, on cooling, crystalline masses of a
greenish-yellow colour; this constitutes the litharge of commerce,
which is generally obtained in the cupellation of lead for the purpose of extracting from it the small quantity of silver which its ores
generally contain.  When the litharge is kept for some time, the
masses of it break up into a brick-red crystalline powder, evolving
heat. This change is technically termed slacking, but it is not due,
like.the slacking of lime, to combination with water, but to a change
of the crystalline form of the litharge.  The yellow form  appears
to be more permanent if the lead be oxidized at a lower temperature,
and, when powdered, was once used as a yellow pigment under the
name of massicot.  This may be produced of the richest colour by
decomposing the subnitrate of lead at a temperature insufficient for
the fusion of the oxide.
This oxide may also be prepared by decomposing a soluble salt
of:lead by caustic potash; a white precipitate is produced, which is
a hydrate of the oxide, 2Pb. + H.O.; by a great excess of caustic potash the precipitate may be redissolved.  The oxide of lead appears
to have the power of uniting with most of the alkalies and earths
to form compounds more or less soluble. A body of this kind, formed by boiling lime and litharge together, is capable of crystallizing,
and is used to dye the hair black.  The hair contains sulphur, and
a black sulphuret of lead'forms in its substance, and is not liable to
change. The protoxide of lead requires 12,000 parts of water to'
dissolve it; the solution reacts feebly alkaline; it is a strong base,
and the only oxide of lead which combines with acids.
Peroxide of Lead, Pb.02, is obtained by digesting the protoxidP




396      OXiDES AND SULPHURET OF LEAD.
in chlorine water, or in a solution of chloride of lime. In the first
case, 2Pb.0. and Cl. produce Pb.02 and Pb.CIl. In the second case,
Pb.O. and Ca.O.Cl. produce Pb.0, and Ca.C].; another simple plan
consists in heating red lead, which is a compound of the prot.oxide
and the peroxide, with dilute nitric acid, until all the protoxide is
dissolved out, washinff the residue well, and drying it at a moderate
heat. The peroxide so obtained is of a dull dark brown colour;
when heated it gives off half its oxygen, leaving litharge. With
muriatic acid it produces chlorine and protochloride of lead, and
with sulphurous acid, which it rapidly absorbs, neutral white sulphate of' lead, Pb.O0 and S.0O producing Pb.O.+8.03. This oxide
of lead does not form salts.
The Red Lead, or Jliinium, Pb304-2Pb.O.+Pb.O,, is produced
when lead is oxidized, so that the oxide formed shall not be fused,
and when the metal is all converted into the yellow powder, increasing the heat to incipient redness.  Oxygen continues to be absorbed
until one third of the metal is converted into peroxide, giving the
constitution above expressed.  This is the pure red lead, the colour
of which is exceedingly brilliant; but the generality of red lead
found in commerce contains an excess of protoxide, which may be!removed by boiling in a solution of neutral acetate of lead.
When red lead is ignited, it gives off oxygen and becomes protoxide; with rnuriatic acid it forms protochloride and chlorine. It
does not form any proper salts, but it dissolves in acetic acid completely, giving a colourless liquor, from which, after a little time,
peroxide of lead separates.
It is probable that there exist other oxides of lead; thus the gray
coating which forms on lead exposed to the air is looked upon by
many chemists as a suboxide; and on heating oxalate of lead to low
redness, a gray powder is obtained of a similar nature, and yields,
on analysis, the formula Pb2O. In general, these bodies have been
considered as mixtures of the metal in powde'r with the real protoxide; but I think the evidence of their definite constitution very
strong.
From the similarity of the formula of red lead, PbO,, to those of
the black oxide of iron, Fe,O4, and of the red oxide of manganese,
MnO4,, it has been suggested that it may contain sesquioxide of lead,
PbO3, similar to Fe2O, and Mn203. The formula of red lead should
then become Pb.O.+Pb,2O; but this idea, though interesting, is only
hypothetical.
Sulphuret of Lead.-There is but one compound of sulphur and
lead, the protosulphuret, Pb.S. It constitutes the abundant lead
ore, galena, and may be formed artificially, either by fusing together
lead and sulphur, or by decomposing a solution of a salt of lead by
sulphuretted hydrogen gas or hydrosulphuret of ammonia  It is
then a black po\vder, insoluble in water, and in alkalies, and dilute
acids. It is rapidly oxidized by nitric acid, being converted into
sulphate of lead. From the perfect insolubility and marked colour
of this sulphuret, a salt of lead and sulphuretted hydrogen are respectively the most delicate reagents for each other.
There are some indications of the existence of other sulphuretm
of lead, which, however, do not require special notice. If a salt of




DETECTION  AND  USES OF  LEAD.-BISMUTH. 3.97
lead be decomposed by bisulphuret of calcium, a red precipitate appears, possibly a bisulphuret of lead, analogous to the deutoxide, and
galena may be fused with metallic lead, forming a homogeneous
mass, in which, probably, subsulphurets are contained.
The detection of lead is simplified very much by its forming but
one series of salts, those of the protoxide. Its solutions are recognised by giving, with caustic potash, a white precipitate, soluble itl
excess; with carbonate of potash, one also white, but insoluble iL
excess; with sulphuretted hydrogen, one dark brown or black,
whose characters are described above; with a solution of bichromate of potash, the salts of lead produce a fine yellow precipitate,
chrome yellow; and with iodide of potassium, the iodide of lead, in
brilliant yellow scales, like fragments of gold leaf. Yellow prussiate
of potash gives a white precipitate, and sulphate of soda a white
sulphate of lead, insoluble in water, but not insoluble in acids. If
the solution contain much lead, any soluble chloride throws down
sparingly soluble chloride of lead, which, however, remains dissolved, if the solution be dilute.
Lead and its preparations are of the most extensive use in the arts.
In. making pipes and cisterns, sulphuric acid chambers, bullets, and
a variety of other purposes, the metal is employed unaltered; and
its alloys are also of important application.  Thus the metal of which
printing types are made consists of three parts of lead to one of
antimony. The inferior sorts of pewter are alloys of lead and tin,
but the fine kinds should be tin with very little lead, and some antimony and bismuth. The solder used for soldering surfaces of lead,
or of tinned iron, to each other, consists of lead and tin, the proportions of which vary from two parts of tin and one of lead, to three
parts of lead and one of tin, according to the object. The more tin
the alloy contains, the more fusible it is. Fine solder fuses at 360'
coarse solder at 500~.
Of Bismut/h.
Bismuth is not a common metal. It is found but in a fewvplaces,
and only in the metallic state in quantity, for the su]phutet of bismuth is too rare to be of technical interest. It is extracted from
the rocks through which it is disseminated by reducing them to
coarse powder, and igniting this in a kind of kiln; the bismuth, being
very fusible, melts out, and collects at the bottom in a trough placed to receive it.
It is a white metal, with a peculiar reddish shade, and remarkably
crystalline structure. It may be obtained in separate crystals of
considerable size, which are cubes, generally hollow at the sides.
To obtain good crystals, the metal should be perfectly pure; this
is effected by deflagrating some nitre on the surface of the melted
metal; the impurities are more easily oxidized than the bismuth, and
hence pass into the scorie which form on the surface.  The crystals so obtained have frequently beautiful rainbow tints on their surface, from an exceedingly thin layer of oxide.of bismuth by which
they become coated.
Bismuth is very brittle and easily oxidized. It is scarcely acted
on by sulphuric or muriatic acid, but it decomposes nitric acid vio



398          BISSM'UTH  AND  iTS  COMPOUNDS.
lently, evolving nitric oxide, and forming oxide of bismuth, with
wvhich the nitric acid combines.  It fuses at 497-', is volatile at a wNhite
heat, and then burns with a bluish-white flame.  Its sp. gr. is 9-9.
The symbol of bismuth is Bi.  Concerning its equivalent, there is
some doubt at present as to whether it should be 886'9, or three
times so much, 2660-7, on the oxygen scale, and hence 71'1, or
213'3, on the hydrogen scale.''he first number assumed would make the oxide of bismuth a protoxide, Bi..,
the last a teroxide, Bi.03. The ground upon which the former view stands is the
supposed similarity of some salts of bismuth to those of magnesia and the protoxide
of copper, but recent examination has gone to show that this analogy is not at all
so strong as had been supposed, and that their difference is more remarkable than
their resemblance. On the other hand, the sulphuret of bismuth is isomorphous
with the sulphurets of antimony and arsenic, and the equivalent deduced from the
specific heat of' bismuth agrees with those for arsenic and antimony, and assigns
tile saine constitution to the compounds of the three. The salts of the oxide of bis..
muth are exceedingly instable, and, like those of antimony, are decomposed by water, so that, while it allies itself' to that metal in every important point of physical
and chemical characters, it recedes in all the important facts of its history from copper, iron, zinc, and the other metals of the magnesian class.  I therefore think
these are sufficient grounds for abandoning the numbers 886i9 and 71 1, given in the
tiable, p. 205, and to assume 2660'7 and 213'3, as the equivalents of bismuth on the
oxyren and hydrogen scales respectively,
Oxide of Bismuth-Bi.03; equivalent 2960-7 or 2373 —may be
prepared by the cornbustion of bismuth at a high temperature, or by
the ignition of the subnitrate of bismuth.  It is a buff-coloured powder, which may be melted.  It combines with acids to form  wellcharacterized salts.
The Suzperoxide of Bismuth, Bi.05, is prepared by boiling finelylevigated oxide of bismuth in a solution of chloride of soda.  A fine
brown powder is produced, which is freed with great difficulty from
admixed unaltered oxide.  When heated to dull redness it is decomposed into oxygen and oxide of bismuth; with muriatic acid it gives
chlorine and ordinary chloride of bismuth.  Its composition was
supposed to corroborate the idea that the yellow oxide was a protoxide, for on that idea this vould be a sesquioxide, Bi2O3, like the
sesquioxides of cobalt and nickel, which it resembles so much in
properties; but the formula, Bi.O,, agrees as well with the analytical results, and I look upon it as corresponding to antimonic acid.
SulpAuret of Bismuth, Bi.S3, exists native, in crystals is6mnorphous
with the sulphurets of antimony and arsenic. It may be prepared
by fusing bismuth and sulphur together, or by adding sulphuretted
hydrogen to a solution of a salt of bismuth: it then precipitates as
a brown powder.  It is insoluble in water and in hydrosulphuret
of ammonia.
Bismuth is easily known by its solutions being precipitated brown
by sulphuretted hydrogen and by iodide of potassium, and yellow
by chromate:of potash.  The caustic and carbonated alkalies prodoce a white precipitate of hydrated oxide of bismuth, wvhich is insoluble in excess.  A strong solution of a salt of bismuth is decom.
posed by the addition of water, whereby a white basic salt is pre.
cipittcd, and the liquor contains free acid.
Bismuth is extensively employed for some purposes in the arts.
The alloy used for casting stereotype plates consists of tin, lead,
and bismuth; and by increasing the quantity of bismuth, the fusibil
M~~\. N~L~~VL7   LLI ICr —— r —---




EXTRACTION  OF  SILVER  FROM  ITS  ORE.  399
ity of this alloy becomes so great, that a compound of two parts of
bismuth, one of tin, and one of lead, fuses at 2010. This is the fu.
sible metal used for the bath in taking the specific gravities of vapours, as described p. 14, and for supplying a steady source of
heat for other purposes.
SECTION VI.
MIETALS OF THE SIXTH CLASS.
Of Silver.
This metal exists native, and in the state of suiphuret, in a great
variety of places; and from the facility with which it may be extracted, and the permanence of its lustre, it became known at a very
early period. The principal sources of silver are the mines of
South America; in Europe, those of Saxony are the most remarkable. A great deal of silver is also obtained from the ores of lead,
the sulphuret of lead being generally accompanied by the sulphuret
of silver in small quantity.
The native silver of America exists, generally speaking, too finely disseminated to be simply melted out. It is washed out by mercury, this fluid metal dissolving the silver, and being then distilled
off, leaves the precious metal behind. A very remarkable process
is used to extract the silver from the sulphuret.  This ore is roasted in a reverberatory furnace with chloride of sodium, by which
chloride of silver and sulphuret of sodium  are formed, Ag.S. and
Na.CI. giving Ag.Cl. and Na.S.  This last is washed out, and then
the chloride of silver being put into barrels with some water, pieces
of iron, and mercury, the iron decomposes the chloride of silver,
forminog chloride of iron and setting the silver free, and this dissolves in the mercury, forming a fluid amalgam; this is strained
through leather bags, by which a great part of the mercury passes
off, and a pulpy mass of amalgam of silver is obtained, which is then
submitted to distillation, by which the mercury is separatecl, and the,
silver remains pure.
The method of extraction of the silver which accompanies the
lead, in galena, is founded on the greater rapidity with which lead
combines with oxygen. In the smelting of the ore, the silver is reduced with the lead, and the: resulting impure metal is melted in a
shallow porous dish made of bone ashes, and when at a full red lieat
a-current of air is urged across it from powerful bellows.  The lead
becomes converted into litharge, as described in p. 395, and new
coatings of oxide of lead succeed one another upon the surface,
until the whole quantity of that -metal has been removed.  WVhen'the silver remains pure, the surface becomes suddenly brilliant, and
the completion of the work is known by the metal thus flashing or
lightening, as it is technically termed. This is the process of cupellation.  The porous bone earth capsule, or cupel, absorbs a great
deal of the litharge, and the rest is blown away from the surface,
as it forms, by the blast of air, and is collected in the front of the
furnace.
This process has been remarkably shortened by the discovery




400              PROPERTIES OF SILYER.
that the quantity of silver may be concentrated in a comparatively
small quantity of lead, by crystallization.  The silver is not difu-ised
uniformly through all the lead, but combined in atomic proportions
with a certain quantity of it, forming an alloy, which is thehn mixed'with the excess of lead.  This alloy is more fusible than lead, so
that when a large basin of lead, containing a small quantity of silver, is melted, and allowed to cool very slowly, so as to crystallize,
the portions which first solidify are pure lead, and these being removed with iron colanders, all the silver remains in the mother liquor.  The process must be stopped, however, before this begins
to congeal.  By a succession of crystallization of this sort the great
excess of lead is gradually got rid of, and the quantity to be oxidized at the cupel diminished in a corresponding degree.
The silver of commerce is never pure, and hefice, for chemical
purposes, must be freed from the metals, generally copper, associated with it. For this purpose it is dissolved in nitric acid, and its
solution precipitated by common salt.  Chloride of silver separates,
which is then reduced by any of the methods described in p. 332,
333. The method of assaying may also be -used to obtain pure silver.  The impure silver is melted with from four to eight times its
weight of lead, and this alloy cupelled as already detailed; the lead
is not only itself oxidized, but the other metals present, which would
not otherwise separate, are converted into oxides, which pass off
with the oxide of lead.  It is in this way that the standard alloys
of silver, for coinage and plate, are verified at the mint and other
offices.
Silver, when completely pure, is very brilliant; it is the whitest
of the metals, and takes a fine polish. It is very ductile and malleable.  Its sp. gr. is 10 5; it fuses at 1873'.  It is not altered by air
or water, but when kept melted for a considerable time, it absorbs
oxygen, which it appears to hold rather dissolved than combined,
for on solidifying it discharges this oxygen, by which the surface is
thrown into irregular granulations. The quantity of oxygen may
be so great as twenty times the volume of the metal.
Silver is very soft.  It is hence necessary, in coin, and in articles
for domestic use, to add a certain quantity of copper, to render it
less liable to deterioration from use or in being cleaned.
When silver is exposed to the air, it gradually tarnishes, which is
due, not to the formation of oxide, but of sulphuret, the air always
containing traces of sulphuretted hydrogen, derived from organic
bodies. It is not acted on by sulphuric or muriatic acid, but is rapidly dissolved by nitric acid, with evolution of nitric oxide gas.
Silver combines with oxygen in three proportions, forming oxides, of which only one, the protoxide, is' well known. The equivalent of silver is 1351'6 or 108'3, and its symbol is Ag., from the
Latin name.
~Protoxide of Silver —Ag.O.; equivalent 1451'6 or 116'3-may
be prepared by adding caustic potash, or lime water, to a solution
of nitrate of silver. A brown powder is thrown down, which may be
dried at a gentle heat without alteration. It then becomes very
dark. W'hen heated strongly, it is decomposed into oxygen and
metallic silver, and this takes place even at ordinary temperatures,




SULPIHURET OF  SILVER.                     401
if It be in contact with organic matter. It neutralizes the strongest
acids, as the sulphuric and nitric, and forms well-characterized salts.
It is not acted on by the fixed alkalies, but with ammonia it gives
fulminating silver, one of a series of bodies to be hereafter examined.
When citrate of silver is heated to 212' in a current of hydrogen
gas, the metal is not reduced, as should have occurred with the pure
oxide, bat one half of the oxygen is removed, and the citric acid
remains combined with the suboxide of silver, kASg0.  This salt dissolves in water, the solution being brown, and giving a brown precipitate of suboxide with potash.  When a solution of this salt is
heated; it becomes colourless, contains a salt of the peroxide, and
metallic silver separates.  Some other silver salts of organic acids
give the same result with hydrogen gas.  When a solution of nitrate of silver is decomposed by the battery, a substance is deposited
upon the positive electrode in needles, sometimes half an inch long.
These are resolved by sulphuric acid into protoxide of silver and
oxygen, and give, with muriatic acid, chloride of silver and free
chlorine.'T'hey are, therefore, crystals of peroxide of silver, probably Ag.O2.
Although silver does not combine with oxygen directly, yet when
it is heated in contact with glass, it stains this of a deep yellow or
orange colour, being converted into oxide.
Sulp/luret of Silver, equivalent 1552'8 or 124'4, exists native
pure, and also in combination with other metallic sulphurets, particularly those of lead, antimony, copper, and arsenic, forming a variety of minerals. It is the most common ore of silver. It may
be formed artificially by fusing together sulphur and silver, the excess of sulphur beinc expelled by the heat. Silver has, indeed, a
remarkable affinity for sulphur, so that it even decomposes sulphuretted hydrogen, and hence arises the tarnishing of silver when exposed to the atmosphere. An exceedingly delicate test for sulphur
in a solid body consists in igniting a miniute fragment of it on charcoal, in the reducing flame of the blowpipe; the fused globule is to
be then laid on a bright surface of silver, as on a clean shilling, and
moistened; if there be a trace of sulphur in the substance, a black
or olive spot will form on the silver where it is moistened.
The sulphuret of silver may be formed also in the wet way, by
adding sulphuretted hydrogen or hydrosulphuret of ammonia to a
solution of a salt of silver. It forms as a black powder, which is
not soluble in an excess of the precipitant.  This sulphuret is a
powerful sulphur base, and in its native forms is generally associated with negative metallic sulphurets.
The detection of silver is very easy; from the facility with which
its oxide is reduced to the metallic state, its solutions are precipitated by the sulphites, by protosulphate of iron, and by protochloride of tin, the silver being reduced. A solution of common salt.
or muriatic acid gives a white curdy precipitate of chloride of silver, which is insoluble in water and in acids, but dissolves in water
of ammonia; when exposed to light in contact with organic matter,
the chloride of silver becomes tinged violet or black, owing to. the
formation of a subchloride; on this is founded its application in
photography, described p. 173. The solutions of silver give, with
~E E E




402 MERCURY1 ITS EXTRACTION  FROM  ITS ORE.
iodide of potassium, a canary-yellow precipitate, insoluble in ammo.
nia, and with sulphuretted hydrogen a deep brown sulphuret of
silver.
The uses of silver are well known; its advantages as a medium
of exchange depend on the steadiness of the quantity of it brought
into commerce, which prevents great changes in its value. and on
its not being corroded or worn down by ordinary agents. I:n a pure
state it would, however, be too soft to be used as coin, and is hence
hardened by being alloyed, in the proportions of 222 parts to IS of
copper; this is the standard silver of the mint; the silver used for
the purposes of luxury contain a greater, but a variable quantity,;
copper.
Of.Mercury, or Quicksilver.
From the remarkable properties of this metal, and its occurring in
the metallic state in nature, it has attracted much attention from
the earliest ages, and formed the object of the most elaborate inquiries of the older chemists. Its volatility and the variety of its
compounds made it enter into the theories of that period as an important element, and hence there is, perhaps, no metal concerning
wvhich so much valuable knowledge was obtained in the infancy of
chemistry.
Mercury is found native, and also combined with gold and silver,
but its most abundant ore is the native sulphuret, cinnabar; from
this it is extracted by one or other of two processes. The first consists in distilling the ore with lime, or with iron in small pieces; inr
the first case, Hg.S. and Ca.O. produce Ca.S., while Hg. and 0. pass
off, the temperature being too high to allow of the formation of oxide of mercury; in the second case, Hg.S. and Fe. produce Fe.S.
and Hg.; this process is carried on in long furnaces, in which are
arranged numbers of earthen or iron retorts, to which are adapted
receivers, in which the mercurial vapours condense. The other
plan, which is that now adopted in the best arranged works, consists of a kiln, like that in which the pyrites is roasted for the manufacture of oil of vitriol: below, there is a grate on which is lighted
a fire of brushwood; over this is a light arch of fire-brick, with nu
merous perforations, and on this is arranged the cinnabar, the poorest kinds being placed below, until the kiln is filled nearly to the
orifice of the chimney, which passes off' at the side; the fire communicating to the ore, the sulphur contained in it burns, and the
mercury is set free, Hg.S. and 20. producing S.0, and Hg. The
kiln is so hot that the metal is completely volatilized, and the mixed
vapour of mercury and sulphurous acid gas are carried by the
draught into the chimney, which leads into a wide chamber of brickwork, the sides of which are hung with leather; on these the mercury condenses in drops, which gradually flow down and collect on
the floor, while the sulphurous acid gas passes away by a small
chimney at the farther end, by means of which the continuous corn
bustion of the ore is sustained; at certain periods, an aperture in
the side of this chamber is opened, and the mercury which had collected is withdrawn.
The mercury is sent into commerce in iron bottles, but generally




OXIDES OF ME~RCUR-Y.                     403
in a very impure state, it being intentionally'adulterated' with the
alloy of -tin, lead, and bismuth, already noticed p. 398, of which it
can dissolve large quantities.  It may be purified by distillation, or
by being left for sonme time in contact with dilute' nitric acid. The
mercury, having less affinity for oxygen than any of the other metals
present, is the last to dissolve, and as soon as the liquor is found to
contain mercury, the metal remaining may be looked upon as pure.
Mercury is distinguished by being liquid at ordinary temperatures; this, together with its resemblance to silver in brilliancy, is
the origin of its various names, hzydra,'igyrum (vn op apyvpeob), quicksilver, argentunm vivunz. If pure, it is not tarnished by exposure to
the air, but in damp air its impurities become oxidized very rapidly,
in consequence of' a complete galvanic circuit being formed with
the mercury and the other metals present. At 39' it becomes solid,
and crystallizes in octohedrons; it then contracts very inuch; its
sp. gr. being 13'5 when liquid, and 14'0 when solid. At 662~ it
boils, and forms a colourless'Vapour, the s4p. gr. of which is 6978.
At and just below its boiling point it absorbs oxygen from the air,
forming oxide, which at a red heat is again decomposed.
Mercury is not acted on at common temperatures by sulphuric or
muriatic acid; nitric acid oxidizes it rapidly, the nature of the product varying with the circumstances. Boiling oil of vitriol is decomposed by mercury, sulphurous acid being evolved, and oxide of
inercury produced.  There are two oxides' of mercury, a suboxide
and a protoxide. The symbol of mercury is Hg., from its Latin
name, and its equivalent is 1265'8 or- 1014..
Suboxide of Mercury. H(g20. Equivalent 2631'6 or 210'8. This
oxide is the basis of many important preparations, and is best prepared by decomposing calomel (subchloride of mercury) by a solution of potash. The calomnel being insoluble, the action must be
favoured by mixing the two together well by agitation in a mortar;
a black powder is produced, which must be dried in the dark, and
by a very gentle heat.' In this process, Hg2Cl. and K.O. produce
K.Cl. and Hg,O0.  Lime water may be used in place of potash.
When this suboxide, or, as it is often called, black oxide of mercury,
is heated, it is resolved into metallic mercury and the protoxide,
and this change occurs slowly at ordinary temperatures if it be exposed to the light. This oxide combines with acids and forms well
characterized salts.
Protoxide of Jilercury- Hg.O.; equivalent 1365'8 or 109'4-may
be prepared in a variety of ways: 1st. By exposing mercury for a
long time to the action of the air, at a temperature just below its
boiling point, it is gradually converted into small deep red crystals
of this oxide; in this state it was the red precipitate per se of the
older chemists.  Od. By heating crystals of nitrate of mercury until
all the water and nitric acid have been expelled, the' oxide remaining is a crystalline powder of an orange-red colour, the red precirjitate by nitric acid.  3d. When a solution of chloride of mercury (corrosive sublimate) is decomposed by caustic potash or lime water,
Hg,.Cl. and K.O. produce:.C1. and Hg.O. It is thus obtained as a
canary-yellow hydrate, ihich, however, when dried, becomes deeper
coloured. The red precipitate also, when finely divided, assumes the
same yellow tint.




404            SULPHURETS OF MERCURY.
This oxide of mercury is slightly soluble in water. The solution
browns turmeric paper slightly, and restores the blue colour of red.
dened litmus. It combines with acids, forming a numerous and important class of salts. At a full red heat it is totally resolved into
mercury and oxygen, as described fully in page 242. It changem
its colour remarkably with the temperature, becoming nearly black
when very hot.
Subsulphuret of Mercury, HgS., may be prepared by decomposing
any salt of the suboxide by hydrosulphuret of ammonia.  It is a
black powder, which, on the application of heat, is decomposed
into the protosulphuret and metallic mercury.
Protosulhluret of Jlercury — Hg.S.; equivalent 1467 or 117'5-con
stitutes the native cinnabar, the usual ore of quicksilver.  It may
be prepared artificially by fusing sulphur in a crucible, and adding
thereto six times its weight of mercury; they colnbine with the
evolution of considerable heat. The mass must be stirred frequent.
ly to favour their union, and covered in order to prevent the sulphur from burning away. In this state it is black, but when sublimed at a red heat in glass vessels, it becomes deep red, constituting factitious cinnabar, and this, when levigated, and exposed to
strong light, in flat dishes covered with a thin layer of water, grad.
ually assumes a very brilliant colour, and forms the pigment vermilion. This sulphuret may also be prepared by adding to a solution
of corrosive sublimate an excess of hydrosulphuret of ammonia ox
sulphuret of hydrogen; it is then a dense black powder. It may,
however, be obtained red, but not so bright as vermilion, in the wet
way, by digesting white precipitate (chloramide of mercury) with
hydrosulphuret of ammonia, to which an excess of sulphur has been
added.  The sulphuret of mercury forms at first black, but after
some time becomes red, which colour may be brightened by the
action of a warm solution of caustic potash.
The phosphurets and seleniurets of mercury are of no importance.
The presence of mercury in solution is very easily ascertained.
By the immersion of a clean slip of copper, the mercury is precipitated in the metallic state, as a gray powder on the surface of the
copper. With a magnifying-glass, this is found to consist of minute but brilliant globules, and the surface becomes brilliant when
rubbed. Protochloride of tin and phosphorous acid also precipitate
the mercury in the metallic state, which, by boiling, aggregates into
larger globules, easily collected and recognised. Any solid body
containing mercury gives, when ignited in a tube of hard glass, particularly on the addition of a little carbonate of potash, a sublimate
of metallic mercury, which, if in very small quantity, fappears only
as a ring of gray powder, but is found to consist of brilliant globules when inspected with a lens.
The two classes of salts which quicksilver forms are very distinctly characterized by their behaviour to reagents.  The salts of
the suboxide give with the caustic alkalies black or gray precipitates.  Sulphuretted hydrogen produces the black subsulphuret.
Solution of chloride of sodium gives a white precipitate, which is
calomel, and the bichromate'of potash produces an orange chromate
of the suboxide.




EXTRACTION AND PROPERTIES OF GO LD. 405
The salts of the red oxide are precipitated, yellowish by an excess
of caustic potash, and white by ammonia; with sulphuretted hydrogen in excess, a black precipitate of protosulphuret; and with iodide
of potassium, a red precipitate, which is redissolved in an excess.
In many cases, the appearance of these precipitates varies with
the nature of the acid with which the oxide of mercury had been
combined; but in all cases ammonia gives a black precipitate with
the salts of the suboxide, and a white precipitate with those of the
red oxide, in the cold.
There is a class of pharmaceutical preparations obtained by triturating mercury With other inactive substances. In these the mercury is only reduced to a state of very minute division; it is not
oxidized. By triturating mercury with sulphur, however, a certain
quantity of sulphuret is formed, although the great mass of the metal and of the sulphur remains uncombined.
Of Gold.
This valuable metal is found only in the metallic state, either
pure or alloyed with other metals, particularly silver, tellurium, and
mercury; the rocks in which it is found distributed are generally
those of igneous origin, but the greater part of the gold of commerce is obtained by wrashing the sands of the rivers which have
their source in such mountains, the particles of metal being carried
down with the detritus of the rock, and, from their greater density,
being deposited first when the sand is washed; any fragments large
enough to be visible are separated by the hand, but the remainder
is dissolved out by a process of amalgamation, similar to that described, p. 399, for the extraction of native silver. When the gold.
is alloyed with silver, they are separated by means of nitric acid,
which dissolves the latter metal; but if the quantity present be small,
the gold protects it from the action of the acid, and a process termed quartation is employed; this consists in alloying the gold with
three times its weight of silver, and then acting on the mass with
nitric acid; when the solution of the silver has once commenced, it
does not cease until the entire quantity present has been removed.
Pure gold is yellow, very malleable and ductile, and nearly as
soft as lead; hence, for the purposes of commerce and of the coinage, it is alloyed with a quantity of copper, amounting to 83 in 1000.
Instances of the exceeding degree of division to which this metal
may be reduced, have been given, p. 15. Gold has no tendency to
combine with oxygen or sulphur, and hence retains its brilliancy in
the open air for any length of time. It melt~ at 2016~; its density
is 19'5; it is not acted on by any single acid, but is dissolved by nitromuniatic acid, and by a mixture of nitric and hydrofluoric acids.
The symbol of gold is Au., from its Latin name, and its equivalent numbers are 24986 or 199'2.
There are two oxides of gold, obtained by the decomposition of
the corresponding chlorides, which will be hereafter described.
The deutoxide of gold, Au.O2, is a green powder, which does not
combine with acids, but dissolves in solution of caustic potash, and
soon separates into the higher oxide and metallic gold. The perox
ide of gold, auric acid, Au.03, is best prepared by decomposing per




406     PROPERTIES OF  GOLD.-PAL.LADIIUM.
chloride of gold by an excess of magnesia; chloride of mngnesium
dissolves, and an insoluble aurate of magnesia remains; this is to
be then digested in cold dilute nitric acid, which dissolves out the
magnesia with a little auriO acid, but leaves the greater part of
this last behind as a reddish hydrate, which, when dried in the air,
becomes brown, and at 2ioo gives off water, and remains black.
This substance does not combine with any acid; by muriatic acid
it' is decomposed, perchloride of gold being formed; it combines
with alkalies strongly, so that the precipitate given by a solution of
gold with a caustic alkali is always a compound of auric.acid with
the base; there are soluble and insoluble aurates, but their atomic
constitution has not been studied. Solutions of auric acid, and even
that body in powder, are decomposed rapidly on exposure to the
light, metallic gold being separated.
Gold is deposited from its solutions by means of any of the deoxidizing agents noticed under silver and mercury. Protosulphate
of iron gives a brown powder, which, under,the burnisher, assumes
the colour and brilliancy: of the metal; protochloride of tin produces a fine purple precipitate, the puple of Cassius, which is not metallic gold, but it appears to be a compound of oxide of tin and a
suboxide of gold, for it is perfectly soluble in water of ammonia,
and mercury digested on it does not dissolve out any metallic gold.
Various processes are given for this preparation, which it is not
easy to obtain of the proper depth and purity of colour; when exposed to a red heat, it is changed into a mixture of peroxide of tin
and metallic gold, but its purple colour remains; it is hence employed for painting on glass and porcelain. When metallic gold is heated on the surface of glass, it appears to become oxidized, and in
that state to combine with the glass, staining it a rich purple colour.
Sulphur and gold combine to form sulphurets similar in constitution to the oxides; they are produced by decomposing the corresponding chlorides by sulphuretted hydrogen; they are brown powders, which are strong sulphur acids, and dissolve in hydrosulphuret of ammonia.
The uses of gold are well known. The commercial value of its
alloys is ascertained, either by cupellation, p. 399, by quartation, p.
405, or by the touchstone, which is a variety of flinty slate (Lydian
stone) or basalt, of a uniform black colour. A streak is drawn on
the surface of the stone with the piece of gold to be tried, and this
is compared with those given by a series of alloys, the composition
of which is.known, until one is found identical in aspect with it,
which must result from the two being of the same degree of purity.
In these trials it is necessary, however, to know beforehand whether the alloy is silver or copper, or whether, as frequently occurs,
both be present.
Of Palladium.
This metal is found associated with platinum, but seldom constitutes more than one per cent. of the ore. After the platinum has
been precipitated from the solution in aqua regia, by means of sal
ammoniac, cyanide of mercury is added, by which all the palladium




COMPOUNDS  OF: PALL.ADIUM.-PLATINUM A.  407
is thrown down as cyanide; this, when ignited, is totally decomposed, and metallic palladium remains.
The general characters of palladium are very similar to those of
platinunl; it is white, almost infusible, but admits of being welded;
it is malleable and ductile; specific gravity 11.5. When heated
be4ow ignition, its surface becomes blue and green, from the formation of a thin layer of suboxide; but by a stronger heat this is reduced, and the metal becomes bright.  Palladium  is not sensibly
acted on by muriatic or sulphuric acid, but it dissolves in nitric
acid with facility. The symbol of palladium is Pd., and its atomic
weight 665.9 or 53'4.
There are three oxides of palladium, of which only one, the protoxide-Pd.O.;
equivalent 765'9 or 61'4-has been as yet studied with much care; this oxide is fobrmed when palladium dissolves in nitric acid, and is obtained as a black powder when
the nitrate is decomposed at a temperature below redness; by the addition of potash
to a salt of palladium, this oxide is thrown down, hydrated, as a brown powder.
If the protoxide of palladium be exposed to a dull red heat, it parts with half its
oxygen, and a suboxide, Pd20., is produced, which gives a series of salts, resembling
in general- characters those of the suboxide of copper.
By decomposing the bichloride of palladium with carbonate of potash, the deutox
ide, Pd.02, is obtained as a yellowish brown powder; it appears to combine both with
acids and alkalies, but of its properties very little is known.
There are sulphuwrets of Palladium, which correspond to the oxides, but farther than
that they are brown powders, generated by the action of sulphuret of hydrogen on
the respective chlorides, they have not been much examined.
Palladium in solution is at once recognised by giving with ammonia a flesh-red
precipitate, which redissolves in an excess, giving a colourless solution; with cyanide of mercury it produces a whitish precipitate, and with iodide of potassium, a
black powder.
Of Platinum.
Platinum  was originally discovered in the sands of some South
American rivers, and from  its similarity to silver (plata), obtained
the name of platina (little silver).  It has since been found more
abundantly in the mountains of the Oural, which separate European
from Asiatic Russia. The supply 6f platinum has increased so
much lately, that a coinage of it, issued some years ago by the
Russian government, was obliged to be recalled, from the rapid
diminution in value which it underwent.
The platinum exists native, but is associated with a great number
of metals, particularly four, remarkable for not being found except
along with it.  The grains of metal are disseminated in rocks of
igneous origin (granite, syenite), and in the sands of rivers which
flow over them. The processes for the extraction of platinum from
the crude ore are very complex, and as the working of it has become a branch of manufacture; the chemist always obtains the pure
metal in commerce, and its details need not be inserted.
Pure platinum  is white like silver, but not so brilliant.  It is the
densest of all bodies, its sp. gr. being 21'5.  It is very malleable
and ductile. It is infusible except by the hydro-oxygen blowpipe, but
at a high temperature may be welded like iron, and thus worked
into the various forms in which it is employed in the chemical arts.
Platinum  may also exist in a state of minute division, and thereby
becomes useful in many operations, particularly those of slow combustion, as noticed in p. 180, 250, 287'. The finely-divided platinum
is of two kinds, spongy platinum and platinum-black.  The former is




408              COMPOUNDS  OF  PLATINUM.
prepared by dissolving chloride of platinum  and sal ammoniac sep
arately in alcohol, and mixing the solutions; the double chloride of
platinum and ammonium is thus produced as a fine yellow powder,
which, while yet moist, is to be made into balls like peas, and heated to full redness. The chlorine is all carried off by the hydrogen
of the ammonia, and the platinum  remains as a light gray sponge,
in the form of the little balls; it is this kind of platinum that is
used in the aphlogistic lamp, in the eudiometer, and for other purposes already noticed.  The platinum-black may be obtained either
by precipitating a solution of bichloride of platinum  With zinc, and
boiling the precipitate in muriatic acid for a few minutes; or, better, by dissolving protochloride of platinum  in a boiling solution of
potash, and adding thereto alcohol, in small quantities at a time,
until all effervescence ceases; a jet-black precipitate is produced,
which is to be boiled successively with alcohol, mauriatic acid, and
potash, and, finally, four or five times in water.  The substance
thus obtained is pure metallic platinum, but it is a dull black powder.  It absorbs oxygen in considerable quantity, and hence, when
brought into an atmosphere of any inflammable vapour, it facilitates
the combination of the two with remarkable energy.  Dmabereiner
terms it an oxyphorus from  this property.  Many interesting reactions in organic chemistry succeed only by the aid of this platinumblack.
Platinum  has no tendency to combine with the oxygen of the
air, but it is oxidized slightly when nitre or even potash is fused in
contact with it. It resists the action of all acids except the nitromuriatic acid and the nitro-hydrofluoric acids, and in these it dissolves more slowly than gold.
The symbol of platinum  is P1.  Its equivalent is 1233'5 or 98'S.
By the decomposition of the chlorides of platinum, two oxides of it
are obtained.
Protoxide of PlatilLn-Pt.O.; equivalent 1333'5 or 106'8 —is produced by digesting the protochloride with as much potash as exactly suffices for its decomposition.
An excess of potash dissolves it, forming a dark olive liquor. When pure it is a
black powder, easily decomposed by heat into platinum and oxygen. It combines
with acids, forming salts, which have been as yet but little studied.
Deutoxide-of Platisnlu.-Pt.02. Equivalent 1433'5 or 114'8. This substance has
a remarkable tendency to combine with bases, and hence cannot be obtained pure
by the direct decomposition of the chloride, as it carries down with it, always, a
quantity of the alkali employed, if this be in excess; and if it be not, then only a
basic chloride is obtained. The nitrate of platinum, however, when decomposed
by soda, yields one half of the oxide of platinum, pure, but hydrated, forming a
brown powd6r like the peroxide of iron; when anhydrous, it is black; by heat it is
resolved into oxygen and platinum. This oxide appears to form two kinds of salts,
one with acids, in which it is the base, and the other with alkalies and earths, in
which it is the acid. In another place I shall notice them farther.
There are two sldpkRets of Platinum corresponding to the two oxides. The first,
Pt.S., is produced by digesting the protoclloride with sulphuret of hydrogen. It. is
a deep brown powder, decomposed by a red heat, but not otherwise interesting. The
bisulphuret, Pt.S2, is produced in a similar way by adding sulphuret of hydrogen to
a solution of bichloride of platinum. It is a brown powder, which absorbs oxygen
rapidly even in drying, and becomes acid. By nitric acid it is converted with intense action into sulphate of platinum.
Phosphurets and seleniurets of platinum have been formed, but they are not important.
The detection of platinum is effected easily by precipitating its
solution by a slip of zinc, when a black powder separates, soluble




IRIDIUM   AND  RHODIUM.                            409
only in aqua regia, and then giving with reagents the following resuits.  A  solution of sal amtnoniac in alcohol gives a fine yellow
crystalline precipitate; a solution of iodide of potassium a black
precipitate, which dissolves in an excess, producing a rich crimson
solution; with sulphuret of hydrogen, the browvn bisulphuret of platinum; an(d with protochlolide of' tin, a chocolate precipitate or a
deep reddish solution, according to the quantity present.
The action of this last reagent is founded on the reduction of the
bichloride of platinum to the state of protochloride by the first portion of protochloride of tin employed.  This test acts, therefore,
also with solutions of the protoxide of platinum, and the metal may
be also known to be in the state of protoxide, when, on the application of iodide of potassium  in excess, the liquor is not coloured
red, but becomes so on the addition of a drop of nitric acid or chlorine water.
The great use of platinum  is for the manufacture of the large
boilers used in the concentration of oil of vitriol; it is also universally employed as the material for the crucibles used in the more
delicate operations of mineral analysis.  Indeed, the accuracy now
attained in that department of research is in a great part due to the
introduction of platinum  vessels into the laboratory; it is also accasionally used in enamelling on glass and porcelain.
Of Iridium anzd Rhodium.
These metals are, like palladium and iridium, found only associated with platinum, and are extracted from the crude ore already noticed; the iridium and osmium
are, however, united, formning an alloy, the crystalline grains of which are merely
mixed with the particles of the platinum ore in which the rhodium  and palladium
are contained; when the platina ore is dissolved in aqua regia, the iridium and osmium ore remains undissolved, and requires to be treated by fusion with caustic
potash; the iridium then becomes oxidized, and combines with the alkali. The processes of purification need not be inserted.
Mletallic iridium resembles platinum, but is still more infusible; when fused by
the voltaic battery, it is white and very brilliant; specific gravity 18S68; after being
strongly heated, it is insoluble in acids, but when obtained in the spongy form by
the reduction of its oxides by hydrogen at a red heat, it becomess lightly oxidized,
and is soluble in aqua regia.
Iridiumr combines with oxygen in fourtproportions; its symbol is Ir., and its equivalent 1233'5 or 98'8, the same as that of platinum.
Protoa:ide of Iriediolr, Ir.O., is obtained by decomposing the protochloride by carbonate of potash; it appears as a greenish-gray hydrate; this oxide combines with
acids. The srsqzioxide, 11'203, is that formed when the metal is ignited with potash;
it is a bluish-black powder, andjs the most permanent of the oxides; it is not decomposed except at a heat above the melting point of silver, whereas the higher and
lower degrees pass into it on the application of heat. This oxide unites with acids,
giving darkl blood-red coloured salts. The dezmdloxide of Iridiqmlt, Ir.02, exists comrnLined with acids, but has not been isolated. The pm3-ozidc, Ir.03, is formed in small
quantity when iridium is ignited with nitre, but is best prepared by the decomposi
tion of the perchloride. Solutions containing salts of the protoxide and of the peroxide together, present a great variety of shades of purple and blue, and hence gave
origin to the name of the metal (Iris).
Rh.odium. —This metal remains dissolved in the nitromuriatic solution of the platinum ore after the platinum and palladium have been separated from it; for the
mode of eliminating it from the many metals which still remain, I refer to the systematic works.
Metallic rhodium is obtained by the decomposition of its chloride at a red heat by
hydrogen gas; when rendered coherent by pressure, it is white, but very brittle and
hard; sp. gr. about 11 0. If completely pure, it is not acted on even by aqua regia,
but it illustrates remrarkably the principle of communicated affinity, describetl   p.
FPr




410        GENERAL  CHARAC TERS OF  SALTS.
237; for, when alloyed with copper, lead, or platina, it dissolves along with the other
metal in aqua regia. Rhodium derives its name from tile beautiful rose (podof) colour of its solutions; it combines with oxygen in two proportions; its symbol is R.,
and its equivalent 661'4 or 52.2.
Of the pyotoxide of R' odiux1, it is only known that it exists in certain salts that
have been but little examined; the sesquioaxide, RO3, is the basis of the most important compounds of this metal. It is prepared boigniting metallic rhodium with a
mixture of' caustic potash and nitre; a brown mass is formed, which, when decomnposed by muriatic acid, yields the oxide as a gray hydrate, insoluble in acids. Berzelius is of opinion that there are two isomneric forms of this oxide, the salts of' one
being yellow in solution, and those of the other being rose-coloured. There are supposed to exist, also, complex oxides of rhodium, resembling, probably, the complex
oxides of iron and manganese. The equivalent of rhodiumn is so nearly equal to
that of palladium, that some relations might be expected:in the constitution of their
combinations, which, as yet, does. not appear to have been experimentally investigated.
CHAPTER XIV.
ON THE GENERAL PROPERTIES AND CONSTITUTION OF SALTS.
THE bodies included under the name of salts may be arranged in
two classes, characterized by a remarkable difference of chemical
constitution; the first comprehends such as are formed by the union
of a simple body of the chlorine family with a metal; thus chloride
of sodium, iodide of potassium, bromide of iron, fluoride of calcium,
are of this kind. The salts of the second class, on the contrary,
are formed by the union of substances already compound, and possessed of those opposite properties by which one is determined to
be an acid and the other a base.  The general characters of acids
and bases, and of the salts formed by their union, have been sufficiently described in many places already (p. 151, 151, 157), and
need not be here repeated. In general, the acids and bases so engaged contain oxygen as their electro-negative ingredient; but there
are classes of salts formed by the union of sulphur acids and sulphur bases, and, as noticed in p. 238 and 294, selenium and tellurium
resemble oxygen and sulphur in: this respect. The history of the
metallic compounds in the last chapter affords many cases of the
existence of such salts, and in the detailed history of the more important salts which will follow, others will be described; but -there
are some points of mnore general interest, touching the salts as a
class, the laws of formation to which they are subjected, and the
relations between their several subdivisions, which I shall now proceed to. notice as briefly as the subject will admit.
I have frequently adverted to the circumstance that the bodies
termed h/ydracids were in reality not acids, but compounds of hydrogen, in which that element acted as a positive metallic constithuent; and that, when they act on a metallic oxide, double decomposition generally occurs, precisely as when a chloride or iodide of
zinc or copper is decomposed by potash or by soda.  Thus C1.H.
and'K.0. produce Cl.K. and H.O., precisely as when Cl.Cu. and K.0.




GENERAL CH A RACTERS OF SA-L T S.                411
produce C1.K. and Cu.. The:chlorides and iodides of hydrogen,
although popularly called. acids (mnuriatic and hydriodic acids), are
thus really salts,.and in all their reactions display that constitution. Also, when a hydracid, is put ill contact with a metal, the
solution of it is determined altogether by its power of' expelling the
hydrogen and of taking its place.,'From Cl.H. and Zn. there are
produced CI.Zn., and H. becomes free, precisely as chloride of copper, Cu.Cl., is decomposed by zinc, copper being: precipitated. The
hydracids, therefore, do not unite with mnetallic oxides to form salts,
but they decompose them, water being evolved.
The hydracids are capable of forming what are termed acid-salts;
thus the fluoride of potassium combines with hydrofluoric acid to
form an acid compound; the chloride of hydrogen combines with
chloride of gold: but these bodies are really double salts. The
compounds of hydrogen, in such combinations, resemnbling the corresponding compounds of zinc, copper, &c., which, under the same
circumstances, all form corresponding double salts.
I have already described the functions of water in the hydrates
of the ordinary oxygen acids: these are salts of water, subject to
the same rules of composition as. the ordinary salts of the same
acid.  WVhen such an acid, as, for example, oil of vitriol, S.03+H.O.,
acts upon a metallic oxide, the water is displaced, and a salt of the
metallic oxide formed.  W'hen such a hydrated acid acts on a metal, this may be dissolved either by substitution for, and displacement
of the hydrogen, as in the ordinary cases of obtaining that gas, or
by-the direct decomposition of a part of the acid, as in the process.
es for obtaining sulphurous acid and nitric oxide (p. 285, 274).
Salts may be either neutral, acid, or basic. A salt is neutral which
does not manifest, in its.,action on vegetable colours, acid or alkaline properties, and consists generally of one equivalent of acid
united to one equivalent of base, this last containing one equivalent
of oxygen. The true neutral salts have, therefore, for bases, either
suboxides or protoxides.  The salts of sesquioxides and deutoxides
generally react:like acids, except where there is an excess of base.
The quantity of acid with which metallic oxides are disposed to
unite in their most neutral salts, is subject to a remarkable proportion, being one equivalent for each'atom of oxygen which: the base
contains.  Thus a protoxide or suboxide combines with one equiv.
alent of acid. The sulphate of zinc is Zn.0.. S.03.; sulphate of cop
per Cu.0.. S.O3;.the subnitrate of mercury, HgO.. N.O. I   A sesquioxide unites with three equivalents of acid, as sulphate of alumina,
A1203+-3S.-0. Salts in which this law is observed to hold are generally described as neutral, even though their action on vegetable
colours may indicate a preponderance of acid; and understanding
by the word, not the absence or presence of the property of changing turmeric or litmus, but the state in which the characteristic
properties of, acid and base are most neutralized, the definition of
a netutral salt may best be that in which the number of atoms of
acid is equal to the number of atoms of oxygen in the base
There are two kinds of acid salts: 1st, those in, which the excess
of acid is present in its hydrated form; and, 2d, those in which
the dry acid is in excess. These differ remarkably in; nature, those




412       GENERAL CHARACTERS  OF SALTS.
of' the first class being not really acid salts, but double salts, of which
one base is water. Thus the common bisulphate of potash, of which
the formula is K.O.. S.03 +H.O.. S.03, is one of a family of double
salts, in which sulphate of potash is united to a sulphate of a protoxide, as sulphate of copper, of zinc, of iron, or of magnesia. T'lere
is thus really no excess of acid. In like manner, the bicarbonate
of potash is a double carbonate of potash and water, K.O.. C.02 -
H.O.. C.02, to which similar analogies exist. These salts resemble
completely the acid salts of the hydracids, described in the beginning of this chapter; K.O.. S.03 —H.O.' S.0 corresponding exactly to K.F.+H.F.
It is only the salts which do not contain water that can be looked
upon as having a true excess of acid. Of these, the chromates of
potash afford the best examples, in which an atom of potash is combined with one, two, or three equivalents of acid, forming K.O.+Cr.O,3, K.O.+2Cr.O3, and K.O.i3Cr.,0.  There exists a similar
compound of sulphuric acid and potash, which is easily decomposed
by water, being changed into the ordinary bisulphate.
Basic salts are those in which there is present more than one
equivalent of base for each equivalent of acid; thus, in turbeth mineral there is 3H{g.O. + S.o3; in basic nitrate of copper, 3Cu.O. + N.
05. H.O.; in basic sulphate of copper, 4Cu.O.-+S.03+ 4-I.O. It has
been thought that the proportion of base in basic salts bore a sirmple relation to the quantity of oxygen in the acid, being generally
equal to it. This idea was founded on the circumstance that the
early analyses of many basic sulphates gave the proportion of three
atoms of base to one of acid; but the basic sulphate of mercury is
the only example I have found really to exist of that constitution,
the other sulphates containing always a quantity of metallic oxide,
amounting to two, or four, or six equivalents.
The first and most remarkable insight into the constitution of
basic salts which we obtained was the principle laid down by Graham, that all salts are really neutral in constitution. The analogies
of hydrogen to the magnesian family of metals, and hence of water
to the oxides of that class, suggested the idea that the excess of
base should not be considered as actually combined with the acid,
but that it replaced the water of crystallization which'the neutral
salt contains. This view was remarkably supported by the evidence of the basic nitrates adduced by Graham, and has been extended to the chlorides and sulphates by my own investigations.
Thus nitrate of copper,- in its crystallized and neutral condition, is
Cu.O.. N.05+3H.O., and the basic nitrate is formed by H.O.. NO,
+3Cu.O. Comparing these two with the hydrated nitric acid, sp.
gr. 1'42, the formule
Nitrate of water,     =H.0.. N.O0+-3H.O.
Nitrate of copper,    = Cu.O.. N.05+ 3H.O.
Basic nitrate of copper, — H.O..  N.05+ 3Cu.0.
evidently correspond, the only difference being that, in place ot
oxide of hydrogen, there is oxide of copper substituted, in a proportion continually increasing. From these conditions it follows,
that with the same acid and base there may be formed a great va.




SALTS OF  POLYBASIC  ACIDS.                   413
riety of basic salts; for the: neutral salt may crystallize with many
different proportions of water, and from each there may be one or
more basic salts derived, by substitution of metallic oxide. Thus
the sulphate of zinc generally contains eight atoms of base to one
of acid; and in its common crystallized form, these consist of one of
oxide of zinc and seven of water; but in becoming basic, the quantity of oxide of zinc gradually increases, and a series of basic salts
is formed, as
S.03+ Zn.0.-7H.0.,    S.0O+ 6Zn.0. + 2H.0.,
S.03 + 4Zn.0.-+4H.O0.,  S.03-+S Zn. 0.
The salts, consisting of a simple body of the chlorine family united with a metal, as chloride of sodium, iodide of potassium, &c.,
and which, from the analogy of common salt, are termed haloid salts
(6;Sc and etdoS), combine frequently swith the oxide of the metal
which they contain, and form basic haloid salts.  Thus we have Cu.
Cl.-+3Cu.0., basic chloride of copper; Hg.Cl.+3Hg.O., basic chloride of mercury; Pb.I.+2Pb.0., basic iodide of lead. Such compounds are, however, generally termed oxychlorides, oxyiodides, &c.;
they are subjected to precisely the same laws of derivation and constitution as the basic salts of the same metals with ordinary acids.
From what has been said above, it might be concluded, that a
neutral salt consisted in all cases of one equivalent of base united
to one of acid, and that, wherever the base was present in larger
quantity, the salt should necessarily be termed basic; but an important distinction requires to be here laid down. There are three
phosphates of silver, which contain respectively one, two, and three
atoms of oxide of silver united to one atom of acid; but we do not
consider the first as being neutral, and the others as containing an
excess of base, for we find them to arise from the state of the phosphoric acid, which, according as it has been combined with more
or less basic water, gives origin to classes of salts containing one,
two, or three equivalents of oxide. The peculiar relations of the
plhosphoric acid, and of arsenic acid also, to water,-and the effect
of it on the composition of these salts. have been noticed already in
p. 297 and 377. In addition, therefore, to ordinary neutral salts,
wvhich are monobasic, or contain an equivalent of base and one of
acid, there are bibasic and tribasic salts, containing respectively two
and three equivalents of base to one of acid, and yet being neutral;
by which is meant, not that they are without action on test paper,
since one tribasic salt may redden litmus, wlfle another may brown
turmeric paper, but that they are derived from a definite combination
of the acid with basic water, and not by the replacement of the water of crystallization by metallic oxide, as in the case of real basic
salts.
A simple distinction between bibasic and tribasic salts on the one
hand, and ordinary basic salts on the other, is, that in the former
the different atoms of base may be of different kinds, while in the
latter the metallic oxide replacing the water is all of the same sort.
Thus, there is basic sulphate of zinc and basic sulphate of' copper,
but there could not be a basic sulphate partly of zinc and partly of
copper, the sulphuric acid being monobasic. But there is a tribasic




414                   D O UB L E  SA I, T S.
phosphate of soda, ammonia, and water;  another oif'manesia, am
monia, and water; othersi of potash and water. - The presence of
two or more bases of different kinds thus distiriguishing completely
the salts of the bibasic and tribasic acids from  the ordinary basic
salts.
These principles, which: are now of the'highest importance in
philosophical chemistry, were first applied by Graham to the salts
of the phosphoric and arsenic acids, but th.y have been found to
throw light upon some of the most difficult questions in the history
of the organic acids, of which a great number have been shown by
Liebig to be similarly circumstanced.
Double salts are formed by the union of two simple salts.: In general, both salts contain the same acid, but different bases, and the
two bases belong to different natural groiups; as whlen sulphate of
potash combines with the sulphates of the protoxides of the metals
of the second isomorphous group, replacing therein the atom  of
constitutional water -which they all contain.  Thus ordinary sulphate of zinc, Zn.O..S.O03. H.O.+6Aq.,gives with K(.O.. S.Os3the
double salt (Zn.O. S.03+K.O.'. S.,0)-}-6Aq.; and sulphate of' copper, Cu.O.. S'.O3. H.O.O+4Aq., gives (Cu.0.  S.S03-K.O.. S.0)+
4Aq. The sulphaite of potash combines also with the sesquioxides
of thethird isotnorphous group, such as alumina, and gives origin
to the various kinds of alums. Similar classes of salts are formed
by the union of the odther alkaline sulphates with the sulphates of
the second and third isomorphous groups. The salts of isomorphous
bases with the same acid do not appear capable of combiningoso as
to produce double salts, but in crystallizing are mechanically mixed (p. 31). This rule, however, is not without exception, as the
constant composition of the magnesian limestone, Ca.0.. C.O2S+-Mg.
O.. C.02, indicates that its elements are chemically united.
Salts of different acids with the same base may -combine to fortn
double salts, as the oxalate and nitrate of lead; and' there are examples, though few, of a double salt containing two acids: and two
bases.
The relations of salts to water have been fully discussed under
the heads of solution and crystallization'(p. 22, et seq.), and of the
chemical properties of water (p. 053), to which it is sufficient to
refer.
The haloid salts combine' together to form double salts, as the
double chloride of gold and sodium, the double chloride of copper
and potassium, and conform therein to the same general principles
that have been just described for the oxygen salts.
It has been always mentioned, that when muriatic acid acts onr a
metallic oxide, water is formed, and a chloride of the metal produced. The question of whether this always occurs is not without
interest, and has been often agitated.  There is no doubt but that
it is the general rule, but I am inclined to think'it may not be without exception.  The difference of properties of the chlorides' of
maunesium and of aluminum in the anhydrous state and when crystallized with water, is so great as to give reason to suppose that
these chlorides decompose water, and that the crystallized hydrated
salts are not A1C1l3+3H.O. and MIg.Cl.+-H.0., but A120+- 3H.Cl. and




CONSTITUTION  OF ACIDS AND SALTS.    415
Mg.O0.+-HCl. Hence it is probable that magnesia and-alumina
combine with hydracids without decomposition.
The sulphur salts consist of a sulphur acid, which is generally a
sulphuret of an electro-negative metal or of carbon, coiiibined with
a sulphur base, which is a sulphuret of an electro-positive metal.
In their constitution they resemble the analogous oxygen salts.
Many of their characters have been described already (p. 282, 386).
The positive metallic sulphurets combine frequently with the haloid, or oxygen salts of the same metal, to form basic salts; this is
the case particularly with mercury. Thus there is Hg.0...S.032H1g.S., similar to Hg.O.. S.O3-+2Hg.O., ordinary turbeth mineral.
It had been long remarked as curious, that bodies so totally different in composition as the compound of chlorine with a metal on
the one hand, and of an oxygen acid with the oxide of the metal on
the other, should be so similar in properties, that both must be
classed together as salts, and should give origin to series of basic
and acid compounds for the most part completely parallel. This
difficulty has been so much felt by the most enlightened chemists,
that doubts have been raised as to whether the acid and base, which
are placed in contact to form by their union an oxygen salt, really
exist in it when formed; and it has been suggested that at the moment of union a new arrangement of elements takes place, by which
the structure of the resulting salt is assimilated to that of a compound of chlorine or of iodine with a metal. This view, at first
sight so far fetched, which considers that in Glauber's salt there is
neither sulphuric acid nor soda, but sulphur, oxygen, and sodium,
in some other and simpler mode of combination, is now very extensively received by chemists; and I shall proceed, therefore, to describe, with some detail, the form which it has assumed, and the evidence by which it is supported.
The greater number of those bodies which are termed oxygen
acids have not beeh in reality insulated, and what are popularly so
called are merely supposed to contain the dry acid combined with
water. Thus the nearest approach we can make to nitrics acid is
the liquid N.O,H.; to acetic acid, the crystalline body C4H404; and
to oxalic acid, the sublimed crystals C004EH.; we look upon these
bodies as being combinations of the dry acid with water, and we
write their formula N.O t+-H.O., and C4,HO+H.O., and C0203~-1H.O. 
but that these dry acids exist at all is a mere assumption. Hence,
with regard to these instances, and they embrace the majority of
all known acids, the idea that the acid and base really exist in the
salt formed by the action of hydrated acids on a base is purely theoretical.
WThen we compare the constitution of a neutral salt with that of
the hydrated acid by which it is formed, we find the positive result
to be the substitution of a metal for the hydrogen of the latter; thuis
S.0,-+H.O. gives with zinc S.03+Zn.O.; and where a metal is
acted on by a hydrated acid, the hydrogen is thus evolved either
directly as gas, or it reacts on the elements of the'acid, and gives
rise to secondary products which are evolved, such as sulphurous
acid, nitric oxide, &c. In all cases we may consider the action of
a metal on a hydrated acid to be primarily the elimination of hv.




416    THEORY RESPECTING  THE INTIMATE
drogen and the formation of a neutral salt. But in this respect the
action becomes completely analogous to that of the metal on a hydracid, except that in the latter case a haloid salt is formed; and
hence we assimilate the two classes in constitution by a very simple arrangement of their formulae.
There are, however, a number of acids which may be obtained
in a dry and isolated form, as the sulphuric, the silicic, the telluric,
the stannic, the arsenic, the phosphoric, &c.; and when they combine with bases, it is most natural to consider the union as being
direct, and that the salt contains acid and base really as such. This
is, accordingly, the strongest point of the ordinary theory. But
other and important circumstances intervene. These acids, although they may be obtained free from water, yet in that state they
combine with bases but very feebly, and require a high temperature
in order to bring their affinities into play.  On the other hand, in
all cases where these bodies manifest their acid characters in the
highest degree, they are combined with water, as in oil of vitriol
and phosphoric acid, and when expelled from combination with a
base, they immediately enter into combination with water in an
equivalent proportion.  Thus, where phosphate of lime is decomposed by oil of vitriol, it is not phosphoric acid (P.O,) which is
found in the liquor, but its terhydrate (P.,04-3H.O.), as is shown
by its forming with oxide of silver the yellow phosphate, P.O —+
3Ag.0. In the case of telluric acid, its hydrate (Te.O'+3H.O ) is
very soluble in water; it crystallizes in large prisms; by 012' two
atoms of water are given off, but its nature is not changed; the
body which remains (Te.O,-H.0.) is still acid and soluble in water, perfectly neutralizing the alkalies; but by a red heat this last
atom of water is driven off, and then the whole nature of the body
changes; it is insoluble in water, and even in the strongest alkaline
solutions, and can only be brought back to its former state by being fused with potash at a red heat. Here it is evident that the
acid properties and the water go together; and we may conclude
that, in order to manifest strong acid properties, the acid must be in
its hydrated form. But in that hydrated form, if the water acted
as a base simply, the tendency of the acid to combine with other
bases would be inferior to that of the dry acid; for if we place
oil of vitriol and barytes together, the water must be first expelled
before the barytes and sulphuric acid can unite, and hence an impediment would exist to their union which would not occur with
cold barytes and dry sulphuric acid in vapour, and yet cold barytes
and oil of vitriol will combine with such intensity as to produce
ignition, while the barytes must be heated before it begins to, combine -with the dry sulphuric acid. The water, therefore, is essential
to the manifestation of strong acid properties, and it does not exist
in combination with the acid merely as a base. What, then, is the
constitution of a hydrated oxygen acid.
When muriatic acid (H.CI.) acts on zinc, the metal is taken up,
forming Zn.CI.,tand hydrogen is expelled; and if, in place of zinc,
oxide of zinc be talen, the effect is the same, except that the hydrogen combining with the oxygen of the oxide forms water, H.Cl.
and Zn.O. giving Zn.Cl. and H.0. Now we have in oil of vitriol




CONSTITUTION  OF ACIDS AND -SALTS.   417
the elements S.04H. combined together; when put in contact with
zinc, H. is expelled, and S.04Zn. is formed; and with Zn.O. and
S.04H., there are produced S.O4Zn., and H.O. is set free. In both
cases, of which the former may be taken as the type of all the haloid salts, and the latter of all salts formed by oxygen acids, there is
H. as the element, which is removable by a metal, precisely as one
metal is replaceable by another, as, indeed, from the real metallic
character of hydrogen, may be considered to occur in this case.
Every acid may therefore be considered to consist of hydrogen
combined with an electro-negative element; whiclt may be simple,
as chlorine, iodine, fluorine; or may be compound, as cyanofen,
N.C2, and yet capable of being isolated; or, as occurs in the great
majority of cases, its elements may be such as can only remain together when in combination. Thus oil of vitriol does not contain
S.0, and H.O., but consists of hydrogen united to a compound radical S.04. Liquid nitric acid does not contain N.O, and H.O., but
consists of hydrogen united to a compound radical N.O,, and the
acetic acid is written C4H304+-H., the oxalic acid C,20,+-., and
SO on.
The elegance and simplicity with which the laws of saline corn
bination may be deduced from these principles is really remarkable
Thus it has been remarked as a fact substantiated by experiment,
that in neutral salts the number of equivalents of acid was propor
tional to the number of equivalents of oxygen in the base, but the
ordinary theory gave no indication of why this should occur. It
follows necessarily from the principles of'the newer theory. Thus,
if a protoxide be acted on by an acid, M. denoting the metal of the
oxide, and R. the radical of the acid, the resulting action is,
M.+O. and H.+R. produce HI.+ O. and MI.+-R.;
and in the neutral salt, there is an equivalent of each. Now in the
case of a sesquioxide, in order that water shall be formed, and so
neither acid nor base in excess, the reaction is that
M2- 03 and 3(H. —R.) produce 3(H.+O.) and M/+1IR3,
a sesqui-compound being formed perfectly analogous to a sesqui
oxide, and the number of atoms of acid, 3(H. +R.), is equal to the
number of atoms of oxygen in the base (M2O3), because that number
of atoms of hydrogen is required for the decomposition of the base.
In like manner, for a deutoxide, there is.+ -02 and 2(H. +R.) producing 2(H.O.) and M.+ R2.
The power of salts to replace water in the magnesian sulphates, so
as to form double salts, becomes much more intelligible when we
compare H.+O. with K.+S.04, than where H.O. was contrasted
with the complex formula K.O. + S.03.
The circumstance that on the new theory (or, as it is now often
called, the Binary theory of salts) it is necessary to admit the existence of a great number of bodies (these salt-radicals) which have
never been isolated, and in favour of whose existence there is no
other proof than their utility in supporting this view, becomes more
powerful as an objection when we proceed to apply its principles
G G 




418           BINARY THEORY  OF  SALTS.
to the salts of phosphoric acid. For it has been already described
that this acid forms three distinct classes of salts, all neutral, and
which have their origin in the three hydrated states of the phosnhoric acid. These states are written on the two views as follows:
Old Theory.       New Theory.
Monobasic acid, P.05~+H.0...   P.06+H.
Bibasic acid,    P.OQ3-,  H.0...   P.07+H2.
Tribasic acid,   P.0+- 3H.0.... P.O+ H3.
Now it appears very useless, where the' older view accounts so
simply for the properties and constitution of these salts, to adopt
so violent an idea as that there are three distinct compounds of
phosphorus and oxygen, which no chemist has ever been able to
detect. But here, again, other circumstances must be studied; first,
the differe.nce of properties of phosphoric acid, in its three states,
is totally inexplicable, on the idea of their being merely three degrees of hydration. Nitric acid forms three hydrates, but when
neutralized by potash, it always gives the same saltpetre; sulphuric
acid forms two perfectly definite hydrates, but with soda forms always the same Glauber's salt; while phosphoric acid, when neutralized by soda, gives a different kind of salt according to the state it
may be in. Also, the permanence of these conditions of phosphoric acid is a powerful proof that they do not consist in the adhesion
of mere water. The idea that the phosphoric acid is a different hydracid in each of its three conditions, on the other hand, not merely explains the fact of these differences of properties, but it renders
the formation of bibasic and tribasic salts, which is such an anomaly on the old theory, a necessary conseqluence of the new; for the
phosphoric salt radicals, P.O,6, P.0,, and P.O,, differ not merely in
the quantity of oxygen they contain, but are combined with different quantities of hydrogen, and hence, in acting on metallic oxides
(bases), there is a different number of atoms required for each to
replace the hydrogen and form water. Thus,
P.06H. and Na.0. give XH 0. and P.O0Na.,. monobasic phosphate of
soda;
P.O,H2 and 2Na.0. give 2H.O. and P.ONa2, bibasic phosphate;
P.O,1sH and 3Na.0. give 3H.0. and P.OLNa1, tribasic phosphate.
A circumstance which gives additional reason to infer that the wa
ter is not merely as base in the phosphoric acid, is the following:
if it were so, then it should be most completely expelled by the
strongest bases, and the bibasic and tribasic phosphates of the alkalies should be those least likely to reta;n arty portion of the basic
water; but the reverse is the fact; while oxide of silver, a very
weak base, is that which most easily and totally replaces the water.
On the idea, however, of hydracids, this is eas;ly understood, for
the oxide of silver is one most easily reduced by hydrogen, and,
consequently, one on which the action of a hydrooen acid, as P.0O
+ —H, or P.O,-k-H2, would be most completely exercised.
A remarkable verification of this theory has been recently found
in the decomposition of solutions of the oxysalts in water by voltaie
electricity. It has been already explained (p. 187, et seq.) that it re



EVIDENCE  IN FAVOUR OF THE  NEW  THEORY. 419
quires the same quantity of electricity to decompose an equivalent
of any binary cobnrpound, such as iodide of lead, chloride of silver,
muriatic acid, or water. Now, if we dissolve sulphate of soda in
water, and pass a current of voltaic electricity through that solution,
we have water decomposed, and also the Glauber's salt; oxygen
and sulphuric acid being evolved at one pole, and soda and hydrogen at the other. Here, on the old view, the, electricity performs
two decolnposing actions at the same time, and, as it thus divides
itself, its action on each must be lessened, and the quantity of each
decomposed be diminished, so that the sum should represent the
proper energy of the current. On measuring these quantities, however, the result is totally different; the quantity of sulphate of soda
decomposed is found to be equal to the full duty of the current, and
an equivalent of water appears to be decomposed in addition. It is
quite unphilosophic to imagine that the strength of a current should
be thus suddenly doubled, and a simple and sufficient explanation of
it is found in the newv theory of salts. The sulphate of soda in solution having the formula Na.S.04, is resolved by the current into its
elements Na. and S.,04, as chloride of sodium would also be; the
sodium, on emerging at the negative electrode from the influence
of the current, instantly decomposes vater, and soda and hydrogen,
of each an equivalent, are evolved; at the positive electrode, the
compound radical S.04 also decomposes water, and produces H.S.04
and 0. The appearance of the oxygen and hydrogen is thus but
secondary, and the body really decomposed by the current is only
Na.S.4Q.
In the case of the salts of such metals as do not decompose water,
the phenomena are much more simple. Thus, a solution of sulphate
of copper, when decomposed by the battery, yields metallic copper
at the negative, and sulphuric acid and oxygen at the positive electrode, and the quantity of copper separated represents exactly the
energy of the current which has passed; for the salt being Cu.S.04,
is simply resolved into its elements, but S.04 reacting on the water,
produces H.S.04, and 0. at the positive electrode. On the old view
it was supposed that water and sulphate of copper were both decomposed, oxygen and acid being evolved at one side, and oxide of
copper and hydrogen being separated at the other; which reacting,
produced water and the metal. Such an explanation, however, is
directly opposed to the law of the definite action of electricity, and
cannot be received.
In the case of solutions of chlorides or iodides, where there can
be no doubt of the relations of the elements, the results of voltaic
decomposition are precisely similar. Chloride of copper gives simply chlorine and copper, no water being decomposed. Chloride of
sodium or iodide of potassium give chlorine or iodine at the one
electrode, and alkali and hydrogen at the other; the evolution of
these last being caused by the action of the metallic basis on the
water of the solution.
Professor Daniell, to whom these important electro-chemical researches are due, considers the truth of the binary theory of salts
to be fully established by them.
If this theory be adopted, a profound change in our nomenclature
sf salts will become necessary.  Graham  has proposed that the




420     VIEWS RESPECTING  DOUBLE  SALTS.
name of the salt-radical should be formed by prefixing to the wom d
oxygen, the first word of the ordinary name of the class of salts, and
that the salts be termed by changing oxygen into oxides. Thus's.
04, sulphatoxygen, gives sulphatoxides; the sulphates, N.O6, nitratoxygen, gives nitratoxides, the nitrates, and so on; but I consider
that the form of nomenclature proposed by Daniell deserves the
preference. It has bleen described (p. 194) that Faraday proposed
to term the elements which pass to the electrodes of the battery,
ions; acting on this, Daniell proposes to term the electro-negative
element of the sulphates, oxysulphion; that of the nitrates, oxynitrion, and so on, and the salts may be termed oxysulphion of copper,
oxynitrion of sodium, &c. It would be desirable, however, for a
long time, to introduce these names only where theoretical considerations rendered their employment decidedly useful, and hence, in
all future description of the salts, I shall make use of the language
of our ordinary views, and treat of their preparation and composition without any reference to the discussion in which we have been
engaged.
The general adoption of the binary theory of salts has deprived
of much of its interest and importance a question which some years
since was very ingeniously discussed, viz., whether, in the fornmation of double salts, the salts which unite had the same relation to
each other that the acid and base were then thought to have. Thus
it was supposed that the electro-negative qualities of sulphuric acid
being less controlled by oxide of copper than by potash, the alkaline sulphate acted as a base to the sulphate of copper when these
two salts combined to form the double sulphate of potash and copper, and so on in other instances; but, in addition to the circumstance that all we have said as to the constitution of the salts militates against this view, we have the positive evidence that, first,
these double salts are formed, not by combination merely, but by
replacement of the constitutional water of the sulphates of the copper or magnesian class, which water nobody would contend to act
in them as a base; and, second, that when a solution of such a double salt is decomposed by the battery, the two salts are not separated as if they were acid and base, but are decomposed independently in the proportions of an equivalent of each, making together the
sum of the chemical energy of the current.
A similar idea was advocated by Bonsdorff regarding the double
chlorides, iodides, &c. He proposed to consider the chlorides of
gold, platina, mercury, &c., as chlorine acids, and those of potassium, &c., as chlorine bases, and so with the iodides. This view,
however, although at first very extensively adopted, has given way
to the gradual growth of knowledge. There is no analogy between
a dry oxygen acid and a chloride; but the chlorides are in perfect
analogy with the neutral salts. Thus Cu.C1. does not resemble S.03,
but Cu.S.O4 and Cu.Cl.+K.Cl. are analogous, not to S.O. K.O., but
to the double salt, Cu.S.04~-K.S.04. Bonsdorff's idea was exactly
counter to the direction of truth; he sought to bring all salts under
the one head, by extending to all the constitution of oxygen acids
and oxygen bases, while the progress of science has led us to the
opposite generalization of reducing all salts to the simple haloid
type.




SALTS OF POTASH.                       421
CHAPTER XV.
tI'ECIAL HISTORY OF THE MOST IMPORTANT SALTS OF THE IN(RGANIC ACIDS
AND BASES.
THE multitude of salts known to chemists is so very great, that
it is only possible to detail the history of the most important of
each class. They are arranged according to their bases, except in
some few cases, where a metal is also the radical of their acid element. In that case, the salts of the acids of the metal are described
after those formed by its oxides with other acids. This plan ihas
been adopted in order to give as much unity as possible to the history of each metal, and influences only the compounds of chrome
and arsenic to any degree.
Of the Salts of Potash.
Chloride of Potassium.-K.Cl. Eq. 932-6 or 7447.  This salt ma3
be artificially produced by neutralizing potash with hydrochloric
acid. It exists abundantly in the water of many brine springs, and
in the ashes of plants. It is very soluble in water, producing so
much cold as to be employed as a freezing mixture; it crystallizes
in cubes, which are anhydrous; its principal use is in the manufacture of alum.
Iodide of Potassiuzm.-K.I.  Eq. 2069'4 or 165.8. A variety of
processes may be employed to prepare this salt. One of the simplest consists in dissolving iodine in solution of potash until this is
completely neutralized. The potash being decomposed, there is
formed from 6I. and 6K.O., 5K.I. and K.O.. 1.0. The solution is
evaporated to dryness, and the mass being heated to redness, is
kept fused as long as bubbles of oxygen gas are given off: the residual salt, which is pure iodide of potassium,.is, when cold, to be
dissolved in its weight of boiling water, and allowed to crystallize
very slowly. A certain loss may occur in this process if the heat
applied be too high, and if the temperature be not high enough, iodate of potash may remain undecomposed; this last effect being
advantageous to the manufacturer by increasing the quantity of
product, is more liable to occur, and may be detected by means of
tartaric acid, as very ingeniously proposed by Mr. Maurice Scanlan.
This acid is without action on pure iodide of potassium, farther
than to liberate hydriodic acid, which remains for a certain time
unaltered; but if a trace of iodate of potash be present, the iodic
acid which is set free immediately reacts on the hydriodic acid,
water being formed and iodine liberated, which may be recognised
by means of starch.
Another process, adopted by the London and Edinburgh Pharmacopceias, consists in putting together iodine, metallic iron, and
carbonate of potash; the iron and iodine unite directly to form a
soluble iodide of iron, which is decomposed as rapidly as formed




422 IODIDEI BROMIDES AND SULPHATE  OF POT A SH.
by the carbonate of potash. Iodide of potassium is produced with
oxide of iron and carbonic acid; a quantity of the latter combines
with the oxide of iron, but as this is not pure protoxide, most of
the carbonic acid is evolved as gas. The reaction consists in Fe.I.
and K.O.. C.O2, giving rise to K.I. and Fe.0..C.O2.  The liquor being filtered and evaporated to a pellicle, the iodide of potassium is
obtained crystallized. This salt crystallizes in cubes; sometimes
in square prisms, which are macles. It is not deliquescent when
pure, and is without action on turmeric paper; by this means it is
known to be free from carbonate of potash. It is sometimes adulterated by chloride of potassium, which may be detected by decolmposing its solution by nitrate of silver, washing the precipitate with
water, digesting it in strong water of ammonia, and filtering; if the
solution, when rendered slightly acid with nitric acid, give a white
precipitate of chloride of silver, chloride of potassium was present,
and its amount may be thus determined.
The iodide of potassium is extensively used in medicine, by the
chemist as a reagent, and for the preparation of other metallic iodides.
A solution of iodide of potassium dissolves iodine in large quantity, forming a brown liquor used in medicine. It is not certain,
however, that in this case any definite compound (as a biniodide)
is formed..Bromide of Potassium.-K.Br.  Eq. 1468'3 or 117'6. This salt
may be prepared exactly as the iodide of potassium, which it resembles in most of its physical characters. It is recognised by
giving, with oil of vitriol, orange-red fumes of bromine.  The commercial article is frequently adulterated with chloride of potassium,
the presence of which may be detected as follows: dissolve 100
grains of the salt in four ounces of water, and decompose it by an
excess of nitrate of silver; collect the precipitate, wash it carefully,
and dry it in a capsule till it ceases to lose weight; then weigh it.
If it were perfectly pure, the bromide of silver should weigh 158.8
grains; but the presence of chloride of potassium.would'have the
effect (from the smaller equivalent of chlorine) of increasing the
weight; therefore, if the precipitate, when quite dry, weighs more
than 158'8 grains, the sample is impure, and the quantity of chloride
present may be calculated from the overplus weight, for 100 grains
of pure chloride of potassium should give 192'6 grains of precipitate. Thus, if there were 10 per cent. of impurity, the precipitate
would weigh 162 grains; if 20 per cent., it would weigh 165'4.
Thus the precipitate increases in weight about 3'3 for each 10 per
cent. of chloride of potassium present.
The properties of the Fluoride and of the Silico-fluoride of Potassium are not of importance beyond what has been already said in
p. 321, 323, and 324.
Sulphate of Potas/. —K.O.. S.O3 Eq. 1091'1 or 87'43. This salt
is produced upon the large scale in the manufacture of the sulphuric and nitric acids, where nitrate of potash is employed. It may be
prepared by the direct union of its constituents, and, being but sparingly soluble, it precipitates as a fine crystalline powder wihen oil
of vitriol is mixed with a strong solution of potash. It is more sol



SULPHATE  AND NITRATE  OF POTASH.    423
uble in boiling water, and crystallizes, on cooling, in right rhombic
prisms, or in six-sided prisms terminated by pyramids, which are
macles, being formed by the union of three simple crystals, as described in p. 28. In the figures, A represents the manner in which
the three rhombic prisms adhere together, the letters   A
marking the corresponding planes in each original, and   l 
B the form which results when all traces of the junctions     AKf.
have disappeared.  This salt does not contain water; its
crystals decrepitate violently when heated, but are not decomposed.
100 parts of water dissolve 8'3 of the salt at 32~, and      B
25 parts at 212~. This salt combines with dry sulphuric acid to form a bisulphate of potash, K.O.+ -
2S.03, which may be prepared by exposing the nei- 
tral salt to the vapour of dry sulphuric acid, or by   v
dissolving it with 1. equivalents of oil of vitriol in
the smallest possible quantity of distilled water.
This bisulphate of potash crystallizes in small prisms, w ich are
gradually decomposed by water, the following salt being formed.
Common Bisulphate of Potash. Double Sulphate of Water nnd Potash.-K.O.. S.0, +H.O.. S.03. Eq. 1704'7 or 136'6. This salt is
produced when nitrate of potash is decomposed by two atoms of
oil of vitriol, and is formed when neutral sulphate of potash is gently heated with half its weight of oil of vitriol to just below redness. It may be obtained crystallized from a strong solution in
right rhombic prisms. It is decomposed into neutral sulphate and
oil of vitriol-by a large quantity of water.  When heated to full
redness, it fuses, and may be obtained, on cooling, in oblique rhombic crystals; it is thus dimorphous (see p. 227); at a higher tern
perature it abandons its excess of acid, and neutral sulphate remains.
There exists also a hydrated sesquisulphate of potash, 2(K.O.. S.03)
+H.O.. S.03, which crystallizes in fine needles.  Similar compounds of sulphate of potash with hydrated nitric and phosphoric
acids have also been described.
JVitrate of Potash.  Saltpetre. Jfitre. —K.O.. N.05. Eq. 1266'9 or
101'5. The general principles of the formation of nitric acid by
the conjoined action of decomposing animal matter and of earthy
bases on atmospheric air, have been described already. By lixiviating the materials thus obtained, whether naturally or from artificial nitre beds, with water, a solution is obtained, containing,
among other saline matters, a considerable quantity of nitrate of
lime; this is then decomposed by an impure carbonate of potash,
and carbonate of lime being precipitated, a solution of nitrate of
potash is obtained, from which the salt is procured by evaporation
and crystallization. Its form is that of a six-sided prism with dihedral summits, derived from the right rhombic system. It is anhydrous; 100 parts of water dissolve 13'3 parts at 32", and 240 parts
at 212~; when heated to redness, it melts and evolves oxygen, at
first pure, but subsequently mixed with nitrogen gas.
As nitrate of potash contains oxygen in large quantity, and gives it out readily to
combustible bodies, it is much employed for the preparation of fireworks, and especially of gunpowder. The action of gunpowder depends upon its generating, when
decomposed, a large quantity of gases, which occupy more than 1000 times its vol



424          MANUFACTURE OF GUNPOWDER.
ume. If this took place instantaneously, all bodies near, which could not resist
this force, would be burst or broken; as takes place with chloride of azote, which, if
placed in a gun, would burst it, but have no power to propel a ball; the decomposition of gunpowder, however, occupying a certain time, the disengagement of gas is
progressive, and the ball is fobrced through the barrel with the velocity due to the ultimate effect of the whole quantity of gas produced. When gunpowder is completely
decomposed, the products are found to be sulphuret of potassium, nitrcgen, and carbonic acid gas, and from these the proportions by weight of its constituents may be
calculated, for S., K,0.. N.Os, and 3C., produce K.S., N., and 3C.02. The parts by
weight are, therefore,
Theory.   French.    English.    rrussian.
S.= 16'1 - 11'8   12-5   10'0   11'5
3C. — 183 - 1.35    12'5   15'0   13'5
K.0. Nl. NO=101'5 - 74'7   75'0   75'0   75'0
135'9  100'0   100'0   100' 0   100)0
The proportions employed in the government factories of the most important countries are given also above. The Prussian mixture agrees best with theory. For the
coarse blasting powder, there are employed sixty-five parts of skltpetre, twenty of
sulphur, and fifteen of charcoal. The excess of sulphur renders the explosion more
intense, but would corrode firearms too much. A mixture of three parts of saltpetre, four of carbonate of potash, and one of sulphur, is decomposed instantaneously
when fused, and with an explosion so violent, that, if it be placed on a thin iron plate,
it may be perforated. If three parts of nitre be mixed with one of finely-powdered
charcoal, a mass is obtained which, when touched with an ignited coal, burns nearly
as fast as loose gunpowder, but totally without explosion. It is therefore the sulphur which determines the violence and rapidity of the deflagration of gunpowder,
while the charcoal produces the great volume of gas on which its mechanical effect
depends.
The preparation of the materials for making gunpowder requires great care.
Most of the success depends on the preparation of the charcoal. This should be
made from a light wood containing little ashes, such as birch, and carbonized in cylinders, very slowly, and at the lowest possible'heat. When reduced to impalpable
powder, this charcoal is so inflammable as sometimes to take fire at ordinary temperatures. The purification of the saltpetre is performed by successive recrystallizations, and by washing the crystals with water already saturated with saltpetre,
which dissolves out any common salt that may be present, but does not act on the
crystals of saltpetre. The description of the mechanical operations of the manufacture would be out of place here.
Hypochlor-ite of Potas/h.-When gaseous chlorine is passed into a solution of carbonate of potash, it is abundantly absorbed, but no carbonic acid is disengaged until
the liquor contains an atom of chlorine for every two atoms of alkaline carbonate,
On examination, it is then found to contain hypochlorite of potash, chloride of potassium, and bicarbonate of potash, which are mixed in solution, and may be partially
separated by crystallization. The reaction' has been such that 2C1. and 41 O.. C.
02 give K Cl., K.O. Cl.O., and 2(K.O.+C.02+-H... C.02). If the stream ofchlo
rine be continued, carbonic acid is copiously evolved, and as much more chlorine is
absorbed, giving ultimately a mixture of K.Cl. and K.O.. C1.. The liquor becomes
deep yellow, owing to the liberation of a quantity of hypochlorous acid by the free
carbonic acid, and hence the quantity of chlorine absorbed amounts to much more
than the exact atomic proportion.
Farther details of the theory of these bleaching compounds are given under the
head of chloride of lime.
Chlorate of Potash.-K.0 O..C.05. Eq. 1532'6 or 122'81.  When
chlorine gas is passed into a stronig solution of potash, it is absorbed
rapidly until the alkali is completely neutralized, and chloride of
potassiumn and hypochlorite of potash are formed; 2K.O. and 2C1.
giving K.Cl. and K.O.. CL.0. If, then, this liquor be boiled for some
time, oxygen gas is given off, the hypochlorite being decomposed,
and chloride of potassium  and chlorate of potash being formed,
9(K.0..  Cl.0.) producing 120. with 8K.Cl. and K.O...C.05.  If car.
bonate of potash has been employed, the absorption of the chlorine
is rapid until half of the salt has been decomposed and the remain



CHLORATE  OF  POTASH.                         425
der converted into bicarbonate, from  combining with the evolved
carbonic acid, as described under the preceding head; but a high
temperature and a great excess of chlorine being necessary to complete the reaction, render the operations tedious and very trouble.
some; and as, owing to the large quantity of oxygen evolved, there
is but one equivalent of chlorate of potash obtained by the action
of eighteen equivalents of chlorine on eighteen of potash, the process is one of considerable expense.
We owe to Graham a method which is free fiom these disadvantages.  If an equivalent of carbonate of potash be mixed with one
of hydrate of lime (by weight about 2 of K.O.. C.0  to 1 of Ca.O..
H.O.), and exposed to a current of chlorine, the gas is absorbed with
avidity, and the solid mass becomes very hot, while water is given
off abundantly.  When saturated, it may be gently heated to complete the decomposition.  No oxygen is given off, th e reaction being
that 6(K.O.. C.02) and 6(Ca.O...O.), acted on by 6C1., produce
5K.Cl., 6Ca.O.. C.O, and K.O.. CI.0, while 6Hf.O. are evolved.
By digesting the mass in water, the potash salts are dissolved out,
carbonate of lime remaining, and the chlorate of potash may be
separated from the chloride of potassium by crystallization. By this
means three times as much product may be obtained from the same
mnaterials as by the older process.
This salt crystallizes in rhomboidal tables of a pearly lustre: it is
anhydrous: 100 parts of water dissolve but 3'5 parts at 32', and 60
parts at 219'. It tastes sharp and cooling, like nitre; when heated,
it melts and evolves oxygen gas, being decomposed into chloride of
potassium and hyperchlorate of potash; on increasing the heat, this
also is decomposed, and chloride of potassium remains pure. Its
uses in preparing oxygen, and the compounds of chlorine and oxygen, have been already noticed. From its supplying oxygen still
more readily than nitre, it is the basis of a variety of defiagrating
mixtures.  When rubbed in a mortar with sulphur or with sulphuret of antimony, it explodes violently. Placed in contact with a
minute bit of phosphorus on an anvil, and struck by a hammer, it
gives a dangerous detonation. The ordinary lucifer matches are
formed by mixtures of chlorate of potash with sulphur and charcoal,
or sulphuret of antimony or of cinnabar, made into a paste with
gumarabic, and applied to the extremity of a bit of stick, previously
smeared with sulphur.  Students should be very cautious how they
employ this salt in such experiments as those now noticed.
Perchlorate of Potash-K.O.. C1.07; Eq. 1732'6 or 138-8-is of importance only
from being one of the least soluble salts of potash, and, consequently, that the perchloric acid may be used as a test for the presence of potash in solution, it giving
a granular crystalline precipitate if that alkali be present. Its preparation is sufficiently noticed in page 306.
The Silicate of PotasA is of considerable importance as a constituent of glass, and
will be noticed as such hereafter.
Iodate of Potash.-K,O.. 1,05, This salt, which is but sparingly soluble in water,
may be obtained by neutralizing the perchloride of iodine with caustic potash; I.
C15 and 6K.O, produce 5K.C1l and K.O.. I.05. This last separates in crystalline
grains. It may also be obtained by adding iodide of potassium to fused chlorate of
potash; the mass froths up, the oxygen passing to the iodine, and there is obtained a
mixture of chloride of potassium and iodate of potash, -which may be separated by
crystallization. This salt has a remarkable tendency to form acid and doul: le salts,
of which, however, none are specially interesting,
-i H H




426              CHLORIDE  OF SODIUM.
Salts of Sodium.
Chloride of Sodium.  Common Salt. Sea Salt —Na.Cl.; Eq. 733'6
or 58.8-exists in great abundance in nature; solid, as rock salt,
and in solution in the water of the ocean, and of many inland seas
and lakes. The deposites of rock salt occur only among the more
recent (secondary) geological formations, lying above the coal, and
in connexion with the new red sandstone, as in Cheshire.  The beds
of salt are sometimes of great magnitude; thus, at Northwich, the
bed now worked is supposed to be not less than 60 feet thick, a mile
and a half long, and 1300 yards wide; and the deposites at Wieliczka, in Poland, appear to be still larger. The origin of these deposites of salt is probably to be found in the gradual drying up, by
evaporation, of salt lakes, to which fresh quantities of salt were continually supplied by the surrounding springs.  Owirg to admixture
of earthy matters, the rock salt, as quarried, is generally brownishcoloured, and hence requires to be dissolved in wvater and crystallized for use. The expense of extracting the salt may be in many
cases lessened, by simply boring down to the bed with a pipe a few
inches in diameter, and letting thereby water run in upon the salt;
a strong solution of salt is thus produced, which is pumped up and
evaporated. The expense of sinking a shaft and quarrying out the
solid salt is thus avoided.
In warm countries, as on the coasts of Portugal and of the south of
France, salt is obtained by the spontaneous evaporation of sea-water, which is allowed, on the rise of the tide, to flow into shallow
basins, being passed from one to another, according as it becomes
more concentrated, and, finally, the evaporation being finished by
means of artificial heat. The sea-twater is not evaporated to dryness, as its other saline ingredients would in that case be mixed
with the common salt. The sea-water is generally composed of
Chloride of sodium... 250 
Chloride of magnesium..   0.35
Sulphate of magnesia. 0'58
Carbonate of lime and             100 00,
Carbonate of magnesia       0021000,
Sulphate of lime.... 001
Water....96.54 )
*with generally some traces of iodide and bromide of magnesium.
According as the evaporation proceeds, the common salt is deposited in crystals, and the mother liquor, or bittern, being rich in salts
of magnesia, is preserved for the manufacture of Epsom salts.
In addition to these sources, chloride of sodium may be obtained
by the direct combination of its elements, or by decomposing carbonate of soda by muriatic acid. In practice, however, this is never
done.
Chloride of sodium crystallizes in cubes. Its taste is purely saline. It is equally soluble in water at all temperatures, 100 of water dissolving 36'5; by a very strong heat it may be volatilized.
Its crystals are anhydrous, but are generally fissured, containing
water, which, when heated, bursts the crystal, producing loud de.




MANUFACTURE  OF GLAUBER'S SALT.                   427
crepitation. A strong solution of salt does not freeze at 0~, but deposites crystals in rhombic plates, which are a hydrated chloride
of sodium. If these crystals be heated beyond 15~ they give out
water, and are changed into minute cubes.
The uses of chloride of sodium are very numerous and important.
Besides being employed in seasoning food, it is now universally the
source from whence the other compounds of sodium, such as the
carbonate and sulphate, are obtained. It is employed also in the
manufacture of glass and of porcelain, and as a manure.
The bromide and iodide of Sodium resemble, in properties and mode
of preparation, the corresponding compounds of potassium, and do
not require special notice.
Sulphate of Soda. Glauber's Salt.-Na.O.. S.0+O 10 Aq. Eq. S92'1
+- 1125 or 71248+90. So named after its discoverer: exists in some
mineral waters, and may be prepared by neutralizing carbonate of
soda by dilute sulphuric acid. For the purposes of commerce, it is
manufactured in great quantities from common salt, as described
under the head of muriatic acid (p. 307).
As it is not the object of the process to economize the muriatic
acid gas, the decomposition is carried on in a reverberatory furnace
similar to that figured in p. 333. Three or four hundred weight of
salt being spread over the floor of the furnace, forming a layer three
or four inches deep, the equivalent quantity (an equal weight) of
sulphuric acid, of the strength 1'600, as taken from the chambers, is
poured in through an aperture in the dome, and a moderate fire kept
up until the materials begin to dry; the fire is then increased gradually until all the muriatic acid gas has been expelled, and the residual sulphate of soda begins to fuse. The acid gas passes up the
chimney, and is either allowed to pass away into the air, or is condensed by meeting with a stream of water, and the weak liquid acid
thus formed is suffered to run to waste. The' greater part of the
sulphate of soda thus produced is immediately used to make carbonate of soda; but to form Glauber's salt, it is only necessary to
dissolve it in warm water, and let it crystallize by cooling.
The sulphate of soda crystallizes in six-sided prisms, as in the
figure, very much channelled at the sides. It is
easily soluble in water, having a point of maxi-   J
mum solubility at 933, as figured in page 22. Its I      -
ordinary crystals contain 56 per cent. of water;   
by exposure to the air it loses all its water by
eflorescence, and falls into a white powder; from
a hot saturated solution opaque rhombic octohedral crystals are deposited, which are anhydrous.
The isomorphism of these crystals with permanganate of barytes,
and the speculations founded on it, have been noticed p. 224. A
bisulp/ate and a sesquisulphlate of Soda may be formed by adding
oil of vitriol to a solution of the neutral salt, and crystallizing by
evaporation. They are much less determinate than the acid sulphates of potash.
JVitrate of Soda.  Cubic.JNitre. —Na.O.. N.O. Eq. 1067 5 or 85 57.
The spontaneous formation of this salt by the atmospheric influence,
probably on a soil containing chloride of sodium, has been noticed




428              PHOSPHATES OF SODA.
p. 277. It may also be obtained by means of nitric acid and carbonate of soda. It crystallizes in rhombs, isomorphous with calc spar
(p. 224). It is very soluble in water, and is slightly deliquescent;
hence it cannot be employ-ed in the manufacture of gunpowder. It
ts used for the manufacture of nitric and sulphuric acids, and as a
manure.
Ityposulphite of Soda.-Na O.. S202+10 Aq. This salt, which
nas become of some practical interest, from its use in dissolving
off the sensitive silver compounds in making photogenic drawings,
may be made by boiling together three parts of dry carbonate of
soda with one of sulphur until this last is dissolved, and then pass
ing a stream of sulphurous acid gas through the liquor until it smells
strongly of it. Na.O.. C.O, with S. and S.02, produce Na.O.. SO2,
while C.0, is evolved. If the three parts of carbonate of soda be
boiled with two of sulphur, and the deep yellow liquor be exposed
to the air until it yields a colourless liquor on filtration, the salt is
more simply produced, the necessary quantity of oxygen being absorbed from the air. The hyposulphite of soda thus formed is easily
soluble in water. Its resemblance to Glauber's salt in form, and its
other properties, are noticed in p. 291.
_Hypochlorite of Soda. Chloride of Soda. Disinfecting Liquor of
Labaraque-Is produced by treating a solution of carbonate of soda
with chlorine as long as this is absorbed, but no carbonic acid
evolved. For farther observations, see the hypochlorites of potash
-and of lime.
A. Tribasic Phosphate of Soda.-The common phosphate of soda
of the shops is a tribasic salt, containing (P.O,52Na.O.+-H.0.)+241 Aq. It is prepared by decomposing the solution of acid tribasic
phosphate of lime obtained from bones (as described in p. 295) by
means of carbonate of soda. Carbonate of lime is thrown down,
and phosphate of soda formed. It is easily soluble in water, and
crystallizes in oblique rhombic prisms, as in the figure, which react alkaline. When exposed to the
air, it loses some of its water by efflorescence (ten
atoms I), but the crystals retain their form. If this
salt be mixed with an excess of caustic soda, the
I   atom of basic water is displaced, and the subphosphate of soda (P.O 05+3Na.0+-24 Aq.) crystallizes in
/    long prisms; and by the addition of hydrated phosphoric acid to its solution, and cautious evaporation,
the acid tribasic phosphate (P.O-+Na.O.+2H.O.)+2 Aq., which
crystallizes in oblique rhombic prisms, is formed: it is dimorphous.
The characteristic of these three salts is to give with nitrate of
silver a yellow precipitate of tribasic phosphate of silver.
B. Bibasic Phosphate of Soda.-Of these salts, that termed the Pyrophosphate of Soda,(P.05+-2Na.0.) -{- 10 Aq., is of interest, as its discovery led the way to the true history of these bodies. It is formed by fusing the common phosphate of soda, (P.O+4- 2NaO. -+ H.O.)
+-24 Aq., at a red heat. All the water of crystallization is given
off at a very moderate heat; but by a red heat the twenty-fifth or
basic atom is expelled, and, when the salt is then redissolved, the
phosphoric acid does not recombine with basic water, but remains




BORATE S OF  SODA.- SALTS OF  BARIb M.  429
united only with the soda. It is recognised by giving a white precipitate with nitrate of silver.
C. The.Monobasic Phosphate of Soda, P.O,-+Na.O., is obtained by
heating the acid tribasic or bibasic phosphates of soda to redness.
All the volatile base being thus expelled, the phosphoric acid remains combined with one equivalent of soda. This salt fuses into
a transparent glass; is deliquescent; its solution does not crystallize. It is easily recognised by throwing down from solutions of
lead and silver, precipitates, which are not powders, but soft, tenacious pastes.
Borates of Soda.-Boracic acid combines with soda in many proportions, forming salts, of which the most important is the biborate,
the borax of commerce (Na.O.+2B.O)+-10 Aq. It exists in the
water of several lakes in Thibet and China, also in Hungary, and
was imported thence in small crystals, smeared with a fatty matter,
under the name of tinkal. The borax of commerce is now obtained
by treating the native boracic acid obtained from Tuscany, p. 326,
by carbonate of soda. On the application of heat, the acid dissolves
with the evolution of carbonic acid and ammonia; the liquor is run
into large vats lined with lead, where it cools very slowly, and the
borax gradually crystallizes in oblique rhombic prisms, as i, u, m,
in the figure. If a strong solution of borax be kept at
33', the salt crystallizes in regular octohedrons with
only five atoms of water.  Although this salt contains
two equivalents of acid, it has an alkaline reaction:  l m 
when heated, it froths up very much, abandoning its
water.  The dry salt melts at a red heat into a colourless glass, which dissolves most metallic oxides very readily, and
hence is serviceable in experiments with the blowpipe, as'enabling'
the metals to produce the coloured glasses by which they are recognised; under the head of glass and porcelain, its use in these
branches of art will be again noticed.
The remaining compounds of boracic acid with soda, as the neutral borate, Na.O.. B.03 + 8 Aq., and acid salts, as Na.O.+4B.03 and
Na.O.+ 6'B.03, are not important.
Silicate of Soda will be described under the head of glass.
Salts of Lithiqm.-From the rarity of this body, its salts require no farther notice
than that its carbonate is but very sparingly soluble in water, yet its solution possesses an alkaline reaction. It thus serves to connect the alkaline with the earthy
bases.
Salts of Barium.
Chloride of Barium.-Ba.Cl. Cl.2 Aq. Eq. 1299'6 +225 or 104'8+
18. This salt may be prepared by decomposing the native carbon
ate of barytes with dilute muriatic acid, or, more economically, by
decomposing the sulphuret of barium, the preparation of which is
described in p. 342, by dilute muriatic acid. In the former case,
carbonic acid, in the latter, sulphuretted hydrogen, is given off
The chloride of barium crystallizes from a hot solution in rhomboidal tables which contain 14'7 of water.
Sulphate of Barytes.-Ba.O.. S.03. Eq. 1458 or 119'5. This salt
exists native, in great abundance, being the most common source
of barytes. It is very generally associated with sulphuret of lead,




430  SALTS OF BARIUM., STRONTI UIM  AND CALCIUAt.
and serves as an indication of the probable proximity ofthat ore.
It is totally insoluble in water.  Its crystalline form is an oblique
rhombic prism, generally very flat, as in the
figure; derived from an octohedron of which
%  i and e are planes; the secondary planes, p
and u, belong to the prism. It is one of the
heaviest of saline bodies, its specific gravity
being 4-3; hence its name of heavy spar and terraponderosa.  When
ground to fine powder, it is used as a cheap substitute for white
lead in painting, for which large quantities of it are employed; but
its crystalline texture prevents it having the opacity or body necessary in a good pigment. It may be prepared artificially by adding
sulphuric acid to any solution containing barytes; it falls as a heavy
white crystalline powder.  Its total insolubility renders its constituents excellent reagents for each other.
J\itrate of Barytes-Ba.Oq +N.05; Eq. 1633-9 or 130-9-may be
produced by acting on carbonate of barytes with dilute nitric acid,
or, more cheaply, by mixing strong hot solutions of sulphuret of barium and nitrate of soda.  The sparingly soluble nitrate of barytes
crystallizes as tihe mixed liquors cool, but the sulphuret of sodium
remains dissolved.  In.this process, from Ba.S. and Na O.. N.Q, we
obtain Ba.O.. N.O, and Na.S. This salt requires twelve parts of
cold water for solution, but dissolves in four of boiling water, from
which it crystallizes on cooling in octohedrons.  These crystals are
anhydrous. WAhen heated, they yield pure barytes.
The other salts of barytes do not require notice.
Salts of Strontium.
Chloride of Strontium. —Sr.CI. - 6 Aq. Eq. 989'9 or 79-32. This
salt is obtained from the native carbonate or sulphate of strontia,
exactly as chloride of barium is obtained from the native salts of
barytes.  It crystallizes in long needles which deliquesce.  It is
very soluble in water.
Sulphate of Strontia. —Sr.O.. S.Q0. Eq. 114,84 or 91-9. This, the
most abundant source of strontia, is found native crystallized, isomorphous with sulphate of barytes. It may be produced artificially as a white powder, by adding sulphuric acid to any solution containing strontia.  It is dissolved by 3600 parts of boiling water, and
remains dissolved after cooling. It is fused by a strong heat; with
charcoal it gives sulphuret of strontium.
NJritrate of Strontia-Sr.O.. N.O; —crystallizes in octohedrons,
which dissolve in five parts of cold, and one half part of boiling
water. Mr. Scanlan has observed, that during the crystallization
of this salt bright flashes of light are emitted. It is anhydrous, but
decrepitates when heated, owing to mechanically included water.
On the application of heat, these crystals evolve oxygen and nitrogen, and leave pure strontia.
Salts of Calcium.
Chloride of Calcium-Ca.C. + 6 Aq.; Eq. 698-7+ 675 or 55'98~54 —is obtained by decomposing carbonate of lime with muriatic
acid. In the laboratory it is abundantly procured as the residue of




FLUORIDE  OF CALCIUM.-SULPHIIATE OF LIME. 431
the preparation of carbonic acid, ammonia, &c. It is very soluble
in water; its solution, evaporated to the consistence of a sirup,
gives, by cooling, long, striated, rhombic prisms, which deliquesce
with great rapidi'v, and when heated undergo watery fusion, soon
after -which it abandons two thirds of its water of crystallization,
and a powder is obtained, Ca.Cl.+2 Aq., in which form it is best
adapted for freezing mixtures.  Heated still farther, it becomes anhydrous, and at a red heat fuses. In this state it is phosphorescent
in the dark, forming Homberg's pyrophorus.  It has a very great
affinity for water, combining with two atoms of it, with the evolution of much heat, and is hence employed to dry gases for experimental purposes, and to remove water from liquids, as in the rectification of alcohol.
This salt combines with lime, forming an oxychloride of calci
urnm, Ca.Cl.J-3Ca.O., which is obtained by boiling a solution of it
with an excess of lime, and filtering.  The new substance crystallizes, on cooling, in small flat rhombs, which contain forty-nine per
cent., or fifteen atoms of water.
The bromide or iodide of Calcium do not present any interest.
Fluoride of Calcium, Ca.F., is an abundant mineral known as fluor
spar, found crystallized in cubes and octohedrons, but principally
massive.  When first extracted from  the earth it is moderately
tough and soft, and is cut into ornaments,which present a beautiful
variety of colours.  Its crystals become strongly phosphorescent
by heat or by electricity. It is insoluble in water; from it all the
other preparations of fluorine are derived, as noticedin p. 319, 324,
and 327. It appears as a gelatinous precipitate when hydrofluoric
acid is added to any soluble salt of-lime.  When heated in contact
with silicious or aluminous minerals, it forms easily fusible compounds, and being thus of use as aflux in the smelting of metallic
ores, its name offluor spar was thence derived.
Sulphate of Lime-Ca.O.. S.-O,+2 Aq.; Eq. 857'2+225 or 68'69 +
18 —may be prepared artificially, by mixing a solution of any soluble salt of lime with siulphuric acid.  It forms a crystalline powder,
nearly equally soluble in hot and cold water, requiring 46 1 times its
weight for its solution. It occurs in nature abundantly, and in various forms: 1st, in distinct colourless crystals; 2d, in semi-transparent masses of crystalline structure, constituting alabaster, and in
amorphous masses, forming extensive rocky strata, in many places,
in which state it is called common gypsum. From thisplaster of Paris
is prepared, by calcining the gypsumn, broken into small pieces, in
ovens at a temperature below 300', until its water of crystallization
is expelled.  In this operation it falls to powder, and is to be put up
in tight vessels so as to exclude the air. When mixed with water
it rapidly 3ecombines with the two atoms, evolving heat and expanding in becoming solid, so as to fill up all interstices of the mould
into which it may be poured.  On this property is founded the art
of casting in plaster and the formation of the various kinds of stucco,
or artificial stone, in which a solution of glue, or of various earthy salts,
may be substituted for pure water.  If the gypsum be heated, in baking, above 300', it is changed in nature, and no longer combines
with water so as to set; it is then converted into a form which exists
in nature crystallized, and which is termed anhydrite.




432    MANUFACTURE  OF  CHLORIDE  OF  LIMIE.
A double salt of sulphate of lime and sulphate of soda is found
native, and termed Glauberite. It is insoluble in water, by which
it is also decomposed. It cannot be formed artificially.
The Hyposulphite of Lime is a soluble salt, the mode of preparing
which is described p. 291.
The Ni/trate of Lime is very deliquescent, and is decomposed by
a moderate heat.
Phosphoric acid combines with lime in several proportions, of
which the most important is the Basic tribasic Phosphate of Lime, or
Earth of Bones.  T'his salt, which constitutes the inorganic portion
of the skeletons of the mnammalia, mixed only with small quantities
of carbonate and sulphate of lime,.and of fluoride of calcium, has the
formula SCa.O.+3P.O0. It may be obtained precipitated by dissolving bone earth in muriatic acid, and exactly neutralizing the solution by caustic ammonia. It falls as a gelatinous powder containing four atoms of water.  As the phosphoric acid of bones is in its
tribasic condition, Graham considers it to be a combination of two
phosphates, thus, 2(3Ca.O.. P.O0+Aq.)-f(H.O.. 2Ca.0.. P.0-+
Aq.). Each of these tribasic phosphates of lime may be obtained
separate, by decomposing solutions of chloride of calcium by solution of the ordinary phosphate, or of the subphosphate of soda.
Hypochlorite of Lime.  Chloride of Lime.  Bleaching Salt.-When
speaking of the oxygen compounds of chlorine, and of the chlorate
and hypochlorite of potash, I have had occasion to notice the diversity of opinion regarding the nature of the bleaching substances
formed by the action of chlorine on the alkalies and on lime.  Or
these the chloride of lime is by far the most important in the arts
It is prepared by generating chlorine in a large still, a, b. A,f, as described p. 301
the materials being kept constantly mixed by means of an agitator moved round b3
the handle d. The gas is conducted by the tube e e to the upper part of a -wood.
en reservoir or apartment, as in the figure, made very tight, i, i, on the floor
I.                l            a  ~~~iR:X
of which pure hydrate of lime is exposed to the action of the gas. The lime is
introduced by the door k, k, and the surface is changed occasionally by stirring
with rakes by means of the apertures 1, 1, 1: the absorption should take place so slowly as not to evolve any sensible heat. In this way 100 parts of slacked lime combine
generally with from fifty to sixty of chlorine. If the process be carried on too rapidly, a quantity of lime is decomposed, chlorate of lime and chloride of calcium being formed, which may be recognised by the product getting damp when exposed
to the air




VALUATION OF CHLORIDE OF LIME.    433
The best bleaching powder thus prepared by the dry way does not conta'in more
Ihan forty per cent. of chlorine; this does not correspond to any exact atomic constitution; but if' lime be diffused through water so as to form a thin crealm, it then
absorbs more than its own weight of gas, and is totally dissolved.  It is probably
the mechanical disadvantages of the dry way which prevents the absorption of the
gas reachiing this limit, and the best bleaching powder may be looked upon as a mixture of true chloride of lime, with about eighteen per cent. of hydrate of lime in excess. Accordingly, when ordinary bleaching powder is treated with water, the true
atomic nompound is'dissolved out, and the excess of lime remains.  Tile composition of the theoretical and best practical substances may, therefore, be expressed as
follows:
Theoretical.                           Best practical.
1 atom chlorine, 35'47    48'63         Chlorine...         40'32
1     lime,   28'57    39'04            Lime...... 4540
1  "  water,   9'00    12'33            Water...... 1428
73'04   10000                                  t100-00
But the generality of good samples in commerce will be found not to exceed thirty
per cent. of chlorine.
The solution of this chloride of lime has a marked alkaline reaction; it is without
any bleaching power except an acid be present, which liberates chlorine, and enables
it to destroy the colouring matter. It is thus that the colour can be reemoved from
certain points without injuring others, which is of very great importance in calico
printing; thus a piece of cloth being dyed uniformly with madder (as Turmkey red),
the pattern is printed on with tartaric acid thickened with gulm, and the whole being
immersed in a bath of chloride of lime, the chlorine is liberated by, the acid at every
point of the pattern, and the cloth is there bleached, giving a white ground, on which
other colours may be applied, while the general surface remains deep red. A solution of bleaching powder in water exhales a sensible odour of chlorine, Owing to the
absorption of carbonic acid from the air, and obtains thereby weak bleaching properties.
As the technical value of bleaching powder depends on the total quantity of chlorine which it contains, this may be determined without reference to its theoretical
constitution. For this purpose a variety of methods have been proposed, and the
process is termed GC/dorometry. The earliest method employed consisted in preparing a standard solution of sulphate of indigo, which, being of a deep blue colour, was
bleached by the chlorine expelled from the lime by the sulphturic acid, and evidently,
the richer the bleaching powder was in chlorine, the more solution of indigo a certain
weight of it could bleach. The action of chlorine on indigo is, however, so complex, that this method was found exposed to numerous fallacies, and may be considered as now obsolete. Latterly, Gay Lussac has proposed to substitute for this
the more definite action of chlorine in acidifying arsenic. He prepares a solution
of arsenious acid in muriatic acid, and dilutes this with water. On adding thereto
a solution of chloride of lime, the muriatic acid takes the lime, and the chlorine, decomposing water, converts the arsenious acid into arsenic acid, and itself forms hy-.
drochloric acid; As.03 with 2C1. and 2I.0. producing As.O5 and 2-I.Cl. The
proportions which I employ in this reaction are as follows: 100 grains of arsenious
acid are to be dissolved in 2000 grains of strong spirits of salt, and this liquor diluted
with distilled water till' it dccupies the volume of 7000 grains of uwater. This is the
standard test liquor; to employ it, 100 grains of the bleaching powder to be tested
are to be diffused through 1000 grains of water, and the test liquor to be gently
poured from a graduated glass on it, in a deep jar, continually stirring the mixture..
A drop of weak solution of soLlphate of indigo is to be occasionally applied, by means
of a glass rod,-to the surface of the liquor; as long as any chlorine remains unalter,
ed, the blue colour of the drop is instantly destroyed, and the addition of the arsenic
liquor is to be continued until the blue drop remains unaltered. Then the quantity
of chlorine present in the 100 grains of bleaching powder is represented by l-I th of
the quantity of the test liquor employed; thus, if there were 2565 grains of the test
liquor necessary to destroy the bleaching power of the 100 grains of chloride of lime,
the quantity of chlorine would be 25'65. This is not absolutely correct; for in theo/
ry, the true quantity of chlorine indicated would be 26'08; but as a few.drops of the
solution are always employed, more than what should by theory be necessary, the
practical proportion of Tl th comes very close to the truth. Even one half part per
cent., which is the limit of error, is quite unimportant in practice.
Another method, which is simple and rapid in execution, is. nearly the same as
that described in p. 355 for determining the technical value of black oxide of manHIi




434  CONSTITUTION  OF  THE  BLEACHING  SALTS.
ganese by means of copperas (green sulphate of iron). The proportion and meth.
od of testing which I employ are as follows: 390 grains of clean and dry crystals of
-green sulphate of iron are to be dissolved in as much water as will bring the solution to the volume of 5000 grains of water. On the other hand, 100 grains of the
chloride of limef are to be diffused through lO0O grains of' water, and the solution of
copperas is to Le added thereto, until the presence of a trace of the protosulphate of
iron in excess is indicated, by the mixed liquor striking a full blue colour vwhen a
drop of it is placed on a slip of paper, imbibed with red prussiate of potash.'TJ:he
quantity of chlorine present in the 100 grains of the blcaching powder is l,t-,lh of thll
quantity of the standard copperas liquor employed; thus, if' 7ic3 grains measure of
the vo)ume of the solution be found necessary, the sample contains 27'83 of chlorine
per cent. For the 27'83 of liquor contains 217 grains of' sulphate of iron, which is
peroxidized by the action of 27'6 grains of chlorine; here, also, the limit of error need
not exceed one half per cent. Other processes have been proposed, fbunded, soime
on the change of yellow prussiate into red prussiate of potash, by means of the chlorine of the bleaching powder; and others, by decomposing the bleaching powder by
means of an excess of water of ammonia, and measurin g the nitrogen gas evolved;
but these are more troublesome and less exact than the processes already detailed,
which are those most worthy of confidence fiom the manufacturer.
As to the theoretical nature of bleaching powder, chemists are
not as yet able to decide positively. The original anti simple idea
of a direct combination between the chlorine and the lime has been
revived by Millon, who advanced that, by decomposing the salts of
lead, iron, and copper by solution of chloride of lime, precipitates
were obtained, which were compounds of the protoxide of the metal
united with as much chlorine as was equivalent to.the oxygen necessary to form  peroxide. Thus, that with lead, a chloroxide Pb.O.
C1.; that with iron, a chloroxide FeOCI.  The chloride of lime,
Ca.O.Cl., would thus be equivalent to deutoxide of calcium, Ca.O.O.
It has been found, however, that the evidence is notyet satisfactory.  The peroxide of potassium  is K 0.O, while chloride of potash
is not K.O.C1t, but K.O.CI. The composition of all these bleachingr
compounds appears to be an atom  of chlorine united to an atom  of
a protoxide, and this may be explained by supposing a hypochlorite
and a metallic chloride to be formed; thus 2Ca.0. and 2C1. may
give Ca.O.q-C1.O. and Ca.Cl.  But, if this happens, the chloride of
calcium  certainly remains combined, forming a double salt; for the
bleaching powder, if properly prepared, has no tendency to deliquesce, and only becomes damp when long kept; and then chlorate
of lime and free chloride of calcium  are formed, and all its bleaching qualities are lost.  There are thus two views equally tenable:
first, that the bleaching compounds are chlorides of oxides, corresponding to peroxides; and, second, that they are double salts of a
hypochlorite with a chloride; but there is no reason to consider
that the chlorous acid, C1.04, comes into play in their manufacture,
although the salts of that acid, when otherwise prepared, do possess
bleaching properties.
Salts of Jil agnesium.
Chloride of Jilagnesium —Mg.Cl.; Eq. 600'9 or 48.16-may be obtained in solution by acting. on the carbonate of magnesia with muriatic acid; by evaporation, it may be obtained in prisms with 6
Aq., which are very deliquescent.  These crystals cannot be deprived:of water without total decomposition, the chlorine passing
off as muriatic acid, and magnesia remaining behind.  The chloride
may, however, be obtained anhydrous, by previously mixing its so



SALTS OF MAGNESIUM AND ALUMINUAf.  435
lution with sal ammoniac, with which it forms an anhydrous double
salt, which, when heated to redness, gives off sal ammoniac, and
the pure chloride of magnesium  remains melted, and forms a clear
crystalline mass when cold. The chloride of magnesium exists in
sea-wvater.
Sulhalte of.agnesia. -Mg O... S.03. Eq. 759'4 or 60'8.' This salt
exists abundantly in saline mineral springs, as those of Seidlitz, Selters, and Epsom, from whence it derives its common name of Epsom
salt.  t; is extracted  principally  from  the magnesian  limestone,
which rS calcined, and the mixed lime and magnesia treated with
dilute sulphuric acid; the sulphate of lime, being very sparingly soluble, is easily separated from the sulphate of magnesia by washing
with wvater; the latter is dissolved out, and the liquor evaporated
and crystallized. A great deal is also made from the mother liquor
of sea-water, or bittern (p. 426).  This is decomposed by sulphuric
acid, and the salt formed separated by crystallization.
The sulphate of rnagnesia crystallizes in  eight rhombic prisms,
as in the figure, containing seven atom-s of water,
of which one is constitutional, and the other six
crystalline; its formula is therefore  gr.O.. S.0. 
H.O. +6 Aq.; when heated to i12' it easily abandons the 6 Aq., but retains the seventh atom  of water even at 400'.  It combines with the sulphate
of potash to form a double salt, (AIg.O.. S.03+ K.
O.. S.O) —- 6 Aq., the atom of constitutional wrater
being replaced by the alkaline sulphate.  The sulphates of' soda and of ammonia act in the same way.
Ni,'rate of AIlnygoeesia. Mg0... N.O5, is very soluble and deliquescent. It cannot be
obtained dry. as it crystallizes with six equivalents of water, of which five are expelled by a moderate heat, and by a higher temperature the nitric acid itself passes
off, and magnesia remains behind; Mg.O.. N.05. H.O. producing Mg.O. and H.O..
N.0O.
The Borate of lragresic constitutes the mineral boracite, whose electricai and
crystalline properties have been already noticed.
There exists a great number of combinations of silicic acid with magnesia, constituting the steatite, or soapstone; the mLeersc/tlam, of which pipe-bowls are cut; olivine and serpmtine, which exist abundantly in the green marble of Galway: these
are simple silicates of magnesia; others, as amapl/ibole and pyroze.ne, are double silicates of magnaesia and. line, more or less replaced by protoxide of iron.
Salts of Xl1mninuum.
CGloride of Altinvisez.-Al.2Cl3. Eq. 16703 or 13384. In a hydrated form this
salt may be prepared by dissolving alumina in muriatic acid, a solution being obtained, which, when evaporated, yields very deliquescent crystals, containing tvwelve
atoms of water. On applying heat to this, the salt itself is decomposed, muriatic
acid is given off, and pure alumina remains. The dry chloride of aluminum is
formed only by a process analogous to that described for chloride of silicon, p. 323.
Pure alumina is mixed with lampblack and ignited in a porcelain tube, while a
stream of dry chlorine is passed over it: the oxygen of the alumina comnbines with
the carbon, and forms carbonic oxide, and the chiorine combines with the aluminum.
The resulting chloride; being volatile, sublimes, and is condensed in the cool portion
of the tube, which is allowed to project some distance beyond the furnace for that
purpose, or a wide glass tube is adapted to receive the salt.
The chloride of aluminum thus formed is a pale-green crystalline mass. Exposed
to the air, it fumes and deliquesces. Once combined with water, it cannot be freed
from it. It is used to obtain metallic aluminuni, as described p. 349.
The Fletoride of AlnmiELum is found in the mineral kingdom. The beautiful genm
the topaz, is a double fluoride and silicate of alumina.




436               MANUFA V,TURE  OF  ALUM.
Sulphate of 4luzmina (A]03 t 3S.03) + 18 Aq.-This salt is obtain.
ed by dissolving alumina in dilute sulphuric acid; it has a sweetish
styptic taste, is very soluble in water, and crystallizes in thin flexible plates; when heated, it abandons its water, and at a red heat
its sulphuric acid, alumina remaining pure.  The  sulphuric acid
unites with alumnina in many other proportions, of which that constituting the mineral aluminite is the most important; its formula is
A120,+S.O3+3 Aq:, the base, acid, and water each containing the
sane quantity of oxygen.  This salt is produced, also, by adding
an excess of caustic ammonia to a solution of alum; hence caustic
ammonia cannot be used to prepare pure alumina (p. 351).
The sulphate of alumina combines with the alkaline sulphates to
form  the remarkable double salts, the common alums.  The most
ordinary kind is the double sulphate of alumina and potash, the formula of which is (K.O.. S.0,3+A1203q-3S.0,)-24 Aq.
From the large quantities of this salt employed in the processes of dyeing, its manufacture is conducted upon the great scale. In the coal districts, and underlying
the beds of good coal, strata of clay-slate are generally fo'und, containing a certain
quantity of coallv material, and through which abundance of hisulphuret of iron is
disseminated in the instable rhombic fbrm (see p. 332 and:358). -When this altm
slate is exposed to the air, the sulphuret of iron rapidly absorbs oxygen and forms
copperas, with an excess of sulphuric acid, which reacts on the clays, with the
alumina of which it combines. This effect is accelerated by the application of heat,
which is applied by building tp the mineral into pyramidal heaps, with some fuel
underneath, and channels through the interior, by which a draught may be established; the fuel below being set on fire, the slate contains coal enough to maintain its
own combustion, and the mass changes in colour as it burns, becoming brick red;
according as the process is carried through, successive quantities of mineral are added to the burning heap, until it often acquires a height of sixty or eighty feet. When
the mass thus calcined has become quite cold, it is powdered and lixiviated with
water; a large quantity of sulphate of alumina and sulphate of iron dissolve out,
and the liquor is brought by evaporation to a certain degree of strength. A solution
of some salt of potash is then added, generally the waste chloride of potassium frlon
soap-boilers, and the sulphate of iron being decomposed, formls sulphate of potash,
which unites with the sulphate of alunina, and crystallizes out as alum, -while the
iron remains as chloride in the liquor.
In some volcanic countries, as Italy, a mineral is found already containing potash
and sulphuric acid united to alumina, from which is obtained a very pure alum,
rock-alunm, which is valued very much by dyers, on account of its total freedom from
sulphate of iron, of which English alum generally contains a small trace, which injures the colours of the dyes.
Alum crystallizes in regular octohedrons, the solid angles being
often replaced by the surfaces of a cube. When heated, the water
is first expelled, and at a red heat it parts with most of its sulphuric
acid, sulphate of potash and pure alumina remaining.  The taste of
alum  is sweet and astringent; it reacts acid, and is soluble in 18'4
parts of cold, and in 0'75 parts of boiling swater.  A-remarkable pyrophorus, that of I-Iomberg, is prepared from  alum; three parts of
dried alum  and one of lampblack well mixed are -to be placed in a
stout glass bottle, and, being bedded with sand in a crucible, are to
be carefully heated to redness, until a blue flame appears at the
mouth of the bottle; when this has lasted a few minutes, the bottle
is to be stoppered with a bit of chalk, and the whole cautiously
cooled.  The bottle contains a black powder, a mixture of lampblack, alumina; and sulphuret of potassium, which last, being in a
state of exceedingly minute division, takes fire when a little of the
product is shaken out of the bottle, and emits considerable light.
Basic dllum.  Cubical.Ilum.-A1203. 2S.03+K.O.. S.03,  This




GL ASS  AXND  PORCE.ELAIN.                       437
substance, which is preferred as a mordant to ordinary alum, is prepared by adding carbonate of potash to a solution of alum, as long
as the precipitate which first forms is redissolved by agitation. It
crystallizes in cubes which have no acid reaction.
The sulphate of soda combining with sulphate of alumina, forms
the soda alum, which is not much used.  The ammonia alum will be
hereafter noticed.
Thel Phosphate of Alutmina constitutes a remarkable mineral found in Cork and
Tipperary, the wavellite.
Th'l  sitmple and double silicates of alumina constitute probably the majority of all
known minerals; such of them as possess technical or pharmaceutic value are
noticed under the heads of the uses to which they are applied. For a description of
the others, I refer to the ordinary works on mineralogy.
One substance, however, of which the constitution is very curious, may, from its
technical importance, here be noticed, the;erpis-lazzlqi, dLlt'amacrixe. It is found in
veins in igneous rocks in Siberia, but particularly in China. It is of a rich blue
colour, not crystalline, and being powdered, serves in paihting as the richest and
most permanent blue; its composition has been found to be, in 100 parts, silica, 35'8;
alumina, 34'8; soda,'232; sulphur, 3'1; carbonate of lime, -31: it is difficult to deduce a formula fiom these numbers, and the state of combination of the sulphur is
not well understood. Attempts at imitating the composition of this body have been
partially successful, and a large quantity of artificial ltramcar'ine is now made for
painters' use by the following process: freshly precipitated silicic acid and alumina
are mixed with sulphur in a solution of caustic soda, all in the proportions above
given, and the mixture dried down; the resulting mass is placed in a covered crucible and exposed to a white heat; it gives a dark and pure blue mass, to which, for
the perfect bringing out of the colour, the air must have had partial access during
its ignition. The product is reduced to impalpable powder by the same process
adopted for the native substance.
Conzstitution of Glass and Porcelain.
I deferred the description of the silicates of potash, soda, and
lime, because they stand so closely allied with the silicate of alumina, in relation to the important manufactures of glass and earthenware, that their properties could only be well understood when
studied in connexion with it.
Silicic acid combines with the alkalies in many proportions, of
which those that contain a considerable excess of base are soluble
in water.  Thus is prepared the liquor off ints, by meltingftogether
one part of powdered quartz and two of carbonate of potash; the
carbonic acid is expelled, and a glassy mass is obtained, which deliquesees in the air, and is very soluble in water. It reacts strongly
alkaline, and gives, with acids, a precipitate of silica in its soluble
form, as described p. 321.  In this preparation, soda may be substituted for potash in a proportion one third less, and a mixture of
seventy parts of carbonate of potash, fifty-four of dry carbonate of
soda, and 152 of fine quartz sand, gives a still more fusible and soluble product.  This substance, under the name of soluble glass,
has been employed to render wood incombustible, several coats of
a strong solution of it being applied under the paint.
When the quantity of silicic acid is greater, the resulting alkaline
silicate is insoluble in water, and possesses the qualities which give
to glass its peculiar value.  These are, first, to solidify, after being
melted, very gradually, and to pass through a condition of pastiness, which admits of its being blown out, cut, and fashioned in every way; and, second, to remain, when solid, quite transparent, and
destitute of any tendency to crystalline structure.  Its coinposition




438               MANUFACTURE  OF  GLASS.
should also be such as to resist completely the action of air and
water.
The materials used in the manufacture of'glass are, 1st, quartz
sand, as free as possible from  iron; 2cl, lime, used sometimes pure,
sometimes slacked; occasionally chalk is employed in place of lime;
3d, carbonate of potash (pearl ashes of commerce);. 4th, carbonate
of soda, or a salt of soda, as Glauber's salt or common salt; 5th,
old broken glass, technically termed cullet; 6th, red lead, which
must be extremely pure; and for corrective purposes, arsenious acid
sometimes, but more frequently black oxide of manganese.
These materials are by no means all employed together; the composition of various kinds of glass differing very much, as is shown in the following table of tha
best analyses of glass.
Constituents.   lassrdwhi ie   Crovn Glass.  Bottle Glalss.  Ft, -'lint Glass.
o._ 1. No.-2. No. 3. No.4.  o 5.  N.6. No. 7. No.8. No. 9.
Silicic Acid.. 717 692 6i28 69-2 604  53 5 59 2 519 4215
Potash..127 15'8 221i 8'0 3'2  5'5 9'0 13'8 11'7
Soda.                25 30..'30.. 3.
Lime...... 103 7'6 12 5 13'01207' 29...    0;5
Alumina....04 12 )    3G04  G60....6           1 8
Magnesia.... 26 0'6 0'6
Oxide of Iron..   03 0'5       1'6 3'8  5 8 04 
Oxide of Manganese  0....   1.0.
Oxide of Lead..  28 2 33-3 43:5
81' 9 9 — 100(0 990 991     8 99'01100'0
Although in some of these analyses a slight loss occurred, yet they are sufficiently
accurate for all purposes. No. 1 is the hard Bohemian glass, so valuable to the
chemist, from the high temperature it bears without softening. No. 2, also a Bohemian glass, is much more fusible, and is that in ordinary use. No. 3 is English
plate, and No. 4 German plate glass. Nos. 5 and 6 are both French. Nos. 7 and
8 are English glass for table use and chemical apparatus; and No. 9 is the glass so
celebrated for optical purposes, made by Guinaud.
It is difficult to trace any definite relation between the acid and bases in these
glasses; indeed, we cannot look upon the different silicates as being really combined
with each other; they are rather in a state of intimate mechanical mixture; hence,
if the glass be kept soft, but not liquid, for a considerable time, the silicates gradually separate; the less fusible crystallizing, and rendering the glass opaque white.
Thlis takes, place most easily with such glass as contains much silicate of lime oI
alumina. In this form, the mass is so hard as to strike fire with steel, and becomes
almost infusible. From the name of its discoverer, it is termed Reamezvr's Porcelain.
The arrangement of the furnaces for the manufacture of glass varies according to
the materials and the kind of product. The materials, reduced to the state of very
fine powder, are intimately mixed, and fused -in crucibles of very refractory clay.
The silica decomposes the carbonates of lime and potash or soda, and, expelling the
carbonic acid, combines with the alkali and earth. If sulphate of soda had been
used, a certain quantity of carbon is added, by which the sulphuric acid is decomposed, sulphurous and carbonic acids being evolved (p. 292), otherwise the silica
could not completely expel the sulphuric acid. From the presence of minute quantities of protoxide of iron in the materials, the glass has. at first, a pale-greenish tint,
which is counteracted by the addition of a little nitre or arsenious acid, these agents
giving oxygen to the iron, which does not colour when peroxidized; with the latter
body the metallic arsenic is evolved in vapour, the bad effects of which should prevent its employment. More generally peroxide of manganese is used, which, acting
on protoxide of iron, produces peroxide of iron and protoxide of manganese, neitheI
of which bodies gives any sensible tint to glass. If there be too much maniganese
employed, the glass acquires a violet tint. There is reason to suspect that soda
glass is greenish even when absolutely free from iron.
The general arrangement of a glass furnace may be illustrated by reference to the
figures, which represent the essential parts of one of the most perfect forms employ.
ed in the manufacture of the fine crown glass of Germany. In the oval furnace
A. which is covered by a dome, the crucibles are arranged in two rows, on banks,




MANUFACTURE OF GLASS.                                     439
of which one is represented in the sectional figure. These crucibles are left open
but if employed for a glass
containing lead, they should
be covered by a hood, presenting only an aperture externaC to the furnace for
the workman, as the glass
would iequire to be thus proteeted from the smoke and   9
comnbustible gases of the furname, which would reduce                         r a 
the lead to the metallic state.    _ ___- __s                                i
Bet;ween the banks is a rec-                              qai  o.h  h
tanguliar space for the fire,
resting on the gratings b b
ewhich are separated by the
partition wall F, and have -
tapertures at the sides for the.....
introduction of the fiel. By
means of the passage D, there is access beneath the grate for the purpose of clearing
it, and the draught is regulated by the opening or closing of the doors e c. The
flame of the fuel, which should be either wood or a very bituminous coal, issues
partly through the apertures in front of the crucibles o o, and partly passes by  intoe
the wings aid chimney; by means of the wings, a great quantity of the heat is
economized for preparatory operations.  Nrext the furnace are placed the firesh crucibles e e, which, being always made in the  lass-house, are there dried, baked, and
ultimately brought to a full red heat, so as to be fit for introduction into the furnace
with a charge of glass. The draught passing in the direction of the arrows over
the low partition, the flame and hot air acts on the space k, on the floor of which are
spread the materials for the next charge of glass, well mixed, and introduced by the
oapertures I       s; these hbein  brought to a dull red heat, undergo a' commencement ot
vitrefaction, and are thus fi'itted, or prepared for the perfect combination by fusion
in the crucibles.  This operation of fritting was formerly performed in a separate
reverberatory furnace.  The draught escapes partly from the small chimney:; but
a portion of the hot air, having passed over the. partition m, is conducted into the
chamber s,  which is filled with wood supported on the grating; the hot air, in passing off, carries away the moisture of the wood, which is thus brought to a state of
perfect desiccation, so as to give the greatest possible effect in the furnace.
For the perfect combination of the materials, and obtaining a mass free from
streaks and air-bubbles, it is essential that the glass should be brought into a state
of perfect liquidity, so as to allow the gases to pass off freely, and then be suffered
to cool until it acquires the pasty consistence which fits it for being worked into the
necessary forms.  In thus cooling down, however, those glasses which contain
oxide of lead frequently separate into two or more layers of glass of different densities, which, when stirred up by the tools of the workman, give by their imperfect
mixture a clouded and streaked appearance to the articles made from  such glass.
This impefection is peculiarly fatal to glass for optical purposes, as each layer may
have a different refractive power, and thus give distorted images.
The great use of glass in the arts and in ordinary life depends upon its plasticity
at a red heat, which renders it capable of being moulded into every form; its insol



440                 COM POSITION  OF  CLAY.
ubility in water; its resisting the action of acids and the generality of chlemical re.
agents under all ordinary circumstances; its transparency and lustre, and the relations to heat, to light, and to electricity, which have been already fully noticed. From
the low conducting power of glass ior heat, thick portions of it are liable to break
when suddenly warmed, the part to -which the heat is directly applied expanding, and
thereby separating from that which remains cold. When a lump of glass is suddenly cooled, as by being laid, while soft, on a plate of cold iron, or being dropped into
water, the internal portions being prevented from contracting, remain in a state of instable arrangement, on which depends its double refracting and polarizing properties
(p. 230). WV hen the molecules o' such a piece of chilled glass are made to vibrate, by
being scratched, or a little fiagment being broken off; they change totally their disposition, and, flying asunder,.the mass crumbles into powder with an explosion.
Pl'ince Rnper ci's ca.'oies, with which this property of glass may be exemplified, are prepared by taking up on an iron rod a little melted glass, and allowing the drops of it
to fall into a vessel of cold water; when one is held in the hand, and the longb projecting tail broken off, a smart blow is felt with a dull noise, and the drop is found
to be reduced to fine powder. As this excessive frangibility would render glass unfit for most household and chemical purposes, it is necessary to lessen it as much as
possible, which is done by allowing it to cool very slowly. For this purpose, the
vessels, when formed, are placed in the aq?2calivlg flurace, or leer, which is a long gal.
lery containing a number of iron trays moveable along it by means of' an endless
chain; the hot glass articles are placed in the trays at one end, where a strong fire
is made, the flame of which sweeps to a certain distance into the gallery. According as new trays come up, those already full are drawn down into the cooler part
of the gallery by the chain, and finally issue at the other end quite cold. The passage down occupying from twenty-four to forty-eight hours, the particles of the glass,
in cooling, have time to assume their most stable arrangement, and may then be exposed, if not very thick, to changes of temperature, provided they be not very
sudden.
The specific gravity of glass varies with its composition from  2'4
to 3'69 the latter being that of flint glass, cont'airiing 40 per cent. of
oxide of lead.  The lighter glasses are generally those which are
hardest, and resist the action of water and of reagents best.  The
oxide of lead in flint glass is acted on by a variety of chemical substances, which unfits it for many laboratory uses.  Where alkali
predominates, the glass is rapidly acted on by the air, attracting
moisture; and thus frequently embarrassing electrical experiments.
Bottle glass which contains much alumina it so rapidly corroded
by the cream  of tartar in wine, as sometimes to become opaque,
and spoil the wine in the course of a few. days.
I have had frequent occasion to notice the various coloured glasses produced by
the addition of metallic oxides (see p. 37); on this principle is founded the art of
painting on, or staining glass, and also the manufacture of artificial gems. These
arts I shall have to notice farther on, and any detail of their methods would be foreign
to a work like the present.
The manufacture of porcelain and earthenware depends on two
principles, first, that of the plasticity and fusibility of clay, and, secondly, the fusibility of a glass by which the substance of the porous
clay may be imbibed, and thus rendered water-tight.  Clay, when
perfectly pure, is a neutral silicate of alumina, AlO3+3Si.0s; but
as the great deposites of clay used for the purposes of the arts are
produced by the weathering (decomposition) of a variety of rocks,
a number of foreign ingredients are intermixed in small quantity,
and produce varieties which influence very much the proportions
used in' the manufacture. The purest porcelain clay is formed by
the decomposition of the feldspar contained in granitic and syenitic
rocks.  The feldspar has the formula K.O.'. Si.03-+(Al.203+3Si.03)
by the action of water, the silicate of potash is dissolved out as soluble glass (p. 437), and the silicate of alumina remains as a fine




MA NUFACTURE  OF  EARTHEN WARE.                         441
powder, perfectly white, impalpable, forming with water a paste
capable of being moulded into any form, and, when heated, abandoning the water and contracting in volume, but retaining the form
which had been given to it.  The pure porcelain clay is seldom
found, and hence is used only for the finest objects; other clays of
greater or less purity are therefore used, either alone, or mixed with
porcelain clay, for such objects as stone-china and delft; and clays
in which a quantity of alumina is replaced by iron, and which, consequently, when burned, assume a red or yellow colour, are employed for common earthenware.  In the clays which contain very
little iron, and hence burn white, there are present, almost universally, certain quantities of alkali, remaining from  the decomposed
feldspar; this is generally potash, but may be soda when the clay
is formed from albite (Na.O.. Si.O -- 3AI203+-3Si.03); and when the
source of the clay is not a pure granitic rock, the associated minerals generally yield a certain quantity of lime which mixes witl it.
Hence the composition of the following clays, from  various countries, used in the manufacture of porcelain, can easily be accounted for:
Clay froml   Mjrl.  ne-.ilo ogs.
Silica.      1'71142 43'6 46'8
Alumina... 26'07 37"7 37'3
Lime..    013.
Potash...  045...     2 5
Water      ~... 120  13-0
Oxide of Iron..  193  1-5
If clay alone were used in the fabrication of earthenware, although, from  its plasticity, it would assume perfectly the required
form, yet, from its'infusibility, it would, when baked, have so little
coherence, and, from  its great contraction, be so liable to crack,
that in practice it could not be beneficially employed. The paste
of which the china and delft articles are made, consists, therefore,
of clay, to which is added silica, lime, and potash-in other words,
the constituents of crown glass —which, being fusible at a hightemperature, cement together the particles of clay, and enable the different portions of the vessel to hold together during the bakings.
Thus, to form the body of ironstone chinaware, forty parts of Devonshire clay are mixed. with from  forty to sixty of feldspar, and
generally about five parts of flint glass and ten of quartz.
It would not bewithin the object of the present work to detail the mechanical process of fashioning articles of earthenware. WVhen formed, they are first dried in the
air, and then heated moderately, to expel as much water as will fit them for the reception of the glaze. This consists in covering them perfectly with a sheet of easilyfusible glass, -which, by entering into all their pores, and varnishing their surface,
renders the vessels impervious to water; the glassy constituents of the paste having,
in quantity and fusibility, only sufficient power to cement the particles of the clay
together, without depriving the mass of its porosity. The composition of the glaze
may vary much in different establishments; an ordinary one, for ironstone china,
consists of feldspar 36, quartz 20, white lead 40, flint glass S. These materials are
fi itted together, and then, being reduced to impalpable powder, are diffused through
v ater, into which the vessel to be glazed is dippel., and is then taken out again. The
clayey substance of the vessel rapidly imbibes the waiter, and the fine powder of the
glaze remains uniformly spread upon the surface. The artitcles so prepared are arranged in capsules of a very refractory ware, and placed in the kiln or furnace to be
baked. The construction of the porcelain kiln is represented in the figure. It is a
K I iK




-442 BAKING  AND  GLAZING  OF  EARTHENWVARE.
vaulted building, generally of three stories, provided with five fireplaces, from which
the flames pass into the
ElFH~~ |lflkiln by the passages b, mn,
a,', nmarked with the ar\4I,7TI          " I   rows; from the third story
the chimney issues. The
highest floor is reserved
for drying the capsules in
baked are arranged; on the
Ii  illlaki   I floor of the second, the ar-,'y,,,,,, —r seetereticles are dried to the de-'/'.'../vl —r-t   gree which fits them for the
reception of the g laze; and
__o_,llolfi'ul,. e, byi various n ~_, in the lowest chamabter, by
the full action of the fire,
the hinal baking is performof,.s-m,-'' si,'z,,i-i-"    ed. The operation cornmmen ces, first, with a moderHa~  I                ate fire, the fuel being introductd into the cavity i,
and supplied with air by
immediately  absorbs telqdm so the apertures e as; the heat
being allowed to rise grad\X~~~                    re\  \ ~~V   \~ ally for six or eight hours,
\  the space becomes full of
ignited fuel, and a strong
iraught is established.  The apertures are then closed, fuel (and for this, as for
glass making, wood answers best) is heaped on the rest b, and the air admitted to
the kiln only after having passed through l. The temperature is thus kept uniformly intense for seventeen or eighteen hours, and then, the kiln being allowed to cool
slowly for three or four days, the articles are extracted in their finished state.
t'ahe glaze on earthenware being a transparent glass, it may be
coloured by various metallic oxides, and thus the patterns produced
which give to the finer kinds of ware so much popularity.  The
coloured glass, being reduced to fine powder, is mixed up with oil
of spike, and either laid on with a brush, as in ordinary painting,
or printed, in a very ingenious manner, by having the pattern engraved on copper, and printing it with the glaze made with oil into'
a very thin ink on damp tissue paper.  The paper with the figure
thus formed is laid evenly on the vessel, which, from its porosity,
immediately absorbs the liquid materials of the ink, and leaves the
powder of the glaze on the surface in all the fine tracings  of the design.  The paper is then cautiously rubbed' off by the finger in a
vessel of cold water, and the uniform glazing applied over all, as
before described. The blue patterns are produced by cobalt; the
black by a mixture of oxides of iron and manganese; the crimson
by gold; and gold and platina are applied also in their metallic
state, by dissolving their chlorides in oil of turpentine, and applying this varnish with a pencil, then burning, and burnishing the metallic surface.
A coarse kind of glazinag, given to the common articles of earthenware, is produced by throwing into the kiln, when intensely hot,
a few  handfuls of common salt; by means of the watery vapour
produced by the combustion of the fuel, the silicic acid on the surface of the earthenwvare decomposes the common salt, which is converted into vapour by the heat; Si.0, with Na.CI. and H.O., producing Na.O.. Si.O3, which forms a transparent   glassy varnish on their
surface, while H.CI. passes off with the excess of watery vapour,
forming copious white fumes.




SALTS OF MIfANGANE SE.                      443
The general characters of the salts of glucimLm, thorium, yttriumt, zircouium, la-m
thanulm, and cerium? have been noticed under the heads of' these respective metals
(p. 351, el seq.), and do not require farther detail.
Salts of iManganese.
Manganese may give origin to four classes of salts, in two of
which it constitutes the base, and in the others forms an element
of the acid; these last, the maniganates and per mranagaates, have been
noticed in p. 356, and. it remains only to describe the former.
Protochloride of JlIanganese. —Mln.Cl.+4 Aq. Eq. 788'5+450 or
63 19 + 36. This salt may be obtained by digesting the commercial
black oxide in muriatic acid until all the excess of chlorine has
been expelled, then evaporating to dryness, and fusing the mass, at
a bright red heat, in a crucible.  The chloride of iron, which is formed by the impurities of the ore, is decomposed by the last portions
of water, and muriatic acid being given off, oxide of iron remains.
Hence, on digesting the melted mass in water, protoebhloride of
manganese dissolves, and all the iron remains insoluble.  The solution, which is of a pale pinkish tint, is to be evaporated, and the salt
crystallized.  The crystals are rhombic tables, rose coloured; by
heat they lose their water of crystallization, but are not otherwise
altered. It is known to be free from iron when its solution gives,
with yellow prussiate of potash, a pure white precipitate.
Perchloride of.lManganese, Mn.C]1, appears to be formed when
stronrg muriatic acid is digested on peroxide of manganese without
heat.  A gentle heat resolves it into protochloride and free chlorine.
Protosulphate of Jianganese.-Mn.O.. S.03 +7 Aq.  This salt may
be obtained pure from the commercial oxide by mixing this into a
thick cream  with oil of vitriol, and heating it in a shallow dish
until it becomes quite dry, oxygen being given off.  The dry mass
which contains the mixed sulphates of iron and manganese is to be
then placed in a crucible, and heated to bright redness; the sulphate
of iron is decomposed, its sulphuric acid being expelled by the heat;
but the sulphate of manganese is not altered, and on digesting the
resulting mass in water, dissolves, and is obtained crystallized by
evaporation and cooling.  This salt crystallizes in oblique rhombic
prisms with 7 Aq.,but is also found with 5 Aq. and with 4 Aq., its
form changing in each case. In all, one equivalent of water is constitutional, and may be replaced by an alkaline sulphate, with which
the sulphate of manganese forms double salts, like those of sulphate.
of magnesia.
Sesquisulp/,ate of Manganese, Mn,O+ 3S..0  may be obtained by
dissolving the sesquioxide in sulphuric acid. The solution is of a
rich crimson colour  when heated, it becomes colourless, giving
off oxygen, and it is instantly bleached by sulphurous acid or any
dceoxidizingo agent.  Its most important property is that of forming
with the sulphate of potash or of ammonia double salts, crystallizing
in octohedrons, which are manganese alums, similar in constitution
to the ordinary alum, but with A1203 replaced by MnO,.
No other salt of manganese requires special notice.




444                   SALTS OF IRON.
Salts of Iron.
There are two series of iron salts, corresponding to the two oxides, proto-salts and sesq*i-salts.
Protophloride of Iron.-Fe.Cl.- 41-H.O.  This salt is formed when
metallic iron is dissolved in muriatic acid, hydrogen being evolved;
the solution, which is of a pale bluish-green colour,, yields, on evaporation, rhombic crystals of the hydrated- chloride, which are slightly
deliquescent.  This solution absorbs oxygen friom the air with great
avidity, and becomes dark-green coloured.  When these crystals
are heated they lose water, and, if the air have not access, a white
mass of dry protochloride of iron is obtained, but otherwise perchloride is formed and the whole decomposed. The anhydrous
protochloride is very elegantly prepared by passing a stream of dry
chloride of hydrogen over fine iron wire, coiled up in a tube of hard
Bohemian glass, and heated to bright redness: hydrogen gas is
evolved, and protochloride of iron formed, which sublimes into the
cold part of the tube as brilliant white spangles. By the action of
the air it is rapidly decomposed.
Sesquichloride of Iron. —Fe2Cl3.  This salt is formed when iron is
dissolved in aqua regia; a deep brown solution is obtained, which,
when evaporated to the consistence of a sirup, gives large red crystals of hydrated chloride, which are very deliquescent. On the application of heat, this salt is totally decomposed; muriatic acid is
given off, and the red oxide of iron remains behind, with some unaltered chloride, as a basic salt.  To obtain the anhydrous sesquichloride, a stream of dry chlorine gas is to be passed over iron wire
heated to redness in a tube of Bohemian glass. The iron burns in
the chlorine, and the salt sublimes into the cool portion of the tube,
where it forms a dark olive crystalline mass, which rapidly attracts
moisture from the air. This salt is very soluble in alcohol.
The sesquichloride of iron, when dissolved along with sal ammo
niac, may form a true double salt, containing an equivalent of each
salt; but the crystals which are generally thus obtained, although
deeply-coloured red, contain but two or three per cent. of the chlo.
ride of iron.
Protoiodide of Iron, Fe.I., is formed by digesting iodine in wa
ter on an excess of iron filings., Considerable heat is evolved, and
a colourless solution is obtained, which, when evaporated, yields a
crystalline mass containing water of crystallization, and which is
decomposed by a farther action of the heat, iodine being evolved.
It absorbs oxygen very rapidly: A solution of protoiodide of iron
dissolves iodine abundantly, becoming brown, and possibly containing the sesqui-iodide, Fe2J3; but it is more likely that the iodine is
not combined, as it is sensible to the test of starch.
The bromides of Iron resemble perfectly the iodides.
Protosul2phate of Iron.  Green Copperas.-Fe.O.. S.O4-  7 Aq. The
manufacture of this salt is conducted on the large scale for the purposes of the arts, by exposing to the action of air and moisture the
nodules of bisulphuret of iron, which are found abundantly in the
strata of alum-slate-clay (p. 436). Oxygen is rapidly absorbed both
by the iron and the sulphur, sulphuric acid and oxide of iron being




SAL'TS OF IRON.                       445
formed, and the liquor which, holding these in solution, drains from
the beds of decomposing pyrites, is run into tanks, where it is put
in contact with pieces of old iron, which serve to neutralize the excess of acid produced from the pyrites, being a bisulphuret, and
also, by means of the hydrogen evolved, to retain all the iron in the
state of protoxide; after proper evaporation, the salt is obtained
crystallized from these solutions. On the small scale, it may be
prepared by dissolving iron wire in dilute sulphuric acid, as in the
process for preparing hydrogen gas (page 247). The protosulphate
of iron generally crystallizes with seven atoms of water, of which
one is constitutional, and may be replaced by an alkaline sulphate,
forming double salts. The form  of its crystal is a short oblique
rhombic prism, i,. u, a, with numerous secondary faces, as A, c, in
the fig. Its taste is styptic and metallic; it dissolves 
in 4164 parts of water at 50', and in 0'30 parts at 212'  w
Like the other protosalts of iron, it is but very sparingly soluble in alcohol.  When heated, it abandons
first its water, and at full red [heat its sulphuric acid,
of which a portion is decomposed into sulphurous acid and oxygen,
by which the iron becomes peroxidized.  The peroxide of iron thus
formed is used in the arts, under the names of rouge and colcothar,
as a polishing material.  On these properties is founded the manufacture of fuming oil of vitriol, described in.page 247. The protosulphate of iron absorbs oxygen rapidly even when dry, and becomes
covered with a reddish crust of basic persulphate, whence its commercial name. In solution, the absorption of oxygen proceeds
quickly, until two thirds of the iron are peroxidized and a reddish
solution obtained, from which alkalies throw down the black magnetic oxide (see page 363). This solution does not crystallize.
Sesquisulphate of Iron.' Fe2O3+3S.O. Eq. 2481'9 or 198'9. This
salt is found native in large quantities in Chili, combined with 9 Aq.
It may be prepared artificially by pouring oil of vitriol on red oxide
of iron, stirring the mass well, and applying a moderate heat to expel the excess of acid. The salt may then be dissolved in water,
forming a red solution, and giving, when evaporated, a deliquescent
mass scarcely crystallized. In this way it retains an excess of acid,
which may be driven off by a heat just below redness. The persulphate then appears as a white powder, which dissolves but very
slowly in water. By a strong heat this salt is totally decomposed.
The protosulphate may be converted into persulphate by adding to
a boiling solution nitric acid in small quantities, as long as any nitric oxide gas is given ofT.  There are several basic persulphates
of iron, of which the most important is the rust-coloured powder,
which precipitates from a solution of protosulphate of iron when
oxidized by exposure to the air; its formula is 2Fe2s03q-.03+3 Aq.
The persulphate of iron combines with the alkaline sulphates to
form a class of alums, which contain Fe2O3 in place of A1203. These
iron alums are generally pale red in colour, but have the form, solubility, and nearly the taste of common alum.
Protonitrate of iron may be formed by dissolving sulphuret of iron
in cold dilute nitric acid; it crystallizes in pale-green rhombs,
xwhich, when heated, evolve nitric oxide gas, and form a basic ni



446      SALTS  OF  IRON; NICKELx AND  COBALT.
trate of the peroxide. 1Metallic iron dissolves in dilute nitric acid
without the evolution of any gas, water and nitric acid being simultaneously decomposed, and oxide of iron and ammonia produced.
Thus N.o0  with 3H.O. and 6Fe., give 6Fe.0. and N.H,3.
Pernitrate of Iron is produced xVhen iron is dissolved in hot nitric
acid; the solution is reddish brown, and gives, by drying, a deliquescent mass easily decomposed by heat.  When a solution of
this salt is decomposed by carbonate of potash added in excess, the
oxide of iron, which first precipitates, is redissolved, and a deep red
liquor obtained, which is sometimes used in medicine under the
name of Stal/l's alkaline tincture ojOIron.
Protophosphate of Iron, Tribasic-H.O.. 2Fe.O.+P.O, —may  be
formed by decomposing a solution of protosulphate of iron with tribasic phosphate of soda.  It is a white powder, which rapidly becomes blue by exposure to the air, a portion of the iron becomrfing
peroxidized.  This blue phosphate of iron is a double salt, which
exists in nature,  forming the bogo ifrn ore, and may be produced artificially by adding solution of phosphate of soda to the solution of
mixed sulpllate of iron, from which alkalies precipitate the black
oxide (p. 363).  The precipitate which forms is of a rich blue colour, and is not 6hanged  by exposure to the air.  Its formula is (H.
0.. 2Fe.O.+P.O,)+(2Fe03a. P.05).  It is used in medicine.
Sesquiph/osphate of Iron, 2FeO3+-P.05, is obtained by decomposing a solution of sesquisulphate of iron by phosphate of soda. It
is a white powder, insoluble in water.  It is used in medicine.
The salts of the protoxide of iron are remarkable for absorbing
nitric oxide in considerable quantity, and forming therewvith a deep
olive-coloured liquor, which rapidly attracts oxygen from the air.
The quantity of gas absorbed is one atom  for two atoms of salt,
and the nitric oxide may be considered as replacing the third atom
of oxygen, which forms the sesquioxide.  Thus the protochloride
gives Fe2 + Cl1. N.O,, and the protosnlphate (Fe2+- O.  N.0,) + 28.O,,
analogous to Fe2+-C1.3 and (Fe,0;,,)q-2S.03.  The utility of this
olive liquor as a test for nitric acid and in eudiometry, has been
noticed in p. 264 and 281.
Salts of.~'ickel and Cobalt.
C/doride of Nic1kel, Ni.CI., may be obtained by dissolving oxide of nickel in dilute
m uriatic acid, or by acting on the metal with the hot concentrated acid. It crystallizes in emerald green rhomhbs. When heated, it loses its water of crystallization,
and gives a yellow powder, which by a red heat sublimes in crystals, resembling
Mlosaic gold.
Sulphlate of Nidckel.-Ni.O.. S.03. This salt is obtained by dissolving the oxide
in dilute sulphuiic acid, or by acting on the metal with a mixture of nitric and sulphuric acids diluted with water; the nitric acid then supplies oxygen. This solu.
tion gives fine emerald green crystals, which vary in formn according to the quantity of water they contain: Wlien the.' form below 60), they are long rhombic prisms,
containing 7 Aq., and isomorphous with the sulphates of zinc and magnesia; Iut
when fortmle at any temperature above (;60, the quantity of water is six atoms, and
the form is an octohedron with a square base. Ii a prismatic crystal be exposed to
a modterate heat or to sunshine, it gives off an atom of water, and becomes oqaque
by breaking up into a numLer of very minute crystals of the octohedral form. In
sulphate ot' nickel one atom of water being constitutional, may be replaced by the
alkaline sulphates, and doubkle salts lbrmed, of which some are very beautiful.
C/hloride of Cobalt, Co.Cl., is formed by dissolving oxide of cobalt, or the ziffre of commerce, in muriatic acid.  The solution is




SALTS OF  COBALT  AND  ZINC.                           447
pinkish, and gives, on evaporation, rose-red crystals of hydrated
chloride; if the evaporation be pushed very far, the liquor becomes
blue, and dark blue crystals of anhydrous chloride are deposited.
If the solution contains nickel, which is always the case when prepared from  zaffre, the colour becomes green, and it is thus that
sympathetic inks of cobalt are produced, and summer and winter
scenes in landscapes alternated; the surface of a drawing washed
with a very dilute solution  of chloride of cobalt being white until
dried before the fire, but then becoming grass green.
Sidopatae of CobdClt, Co.O.+S.03, is obtained by treating zaffre with sulphuric acid.
In its general characters it resembles the chloride; wuhen heated strongly, it gives
off sulphuric acid, and oxide of cobalt remains; it contains six atoms of water of
crystallization, and gives a double salt with sulphate of potash.
Pfios.plate of Coballt, 1.O.. 2C'o.O.A-P.O, is precipitated in dark violet flocks when
solution of sulphate of cobalt and phosphlate of soda are mixed together. This substance is the basis of a very beautiful pigment,'Viieinrz'ss BhIo<, which is prepared by
mixing intimately one part of phosphate of cobalt with two or three of alumina,
and exposing the mixture to an intense white heat in a wind furnace. The blue
tint thus given to alumina serves as a test fobr that earth, particularly to distinguish
it from magnesia by the blowpipe. (See p. 349 and 351).
Silicate of Cobalt constitutes the blue smalts employed to tinge
paper and to colour glass; the finest kind is known in coimmnercle
as azure.' Its manufacture is conducted on the great scale in Saxony and Sweden, and is the process in wrhich most of the arsenic
of commerce is obtained, that being expelled in the roasting of the
cobalt ores (p. 306, 376).  From  the zaffre a sulphate of cobalt is
prepared, and on the other hand a silicate of potash, by melting together fine sand and carbonate of potash; these solutions being
mixed, silicate of cobalt is precipitated, while sulphate of potash
remains dissolved.  This precipitate is the best material for colour
ing porcelain and glass; but the ordinary smalts are formed by melting impure carbonate of cobalt with potash and quartz into a blue
glass, which is then reduced to impalpable powder, and sorted according to the quality, for commrnerce.
Salts of Zinc anad Cadmium.
Chloride of Zic —Zn..C1.; Eq. 845'9 or 671'78-may be prepared by burning meta,lie zinc in chlorine, or by dissolving the metal in muriatic acid. The solution is
colourless; when evaporated, it yields rhombic crystals, which contain water, and
deliquesce with extreme rapidity. The dry salt is white, and melts a little above
212~, so that a solution, when evaporated, never becomes solid. It is hence sometimes applied as a bath in place of oil or fusible metal, in taking the specific gravity
of vapouws (p. 14). From its fusibility and softness, it had formerly the name of
Bultter of Ziibc. From its affinity for water, it acts powerfully as a caustic on the living tissues, and is employed in medicine as such.
Chloride of zinc combines with oxide of zinc in many proportions, forming oxychllorides, of which there are three worthy of notice: the first, which is long known,
is formed by decomposing chloride of zinc by a small quantity of ammonia; its formula is Zn.Cl.+3Zn.O.+4 Aq. The second result- from the action of water on
the ammoniacal chloride of zinc; its formula is Zn.CI.+6Zn.O.+10 Aq., and is that
whose analogies to the liquid muriatic acid have been pointed out in p. 309. The
third is formed by acting on chloride of zinc with an excess of potash; its formula
is Zn.Cl.+9Zn.O.~-14 Aq.
The bromide and iodid/e of Zinc resemble completely the chloride in general characters: a solution of iodide of zinc is capable of dissolving a large quantity of iodine.
Sulphate of Zinc, Zn.O.. S.03+7 Aq., may be produced  by dis
solving the im-etal in dilute sulphuric acid.  For the purposes of the
arts, it is made upon the great scale by roasting, in a current of hot
air in a reverberatory furnace, the native sulphuret of zinc, blendle




448                     SALTS O F  TIN.
The metal and sulphur both combining with oxygen, a neutral sulphate of the oxide' is formed, which being then dissolved out by
water, the solution is evaporated to a peilicle, and allowed to crystallize.  Sometimes the blende, in place of being roasted, is exposed
on sloping beds to the action of the air and moisture, when it gradually attracts oxygen, and is treated as has.been described uinder
the head of' sulphate of iron.  The crystals which first form  are
heated until they undergo wvatery fusion, and are then poured into
conical moulds, where they solidify, and the salt is thus sent into
/-_-. —.  commerce in masses lilke sugar-loaves: its comnmercial name is white vitriol.  The crystals of sulp hate of zinc are eight rhombic prisms, as in the
figure, containing 43-9 per cent. of water, and are
soluble in two and a half times their weight of' cold
water.  It is permanent in the air.  It corimbines
w ith the alkaline sulphates, whic'h replace its constitutional water, forming double salts, and with oxide of zinc to form  basic salts, of which several are known, and
which agree in constitution with the oxychlorides of zinc.  Their
composition has been already noticed in p. 368.
Nitr'ate of Zinc, Zn.O... NOs5, is obtained by dissolving' the metal in dilute nitric
acid; it crystallizes in flat four-sided prisms. It is deliquescent, and soluble in alcohol.
No other salt of zinc is of importance.
Chloride of C.rl'olidsn, Cd.Cl., crystallizes in large four-sided prisms; it is not deliquescent. The other salts of cadmliurm resemble completely the corresponding
salts of zinc, and do not require notice.
Salts of Tin.
Protochloride of Tin.-Sn.C1. + 3 Aq.  Eq. 1177'9 + 337.5 or 94-39
+ —27.  This salt is obtained anhydrous by heating tin in a current
of muriatic acid gas, hydrogen being evolved; or'by distilling a
mixture of equal parts of tin and corrosive sublimate in a glass retort, the metallic mercury first passes over, and, finally, the protochloride of tin sublimes at a strong red heat. It forms a gray glassy
mass.  In combination with water, it may be obtained by dissolving
tin in strong muriatic acid until it is saturated, and on evaporation
the salt crystallizes in long prisms, which contain three atoms of
water.  When these crystals are heated, they first lose water, but
afterward muriatic acid passes off, and a basic salt remains. This
crystallized protochloride, under the name of salt of tin, is used extensively in dyeing as a mordant; in its preparation on a large
scale, copper vessels may be employed, because, as long as any
metallic tin is present, the copper is electrically protected by it,
and is not acted on by the acid. This salt is very soluble in water,
but is decomposed by a large quantity, a basic salt, Sn.CliSn.O.,
being thrown down; hence, in order to have a dilute solution clear,
it requires the addition of a few drops of muriatic acid. Protochloride of tin is remarkable for its affinity for oxygen and for chlorine;
it reduces the salts of silver, quicksilver, and gold to the metallic
state, and the salts of copper, iron, and manganese to the lowest
state of oxidation.  It acts similarly on many organic substances,
as indigo, litmine, orceine; forming colourless compounds, which
have some important applications in the art of dyeing.




SALTS  OF  TIN, CHIROMIUM, AND  VANADIU M.  449
The protochloride of tin combines with chloride of potassium and
with sal ammoniac to form  double salts, which were analyzed by
Apj ohln.
Perchloride of Tin, Sn.C12, is prepared anhydrous by distilling a
mixture of four parts of corrosive sublimate and one of metallic
tin; at a very moderate heat, a colourless liquid distils over, which
forms dense white fumes where it comes into contact with the air:
this is the bichloride of tin, the fuming liquor of Libavius.  Metallic
mercury remains in the retort.  This singular compound boils:at
924,8  Fah.; the specific gravity of its vapour is 9'12.  When mixed
with one third of its weight of water, it solidifies into a crystalline
mass, and it is hence that it forms such dense fumes by exposure
to damp air.  It may be prepared in this crystallized form  by dissolving tin in  nitromuriatic acid and evaporating the solution, or
by passing chlorine into a solution of protochloride as long as it is
absorbed.  If the crystals be heated, they are decomposed, muriatic acid being given off, and peroxide of tin rernaining.
Porto-ioodidce oqf' i,, Sn.I., mnay be forrmed by -teating together tin and iodine, or'by
mixing solutions of iodide of potassium with a slight excess of protochloride of tin.
It is a brownish red mass, soluble in water, and crystallizing from the solution in
lona prisms of a bright orange colour. It is decomposed by a large quantity of water. It combines with the iodide of potassium to form a soluble double iodide. The
biniodide of tin crystallizes in yellow needles, which are decomposed by much water.
The bm'on7iies of Tohm are not important.
Protosdl~d/mate of T7in, Sn.O.. S.Os, is formed when tin is dissolved in strong sulphuric acid. A saline mass is obtained, which dissolves in water, giving a brown
solution, from which the salt crystallizes in small needles. BancrofJ's mqt-odsia.t, for
dyers, is prepared by digesting two parts of tin with three of strong muriatic acid for
an hour, and then adding one alnd a half parts of oil of vitriol very cautiously. The
mass becomes hot, and the. tin is rapidly dissolved. The heat is to be kept up on the
sand-bath as long as hydrogen is evolved. The solution, on cooling, forims a crystalline mass, which is to be dissolved in water, so that eight parts of the solution
shall contain one of tin.
The sulphuric and nitric acids may be neutralized by freshly-precipitated peroxide
of tin; but these salts possess very little stability, and are of no technical or scientific
interest. The peroxide of tin itself acts as an acid, and its relations to the alkalies
have been described in p. 371.
The sulphurets of tin act as sulphur acids, combining with the sulphurets of the
alkaline metals. The bisi'lphrlret, forms with sulphuret of sodium  a crystallizable
salt, 2Na.S.+Sn.S2+ —12 Aq., s7liphostannate of Sodium.
Salts of Chromium  and Vanadium.
There are two kinds of salts of chrome, one in which the oxide of chrome is the
base, and the other in which the chromic acid is combined with bases.
A. Salts of Oxide of Chrome.
Chloride of Chr'mee.-Cr2Cl3. Eq. 2031'6 or 162-8. WVhen oxide of chrome is mixed with lampblack, and treated by a current of dry chlorine at a red heat, as described for the preparation of the chlorides of silicon and aluminum, the chloride is
obtained sublimed in the cold part:of the tube in peach-blossom-coloured scales of
exceeding beauty. It may also be obtained by dissolving oxide of chrome in muriatic acid, and evaporating the solution; it remains as a green mass, in which it is
combined with 3H.0. When heated to 450~, it froths up very much, gives off that
water, and forms a rose-coloured mass not so beautiful as that obtained by the process first described.
C/ldoroc7lomic Acid. —Cr.ClS+2Cr.03. This singular compound is obtained by
melting together in a crucible ten parts of common salt and seventeen of bichromate
of potash; the melted mass is poured out on a slab, and broken into small pieces,
with which a tubulated retort may be filled, and after a receiver and condensing apparatus have been attached, forty parts of oil of vitriol are to be poured on the mass.
The decomposition occurs so violently, that in a few minutes all the producel distils
ever, without the application of external heat. This substance is a thin bl. od-red
LL L




450                CHROMATES OF POTASH.
kiquid. appearing black by reflected light; it fumes much by exposure to the air; iti
vapour is red like nitrous acid. When its vapour is heated to redness, it is decom
posed, as described in p. 373. It is decomposed by water. Alcohol placed in con
tact with it takes fire, burning with a bright flame; phosphorus acts in the same
way. This substance may either be looked upon as a compound of perchloride of
chrome with chromic acid, Cr.Cl3+2Cr.03, or as a compound of chlorine with a
deutoxide of chrome, Cr.02CL. The analogy of the sulphuric to the chromic acid
is supposed to favour this latter view, as also the sp. gr. of its vapour, which is 5 9.
Sldphate of CL'rome, Cr203+3S.03, may be formed by dissolving oxide of' chrolne
in dilute sulphuric acid, but does not crystallize. Its only important character is,
that it combines with the sulphates of potash or of ammonia to form double salts,
the chrolte alims, which crystallize in dark purple octohedrons, and which contain
the same proportion of acid, alkali, and water as common alum, but oxide of chrome
in place of alumina. The solution of chrome alum in cold water is pulple, but
when heated it becomes green, and the elements of the salt are then found, to be no
longer united, as by evaporation they may be separated. It would appear. indeed,
that almost every salt of chrome may exist in either a green or a red condition, and
that in the former they do not crystallize. The chrome alum is obtained abundantly by setting aside for a few days the residue of the process for making aldehyd, as
described fIrther on.
The Pemfluoride of Chr'oome, Cr.F3, is formed by acting with oil of vitriol on a mixture of powdered fluor spar and bichromate of potash in a platinum retort. It is a
gas o' a rich crimson colour, which can only be collected in a platinum crucible inSverted in the quicksilver trough. Its decomposition by wSarter, and the consequent
formation of chromic acid, has been already noticed, p. 373.
B. Salts of Chromic  /cid.
Chromates of Potash. —The manufacture of the bichromate of potash, K.O.-+-2Cr.03, is carried on extensively, as it is from  that salt
that all the compounds of the metal used in chemistry or in the arts
are prepared.  It is made from  the only abundant ore of clhron-me
the chro me-iron, Fe.0.q-Cr03,, by the following process.  Two parts
of the ore, ground to a fine powder, are intiinately  mixed with one
part of saltpetre, or four parts of ore are used with two parts of
pearl ashes and one of saltpetre, and the mixture exposed for several hours on the floor of a reverberatory furnace to a violent heat.
Under the influence of the potash, the oxide of chrome absorbs the
oxygen from  the air, and forms chromic acid.  The calcined mass
is lixiviated with water, and a deep yellow liquor is produced, which
contains neutral chromate of potash, which may be obtained crystallized by evaporation; but as this salt is not well suited for the
purposes of commerce, it is generally changed into the bichromate
by adding to the liquor a quantity of sulphuric acid, which takes one
half of the potash, and the bichromate is then obtained by crystal]ization in tanks lined with lead.
Bichromnate of Potash crystallizes in large four. sided prisms and
square tables of a rich orange-red colour.  It melts easily, and in
cooling crystallizes in another form.  It is soluble in ten parts of
cold water.  It is not decomposed except by a white heat, which
expels oxygen, and leaves a mixture of oxide of chrome and neutral
chromate of potash.
The neutral Chromate of Potasfh, K.O.. Cr.O0, may be prepared by
adding to a solution of biehrornate of potash as much
more alkali as it already contained.  It is soluble in twice
i-   its weight of cold water.  Its solution is intense golden
yellow; it crystallizes in rhombic prisms, isomorphous
with those of sulphate of potash, as in the figure, of which
n n.and %, u are primary, and i, m are secondary planes.




SALTS  OF  TUNGSTEN1  MOLYBDENUM1  ETC. 451
If bichromate of potash be dissolved in hot dilute nitric acid, a
terch/romate of potash, K.O.. + 3Cr.0,, crystallizes when the solution
cools.
When bichromate of potash is dissolved in rather more than its
own weight of strong muriatic acid, with a very gentle heat, so that
no chlorine shall be evolved, and the liquor shall retain its clear
orange colour, a salt crystallizes on cooling in fine four-sided prisms,
which is very remarkable in constitution, consisting of an equivalent of chloride of potassium  united to two of chromic acid, K.C1.
-'- 2Cr.03.
None other of the chrornates of the metals that have been as yet
described possess interest.
1Vanadium is the basis of several classes of salts, which, however, from the exceeding rarity of the metal, have been but little studied. The salts containing the
vatadic ozxide are generally splendid blue; those containing the vanzadic acid as basis
are red or yellow, while those which contain vanadic acid as acid are colourless, oi
coloured according to the nature of the base with which it may be combined.
Salts of Tungsten, JMlolybdenum, Osmium, and Columbium.
Tungsten combines directly with chlorine in two proportions, forming the bichloride and perchloride, according as the metal or the gas is in excess. Both are volatile, and condense in red needles. They are decomposed by water, giving muriatie
acid and tungstic oxide, WV.O2, or tungstic acid, W.Os. A chlorotungstic acid exists,
W-.02C., analogous to the chlorochromic acid.
None of the compounds of tungsten with oxygen act as bases. The nature of the
salts of tungstic acid has been sulficiently explained already in p. 374.
- llyblid:rvlm takes fire when heated in a stream of chlorine gas, and forms the terchloride, Mo.C13, which crystallizes in the cold part of the tube in brilliant black
scales, like iodine. Its vapour is dark red. Two other chlorides of this metal, Mo.
C1. and Mo.Cl12, are known to exist.
The protoxide of molybdenum forms salts with the oxygen acids, which are purple or black coloured, and are very easily decomposed by heat. Thus the sulphate
is resolved into sulphurous acid gas and molybdic oxide. The molybdic oxide also
forms a series of salts, generally red coloured, which do not possess any special interest.  The molybdic acid forms two series of salts, in one of which it acts as base,
and in the other as an acid.
OsL.tilmm, is the basis of several salts which are as yet very little known. When
metallic osmium is heated in a strean of dry chlorine, in a long glass tube, a volatile
mixture of protochloride and perchloride of osimium  is produced. The former,
which is the less volatile, condenses near the heat in long needles of a fine green
zolour; while the latter, being carried much farther by the current of gas, is deposited as a red powder destitute of any crystalline texture. Both these salts combine
with the alkaline chlorides, forming double salts. All three oxides of osmium combine wi h the oxygen acids to form salts which do not crystallize, and have been
very little studied.
Ceolu.obiolm forms a volatile chloride. Its oxide, Ta.02, does not combine with
acids, and the columbic acid forms salts which are not of practical importance.
Salts of lrsenic.
C/iloridl of A -Soznic —As.C13; Eq. 2268'0 or 181-74-is formed when the metal burns
spontaneously in chlorine; it is a volatile liquid, which forms dense white fumes on
exposure to the air.  It may be obtained, also, by mixing intimately one part of at
senious acid and three of common salt; putting them into a retort to which a con
denser is attached, and adding four parts of oil of vitriol. By a moderate heat the
chloride of arsenic distils over as a dense liquid. By much water it is resolved intc,
arsenious and muriatic acids. The sp. gr. of its vapour is 6295.
Inli'le of Ars.eirC, As.I!, is best prepared by digesting one part of arsenic with.
five of iod line and fifty of water, until the iodine disappears; on cooling, the ioaide
separates in orange-red crystals. It is decomposed by water into hydriodic and an
senious acids. The bromide of arsenic may be similarly formed.
Ar;enic does not form any compound with chlorine, bromine, or iodine analogout
tc arsenic acid.




452. SAL'T S  OF  A ARSE N IC.
Neither compound of arsenic with oxygen is capable of acting as a base, and
hence the only classes of salts of arsenious or arsenic acids, are those in  hllich
they constitute the electro-negative element.,qrisenious./cid is dissolved in large quantities by the caustic and
carbonated alkalies, but the salts thus formed cannot be obtained
crystallized, and appear. to be very indefinite in constitution.  The
combinations of arsenious acid with the earths are white powders,
of which the only one of interest is adrsenite of Lime, H.O.. 2Ca.O.+
As.O, which precipitates when arsenious acid is mixed with limewater, or arsenite of potash with a salt of lime.  It is redissolved by
an excess of any acid.
Arsenious acid is decomposed by peroxide of iron, an arseniate
of the protoxide being produced; on. this is founded the efficacy of
the peroxide of iron as an antidote to the poisonous effects of arsenious acid (see p. 384).
The arsenite of Cobalt is found native, as a rose-red powder, and
the arsenite of N'ickel exists as a mineral of a pale-green colour; both
contain combined Awater.  The arsenites of copper and silver will be
described under the heads of these metals, and have been already
noticed in p. 381, et seq.
The constitution of the salts of arsenic acid has been already
mentioned in p. 377.  They are all tribasic, and are isomorphous
with the corresponding tribasic phosphates.  Some of them are of
technical and medicinal importance.' The neutral arseniate of potash, H.O.. 2K.O.-F-As.O, forms a deliquescent saline mass.  The
binarseniate of Potash, 2H.O.. K.0.+As.OQ, is formed by adding to
the former as much arsenic acid as it already contained, or by igniting in a crucible equal weights of arsenious acid and nitrate of
potash; red fumes are given off, and on dissolving the residual mass
in boiling water, the salt is obtained in large crystals, which are
modifications of the square octohedron.
There are three arseniates of Soda,. which resemble the three tribasic phosphates of soda. The first, (3Na.0. O.As.05) - -24 Aq., is obtained by igniting arsenic acid with an excess of carbonate of soda.
When a solution of arsenic acid is neutralized by carbonate of soda,
the salt H.0.. 2Na.0. + As.0D is obtained, which may be had either
with 24 Aq. or 14 Aq., according to the temperature at which it
crystallizes. The binarseniate of Soda, 2H.O.. Na.O.+-As.05, resembles the corresponding salt of phosphoric acid.
The arseniates of the earths are white powders, insoluble in "water, but soluble in an excess of any acid../rseniates of Iron..-.That of the protoxide, H.O...2Fe.+As.Os, is
a white powder, which, by exposure to the air, gradually becomes
green -by absorbing oxygen, thereby approaching to the constitution
of the native arseniate of iron, in which the iron is in the state of
blackl magnetic oxide. This salt corresponds to the blue phosphate
of iron, its formula being (2Fe.0.. H.O. +As.0s) + 2Fe203. As.05+
12 Aq.
The perarseniate of Iron is a white powder, which, when heated,
gives off 1i2 Aq. and becomes red; it has the singular property of
dissolving totally in water of ammonia.
Arsem;iate of Nickel is a pale green powder. Arsevniate of Cobalt is a rose-red powder, and inmar be used in place of phosphate of cobalt in preparing Thenard's blue




CHILORIDE  OF  AN'TIrMONY.                        453
(p. 4t7). It is prepared on the large scale by roasting the native arseniuret of cobalt, Co3 As.
The sulphur salts of arsenic are some of the best characterized among that class
(p. 379). There are three sultphocarsenictes of Potassium, having respectively the fornule (3K.S.+As.SL), (2K.S.+As.S5), and (K.S.+As.Ss). They are all deliquescent, and. crystallize with water. It would be very interesting to find whether the
second and third salts contain basic water, such as would keep up the tribasic character of the first. The sullhoa/rseniactes of Sodium resemble those of potassium. The
basic salt (3Na.S.+As.S-l-15 Aq.) crystallizes in large colourless rhomboidal tables. When orpiment is dissolved in solution of sulphuret of' potassium, szlaphoarsetbite of potassium is obtained, K.S.+ —As.S3, which, when evaporated, is decomposed,
and deposites a brown powder, which consists of K.As.S3, and appears to contain a
bisulphuret of' arsenic, As.S2, combined with K.S., which is decomposed when separated from the state of combination.
Salts of Antimony.
Sesquichloride of antimo7ny.-Sb.C13.  Eq. 3383.5 or 271'1.  To
obtain this salt completely pure, sulphuret of antimony in fine powder is to be mixed with its own weight of corrosive sublimate, and
distilled in a hard glass retort.  The chloride of antimony distils
over with a gentle heat as an oily liquid, which gradually solidifies
into a white crystalline mass. It is very deliquescent, and becomes
soft on exposure to the air, whence its old name of Butter of.]ntimony; it may be obtained more cheaply for surgical use, but not
quite dry, by mixing together two parts of fine common salt and
one of crocus of antimony (oxysulphuret, see p. 385), and distilling
them  in a retort with one part of strong oil of vitriol.  Chloride of
antimony distils over, and there remains behind sulphate of soda
mixed with sulphuret of antimony.  In this operation, the crocus
antimonii being 2Sb.S,+Sb.03, the former remains passive; but the
latter, acting on 3Na.C1. and 3S.03, produces Sb.Cl3 and 3Na.0.. S.
03.  As there is, however, some water supplied by the oil of vitriol, the product is not solid.  It is, however, quite strong enough
for its successful application as a caustic.
When chloride of antimony is put in contact with much water,
both are decomposed, and a white oxychloride is precipitated, called Powder of.l1garotti, from the name of its discoverer.  If the water be hot, the precipitate is distinctly crystallized. In it one fourth
of the metal is combined with chlorine, and three fourths with oxygen; it contains also water, its formula being, according to Berzelius, Sb.C13+3Sb. O+3 Aq.  The formula given by Malaguti and
Johnstone is 2Sb.Cl3+9Sb.03, and it is possible that there are two
oxychlorides, which may be produced separately or mixed, according to the circumstances of the precipitation.  This oxychloride is
employed to furnish oxide of antimony in the preparation of tartar
emetic, and of some other salts of antimony.
The terchloride of antimony combines with the chlorides of the
alkaline metals, forming double salts, consisting of an equivalent.of
each constituent.
Perchloride of Jntimony, Sb.CI,, is formed when  metallic  antimony is burned in chlorine gas.  It is a heavy liquid, which fumes
in the air, and has a very bad smell; with a small quantity of water it forms crystals (hydrate); with a large quantity of water it
gives antimonic and muriatic acids: it is formed, also, by heating
sulphuret of antimony in chlorine gas.




454     SALTS -OF  TITANIUM, TELLURIUMA   ETC.
The bromide and iodide of Antimony are prepared by the direct combination of their
elements; the operation does not require external heat; the former is colourless,
the latter orange-red. They are both easily fusible, volatile, and decomposed by
water.
The sulphurets of antimony act as sulphur acids (p. 387, 388), combining with
the sulphurets of the alkaline metals to form double salts, of which several may be
crystallized in large rhomboidal tables, perfectly colourless. The basic hyposulphoantimonite of Potassiumn which remains in solution after the precipitation of Kermes
by cooling, crystallizes on evaporation in colourless deliquescent plates.
The sesquioxide of antimony combines with oxygen acids to ibrm salts, which
possess but little interest. Metallic antimony decomposes hot oil of vitriol, evolving sulphurous acid gaS, and forming the szdLp/tat of AItimonLy, a white salt, which is
decomposed by water..,ntimonial Powder. James's Powder.-This preparation, to wlhich,
at one time, the highest medicinal virtues were attached, is prepared by mixing together equal parts of sulphuret of antimony and
hartshorn shavings, and calcining them together in an iron pot, at a
dull red heat, until the mass becomes ash-gray; this is to be then
placed in a loosely-covered crucible, and exposed to a white heat
for two hours, or until the mass becomes quite white; it is then to
be reduced to a fine powder.  In this process the sulphur, and the
carbon and hydrogen of the hartshorn, are burned away, and the antimony is converted into antirnonious acid, of which a small quantity unites with the lime that had been as carbonate in the bone;
the rest of the lime remains as phosphate, mixed with the antimonite of lime and the antimonious acid. Its composition varies very
much; it seldom  contains more than one per cent. of antimonite of
lime, which is its only soluble and active principle; and where it
has been washed, as is sometimes done, even this is removed. It
is also a mere mechanical mixture of its ingredients.
Tartar emetic will be described under the head of tartaric acid
and its salts.
Salts of Titanium, Tellurium, and Uranium.
Chloride of TitaniLum, Ti.C12, is best prepared by treating a mixture of titanic acid
and lampblack by chlorine, as for the preparation of chloride of silicon. It is a colourless liquid, very volatile, fuming in the air, resembling closely bichloride of tin;
it combines with water so violently as to produce explosion, and is decomposed by
a large quantity.
There are no oxygen salts of titanium of any interest.
Bichloride of Tellur'iuinm, Te.C12, is produced by heating tellurium in a current of
dry chlorine; a thick liquid is produced, at first dark red, but becoming yellow as it
cools, and at last solidifying into a snow-white crystalline mass. This salt is decomposed by water into tellurous and muriatic acids, and combines with the alkaline chlorides to form double salts. The protochloride is prepared by melting together equal weights of the bichloride and of tellurium, and distilling; it condenses as
a deep yellow liquid, which solidifies, but does not appear crystalline. It forms
double salts.
The tellurous acid appears to possess feeble basic properties, as it unites with the
strong acids to form compounds which are not imFportant. The relations of tellurous and telluric acids to bases have been already noticed at sufficient length (p. 389).
The chlorides of Uranium, U.CI. and U2C13, give yellowish green solutions, but
do not crystallize. With the alkaline chlorides they unite, forming crystallizable
double salts.
ProtosUldphate of Uranium~n  crystallizes in green prisms.
Sesquisulphate of Uraniuam, U203+3S.03, is not itself crystallizable, but combines
vith sulphate of potash in several proportions to form double salts of very complex
Constitution.
The Sesquinitrate of Uraninm, U203+3N.Os, crystallizes in large tabular crystals
of. a bright yellow colour. This salt is remarkable as the most definite nitrate of a
W'squioxide that is known to chemists.
All these salts are prepared by dissolving the oxides of uranium in the dilute acids.




SALTS OF  COPPER.                          455
Salts of Copper.
Copper forms two series of salts, one corresponding to the sub.
oxide, and the other to the black oxide.  The former are generally
white, and the latter blue or green.
Chloride of Copper, Cu.Cl., is produced by dissolving copper in
aqua regia, or oxide of copper in inuriatic acid. Its solution is green,
and it gives, on evaporation, the hydrated salt in long, slender green
prisms, Cu.Cl. +-2 Aq., which are slightly deliquescent, and are soluble in alcohol. When heated they give off water, and the dry chloride remains as a brown powder, which recombines with water, with
the evolution of much heat.  Strongly heated, it fuses, gives off half
its chlorine, and the subchloride remains, melted into a brown resinous-looking mass, whence its name of resina cupri. By the action
of an alkali on a solution of chloride of copper, an oxychloride may
be formed, which precipitates as a fine green powder, having the
formula Cu.Cl.+3Cu.O.-1-Aq., and which is used as a pigment by
the name of Brunswick Green.  There exist two other oxychlorides
of copper, which have the formule Cu.Cl. +-2Cu.O. + 3 Aq., and Cu.
Cl.+4,Cu.0.+6H.O., prepared by the decomposition of the ammoniacal chlorides of copper.
The Subchloride of Copper, Cu2Cl., may be prepared either by heating the chloride as above, or by digestino the clippings of thin copper in a strong solution of chloride of copper, to which some inuriatic acid had been added. The liquor gradually acquires an olive
colour, and the subchloride is deposited in the form of a white powder. In this case the Cu.Cl. combines with a second equivalent of
copper, forming Cu2Cl. It also precipitates when chloride of copper
is acted on by protochloride of tin, 2Cu.CI. and Sn.Cl. producing
CuCl. and Sn.C12. This subchloride is insoluble in water; it dissolves in mruriatic acid, which lets it fall by dilution with water.  It
absorbs oxygen rapidly from the air, and becomes green. It forms
with water of ammonia a colourless solution, which rapidly becomes
blue on exposure to the air.
Both chlorides of copper combine with the chlorides of the alka
line metals to form double salts.
The Bromide and S&tbbromide of Copler, Cu.B.Er. and CuLBr., resemble in every respect the chlorides just described.
The Iodide of Coppe, Cu.I., does not appear to exist except in combination. If solutions of iodide of potassium and chloride of copper be mixed, the subiodide is precipitated, while half the iodine is set free, 2Cu.Cl. and 2K.I. producing 2K.CI. and
Cu2I., with free I. But if an excess of iodide of potassium be added, these elements
recombine, and a double salt, Cu.I.+-K.I., may be obtained. The preparation of
the subiodide of copper just given involves the loss of an atom of iodine, which is
avoided by previously mixing the liquor with an excess of solution of protosulphate
of iron, by which the copper salt is reduced to the state of suboxide, and all the iodine then precipitated as subiodide. Thus made, it is a pale yellow powder, unaltered by the air.
Sulphate of Copper.-Cu.O.. S.03. H.O. +4 Aq. Eq. 996 9+562'5
or 79'9+45. For the purposes of the arts, in which this salt is extensively employed, it is prepared by treating the native sulphuret
of copper in the manner described under the head of the sulphates
of iron and zinc. It may also be obtained by boiling oil of vitriol
on metallic copper, when sulphurous acid gas is given off, or by
acting on the metal with dilute sulphuric acid, to which some nitric




456  SCHEELE7S GREEN AND EMERALD  GREEN.
acid had been added.  It crystallizes in large doubly-oblique
rhombs, of a fine blue colour, whence its name, Blue Vitriol. In the
figure, the primary rhomb and the most usual
~~- i ~~   \~  secondary form are given, i, u, v marking the
-.. -.- " \ primary planes in each. These crystals dissolve in four parts of cold and two of boiling
z      i,   water.  Of the five atoms of water which it
Xv'contains, one is constitutional, and may be replaced by the alkaline sulphates, to form  a
class of double salts of great beauty. By the
action of a small quantity of ammonia, a basic
sulphate is obtained, of which the formula is Cu. 0.. S.03 + 3Cu.O. +
4 Aq.; and another, containing Cu.O.. S.0+-7Cu. 0.+-12Aq., is occasionally observed to form.
NJitrate of Copper.-Cu.O.. N.O,+ 3 Aq.  This salt is obtained
when copper is dissolved in dilute nitric acid; it crystallizes in oblique rhonmbs of a rich blue colour, and sometimes in paler rhomnboidal plates, which contain 6 Aq. This salt deflagrates violently
when thrown on burning coals, or when struck on an anvil with a
little phosphorus. If some of it be wrapped up tight in tin foil, it
becomes very hot, swells up, fumes, and oxidizes the tin so rapidly,
that in some points brilliant sparks are thrown out.  When heated
above 2000, it loses acid, and a basic nitrate remains, which may
also be formed by adding a small quantity of ammonia to a solution
of the neutral salt. The formula of the basic salt is H.O.. N.0S3Cu. 0.
Phosphate of Copper, 11.0.. 2Cu.0. +P.O., and the arseniate of Copper, H.0...2Cu.0. -As.QO, are pale green powders, obtained by double decomposition..Jrsenite of Copper, H.O.. 2Cu.O+As.03, is obtained by the decomposition of arsenite of potash and sulphate of copper: it is a
fine apple-green powder, the importance of which, as a test for arsenic, has been already discussed (p. 381). It is employed in the
arts, under the name of Scheele's Green, as a pigment, and is prepared
on the large scale by dissolving two pounds of pure sulphate of copper in twelve quarts of water, previously heated in a copper pan.
In another pan two pounds of pure calcined pearlash are dissolved,
with eleven ounces of arsenious acid, in four quarts of pure water.
Both liquors are strained through linen, and then the arsenical solution is gradually added to the solution of copper. The precipitate is collected on a cloth and carefully dried.  The produce
should be 1 lb. 6- oz. A still more beautiful pigment, which may
be best described here, is prepared under the name of Schweinfurt
Green, or Emerald Green; it is a compound of acetate of copper and
arsenite of copper, Cu.O.. X+ 3(H.O.. 2Cu.O. + AAs.03).  It is prepared bymixing up ten parts of pure verdigris with as much hot
water as will make it into a thin pulp, and straining it through a
sieve to separate the impurities: nine or ten parts of arsenious acid
are to be then dissolved in 100 parts of boiling water, and while
boiling, the verdigris pulp is to be gradually added thereto, continually stirring.  At first a mere arsenite of copper. falls, and all
the acetic acid remains in the liquor.; it being only after much agi



SALTS OF L:E A D.                     45-7
tation that the double salt is produced, which is known by the light
flocculent precipitate changing into a heavy granular powder of a
brilliant green colour.
The salts of the suboxide of copper with the oxygen acids pos
sess no practical interest.
Salts of Lead.
Chloride of Lead, Pb.Cl., nmay be produced by boiling lead in
strong muriatic acid, or by acting on oxide of lead with the same
acid; but more simply by adding to any soluble salt of lead a solution of chloride of sodium: A curdy white precipitate falls, which
dissolves in boiling water, and, on cooling, crystallizes in opaque
plates of a pearly lustre, which do not contain water.  This salt
requires 135 parts of cold water to dissolve it, but is much more
soluble in boiling water. It is easily fused, and, on cooling, forms
a semi-transparent mass like horn, whence the old name, plumbum
corneum. By the action of ammonia on chloride of lead, several
oxychlorides may be formed, of which none are now of interest.
Bromide.of Lead resembles perfectly the chloride.
Iodide of Lead, Pb.I., is formed by adding iodide of potassium to
a solution of nitrate of lead; a bright lemon-yellow precipitate falls,
which requires 1235 parts of cold, and but 194 of boiling water to
dissolve it. The solution is colourless, and, on cooling, deposites
the iodide of lead in splendid gold-coloured six-sided plates, which
maintain their metallic lustre perfectly in drying. The iodide of
lead forms double salts with the alkaline iodides, and gives, with
ammonia, oxyiodides when the alkali is not in excess.
Sulphate of Lead.-Pb.O.. S.O3. This salt is found in the mineral
kingdom  in large transparent rhombs, isomorphous with sulphate
of barytes, and of which the octohedron i, y, in the figure, is the
primary form. It may be also formed by adding to
any solution containing lead sulphuric acid or a sul-   
phate. It falls down as a white powder, which, from
its insolubility, furnishes a good test for lead. When
strongly ignited, it melts without decomposition, but
with charcoal it is reduced to sulphuret of lead. The sulphate of
lead is soluble in strong acids; and hence the oil of vitriol, manufactured in leaden chambers, generally contains a small quantity of
it dissolved, which is precipitated on the addition of water.
J\ritrate of Lead, Pb.O.. N.05, is obtained by dissolving lead in dilute nitric acid, and evaporating. It crystallizes in regular octohedrons, often modified, which are generally opaque; it is soluble in
seven and a half parts of cold, and much less of boiling water. It
is not soluble in nitric acid. When heated, it gives out a mixture
of oxygen and nitrous acid gases (p. 276), and leaves melted protoxide of lead. By the action of ammonia, a series of basic salts are
obtained, which contain two, three, and six atoms of oxide of lead
united to one of nitric acid.
When a solution of nitrate of lead is boiled on finely-divided
metallic lead, this dissolves; and on cooling, brilliant yellow plates
are deposited, which are basic nitrite of Lead, 2Pb.O.+N.O4. By
adding sulphuric acid to a solution of this salt, a neutral nitrite is
AM  M




44e8 CHROMATES OF LEAD. -SALTS OF BISMUTH.
obtained, Pb.0.. N.,04II.O., which crystallizes in yellow octohe.
drons.  If an excess of lead be used in the preparation of the nitrite, the acid is still farther deoxidized, and a hyponitrite of Lead,
3Pb.O.+N.O,+3 Aq., is produced, which crystallizes in rose-red
scales.  These salts are of interest, as it was doubted whether the
nitrous acid (N.04) could cotmnbine with,bases, and it is only in
these cases that we have obtained positive evidence of its doing so,
% hich wre owe to Peligot.
Phosphate of Lead, H 0.. 2Pb.O.+P.O, is formed by the action
of common tribasic phosphate of soda on a solution of nitrate of
lead; t is a white powder, which is changed by ammonia into 3Pb.
O.+P.O5.
Silicate of Lead has been noticed in relation to crystal and to flint
glass.
Chromate of Lead —Pb.O.. Cr.O. —Chrome Yellow is formed by
mixing together solutions of nitrate of lead and bichromate of potash. It precipitates as a fine lemon-yellow powder, insoluble in
water. It occurs native in ruby-red crystals, constituting the red
lead ore. This salt is manufactured largely for a pigment, which is
found of various shades of yellow and orange in the market, being'
mixtures of the true neutral chromate, prepared as above, with the
basic chromzate of Lead, 2Pb.0. -+- Cr.O,, which is of a bright vermilion
colour, and is termed Chrome Red. This may be prepared by adding
potash to a solution of chromate of potash until this reacts strongly
alkaline, and then mixing it with nitrate of lead, or by digesting
the neutral chromate of lead in a -warm solution of potash, which
removes half the acid. These give products, however, inferior in
brilliancy of tint to the following.  Saltpetre is to be melted in a
crucible at a dull red heat; and chrome yellow gradually added thereto, as long as effervescence, with escape of red fumes, occurs. The
potash abandons the nitric acid and takes half the chromic acid, and
basic chromate of lead is formed.  The mass becomes black, and is
then to be allowed to settle, and the melted salt poured off from the
heavy powder at the bottom; this, when cold, becomes of a splendid
vermilion red, and is to be taken out and washed with the smallest
possible quantity of water.
Salts of Bismuth.
Chloride of Bismuth, Bi2,C3, is formed by dissolving bismuth in
hot strong muriatic acid; by evaporation it forms a crystalline mass
which is very deliquescent, volatile, and fusible. By water it is
decomposed, giving the oxychloride of bismuth, a white powder,
having the composition Bi2ClI3+-2Bi0, +3H.0.  In the arts this powder is sometimes employed under the name of Spatnish White or Pearl
White.
The chloride of bismuth combines with the chlorides of the alka
line metals, forming double salts, in which the chlorine combined
with the bismuth is to that combined with the other metal as three
to two. In the double salts formed by protochlorides, this relation
is never observed, and hence it furnishes additional proof that the
chloride of bismuth is a sesquichloride, on which idea the formula
~;ecome o2K.C. +Bi2C13+2 Aq. and 2Na.Cl. +Bi2C]l3+3 Aq.




S-ALTS OF  SILVER.                      459
Sulphate of Bismuth, Bi,20+3S.03, is formed by dissolving bismuth in hot sulphuric acid. It forms a deliquescent mass of acicular crystals, which are decomposed by water, giving a white powder, the basic sulphate of B]ism'uth, Bi,203-S.O3.
The JVritrate of Bismuth, BiO0+-3N.O:+- 9 Aq., is formed by dissolving the metal in dilute nitric acid; by evaporation and cooling
rhomboidal crystals are obtained, which easily deliquesce; when
heated, they lose water and nitric acid, and form a basic salt, and
finally oxide of bismuth remains behind.  Like the other salts of
bismuth, this is decomposed by water, and may produce one or other
of two basic salts, according  to circumstances.  When the crystals,
without any excess of acid, are decomposed by water, the precipitate has the composition 4BiO03+3N.0O +9H.0.; while, if an acid
liquor be decomposed by water, the precipitate has the formula Bi.
03+N.O,.  Both of these salts yield very nearly the same quantity
of oxide of bismuth on analysis, and were hence long confounded
together. Many reasons for considering the oxide of bismuth to be
a sesquioxide have been given (p. 398).  These subnitrates of bismuth are used indiscriminately in mnedicine, but the latter form is
more generally found in the shops.  The names Pearl WThite, &c.,
are also applied to these bodies.
Salts of Silver.
Chloride of Silver —Ag.C].; Eq. 1794'3 or 143-8 exists native as
an ore of silver, horn silver, and may be formed by mixing a solution of common salt with a soluble salt of silver. It forms a curdy
white precipitate, perfectly insoluble in water and in acids, but easily soluble in water of ammonia.  When heated, it fuses below redness, and on cooling, congeals into a semitransparent mass of a
horny aspect, whence its old name.  When freshly precipitated, it
is exceedingly sensible to thie action of light, becoming pink, violet,
and ultimately black by exposure to the sun's rays; but for this reaction, it is necessary that organic matter or water should be present, with the hydrogen of which the chlorine may combine, and that
thus a thin layer of subchloride or of metal may be produced.  The
relatiQos of chloride of silver to light are of the highest impoyr[nce
in photo'graph-y,...in.l   exami.ning the structure of the so1l.rays,nas
nbiced ii p. 173, et seq. The processes for the reduction of chlorid'e''"6-f'silver to the metallic state have been described in p. 399,
400.
Iodide of Silver, Ag.I., is obtained by decomposing a soluble salt
of silver by iodide of potassium; a primrose-yellow precipitate
falls, which is insoluble in water and in ammonia; at least it requires
2500 parts of strong water of ammonia to dissolve one of iodide of
silver. It is easily fusible, and becomes opaque on cooling. In
certain forms it is still more sensible to light than the chloride, and
is hence the basis of the impression in the photographic process of
Daguerre (see p. 175).. It is reduced to the metallic state by the
same means as the chloride.
-Bromide of Silver, AgBr., resembles the chloride in every particular respect.
Sulphate of Silver, Ag.O. S.O,, is formed by boiling metallic sil




460                 S ALTS OF  S ILVER.
ver in oil of vitriol; sulphurous gas is given off, and a white saline
mass formed, which, when more strongly heated, is totally decomposed, leaving metallic silver.  This salt dissolves in eighty-eight
parts of boiling water, and crystallizes, on cooling, in snmall needles.
Hy:posulphite of Silver.-2Ag. O.+S202.  The relations of hypo
sulphurous acid to oxide of silver are very curious. On adding a
neutral solution of nitrate of silver to a solution of hyposulphite of
soda, a white precipitate appears, which at first redissolves, but
subsequently becomes permanent.  It soon loses its pure colour,
especially if' heated, and at last becomes black from sulphuret of
silver, while the liquor contains sulphate of silver; thus 2Ag.O.S,20 produce Ag.S. and Ag.O.. S.O,. The solution of this salt is
extremely sweet.  So great is the affinity of hyposulphurous acid
to oxide of silver, that a solution of it dissolves chloride of silver,
forming an intensely sweet liquor; and the solutions of the alkaline
and earthy hyposulphites dissolve all the salts of silver insoluble in
water, except the arseniate and the iodide, and form  double salts
of exceedingly sweet taste.  The double hyposulphites contain
generally one equivalent of hyposulphite of silver to two of the
other salt, but our knowledge of these salts is not, as yet, by' any
means complete.
NV'itrate of Silver.-Ag.O.. N.O5. Eq. 2128'5 or 170'57.  This is
the most important salt of silver; it is manufactured on a very large
scale in the Apothecaries' Hall of Ireland for medicinal use.
It is prepared by dissolving granulated silver in dilute nitric acid,
which at first occurs without the disengagement of any gas, as the
nitric acid dissolves the nitric oxide formed, but towards the end
copious red fumes are evolved. By evaporation and cooling, the
salt is obtained in colourless rhomboidal plates, as in the figure,
often four inches across, which are anhydrous.  It is soluble in its own weight of
[\      ~ "X~yx  cold water.  When heated to about 430'......   it melts into a colourless liquid, which is
poured into cylindrical silver moulds, and
\ congealing, forms the sticks of lunar caustic used in surgery.  This fused salt should
be snow-white; it is not affected by light unless organic matter be
present, as has been fully shown by Scanlan; but with organic matter it soon becomes quite black, silver being reduced.  It is hence
used as marking ink, and for staining hair black. When strongly
heated, nitrate of silver is totally decomposed. It yields its oxygen readily to combustible bodies; thus, if a few grains of it be laid
on an anvil with a little bit of phosphorus, and struck with a hammer, it explodes violently. Its solution is reduced to the metallic
state by all deoxidating agents.
Hypornit-ite of-Silver, Ag.O..-N.O, is obtained in granular crystals by adding the soda salt prepared by melting nitrate of soda (p.
428) to a boiling solution of nitrate of silver, and filtering while
very hot.
Tribasic Phosphate of Silver, 3Agr.O. +P.O,, is the canary-yellow
precipitate, produced by adding a tribasic phosphate of soao to a
solution of nitrate of silver.  Its relations to the other phosphates




SALTS OF MERC'URY.                        461
of silver, and to the: silver test for-arsenic, have been noticed in p.
298 and 381..drseniate of Silver, 3Ag.O.+-As.O,, is precipitated as a reddishbrown powder on adding any solution of an arseniate to a solution
of nitrate of silver. Its formation is one of the most characteristic
properties of arsenic acid.?/lrsenite of Silver, H.O.. 2Arg.O. 4-As.O,, is produced, as has been
noted in p. 401, by adding a solution of arsenious acid to the amnoniacal nitrate of silver, or of arsenite of potash to nitrate of silver. It is a canary-yellow powder, soluble in ammonia and in nitric acid.  When heated, it first yields water and becomes brown;
then it gives oxygen, arsenious acid, and leaves metallic silver.
Salts of Mercury.
Chloride of Jriercury.  Corrosive Sublimate-Hg.C1.; Eq. 1708,5 or
136'9-may be prepared by dissolving red oxide of mercury in muriatic acid, and evaporating.  It crystallizes in long right-rhombic
prisms, generally opaque. It may also be very economically prepared by dissolving the basic sulphate (turpeth mineral) in strong
muriatic acid, and crystallizing; the sulphate of mercury remains in
the mother liquor, and may be again converted into basic sulphate
by the action of water.  The corrosive sublimate is, however, generally prepared, for pharmaceutic purposes, by the dry way, as follows: sulphate of mercury, Hgu.O.. 8.03, is to be well mixed with.
its own weight of common salt, Na.C1., and the mixture introduced
into a wide-necked glass retort, or, on the large scale, into a stoneware pot, to which a globular glass head is attached.  The retort
or pot, being bedded in sand, is gradually heated to redness; decomposition occurs, the chlorine of the common salt combining with the
mercury, while the sodium  takes the oxygen and acid; we have
therefore formed Hg.Cl., which sublimes into the head, forminig a
mass of prismatic crystals, -which, being partly fused by the heat, cohere strongly together, and sulphate of soda, which remains behind 5
Hg.0.. S.03 and Na.C1. giving Hg.C1. and Na.O.. S.0,.
The sublimed chloride of mercury crystallizes in a right-rhombia
prism, as represented in the figure. Its specific gravity is 5'4; it
melts at 509', and bo(ils at 563 T. The specific gravity
of its vapour is 9420. It dissolves in two parts of
boiling and in twenty of cold water; the hot solution
crystallizes, on cooling, in prisms of a different form
from that of the sublimed salt; it is therefore dimorphous; it is soluble in 2'- parts of cold alcohol, and in
three parts of cold ether; it dissolves much more
readily in muriatic acid and in solutions of the alkaline chlorides, than in pure water, as it forms with these bodies
double salts, which are very soluble; of these, the double ciloride
of mercury and ammonium, sal alembroth, is employed in pharmacy.
It will be specially described hereafter. A solution of corrosive
sublimate yields all the reactions of a salt of the red oxide of mercury, described in p. 403. When a small quantity of potash is added to a solution of sublimate, a brown precipitate falls, which by
~boiling becomes black and crystalline; the same substance may be




462           PREPARATION  OF CALOMEL.
formed by boiling red oxide of mercury in a solution of sublimate 
it is an oxychloride of mercury, whose formula is Hg.CI-.+3Hg.0.
If a solution of sublimate be treated by a small quantity of sulphuret of hydrogen, a precipitate forms, at first brownish, but which ultimately becomes quite white, provided there be sublimate in excess;
it is a c/lorosulphuret, of which the formula is Hg.CI.+2Hg.S.
Subchloride of JLJercury.  Calomel.-Hlg2Cl. Eq. 29743 or 238.3
This important medicinal agent may be prepared either by precipitation or by sublimation. For the former object, nine parts of mercury are to be digested in eight parts of nitric acid, sp. gr. 1'25,
without heat, until no more mercury appears to dissolve, and the
liquor begins to assume a yellow colour; eight parts of common
salt are next to be dissolved in 250 parts of boiling water, to which
a little muriatic acid may be added: these solutions being mixed,
the calomel immediately precipitates, and thus prepared, it is absolutely pure. The mercury dissolving in the nitric acid, forms nitrate
of the suboxide, and by the chloride of sodium, nitrate of soda and
subchloride of mercury are formed; Hg20.. N.O, and Na.Cl. giving
Hg,CI. and Na.O.. N.05.
To obtain calomel by sublimation, four parts of corrosive sublimate may be rubbed up with three parts of mercury, so intimately
that no trace of metal shall be visible; and the mixture being introduced into an earthen pot to which a glass head is fitted, heat is
to be gradually applied until the materials have all sublimed. In
this operation, Hg.Cl. combining directly with Hg., gives HgMCl.
The union is never perfected by the first sublimation, and the product is to be again powdered, well mixed, and again sublimed. The
process followed by the British pharmacopueias is different, and is
best carried on in the following proportions: Thirty-one parts of
dry sulphate of the red oxide of mercury (persulphate)are tobe intimately mixed with twenty and one third parts of metallic mercury
and twenty parts of fused common salt, and the whole rubbed together until the mercurial globules totally disappear. This method
is the same as the former in principle, except that the corrosive
sublimate is generated only when required to combine with the additional quantity of mercury to form calomel. The sublimation is
carried on as described above. The sublimed mass is always contaminated with some undecomposed sublimate. Hence it must be
carefully levigated, and washed with boiling water as long as the
washings give any milkiness on the addition of a few drops of water of ammonia.
The precipitated calomel is a pure white powder. When sublimed, it forms a crystalline mass,
whose primitive form, as in the figure, is a square
prism.  It is insoluble in water; and the minute division of the sublimed calomel may be
elegantly secured by conducting its vapour into
a vessel containing boiling wrater, by the vapour
of which it is suddenly condensed, and falls as
an excessively fine powder.  Its specific graviomel of the shops is' detected by boiling for (i few
minutes in alcohol, and adding to the alcoholic 1l




IODIDES OF  MERCURY.                          463
quor some water of ammonia, which gives a white precipitate if
corrosive sublimate be present.  By boiling with muriatic acid, or
with solution of common salt or sal ammoniac, calomel is gradually
decomposed into sublimate, which dissolves, and metallic mercu.ry,
which remains behind.
rT/Lc Brso'iide cand Sblib'omide of Mlircto7y, Hg.1Br. and Hg.2Br., may be preparet,
the first by acting directly on mercury witLi bromine, when a colourless solution is
obtained, which gives prismatic crystals by evaporation; the second, by decomposing nitrate of' the suboxide by bromide of'ptassium. These bodies resemble completely sublimate and calomel in their properties.
Iolidce of Miercury. Red Iodide-F-Ig.I.; Eq. 28I15'0 or 228'0 —rnay
be formed by the direct combination of its elerments, even without
heat, by trituration together with a few drops of' alcohol. It is then
dark red, but may be obtained of a brilliant red colour by precipitating a solution of corrosive sublimate with an equivalent of iodide
of potassium.  An excess of the latter redissolves the precipitate,
as it forms a double salt (K I.+Hg.I.), soluble in water, and crystal
lizable in octohedrons.  The iodide of mercury is insoluble in water; when [heated, it fuses and sublimes, condensing in a crystalline
mass, formed of rhomboidal plates, which, when broken or scratched, gradually become red, breaking up into a number of minulte
crystals of a different form. It is somewhat soluble in alcohol, and
abundantly in aqueous hydriodic acid. A hot solution of iodide of
potassium dissolves much more than the atomic proportion of it;
the excess crystallizes in long, red, square prisms, according as the
solution cools.  It dissolves also in a strong solution of corrosive
sublimate, with which it combines in two proportions.  It forms a
class of double salts, equally extensive waith that produced by corrosive sublimate.
Subiodide of JMercury, Hg2I., may be formed by triturating iodine
with mercury, or by precipitating a solution of iodide of potassium
by a slight excess of nitrate of the suboxide of mercury.  It is an
olive-green powder, which is resolved by heat into metallic mercury and iodide, and is similarly decomposed by a solution of iodide
of potassium, with which the iodide of mercury formed cornbines.
Sesquiodide of MJlercury, or Yellow Iodide. —HglI3 or 2Hg.I. + Hg2I.
To obtain this substance, a solution of iodide of potassium, to which
half as much iodine as it already contained has been added, is to be
decomposed by a slight excess of a solution of the subnitrate -of
mercury.  The bright yellow powder which precipitates must be
dried cautiously with little exposure to light. By means of a solution of iodide of potassium, it is resolved into red iodide and tmetallic mercury. The reaction by which it is formed is that, of the
subiodide first produced, by the K.I. and HgrO.. N.O;, one half is
converted into red iodide by the additional atom of iodine which
is supplied; 2(K.I.)~-I. and 2(fHg20. N.O,) giving 2(K.O.. N Oj),and Hg2I. +2Hg. I.  This preparation is employed in pharmacy.
A. preparation which has been proposed by Donovan, under the
name of Iodo-hydrargyrate of dArsenic, is prepared by rubbing togeth-,er 6'08 grs. arsenic, 15-38 grs. of mercury, and 50 grs. iodine, with
a few drops of alcohol, until they combine, and then adding eight
ounces of water with a few drops of hydriodic acid; a solution is
obtained, at first colourless, but soon becoming yellowish-brown by7n




464          OXYGEN  SALTS  OF MERCURY.
light, from iodine being set' free. This preparation is not a cnem
ical compound; but the iodide of arsenic being decomposed by the
water, the iodide of mercury is dissolved by the hydriodic acid
formed, while arsenious acid exists free in the solution.
Suzlphate of MJlercury-Hg.O.. S.03; Eq. 1867 or 149'6 —is produced by boiling oil of vitriol on mercury, until it is converted into a
white saline mass, which requires to be finally heated nearly to redness to expel the excess of acid.  Sulphurous acid is evolved, Hg.
and 2S.OA giving.Hg.O. S. O   and S.O; but this may be avoided
by adding from time to time a small quantity of nitric acid, by which
oxygen will be supplied.  This salt forms a white powder', not crystalline; at a full red heat it is resolved into mercury, sulphurous
acid, and oxygen. Its use is extensive in preparing calomel and
sublimate.  By a large quantity of wVter it is decomposed into free
acid and basic stllphate, turpeth mineral, 3Hg.O.+S.03, wbhic.h is a
bright yellow powder, which, when heated with muriatic acid, gives
neutral sulphate and corrosive sublimate, 2H.C1. and (3Ha.O.+S.
03) producing 2Hg.Cl. and Hg.0.. S.,03, water being formed (see
p. 461).
Subsulphate of.Mercury-Hg20.. S.03,-Sulphate of the Black Oxide may be formed by heating metallic mercury with oil of vitriol,
provided the heat do not pass beyond 212'; or by mixing strong
solutions of nitrate of the black oxide and of sulphate of soda.  It
is a white powder, very sparingly soluble in water, by which it is
not decomposed, and is thereby distinguished from the preceding
salt.
Jitrate of JMerctry. Jr'itrate of thle Red Oxide. —Hg.O.. N.O-+
2 Aq. This salt is formed when mercury is dissolved in an excess
of nitric acid with heat. It crystallizes in rhomboidal plates, which
are deliquescent, and soluble in a small quantity of xwater.  Its solution is decomposed'when diluted, a basic nitrate of the Red Oxide
being precipitated of a bright canary colour, and having the formu1a H.O.. N.O5- +3Hg.O.  If this powder be boiled with much water,
a still more basic salt is formed, which has the formula N.0-+ -6H1g.
O. Both this salt and the sulphate, when heated by sulphuretted
hydrogen not in excess, give white basic compounds, like the chlorosulphuret (p. 464), having the formula  Hg.O.. N.05-q-2H1g.S. and
Hg:O.. S.O,3 +2Hg. S.
Subnitrate of MJercury. JVritrate of the Black Oxide.-When mercury is dissolved in dilute nitric acid, without any heat, or with only
as much as sustains a very moderate action, the black oxide forms,
and may unite with the nitric acid in various proportions.  Ist. If
there be nitric acid in excess, the solution gives by cautious evaporation clear transparent rhombs of neutral subnitrate, having the formula Hg.20.. N.05-2H1.O.  2d. If there be an excess of mercury,
large opaque white rhombic prismns sometimes form, which.have the
cornposition(3Hg20.+2N.05+3H.O.).  3d. By letting this solution
stand, these crystals gradually disappear, and very small canaryyellow crystals, nearly spherical, with numerous brilliant, facets, are
produced: this is a basic salt, the formula being H.O.. N.05-,-2Hg.
O. This salt may also be formed by the action of water on either
the first or second; both being decomposed into free acid, and the




SALTS OF GOLD AND PALLADIUM.                                465
basic salt, which is not farther altered even by boiling water.  The
second salt may be looked upon as a compound of the first and third,
since (3Hg90.+2N.5+ 3H.O.)=(Hg:O.. N.O5+2H.O.)+(H.O.. N.
05+ 2HggO.).
S!,tbctOIltate (f 3M'vi.?o, Hg20.+Cr.Oa, produced by mixing solutions of chro-.
mate of potash and subnitrate of mercury, is a bright orange powder, insoluble in
water; when heated to redness, it gives off mercury and oxygen, and chromic oxide
of a fine green colour remains (p. 37'2).
Red nitrate of mercury combines with iodide of mercury to form a double salt,
which is formed by half precipitating a solution of the mercuric salt by iodide of potassium, and boiling until the precipitate redissolves; on cooling, the new salt is deposited in brilliant red crystalline scales, which are decomposed by much water.
Salts of Gold.
Perchloride of Gold.-Au.C13.  When gold is dissolved  in nitromuriatic acid, and the solutiop evaporated very cautiously to dryness, this salt remains as a ruby-red crystalline mass, which dissolves
with a yellowish-red colour in water. Its solution is acid, and is
decomposed by the light, and by all deoxidizing agents.  It combines
with muriatic acid, and forms a deep yellow  liquor, from  which
the acid chloride of Gold crystallizes in long yellow  needles.  It is
soluble in alcohol and in ether, from which last solution it is deposited in the metallic state on evaporation, the chlorine combining with
the ether.  In this way some forms of gildin(r are effected, as on
steel.  The chloride of gold combines with many other chlorides,
formina double salts.  The chloride of gold and potassium, Au.9Cl+
K.Cl.+5 Aq., crystallizes in orange-red striated rectangular prismns.
It effloresces in the air, and may be obtained anhydrous; it is then
ruby-red. Chloride of gold and sodium (Na.Cl.+Au.C13+4 Aq.)
forms crystals of the same form and colour, but which do not effloresce: when heated, they fuse in their water of crystallization.
Subchloride of Gold, Au.Cl,, is produced by heating the chloride to
about 4503 in a porcelain  dish, stirring it very carefully until no
more chlorine is given off.  It is a yellowish-white mass, insoluble
in water, by which it is gradually decomposed into chloride and
metallic gold. It is in this way only that a solution of chloride of
gold perfectly free from an excess of acid can be obtained.
olodides of Gold.-When solutions of chloride of gold and iodide of potassium are
mixed, a greenish precipitate occurs of subiodide of Gold, Au.I., while two thirds of
the iodine become free. If the iodide of potassium be in great excess, however, the
iodine and subiodide are both redissolved, and a double salt obtained, which crystallizes, and which contains iodide of Gold; its formula is K.I.+Au.I3; by the cautious
addition of chloride of gold to a solution of this salt, a greenish precipitate may be
obtained without any liberation of iodine, and which hence must be the iodide.
The oxides of gold do not act as bases, and the general nature of the salts which
they form, as acids, has been noticed in p. 406.
Salts of Palladium.
Chloride of Palladiiuwm, Pd.Cl., is formed by dissolving palladium in nitromuriatic
acid. Its solution is deep brown, and it forms, by evaporation, a crystalline mass;
by the action of a small quantity of caustic alkali, a basic salt, or ox.vchloride of Palladislo, Pd.Cl.+3Pd.O.+4 Aq., is produced; it is a brown powder, insoluble in water. The chloride of palladium combines with other chlorides to form double salts:
when heated to about 6000, it abandons half its chlorine, and subchlcr'ide of PalladiElm remains, an olive-brown powder insoluble in water. By a strong red heat this
is totally decomposed.
Deuttochloride of Palladiumnt, Pd.C12, is formed when the chloride of palladium is
gently heated with aqua regia; it forms a dark brown liquor, which gives, with a
N N 




466 SALTS  OF  PLATINUMi IRIDIUM2 AND  RHODIUM.
solution of chloride of potassium, a sparingly soluble double salt, K.Cl.+Pd.Cl2.
This deutochloride cannot be obtained solid, its solution giving off chlorine, and
chloride remaining.
Iodide of Palladium, Pd.I., is a black powder, obtained by double decomposition.
It forms double salts with other ioclides. By heat it is decomposed, without formn
ing any subiodide.
XSilp/hate of Pailladliut, Pd.O.. S.O3, is produced by dissolving the metal in a mixture of nitric and sulphuric acids. By evaporation, a saline mass is obtained,
which is decomposed by water.
Nil aZe of Palladium, Pd.O.. N.05, is obtained by acting on the metal with nitric
acid. At first it dissolves without any evolution of gas, forming a deep olive liquor;
but when heated, it gives off N.O2, and becomes brown. The nitrate of palladium
is decomposed by water, giving basic salts.
Salts of Platinum.
Protoc/loride of Platinum, Pt.CI., is formed by exposing the bichloride, in fine powder, to a temperature of about 5003 in a porcelain dish, and frequently stirring; one half of the chlorine being
evolved, a greenish olive powder is produced, which is the protochloride.  It is insoluble in water; by a red heat it is resolved into
chlorine and metallic platinum. If the bichloride be exposed only
to a temperature of about 400', water dissolves from  out of the resulting mass, a substance which colours it intensely brown, and
which is, probably, a sesquichloride, Pt2Cl,.
Bichloride of Platinum.  Pt.Cl,.  This salt is produced by dissolving platinum  in  nitromnuriatic acid.  The solution, when free
from  excess of acid, is intensely yellow; on evaporation, it gives a
crystalline deliquescent mass. This salt is very soluble in alcohol,
and is so used for the detection of potash (p. 339).  It combines
with other chlorides, forming double salts, of which some possess
considerable interest.  Those with chloride of potassium, K.CI.Pt.Cl,, and with sal ammoniac, N.H4Cl.+Pt.C12, are precipitated as
yellow  powders from  strong solutions, or as minute octohedral orange-red crystals from  dilute solutions of those alkalies, and are
hence used for their detection.  These salts are insoluble in alcohol.  The sodium  double salt (Na.Cl.+Pt.C12) is, on the contrary,
easily soluble both in alcohol and water.
The lodides of Platintum are black powders, insoluble in water, formed by the
double decomposition of iodide of potassium with the respective chlorides. The
biniodide combines with iodide of potassium to form a double salt K.l.+Pt.I2, which
dissolves in water, giving a solution so deeply claret-coloured that it may serve to
detect a very minute trace of platinum in solution.
Although many oxygen salts of platinum are described in the systematic books
(sulphate, nitrate, &c.), I consider that we possess no accurate knowledge whatever
of that class of combinations.
Salts of Iridium  and Rhzodium.
There are four chlorides of iridium. The protoclhlride, Ir.Cl., is prepared by
heating metallic iridium to redness in chlorine; it is an olive-green body, which is
insoluble in water, but combines with other chlorides to form double salts. The
sesquichloride, Ir2C13l is formed by dissolving the sesquioxide in muriatic acid. It i;
a brown crystalline substance, volatile, and forming double salts. The bichloride,
Ir.C12, is produced when a concentrated solution of the former is treated with aqua
regia. It forms a dark brown solution, giving, when dried, a black mass. It gives
with chloride of potassium a sparingly soluble double salt in black octohedral crvstals. The percldoride, I.C13, is not known except in the state of a double salt, K.CI.
+I.C13, which is produced by processes, fbr which I refer to the larger systematic
works.
Time protoxide, sesquioxide, and deutoxide of iridium form salts with the oxygen




ELEiMENTS OF  ORGANIC  BODIES.                        467
acids; the solutions of the first class being green or purple, those of the second class
blood-red, and those of the third orange, produce the variety of tints which gives the
name Iridimrn  to the metal; they are not otherwise important.
&SsqmichloAride of R"tordizmrlt, R2C13, is prepared by decomposing the double chloride
of rhodium and potassium by hydrofluosilicic acid. The filtered liquor gives, when
evaporated, a brown-red mass, destitute of crystalline structure; by heat it is completely decomposed. It combines with other chlorides to form well-defined double
salts, such as that 2K.Cl.+R2C3-+2 Aq. formed by acting on metallic rhodium and
chloride of potassium by aqua regia. WVhen metallic rhodium alone is treated by
chlorine, a rose-red powder is obtained, insoluble in water and acids, which is a similar compound of protochloride and sesquichloride of rhodium, R4C15=2R.CL.+
R,2C1.a
By igniting metallic rhodium with bisulphate of potash, a double salt is obtained,
which does not crystallize. The nitrate of rhodium is a dark red deliquescent salt,
which gives with nitrate of soda a double salt in dark red crystals.
CHAPTER XVI.
ON THE GENERAL PRINCIPLES OF THE CONSTITUTION OF ORGANIC BODIES.
ORGANIC bodies are distinguished generally by a much greater
complexity of composition than occurs in substances of mineral origin. Except in the case of carbonic oxide, there is no example of
an atom of an organic compound containing but two simple atoms;
and carbonic acid and cyanogen are the only examples of an organ-.
ic atom being formed by three elementary atoms. On the contrary,
the number of simple atoms entering into the composition of an organic body is sometimes very great: thus an equivalent of oleic acid
contains o270 simple atoms; an atom  of albumen is formed of 883
simple atoms; an atom  of spermaceti includes 468 simple atoms;
numbers to which we find no form  of combination approaching in
inorganic comupounds.
Besides this greater complexity of constitution, organic bodies
are distinguished by the nature of their elements.  I have had occasion already to describe as inorganic fifty-four undecompounded
bodies, which, by their reunion in various proportions, generate the
compound substances which constitute the mineral crust of the
globe; but- amongr organic bodies we meet with few of these.  Although equalling in number and surpassing in variety of properties
the mineral species, the products of the animal and vegetable kingdomn lnay be looked upon as consisting almost exclusively of six
elements, of which two, sulphur and phosphorus, are met with but
seldom; nitrogen is much more extensively found, especially in
animrnal substances; oxygen and hydrogen exist in almost all; but
the element which is peculiarly organic, and which, with the one
exception of ammonia, exists in all bodies derived from an animal
or vegetable source, is Carbon. It is henco that I have deferred the
description of carbon and its compounds until I could pass directly
from  it to the great variety of organic bodies of which it is the basis.  With the constituents of inorganic bodies it has but an accidental connexion; for, as I shall hereafter show, there is no form of




468         CLASSES OF ORGANIC  BODIES.
carbon which has not at some time made part of an organized being.
Besides these six elements of organic bodies, there are many which
enter into the structure of animals and plants, and are subservient
in an important degree to the proper performance of their functions, without being really constituents of their organic tissues or
secretory products. Thus iodine and bromine exist in many marine plants and sponges; common salt and oxygen salts of potash,
soda, lime, and magnesia exist in most animal and vegetable juices;
phosphate of lime constitutes the bony skeleton of one, and carbonate of lime the testaceous covering of another tribe of animals,
while silica forms the solid basis of some of the lower tribes of zoophytes. In the red colouring matter of the blood, iron is an essential element, and the same metal has been found in minute quantity
in other parts of animals; indications of fluorine and of silica have
been found in the bones and teeth; but in all these instances, except the one fact of the iron element of red blood, we find these
saline substances to be contained in fluids in a condition of mere
physical solution, or to be deposited as solids in the bones or teeth
in a purely inorganic form, clearly to be distinguished from the
proper state of organic combination, in which the carbon, hydrogen, oxygen, and nitrogen of the tissues and secretory products are
united.
Among organic bodies, it is necessary to distinguish three classes, which differ no less in complexity of composition than in the
circumstances under which they are formed, and their relation to
organic bodies. These are, first, those bodies which are directly
elements of an organized and living being, and which, while in connexion with it, appear to possess the power of elaborating, from
certain nutritious juices, additional material similar to themselves.
Such are the organic constituents of the animal and vegetable tissues and of the blood, which, while in connexion with, and forming portions of the animal or plant, participate to a certain degree
in its vitality, and do not obey the laws of ordinary affinity, unless
by being, in the first instance, killed; these bodies should be more
properly called organized than merely organic; their chemical relations commence only when they have been deprived of their most
essential character, life. They are organs; their constitution cannot be expressed in formulae, nor their properties accounted for by
analysis. After their death we may obtain from them, by chemical
treatment, a variety of organic bodies; but that they wrere composed
of these bodies, and that their properties resulted from the cornbination of such elements as we extract from them, it would be false
philosophy to imagine. The fibrine and albumen of the blood, the
muscles, and the cellular tissues, the fatty matter of the brain, perform their functions in virtue of vital power, and not of any chem.ical properties they possess. The albumen of the egg is not a chemical substance, but a delicately-constructed mass, destined to be
transmuted into the organs of the chick, and by participating in its
life, protected from putrefaction. But when albumen is precipitated
by corrosive sublimate, it is killed, and the product of its decompo —
sition combines with the oxide of mercury.
This class of bodies have their origin, therefore, in actions purely




RELATION OF ORGANIC FORCE  TO AFFINITY. 469
vital. They have a structure organic-molecular, totally different
from crystallization, and for the most part consisting of minute
cells. When dead, these tissues undergo spontaneous decomposition, with more or less rapidity, according as their composition is
more complex; but for this water must be present. Some forms
of animal tissue, which appear to lose the organized structure and
vitality with which they were at first formed, are capable still of
remaining in connexion with the living system, and, although dead,
have no tendency to putrefy, probably from not being in any degree soluble in water. The formation and growth of nails and
hoofs, hair and horns, are examples of the important uses of this
property.
It is by virtue of the vital forces of the bodies of this first class,
not individually, but united together so as to constitute the tissues,
glands, &c., of plants and animals, that the organic bodies of the
second class have their origin. These are substances produced (secreted) from the elements by which organized bodies are nourished,
probably -by the union, under peculiar conditions, of such portions
of the constituents of the food as were not proper or proportioned
to be assimilated to the organized tissues of the living being itself.
It is thus that, by a plant which uses water, carbonic acid, and atmospheric air as nutriment, after the assimilation of a certain quantity of their constituents to its proper tissues, sugar, starch, and albumen, adapted for the nutrition of its young, may be formed as
secreted products, and oils, resins, colouring matters, &c., rejected
as useless or injurious.
The third class of organic bodies contains those which are evolved by the chemical decompositions, whether spontaneous or artificial, to which substances of the first and second class are subjected. Thus sugar, by fermentation, yields alcohol and carbonic acid;.
alcohol, by oxidation, yields acetic acid, or aldehyd; acetic acid,
variously treated, produces acetone, or alkarsin; while ligneous
fibre gives origin, when heated, to a crowd of organic products, of
which pyroxylic spirit is an example.
It is very interesting to contrast these classes of bodies with each
other, in relation to the forces by which their constitution is regulated, as compared with the simpler forms of affinity by which the
actions of inorganic elements are controlled. In the first there is
found nothing referrible to chemical attraction; all affinity is annulled by the supremacy of life and organization. Hence it is only
when dead that such bodies can be analyzed, and by treatment with
reagents a crowd of products belonging to the third class be obtained from their more or less evident decomposition.  No matter,
therefore, how perfect our mediate or immediate analyses of such
substances may be, the synthesis of such bodies, or their production
by the union of their elements, is strictly impossible to the chemist.
The formation of a molecule of albumen would not be a case of
chemical combination, but of the formation of a portion of an organized cell; it would require not merely the combination of its elements, but also that the compound should have life imparted to it.
In relation, however, to the second and third classes, the circumstances are quite different; although we cannot trace, precisely,




470       T HEORY OF COM{POUND  RADICALS.
the force by which the organized tissues act in eliminating from a
liquid of uniform composition, such as the blood or sap,'the various
secretions which constitute the second class, yet the circumstances of their formation admit of being exhmined, and already some
insight has been obtained as to the way in which organic bodies
may separate, or be converted into others, without reference to the
mere affinities of their elements, by means of the influence that has
been already described as catalytic (p. 236, et seq.); in this way the
functions of organized tissues may be imitated, and a true synthesis
of organic bodies of the second class may be effected. With the
bodies of the third class we find, also, that the circumstances of
their formation are either purely artificial, or capable of being easily imitated, and the reactions by which they are evolved, although
often catalytic, fall, in the majority of cases, under the rules of ordinary affinity. In structure, also, the bodies of the second and
third class range themselves with inorganic compounds; those
which are solid may, for the most part, be obtained crystallized, and
the liquid substances possess definite freezing and boiling points.
Between such organic bodies and mineral substances we find the
greatest similarity, not merely in their physical relations, but in
chemical properties also. The great classes of acids and bases exist, well marked, among organic bodies, and in their combinations
with each other, the same principles of multiple and equivalent
combination are followed as hold for inorganic compounds. So
perfect is the analogy of general characters, that it has long been
an object with chemists to unite, under one principle, the laws of
composition of organic and inorganic bodies; and as the characteristic distinction of mineral substances is to consist of a series of elements which are respectively combined, two and two, in virtue of
their opposite affinities, attempts have been made to reduce the
complex constitution of organic bodies to the same principle of binary union, by supposing that certain of the elements are, in the
first instance, grouped together so as to form a single molecule,
and that this, acting as a simple body, combines with the element
which remains. It is from the discovery of cyanogen, and the discussions as to the nature of the ethers and of the ammoniacal salts,
that we must date the positive introduction of this theory of compound radicals into chemistry. Its utility has not been limited to
the explanation of the constitution of organic bodies; on the contrary, it has been applied successfully to explain the phenomena presented by numerous classes of inorganic compounds, such as the
compounds of sulphur and oxygen, noticed p. 292, and especially
to the foundation of the binary theory of salts, as described in the'fifteenth chapter.
Were we, however, to apply the theory of compound radicals indiscriminately to explain the constitution of organic bodies, we
should be liable to fall into continual error. The criterion which 1
would assume as decisive of the constitution of an organic body is,
whether certain of its elements may be exchanged for others, in accordance with the ordinary laws of substitution of inorganic bodies,
and thus a series of compounds be produced, through which some
elements of the original substance shall have passed untouched,




THIIEORY OF COMPOUND RADICALS.                   471
and from which again, by suitable reactions, the original substance
can be obtained unaltered. In such case I would consider those
elements which remain unaffected as being strictly united with each
other, and constituting a compound radical, which, combining with
other bodies, gives origin to a series of compounds more or less extensive. Thus, if we treat oil of bitter alinonds, c,H,a02, by chlorine,
we obtain a compound C,4,HOC., which gives, with iodide or sulphuret of potassium, bodies whose formulam are respectively C,,H,50
I. and C,,4H,02S. Again acted on by oxygen, it gives crystallized
benzoic acid, Cj4HfO4, or, rather, C,4H,03+Aq. Now it will be seen
that, throughout this whole series, the element C,,HO, has remained
unaltered. In the oil it was combined with hydrogen; in benzoic acid
it unites with oxygen; in the other bodies it is united with chlorine,
iodine, &c., and from these the oil may be recovered by processes
by no means indirect. Now when we state that in these compounds
the elements C14H502 are united, first with each other, by an affinity which ordinary reagents cannot overcome, and that this com.
pound group unites with the simple bodies, hydrogen, oxygen, &c.,
by an affinity so much weaker that they can be readily substituted
for each other, we state only an established fact, and in denominating the group, C,,H,O,, the root or radical of the series of bodies
thus produced, we involve no hypothetical idea. For brevity, we
express that compound radical by the symbol Bz., and we term it
Benzyle; we write the formula of its combinations, respectively, Bz.
H., Bz.Cl., Bz.I., and Bz.O.+Aq.
But we must not be induced, by the brilliancy shed' on certain
branches of organic chemistry through the application of this principle, to transgress the boundaries of sound induction.  There are
numerous organic compounds in which I believe that no binary
structure exists, and, consequently, to which the theory of organic
radicals should not be applied. It is the class of bodies characterized by a remarkable indifference to combination, and which, when
decomposed by the influence of reagents, lose not merely one constituent and gain another in its place, but are totally transformed
into new compounds, into which all of their original components
enter, and towards which the reagent that had been applied frequently appears indifferent, so that the action appears to have more
the character of catalysis than of true chemical affinity. Such bodies are gum, sugar, starch, some of the oily and colouring matters,
urea, and many others: treat these bodies as you will, there are no
phenomena of true replacement; they may be decomposed, but bodies of a totally different type are formed, and' the original substances
cannot be regenerated.
The orgfanic radical which is thus assumed as the basis of a series of compounds, acts as a simple body, but it does so only in relation to the nature and intensity of the forces that act upon it; it
may be decomposed, and frequently it cannot be separated from
combination without total decomposition; hence few compound
radicals can be isolated. But they can be decomposed, even while
still in combination, by the intervention of powerful affinities; and
this decomposition may be either total, so as to ]eave no trace of
the original constitution of the substance, or by giving origin to




472           ITS APPLICATION  LIMITED.
another series of combinations, may indicate a still more intimaie
constitution, and unveil an organic radical of a simpler structure
acting as the basis of the first.
Thus we have seen what: positive grounds there are for admit
ting benzyle, C,,4HO,, to be the radical of the oil of bitter almonds
and of benzoic acid; but if we digest oil of bitter almonds with
ammonia, all oxygen is removed, and we obtain a compound of ni
trogen with the body, C JH., which may also be obtained in other
forms of combination. Now this orgafic substance, C,,,H3, acts as
the basis of benzyle, for. the oil of bitter almonds can be reproduced
from it; and we thus obtain evidence of three stages of constitution
in benzoic acid, whose formula should be written, therefore, as (CA4
1H+O)-,-O.  The considerations described in p. 291 point out a
perfect analogy to this in the constitution of sulphuric acid. Reduced to its ultimate elements, its formula is S.0; but powerful evidence shows that its real basis is sulphurous acid, and not sulphur,
its rational formula being S.O,+O. Now here the primary radical,
CQ4H-, corresponds to sulphur, and benzyle to sulphurous acid; the
total quantity of oxygen in such acids being divided into two portions, differing in order and intensity of combination with the ultimate radical. If we add to these considerations the view of saltradicals, and consider the salts of benzoic acid as expressed by the
formula Bz.O,2+M., as that of the sulphates has been shown to be
S.O2. O2-FM., we observe even a fourth degree to which the molecular structure of the complex organic radical may be traced.
It is, indeed, when applied to explain the constitution of the organic acids, that the theory of compound radicals, as employed inl
the new views of the constitution of oxygen salts, appears most interesting, as the anomalies of properties and composition presented
by the salts of the organic acids were more numerous and more extraordinary than any which the mineral acids presented, and wvere,
indeed, totally unintelligible, until illustrated by the conjoined investigations of Dumas and of Liebig. An example of this may easily be selected. Of the organic acids, the majority are monobasic,
but there are also many bibasic and tribasic; thus the citric acid,
whose formula is C,,2HO,1, combines with three atoms of base; the
meconic acid, C,1H.O,,, is also tribasic; the tartaric acid, C,,40,,,
and the mucic acid, C,2H1804, are bibasic. In these instances, the
quality of combining with many atoms of base, which is so anomalous on the older view, necessarily follows from the formulma of the
hydrated acids, which become respectively, for citric acid, C,2H,014
+H3; for meconic acid, C,01.O 4+1-3; for tartaric acid, CsH4O,.2+H2;
and for mucic acid, C2H8,O,,S+H2. By its means many other singular properties of organic acids are explained: thus there appear to
exist three acids, having absolutely the same composition of CN.
O., viz., the cyanic, the fulminic, and the cyanuric acids; they are
isomeric; they possess excessively different properties. Whence
has that difference its rise' If we say that the cyanic acid contains
cyanogen ready formed, and that the others do not, it still remains
to explain the isomerism of the others; and we find that the cyanic
and cyanuric acids are transformed into each other by the slightest
causes. We obtain, however, at once the key to this isomerism,




CONSTITUTION OF COMPOUND  RADICALS. 473
when we study the salts formed by these acids. The cyanic acid
is monobasic; its hydrate is C2N.O. + H.O.: the fulminic acid is bibasic; its hydrate is C4N202,,2H.O.: the cyanuric acid is tribasic;
its formula is C6NO3+3H.O.  These acids are thus found to have
different atomic weights; their molecular groups are ascertained to
contain different numbers of molecules, and hence to admit of totally distinct internal structure. When expressed in formulae on
the binary theory, we have CN.0O+H. for the cyanic, C4N204-+H,
for the fulminic, and C,NO3+-H3 for the cyanuric acid; and not
merely the difference in nature of the acids, but also the distinctive
characters of their salts necessarily result.
Although chemists are unanimous in regarding the principle of compound radicals as the basis of the philosophy of organic chemistry,
yet science has not yet arrived at the point when the principle is
adopted by all in the same form of detailed application. On the
contrary, there are few specific examples of that principle that are
not still open to discussion. The views of Berzelius on this subject
are specially of importance. He considers that the compound radicals of organic bodies consist only of carbon and hydrogen, or of
carbon and nitrogen: that they never contain oxygen. Hence he
does not admit the existence of benzyle in benzoic acid or in oil
of bitter almonds; he considers the only radical to be the carbohydrogen, C04H1, and benzoic acid to be directly C,,H,5 —O0. He
looks upon the oil of. bitter almonds as containing ready-formed
benzoic acid, combined with the true hydruret of the radical, as 3
(C,14HO2) =2(C,4H + 0O3) + (C,4H-+ H,). The chloride of benzyle he
looks upon as an oxychloride, 3(C,4HE. 02C1.) being equal to 2(C,4115
+  3O) + (C4aHs+0 1 C13).  This is evidently the same difference of view
that exists as to the nature of the sulphurous acid compounds, which
Berzelius also regards as more complex. Thus the chlorosulphurous acid is, according to him, a compound of sulphuric acid with
a terchloride of sulphur, 3(S.OC1.)=2S.O3+S.C13; and so in all
other bodies similarly circumstanced.
The opinions of a man to whose extraordinary industry and genius we owe some of the most important additions, both theoretical
and practical, that science has received since the epoch of Lavoisier,
should not be rejected without much consideration; but on applying those ideas to express the constitution of the crowd of bodies,
containing four or five elements, which have recently been discovered, we are led to suppositions destitute of experimental proof, and
yet which, assuming the existence of numerous hypothetic bodies
of anomalous constitution, and combined in very unusual ways,
would require for their legitimate admission into science a very
strong body of experimental evidence. It would be impossible here
to discuss the principles of his opinion in detail; I am led to conclude, from the consideration of the whole body of facts which bear
upon it, that it is inferior in power, and simplicity of explanation of
known facts, and as an instrument of discovery, to the simpler view
of the constitution of organic bodies which has been described; and
being thus deficient in all the important duties of a sound theory, 1
do not hesitate to reject it.
The proposition of the theory of types by Dumas (see p. 23-)
0 o o




474         THEORY OF CHEMICA L TYPE S.
will probably constitute an epoch in science, by fixing attention on
the permanent equivalency of an organic atom, notwithstanding
complete alteration in the nature of its elements. This did not follow necessarily from the theory of compound radicals, nor does the
conservation of the type require that the radical be preserved unaltered, but only the type of the radical.  Thus, when aldehyd is
changed into chloral (C411.,02 into C411.. C1O02), the type is preserved,
since the hydrogen is replaced by an equivalent of chlorine; the
radical is altered, since acetyl, C4H3, is changed into C4C01, but the
new radical is still constructed on the type of the original. The
theory of types, so far from being inconsistent with the theory of
compound radicals, is in perfect harmony with it, at least as I un
derstand it, and as I believe it to have been proposed by Dumas
The bases upon which it rests may be announced as follows:
1st. That the hydrogen of a compound radical may be replaced
by chlorine or by oxygen, &c c, equivalent for equivalent, and a new
radical thus produced, which, being constructed on the same type
as the original, will have the same general laws of combination, and
will hence form compounds of the same type as those containing
the original radical. Thus, from C4H3 may be formed C4C1], and
these, combining with oxygen and water, form CHO.+Aq. or CQ
H303+Aq., and C4C130.+Aq. or C,4C103+Aq.: also, by uniting
with chlorine, they produce COHC1. and C4C13C1.
2d. That when bodies of the, same type, and containing radicals
of the same type, are subjected to the action of strong affinities, by
which their constitution is broken up, the resulting products-are
constituted also upon the same plan, although differing in composition; thus C4H404, when heated with potash, gives 2C.0O and CH,4;
and CH.. Cli0,, similarly treated, gives 2C.02 and C2H.C03; the
types of CH.H3 and C2H.C13 being the same, and containing equivalent radicals.
3d. When bodies of the same chemical, though of different mechanical types, or, as I would term them, bodies of the same natural
families, as the alcohols, are submitted to the action of affinities of
equal power, the bodies generated have the same relation to one
another as the original bodies had; and the radicals are either unchanged, or all changed in a similar degree. Thus from wine alcohol (C4H,60), methylic alcohol (CHO,2), essential oil of potato
spirit, CloH202, and ethal, C32H,,40, there are produced by the action of potash a series of acids, each having the same type and
containing the same radical as its alcohol; thus the acetic acid (C,
H404), the formic acid (C2H,,04), the valerianic acid (C,H,,004), and
the ethalic acid, C32H3204.
Considered in this way, the theory of types is an important addition to our ideas on the constitution of organic bodies. It serves
to attach, under a few very simple principles, numerous classes of
compounds, whose composition would otherwise appear very complex and anomalous, and will probably, when applied to the study
of such bodies as, not containing compound radicals, give only their
molecular group as a mass to our examination, become a source of
still more important additions to our knowledge.
Although each organic substance gives, when acted on by re



PRiNCIPI, E  OF ACTION  OF REA GBNTS.    475
agents, products which are characteristic of, and often peculiar to
itself, yet there are some general rules which, being now noticed,'will obviate the necessity of much detail hereafter.
When an organic substance is treated with dry chlorine, it eithei
combines directly writh the gas, or, as more frequently happens, hydrogen is removed to an amount equivalent to that of the chlorino
absorbed. Even in the first case, the direct union is often but apparent, and arises from  the muriatic acid formed combining with
the true product. Thus olefiant gas, C4H4, gives the oily liquid C4
14,C12; but this, in place of being a direct combination, consists of
C0HCI., which is the true product formed by substitution of Cl.
for H., but is united with the H.C1. thus generated.
If water be present, it influences the reaction very much, being
generally decomposed. In some cases, all the chlorine unites with
its hydrogen, while the oxygen combines with the organic substance; but, generally, the chlorine unites with both elements of
the water, forminng muriatic acid, which remains free, and hypochlorous or chlorous acids, which enter into the composition of the organic product. in other cases, again, the presence of water does
not appear to exercise any influence.
When an organic substance is treated with nitric acid, it is always
raised to a higher degree of oxidation. Very rarely does the action
stop there. Hydrogen is usually separated, and oxygen put in its
place; while the new products formed contain usually a smaller
number of molecules than the original organic substance.  Thus
gum (C,2H,,O,,), when acted on by nitric acid, gives, first, by simple oxidation, mucic acid (C,2H,000,6); but, if the action of the acid
be more violent, all hydrogen is removed, and two atoms of oxygen
substituted, thus producing C,2O,,, the elements of six atoms of oxalic acid.
In many cases, the action of nitric acid is not limited to the oxidation, whether direct or indirect, of the organic substances; but,
by the removal of some hydrogen from it, in combination with some
of the oxygen of the nitric acid, water is formed, and the nitrogen,
or nitric oxide, or nitrous acid, combines with the remaining organic elements, and forms new products.  Thus, from napthaline and
benzine, numerous substances containing nitrogen are derived.
This fixation of nitrogen may occur even with bodies which already
contain it; thus indigo, treated with nitric acid, produces bodies,
the indigotic and the picric acids, which contain a larger proportion
of nitrogen than the indigo itself.
The peroxides of manganese and lead often serve to oxidize organic bodies in a more regulated manner than nitric acid, the new
substance combining with the protoxide of the metal; thus, by Pb.
0.2, uric acid is decomposed into allantoin, urea, and oxalic acid.
By fusion with hydrate of potash, the oxidizement of organic
substances is very powerfully effected; water being decomposed,
its hydrogen evolved, and the oxygen uniting with the organic body
to form an acid, which remains combined with the potash. Thus
alcohol, C4H,602 and 11H.0., produce acetic acid, C4H11404, and 114 becomes free.' Often the organic substance is merely broken up into
other bodies of simpler constitution, as when tartaric acid, CH40(o,




476          ORGANIC ORIGIN  OF CARBON.
by fusion with potash, is decomposed into acetic acid, C4H4),, and
oxalic acid, 2(C,,0). In every case, if the temperature be much
raised, carbonic acid is one of the products; thus acetic acid (C4114
O,) separates into CI.4 and 02C.O.
The action of sulphuric acid on organic bodies may be very different, according to circumstances; thus from starch we may obtain, by a merely catalytic influence, gum, grape-vgar, anrd ultimately sacchulmine. In these cases, the sulphuric acid remains
totally unchanged and. free, but generally it enters into combination
with the organic body, either without decomposition, as in the sulphovinic and sulphomethylic acids, or else water is formed by its
reaction on the organic body, which, thus deprived of an atom of
hydrogen, combines with hyposulphuric acid. S20,. It is thus that
the sulphurous element exists in the sulphobenzoic acid, the isethionic acids, &c.
If an organic substance containing nitrogen be acted on by these
reagents at a high temperature, this is generally separated under
the form of ammonia; water being decomposed, and its hydrogen
so applied, while its oxygen forms the ordinary oxidized organic
products. If potash be the reagent, the ammonia is expelled, and a
salt of potash with the new organic acid remains; if sulphuric acid
be the reagent, the organic acid is set free, and a sulphate of am
monia remains.
By the action of heat upon fixed organic compounds, a variety of
products are formed, which may generally be described as formed
by the abstraction of a portion of carbon and oxygen, as carbonic
acid, and of hydrogen and oxygen, as water. Hence such pyrogenic products are always richer in hydrogen and carbon than the bodies they are formed from, and of less acid characters. This kind
of decomposition will, however, require to be described in a distinct chapter.
CHAPTER XVII.
OF CARBON, AND ITS COMPOUNDS WITII OXYGEN, SULPHUR, AND CIHLORINE.
CARBON exists in large quantities, and very extensively distributed
in nature, as a constituent of all vegetable and animal bodies. It is
found, also, in the mineral kingdom, under forms, however, which
may be shown to have originally been derived from organic bodies.
Thus the different varieties of coal have been produced by the aggregation of great quantities of wood, the materials of primeval forests, which, being submerged in water, and covered by the gradually-deposited layers of sand and mud, have been elevated, in connexion with the strata of clay and sandstone so produced, to their present situations. The wood thus circumstanced has underdone a kind
of decomposition, which shall be hereafter fully noticed, and the
mixture of fixed and volatile organic products, which constitute our




NATURE  OF LIMESTONE  ROCK.-DIAMOND. 477
coal, has thus its origin.  This formation of coal, as well as the
formation of peat and turf at the present day, almost at'the surface,
is accompanied by a disengagement of carbonic acid in large quantity, and hence the probable source, in the air and in mineral waters, of that substance, of which, also, much may be derived from
the respiration of animals.
A more strictly mineral form of carbon is that of carbonic acid
united to lime, and to other metallic oxides, forming the numerous
class of native carbonates.  Of these the most abundant is the carbonate of lime, which, under the form of chalk, oolite, coral, mountain limestone, &c., constitutes a large proportion of the geological
formations of our globe. In all these cases, the rock is formed of
shells of animals, aggregated together in great masses; these geological formations, resulting from the collection, at the bottom of a
sea or lake, of the spoils of myriads of generations of those aninmals,
which, by superincumbent pressure, may be more or less densely
agogregated; or by proximity of igneous rocks, may be partially or
completely fused, and their organic characters obliterated to a greater or less degree. In this way the crystalline marbles are formed,
in which few or no traces of organic origin remain.  The comparatively small quantity of carbonate of lime, which is found separately
and distinctly crystalline, either as arragonite or cale spar, may be
traced to the solvent action of water impregnated with carbonic acid,
filtering through strata containing shells, and then gradually depositing, in favourable situations, the matter it had thus taken up, in
crystals, the form of which depends upon the temperature at which
they are produced (page 225).  The other native carbonates, of
which the quantity is very small in comparison with that of the carbonate of lime, may have been produced by double decomposition.
Thus a water, holding carbonate of lime in solution, filtering'across
a stratum  containing oxidized iron or copper pyrites, would give
origin on the spot to a crystalline deposite of sulphate of lime, and,
at a certain distance, carbonate of iron or of copper would be separated. Those instances suffice to point out the reasons for considering carbon as truly the organic element, and that its appearance
in a mineralized condition arises from secondary actions.
Carbon presents itself in a great variety of forms. Absolutely
pure, it constitutes the diamond, which, from its exceeding hardness,
brilliancy, and rarity, ranks as the first of gems. It is found disseminated in alluvial strata in Golconda, Brazil, &c., and is separated from the sand and mud by processes of washing. No deposition
of diamond in rocks has ever yet been found. It crystallizes in
forms of the regular system, generally having a great number of
sides, bounded by curved edges, in virtue of which it splits glass
like a wedge, in place of scratching it as a file. Its crystals are
generally hemihedral, and frequently rough and discoloured at the
surface. These crystals all cleave parallel to the faces of a regular
octohedron (fig. f, p. 26), but the properties of the diamond separate
it completely from the proper mineral crystals of the regular system.
Thus it possesses double refraction in some cases; it polarizes light
elliptically; its structure has been found by Brewster to consist in
layers, sometimes containing cavities, indicating that the crystal had




478      ORIGIN  AND NATURE OF PLUMBAGO.
been originally soft, and only concreted by degrees; and in the re.
cent researches of Dumas on the atomic weight of carbon, it was
found that, when burned, diamonds generally leave behind a minute
skeleton of inorganic matter. These considerations fully show that
the diamond derives its origin from the decomposition of organic
matter.  The diamond is the hardest body known; it cuts every
other, and can be ground only by means of its own powder. It is
usually colourless,'but sometimes brown or rose-coloured; its refractive power is very great (2-439), whence its great brilliancy.
It conducts heat and electricity very badly; it resists most chemical agents, but burns in melted nitre brilliantly, forming carbonate
of potash; it burns, also, when heated to redness in oxygen gas, and
evolves sufficient heat to maintain the continuance of the combustion; its specific gravity is about 3-5.
Another very remarkable form of carbon is that of plumbago or
graphite. This is found in many localities, but sufficiently pure for
the purposes of the arts only in Borrodale, in Cumberland. It is
perfectly opaque, crystallized in rhornbohedrons, or six-sided tables; but its usual appearance is in brilliant leaves or spangles; it
is soft and unctuous to the touch, and oives, on paper, a continuous
gray streak, whence its name of blacklead, and its use in making pencils. Its formation appears to be connected with the action of iron,
and with a high temperature: it is found only in igneous rocks,' as
granite and mica slate, and contains almost always a large quantity
of iron intermixed in the metallic state, so that it was once supposed to be a carburet of iron. Graphite may be formed artificially by adding charcoal to melted cast iron.; the charcoal dissolves
largely, but on cooling is found to separate in brilliant flexible
plates, more or less regularly six-sided.  Graphite is lighter than
diamond, its specific gravity being 2'5, and it conducts heat and
electricity much better. It is very hard to set on fire, and does not
continue to burn unless heat be applied from without.
Carbon, in a form  more or less mixed with foreign matters, is
obtained by the application of a very high temperature to animal
or vegetable substances in close vessels. The kinds of carbon thus
produced still differ very much. Thus coke is obtained by heating
coal in iron retorts until all the volatile products are driven off,
and the excess of carbon remains mixed with the earthy matter
which all coal contains. The properties of coke approximate more
or less to those of graphite, according to the temperature at which
-it has been produced. By the proximity of igneous rocks to coal
under the earth, a similar expulsion of its volatile matters may be
effected, and a form of carbon nearly pure, anthracite, results. These
fuels are difficult to light, but, when once ignited, give out an intense heat by their combustion.
If an organic substance, which contains hydrogen and carbon, be
set on fire, and there be a copious supply of air, it is totally converted into water and carbonic acid; but if the supply of air be
limited, the affinity of the hydrogen for the oxygen preponderates,
and no carbon is consumed until all hydrogen is converted into water. By this method of imperfect combustion, several forms of carbon are prepared, such as wood-charcoal and lampblack.  If wp




CHARCOAL  AND  LAMPBLACK.                         479
take a splinter of wood and set it on fire, we observe that at first
only the volatile products of the wood burn with flame, and that a
mass of charcoal forms inside, and remains unaltered as long as, being surrounded by flame, it is protected from the air; but when the
end projects beyond the flane, it ignites and burns away, leaving
only a trifling ash.  If', however, a tube be taken, and, as in the figure, as tile combustion advances along the stick b, the burned portion a be gradually plungoed into a narrow tube, this b
becomes filled with carbonic acid, which does not support
combustion, and the cylinder of charcoal formed may thus I
be permanently preserved; on this principle'wood-charcoal is
prepared.  Billets of wood are heaped together regularly, so
as to form a hemispherical mass of about forty feet diameter;
in the centre a hole reaches fromrn the top to the bottom, forming a chimney.  The outside is then coated with sods, so as
to render it impervious to air except at the bottom, where
some apertures are left. Burnino- charcoal is then thrown into the
chimney, and the fire commuriicating to the billets, these burn with
a supply of air so limited that the charcoal remains unconsumed,
the combustion commencing at the top and proceeding down. The
outside of the heap is then covered with denser sods, so as to cut
off the supply of air as the combustion proceeds.  When the carlonization has been completed, the whole mass is covered up and
allowed to cool perfectly before being opened.  In this country,
most of the charcoal used is obtained in the preparation of vinegar
by the destructive distillation of wood, as will be hereafter noticed.
The quantity of charcoal produced from wood varies very much
with the rapidity of the process; the generality of fresh woods
yielding but thirteen or fourteen per cent. by a rapid decomposition,
while, when slowly charred, they may yield twenty-five or twentysix. The mode of conducting the process,. therefore, must be changed according as the residual charcoal, or the volatile materials, are
the most valuable products.  The charcoal preserves, in a remarkable manner, the structure of the wood from which it is produced,
so that by the microscope some of the most delicate forms of vegetable organization may be traced in charcoal that has been slowly
prepared.
Lpzbplarck is formed by a still more direct application of the principle of imperfect combustion. In the apparatus represented in the figure, a is a pot placed in a
furnace which is vaulted'over, so that all vapour from it
may pass into the chamber b, c, while by some apertures,
a small quantity of air is allowed to sweep over its surface; the sides of the round chamber are lined with leather, and above is a conical cover of coarse linen, d,
through which the draught from the furnace passes, and
which may be lowered or raised by the cord and pulley.
A quantity of pitch or tar is placed in the pot and made
to boil; it takes fire, and, as the quantity of air which 
has access to it is very small, the hydrogen alone burns,
and the carbon, being carried up by the current in a very  i 
finely-divided state, is deposited on the sides and cover  I
as an impalpable powder..lniinal charcoal is produced by the decom- 
position of animal matters in close vessels.
From its properties, which I shall just now notice, it is manufactured




480       PROPERTIES  OF  ANIMAL  CHARCOAL.
in large quantities for the arts, especially from bones, and is hence
called Ivory-blacck or Bone-black.  The bones are placed in iron cylinders, which are arranged, vertically or horizontally, in a furnace,
in connexion with a series of condensing vessels containing water;
the volatile constituents of the animal matter being expelled principally as carbonate of ammonia, of which a large quantity is thus
made, the excess of carbon remains in a state of very minute division, mixed with the earth of bones (phosphate of lime).
Some of the most important uses of carbon are founded on prop.
erties which the various forms of it possess in different degrees.
Its inflammability varies with its density and closeness of aggregation; being least in graphite, and becoming so great when wood
charcoal, prepared at a low temperature, has been reduced to powder for the preparation of gunpowder, as to inflame sometimes spontaneously, and give rise to destructive accidents.  Carbon possesses
a remarkable tendency to unite with colouring and odorous substances.  This property is specially possessed by ivory-black, in consequence of the extreme degree of division of its particles.  When a
purely organic body yields carbon, the molecules of the latter aggregate themselves to a degree which depends on the temperature;
and if, as in wood, there be a fusible ash present, this acts as a cement, and diminishes the porosity very much.  If the organic substance be fusible, as starch or sugar, the closeness of texture of the
charcoal becomes still greater, and its utility less; but in bones, the
molecules of organic matter are separated by an infusible earthy
salt, and when carbonized, the charcoal is obtained in the greatest
possible state of comminution.  A still more efficient charcoal is
formed by calcining dried blood, hoofs, or horns, with carbonate of
potash, which prevents the aggregation of the particles of carbon,
which, the alkaline salt being washed out with water, is left in the
most active condition possible. In the arts, this property is applied
to the purification of sugar; to clearing solutions of many organic,
substances; and barrels in which water is to be kept are charred on
the insides, in order to remove any organic matter described in the
water, which might be liable to putrefy.
The following table contains some numerical results of the relative decolorizing power of equal quantities of carbon in various
forms; the first column containing the number expressing the power of removing the colour of a solution of indigo, and the second
column that of a solution of coarse sugar.  The power of ivoryblack is taken as the standard:
Kinds of Charcoal.          Indigo. Suma,.
Common ivory-black........ 1 1
Well ignited lampblack......... 4   31
I,ampl)lack ignited with pot ashes.1 1.0. 17  10
Clhacoal from the decomposition of acetate of potash. 576 414
Starch ignited with pot ashes.........119 89
Blood ignited with phosphate. of lime....   11'9 10
Ivory-black digested in muriatic acid.        9...1-9  1'7
Ivory-black digested in muriatic acid, and afterward
ignited with pot ashes.......   45 3 20
Blood ignited with pot ashes........ 5.0  20




ATOMIC  WEIGHT  OF  CARBON.                     481
The decolorizing power is thus not the same for all bodies. If
charcoal  that had once been used be again ignited, it does not recover its activity, as the colouring matter fuses before charring, and
thereby lessens its porosity. Charcoal possesses also a remarkable
power of absorbing gases.  If a fragment of wood charcoal, which
had beenl strongly heated, and allowed to cool without access of
air, be introduced into a tube containing ammoniacal gas, in the
mercurial pneumatic trough, an immediate absorption occurs, to
the amount of ninety times the volume of the charcoal.  In other
cases the absorption is not so great; a cubic inch of boxwood char
coal, which is the most active, absorbing
90 cubic inches of ammonia;      40 cubic inches of nitrous oxide
85 "    "    muriatic acid.      35    " "    carbonic acid.
65       "    sulphurous acid.    9-25 " oxygen.
55 "    "    sulphuretted hydro-   75     "    nitrogen.
35    " "    oletiant gas. [gen.   1-75   "    hydrogen.
These gases in this absorption undergo no chemical change, but
appear to be retained on the surface of the pores of the charcoal by
powerful cohesion, and probably in the liquid form, as it is such
gases as may be rendered liquid by pressure that are absorbed in
la.rger quantity.
The number expressing the atomic weight of carbon is not at
present exactly known. By Drs. Prout and Thompson it was fixed
at seventy-five upon the oxygen, and six upon the hydrogen scale;
but the investigations of Berzelius and Dulong induced the majority
of chemists to adopt a higher number, 76'4 or 6-13. The latest
experiments of Dumas and Stass directed to the determination of
this point, induce those eminent chemists to recur to the original
number, 75; while Liebig and Redtenbachar have deduced front
their researches the numbers 75'8. Dr. Clarke, from a re-examination of' Berzelius's results, finds that they give, when corrected
for some minute sources of error, 756; and, until opinion becomes
more unanimous upon this important point, I shall assume as the
number expressing the equivalent of carbon, 7536 upon the oxygen,
and 6-05 upon the hydrogen scale.
If we admitted the truth of Dulong and Petit's law (p. 66, 219),
connecting the specific heat with the atomic weights of bodies, we
should consider the equivalent of carbon to be double that above
given, as Regnault has found the specific heat to be 0'241.  This
idea appears favoured by the fact, that it is doubtful whether there
really exists a combination of carbon containing an odd number of
equivalents, taking the number as 6'05. But the force of this result
is totally obviated by the fact that the specific heat of carbon varies
with its state of aggregation so much, that for poplar charcoal it is
0'296, and for diamond but 0'147; hence we cannot connect these
numbers with the chemical equivalent of the body.
Notwithstanding that carbon is absolutely infusible and fixed, yet,
from the variety of gaseous and volatile compounds into which it
enters, and whose constitution is remarkably illustrated by the application of the theory of volumes, carbon vapour is frequently spoken of by chemists, although its existence is purely hypothetical.
[ have mentioned (p. 215) the difference of opinion as to its specific
P r P




482           ANALYSIS  OF  ORGANIC  BODIES.
gravity, which I assume at 843.  The new results would appear to
show  that it is really but 836'8 upon the one, or 4184 upon the
other view.
General Principles of Organic.Analysis..
Substances which contain much carbon are, in general, easily recognised, by then
being more or les. combustible, and forming carbonic acid when burned, besides
often leaving a carbonaceous residue. Even where the bodies are not inflammable
simply, they defiagrate more or less violently when heated with nitre, and Ibrmn carbonate of potash.
Although it is not within the scope of the present work to embrace the details of
chemical analysis, it would yet be improper to omit a general description of the
methods adopted for the determination of the quantities of carbon, hydrogen, and nitrogen, which enter into the constitution of organic ljodies. The general principle
upon which this process is carried out, consists in supplying oxygen so abundantly
to the organic substance, as that all its carbon shall be converted into carbonic acid,
and all its hydrogen into water, and yet the supply of oxygen shall be so graduated
and the decomposition so regularly progressive, as to admit of the products being
collected with accuracy. The nitrogen is always determined by an independent
operation, in which the other elements are neglected; and, although processes have
been proposed which provided for a direct valuation of the oxygen, it is found in
practice better to obtain its value by subtracting the weight of all the other constituents froin that of the substance employed. For the analysis of an organic substance, there are, therefore, two processes; the first, to determine the carbon and hydrogen., and the second to determine the amount of nitrogen.
The substance generally used to supply oxygen is the black oxide of copper, prepared by gently igniting the nitrate. Sometimes chromate of' lead is employed, particularlv for bodies rich in chlorine. W.here the substance to be analyzed burns
with difficulty, it is often necessary, in order to be certain of the complete combustion of the carbon, to pass a stream of oxygen gas over it at the termination of the
process.,
A straight tube of hard Bohemian glass, of about sixteen inches long, and from
one third to half an inch!i.'*         in diameter, is to be drawn
out at one end to a point,! ~ -~ ~'~ — — _~~-~~-~~-~ _='   which is to be sealed and
turned up,' as in the figare. Some oxide of copper (or chromate of lead, as the case may be) is to be then
poured in so as to occupy about two inches of the tube next the bottom. As much
axide of copper as will occupy about six inches of the tube is to be then intimately
mixed with the substance to be analyzed, if it be solid, by rubbing in a mortar, and
this mixture then introduced. The mortar is next to be- rinsed out with as much oxide of copper as will fill two or three inches; and, finally, pure oxide of copper is to
be placed for about three inches in front of all. The whole materials thus introduced will occupy about fourteen inches of the tube, when it is shaken down by tapping it, nearly horizontally on the edge of a table, so as to leave, as in the figure,
where the dotted lines mark the spaces of the several portions, a free passage above
the materials from end to end of the tube. In these operations the greatest care
must be taken to avoid all access of moisture; the tube,.the mortar, and the substance must be made absolutely dry, and the oxide of copper,. being powerfully hygroscopic, should be ignited before each operation, and allowed to cool under a bell
glass with a capsule of oil of vitriol, or by being placed while very hot in a long dry
tube,'which is then to be corked completely tight. After the substance and oxide of
copper have been placed in the tube, it is generally necessary to remove even the traces of damp which might have been absorbed by exposure to the air during the mixing in the mortar. This is done by means of a small exhausting syringe, which is
attached to the combustion tube by a cork, a tube containing fused chloride of ca..
ciumn being interposed. The combustion tube is bedded in warm sand, and by
means of the syringe, the damp air it contains is withdrawn, and replaced.by a:.r,
which; passing over the chloride of calcium, becomes completely dry.'After a few
repetitions of this process, all moisture is removed, and the combustion tube is
ready to be attached to the other parts of the apparatus.
These are, 1st, a tube of the form repr.
sented in the figure, into which. a little cot-'a               b     ton wool is dropped at a, and it is then filled




ANALYSIS: OF ORGANIC  BODIES.                               483
with recently-fused chloride of calcium in fragments of the size of a split pea. At b a
little cotton wool is also placed, and a sm;.ll tube is connected with it by a cork.
To its smallel end a cork is adapted, which accurately fits the end of the combustion tube, and which has been carefully dried. This apparatus (but without the last
cork) is carefully weighed before the operation.
The second apparatus is the poleas/l bllb-ltube, the invention of which by Liebig was
the great cause of the rapid progress of organic chemistty within the
last few years, as it facilitated the analysis of organic bodies in a remarkable degree. It consists of a tube on which are blown five
bulbs; the'three interior commnunicating by pretty wide openings,,
but each outer bulb separated from the others by a couple of inches 
of tube. The proportions of the respective bulbs may be collected
from the figure, which represents also the form into which the tube
is bent. The three central bulbs are to be nearly filled with a strong
solution of caustic potash (sp. gr. 125), and the apparatus attached to the small
tube, b, of the wiialce' tube by a caoutchouc connector tied very carefully on. It is to
be allowed to incline, at the angle represented in the next figure, so that the carbonic
acid gas, when passing through it, shall bubble from bulb to bulb, without any danger ot' expelling any portion of the liquor.
The combustion tube is to be placed in a sheet iron furnace, the form and size of
which may be collected from the figure, its open end so far projecting (1- inches) as
that the cork by which the water tube is attached shall not be in any danger of being charred, but yet shall be so hot that no water can condense upon it. The jointings being f/ound to be completely tight, and the water tube and potash bulbs being
attached, and arranged as in the figure, the analysis may be proceeded with. Some
ignited charcoal is to be placed round the first three inches of the tube, and
when the pure oxide of copper is completely red-hot, the next portion, which, having
rinsed out the mortar, contains some traces of the organic substance, is to be similarly ignited. The hydrogen of the substance reduces the oxide of copper, and forms
water, which is collected by the chloride of calcium in the water tube, and the carbon, also r.ducing the oxide of copper, is converted into carbonic acid, which, being
dried in passing over the chloride of calcium, is totally absorbed by the potash in the
bulbs. By the addition of burning charcoal, the combustion of the organic matter
is made to progress down the tube, the operator being directed in his proceedings by
the rate at Mwhich the evolution of carbonic acid and its absorption proceed, until he
arrives within two inches of the end of the tube. He then stops until he has made
the point and the pure oxide of copper near it red-hot, and then, closes in the charcoal on the remaining space.
The combustion being, thus completed, the tube remains, however, occupied by a
mixture of watery vapour and carbonic acid, which must not be lost; for this the
point of the tube serves. It is broken with a nippers, and then a current of air is
gently sucked, by means of a tube fitted to the potash bulb-tube, through the whole
apparatus; this carries the water vapour to the water tube, and the carbonic acid to
the potash, so that all the products of the combustion are obtained. The apparatus
is then taken asunder, and the potash tube and water tube weighed; the increase of
weight gives, of course, the quantities of carbonic acid and of water collected, and
hence, by simple calculation, the proportions of carbon and hydrogen contained in
the quantity of substance that had been operated on.
If ihe substance had been one very difficult to burn, and hence requiring oxygen
to finish its combustion, the tube is not drawn out at the end, but widened a little, so
as to form a small bulb, in which some chlorate of potash is placed. At the end of
the process, this being heated evolves oxygen, which not only burns any traces of car-.
bon that might remain, but serves also to carry the carbonic acid and vapour fully
into the water tube. and bulbs.
There are a variety of circumstances to be attended to in this operation, in order to
obtain the high degree of accuracy which alone confers value on numerical results.
These can be learned ony in the laboratory, and not even fromn the most detailed l!e



484           DE-TERMINATION  OF  NITROGEN.
scription. Mly object is merely to afford an idea of the general principles of the
metlhod.
If the substance to be analyzed be liquid and vol_3    _ atile, it is introduced into small bulbs of the size of
the figure, by the method given in page 11. There
are generally two of these bulbs, one placed about'two and the other about six inches from the sealed end of the tube, as shown in the
figure; the little stem is broken
across in the act of introducing, ( {,,  = =,  a them, so that the liquid may
easily flow out, when, by the
approach of a piece of red-hot charcoal, it is gently heated, so as to form a vapour.
Tihe peculiar precautioils necessary in the management of the analysis of such bodies, and tile methods adopted for non-volatile liquids and other bodies of peculiar
properties, can only be learned by experience, and do not fall within my purpose to
describe.
To determine the nitrogen of an organic substance, a long combustion tube is
taken (2 or 2'5 feet), sealed at one end, but not drawn out, as in the figure. Next
the sealed end is placed carbonate of copper for a space of six or eight inches, and
then the pure oxide of copper, the mixtuxe, the rinsing of the mortar, and again,
pure oxide, occupying fourteen or fifteen inches, exactly as in the former case; in
front of all, live or six inches are occupied by clean metallic copper in a finely-divided state, either as reduced by hydrogen from the oxide, or as very thin turnings.
These divisions and the general form of the tube are given by the figure.  To the
combustion tube there is fitted by a tight cork a quill tube, which is in connexion
on the one hand with an exhausting syringe, and then, by a vertical tube more than
thirty inches long, passes to the mercurial pneumatic trough. All the joinings being
ibund tight, and the combustion tube arranged in the furnace, red-hot charcoal is applied to the closed end of the tube, where it disengages carbonic acid from the carbonate of copper, which, sweeping through the apparatus, expels the atmospheric air.
To render this the more effectual, the whole apparatus is exhausted by the syringe,
and again filled Kwith carbonic acid, and this is continued until the bubbles of gas
which come over are perfectly absorbed by solution of potash. In this expulsion of
the air of the apparatus, not more than one half of the carbonate of copper should
have!b:eent ised.
The fire is now to be withdrawn from the closed end of the tube, and applied to
the part occupied by the metallic copper. When this is red hot, the combustion is
carried backward, just as in the former example; and when all the substance has
been burned, the coals are applied to the remaining carbonate of copper, which,
evolving carbonic acid, clears out all the nitrogen of the apparatus, just as it had in
the co-mmencement cleared out all the atmospheric air. The mixed gases that are
produced in this operation are received in a bell-glass which contains some strong
solution of potash, by which the carbonic acid is absorbed, and the nitrogen remaining may then he measured. The volume of gas is next to be corrected for temperature and pressure, as directed in p. 57 and 20, and its weight then calculated.
The use of the metallic copper in the front of the mixture requires notice; when
nitrogen passes over red-hot oxide of copper, there is always some nitric oxide formed, which would fllsify the result, as its volume is double that of the nitrogen it contains; but nitric oxide is completely decomposed by red-hot metallic copper, pure
nitrogen being evolved, and hence the purity of the resulting gas is secured by this
arrangement.  Indeed, in all combustions of an azotized body, the mixture should
have some bright metallic copper in front of it.
The direct valuation of nitrogen is thus a very delicate operation, and occupies
several hours. If the substance contain a large quantity of nitrogen, its amount
ma.y be indirectly ascertained in a much simpler way. The quantity of carbon in
the substance is first learned by an ordinary analysis, then another combustion tube
is arranged with very clean copper in front; but, in place of adapting the water tube
and bulb:, the water is taken no count of, and the gases evolved are collected in
narrow graduated tubes, over mercury. In order to clear out the air from the tube,
some of the mixture next the sealed end is first ignited, and the gas allowed to escape, the tubes being filled from the products of the subsequent periods of combustion. In this case no weights need be attended to, as it is only the analysis of the
gas in the t:L.bes that is required for the result. The volume- of gas in a tube being




CARBONIC  ACID) ITS  PREPARATION, ETC. 483
marked, some solution of potash is introduced and agitated in it. The carbonic
acid is absorbed, and the nitrogen remains, the volume of' which is read off, taking
care that the level of the mlercurv is the same inside as outside the tube. The
relative volumes of the carbonic acid and nitrogen gases are thus fbund; and as an
equal volume represents an atom for each, the relative number of atoms of carblon
and nitrogen is thus determined; and as the total quantity of carbon is known by a
previous experiment, the total quantity of nitrogen may be calculated. When the
relation of the number of atoms of carbon to those of' nitrogen is simple, as occurs
in cyanosen and oxamide, C2N., mellon, C3N2, caffeine andtaurine, C4N., this method
gives very accurate results.
Where the organic substance contains chlorine, sulphur, arsenic, &c., it is to be
destroyed by nitric acid, or by ignition with potash or lime, and the inorganic constituents then determined in the ordinary way. In organic salts the metallic basis
is determined by igniting the substance, burning away the organic element, and determining the'quantity of inorganic base by whatever method is best suited to its
individual nature.
Carbon combines with oxygen in several proportions, of which
three, those in which it forms the carbonic oxide, and the carbonic
and oxalic acids, are the most important, and deserve the most detailed description.
Of Carbonic d./cid.  Eq. 275-6 or 22'05.
Carbonic acid exists in the atmosphere as a product of combustion  and of the respiration of animals.  Combined with metallic
oxides, it forms the numerous class of native earthy and metallic
carbonates, of which the- carbonate of lime is much the most important.  It is a result, also, of the slow decomposition of most vegetable substances, and is evolved in great quantity from  the ground
in volcanic countries. In the fermentation of sugar it is produced
in abundance along with alcohol.  For the purposes of the chemist,
it is generally prepared by decomposing marble or cale spar by
means of any stronger acid; from its cheapness, and the solubility
of the residual salt, muriatic is generally employed. Some fragments of white marble being placed in a wide-necked bottle, the
acid, diluted with its own volume of water, is poured in by a funnel
tube, as in the figure, p. 247, and the gas which is evolved is conducted by the bent tube, to be made use of as required. The reaction consists in H.CI. and Ca.O.. C.02 producing H.O. and Ca.CI.,
which remains in the bottle, while C.02 is driven off.  Carbonic acid
being dissolved by water, and it being generally required in larger
quantity than it is convenient to collect over mercury, we take advantage of the density of the gas to collect it in dry jars, as described and figured for chlorine in p. 301. The jar is known to be
full when a lighted taper, applied near the mouth, is instantly extinguished.
The properties of carbonic acid are very remarkable; it is perfectly colourless and invisible; it is irrespirable, producing, when
an attempt is mnade to breathe it, violent spasms of the glottis.  If
it be inspired, mixed with air, even in the proportion of 1 to 10, it
gradually produces stupor and death, acting as a narcotic poison.
Its specific gravity is 1'521.  It hence, when disengaged in large
quantities, whether by natural operations or in processes of manufacture, accumulates in all cavities within its reach, and may cause
fatal accidents to animals who enter unadvisedly. Thus workmen




486      LI-QUID  AND  SOLID  CARBONIC  ACID.
engaged in cleaning out dry wells or vaults, or the large vats from
which fermenting liquors have been run ofW, should carefully observe whether a candle can remain for some time burning brightly
at the bottom. "In volcanic countries, caverns are frequently occupied to the level of their surface by this gas, exhaled from  the
ground; and an experiment often tried, to amuse the traveller, consists in walking into such a cavern with a dog, which, holding the
head near the floor, is almost instantly asphixiated by the layer of
carbonic acid, while the men, whose heads are above its level,
breathe pure air; the- dog, on being throw.n immediately into a
neighbouring' pond, recovers from his stupor. Carbonic acid does
not support combustion.'A taper plbnged into a jar full of the gas
is instantly extinguished, and the high specific gravity of the gas
may be well shown by placing a lighted taper at the bottom of a jar:containing air, and taking in the hand another jar containing carbonic acid; on inclining this jar, the heavy gas pours over the edge,
nearly as water would do, into that in which the taper is placed,
and, falling to the bottom, extinguishes it.
Water dissolves its own volume of carbonic acid gas, forming a
solution of an agreeably acidulous taste, which sparkles when agitated; it colours blue litmus paper of a wine-red, which disappears
on exposure to the air or by heat. By means of pressure, water
can be made to absorb a large quantity of carbonic acid, which escapes with effervescence when the pressure is removed, and is thus
the basis of -a variety of agreeable' effervescing beverages. Solution
of carbonic acid in water precipitates solutions of lime and barytes
white, forming carbonates, which redissolve in an excess of the carbonic acid.
Under a pressure of thirty-six atmospheres, carbonic acid may
be liquefied. It then' forms a' colourless, exceedingly mobile liquid,
of specific gravity 0O'83 at 32-, which is remarkable for its excesssive expansibility by heat, it having four times that of air, or nearly
one per cent. for each degree of Fahrenheit. When the pressure
is suddenly removed from this liquiid acid, it gasefies with such rapidity that, one portion:absorbing heat from the other, this latter is'rendered solid (see page 86).  Solid carbonic acid can thuis be obtained in large'quantity by the apparatus contrived by Thilorier.
It is a white body, in' filamentous masses, like asbestus; it evaporates
but slowly; it is very soluble in alcohol and ether; the ethereal solution produces by its evaporation the most intense cold'known, estimated at -180 degrees of Fahrenheit.
The composition of carbonic acid may be determined
by very simple experiments. If into a bottle of pure ox- ygen gas we insert a little bit of charcoal, ignited at one
point, attlihe end of the wire a, as ii the figure, it burns
with vivid scintillations, and'the oxygen is all converted
into carbonic acid.  The stopper of the bottle, through
which the wire passes, being' perfectly tight, it will be
found' that the' volume'of the gas, when cold, has not
sensibly altered, and thus that carbonic acid' contains its
owvn volume of oxygen'. It ctnsists, therefore, of




MANUFACTURE  OF  PO T ASHES.                     487
Two volumes of oxygen. 11026 X2 —2205'2
One volume of carbon vapour.... 843'0
Forming two volumes of carbonic acid 2. 3048'2
Of which one volume weighs, therefore, — 15241
The corrected specific gravity of carbonic acid, 15211, indicates
that the theoretical density of carbon vapour should rather be taken
as S36 than 843.
To demonstrate the existence of carbon in carbonic acid gas, it
is sufficient to heat to dull redness, in a current of the gas, a sinall
globule of potassium. The metal takes fire, burning with a brilliant
violet flame, and forms potash, while carbon is abundantly deposited as a brilliant jet-black film on the interior of the tube.
Carbonic acid combines with the bases, forming a very important
class of salts, the carbonates.  It forms neutral, basic, and acid salts,
which last are really double salts, containing carbonate of water,
which, however, exists only in combination, as the carbonic acid
does not combine with water directly in definite proportions. All
salts of carbonic acid are known, by yielding, when acted on by
muriatic acid in the cold, the gas possessing the properties now
described.
Carbonate of Potash.- K.O.  C.O.- Eq. 866.3 or 694.  This salt,
which is the great source of all other combinations of this alkali, is
obtained for the purposes of commerce from the ashes of plants
growing at a distance from the sea.  The vegetable juices contain
potash, combined with various acids, as the nitric, oxalic, acetic,
rnalic, &c., which, by the burning of the wood, are converted into
carbonates.  The produce differs according to the kind of wood,
and with the season.  The softer and more juicy the plants are, the
more potash they yield.  Plants of the natural families composite
and cruciferm are the richest; the grasses rank next; and among
the woods, the leaves yield more than the small branches, and these,
again, more than the stems. In countries where there are large
forests, as America and Russia, the small wood is burned, and the
ashes collected; these are boiled with water in large iron pans or
pots, from whence the name potash is derived.  By this means, a
large quantity of insoluble salts is separated, and the carbonate of
potash, which dissolves, is obtained in a purer form by evaporation
to dryness. It then constitutes the pearlashes, or refined potashes
of commerce.` Even these still retain much silica, sulphate of potash,
and chloride of potassium, so that the best American pearlashes seldom contain more than eighty-five per cent., and Russian potash
often not sixty per cent. of true carbonate of potash.
The purification of pearlashes being difficult, carbonate of potash is best prepared for chemical purposes by
calcining cream of tartar; the tartaric acid which it contains is decomposed, and carbonic acid formed, which  /
combines with the potash; the mass is digested with
water, filteredito-separate the excess of charcoal, and
evaporated to dryness in a clean iron vessel. A white
granular mass is obtained, the salt of tartar of the older
pharmacopmias.  It is very deliquescent, soluble in half
its weight of water, and crystallizes with two atoms of water in




488              CARBONATE  OF  SODA.
oblique rhombic octohedrons, a, a', a", a"', as in the figure (R.O.
C.0,+ 2 Aq.). It reacts strongly alkaline. It is almost insoluble in
alcohol, and when added to weak spirit, combines with the excess
of water, forming a heavy fluid, which remains separated from the
lighter and stronger alcohol above.
As it is only the carbonate of potash that constitutes the value of
pearlashes in the manufactures to which it is applied, it is important
to be able to determine, by a single and simple operation, the relative
worth of commercial samples. This process is termed alkalimetry.
The best method of performing it will be described under the head
of " Carbonate of Soda."
Bicarbonate of Potashl, K.O.. C.02 + H.O.. C.02, is formed by passing
a current of carbonic acid gas through a saturated
solution of the neutral carbonate, the temperature
of which should not be above 100'. On cooling,
it crystallizes in right rhombic prisms of eight
sides, as in the figure. It dissolves in four parts
of cold water, and in much less when hot. If its
--    solution be boiled, it abandons its second atom of
carbonic acid, and becomes neutral carbonate. Its
reaction on vegetable colours is feebly alkaline.
Carbonate of Soda-Nat.O.  C.02+ 10 Aq.; Eq. 667'3+ 1125 or
53'47+ 90- is manufactured upon a very large scale, for the purposes
of commerce, from common salt, which must first be converted into
sulphate of soda in the manner described in page 427.
The dry sulphate of soda is to be mixed with its own weight of
limestone or chalk, and half its weight of small coal, and the mixture being reduced to fine powder, is introduced into a reverberatory furnace, such as is figured in page 333, in charges of about 2 cwt.
each. After being exposed to a full red heat for about an hour, on
the floor of the furnace, the mass fuses, and being well stirred for a
few minutes, is raked off through the opening in the side, and re
ceived in metal boxes. It forms a black mass, which is known it,
commerce as black-ash, or British barilla. The theory of this process
is very remarkable; the sulphate of soda being melted in contact
with the coally matter, is deoxidized, its oxygen being carried off by
the carbon, and sulphuret of sodium remaining. This is immediately
decomposed by the carbonate of lime, sulphuret of calcium and
carbonate of soda being produced. S.03. Na.O. and 2C. form
2C.,2 and Na.S., which, with Ca.O.. C.O,, gives Ca.S. and Na.O.. C.
02. As, however, much of the carbonic acid of the chalk is expelled
by the heat, a certain quantity of the soda remains caustic in the
produce, and also some sulphuret of sodium undecomposed. This
black-ash generally contains about 22 per cent. of real alkali. To
obtain the soda under a purer form, the masses of black-ash are
broken up, and digested in warm water until all soluble matter is
extracted. The residue consists of sulphuret of calcium and the
excess of coally matter. The liquor is then evaporated to dryness,
and the saline mass obtained is calcined in a reverberatory furnace
with one fourth of its weight of sawdust, in order to convert all of
the alkali into carbonate, and to burn out some traces of sulphur
which still renmain; on being then redissolved in water, and the clear




METHOD  OF  ALKALIMETRY.                             489
solution dried down, it constitutes white-ash, or soda-ash of the best
quality, containing from 45 to 50 per cent. of real alkali.
For the preparation of the crystallized carbonate, the soda-ash is
dissolved in boiling water, and the solution being evaporated to a
pellicle, is left to crystallize for some days.  The mother liquor,
when drained off the crystals, yields, when dried down, an inferior
soda-ash, which is, however, applied to many manufacturing uses.
The pure carbonate of soda crystallizes in flat. oblique rhomboidal
prisms, as in the figure, which contain
ten atoms of water, Na.. C.O,+ 10 Aq.
In a dry atmosphere, they lose by effloreseence all their water, and fall into a
white powder. It dissolves in five parts
of cold, and in less than one of boiling water.  By a gentle heat,
the salt undergoes aqueous fusion, and when dried, gives a white
powder, soda siccata.  By a strong heat, the carbonate of soda melts,
but is not otherwise affected.
Prior to the invention of the soda process described above, the
carbonate of soda was obtained from the ashes of marine plants, as
the salsola, and various fuci, which were burned in large quantities
on the west coast of Ireland, in the Orkneys, and on the coasts of
France and Spain. The saline products thus obtained were known
in commerce as kelp, barilla, varec; but these sources of alkali may
now be considered as extinct. Graham states, on the authority of
Mr. Muspratt, that in 1838 there were manufactured from  common
salt 50,000 tons of soda-ash and 20,000 tons of crystallized carbonate, and the manufacture is continually on the increase.
To the practical chemist and the manufacturer, it is important to be able to determine, by a rapid and easily executed process, the real quantity of alkali present in
any sample of pearlashes or soda-ash that may be in the market. All such processes depend on measuring the quantity of sulphuric acid necessary to produce a
neutral salt with a certain weight of the sample; but in the management of the details considerable difference may exist. A mode which I have found to be very accurate, and easily executed even by ordinary persons, consists in preparing beforehand a stock of a dilute sulphuric acid, of sp. gr. 106G8 at a temperature of 600. This
acid may be formed by mixing one ounce of the strongest oil of vitriol with nine
ounces of water; but its sp. gr. should be verified by trial beibre being used.
One hundred grains of the sample to be tried are then to be powdered and stirred
up in a capsule with an ounce of water. A glass jar about a fobot high and an inch
wide, provided with a lip to pour from and a steady foot, and graduated into 400
parts, of which each part indicates five grains of the standard acid, is to be filled
with the acid up to the 400th mark, and then, by pouring very cautiously from the
lip a few drops at a time, the alkaline liquor in the capsule is to be exactly neutralized. A little bit of litmus paper may be left in it, and stirred about well after each
addition of a few drops of acid. A drop of acid in excess reddens the litmus paper
permanently; and as this does not injure the result sensibly, it may be done in order
to secure complete neutralization. The graduations of the glass being numbered
from above downward, simple inspection shows how much acid has been employed;
and it is only necessary to multiply the number of divisions by thirty-one if the alkali be soda, or forty-seven if the alkali be potash, and divide in each case by 100,
to obtain the quantity of real alkali present in the 100 grains examined.
The principle of this method is, that 100 grains of the standard acid contain eight
grains of dry sulphuric acid, and hence 100 measures contain forty grains, which
number being that of the equivalent of the acid, neutralizes almost exactly thirtyone grains of soda or forty-seven grains of potash, which are the equivalent weights
also. To find, therefore, the quantity of either alkali in a sample neutralized by,
for example, 137 measures of acid, we say,
For potash,  100: 47:: 1307: Xm —T,1x 47'644;
And for soda, 100: 31:: 137: x     7 X 31 425.
QQQ




490               CARBONAT'E  OF  LIME.
A. table may easily be constructed beforehand on those principles, so as to save
even this little calculation.' The greatest amount of error at all likely to occur in
this process is one division of acid in excess. The difference made by this, however,
does not influence the result for commercial purposes; thus, in the examples above
taken; if the quantity of acid had been measured wrongly at 138, the indications
would be, for potash, 64'9, and for soda, 42,8; the error in no case exceeding half' a
part per cent., and being exactly connterbalanced by taking the numbers 31 and 47
instead of the correct equivalents, 31,3 and 47-3.
Bicarbonate of Soda, H.O.. C.O2 + Na.0. C.02, is formed by passing a current of carbonic acid gas through a cold solution of carbonate; the new salt precipitates in small opaque crystals, having the
appearance of starch.  It requires fifteen parts of cold water for its
solution; it has an alkaline reaction, but is not disagreeable to the
taste.
Sesquicarbonate of Soda occurs native on the banks of certain lakes
in northern Africa, whence it is exported under the name of trona.
Its formula is 2Na.0.. C.2+S3C.0,- 4H.O.  It cannot be formed
at will.
Carbonate of Barytes.-Ba.O.. C.O.  This salt exists native, crystallized in oblique rhombic prisms; it is insoluble in pure water, but
dissolves in water containing carbonic acid.  It is very poisonous.
It may be prepared artificially by mixing solutions of chloride of
bariuin and carbonate of ammnonia; a white precipitate falls, which,
being well washed and dried, is pure carbonate of barytes.  It is
used in the analysis of minerals containing alkali, and for the preparation of various salts of barytes.  It has been used in the manu
facture of glass.
Carbonate of Strontia resembles perfectly the former.
Carbonate of Lime.-Ca.O.. C.O2.  Eq. 632'5 or 50'7.  The circumstances and forms under which this salt exists in nature have
been so frequently noticed (p. 477, 225), and the molecular constitution and peculiar relations tolight of its crystals so fully described,
that it is not necessary to enter upon its history here farther.  It
may be prepared pure by:decomposing chloride of calcium by means
of carbonate of ammonia; it forms then a white powder insoluble in'pure water, but dissolving in water containing carbonic acid.  This
is not due to the formation of a bicarbonate of lime, but owing to a
specific solvent power which a solution of carbonic acid in water
has on many bodies, as silica, phosphate of lime, &c., which-are insoluble in pure water.  It is thus that carbonate of lime is held dissolved in most waters, and is deposited as a crust on the interior
of any vessels in: which such water may be boiled.  By the gradual
dissipation of the carbonic acid on exposure to: the air, the carbonate
of lime may be slowly deposited, and then crystallizes; thus are
formed the remarkable stalactites, &c.:, of limestone caverns.
Carbonate of JITagnesia. —Mg.O..C.O2.  This salt exists anhydrous
in nature, crystallized in rhombohedrons like cale spar.
By dissolving magnesia in water by a stream. of carbonic acid, it may-be formed, and is gradually deposited~in rhomboidal prisms ofjsix or eight sides, as m, i,
a, in the figure, which contain three atoms of water.  It
is this salt, Mg.O.. C.0,2+3 Aq., which exists in Murray's solution of magnesia.  When acted on by pure hot
water, this salt is decomposed, carbonic acid escaping,




CARBONATE  OF IRONS  ETC.                    491
andbasic carbonate of magnesia being produced. It is this basic carbonate w'hi(ch constitutes th? magnesia alba, or common carbonate of
magnesia of the shops. It is prepared by mixing boiling solutions
of sulphate of magnesia and carbonate of soda, leaving the former
slightly in excess.  The precipitate is very light and bulky, and almost totally insoluble in water.  One' fourth of the carbonic acid is
given off in this reaction, and the precipitate is found to be a compound of carbonate and of hydrate of magnesia, Mg.0.. H.0. —-3
(Mg.O.. C.02. H.O.), or 4Mg.0.-.+3C.02+4 Aq.
The nature of dolomite or magnesian limestone has been already
sufficiently noticed (p. 348).
Carbonate of.lianganese, Mn.O.. C.0O, is a white powder formed
by double decomposition, and decomposed by a red heat.
Protocarbonate of Iron, Fe.O.. C.O, exists native in rhombs iso
morphous with calc spar.  It may be prepared by decomposing
protosulphate of: iron by carbonate of soda; it forms a white precipitate, which, by exposure to the air, rapidly absorbs oxygen and
gives out carbonic acid, becoming green, and ultimately red, being
then mere peroxide of iron.  The carbonate of iron can therefore
scarcely be obtained pure; but by mixingf tile fresh precipitate with
sugar, and evaporating to dryness with constant agitation, a quantity
of the carbonate remains undecomposed, being protected from the
air by a varnish of sugar on its particles, and thus constitutes the
carbonas ferri cum saccharo of pharmacy.  The carbonate of iron is
soluble in water containing carbonic acid, and exists thus dissolved
in chalybeate spas.
Whien solutions of sulphate of zinc and carbonate of soda are
mixed together, a basic carbonate of Zinc is formed; consisting of 2
(Zn.0.. C.O0,)+3Zn.0.. H.O. if the solutions were warm, but of Zn.
0.. C.O2+2Zn.0. H.O. if cold; carbonic acid gas is given off in
both cases.
There are two carbonates of Copper, both basic; the green carbonate exists native (malachite), and is used as a pigment. It may be
formed by mixing solutions of a salt of copper and an alkaline carbonate; the precipitate is at first flocculent, and of a fine pale blue,
but when boiled it becomes dense, granular, and bright green: its
formula is 2Cu.0.+C.O,2+H.O.  The blue carbonate exists also
native (Colfper-azure), but cannot be prepared artificially so as to be
permanent: its formula is 3Cu.0.+ 2C.02+H.O.
Carbonate of Lead, Pb.O.'. C.02, exists native, crystallized in
forms isomorphous with those of the carbonate of barytes, and may
be formed as a finely-crystalline powder by decomposing solution
of nitrate of- lead by carbonate of soda. There are several basic
carbonates of lead, which, in a greater or less degree of mixture,
constitute the White Lead, or Ceruse of commerce, so much used in
painting.  The composition of white lead generally falls between
those given by'the formulae 3Pb.0.+2C.OQ2+H.0. and 4Pb.0+3C.
02+H.O.
For the manufacture of white lead, very thin sheets of the metal
are exposed to the fumes arising from vessels containing weak vinegar, which are kept moderately warm by being imbedded in fermenting tan; the lead, absorbing oxygen from  the air, combines




492                 CARBONIC  OXIDE.
with the acetic acid, forming a basic acetate of lead, which is de.
composed by the carbonic acid of the surrounding air, basic carbon.
ate of lead being produced, and neutral acetate of lead remaining;
this, under the action of the air, tales up a new quantity of lead,
and the same decomposition is renewed, a minute quantity of acetic acid thus serving to prod'uce a very large quantity of ceruse.
This process has lately been much improved by exposing litharge,
finely ground and mixed with one per cent. of acetate of lead, to a
stream of carbonic acid, generally derived from the fermenting vats
of a brewery; the one portion of neutral acetate successively unites
Iwith all the litharge to form basic acetate, the successive portions
of which are decomposed by the carbonic acid, white lead being
formed, and the original quantity of neutral acetate remaining uncombined at the end.
The carbonates of the other metals are unimportant.
Carbon combines with the metals to form carburets, of which the
best known are those of iron and silver; the former has been fully
noticed in the description of cast-iron and steel (p. 360), and the
carburet of silver is a gray powder, which remains when certain
silver salts of organic acids, as the citrate and tartrate, are imperfectly burned away.
Carbonic Oxide.-C.O.  s/tomic Weight 14-05.
If carbonic acid gas be passed through a tube containing red-hot
charcoal, it takes up as much more carbon as it already contained,
and forms carbonic oxide; its volume being thereby doubled. The
gas may also be prepared by heating to redness, in an iron retort,
a mixture of charcoal and chalk, when the carbonic acid evolved
from the latter combines with the excess of carbon, and forms car.
bonic oxide; in place of charcoal, iron filings or zinc may be used;
the metal, in this case, takes half of the oxygen from the carbonic
acid, C.O0 and Zn. giving Zn.O. and C.O.
A very simple and elegant way of obtaining this gas consists in
warming strong oil of vitriol with crystals of oxalic acid, in a flask,
a b, from which a tube,f, passes to a bottle containing solution of
caustic potash, a, as in the figure;
from  this another tube conducts to
the pneumatic trough. The oxalic
acid, C203+ H.O., yields up its basic
water to the sulphuric acid, and, as
the oxalic acid cannot exist except
o I        s in combination with some base, it is
9                      resolved in carbonic oxide and carbonic acid (C203- C.0. + C.O,), which
are evolved as gases, mixed in equal
volumes; in bubbling through the
bottle containing potash, the carbonic acid is completely absorbed,
and the pure carbonic oxide may be collected over water.
It is a colourless, inodorous gas, and has no action on vegetable
colours; it extinguishes a taper, but is combustible, and, burning
with a pale blue flame, forms carbonic acid. It is this gas which
produces, on the top of a clear coke fire, a blue flame, which ap.




MANUFACTURE OF  OXALIC ACID.                    493
pears purple when seen with the red background of the glowing
cinders. It contains half its volume of oxygen; its specific gravity
is 972'8. Carbonic oxide appears to enter into union with a great
variety of bodies, and to act in such compounds as a compound
radical.
Oxalic.Acid.-C203 or 2(CO.)+O. Eq. 451'2 or 36'1.
Oxalic acid is one of the most important organic bodies. It is
found combined with potash, forming the Salt of Sorrel, in several
plants of the genera oxalis and rumex, and combined with lime in
the roots of rhubarb, and in a variety of lichens. It was formerly
extracted principally from the oxalis acetosella, from whence its
name is derived, but is now manufactured in larger quantities artificially. It is generally a product of the oxidation of vegetable substances by nitric acid, on which fact its mode of preparation is
founded. The substances employed are usually starch or sugar, a
quantity of which is placed in an earthen pipkin, of which a great
number are arranged in a shallow vessel containing warm water;
about four parts of nitric acid, specific gravity 142, are poured into
each pipkin.  The starch is rapidly oxidized, and nitrous umnes given o ffabundantly; when the action has become slow, one part more
of acid is to be added, and the heat increased. The liquors so obtained, are mixed, evaporated to a pellicle, and set aside to crystallize, and the crystals are purified by re-solution and crystallization.
From the mother liquors new quantities of oxalic acid may be obtained by heating with more nitric acid.
If we consider the sugar in its dryest form as being C,2H,0,, the
action of the nitric acid should consist in first removing the nine
equivalents of hydrogen, and substituting for them nine equivalents
of oxygen; thus C:,E1IO, and 6N.0,, should give 6(CO,) with 91H.O.
and  N.0,,. But the action is not so simple, as other products, especially the Saccharic icid, are at the same time formed. By means
of permanganate of potash, however, the carbon of sugar may be
very elegantly and directly changed into oxalic acid, CQH:O, and
6(AMn20;+K.0.) producing 12(M1n.02) with 9H.0. and 6(CO03+K.
0.), the oxalic acid formed exactly neutralizing the potash of the
manganic salt employed.
The oxalic acid crystallizes from its solution in oblique rhombic
prisms, of which those planes marked i c are prima 
ry, and af secondary: the summit is often dihedral,   __, \
in which case the plane a, and that vertically oppo-    c
site to it, are absent.  These crystals contain three c\
atomns of water, of which one is basic: CO,+H.O.
+2 Aq.  When warmed, they give off 2 Aq., and the hydrate of
oxalic acid remains as a white powder, which melts at 350', and
when heated farther sublimes, a portion being, however, decomnposed; the products of the reaction of oil of vitriol on oxalic acid have
been already noticed (p. 492). Oxalic acid is converted into carbonic acid by contact with many peroxides, as the peroxide of manganese, by which means the technical value of manganese ores may
be determtwined (see p. 355). By contact with a great excess of hot
nitric acid or of chlorine, it is also converted into carbonic acid.




494              OXALAT-ES OF POTASH.
The acidity of oxalic acid is very, great;: a grain of it dissolved
in 30,000 grains of water will still affect litmus paper. It neutralizes the alkalies perfectly, and forms with-them two series of acid
salts. In the neutral oxalates, the oxygen of the acid to that of the
base is 3: 1. By heat, those of the metals proper are generally converted into carbonic acid and metal, C,203+M.0. giving C204and MI.
Those of the earths and alkalies evolve carbonic oxide, and produce
a carbonate, C20q,+M.O. giving, C.O. and C.O,+M.O.  The formner
action is usefully applied.to obtain cobalt and nickel. in the metallic state.
Oxalic acid is detected easily by its strong acidity, and its not
leaving a carbonaceous residue when heated. Its solution gives,
with lime-water, a precipitate which is insoluble in an excess of oxalic acid, or of any organic acid. It precipitates, also, the solutions of barytes.and lead. It acts violently'on animals as a poison;
for an antidote magnesia is the best, but chalk or whiting is the most
readily proc ured.
Several of the oxalates deserve special. notice.  There are three
oxalates of Potash, remarkable.as being the bodies by which Wollaston satisfied himself of the truth of. the law of mnultiple combination,
p. 208, their proportions of acid being, as 1: 2: 4.
The neutral Oxalate of Potash, K.O.. C203+Aq., may be formed
by acting on sugar by permanganate of potash, or by heating any
fixed organic matter, as. sawdust or paper, with an excess of potash,
below redness. It is more simply produced by neutralizing oxalic
acid, or the following salt, with carbonate of potash.; it crystallizes
in rhombic prisms, of a bitter taste, which dissolve in three parts
of water, and are insoluble in alcohol.
Binoxalate of Potash, K.O.. 0C203+-H.O.,  203+2 Aq., exists naturally in the various kinds of sorrel, from whence it was originally.
extracted under. the name of Salt of Sorrel, but is now artificially
made. One part of oxalic acid is exactly neutralized by potash,
and then exactly as much more oxalic acid is added to the% solution,
from whichi  by evaporation and cooling, the salt crystallizes in oblique rhornbic prisms, which are soluble in forty parts of cold and
in six pnarts of boiling ivater. Its taste is strongly acid and saline,
and it is poisonous, though less so than the acid uncombined.
When heated, the salt is decomposed, evolving carbonic acid and
carbonic oxide, and leaving a residue of carbonate of potash, which
should be scarcely coloured if the salt were pure.
Quadroxalate of Potashz, K.O.. C0,+3H O.. C203-+4 Aq., is formed by neutralizing one part of oxalic acid by potash, and adding to
the solution three times as much oxalic acid more. It may also be
prepared by dissolving the binoxalate in muriatic acid, which takes
half of the alkali, and the quadroxalate crystallizes out.  This and
the last salt are indiscriminately sold in commerce as salt of sorrel, and also often as Salt of iemzons, for removing iron moulds and
stains of ink, which they do by forming, with the peroxide of iron,
a soluble double salt.
There is but one oxalate of Soda; it is not important.
Oxalafe of Lime, Ca.O.. CO,3+2 Aq., exists abundantly in nature,
forming the hard earthy basis of many lichens, and may be prepared




DOUBLE  OXALATE-S  OF  POTA SII  ETC.    495
oy mixing solutions of oxalate of ammonia and of any soluble salt
of lime.  It forms a white flocculent precipitate,. which, by boiling,
becomes heavy and granular.  It is totally insoluble in water, and
is hence used as a means of removing lime from solutions, and determining its quantity.  It dissolves in the mineral acids, but is insoluble in all organic acids, even the acetic. When heated, it leaves
a perfectly white residue of carbonate. of lime.
The remaining simple oxalates are not important, except the oxalate of Silver, which is a white powder, prepared by double decome
position, and remarkable for being decomposed by a moderate heat,
with a slight explosion, into carbonic acid and metallic silver.
There are several double oxalates of interest.
Oxalate of Potash an/d Peroxide of Iron, (Fes03+3C203)+3K.O.. C203+6 Aq.,
is prepared by dissolving peroxide of iron in solution of binoxalate of potash; it
crystallizes in fine grass-green tables, which are permanent in the air. There exists
a similar salt containing soda.
Oxalate of Potash andl Cirome, (Cr203+3C203)+3K.O.. C203+6 Aq., is prepared.
by dissolving together in hot water one part of bichromate of potash, two of crystallized oxalic acid, and two of binoxalate of potash. A copious evolution of carbonic acid occurs, the chromic acid being deprived of half its oxygen by a part of
the oxalic acid, with the remainder of which the oxide of chrome unites. The liquor assumes a fine purple colour, and on cooling, yields prisms of a splendid blue
colour, so deep as to be perfectly opaque, unless the crystals be very thin.
Oaltcate of Copper a.7d Potash, K.O..  C203+Cu.O.. C0+'2 Aq., is formed by digesting a solution of binoxalate of potash on oxide of copper, It crystallizes in fine
blue prisms. It may be obtained with 4 Aq.
Chloro-carbonic  dcid. —C.O. t C1.  Eq. 619'1. or 495.  When
equal volumes of carbonic oxide and chlqrine are exposed for some
hours to the light, they gradually combine, forming a colourless gas,
which was termed by J. Davy, its discoverer, Phosgene Gas.- Its
odour is very irritating; the volume being diminished to one half,
its density is 3412.  It is decomposed by water, carbonic and muriatic acids being formed.  It is decomposed by most metals, which
unite with the chlqrine and liberate carbonic acid. Its action, on
ammonia and on alcohol will be hereafter noticed.
Combination of Carbonic Oxide and Potassium,: and the Products
of its Decomposition.
If potassium be heated in a current of carbonic oxide, the gas is
rapidly absorbed, but no charcoal is separated, as occurs with carbonic acid gas.  The metal is converted into a blackish.-green porous mass.  If the air be admitted to this while hot, it inflames;
when brought into contact with water, it is immediately decomposed,
a peculiar gas beingsgiven of, and a rhodizonate of potash formed.
This oxycarburet of potassium is obtained in quantity in the process
by which potassium  is procured, and constitutes the great obstacle
to obtaining that metal, as described in page 337.  It is also formed,
but very impure, by merely brightly igniting cream  of tartar in a
covered crucible for an hour.  The composition of this body is not
yet known, and hence the mode of its decomposition cannot be expressed in formula.  The gas which it evolves by solution in water
has been examined by Mr. Davy.  It is colourless and inflammable,
and burns more brightly than olefiant gas.. Its characteristic property is to detonate with a brilliant flash, and deposite charcoal when
mixed with chlorine, even in the dark.  He assigns to it the formula
C1H.




496          I S O M E R I C OXIDES  OF  CARB3N.
Rhodizonic./cid.-This is formed when the oxycarburet of potas
sium  is dissolved in cold water.  It is, when dry, isomeric with
carbonic oxide, C,O,, but it appears to be a tribasic hyd'racid, and
its formula CO,,0+11.  Its salts are of a fine scarlet red colour,
whence its name.
Croconic Scid, C0O4, is formed when a solution of rhodizonate of
potash is boiled; an atom of potash becomes free, and croconate
and oxalate of potash are produced; C,07+3K.O. giving K.O. and
C2QO+K.O., with C704'K.O.  The salts of croconic acid are bright
yellow coloured, but do not require other notice.
MJ.ellitic Adcid, C40r, when dry, is found only native, combined
with alumina, in a very rare mineral, mellite or honeystone.  It crystallizes with water, C403-H.O., and from its characters, especially
the properties of the rnellate of silver, it appears to be properly a
hydrogen acid, having carbonic oxide as its radical, and its formula
to be C404,,+H.  When its ammonia salt is decornposed by heat, it
is resolved into two very singular bodies, paraban and euchroic acid,
whose history, however, is not important here.
In concluding this account of the oxygen compounds of carbon, it
is proper to notice the peculiar function which the carbonic oxide
appears to play.  From the composition of its chlorine compound,
it is certain that the equivalent of the gas is C.O., and, combining
with oxygen, it forms carbonic acid, C.02.  But I consider that we
cannot look upon oxalic acid as being a lower degree of oxidation
of the same radical as carbonic acid.  On the contrary, the body
CO,, which is the basis of it, enters into a completely distinct series
of compounds, such as oxamide, and is probably merely isomeric
with carbonic oxide, into which it may be changed by a variety of
reactions.  Still less is carbonic oxide the basis of the rhodizonates,
C 07, or of the croconates or mellates; but the gas is changed into
these more complex bodies by an isomeric action, which appears to
occur at the moment that it combines with the potassium. I look
upon the carbonic oxide gas, therefore, as being the basis only of
carbonic acid and phosgene gas, and that the radicals of the oxalic
acid and the bodies of its series, as well as of the rhodizonic and
other acids, are compounds of carbon and oxygen, isomeric with
carbonic oxide, but not yet isolated.
Of Sulyhuret of Carbon.-C.S2.  Eq. 478'7 or 38.3.
This remarkable substance is formed whenever sulphur comes
into contact with red-hot charcoal. It may be prepared by means
of the apparatus figured in page 323; the tube a, c being filled with
pieces of' charcoal about the size of almonds, and bits of sulphur
introduced from time to time at h, which is to be then tightly closed with a cork.  The sulphur fuses, and the tube being a little inclined, runs down upon the ignited charcoal, combines with it, and
the product passing as vapour into the long glass tube e, f, is condensed, and collected as a liquid in the bottle.
In large quantity, it is more conveniefntly prepared by fixing, air tight, into an iron
cylinder about a foot high (such as a quicksilver bottle), two iron tubes, one long, b,
reaching nearly to the bottom, and projecting a foot above the top, and. the other
short, c, and bent at a right angle, serving to convey the product to the condensing
apparatus. By means of the tube c, the bottle may be filled with small fragments




SULPHURET  OF  CARBON.                            497'
fb  I
of charcoal, and then, being placed in a furnace, the wide glass tube c, and the natrower f, are to be attached by corks. From the cock d a stream of water flows,
which, guided by the tin-plate gutter o, cools the tubef, and is conducted by the
thread /h to the basin x. When the bottle is bright red, small pieces of' sulphur are
to be dropped in by the long tube, the end of which is to be then carefully closed up
by a cork. The sulphur, being vaporized, acts on the charcoal, and the shlphnret o
carbon formed being condensed in the narrow tube cf, collects in the bottle et, which
is half filled with ice in order more perfectly to preserve it. Any incondensible gases that may be formed escape by the tube m. The process might be continued until
all the charcoal in the bottle had been converted into sulphuret; but if sulphur were
allowred to be present to excess, it would melt the bottom of the bottle. The pro'cess,
therefore, should not be pushed so far.
The sulphuret of carbon thus obtained contains an excess of sulphur dissolved in it, and must be purified by redistillation at a very
moderate heat (in a water bath); when about nine tenths have dis
tilled over, by allowing the residue to evaporate spontaneously in a
capsule, very fine right rhombic crystals of sulphur may be obtained (p. 284).
The sulphuret of carbon is a colourless liquid, of a very disagreeable garlic smell. It does not mix with water, but dissolves in al
cohol and ether.  It dissolves sulphur and phosphorus in large
quantity.  Its specific gravity is 1'272.  It boils at 108-: Fah., and
forms a colourless vapour, whose specific gravity is 2.62l1.  From
its volatility, it obtained the name of. /lcohol of Sulplur'.  In evaporating it produces great cold; mercury may be frozen by suspending under a bell-glass:a thermometer, the bulb of which is enveloped by cotton moistened by this fluid, and rapidly exhausting the
air. It is very inflammable, burning with a blue flame, and producing
carbonic and sulphurous acids.  If a few drops of it be let fall into
a strong bottle containing oxygen, so much of it evaporates as to
form  an explosive mixture with the gas, which then detonates when
touched with a lighted taper, like a mixture of oxygen and hydrogen.  When the sulphuret of carbon is heated in contact with a
metal, carbon is separated, and a metallic sulphuret produced. It is
thus found to consist of one atom of carbon united to two of sulphur, and its formula to be C.S2.
It is a powerful sulphur acid, combining with the sulphurets of
the alkaline metals and forming sulphur salts, which are crystallizable; with the sulphurets of lead, silver, copper, &c., it forms in



498        CHLORIDES  OF  CARBON.-A MMONIA.
soluble compounds, which correspond closely in composition to the
ordinary carbonates. This substance is, in fact, exactly equivalent
to carbonic acid, C.O2, the sulphur being replaced by oxygen, with
which its analogies have been already noticed in p. 291.  The sulphuret of carbon is hence often called Sulphocarbonic./cid.
Moist chlorine converts this body into a crystalline substance:ike
camphor; but this,'as well as the products of the action of nitric
acid and of strong alkalies, have not yet been accurately examined
Chlorides of Carbon.
Subchloride of CarbOn, C2C1., is formed by passing the vapour of the protochlorite
many times through an ignited glass tube; chlorine is given off, and the sulchlo.
ride deposited in silky crystals, which are fusible, and sublime at about 3000 unchanged.
Protochlmoide of Ca'lbon, C2C12, is also formed from the sesquichloride of carbon
by heating its vapour to redness, when chlorine is given off; or better by distilling
the sesquichloride with an alcoholic solution of sulphtret of potassium, which removes one third of the chlorine. It is a limpid fluid, boiling at 160~; the sp. gr. of
its vapour is 2862. By a strong heat it gives subchloride and free chlorine.
Sesquichloride of Carbon, C2C13, is produced by the action of a great excess of chlo
rine in bright sunshine on olefiant gas or on muriatic ether; all the hydrogen of
these bodies is removed, and the carbon remains united with chlorine. It forms a
white crystalline mass like camphor, which is insoluble in water, but soluble in alcohol and ether. It melts at 320~, and sublimes at 360~ unchanged; at a red heat it
abandons chlorine, and forms the bodies last described.
Bichloride of Carbon, CEC14, is formed by exposing a body termed chloroform,
whose formula is C2HI.C13, or marsh gas, C2H4, to an excess Of chlorine in bright sult.
light. The hydrogen is gradually removed and replaced by chlorine. it is liquid;.
its sp. gr. is 1'6; it boils at 192~. The sp. gr. of its vapour is 5302.
CHAPTER  XVIII.
OF TIlE COMPOUNDS OF NITROGEN AND HIYDROGEN.  ALMMIONIA, ITS DERIVATIVES AND COMPOUNDS.
ALTHOUGH there is very perfect evidence that hydrogen and nitrogen unite in two, perhaps in three proportions, we as yet know
but one of these in an isolated form, which is the volatile alkali,.lmmonia.  This was known to the earliest chemists, but the importance of its history to the progress of chemical philosophy has
been but lately felt to its just extent.
Anmmonia is produced in almost all reactions where nitrogen and
hydrogen are brought together, one or both being nascent.  Thus,
when an electric spark is passed through damp air, nitric acid and
ammonia are both formedl, and hence the rain which falls after thuit.
der-storms contains nitrate of ammonia.  It is evolved  in large
quantities in the putrefaction of organic substances containing nitrogen, and is formed also by their distillation at high temperatures,
whence the greater supply of ammonia used in the arts is derived
When any oxide of nitrogen is mixed with hydrogen, and passed
through a tube containing red-hot spongy. platinum, ammonia is
formed; and, lastly, it is produced abundantly when- -iron or tin is




PREPARATION  OF AMMIONIA.                    499
oxidized violently by nitric acid, the oxygen being taken both from
the acid and water, the nascent hydrogen and nitrogen unite. Am.
monia is also a product of organization, being contained in the
areat of animals, and being exhaled by the flowers of many plants,
and by the leaves, also, of the cruciferEe.
For the purposes of the chemist, ammonia is obtained from the
tmuriate of ammonia, or sal ammoniac, which is manufactured in
large quantities for commerce, by processes to be hereafter described. Equal parts of the sal ammoniac, in powder, and slacked
lime are to be intiiately mixed and heated in a flask, from which
a bent tube passes; the gas which issues is to be conducted through
a tube, as in the figure (p. 310), containing dry lime or fused potash, by which adhering moisture is removed, and it; may then be
collected over mercury. It is colourless and transparent. Its odour
is strong, pungent, and irritating, well known as the smell of hartshorn.  When perfectly dry, it has no action on vegetable colours;
but if damp, it reacts powerfully alkaline. The brown colour which
it produces on turmeric disappears when heat is applied, by which
it is distinguished from the browning by the fixed alkalies or earths.
By a pressure of 6' atmospheres, or at a temperature of -61~, gas
eous ammonia is liquefied. When inspired pure, it proves excess
ively caustic and poisonous.
Ammonia is slightly combustible. It does not support combus
tion. When a series of electric sparks is passed through a quan
tity of the gas confined over mercury, its volume enlarges, and ultimately becomes double. It is then totally decomposed, and the
resulting gas consists of three volumes of hydrogen and one of nitroogen: the specific gravity of ammonia is therefore 591'5, as deduced in p. 215, and its formula N.Hs. If a current of ammoniacal
gas be passed through a red-hot tube filled with iron wire, it is decomposed in the same way as by electricity. If the tube contain
red-hot charcoal, carbon is taken up, and prussiate of ammonia and
carburet of hydrogen produced.
Ammnoniacal gas is rapidly absorbed by water, which takes up
780 times its volume at 323. Great heat is thereby evolved, and
the solution, which augments two thirds in volume, has a specific
gravity of 0'872, and boils at 1'203. It contains then about 32 per
cent. of ammonia, and approximates to the formula N.H1+-4 Aq.
This solution is termed Water of  nzmmonia, or, improperly, Liquid.ammonia. To prepare it upon a larger scale, the matrass and series of three-necked bottles, described and figured in p. 308, may
be employed. Five parts of lime, slacked, and mixed with as much
water as will convert it into a thin paste, are to be introduced, with
four parts of powdered sal ammoniac, into the matrass, which is
then to be placed upon the sand-bath, and connected with the range
of bottles. The first bottle is left empty, in order to catch any water or mixture that nmay be carried ovei' a''d it should be allowved
to grow warm, in order that it may retain no gas; in the other bottles water is placed, by which the gas is absorbed, and they are
kept cool by damp cloths applied to their surface. For ordinary
purposes, water of ammonia need not contain more than 18 per
cent. of gas; it then has a specific: gravity of 0'930.




500          CONS TITUTION- OF AMMONIA.
The watery solution of ammonia possesses all the characters of
the gas in a strong degree. It neutralizes the strongest acids, and
acts in all respects as a strong base, ranking next to lime. It forms
many classes of combinations, in some of which it exists unaltered,
but in others it first undergoes peculiar decomposition.  Its action
on chlorine is very violent, and accompanied by flame; sal ammoniac is lormed and nitrogen set free, as described in p. 261.
Ammonia is very easily recognised: its odour, the brown colour
given to turmeric paper, which is removed by a gentle heat, and its
forming dense white fumes on the approach of a glass rod moistened with strong muriatic acid, characterize it when free.; all substances which contain ammonia are either volatilized by heat, or
decomposed, the ammonia being generally liberated; in all cases,
by heating the body with moist caustic potash, ammonia is evolved
as gas, and may be known by the properties now described.'The real nature of ammonia has recently been the subject of
much inquiry; its equivalent is satisfactorily determined to be
17'1, and hence its formula is N.H,, and its equivalent volumle 4. It
may enter into combination directly with dry oxygen acids, but it
does not then form the proper ammoniacal salts, which all contain
an atom of water essential to their constitution. It combines wit.h
a great number of saline bodies, and then resembles, in its functions,
their water of crystallization. Its most remarkable property, however, is, that, in acting on metallic compounds, and on certain organic'acids, it abandons an atom of hydrogen, and the remaining
N.i, combines with the metal, or with the radical of the acid. Thus,
with Hg.Cl. and N.H3 there result Hg.N.H, and H.C1.; with Pt.C1,
and 2N.H3 there are formed Pt. + 2N.H2 and 2H.CI.; from Hg.. N.O0
and N.Hs are produced Hg.N.H2 and H.N.O,. Of organic bodies,
oxalate of ammonia gives, when heated, C202+N.H2, and benzoate
of ammonia produces similarly C,4HO,2q-N.H2. It is hence evident
that the third atom of hydrogen is not so intimately combined with
the nitrogen as the remaining two; it may be eliminated by the
simplest reactions, but the N. and H2 remain much more firmly
united, and separate only when the constitution of the ammonia is
totally broken up. I hence concluded that the N.H2 should be considered as the radical of ammonia, and proposed to term it snmidogene, and its symbol Ad. The ammonia is then.qmidide of Hydrogen, and its rational formula N.H2H. or Ad.H. Ammonia is thus
assimilated to water, and to chloride of hydrogen in constitution,
the radical amidogene having the closest analogy to oxygen and
chlorine. These conclusions have been almost unanimously adopted by chemists.
These views are remarkably illustrated by the action of ammonia
on potassium; when this metal is heated in the dry gas, hydrogen
is disengaged, and a fusible olive-green substance is obtained. The
quantity of hydrogen evolved is the same as that which the metal
should evolve from water, that is, one atom, and the olive body consists of K.N.H2. It is.qimidide of Potassium. When put into water,
potash and ammonia are produced, K.Ad. and H.O. giving K.O. and
H.Ad. When this olive substance is heated nearly to redness, ammonia is expelled and JV'itruret of Potassium remains, 3K.. N.H2 giv



COMPOUNDS OF AMIDOGENE.                      501
ing.2N.H3 and KN. The phenomena are exactly the same with
sodium, an amidide and a nitruret of sodium being thus formed.
In describing the compounds of ammonia, it is necessary to distinguish those in which ammonia acts simply as amidide of hydrogen, resembling in its functions the oxide or chloride of hydrogen,
from the class of bodies in which the ammonia is associated with
water, the proper salts of ammonia, which, as already noticed, are
isornorphous with those of potash. I shall have occasion to discuss
the theory of these bodies farther, but shall first describe the most
important members of the former class.
4n mmonia and CIhorine.-If a bottle full of chlorine gas be inverted in a cup containing a solution of sulphate or muriate of ammnonia, it is gradually absorbed, and a heavy yellow liquid collects
in globules in the bottom of the cup. This substance must be treated
with the utmost caution; if strongly rubbed or struck, or if it be
touched with any greasy body, or with phosphorus, it explodes with
intense violence; a globule as large as a pin-head, on being exploded
in a teacup, shatters it to pieces. Almost every chemist who has
examined it has been severely hurt, and hence its composition is
not yet well known. Sir Humphrey Davy found that, when decomposed over mercury, it gives nitrogen and chlorine in the proportions by volume of 1: 3, and hence it was concluded to be Chloride
of.qzote, N.C13, under which name it is described in most books. It
has been observed, however, that traces of sal ammoniac are formed
when it is decomposed; it consequently must contain hydrogen,
and it may probably be bictloride of.dmidogene, Ad.CI2, which, when
decomposed, should produce N. and C13, besides Ad.H.. H.C1.
iodine and.mmonia.-When the semi-fluid compound of iodine
and ammonia is put into water, it is decomposed into hydriodate
of ammonia, and a brown powder which is usually described as Iodide of.lzote, N.I3. This substance may also be prepared by digesting iodine in water of ammonia, the iodine gradually changing into
the brown substance, and the solution containing hydriodate of amnionia: this body must be collected on filters in very small quantity,
and dried merely by exposure to the air; if it be rubbed, even under water, it explodes with a violent detonation, though not so powerfully as the previous body. The cloud of hydriodate of ammonia,
formed by its decomposition, is very evident; it therefore contains
hydrogen, and I look upon it as a biniodide of d.lmidogene, Ad.I2.
A corresponding compound containing bromine has been formed.
By the action of ammonia on metallic oxides, a numerous class
of bodies may be formed, which all possess more or less violent
detonating properties; they all contain combined water. It is imnpossible to say, positively, whether the ammonia exists undecomposed in these bodies; I rather think it does, and I shall hence
term them amzmoniurets..Ammoniuret of Silver.-This is the most violent of all these com-;
pounds: it is prepared by digesting recently-prepared oxide of silver in water of ammonia, or by dissolving nitrate of silver in an excess of water of ammonia, and,precipitating the solution by caustic
potash. It is a brown powder, which detonates violently by the
slightest shock or friction; when exploded, it is said to produce




502          NITRURETS ~AND  AMMONIURE TS.
water, azote, and metallic silver, which should give for its formula
N.H3+3Ag.O.+Aq.  But the facility of its decomposition, which
has been the cause of many serious accidents, has prevented it being accurately analyzed.
-.mmoniuret of Gold, Au.O3-+2Ad.H., is produced by the action
of water of ammonia on peroxide of gold.  It is a brown powder,
nearly as explosive as the former body, but it has been accurately
analyzed by Dunas.  These bodies are known as Fulminating Gold
or Silver.
The  dnmmoniuret of Platinum  is formed by digesting hydrated
oxide of platinum in water of ammonia. It is a light-brown powder,
not yet analyzed, and qu:eu different from  the impure substance
described in books as Davy's fulminating platinum.
I have examined the ammoayiu-els of Coppnr and M/zrncury formed by digesting the
oxides of these metals in water of ammonia: the first is blue, the second yellow;
their formula are 3Cu.0.+2Ad.H.-+6 Aq., aiid 31rg.0+Ad.H.+2 Aq. They detonate feebly when heated. There exist, also, cempounds of ammonia with the oxides of uranium, of iron, and of osmium, which have not been accurately examined.
By the action of heat on some metallic compounds of ammonia, true nitrurets of
the metals have been obtained, of which the most remarkable are those of copper
and mercury. The nitrt'ret of Coler was fbrmed by passing ammonia over anhydrous oxide of copper at a temperature of 480~ Fah.; water is evolved, and the
nitrogen and copper unite, forming a black powder, which, at the temperature of
5400, is decomposed, with the evolution of a red light, into its elements. Its formula
appears to be Cu6N., which corresponds to the suboxide Cu20., as when replacing
oxygen N is equivalent to O. (see p. 26.) and Cu6N.-3(Cu2+N). Schrzeter, to whom
the discovery of the above compound is due, formed also a nitru?'l of Ckrorfe, whose
formula is not quite ascertained.
Ammonia is absorbed in large quantities by the chlorides of phosphorus and of
tulphur, and substances produced which possess singular properties.
Ammoniacal Protochloride of Phosphorus, P.Cla+5Ad.H., is obtained by exposing the
liquid chloride of phosphorus to a current of dry ammonia. It forms a white powder, which, when put in contact with water, produces sal ammoniac, and an insoluble white substance that. has not been analyzed; the reaction is probably that
3(C1.H.. Ad.H.) and P.N2H3 result. If the ammoniacal protochlotide of phosphorus
be calcined without access of air, a very remarkable body, phosphlaret of Azole, the
formula of which is P.N2, is produced, while phosphorus, hydrogen, ammonia, and
sal ammoniac are expelled. The phosphuret of azote is insoluble in water, and resists the action of the most powerful acids and alkalies. The composition of the
ammoniacal perchlorides of Phosphorus is not quite certain, as these bodies appear to
decompose each other. The formula is P.Cls+2Ad.HI. When calcined they yield
phosphuret of azote.
Gaseous ammonia and chloride of sulphur combine in two proportions, according
as each ingredient is in excess. The formulm of these bodies are S.C1.+Ad.I. and
S.Cl.+2Ad.H. The former is a brown powder, soluble in alcohol and ether; the
latter is a citron-yellow powder. They are remarkable for delivering as a product
of their decomposition, by water or by heat, the snyiphLret of Azote (SAN.), which is a
volatile yellow powder, decomposed by the prolonged action of water into ammonia
and hyposulphurous acid, 2(S3N.) and 6H.O. giving 3S202 and 2Ad.H.
When chloride of sulphur is digested with water of ammonia, a brown substance
is formed, whose composition is CI.S4. N3H6. It is probably formed of chloride and
amidide of sulphur, S.Cl.+3(S.Ad.)
Ammoniacal gas is absorbed in great quantity by the volatile chlorides of boron,
arsenic, tin, and titanium. The compounds formed are white and crystalline; they
are decomposed by water, and the solution contains sal ammoniac, and the metal
or the boron, in combination with oxygen.
There.are few metallic salts which do not absorb ammonia when exposed to a
current of the dry gas; but certain metals are specially distinguished by the character that ammonia added to their solutions produces precipitates which either contain
ammonia or amidogene, as Is the case with mercury, palladium, and platinum, or
by an excess of the ammonia the precipitate is redissolved, and soluble compounds
containing ammonia are produced, as occurs with zinc, copper, nickel, cobalt, and
also palladium and platinum. The number of combinations thus formed is so very




A MMONI A -SALTS  OF  ZINC) COPPERS  ETC.   503
great that it would be tedious to describe all, and I shall hence notice only such as
possess scientific or pharmaceutical importance.
1. smmonia-Salts of Zinc.
Dry sulphate of zinc exposed to a current of dry ammonia absorbs it, producing a
white powder, 2(Zn.O.. S.03)+5Ad.H., which dissolves perfectly in water.
If water of ammonia be added to a solution of chloride of zinc, a basic chli ride is
precipitated, which being redissolved by an excess of ammonia, a colourless solution is obtained, which crystallizes on cooling. According to the proportion of ammonia in excess, I have found that one or other of two compounds may be formed,
one in long and brilliant prisms, the other in fine pearly tables. The latter salt consists of' Zn.Cl.-t2Ad. H.+H.O., the former of 2(Zn.Cl.)+2Ad. I.+H.O. In these
salts, as in all such as are produced by the action of an excess of ammonia on: a
metallic salt, I consider that the acid exists combined with ammonia, and not with
the metallic oxide, in which they differ essentially from those produced by the direct absorption of ammonia by a salt, in which I conceive the union of the acid arnd
oxide. not to be disturbed. Hence I write.the formula of the tabular anzlooia-chlloride
of Zinc as Ad.H.. H.Cl.+Ad.H.. Zn.O. When heated it gives off ammonia and
water, and a white powder, Ad.H.. Zn.Cl., remains.
By the action of an excess of ammonia on a solution of sulphate of zinc, the am.
monia sulphate of Zinc is formed: its formula is Ad.I.. H..O.. S.03+Ad.H.. ZnO.
It crystallizes in short prisms; wlien heated it evolves Ad.H.. HO., and a white
powder, Acld.H.. Zn.O.. S.03 remains. In crystals it contains 3 Aq., of which it
loses two by efflorescence, and the third by a moderate heat.
2../]mmonia-Salts of Copper.
Chloride of copper absorbs dry ammonia, forming a blue compound, Cu.Cl.+33Ad.
H., soluble in water.
When ammonia is added to a strong and hot solution of chloride of copper, until
the precipitate which first forms is perfectly redissolvecl, a deep purple liquor is
produced, from which octohedral crystals are deposited on cooling.  Their formula is Ad.H. H.Cl.+Ad.H.-. Cu.O. When heated, these crystals evolve ammonia and water, and a blue powder, Ad.I-I.. H.CI., remains, which is totally decomposed by a strong heat.
Dry sulphate of copper exposed to a current of dry ammonia forms a fine purple
powder, whose formula is 2(Cu.0.. S.03)+5Ad.H.
An excess of ammonia gives, with a strong solution of sulphate of
copper, a rich purple liquor, from which the azamolniacal snlphaie of Copper crystallizes on cooling in large right rhombic prisms, lu, it', with  L
dihedral summits, i, i, as in the figure, in being a secondary plane. I m   t
consider these crystals, however, to be macles. The formula of this
salt is Ad.H.. H.O.. S.O3+Ad.H.. Cu.O. When heated, it gives off
ammonia and water, and a green powder, Ad.H.. Cu.O.. S.Os, remains.
Under the name of cuprusm armmoniatlm, the ammoniacal sulphate of copper is employed in medicine. It is then prepared by rubbing together sulphate of copper and
carbonate of ammonia in a mortar. The mass becomes pasty, owning to the water
of crystallization of the sulphate of copper becoming free, and carbonic acid is given off. The purple mass which results is soluble in water, and generally contains
carbonate of ammonia in excess.
When a hot and strong solution of nitrate of copper is decomposed by an excess
of ammonia, and allowed to cool, the amenoniacal,itrate of Ci)pper crystallizes in
rhombic octahedrons of a fine purple colour: its formula is Ad.H.. H.O..N.05+
Cu.Ad. In this body there is no doubt of the metal being combined with amidogene,
and not the oxide with ammonia; hence probably arises its remarkcable character
of deflagrating violently when heated until it begins to melt.
The iodide and fluoride of copper produce compounds resembling those of the
chloride.
3. aJmmonia-Salts of NJickel and of Cobalt.
These resemble the corresponding salts of copper so perfectly, that it is sufficient
to refer to the foregoing for their properties: and their composition is obtained bv
substituting Ni. or Co. for Cu. in the formulae.




:04  AMaONIA-SALTS  OF  SILVER R  PALLADIUM; ETC.
4,.  Rmmonia-Salts of Silver.
The chloride of silver is soluble in water of ammonia. The solution gives opaque
white rhombic crystals, which exhale ammonia when exposed to the air, and leave
chloride of silver.
When the sulphate or the nitrate of silver is treated with an excess of water of
ammonia, colourless solutions are obtained, which yield by evaporation double salts,
in rhombic prisms, having the formule Ad.H.. H.O.. S.03+Ag.Ad. and Ad.H.I. H.
O.. N.Osj+Ag.Ad. In both salts the silver is combined with amidogene. Chromate
of silver and ammonia gives a similar salt. The ammonia-nitrate of silver is employed in testing for arsenic and in preparing fulminating silver. A remarkable property of it -is, that when fused it evolves ammonia and nitrogen, and metallic silver
remains mixed with ordinary nitrate of ammonia, and coats the sides of the glass
containing it with a brilliant mirror surface. By a higher temperature the nitrate
of ammonia is decomposed, and nitrous oxide evolved.
5. ammonia-Salts of Palladium.
This metal is remarkable for giving with ammonia two series of salts, of whien
one is soluble and the other insoluble in water.
When ammonia is added to a solution of protochloride of palladium, a flesh-coloured precipitate is' produced,: having the formula Pd.C1.. Ad.H. WVhen more ainmonia is added, it dissolves, and from the solution the second salt crystallizes in
long rectangular prisms, having the formula Ad.H.. H.Cl.+Pd.O.. H.Ad. By a
gentle heat, an atom of water is given off, and the metal exists then in the salt as
amidide. If, in a solution of this salt, the excess of ammonia be neutralized by muriatic acid, a yellow crystalline precipitate forms, which has the same formula as the
first salt, Pd.Ci.+H.Ad.
With solution of sulphate of palladium and water of ammonia, a precisely similar
series of salts is formed; the first being flesh-red, Pd.O.. S.Oa3+H.Ad.; the second
salt in colourless prisms, Ad.H.. HO.. S.03-Pd.O.. H.Ad., and, when dried, the
last member becoming Pd.Ad.; and by a small quantity of an acid, a crystalline
precipitate, which consists also of Pd.O.. S.O3+H.Ad.
The iodide of palladium gives similar salts. With the nitrate no other than the
colcurless crystalline salt can be obtained, whose form is thin rhombic plates, Ad.
H:.. H.O.. N.Os+0Pd.Ad. When heated, it deflagrates like loose gunpowder, and
leaves behind metallic palladium as a black powder.
In the red and yellow insoluble ammonia-salts of palladium, although the experimental composition is the same, I consider that an important difference of constitution exists. The red salts are formed by adding ammonia to a simple salt of the
metal; direct union then occurs, and we have, for example, Pd.Cl.+H.Ad. - But
when we form the yellow salt by adding an acid to a solution of the soluble ammonia-salt, I conceive that the acid unites directly with the amidide of the metal, and
thus forms, for example, Pd.Ad.+H.Cl. The yellow ammonia-iodide, Pd.Ad.+IH.I.,
gradually changes itself back into the red substance, Pd.I.+H.Ad.
6. dmmonia-Salts of JMercury.
From the great inhfluence these bodies have had on the theory of ammonia, and
their importance in pharmacy, the mercurial compounds containing ammonia deserve more detailed notice than those of any other metal.
A. a.ction of a.mmonia on the Haloid Salts of.IMercury.
When corrosive sublimate is heated in a current of dry ammoniacal gas, it unites
therewith, forming a white compound, fusible and volatile, having the composition
21Ig.Cl.+-H.Ad. By contact with water, this body is decomposed into sal alembloth and white precipitate; the former, a compound of sublimate and sal ammoniac, di, solving, and the latte-r, whose composition will be next studied, separating
as a whtne powder.
If we add to a cold solution of corrosive sublimate a very slight excess of ammonia, a copious white precipitate is produced, and the liquor is found to contain exactly half the chlorine of the sublimate combined with hydrogen and ammonia as sal
ammoniac; the white powder, which had been known to the early chemists as Whlite
Precipitate of Mercury, contains all the mercury and the remaining half of the chlorine of the sublimate. It was supposed to contain, also, ammonia and oxygen, but I
have proved that it contains only the. elements of amidogene and no oxygen; that its




PRECIPITATES OF MERCURY.                              505
formula is Hg.Cl.+Hg.Ad., it being a true chloro-amidide of mercury. The theory
of its formation is very simple, 21-g.Cl. and 2H.Ad. producing, by interchange of
the elements of one equivalent of each body, Hg.Cl.+Hg.Ad., which precipitates,
and H.C1.+H-l.Ad., which remains dissolved. This was the first instance in which
amidogene was discovered to be combined with a metal, and firom its establishment,
the true constitution of ammonia was first recognised.
WT'ite Precipitate is insoluble in cold water. It is decomposed by boiling water,
two atoms of which, reacting on two of white precipitate, produce sal ammonia%,
which dissolves, and a heavy yellow powder, which is insoluble in water, and has
the iormula Htg.Cl.+2'2Sg.0.+I-I. Ad. IThis body is completely analogous to the
oxychloridle of mercury, l-Ig.Cl.+3H1g.O., from which it may be prepared by the action of almoniacal gas, the third atom of Hg.0. and H.Ad. giving HIg. Ad. and
11.O., which is expelled.'When whllite precipitate is heated suddenly, it is totally
conve ted into calomel, nitrogen, and ammonia, but by careful management of the
heat, sublimate and ammonia are given off, and a red powder relmais, which is a
cormpound of chloride and nitruret of mercury, Hg.Cl.+Hg3N.; or, rather, as the nitrogen here replaces oxygea, and has hence the one third atomic  weight, Hg.Cl.+
3Hg.N, exactly analogous to the oxychloride; by careful management, all the sublimate may be expelled, and the aozotllet of ltercu'ry, H1g. J, is obtained as a brown powder, which detonates with great violence when struck.
The white precipitate which has been now described must be distinguished from
another body which has been confounded with it in the pharmacopceias, until the
difference was shown by Woehler's observations and my analysis. This second or
beta-white precipitate is prepared by adding caustic potash to a cold solution of the
double salt formed by corrosive sublimate and sal ammoniac. It may also be formed by boiling alpha-white precipitate in a solution of sal ammoniac. It has a crystalline aspect, and is not decomposed by boiling water; when heated, it fuses, and
gives off ammonia and azote, while a mixture of calomel, sublimate, and sal ammoniac sublimes. Its formula is very simple, Hg.Cl.+H.Ad.; but it may also be looked upon as a compound of alpha-white precipitate and sal ammoniac, (Hg.Cl.-tHg. Ad.)+(H.C1.+ H.Ad.):-2(Ig.CIl.+H-I.Ad.).
WThen calomel absorbs dry ammonia, it forms a darit gray powder, which is 2
Hg2Ci.+H.Ad.; by a gentle heat all ammonia may be expelled, and the calomel
remains quite white.
If the calomel be, however, digested in water of ammonia, one half of its chlorine
is converted into sal ammoniac, and a dark gray powder results, which is a compound of subchloride and subamidide of mercury, Hg2CI.+IHg2Ad. This body,
which I have termed Black Precilitate, is formed by a similar reaction to that by
which alpha-white precipitate is produced, 2Hg2C1. and 2H.Ad. giving HgaCl.+
Hg2Ad. and HI.Cl.+I-1.Ad. By several chemists, the action of water of armmonia
on calomel is given as a means of preparing black oxide of mercury, which is quite
incorrect. The compound formed contains no oxygen.
The action of the bromides of mercury with ammonia has not been so minutely
studied as that of the chlorides; it is known, however, that bromide of mercury gives
with water of ammonia a white precipitate, consisting of bromide and amadide, Hg.
Br.+Hv.Ad., and analogous to the alpha-white precipitate. The subbromide of
mercury produces with water of ammonia a black powder, consisting of HgL2Br.+
Hg2Ad.
Iodide of mercury dissolves plentifully in hot water of ammonia, and the solution
deposites, on cooling, long prisms of a snow-white colour, which, however, rapidly
exhale ammonia when exposed to the air, and leave red iodide of mercury in pseudomorphous crystals. This white body has the formula 2Hg.I.+H.Ad.
There is no iodine compound analogous to alpha-white precipitate; but when that
substance is warmed in a solution of iodide of potassium, ammonia is evolved and a
brown powder is formed, having the formula Hg.I.+2HUg.0.-+Hg.Ad.
B. Rction of.3mmonia on the Oxygen Salts of Jlfercury.
When sulphate of mercury is digested in water of ammonia, it is converted into a
white substance, to which I have given the name of ammonia7htrpetth. It. is not acted on by water nor by alkalies. Its formula is 3Hg.O.+S.Os+Hg.Ad. It is therefore ordinary turpethl mineral combined with amadide of mercury.
When water of ammonia is added to a solution of nitrate of mercury, being cold
and not in excess, a white precipitate is formed, a basic ammonia-nitrate, which is
found to consist of H.Ad.. N.05 —3Hgg.0. It is therefore a basic nitrate of mercury, analogous to the ordinary basic nitrate, H.O.. N.0O+311g.0., except that am.
Sss




506           AMMONIA-SALTS  OF  PLATINUM.
monia (amidide of hydrogen) is substituted for water (oxide of hydrogen). If an ex.
cess of ammonia be added, and the' mixture boiled, the white precipitate becomes
heavier and granular, and is then found to consist of H-.Ad.. N.05+3Hg.0. This
substance, the: basic amzonia-i-itrate, is evidently analogous to the former, the hydrogen being replaced by mercury, and it corresponds accurately in constitution also
to the ammonia-turpeth.
If either of these basic ammonia-nitrates be boiled in water containing much
nitrate of ammonia, they dissolve and form double salts; that usually formed is in
short opaque white prisms, having the very simple composition 4Hg.O.+3(H.Ad..
1-1.O. N.Os); but as it is decomposed by water into the f3 basic ammonia-nitrate,
its formula must be (Hg.Ad.. N.O0+3Hg.O.)+2(H.Ad.. N.Os+3H.O.). The doublesalt, which forms less frequently, is in yellow plates, and has the formula (I-g.
Ad.. N.(),+3Hg. O.)+(H.Ad.. N. 0. H.O.).
These double salts may also be generated by boiling oxide of mercury in solution
of nitrate of ammonia. If the common basic nitrate of mercury be boiled in a solution of nitrate of ammonia, this is decomposed; the ammonia being employed in
forming amidide of mercury, and the nitric acid being set free, as may be recognised by litmus.
The subsulphate of mercury, IHg20.. S.0s, acted on by water of ammonia, produces a black powder, the formula of which is Hg20.. S.Os+Hg2Ad.: it is easily
decomposed.
By acting on a solution of subnitrate of mercury in water with ammonia added
dilute, and in such quantities as to leave a portion of the mercurial salt undecomposed, a fine velvet black precipitate is obtained, known in pharmacy as Ia/hzemann's
soltble Mercutry. It is very easily decomposed by heat or by an excess of ammonia.
In order to obtain it pure, the solution should be quite free fiom red oxide, and not
more than three fourths of the whole quantity of mercury should le precipitated.
TWhen quite pure, I have found its formula to be H.Ad.. N.Os+0 Hg2O., it being
perfectly analogous to the common basic subnitrate H.O..  N.O-S+2Hg2O., the oxide of hydrogen being replaced by the amidide.
The results with the other salts, both of the red and black oxide of mercury, are
similar to those above described; but as none of them are specially important, I shall
not occupy space with their description.
7.  rmmonia-Salts of Platinum.
When protochloride of platinum is dissolved in muriatic acid, and an excess of
ammonia added, a green precipitate is produced, composed of Pt.CI.+H.Ad. It
may be prepared in larger quantity by passing a current of sulphurous acid gas
through a solution of bichloride of platinum until it assumes a deep brown colour,
and then adding ammonia. By boiling this green substance in strong water of ammonia, it forms a white powder, the formula of which is Pt.C1.+2H.Ad.
The action of ammonia on a solution of bichloride of platinum is very complex;
it gives origin to a series of bodies, composed of bichloride, binoxide, and binamidide of platinum, in proportions which vary with the temperature and proportions
used. The ultimate effect is the formation of a colourless solution, when the ammonia is boiling and in considerable excess, from.which a white powder separates by
cooling, or by the addition of alcohol. This powder, which consists of(Pt.CI2+Pt.
Ad2)+2H.Ad.-+2 Aq., combines with acids, and generates a very remarkable series
of double salts, discovered by Gr0s, who formed them differently, having obtained
the nitric acid salt by heating the green substance Pt.Cl.+H.Ad. with nitric acid,
an(i the other salts by double decomposition. Liebig proposed to consider, that in
these salts there exists a compound radical, Pt.C1.. N1I-T6, which combines with chlo.
rine and with oxygen, and the oxide of which unites with acids. Thus the oxalate contains Pt.C1.. N2H60.+C20O, &.c. But as the gradual formation of this supposed oxide can be traced from the bichloride of platinum, we must admit it to contain a compound of bichloride and binamidide, similar, in many respects, to white
precipitate, and we must look upon the salts formed by Gros as consisting of that
compound united to ordinary amnmoniacal salts, just as are the double ammonia-nitrates of mercury.
The formula of Gros's salts are upon my view:
(Pt.C12+Pt.Ad2)+2(H.O.. H.Ad.), the base of the series.
(Pt.Cl2+Pt.Ad2)+2(H.CI.. H Ad.), the muriatic salt.
(Pt.C12+Pt.Ad.,)+2(H.O.. N.O5. HTAd.), the nitric salt.
(Pt.C1+Pt.Ad2)-4-2(H.O.. S.03. H.Ad.), the sulphuric salt.
(Pt.Cl2+Pt.Ad2)+2(H.O.. C203. H.Ad.), the oxalic salt.




AMM ONIACAL  SALTS.                             507
The action of ammonia on biniodide of platinum is more simple; a deep red powder is formed, which has the formula Pt.l2+Pt.Ad2+4 Aq.
Our knowledge of the action of ammonia on the oxygen salts of platinum is yet
too inexact to justify me in bringing fobrward here the statements that have been
made concerning the results.
By the action of ammonia on perchloride of gold, an olive-brown powder is produced, which fulminates when rub)bed. It is decomposed by water, and its real formula has not yet been established.
Products of the Action of Ammonia on the Anhydrous A]cids.
When chloro-sulphurous acid, S.02C1., is exposed to dry ammonia, it is converted
into a white saline mass, which is a mixture of sal ammoniac and sldplt-auilie, S.
O2C1. and 2Ad.H. giving S.O2Ad. and H.Cl.+H.Ad, The former, which consists
of amidogene united to sulphurous acid, is soluble in water, and may be obtained
crystallized, but when boiled with water it is changed into common sulphate of
ammonia, 2H.O0. and S.O2Ad. giving S.O0+Ad.H.. H.O.
When dry sulphurous acid and ammonia gases are mixed, they combine to fobrm
a reddish substance, which is decomposed by water; there appear to be two proportions, giving the bodies S.O2. H.Ad. and 2S.02. H.Ad.
Dry sulphuric acid unites with dry ammonia in two proportions, forming S.Oa. H.
Ad. and 2S.O,. H.Ad. I consider these compoundsas corresponding to the English
and German hydrates of sulphuric acid, the ammonia playing the part of water.
A solution of these bodies is not at first precipitated by barytes, but gradually becomes changed into ordinary sulphate of ammonia.
It was supposed that the chloro-carbonic acid, C.O.C1., combined directly with
ammonia, but Regnault has found that decomposition occurs, and that sal ammoniac and amidide of carbonic oxide result. This body, which he terms carb-antide,
C.O.Ad., is white, Soluble in water, is not deliquescent, and resists the action of a.lkalies and acids, unless they be very concentrated.
Of the Common r/mmoniacal Salts.
From the great number of classes of compounds described in the
preceding sections, it is evident that ammonia enters into combination with acids and with bases, with haloid and with oxygen salts,
in such manner as assimilates it fully to the oxide and chloride of
hydrogen in its action, but removes it totally from all analogy with
the alkalies, to which it, in other points of view, strictly belongs.
For the ordinary salts of ammonia, of which the description now
comes, are isomorphous with the corresponding salts of potash, and
the strong basic characters of the solution of ammonia had given to
it, from  the earliest times, the name of the Volatile, or the Animal.Alkali. The characteristic distinction is, that in all cases where it
acts as anr alkali, ammonia is associated with water: it is not Ad.H.,
which is the alkali, but Ad.H.+H.O., or, rather, N.H,40., the element which replaces potassium  in the isomorphous salts being subamidide of Hydrogen, Ad.H2, or N.H4.
At the time when Mitscherlich showed the isomorphism  of the
potash and ammonia salts, nothing was known of the true constitution of ammonia or of amidogene; and, in order to explain the necessity of the presence of water, a very ingenious theory was proposed by Berzelius and Ampere.  It was, to consider that these
ammoniacal salts do not contain ammonia at all, but another compound of nitrogen and hydrogen, NI.H4, which is metallic, and resembles potassium in all general characters, and for which the name.Ammonium was proposed.  This view  squared accurately with experiment, as in every oxygen salt of ammonia there is just so much
water as may form  with the ammonia Oxide of Ammonium, N.H4
0.; and in every haloid salt, the electro-negative body is combined




508             AMMONIACAL AMAI LGAM.
with as much hydrogen as may convert the ammonia into the cornpound metal; thus N.H3. H.O.+S.03 and N.H,~ H.Cl. would give
N.H40O. 1S.03 and N.H4C1. Not merely was this theory consonant to numbers, but experiment gave very good reason to believe
in the real existence of this compound metal, by the remarkable
properties of the ammoniacal amalgram.
When a globule of mercury, immersed in water of ammonia, is
made the negative pole of a galvanic battery, it increases fifty times
in volume, becomes semi-fluid and covered with warty excrescences, and finally becomes so light as to float on water. No hydrogen is evolved from its surface, but oxygen is copiously given off
from the positive electrode. If the current be interrupted, a copi.
ous disengagement of hydrogen occurs from this metallic sponge
which also gives off ammonia, and it soon falls back to its original
appearance. By cold, this decomposition may be retarded; the
pasty mass may be removed from the liquor, and is found to crystallize in cubes at a cold of 0~; and if decomposed wh'en dry over
mercury, it evolves ammonia and hydrogen, by volume in the proportion of 2: 1. This indicates that the mercury is therein combined with a body which consists of N.H4, and as the mercury retains its lustre, the compound formed is properly an alloy, and the
body N.H4 is of a metallic nature. It may be the metal dqnmronium,
almost perfectly isolated. All these phenomena may be observed
by dissolving one grain of potassium in 100 grains of mercury, and
dropping the globule into a glass containing strong solution of sal
ammoniac. By the action of KI.Hg. on N.H4C1., there are produced K.CI. and Hg.N.H4; the globule of mercury swells up rapidly, and the amalgam is sufficiently permanent to be easily examined.
I have no doubt there is thus obtained a substance possessing
some metallic characters, and consisting of ammonia and hydrogen;
in fact, subamidide of Hydrogen, Ad.H,; but whether the water which
is found in the common ammoniacal salts exists therein as such, or
whether these salts contain true oxide of ammonium, is not thus
decided. In fact, among the metallic compounds of ammonia already examined, we have found bodies every way similar to the
ordinary salts of ammonia, except that a part of the hydrogen is
replaced by a metal. Thus, if we compare sal ammoniac with other
similar bodies, as in the following formulae,
1. CI.N.H4,           5. C1.N.. H3Ni.,
2. C1.N.. H3Cu.,     6. C1.N.. Hg.,
3. C1.N.. H3Zn.,     7.'CI.N.. H2Hg2,
4. C1.N.. H3Pd.,     8. C1.N.. H2Pt2,
and find them all produced by the action of ammonia on a chloride
of a metal, just as sal ammoniac is formed by the action of anmmonia on chloride of hydrogen, ve must admit their similarity of
constitution; and if we say that in No. 1, N.H4 forms a compound
metal, we must consider all the others as chlorides of compound
radicals also. Still more, the connexion is so perfect from these
bodies to such as resemble the yellow powder, Hg.C1.+2HEg.O.+
Hg.Ad., and from that to the oxychloride, Hg.Cl. + 3Hg.O., that if
we insist on assuming the compound metal ammonium to exist
ready formed in the salts of ammonia, we must lay -down as a gen




MANUF.ACTURE  OF  SAL AMMMONIAC.                     509
eral principle that all basic salts are salts of compound metals,
which could not be tolerated in an exact science for a nmoment. At
the same time, therefore, that I consider the ammoniacal amalgam
to contain amminonium, I believe it to be formed only at the tiimer
and that the ordinary salts of ammonia contain ammonia and water,
the latter being united as the constitutional water is in the magne.
sian sulphates, but more intimately.  Thus, sulphate of ammonia,
S.03+Ad.H.. H.O., I consider to resemble the bihydrated sulphuric
acid, S.0+H.O. H. HO. In both cases an atom of water may be replaced by an oxide of the magonesian class.
It will be necessary only to notice the mlore important of the ordinary salts of ammonia.
JlMuriate of dlznmonia. Sal dmsnmoniac.-C1.H2Ad. Eq.666'8 or 53'5.
This salt, formerly derived from  Africa, is now manufactured on
the large scale from the ammn;oniacal liquor obtained in the destructive distillation of horns, bones, coals, and such other organic matters as contain nitrogen. Those liquors which contain ammonia,
combined principally with carbonic acid and sulphuretted hydrogen,
are decomposed by means of muriatic acid added in slight,-xcess.
By evaporation to a pellicle and cooling, the sal ammoniac is obtained in small crystals, deeply coloured with tarry matter. They are
purified by re-crystallization, and finally placed in cast iro.n pots,
set in a furnace, lined with fire-tiles, and fitted with leaden' heads,
into which the sal ammoniac is sublimed.  The temperature is so
managed that the sublimed salt forms a coherent, hemispherical
mass, often weighing 100 lbs., alnd when pure should be perfectly
free from  yellow stains, and nearly transparent.  If muriatic acid
be dear, the ammoniacal liquor may be neutralized by sulphuric
acid; sulphate of ammonia is formed, which is decomposed by the
addition of common salt, and the sulphate of soda and sal aimmoniac separated by crystallization.
Sal arnmoniac is very soluble in water; it crystallizes both by
sublimation and solution, in cubes and octohedrons; it is slightly
deliquescent, and is soluble in alcohol; it volatilizes below  a red
heat.  When heated with lime or potash, it yields ammonia, as described in p. 499. It consists of an equivalent of each element, its
formula being H.Cl.. H.Ad.  It may be formed by their direct combination.  When equal volumes of dry muriatic acid gas and ammonia are mixed together, the two gases disappear, and a snowwhite powder of sal ammoniac results.  Hence arise the white
fumes when a rod dipped in water of ammonia is brought where
chlorine or muriatic acid gas is evolved, or when a rod dipped in
muriatic acid is brought to where ammonia is escaping.  It thus
renders these bodies the means of detecting each other.
Sal ammoniac is remarkable for the number of double salts which it produces,
and of which some deserve notice.
With chloride of magnesium, it forms the anhydrous salt Ad.H2Cl.+Mg.CI.,
which is used in preparing metallic magnesium.
With perchloride of iron, it crystallizes in fine red octohedrons, Fe2Cl3+3(Ad.H11
C1.). When these are heated, sal ammoniac sublimes, coloured by some chloride
of iron, and forms thus the Flmoes Marti ales.
The double salts formed with the chlorides of copper, zinc, and nickel, crystallize
in cubes, They are all composed like that of copper, which is Cu.Cl.+Ad.H2CI.-+
2 Aq.




510    HYDROSULPHURETX  ETC.1 OF  A.MMONIA.
Corrosive sublimate unites in two proportions with sal ammoniac. The first salt,
of which the formula is Hg.CI.+Ad.H2,Cl.+Aq., is very soluble in water, and crystallizes in flat rhomboidal tables, which effloresce when exposed to the air. This is
the Sal Alembr'otAl of the older chemists. The second salt crystallizes in rhomboidal
prisms, which sublime unchanged, and have the formula 2Hg.Cl.+Ad.H2Cl. It is
by the formation of these salts that corrosive sublimate becomes so easily soluble in
a solution of sal ammoniac.
Sal ammoniac and bichloride of platinum form a double salt, whose formula is
Pt.CI1+Ad.1:2Cl. It precipitates as a bright yellow powder when solutions of its
constituents are mixed, and especially if alcohol be added, in which it is quite insoluble. It is but very sparingly soluble in water, but more so in boiling water, from
Which it crystallizes in orange-red octohedrons. When ignited, it leaves behind
metallic platinum in the form of a light sponge. It is of use in preparing spongy
platina, and in the detection of ammonia.
With chloride of gold, sal ammoniac forms a double salt, which crystallizes in
orange-red cubes, having the formula Au.Cl3+Ad.H2Cl.+2 Aq.
The hydrobromate and hydriodate of ammonia do not require notice. They resemble the sal ammoniac in all important characters, and combine with the metallic bromides and iodides to fbrm similar double salts.
Hydrosulphluret of dmn0onia.-W hen sulphuretted hydrogen and
ammonia gases are mixed in equal volumes, in a vessel cooled by
ice, they combine, forming colourless needles, which evaporate at
ordina:'y temperatures.  The formula of this compound is S.H.-+H.
Ad., or S.N.H4, analogous to protosulphuret of potassiun, S.K. Like
that, it combines with as much more sulphuret of hydrogen, forming
a volatile crystalline compound, Ad.HS.+~ H.S.  This bi/hydrosulp/huret of JnLmrnonia is formed also when sulphuretted hydrogen is
passed into water of ammonia, as long as it is absorbed.  For each
atom  of ammonia present, two atoms of sulphuretted hydrogen are
taken up. By exposure to the air, this solution becomes yellow,.owing to the absorption of oxygen and the liberation of sulphur.  It
is capable of dissolving a large quantity of sulphur, forming compounds analogous to the higher sulphurets of potassium.  This hydrosulphuret of ammonia is of great importance in the detection of
the metals, from  the formation of metallic sulphurets   It is a sulphur base, and forms salts with the sulphur acids, analogous to those
formed by sulphuret of potassium.
Sulplate of.Ammonia. —Ad.H2. O.S.03 + Aq.  This salt is formed
on the large scale in the manufacture of sal ammoniac; it may be
prepared pure by neutralizing water of amnlonia by sulphuric acid; it
crystallizes in flat rhomboidal prisms, as in the figure, or in
macles, isomorphous with the crystals of sulphate of potash.  It is very soluble in water, but insoluble in alcohol;
u /\ < when heated, it gives off water, ammonia, and azote, and
sulphite of ammonia sublitnes.  It combines waith the sulphates of copper, zinc, iron, alumina, &c., forming double salts exactly analogous to those formed by sulphate of potash.  With oil
of vitriol it unites to form bisulphate of dmnmonia, which is deliquescent and soluble in alcohol.
JAritrate of. lmmonia, Ad.H,O0.. N.O0, is formed by neutralizing nitric acid by ammonia.  It crystallizes in striated hexagonal prismls,
isomorphous with nitre, of a bitter saline taste; they are deliqtiescent and very soluble in water.  When heated, they fuse at 230',
and at about 460  are rapidly decomposed into nitrous oxide and
water, as described p. 272.  By the presence of a large excess of
sulplhuric acid, this action takes place at muach lower temperatures.




PHOSP HATES OF AMMO NIA.                      511
When heated with combustible bodies, it deflagrates with extreme
violence.
P/ioph/vtes of slnzmonia.-The tribasic phosphoric acid forms with
ammylonia two salts; the first, whose formula is (P.O,+Ad.I-IO.+
H.O.)-t-Aq., is prepared by addinr the acid in excess to vwater of
%mmonia; it crystallizes in rhomibic prisms, which are very soluble
an water. T'heir reaction to test-paper is strongly acid.  If the amvnonia be added in excess, a salt crystallizes, possessing nearly the
same characters, except that its reaction is alkaline, and its formula
P.O,4-2( Ad.HO.)+t-I.O.  Both of these salts yield, by ignition,
phosphoric acid..d/mnnmoniaco-Magnesian PFhosphate. —When a solution of a salt of
magnesia is added to any soluble phosphate, and the liquor rendered
alkaline by ammnonia, a crystalline precipitate is formed, which is
soluble in acids, sparingly soluble in vater, but insoluble in alkaline
liquors.  Its- formula is P.OA-(Ad.H,OQ. +2Mg.O.)+ 12 Aq. Its
formnation is ofteo of use for the detection of magnesia, and it is
9ccasionally generated in urine by the action of ammnonia, produced
Dy the spontaneous decomposition of urea upon the soluble phosphates of magnesia wvhich it contains. It then constitutes a coinmon variety of calculus.
Phosjphate of 1nmmonia and Soda.-This salt, of which the formula
is P.O,+(Ad.HO2.+Na.O.+H.O.) 8 Aq., is easily produced by
mixingr together, in solution, six parts of common phosphate of soda
and one of sal arnmoniac. On cooling, it crystallizes in large prisms,
which effloresce in the air.  When heated, it gives monobasic phosphate of soda and free phosphoric acid, as a source of which it is
muchl used in blowpipe experiments, under the name of.Microcosmic
Salt.' It is found in all the animal fluids.
Carbonates of.mnmonia.-The salt which,under this name,is used
for medicinal purposes, is prepared by mixing together one part of
sal ammoniac with two of powdered chalk, and exposing the mixture
in an earthen pot to a heat below redness.  These bodies reacting,
produce chloride of calcium and carbonate of ammonia, which sublimes, and is condensed as a crystalline senli-transparent mass, in a
dome-shaped receiver, which is fastened on the subliming pot.  By
right, this should be a neutral salt, Ad.HC,l. and Ca.O.. C.O, giving
Ca.C1. and Ad.HO.. C.O,; but a quantity of ammonia and water is
given off, and the sublimed salt was considered to be a sesquicarbonate, consisting of 2(Ad.H,O.)+3C.O2, until Scanlan showed that
it was a mixture of two different salts, which may be separated by
water. Rose has recently thoroughly examined tlie carbonates of
ammonia, of which there are a great number, but only four sufficiently important to be noticed here.
The proper neutral carbonate of ammonia, Ad.IHO..C.O, does
not exist except in combination, but its compounds are very nu
merous; it forms,
1st. With carbonate of water, the ordinary bicarbonate of.:znmonia,
Ad.H,0.... -0. H.O.. C.O.  This is prepared by washing the commercial sesquicarbonate with cold water or alcohol, when it remains
behind as a skeleton of crystalline grains, which are isornorphous
with bicarbonate of potash.  It evaporates spontaneously, with a




512  CARBONATES AND  OXALATES OF AMMONxIA.
weak odour of ammonia. Its solution reacts feebly alkaline. By
pouring on the commercial sesquicarbonate as much boiling water
as dissolves it, andletting the solution cool in a close bottle, so that
no carbonic acid can escape, this salt may be obtained in large rhomboidal crystals, which contain one and a half atoms of water.
2d. The substance which is dissolved out of the sublimed mass
of sesquicarbonate by alcohol is identical with that formed by the
union of dry carbonic acid and ammonia. Its formula is therefore
Ad.H.. C.O2, and the ordinary sesquicarbonate is a mechanical mix
ture of it with the. bicarbonate.
When the sublimed sesquicarbonate is distilled at a moderate
heat in a retort, it. abandons' carbonic acid, and two salts, differing
in volatility, are condensed in the neck. The more volatile consists
of Ad.H,20.. C.O- +H.Ad.. C.O, being a compound of neutral carbonate with dry carbonate, oi a bicarbonate in which the basic oxide of
hydrogen is replaced by amidide of hydrogen, the two double salts,
Ad.H20.. C.02+H 1.O.. 0C.0, water-bicarbonate of ammonia,
Ad.HO.. C.O0+H.Ad.. 0C.O,, ammonia-bicarbonate of ammonia,
being precisely equivalent in composition. The less volatile product
is of very complex composition; its formula is 4(Ad.H20.)+5C.02,
or it consists of an atom of neutral carbonate united to an atom of
each of the different bicarbonates, thus:
Ad.H:,O.. C.0:,
Ad.H10...   O+.O.02+.. 0.02  =4(Ad.H0.)+ -i5C.02
Ad.H;1O.. C.0,+H.Ad.Co2 ~
Oxalate: of -dmmonia, Ad. HO.. CO, may be prepared by neutralizing oxalic acid by water of ammonia; it crystallizes in
right rhombic prisms, as in the figure,  where p, u, u are
primary, and i, t secondary planes. These crystals con-.1 -..:  tain an atom. of water, which they lose by effiorescence
in dry air. WShen heated, it is completely decomposed,
water being evolved, and oxarmide subliming, Ad.H,20.. C,
03 producing 2H.O. and Ad.C,0,. This neutral oxalate of ammonia
combines with oxalic acid, forming a binoxalate and a quadroxalate
like those of potash.
The oxamide may also be prepared by acting on oxalic ether with
water of ammonia, or by dissolving oxalic acid in a mixture of equal
volumes of oil of vitriol and alcohol, and adding ammonia in excess.
It is a light white powder, tasteless and insoluble in water; it is decomposed by acids and by strong bases, in contact with water, oxalic acid and ammonia being regenerated. Its discovery by Dumas
laid the foundation of our present knowledge of the nature of ammonia, by leading hitn to the idea of the probable existence of anmidogene.




P R E P AR AT I O NO F CY A N O G EN.        513
CHAPTER XIX.
OF CYANOGEN AND ITS COMPOUNDS, AND OF THE BODIES DERIVED FROMI IT
THERE is no class of organic bodies of which our knowledge is
more extensive and exact, than those which have cyanogen as their
basis. The powerful affinities which this radical exerts, the simplicity of its constitution, and, above all, our being able to prepare it
in an isolated form, and to generate its compounds directly from it,
as we could those of a truly simple body, render its history the most
advanced portion of organic chemistry, and that to which the analogy' of mineral bodies and the theory of compound radicals is most
undeniably applicable.
Cyanogen does not exist in nature ready formed; the kernels of
peaches, plums, bitter almonds, &c., and the leaves of the cherrylaurel, yield; by simple distillation, abundance of prussic acid (cyanide of hydrogen), but this is only then produced by the decomposition of other substances containing nitrogen.
Cyanogen may, however, be formed abundantly, and in a simple
manner, by bringing its elements together at a high temperature, in
contact wi.th substances with which it may unite.  Thus, when any
organic substance containing nitrogen is calcined with potash, the
nascent carbon and nitrogen unite, and cyanide of potassium  is
formed; even with pure charcoal this occurs, nitrogen being derived
from the air; and Mr. Fownes has shown, that when a mixture of
pure charcoal and potash is ignited in a tube, and a current of
pure nitrogen passed through it, this is absorbed, and carbonic oxide
gas being given off, cyanide of potassium is produced, 3C. with K.O.
and N. giving C.O. and C2N.K. By the action of ammonia, also, on
ignited charcoal, cyanogen is formed in abundance; it combines
with hydrogen and the excess of ammonia, and produces prussiate
of ammonia. In this case 2C. and 2N.H3 produce CH.+N.H3, and
HI2 become free. It is by virtue of these processes that cyanogen
is produced for its various applications in the arts; but, as I shall return to them in detail, I shall now only consider farther the mode
of obtaining it free and pure.
Cyanide of silver, or cyanide of mercury, of which the preparation will be described hereafter, is to be introduced into a small
glass retort, and heated to just below redness; a gas is given off,
which must be collected over the mercurial trough; the cyanide of
silver separates simply into metal and cyanogen; but when cyanide
of mercury is used, a brown powder appears, the quantity of which
is less as the temperature of decomposition has been lower. The
gas which comes over is, however, cyanogen completely pure.
Its properties are very marked. It is colourless, of a sharp smell,
which irritates the eyes. Its sp. gr. is 1819. If a quantity of cyanide of silver be sealed up in a strong tube, bent as in the figure,
and then heated at one end, a, the cyanogen is condensed by a pressTTT




514                    CYANIC ACID.
ure of about four atmrospheres, and
cr.            \   b  collects at the other end, b, as a cola —~~-'.... _2 ourless liquid.  It is combustible,
burning with a beauiiful rose-coloured flame, and producing two volumes of carbonic acid and one of
nitrogen. It is constituted, therefore, of equal volumes of carbon
vapour and nitrogen, the two volumes being condensed to one;
hence 84 3+976-1819 is its sp. gr. It dissolves abundantly in alcohol and water, but these solutions soon undergo very complex
decompositions, the liquor being found to contain carbonic acid,
prussic acid, ammonia, urea, and oxalic acid, besides a brown insoluble matter. A similar decomposition is produced much more
rapidly by contact with water of ammonia. The composition of
this brown matter appears to be CN2. H.O. It dissolves in alkalies,
and gives precipitates with the metallic salts; it has been termed
hence./Izulmic acid.  When heated, it gives off water, and leaves a
deep brown powvder, of the same composition as cyanogen, and
which has been termed Paracyanogen.  This may be also formed by
heating cyanide of mercury very strongly. It dissolves in hot nitric acid, and the solution gives, with water, a yellowpprecipitate,
which combines with bases, and has been termed Paracyanic acid.
By strong ignition, paracyanogen evolves nitrogen, and a very dense
carbon remains.
Cyanogen combines directly with hydrogen and with the metals,
but its oxygen combinations require to be indirectly formed; there
are three compounds of cyanogen and oxygen, which are all acids,
and are polymeric bodies. It unites also with sulphur, and its compounds have a remarkable tendency to form double and triple cornmbinations.
The formula of cyanogen is indifferently written C2N. or Cy. ]ts
equivalent number is 328'6 or 26'05.
SECTION I.
NON-METALLIC COMPOUNDS OF CYANOGEN.
Compoutnds of Cyanogneh and Oxygen.
Cyanic JAcid-Cy.O.; Eq. 428'6 or 34'05-is very easily obtained
in combination, by calcining the cyanide of potassium in contact
with the air, at a temperature below redness, in which case oxygen
is directly absorbed; or by heating the cyanide with nitre, or with
peroxide of manganesel which yield the oxygen required. For this
purpose the yellow prussiate of potash of commerce may be employed, as the cyanide of iron which it contains is totally decomposed, and the cyanide of potassium then acts as if it were completely pure. The cyanic acid cannot, however, be isolated from
these salts by a stronger acid, as it then rapidly changes into bicarbonate of ammonia, uniting with the elements of three atoms of'water; thus C2N.O. and 3H.0. produce N.H, and 2C.O,.
The cyanic acid can be obtained free only by distilling the cyanuric acid, CyOa+3H.O., which then transforms itself into the hydrated cyanic acid, Cy.O.H.O0., and is to be collected in a receiveri surrounded with snow. It is a colourless liquid, of a very pun



SALTS  OF CYANIC  ACIDS ETC.                    5-15
gent odour, cauterizes the skin, and, when mixed with water, is
decomposed as above stated.  When preserved in its most concentrated form, it soon transforms itself into a white mass, like porcelain, of the same composition, CN..EI.O2, which has been termed
Cyanamelide.  This body is insoluble in water, b-ut by heat is transformed back again into hydrated cyanic acid, and by strong acids
is resolved into carbonate of ammonia.
Cyanic acid does not exist in the anhydrous state.
The cyanic acid forms but one series of salts, being monobasic;
those of the alkalies are soluble; the others are white insoluble
powders.
Cyarate of Potash.-Cy.O.. K.O. The yellow prussiate of potash
of comrnmeice, being roasted in an earthen dish, absorbs oxygen, and
the cyanide of potassium is converted into cyanate of potash.
VWhen the mass becomes adhesive from the fusion of the product,
it is to be digested with alcohol, from which the pure cyanate crystallizes, on cooling, in rhombic tables like chlorate of potash. In
contact with water this salt is rapidly decomposed, ammonia being
evolved, and carbonate of potash formed.  If dry cyanate of potash
and dry crystals of oxalic acid be rubbed together in a mortar, oxai.lte of potash is formed, and the cyanic acid changes into cyanainelide.
C(yanic.Acid and Jummnonia.-If hydrated cyanic acid be placed in
contact with dry ammt-onia, they combine, and form a white, woolly
mass, which dissolves in water, and acts as an ordinary cyanate; It
appears to contain Cy.O. - H.O.+2NF1.H3.  If it be gently heated it
gives off'ammonia, and is transformied into an important substance,
Urea, which, though thus capable of being artificially produced, will
be specially described as a product of the organization, in another
chapter. ~Whenever we attempt to form  the neutral cyanate of
annmmonia, Cy.O.. N.t. H.O0., urea is produced; thus, by acting on
cyanate of silver with muriate of ammonia, or by mixing solutions
of sulphate of ammonia and cyanate of potash. But still we cannot
consider urea to be merely cyanate of ammonia, to which it bears
the samte relation that cyanarmelide dcoes to hydrated cyanic acid.'mdlvminzic./Icid. -Cy:O + 211.O.  This acid, which has attracted
mnuch attention from. the detonating properties of its salts, is prepared by the action of nitric acid on alcohol, in presence of oxide
of mercury or silver.  The reaction is very complex; a crowd of
products of the oxidation of the alcohol being evolved, as aldehyd,
formlic, acetic, and oxalic acid, &c.  If the action were limited to
the essential conditions, it wouild probably consist in two equiva
lents of alcohol and two of nitric acid, producing o.ne of acetic acid,
one of fulminic acid, and eight of water; thus 2N.0 and 2(CH,,602)
give C4H1-404 and QCN,.02, besides 811.0.'The fulminic acid cannot be obtained in an isolated form; when
we attemrpt to separate it from  bases, it is instantly decomposed.
Thuis, if' fulminate of silver be acted on by dilute muriatic acid,
chloride of silver, and a peculiar acid containing chlorine and cyanogen, tre produced.  The fultm-inic acid is bibasic, and forms two
series of salts, of whicih the neutral contains two equivalents of fixed
base, the acid salts containing one of fixed base and one of water




516 FUL M IIXNATEES' OF  SILVER  AND MERCURY; ETC.
Fulminate of Silver.-Cy202+2Ag.O.  It is prepared by dissolve
ing silver in ten parts of nitric acid, specific gravity 1'35, and pouring the solution, when cold, into twenty parts of rectified spirits of
wine. The mixture is to be gently heated till it begins to boil, and
then left to cool slowly.  The fulminate of silver is deposited in
fine silky crystals, snow-white, and equal in weirght to the silver
employed. It is very sparingly soluble in cold water. It detonates
with the slightest shock, or by contact with sulphuric acid. When
acted on by a caustic alkali, as potash, half of the silver separates
as oxide, and a salt is formed, Cy202-+K O.. Ag.O. If it be dissolv
ed in warm dilute nitric acid, half of the silver is also removed and
replaced by water, and on cooling, the acid fulminate of silver, Cy,
02+OH.O.. Ag.O., crystallizes out. This explodes more readil)
than the first salt, by friction, and by contact with oil of vitriol (i
chlorine gas.
By digesting these fulminates of silver with metallic zinc or
copper, fulminates of these metals with two atoms of oxide are ok
tained; and by acting on these salts with an alkali or barytes, saltt
with two different bases may be formed. In no case, however, cal
a fulminate containing two atoms of an alkaline base be produced.
All these salts possess detonating properties more or less violent.
Fulminate of the Suboxide of.JAercury.-Cy20+,O,-2g20. This, the
most important salt of fulminic acid, is prepared by dissolving mercury in nitric acid, and treating it by alcohol, as in preparing fulminate of silver. As the solution cools, some metallic mercury
precipitates, and the fulminate of the suboxide is deposited in hard,
opaque, white crystals, generally very minute.  It is to be washed
and redissolved in boiling water, and crystallizes then in fine silky
needles.  This salt detonates violently when struck between two
hard bodies. It is extensively used in the manufacture of the percussion caps used for firearms. As a great quantity of alcohol is
wasted in this process, it was proposed to carry on the action in
close vessels, and condense the spirit, which, however, was found
to be unfit for any but the same use, from containing a large quantity of prussic acid.
Cyanuric.Acid.-Cy3,, — 3H.O.
This acid is produced under a variety of circumstances where
the elements of cyanic acid become free. Thus, if the solid chloride of cyanogen be treated with water, Cy.CI. and H.O. produce
H.Cl. and Cy.O., butf this transforms itself immediately into cyanuric acid.  It is formed abundantly, as a white sublimate,.in the dry
distillation of uric acid, and may be very simply produced by heating urea a little above its point of fusion in a glass retort; ammonia is given off, and the urea changes into a dry, gray mass, which
is to be dissolved in strong sulphuric acid, and treated with nitric
acid, added in'small quantities, until it becomes quite colourless.
Being then diluted with its own weight of water, the liquor yields
crystals of cyanuric acid on cooling. It is evident that three atoms
of urea, 3(C2H4. N202), contain the elements of three atoms of ammonia and one of cyanuric acid, CN,03~+ 3H.O.
By means of a substance which will be hereafter noticed, termed




PREPARATION OF PRUS SIC ACID.                   517
Jelam, cyanuric acid may be formed simply and in quantity. The
details of the process will be given when describing the properties.of that body.
Cyanuric acid is colourless and nearly tasteless, possessing a very
slight acid reaction. It crystallizes in oblique rhombic prisms, which
have the formula Cy3O3-3H.O.+4 Aq. By a moderate heat, the 4
Aq. are expelled, and when more strongly heated, the dry acid changes into hydrated cyanic acid. This acid, being tribasic, forms
thre.e distinct classes of salts, which differ as the quantity of fixed
base is one, or two, or three atoms. If any of these salts be acted
on by a stronger acid, the cyanuric acid is completely liberated.
Cyanide of Hydrogen. Hlydrocyanic.fcid. Prussic Acid.
This remarkable substance may be formed by the direct cormbination of hydrogen and cyanogen. It exists in the water distilled
from bitter almonds, or from the leaves of the cherry-laurel, being
produced by the decomposition of a peculiar substance, 4]mygdaline,
which those plants contain.  For the purposes of medicine and
chemistry, it is prepared by indirect processes of many kinds.
Thus, if formiate of ammonia (CH.O3+N.H40.) be passed in vapour through a red-hot porcelain tube, it is totally converted into
prussic acid and water, C.N.H. and 4H.O. Also, by passing ammonia over red-hot charcoal, hydrocyanate of ammonia is formed in
such quantity that prussic acid may be economically prepared from
it. If cyanide of silver be decomposed by muriatic acid, chloride
of silver and cyanide of hydrogen are produced (Ag.Cy. and H.CI.
giving Ag.Cl. and H.Cy.); and by sulphuret of hydrogen, cyanide
of mercury gives sulphuret of mercury and prussic acid. For its
preparation on the large scale, however, the substance used is the
yellow prussiate of potash of commerce.
This salt, the preparation of which will be hereafter described,
consists of cyanide of iron united to cyanide of potassium; by the
action of sulphuric acid, three fourths of the latter are decomposed,
bisulphate of potash being formed, and prussic acid liberated, 2(S.
03+H-.Q) and Cy.K. giving (K.O.. S.O-I-H0.. S.O3) and Cy.H.
The cyanide of iron remains still combined with the other fourth
of the cyanide of potassium, forming a compound first described by
Mr. Everitt, The prussic acid thus produced contains, therefore,
one half of the cyanogen which existed in the salt employed. The
precise decomposition is, that two equivalents of the yellow ferroprussiate of potash, 2(Fe.Cy.+2K.Cy.), acted on by six atoms of oil
of vitriol, 6(S.O0+H 0.), produce three atoms of bisulphate of potf.
ash, 3(H.O.. S.03+K.0.. S.03), and three atoms of prussic acid, 3H.
Cy.; there remains then an atom of Everitt's salt, 2(Fe.Cy.+K.Cy.),
which, when first formed, is yellow, but by rapidly absorbing oxygen
it becomes greenish, and, abandoning its cyanide of potassium, is
finally converted into basic Prussian blue.
The mode of conducting the process depends on the degree of
strength at which the prussic acid is required. To obtain the anhydrous acid, three parts of yellow prussiate of potash, in fine powder, are to be decomposed by a mixture of two parts of;'oil of vitriol and two of water, in a small retort, at a very gentle heat, and




518         PROPERTIES OF PRUSS 1 C ACID.
the product collected in a receiver, surroundel by ice, and containl
ing some fragments of recently-fused chloride of calcium, by which
any traces of water which come over are absorbed.  The process
originally employed by Gay Lussac consists in decomposing cyan.
ide of mercury by strong muriatic acid, and passing the vapour
through a long tube, of which the half next the retort contains small
fragments of marble, and the other half fragments of recently-fused
chloride of calcium; any muriatic acid vapour is arrested by the
former, and the prussic acid is rendered anhydrous by the latter;
the vapour is then condensed in a receiver, surrounded by ice.
Pure prussic acid is a colourless liquid; its specific gravity at
673 is 0'6969; at 5~ Fah. it congeals into a mass of fibrous crystals,
and at 80~ boils. In consequence of this great volatility, if a drop
of it be suspended from a glass rod, one part of it will be solidified
by the cold, produced by the rapid evaporation of another portion.
The density of its vapour is 943'9, consisting of equal volumes of
cyanogcen and hydrogen, united without condensation, as (1819'0 q68'8)-.2=943'9. It reddens litmus paper feebly, and the tint disappears by heat. Its odour is extremely suffocating and pungent,
and resembles that of bitter almonds.  Its taste is bitter and acrid.
It is combustible, burning with a bright white flame. Being a poison of intense activity, the greatest care should be used in manipulating with it in this concentrated form.
Anhydrous prussic acid decomposes rapidly, especially if exposed
to light.  It forms ammonia, and a brown substance, probably the
same as that produced from a solution of cyanogen in water, and
termed vtzulmic aIcid, as noticed p. 514, but of which the composition is not well known. By contact with a strong acid, prussic acid
assimilates the elements of three atoms of water, and produces formic acid and ammonia (C2N.IH. and 311.0. giving C2I-.O3 and N.
H3). Hence, in the preparation of prussic acid, an excess of any
mineral acid should be avoided.  With chlorine, prussic acid forms
muriatic acid and chloride of cyanogen, and with iodine it acts
similarly.
For medicinal use, the prussic acid is prepared in a very dilute
condition.  The directions sometimes given in pharmacopoeias to
distil over an acid of a specific strength, are, in practice, very difficult to execute, and might give rise to serious errors. The proper method is to prepare an acid stronger than that required; then,
to ascertain by accurate analysis its strength, and dilute it with distilled water until it be brought exactly to the degree required.
This process is carried on in the manufacturing laboratory of the
Apothecaries' Hall of Ireland as follows: 1 lb. of crystallized yellow
prussiate of potash, in fine powder, is placed in a capacious retort,
and 2 lbs. of water poured on it; to this is added a mixture of 12
ozs. of oil of vitriol and 2 lbs. of water, previously suffered to cool.
These materials are well agitated, and allowed to digest for three
or four hours, and then between 2 and 3 lbs. of dilute acid are distilled over into a receiver containing already i lb. of distilled water;
there are obtained thus 3 or 4 lbs. of an acid containing fiom 6 to
8 per cent. of real acid.  200 grs. of this are weighed and decomr
posed by an excess of nitrate of silver; the cyanide of silver pre.




DETECTION  OF  PRUSSIC  ACID.                           519
cipitated  is carefully  collected, washed, and  dried.  Being then
weighed, the exact per centage of acid present is found by calculation, and the necessary quantity of water is added, so as to bring
it to the standard strength of the Dublin pharmacopcoia, which is
that of 1-6 per cent. of real acid, and specific gravity of 0'998.
As an example of this process, let us suppose that the 200 grs. of' disilled acid gave
with nitrate of silver, 74 grs. of cyanide; as this contains 14'95 of cyanogen, the 20
grs. contained 15'53 of real acid, or 7'76 per cent.; now, to reduce this to the Dublin
standard, divide 7'7t) by 1I6, which gives 4,85; indicating that by adding 3-85 lbs.
of distilled water to each pound of acid, the mixture will have accurately the strength
directed by the pharmacopceia. Some of this calculation may be spared by considering the cyanide of silver to be equivalent to one fifth of its weight of real prussic
acid; the quantity per cent. in the supposed example should then be one tenth of
the weight of cyanide of silver obtained from the 200 grs., that is, 7'4 per cent.; and
the nwater necessary to bring it to the Dublin standard should be 3'63 times its
weight. The error introduced by this simplification is not sensible, being but 0O003O
per cent.
The strength of the prussic acid directed by the British pharmna.
copacis differs very mulch: that prescribed by the London College
contains about 2 per cent. of real acid; that of the Edinburgh College contains about 4 per cent.; while the Dublin strength is but
1.5 or 1.6 of real acid per cent.  This should be carefully attended
to in practice.
A method has been proposed for determaining the value of prussic acid, by digest.
ing it on a known quantity of red oxide of mercury; when the prussic acid has saturated itself with the oxide, what remains is to be washed, dried, and weighed.
Now, as 116'4 of oxide of mercury is converted into cyanide by 27'1 of prussic acid,
which proportion is nearly 4 to 1, the quantity of prussic acid is pretty correctly one
fourth of the weight of the oxide of mercury dissolved. But as cyanide of mercury
may combine with an excess of oxide, and as the quantity thus liable to be taken
up is not constant, it is dangerous to rely on this method for medicinal or analytical purposes.
The detection of prussic acid is very simple.  Ist. Its solution
gives, with nitrate of silver, a white precipitate, cyanide of silver,
insoluble in strong nitric acid when cold, but dissolved by boiling;
it is insoluble in ammonia.  If a liquor containing even a very small
trace of prussic acid be boiled, the vapour produces a white cloud
on a piece of.glass moistened with solution of nitrate of silver. 2d.
If a solution of sulphate of iron be added to prussic acid, there is
no change; but on adding some potash liquor, a dirty greenish precipitate is produced, from which muriatic acid dissolves out the excess of oxide of iron, and leaves Prussian blue (cyanide of iron) of
a very rich colour: it is essential to the proper action of this test,
that both protoxide and peroxide of iron be present in the solution.
3d. If a solution of sulphate of copper be added to the liquor containing prussic acid, and then treated successively with potash and
inuriatic acid, as above, a white precipitate remains undissolved,
which is cyanide of copper. The theory of these last actions is,
that the prussic acid is too weak to decompose, by itself, either
metallic sulphates, but, on the addition of potash, double decomnposition occurs, sulphate of potash and a metallic cyanide being form.
ed. As the potash is always added in excess, a quantity of metallie oxide is at the same time precipitated, which masks the colour
of the result, but is removed by the addition of the muriatic acid.
4th. These insoluble cyanides may be recognised very elegantly by
heatinog them  wvith a little potash and sulphur, and dissolving the




520            CYANIDE  OF  POTASSIUM. ETC.
fused mass in water. The solution gives, with a persalt of iron, a
fine blood-red colour.  5th. The cyanide of silver, also, is known
by giving off cyanogen when heated.
There are two chdlorides of Cyan~og'e of the same composition, and bearing to each
other the same relation as the cyanic and cyanuric acids. One is gaseous, the other
solid; the first is prepared by acting on moist cyanide of mercury by chlorine, or by
passing chlorine into weak prussic acid, and warming the mixture in which the
chloride of cyanogen dissolves. This gas, which is very irritating and poisonous,
may be obtained crystallized in needles by exposure to a very low temperature. It
combines with ammonia, forming a crystalline substance.
The solid chloride may be prepared by acting on anhydrous prussic acid with
chlorine, or by heating sulphocyanide of potassium in a current of chlorine. It sublimes in white transparent needles. It dissolves unaltered in alcohol and ether, and
is decomposed by hot water into hydrochloric and cyanuric acids.
Iodide (f C?/amog'cib is prepared by distilling, in a retort, a mixture of iodine, cyanide of mnercury, and water. At a moderate heat, the iodide of cyanogen passes over,
and condenses in the neck of the retort as a flocculent mass of snow-white needles.
These crystals irritate the eyes: they dissolve in water unaltered, and volatilize at
1l13.
SECTION II.
OF THE MIETALLIC CYANIDES.
Cyanide of Potassium;, K.Cy., may be formed by the direct union
of its elements, or by adding an excess of prussic acid to a solution
of potash, and evaporating rapidly without the access of air.  It is
produced also whenever carbonaceous matter is calcined in contact
with potash, provided nitrogen be present.  The best mode of obtaining' it, however, is to expose the yellow prussiate of potash to a
full red heat, in a close iron crucible.  The cyanide of iron is decomposed, nitrogen being given off and carburet of iron remaining
with the unaltered cyanide of potassium.  The half-melted mass is
to be coarsely powdered, and digested in boiling, weak spirit of
wine, from  which the salt crystallizes in cubes on cooling.  Spirit
of specific gravity 0'900 at 60', is remarlkable for dissolving a large
quantity of cyanide of potassium  when boiling, but depositing it
nearly totally when it cools.
This salt in solution reacts alkaline, and smells of bitter almonds,
and hence probably decomposes water when dissolved.  Its crystals
deliquesce and are decomposed, even in close vessels, after a short
time, by contact with water, into ammonia and formiate of potash.
The properties of the cyanide of sodium and of the hydrocyanate
of ammonia are quite similar.
The Cyanides of Bariurm, strontium, calcium, and magnesium are soluble in water, and crystallizable.
Cycanide of Zinc is prepared by adding prussic acid to a solution of acetate of
zinc, when it precipitates as a white powder. Chloride of zinc is not decomposed
by prussic acid. With cyanide of potassium it forms a double salt.
Cyanide of Copper is formed as a whitish precipitate when prussic acid and potash
are added to a solution of sulphate of copper. When boiled it becomes yellowv, and
combines with the oxide of copper to form an oxycycanide of a lively green colour.
It forms doable salts with the alkaline cyanides.
Cyanide of Jfercury-Hg.Cy.; Eq. 1594'4 or 127-45-may be prepared by boiling two parts of Prussian blue with one of red oxide
of mercury and eight of water, until the residue becomes red-brown.
The filtered liquor yields cyanide of mercury in crystals, which,
however, are not quite free from  iron, and require to be digested
with a little more oxide of mercury and recrystallized.  The best




CYANIDE  OF  MERCURY, ETC.                            521
mode of preparing it is to distil fifteen parts of yellow prussiate of
potash, with thirteen of oil of vitriol and 100 of water, nearly to dryness, and to digest the prussic acid so obtained with twelve parts
of finely-powdered oxide of mercury, until this is completely dissolved.  The solution yields, by evaporation and cooling, fourteen
parts of pure crystallized cyanide of mercury.  By washing out the
residue in the retort with water, five parts of pure Prussian blue may be obtained.
Cyanide of mercury crystallizes in colourless rectangular prisms, as q q, in the figure, terminated by numerous secondary faces, as e e.  These crystals are anhy- 
drous, and occasionally opaque.  When heated, it is resolved into mercury and cyanogen, of which a portion is resolved
into the brown powder (paracyanogen).  It is sparingly soluble in
alcohol.'t tastes as the other mercurial salts.  So great is the
affinity of mercury to cyanog'en, that cyanide of potassium, when
boiled with oxide of mercury, is decomposed, and caustic potash
liberated. In a solution of cyanide of merctury, no test indicates
the presence of the mietal except sulphuretted hydrogen.  It is not
decomposed by oxygen acids, but muriatic acid forms prussic acid
and chloride of mercury.
Cyanide of mercury, when digested with an excess of oxide of mercury, combines
with it in two proportions, forming the oxz~/cyaniides of M/rfer'Cy1u', Hg.Cy.+f-Ig'.O. andl
Hg.Cy.+3-Ig.0. These bodies are soluble in water, and crystallize in prismatic
needles.
5With iodide of potassium, cyanide of mercury combines, forming a substance, 2
-g.Cy.+K.I., uwhich is very soluble in boiling water, and crystallizes in brilliant
white micaceous plates on cooling  This salt is instantly reddened by any mineral
acid which liberates iodide of mer cury. With sulphocyanide of potassium a similar compound is formed, 21Hg.Cy.+-K.Cy.Sz.
Cyanide of mercury combines with the alkaline cyanides, and with the alkaline chlorides and bromides, forming double salts possessing no special interest. It
combines with many oxygen salts also, as the chromate and formliate of' potash.
As prussic acid is now no longer prepared from cyanide of mercury, this body is
not so imlportant as formerly. It is poisonous, anid is occasionally employed in
medicine.
Cyanide off Silver, Ag.Cy., is a white powder insoluble in water, which combines
with other cyanides to form double salts. It is soluble in water of ammonia, but
insoluble in nitric acid, except it be strong and boiling. Heated, it gives cyanogen
and metallic silver.
Cyanide of Palladiseer.-In its affity for cyanogen, palladium resembles mercury.
Every soluble salt of palladium is decomposed by prussic acid, a pale yellow precipitate being formed. This cyanide of palladium is insoluble in water, but soluble in
acids and in ammonia. Heated, it gives cyanogen and leaves the metal. It forms
a very extensive class of double salts.
Cyanide of Gold, Au.Cya, is a pale yellow powder, forming double salts with the
alkaline cyanides.
Protocya6nide of Iron, Fe.Cy., is not known in an isolated folu   S at it enters into
combination with the other metallic cyanides, forming double salts, which are some
of the most interesLing of the cyanogen compounds. The iron in these salts cannot
be separated by an alkali, and hence may be looked upon as an element of the negative constituent; they are hence often termed ferrocyaceides, or fer?'opr',ssiitzs of
whatever other metal they muay contain.
Ferrocyanide of H1ydrogen.  Ferrocyanic  adcid.-Fe.Cy. + 2H.Cy
When the ferrocyanide of lead is decomposed by sulphuret of hy
drogen, a solution is obtained, which yields, on evaporation in vacuo,
small granular crystals, which have a well-marked acid reaction,
and produce, by acting on metallic oxides, all the ordinary ferrocyanides. If the solution be boiled, it is resolved into prussic acid,
Uu U




522          FERROCYANIDE  OF POTASSIUM.
and a white precipitate, which becomes blue in the air. The crys.
tals undergo the same change spontaneously after some time.
Ferrocyanide oJ Potassium.-F e.Cy. 1- QK.Cy.  + 3 Aq.  Eq.  656' 9
or'2125.  This'compound, of which I have often spoken as Yelloiw
Prussiate of Potash, is prepared on the large scale for the purposes
of the arts and of pharmacy, by calcining  together some animal
matters, ais blood, hoofs, horns, &c., with pearl ashes and iroc
filings.  It may be fo-rmfed even if the organic matter do not contain
nitrogen, as that element may be supplied from the air.'The operation is conducted in large iron pots arranged in a furnace, so that
the mass can be heated to dull redness, andi continually agitated as
it forms a tenacious paste, the calcining of which is continued as
long as it burns with a white flame; it is then taken out of the pot,
and when cold, boiled in water, which, by evaporation, yields the
salt in crystals.  If it has not dissolved iron enough, sorne copperas
is added as long as the Prussian blue, which at first forms, is found
to redissolve.  After what has been said of the formation of cyanogen (p. 513), the theory of this process inay easily be understood.
The ferrocyanide of potassium crystallizes in truncated octohe3../.& __.-'_~_..:._ 3_- ~ ~ drons with a rectangular base, e e' e",
e'.. ".... —-:. as in the figure, of which A represents
/~;_-./ - -------— e' 7   the tusual simlple, and B a more com_ —~'5't  plicated form; the secondary plane n
often being so large as to render the crystal merely tabular.  Its
colour is fine citron-yellow, but when dried it becomes white.  By
-. farther heat in close vessels it fuses,. and when ignited gives off
nitrogen, and leaves cyanide of potassium  and carburet of iron.
Heated in open vessels, it absorbs oxygen, and forms cyanate of
potash.  Its use in the preparation of these bodies and of prussic
acid has been already detailed.  If it be digested with oxide of mercury, cyanide of mercury is formed, and oxide of iron and caustic
potash set free. With sulphate of mercury it gives sulphate of potash, cyanide of mercury, and Everitt's yellow salt.
With cyanide of mercury, ferrocyanide of potassium  forms a
double salt, whose formula I found to be 3Hg.Cy.+(Fe.Cy.+ —2K
Cy.)+4 Aq. It crystallizes in pale yellow rhombic tables.
In the arts, the ferrocyanide of potassium is of importance for
dyeing various shades of blue; to the chemist it is specially of interest, as from it all the cyanogen compounds are most economically formed, and from the peculiar precipitates it gives with solutions of most metals, it is of eminent service in their detection.
Thus, with solutions of silver, mercury, bismuth, tin, lead, nswkel, zinc,
manganese, and cerium, it gives white precipitates; that with mercury gradually becomes blueish, and that of manganese reddish.  With
copper, thle precipitate is of a rich chocolate colour; with cobalt,
greenish, changing to red; with uranium and molybdenum, brown;
and with chrome, grayish-green.  All these precipitates contain cyanide of iron, united to two atoms of cyanide of the other metal,
being true ferrocyanides.
It is on solutions of iron that the action of this reagent is the most
remarkable.  With solution of protosulphate of iron, a whitish precipitate is obtained, which consists of the cyanides of iron and po



PRIEP VRATION  OF  PRUSSIAN  BLUE, ETC.   523
tassium, united in proportions which are not well known.  Exposed
to the air, this body absorbs oxygen and becomes blue.  With a solution of sulphate of iron pure Prussian Blue is precipitated.  This
substance is insoluble in water and in muriatic acid, and gives with
caustic alkalies oxide of iron and ferrocyanide of potassiu: m; its
formula is Fe-Cy,, or it consists of 3Fe.Cy.+2Fe?,y3.  Its formation involves 3(Fe.Cy. + 2K.Cy.) and 2      0FeO3 + 3 S.O), and there remain dissolved six atoms of sulphate of potash.  For tile manufacture of Prussian blue for the purposes of the arts, the impure liquor
obtained by digesting in water the calcined imass of animral matter,
potash and iron, described p. 522, is decomposed by an excess of
sulphate of iron, and the resulting precipitate digested in rnuriatic
acid, and exposed to the air until it assumes its proper colour.  It
is then dried carefully at a moderate heat.
Another kind of Prussian blue is pi'oduced when Everitt's salt,
or the white precipitate produced by protosulphate of iron with yellow prussiate of potash, is exposed moist to the air.  It is termed
basic Prussian Blue.  As Everitt's salt consists of 2Fe.Cy.+K.Cy.,
and this last dissolves out, there is the same number of' atoms of
cyanogen and iron, and the excess of iron above that necessary to
form  true Prussian blue combines writh the oxygen of the air, the
oxide so formed remaining united with the Prussian blue.  From  9
Fe.Cy. and 30. there is thus formed 3(Fe.Cy. +- 2FeCyC3+Fef0), the
basic compoulnd.
Tie forr.o':ycvbids- of,Sod'iuo;, B cwrii:7, &c., possess all the essential characters of
the potassiun salt, and need not be firther noticed.
The ferrocyanides in many cases combine with each other, forming salts, which
contain three difierenit metals combined with cyanoen.
S'csqpicyai(ide of Iron, 1,eO2Cy3, is not known in an isolated form, but, like the protocvanide, enters into a number of combinations withl the other mletallic cyanides,
which mRav be called either pf'irrocyrbides or fre'riilhnpil,   as proposed by Liebig.
Fe rridcyanide of Potassiunz -Red Prus'siate of Potash, Fe2Cy,+ 3K.
Cy., is formed by passing chlorine through a solution of yellow prussiate of potash until it ceases to give Prussian blue with solution
of persulphate of iron.  The liquor becomes of a deep green colour,
but on evaporation yields anhydrous fine ruby-red prismatic crystals, which are generally inacles.  The products of its decomposition by heat are the same as those of the yellow salt.  It dissolves
in thirty-eight parts of cold water; its solution, if pure, is yellow,
but more commonly is green.
This salt rivals that already described in its utility as a reagent
for the proper metals.  The precipitates it gives with their solutions
are, tin, white; mercuiry, silver, and zinc, yellow; titanium, nickel,
copper, and bismutth, yellowish brown; and cobalt, uranimnz,'and manganese, brown.  It is, however, with the salts of' iron that its reaction is most remarkable.  With a persalt of iron it merely colours
the liquor green, but with a solution of a protosalt it gives a blue
precipitate, even richer in colour than the proper Prussian blue, and
consisting of Fe,Cy6, or of FeCy+3~Fe. Cy.; thus containing the
same protocyanide with half as much sesquicyanide as exists in
common Prussian blue.  This ferridcyanide of Iron is made for
commerce, and sold as Turnbull's Prussian Blue.
Ferridcyanide of Hydrogen. If we digest ferridcyanide of lead




524      TH EORY  OF  TIlE  COIMPLEX  CYANIDES.
with dilute sulphuric acid, a red liquor is obtained, which yields on
evaporation a mass of minute brownish-yellow needles, the formula
of which is Fe,Cy3+3Cy.H.  This body reddens litmus, and has a
sour astringent taste; upon another theory it is considered to be a
compound of hydrogen with a compound radical, (Fe2Cy6), and is
termed Ferridcyanic /tfcid.
In the history of these complex cyanides we meet three facts, on which the theories of their constitution must be founded.  1st. The extraordinary tendency to
double combination, which no other body possesses in the same degree. 2d. In
almost all cases, the cyanogen enters into the compound in the proportion of three,
six, or nine atoms; and, 3d. One metallic element, as iron, in each compound, is
retained with extraordinary force, not being detected therein by its ordinary reagents. The original view proposed by Berzelius, of considering these compounds
as mere double salts, and upon which the fhrrnulau given hitherto have been constructed, does not account sufficiently for these facts, and I hence consider it as
less applicable to them than the theories suggested by Graham and by Liebig.
The latter chemist founds his view upon the third fact, and supposes that there
exists a series of compound radicals, consisting of cyanogen united Ewith a metal.
Thus, Ferrocyanogzn, (Fe.GCy3) or Cfy., and Ferridcyanogecn, (Fe2Cy6) or Cfy2, these
two being isomeric; Cobaltocyanogen, (Co2Cy6) or Cky., and many others; and these
radicals combine with hydrogen to form polybasic hydracids, fiom which, the hydrogen being replaced by a metal, result the ordinary complex cyanides. Thus,
the ferrocyanogen being bibasic, its acid is Cfy.t2H.; its potash salt, Cfy.J,-2K.;
its copper salt, Cfy.+2Cu.; and if each atom of hydrogen be replaced by a different
metal, then the triple salts formed by Mosander are produced: thus, the salt written on Berzelius's view as (Fe.Cy.+2K.Cy.)+(Fe.Cy.+2Ca.Cy.) becomes Cfy.+
Ca.K., and similarly there is Cfy.+Ca.K., &c.
The red prussiate of potash Liebig supposes to contain a radical, (Fe2Cy6) or
Cfy2, isomeric with, but of double the atomic weight of ferrocyanogen; this ferridcyanogen forms with hydrogen a tribasic acid, Cfy2,-H3, by replacement of the
hydrogen, in which, by three atoms of the same or of different metals, the various
ferridcyanides are produced, as Cfy2,+K3, Cfy2+3Cu., &c.
Tile Prussian hlues, on this theory, are considered to be compounds of ferrocyanide with ferridcyanide of iron; thus,
3Cfy.Fe2-Cfy2Fe3 expresses common Prussian blue.
Cfy2Fe3               "    Turnbull's Prussian blue.
3Cfy.Fe2+Cfy2Fe3+Fe23Fe      " basic Prussian blue.
This theory accounts very strictly for the first and third of the fundamental
facts which I have described as characterizing the cyanogen compounds. The
theory of Graham is specially based upon the tendency of three atoms of cyanogen
to enter together into combination with other bodies, as is shown not only in its re.
lation to metals, but to oxygen, as in cyanuric acid, and hence we may assume
that cyanogen, as Cy3, with three times its ordinary atomic weight, forms a distinct radical (paracyan?), which forms with oxygen and with hydrogen tribasic
acids, Cy303 and CyI3H. From the replacement of more or less of this hydrogen
in the latter by equivalents of one or more metal, the various cyanides may be
formed. Thus, for example,
Cy3+Fe.2K.       yellow prussiate of potash.
Cy3+-Fe.K.Ca... ferroprussiate of lime and potash.
Cy3+ —Fe.2HI.-.    ferroprussic acid.
The basis of the red prussiate of potash should be, then, another polymeric cyano.
gen, Cy6, which would form, with hydrogen, a pentabasic acid, Cy6s-Hs, in which
more or less of replacement by metals should give: the various ferridcyanides.
Thus ferridprussic acid should be Cy6+-Fe2Hs, and red prussiate of potash Cy6+
Fe2K3, and so on; Turnbull's Prussian blue becomes, on this theory, simply Cy6+
Fe5; the common Prussian blue is (Cy3aFe2)+-Cy6Fe5; and, by the addition of
Fe203 to that, the basic Prussian blue is formed.
I am rather inclined to adopt Graham's view, although, in the present state of
our knowledge, we have not grounds for positive decision. He proposes to term
the radical Cy3 Prussine, but has not given any name to that whose formula is Cys.




METALLIC SUT P IIO CYANIDE S.                 525
Of Sulphocyanooen, andz tIke Products of its Decomposition.
If yellow prussiate of potash, well dried, and mixed carefully with
half its weight of sulphur, in fine powder, be heated in an iron vessel to perfect fusion, which takes place at a dull red heat, the sulphur combines with all the cyanogen, forming sulphocyanogen,
which unites with the potassium, while the iron is converted into
sulphuret. By digesting the fused mass in water, the former dissolves, and is obtained, by evaporation and cooling, in long striated
prisms, similar to those of nitre. If the temperature be not raised
too high, the iron forms also sulphocyanide, which dissolves, and
may be decomposed by the addition of a slight excess of carbonate
of potash; by this means one half more product may be obtained
than is yielded if the sulphocyanide of iron be too violently heated,
and thereby converted into sulphuret.
Sulphocyanogen is prepared by passing a current of chlorine gas
Into a solution of the salt thus formed, or by heating it in dilute
nitric acid; chloride, or nitrate of potassium is formed, and a deep
yellow precipitate produced, which contains all the sulphur and cyanogen of the salt, its formula being Cy.S,. It is very light, and
insoluble in water. It combines with all the metals and with hydrogen, forming well-defined salts.
Hydrosulphocyanic  Jcid, Cy.S2+HI., is formed by decomposing
sulphocyanide of lead by dilute sulphuric acid, or by sulphuret of'
hydrogen. It is a colourless liquid, which reacts, and tastes acid.
By distillation it is decomposed.
Sulp/hocyanide of Potassium.-Cy.S-+K.  This salt, of which the
mode of preparation has been just described, forms anhydrous
prisms, cool and pu-ngent in taste; it is abundantly soluble in water
and alcohol, and slightly deliquescent. It is employed in the laboratory as a test for peroxide of iron.
Sulphocyanide of Lead is a crystalline powder, prepared by mixing solutions of a salt of lead and of sulphocyanide of potassium.
Of the sulphocyanides of Iron, the protosalt, Fe.q-Cy.S2, forms a
colourless solution, which becomes red on exposure to the air. The
sesquisalt, Fe,+3Cy.S2, forms a deep blood-red liquor, when a soluble sulphocyanide is mixed with any salt of the peroxide of iron.
It serves thus as a very delicate test of the presence of iron, and
also for that of cyanogen; it is so applied to the detection of prussic acid, as noticed p. 520.
These sulphocyanides may be considered either as double sulphurets of cyarmogen and of a metal, as Cy.S.+S.K., &c., or as salts
of the compound radical sulphocyanogen, Cy.S2+K., &c. The
latter view has been almost universally adopted by chemists.
It appears, however, from  the researches of Parnell, that although sulphocyanogen really exists in these salts, yet the yellow
substance extracted from them by chlorine or by nitric acid, as described just now under that name, is only a product of the decomposition of the real sulphocyanogen, which has not been as yet isolated. The formula of the yellow powder he finds to be S,,2C,,2N6 
EO30. When acted on by alkalies or by nitric acid, it produces an
acid which he terms the Thliocyanic, which is polybasic. It is a




526                  MELLON,  MELAMI   ETC.
pale yellow  powder, sparingly soluble in water, more so in alcohol.
Its formula *is S,,C,0N. HO,.  Its compounds with the oxides of
lead, silver, mercury, &c., are insoluble.  This new acid is but one
of the bodies produced in this reaction; the others have not been
examined../Tellon.-When sulphocyanogen is heated, it is decomposed,
yielding sulphur, sulphuret of carbon, and a yellow  powder which
remains as fixed residue, and to which Liebig has given the name
of MJlellon.  This is a compound radical, analogous to cyanogen in
its characters. It is insoluble in water, alcohol, or dilute acids. Its
formula is C6N., or Ml., and when strongly ignited it is decomposed
into three volumes of cyanogen and one of nitrogen.  Heated with
potassium, they unite with combustion; and if it be fused with the
iodide or bromide of potassium, iodine or bromine is expelled, and
mellonide of potassium formed.
Hydrontellonic Acid, H Ml., is formed by dissolving mellonide of potassium  in
boiling water, and adding a strong acid. A gelatinous white precipitate forms,
which dries into a yellowish powder, H.Ml.+Aq.
AMellonide of Potassium, K.M1., is produced by adding mellon to sulphocyanide
of potassium, fused in a porcelain capsule; sulphuir and sulphuret of carbon are
evolved. On dissolving the brown mass thus formed in boiling water, the mellonide of potassium crystallizes, on cooling, in fine colourless needles.
If we take the formula of sulphocyanogen at C2N.S2, the formation of mellon consists in 4(C2N.S2), producing 2(C.S2) with 4S., and leaving C6N4; but, on Mr. Parnell's view, the decomposition is by no means so simple.
When mellon is boiled with strong nitric acid, it dissolves, and, on cooling, the
liquor yields octohedral crystals of Cyanilic Acid. This substance has the same formula as cyanuric acid, Cy303+-3 Aq., but its relations to bases are not well understood. Nitrate of ammonia is formed; mellon, C6N4, and three atoms of water,
giving C6N303 and N.H3.
Melam. —ClHgNo,.  Sulphocyanide of ammonium, on being heated, is decomposed into ammonia, sulphuret of carbon, and sulphuret of hydrogen, which pass off,
while a grayish-white powder remains, which is Melan. The same result is obtained by heating to fusion a mixture of sulphocyanide of potassium and sal am-*
moniac: in this case chloride of potassium  also remains behind, but may be
removed by washing. Melam is insoluble in water and alcohol. It is dissolved
and decomposed by boiling acids and alkaline solutions, giving origin to a series of
remarkable bodies.
Mcelanzine. C6C6N6, is prepared by boiling melam with a dilute solution of' caustic
potash until the liquor becomes quite clear; it is then to be evaporated until it begins to deposite small crystalline plates, and being then allowed to cool, the mellamine crystallizes out in colourless octohedrons, scarcely soluble in cold water.
It has no action on vegetable colours, but it combines with dilute acids, acting as
a base, and forming well-defined salts, which have an acid reaction, and may be
obtained crystallized.
Ammeline.-C6N5. H502. After the alkaline solution has deposited the melamine
by cooling, it contains ammeline, which precipitates when acetic acid is added.
This is to be purified by solution in dilute nitric acid, and precipitation by carbonate
of ammonia. It then forms fine silky needles, insoluble in wattr and alcohol. It
combines with the dilute acids, forming crystallizable salts.
The origin of these bodies consists in the melam decomposing two atoms of
water, and then C(,2H,. N1102 producing C6H6N6 and C6N5. H502.  By boiling
melai,, in dilute muriatic acid, the same decomposition occurs, and the muriates
of irelamine and ammeline crystallize together on cooling.
If anvy of the albove three bodies be dissolved in strong sulphuric acid, and the
solution be precipitated by alcohol, a white powder-is obtained, insoluble in water
and alchol, but solubie in strong acids and alkalies. It is nearly indifferently acid
or base, as it combines with nitric acid, and also with oxide of silver. It is termed
Atnmellide.  Its formula is C1.2H7. NsO4+2 Aq. When this body is boiled for a long
time with dilute sulphuric or nitric acid, it is resolved into almmnonia and Cyanuric
Acid, which last is the ultimate product of the similar treatment of all the bodies of
this series.




OF  STARCH, ETC.                           527
The theoretical constitution of these bodies remains exceedingly obscure. TIhe
bases, nielamine and aminmeline, are of great importance, from their close analogy
to the alkaloids, which are found naturally in many plants; but still we have no
idea of the mode of arrangement of their elements.
Some other sulphur compounds of cyanogen are known, but do not require mnuck
notice. Cyanogen anti sulphuretted hydrogen coambinng, form orallge crystals, insoluble in water.
CHAPTER XX.
OF STARCH, LIGNINE,  GUMI, AND SUGAR, WITH THE PRODUCTS OF THEI'llR
DECOTMIPOSITION BY ACIDS AND ALKALIES.
Tim substances now to be described form a very remarkable clt:ss
of organic bodies.  They are found abundantly in most pl lalts, but
varying  somewhat in characters, according  to  their inmmediate
source, and are subservient to the most important offices of the
vegetable organization, being the materials from whence the tissues
and secretions of the plant are elaborated.  In a chemnical point of
view, they are distinguished by a remarkable similarity of comnposition, all containing the same quantity of carbon (twelve atonms) in
the equivalent, united to oxygen and hydrogen, which are always
present in the proportions to form water. In this tnaty be found the
cause of the extraordinary transmutations of these bodies from one
to another, by the mere fixation of the elements of water, effected
by the influence of reagents, or by the organic power of' the plant.
In these bodies, also, we find an example of the difficulty of distinguishing between a constitution derived from physical, and that resulting from vital force.  In the different kinds of sugar, the crys.
talline condition, solubility, &c., indicate that the elements are
combined by forces merely chemical; but in the different varieties
of starch, and especially in lignine, traces of organized structure
are found, and properties manifested, which attach their history as
closely to the physiology as to the chemistry of plants. Under this
point of view they shall be hereafter reconsidered.
Of Starch, its Varieties and Products.
The most important variety of this principle is that linown aj.
Conmmon Starch.  It exists in most plants, and in all parts of themn.
It is extracted from the seeds of wheat and barley; from the tubers
of the potato; from  the root of the jatropha manihot, as T7lhpioca or
Cassava, and of the maranta arundinacea, as 4trrotw-root; arnd from
the stems of palms, as the sagus rumphii, which furnishes the S(go
of commerce.  The starch is imbedded in the cellular tissue of the
plant as small white grains, totally destitute of any crystalline strtcture.  They differ in size in almost every plant.  Those of the potato, which are the largest, do not exceed in diameter s-th of' an
inch; those of arrow-root, which are some of the smallest, do not
exceed  -1th. In form, these grains vary also, some being globular,




528         PREPARATION OF STARC I-I  ETC.
others ovoidal, and often, even' in the same plant, irregular. Each
grain is formed by a number of concentric layers, which increase in
density and consistence from the centre; the most external being
so hard as to' resemble a membranous envelope filled by a softer
material.
The grains of starch are quite insoluble in cold water; in boiling
water they dissolve, except the outer layers, which, floating in the
liquor, give it a peculiar opalescent aspect.  On cooling, the solution gelatinizes.  If the solution of starch be dried at a gentle heat,
and then digested with cold water, the outer layers of the grains
may be separated by filtration, and a colourless transparent solution
of starch thus obtained.
The preparation of starch rests on its insolubility in cold water.
The texture of the plant is first broken up by rasping or coarse
grinding, and being then mashed up with water, the starch grains
fall out from the ruptured cells, and are carried off by the current,
from which they deposite themselves wlien the liquors are left at
rest. In obtaining starch from wheat, this liquor is allowed to ferment and become sour, by which a quantity of gluten that would
otherwise attach itself to the starch is removed. If th;e moist starch
grains be dried at a temperature of about 140', they gelatinize to a
semitransparent mass, which remains so when dried, and is not
granular or mealy.  It is thus that the peculiar aspect of tapioca
and sago is produced.
By the vital action of the seed in germination, the transformation
of starch into sugar is effected, and constitutes the saccAharine fer.
mentation. It is artificially induced by mralting the grain, for the
preparation of alcoholic liquors by brewers and distillers.  The circumstances of this change will be specially noticed when describing
the mode of nutrition and of the growth of plants.
If starch be heated beyond 240', it softens and becomes brown.
If the heat be increased until the mass smokes, it is found to be
changed into a substance totally soluble in cold water, and known
as British Gum.
The action of reagents on starch is very remarkable. By boiling
with dilute sulphuric or muriatic acids, a kind of saccharine fermentation is induced, it being changed successively into gum, sugar,
and sacchulmine.  By boiling with nitric acid, it gives saccharic
and oxalic acids.  These reactions will be hereafter studied in detail. A solution of it is precipitated by basic acetate of lead and by
infusion of galls.  With bromine it gives a yellow precipitate, which
is decomposed by heat, the bromine being expelled.  With iodine
it produces a compound of an intense blue colour, which is its most
remarkable property.
Iodide of Starch is produced when a solution of free iodine is added to a solution of starch. Its colour is violet blue or nearly black,
according to the proportion of starch. It is very soluble in water,
but insoluble in alcohol, and may be obtained solid by adding alcohol to a very strong aqueous solution, and collecting the precipitate on a filter. It is decomposed by alkalies and by chlorine; indeed, by all bodies which combine with iodine; and its formation
serves, therefore, as a test only for free iodine, as described in p.




INULIN,  LICHENINE, AND  LIGNINE.                       529
313. When a solution of iodide of starch is heated, it becomes
quite colourless below 200~, and, if it be not boiled, regains its colour perfectly as it cools.  When the liquor remains colourless after
cooling, the blue may be restored by oxalic acid or by chlorine,
which expels the iodine from the combination it had formed.
The composition of starch, no matter what plant it may be derived from, is C,,H,,O,,, as confirmed by a variety of reactions. Its
combination with oxide of lead, dmnylate of Lead, is G,2HJ0o1o+2
Pb.O.
Imdiein.-This kind of starch is found in the roots of the inula, dahlia, angelica,
leontodon, and many other plants. It may be prepared in the same way as common
starch. It is a white and very fine powder, almost insoluble in cold water, but easily dissolved by boiling water; forming a liquor which becomes thick, but not gelatinous, when it cools, and deposites the greater part of the inulin unchanged. It is
transformed by acids, like common starch, but more easily. It is precipitated, like it,
by solutions of borax and subacetate of lead, and by infusion of galls. It is peculiarly distinguished from it by not giving with iodine any blue colour, being merely
tinged yellow. The structure of the grains of inulin has not been accurately examined. Its formula is Civ2HoOlo, like that of common starch, but in combining
with oxide of lead it appears to lose one atom of water, and to become Cl2I909, as
remarked by Parnell.
Liclenine. —This variety of starch, which is found in many lichens, especially the
Iceland moss and the carrigeen (sphcerococcus crispus), is not contained in the
plant in grains, but in a soluble condition. To obtain it, the lichen is first digested
in a cold dilute solution of carbonate of soda, to dissolve the bitter resinous principle, and this being completely washed away, the lichen is boiled for a long time
in water; a liquor is obtained, from which, on cooling, the lichenine separates as an
opaque gray jelly, which, when dried, is black, hard, and glassy. Its properties are
very similar to those of inuline. It gives with iodine a greenish-brown colour. Its;
composition is expressed by the same formula as the others, Cl2H1oOo.
Of Lignine.  Principle of WBoody Fibre.
When any kind of wood is treated successively and repeatedly
by dilute acids and'alkalies, by water and by alcohol, so that every
soluble material is removed from  it, we find that the substance
which remains is of very constant composition, being expressed by
the formula,,2HO,.  Of this substance, Lignine, the proper wood
of the plant is constituted; its molecules being arranged so as to
form the tubes and cells of the vegetable tissues, and cohering so
firmly as to produce the fibres of flax, cotton, and hemp, which constitute the materials of our most important woven textures, of paper, &c. Although the lignine is thus rather the remains of an organized body than a mere chemical substance, it forms some combinations which are of great importance in the arts.  Thus, if linen
or cotton cloth be dipped in dilute solution of acetate of alumina,
the earth abandons the acid to combine with the lignine, and thus
serves as the means of fixing on the cloth the various colouring
matters used in the processes of dyeing.  The same occurs with
oxide of iron; and other metallic oxides have a similar, though
weaker affinity for lignine, and thus serve as mordants for various
colours.
Lignine, when quite pure, is white; the bleaching of linen, cotton, paper, &c., being effected by destroying, by means of the air
or of chlorine, the resinous and other matters which are associated
with the lignine in the fibres or cells of the plants; the lignine itself resists these agents, unless applied in a very concentrated form
Xxx




530         ARABINE  AND  TRAGACANTHINE.
With cold nitric acid lignine combines directly, forming a -very re.
markable substance, Xylo'idine, which may be produced by immersing for a moment a piece of paper in strong nitric acid, and then
washing it well in pure water.  It assumes the feel and toughness
of parchment, and is so combustible as to serve for tinder. Hot
nitric acid converts lignine into oxalic acid; with sulphuric acid it
is changed into gum, and ultimately into sugar, as will be detniled
farther on.
If sawdust be heated with a warm  solution of potash for some
hours, the liquor will be found to contain a considerable quantity
of common starch, capable of striking a blue colour with iodine;
but by this means the ligneous fibre is dissected, and not decomposed.  The starch may be extracted also by mechanical means,
and pure lignine does not yield any. If lignine be strongly heated
with hydrate of potash, hydrogen is evolved, and a mixture of acetate and oxalate of potash results; C,2HO, and 4,H.O. giving 611.,
with 2(C2O3) and 2(C4H130,).
In dry air, or immersed under water free from air, lignine remains
for an indefinite length of time unaltered; but if both air and water
have access, oxygen is absorbed, and carbonic acid and water given:out, and a series of products of decomposition result, which form
the basis of vegetable soil, and thus serve as the materials for a new
generation of plants. By the conjoint action of heat and water, lignine produces another class of products, and a third series arises
from the destructive distillation of dry wood. These subjects will
be examined specially in their proper place.
Of the different Varieties of Gum.
It is necessary to distinguish three varieties of gum, to wrhich
the names of.Rrabine, Cerasine, and Dextrine m'ay be given.  The
first two are natural, the last is a product of the transmutation of
starch../rabine is found in the juices of many species of acacia and prunus; it exudes from crevices in the bark, and forms lumps, in which
state it is found in commerce (Gum.'rabic and Gum Senegal). The
roots of mallow, comfrey, and many other plants contain a great
deal of arabine. It is never crystalline, and is colourless and transparent, with a vitreous fracture.  It is dissolved by water in all
proportions, forming a thick, adhesive liquid (mnucilage). It is not
dissolved by alcohol, which precipitates its watery solution. It
combines with bases, forming wrell-defined, insoluble compounds,
and is not in any way acted on by iodine. A solution of arabine
exercises sinistral rotatory power on a ray of polarized light (p. 41).
By contact with sulphuric acid, arabine is gradually converted into
dextrine, and, if the digestion be continued, this then changes into
sugar.  With nitric acid arabine gives mucic acid, and afterward
oxalic acid; another characteristic property of it is, that of giving
a precipitate with solution of silicate of potash (soluble glass, p.
437). Its composition is-expressed by the formula C,2H,1O,,.
Tragacanthine, or Vegetable Jlfucus, exists in cherry-tree gum mixed with arabine, but is purer in gum tragacanth, in flaxseed, and in
quince-seed. It is extracted by digestion in water, when it gradu



D E X TRINE.-CANE-SUGA.H.                   531
ally swells up and appears rather to imbibe the water than to dissolve; a thick tenacious liquor is obtained, which is precipitated by
alcohol and by solution of basic acetate of lead, but not by silicate
of potash.  With sulphuric and nitric acid, the same products are
formed as from arabine.
The Salep of commerce is the tragacanthine extracted from the.oots of various species of orchis, and dried.
Dextrine.-This variety of gum is formed from the starch of the
seed, in germination, and may be obtained by digesting starch in
dilute sulphuric acid. If five parts of starch, wvith one of oil of vitriol and fifteen of water, be kept at 200' for some time, the starch
completely disappears, the solution loses its power of gelatinizing;
it acquires the characteristic rotatory power of Dextrine, and colours
iodine of a port-wine red, without any tinge of blue. If the liquor
be neutralized by carbonate of barytes, the whole quantity of sulphulric acid separates, and by evaporation, the dextrine is obtained
as a pale yellow mass of a vitreous fracture; it is not adhesive like
common gum, nor does it yield any mucic acid when acted on by
nitric acid.
Dextrine precipitates a solution of basic acetate of lead, but is not
affected by silicate of potash. If dextrine be boiled too long with
the sulphuric acid, it passes into a substance more analogous to
tragacanthine, which is also formed when arabine or lignine is so
treated. In this state its rotatory power is feeble, and it is not at
all coloured by iodine. In both these forms the composition of
dextrine is C,,2H,,,,0.
Of th1e different Varieties of Sugar.
The species of sugar are much better distinguished from each
other, both by properties and composition, than the various kinds
of starch, or of gum, have been found to be. They are all characterized by being capable of undergoing the alcoholic fermentation.
Cane-sugar.-C,2HO1lo+Aq. when crystallized.  This species of
sugar is found abundantly in the juices of many plants. It is extracted for use from the sugar-cane, the maple, and the beet-root.
The juice, when fresh, runs into fermentation with greait quickness, and is therefore clarified by being warmed to 150Q, with a little lime, by which the vegetable albumen is coagulated, and the fermentation checked. The juice is then evaporated with as little
heat as possible, and allowed to cool in vessels, at the bottoln of
which a number of small apertures, stopped with plugs, are situated.
The sirup congeals into a granular mass, and when it is quite cold,
the apertures below are opened, and the liquid portion allowed to
run out.  The sugar thus obtained in fine crystalline grains is
brownish-coloured, and is termed.AMuscovado, or Raw Sugar. The liquid uncrystallizable portion constitutes MAIolasses, or Treacle. To obtain the sugar pure, it is redissolved, and the liquor having been
cautiously evaporated (in some establishments, in vacuo, see p. 85)
to the necessary degree, is poured into cones of unglazed earthenware, which are placed on their summits, the orifice in which is
stopped by a plulg.  Wbhen, by cooling, the sirup has crystallized,
during which the mass is continually stirred about to render the




532       SACC HUL MIN E.-SACCHARIC  ACID.
crystals very minute and close, the plug below is removed, and the
coloured liquor drainsout; thie last portions of it being removed by
laying a sponge, moistened with some spirit or with h clear sirup,
on the sugar at the base of the cone, and allowing the pure liquid
to filter through. Thus is obtained refined, or Loaf-sugar. If a strong
sirup be laid aside in a warm place, it crystallizes in very beautiful
oblique rhombs, which constitute the Sugar-candy of commerce.
Cane-sugar is perfectly colourless.  Its sp. gr. is 1-6; when heated, it fuses at 350' into a clear yellow liquid, and congeals, on cooling, into a hard brittle mass (barley-sugar), which, after some weeks,
becomes opaque, white, and crystalline. If the temperature rises to
630~, water is given off, and the sugar becomes dark brown, beingchanged into Caramel; more strongly heated, it is totally decomposed. Sugar dissolves in one third of its weight of cold, and in all
proportions in boiling water. A saturated solution becomes quite
solid when it cools. If a strong solution of sugar be kept for some
time near its boiling point, it is gradually changed into uncrystalli.
zable sugar; hence arises the most important source of loss in the
manufacture and refining of sugar.  It is sparingly soluble in absolute alcohol, and but moderately in weak spirit.
Sugar combines with some bases and salts, acting as a feeble acid;
the compound with oxide of lead is insoluble, and has the formula
C12Hjo0,o+2Pb.O.; that with barytes is crystalline: its formula is
C,12H,0,0o+Ba.O. With common salt sugar combines, foxrming crystals, easily soluble in water, and consisting of C,2H,O,0q —Na.Cl.
The action of acids on cane-sugar is very remarkable.  When digested with very dilute sulphuric or muriatic acid, it is converted
into grape-sugar; but with stronger acids, it is changed into two
brown substances, insoluble in water, one of them soluble, the other
insoluble in alkaline liquors.  The former is termed Sacchulmine,
the latter, Sacchulrmic Acid. These bodies are formed even- with
very dilute acids if the digestion be continued for a long time. According as the reaction proceeds, the sacchulmine separates in minute brilliant brown crystalline plates, mixed with a dull brown
powder, which is sacchulmic acid. They are separated by water
of ammonia, which dissolves the latter. The composition of these
bodies is not. quite definitely establisl~d, as it appears to be influenced by the strength of the acid used and other circumstances.
The best-grounded idea is, that they have both the same composition, C30H,150,, being isomeric with ulmine. If in this reaction the
atmospheric air have access, oxygen is absorbed, and a large quantity of formic acid generated.
The preparation of oxalic acid by means of nitric acid and sugar
has been already described (p. 493). If dilute acid be used, so that
the oxidation may not be forced so far, a liquor is obtained which
gives with carbonate of lime a neutral solution.  When this is de
composed by acetate of lead, a white precipitate is thrown down,
which being acted on by sulphuretted hydrogen, the acid is set free,
and may be obtained crystallized by evaporating and cooling its so,
lution. This is termed the Saccharic.Rcid. It gives an extensive
series of salts, being a pentabasic acid. Its formula is C,2HO,,+5
H.O. when crystallized.  Its potash salt is C02HO51+K.O0. * 4H.O.




G R A P E-S U G A R.                  533
Its lead sAt C,2HO,,+5Pb.O.  The saccharate of lime is sparingly
soluble in water, but dissolves in a very slight excess of acid, which
distinguishes it from an oxalate.  An ammoniacal solution of saccharate of silver is decomposed by heat; metallic silver being deposited, and forming a mirror-surface on the interior of the vessel.
The Caramel formed by heating sular to 650' appears as a porous,
shining, jet black mass. It is completely soluble in water, and free
from any empyreumatic taste. It is insoluble in alcohol; it combines with bases; its formula is C,,HO,. The sugar, in forming it,
therefore, loses the elements of an atom of water, besides its water
of crystallization.  By heating sugar with lime, a volatile liquid is
obtained, which has the formula C0H1O., and is termed.Metacetone.
Grape-sugar. Glucose. -C,H,,O,,J+3 Aq. when crystallized. This
kind of sugar is still more extensively distributed in nature than
the former. It gives the sweet taste to fruits, and forms the solid
part of honey.  It is produced in the animal body in certain forms
of disease, as diabetes, and by the transformation of starch in germination, and by artificial processes.  In consequence of this variety of sources, it is better to term it glucose, as suggested by Dumas, than to use a name indicating any one special origin.
Glucose may be obtained from  raisins or honey by digestion,
first with cold, strong alcohol, to remove the uncrystallizable sugar,
and then expressing the residue, which is to be dissolved in water,
and neutralized by chalk. The liquor so obtained may be clarified
by white of egg, and evaporated to crystallization.
From starch, gum, or cane-sugar, it may be prepared by the action of sulphuric acid as follows: one part of potato-starch is to be
boiled with four parts of water and -'lth of oil of vitriol during 36
or 40 hours, the water which evaporates being replaced. The jelly
does not assume any consistence; the liquor remains clear, and the
material used is found completely converted into sugar. By means
of chalk, the acid is removed, and the solution being evaporated,
the sugar crystallizes.
If starch paste be moistened with an Infusion of pale malt, it is
rapidly converted into dextrine, and thence into grape-sugar. This
occurs from the catalytic influence of a principle termed Diastase,
which exists in the malt, and the formation of which will be detailed under the head of germination.
To convert lignine into sugar, bits of paper or linen are to be imbibed with their own weight of oil of vitriol, until they are converted into a uniform viscid mass, taking care that it shall not become
hot; this is then to be diluted, and the liquor boiled for some time.
The acid being then removed by chalk, the sugar is obtained pure,
by crystallization, as in the former case.
Sugar of grapes crystallizes in hard colourless tables or in hemispherical grains, consisting of minute needles closely aggregated
together; its specific gravity is 1-38; it is much sweeter than canesugar, and less soluble in water. When heated to 212~, it gives off
two atoms of water, which it recovers when redissolved; but by a
stronger heat it is changed into caramel. It is soluble in twenty
parts of bhiling absolute alcohol, and separates almost totally on
cooling, in granular crystals, which contain alcohol combined. It




534        CONSTITIUTION  OF GRAPE-SUGAR.
combines with bases, forming compounds analogous to *hose given
by cane-sugar.
The composition of crystallized grape-sugar is C,2H,4014, or C,2H,,
0,,+3 Aq. When fused at 212~, it becomes C,2H,2012, or C2,H,,O,,
+Aq.  Its compound with chloride of sodium, which crystallizes
in fine double six-sided pyramids, consist of 2(C,2H,2O,2) +~Na.C1.+
2 Aq.  With a solution of basic acetate of lead it gives a white
precipitate, the formula of which is C,2H,,0,,+3Pb.O., corresponding to the crystallized sugar. The dry grape-sugar has evidently
the same composition as the crystallized cane-sugar.
The kinds of sugar (glucose) derived from these different sources
are not so really identical as has been generally supposed, since
they are found to act differently upon polarized light.  Grape-sugar,
as contained in the grape-juice or in the juice of the floweringc
grasses, rotates the plane of polarization to the left; but if the juice
be evaporated and the sugar crystallized, its molecular constitution
is so totally altered, as that, when redissolved, it gives a rotation to
the right.  The starch-sugar, as well as cane-sugar, rotates also to
the right, but in a much inferior degree to the starch-gum, which,
as already mentioned, receives its name of dextrine from  that
quality.
As lignine, starch, gum, and cane-sugar all contain the same quantity of carbon (C,,2), their transformation into grape-sugar consists
evidently in the fixation of the elements of water; thus lignine,
C,2Hs08 takes 4H.O., and 100 parts of sawdust have been found to
give 115 of sugar; starch (C,2H00O,O) takes 2H.O., and 100 parts of
it usually yield 106. It has been remarked, that a certain quantity
of JMannite is at the same time produced, besides sacchulmine.
Grape.sugar yields, when treated with dilute sulphuric acid, the
same brown substances as cane-sugar; but if the sulphuric acid be
concentrated, it forms with the elements of the sugar a peculiar
acid termed the Sulphosaccharic.  Sugar of starch or grapes is to be
fused at a low heat, and 1~ parts of oil of vitriol then well mixed
with it. If the sugar be pure and the temperature be kept low, the
product is not coloured.  Its constitution is not rigidly determined,
but its lead salt consists of 2(C,2H,O,,)~+S.03+4Pb.O.
In acting on grape-sugar, nitric acid gives rise to the same products, oxalic and saccharic acids, as cane-sugar; indeed, it appears
probable, that, like the other strong acids, this also first changes the
cane-sugar into glucose, and that the saccharic acid is really derived from the latter.  On this view its formation is more easily
explained; for as the dry glucose is C,2H1,O,,, and the saccharic acid
is C,2H5O,,, the oxygen of the nitric acid simply removes six atoms
of the hydrogen of the grape-sugar, and the elements of the acid remain.
By contact even with the strongest bases, cane-sugar is but slowly
altered, and hence lime may be employed to clarify the vegetable juices which contain it; but, under the same circumstances, grape-sugar is rapidly decomposed and an acid formed, which is termed Glucic dcid. It is very soluble in water, and does not crystallize; with
lime, barytes, and lead, it forms neutral soluble salts, but it precipitates a solution of basic acetate of lead. Its taste is purely acid,




LA C T I N E.-M     A N N I T                      535
and it reddens litmus.  Its composition is C,,H,,08, and it is isomeric,
therefore, in its dry state, with lignine.  When a strong solution of
caustic potash is added to fused grape-sugar boiled, the glucic acid
which at first forms is decomposed.  The  liquor becomes deep
brown, and yields, on the addition of muriatic acid, a black floccu.
lent precipitate of l]Melassic./Acid. The formula C24H,20,o has been
assigned to it, but its nature is not well known.
Llctine, or Satgar of Milk.-This remarkable substance, which is found only in
the milk of the mammalia, is obtained by evaporating whey to a pellicle and setting
it aside -to cool, when the sugar crystallizes in small square prisms, white, sernitransparent, hard, and gritty under the teeth.  The taste of the crystals is but
slightly sweet, but that of a strong solution is much more so. It dissolves very
slowly in water, and is insoluble in alcohol.
When, the crystals of lactine are gradually heated to 270~, they give off two
atoms of water; at about 300C they fuse, and give off three atoms of water more.
The composition of the dry sugar thus obtained is C24119019, and of the crystals
C2lH-I,909+5 Aq. By mixing solutions of sugar of milk and of basic acetate of
lead, a white precipitate is produced, the formula of which is C24,19019+5Pb.O.
By digestion with dilute sulphuric acid, sugar of milk is changed into grape-sugar,
and then produces the other reactions already described.  With alkalies the decomposition is also the same as that of glucose, but the action of nitric acid on lactine
differs from that on any other sugar, as the acid formed is not the saccharic, but
that already noticed as obtained from native gum, the Meacic Acid.
To obtain mucic acid, one part of gum or lactine is to be dissolved in four parts
of nitric acid, specific gravity 1'42, mixed with one part of water. Heat is to be
applied until all effervescence has ceased, and the mucic acid is deposited on cooling. It is a crystalline powder, gritty under the teeth, and feebly acid. It dissolves
in six parts of boiling water; but is insoluble in alcohol. Its crystals have the formula C,2H,1006, being formed froim gum by the simple addition of six equivalents of
oxygen.  This formula contains, however, 2 Aq., as it is a bibasic acid, and its salts
consist of C21Hs80,142M.0.  The alkaline mucates are soluble, the earthy and metallic salts are insoluble in water.
When mucic acid is long boiled with water, its acid properties become much
stronger, and it becomes more soluble in water and soluble in alcohol; it gradually
returns from this state to its ordinary condition, even when combined with bases.
If mucic acid be distilled at a high temperature, water and carbonic acid are evolved, and a sublimate forms in brilliant white plates, which are soluble in alcohol and
water; C12Ho0016 give 2C.02 and 6H.0., besides C,0H406, which is the formula of
the hydrated Pyromucic Acid. This substance fuses at 2700, and is volatile at 2900
without decomposition. Its salts contain one equivalent of base; those of lead,
barytes, and silver are insoluble; those of the alkalies are very soluble in water.
With this acid a certain quantity of chlorine may be combined, forming Chloropyromnucic Acid, CloH3. C1405, which is prepared by acting with chlorine on Pyromucic Elher.
Slg, (ar of lfuashroomns is deposited in rhombic prisms from the watery solution of
the alcoholic extract of ergot of rye.  They are insoluble in ether; they give oxalic
acid by nitric acid, and undergo the alcoholic fermentation. Their composition
was found to give the formula C12H113013, but little is known accurately of this variety of sugar.
Of MJkfannite and GlycyrMhizine.
These bodies are connected so closely with the true sugars, that, although want.
ing in the characteristic of forming alcohol by fermentation, they may be best described here.
Mannite, CH11706, is found in manna, of which it constitutes the sweet principle.
It exudes also from the bark of other trees, and exists in most mushrooms.  It is
produced by the decomposition of cane-sugar in certain cases. To obtain it, manna
is digested in boiling alcohol, and the liquor filtered while very hot; on cooling, the
mannite is deposited almost totally, and may be purified by repeated crystallizations. Its taste is slightly sweet; it is very soluble in water, and it crystallizes in
brilliant white prisms of silky lustre. When heated gently, it fuses without losing




536           LACTIC  ACID.-GLYCYRR HIZINE.
weight. With nitric acid it gives oxalic and saccharic acids. It does not appeal
to combine with bases.
If the unclarified juice of the beet or carrot root be kept at a temperature of 100C
for some time, a tumultuous decomposition sets in, which is termed the mucous fermentation. All the sugar disappears, and the liquor is found to contain a large
quantity of gum and of mannite, with a peculiar acid, which exists naturally in all
the animal fluids, but especially in milk, and is termed the Lactic Acid. At the
same time, carbonic acid gas is evolved, and the liquor contains ammonia. This
reaction is too complex to be expressed in formula, but it may be noticed that one.
equivalent of dry cane-sugar contains the elements of two equivalents of lactic acid;
while, by abstracting two atoms of oxygen fiom an equivalent of crystallized grapesugar, the constituents of two atoms of mannite remain.
Lactic acid is most easily prepared by means of this mucous fermentation, but
may be also obtained abundantly from sour whey, or the sour waters obtained in
making wheaten starch. The acid liquor is to be neutralized by carbonate of lead,
and the solution of lactate of lead evaporated until it is tolerably concentrated. It
is then to be decomposed by sulphate of zinc, and the precipitated sulphate of lead
being removed by the filter, the lactate of zinc may be obtained in large crystals,
easily rendered quite pure by re-solution and crystallization. A solution of pure
lactate of zinc being decomposed by water of barytes, lactate of barytes is obtained,
which, with sulphuric acid, gives sulphate of barytes, and the pure lactic acid dissolves. The solution is to be placed in vacuo over sulphuric acid; it gives a sirup.
thick liquor, which has the formula C6H606 or C6H505+Aq., as it contains an atom
of basic water; it tastes strongly, acid. When heated to 4800 it gives off water,
and a white sublimate forms in brilliant white rhomboidal plates, which is Paralac
tic Acid. It is purified by solution in boiling alcohol, from which it crystallizes.
The composition of this body is C6H1404; it fuses at 2250, and sublimes at 4500; it
tastes very slightly acid, and dissolves but very slowly in water; the solution gives,
when evaporated, only the sirupy liquid of the hydrated acid, and does not crys
tallize.
The lactic acid coagulates albumen; it mixes with milk when cold, but coagu.
lates it when boiled. It forms monobasic salts, in which its formula is C6H505.
They are all soluble in water, and crystallize but imperfectly, except that of zinc,
which forms brilliant white four-sided prisms, containing three atoms of crystalwater. The Protolactate of Iron, C6H50s-+Fe.O.+3 Aq., may be obtained crystallized in small prisms of a greenish-yellow colour. The Perlactate of Iron dries into
a reddish transparent mass like shell-lac. These last are used in medicine.
The lactic acid will be again noticed as a constituent of the animal system.
Glycyrrhizine.-This substance, which is found in the liquorice-root, and in some
other sweet woods, is obtained by boiling the root or liquorice in water, and, after
concentrating the liqubr, adding thereto sulphuric acid. A white precipitate, containing the glycyrrhizine combined with sulphuric acid an(l albumen, is formed.
This. is to be washed with acid water, and then with pure water, and to be dissolved in alcohol, which leaves the albumen. The alcoholic solution is to be decomposed by carbonate of potash, which throws down ths sulphuric acid, and by evaporating the filtered liquor, the sweet principle remains pure as a yellow transparent
mass.
Its most remarkable property is that of combining very definitely with acids and
bases, and with several neutral salts. Almost every acid precipitates a compound
from a solution of glycyrrhizine. It expels the carbonic acid from the carbonates
of potash, soda, and barytes, combining with the base, and it precipitates the solutions of most of the ordinary metallic salts. Neither the pure substance nor any
of its compounds have been accurately analyzed.




GLUTENo MUCINo AND  ALBUMEN.                      537
CHAPTER  XXI.
OF THE ALCOHOLIC AND ACETIC FERMENTATIONS-OF ALCOHOL, THE ETHERS,
ALDEHYD, ACETIC ACID, AND OTHER BODIES DERIVED FROM IT.
AN aqueous solution of pure sugar may remain perfectly unaltered foi
any length of time, if carefully excluded from the air.  If the air have
access, it is gradually decomposed, becoming brown and sour, but no al.
cohol is generated. If, however, the solution of sucgar be brought in con.
tact with any organic substance which is itself in the act of slow decomposition, then the particles of sugar participate in the change which is
going forward, and carbonic acid and alcohol result.
The substance which is specially active in inducing this kind of fer
mentation is an azotized body termed yeast; but a number of animal
and vegetable substances can also effect it.  Blood, white of egg, glue,
flesh, if they have begun to putrefy, are capable of exciting it; but the
bodies of most practical importance in that respect are vegetable albumen and gluten. These bodies exist in all fruits and seeds, in greater
or less proportion, but they differ in character, according to the plants
they are derived from, nearly in'the same way as the varieties of starch.
I shall here only notice them as derived from wheat and from beans, as
I shall have occasion to describe some other forms hereafter. If wheaten
flour be washed with water in a linen bag, the starch passes off, and a
tenacious paste remains, which consists of albumen and gluten mixed.
They may be separated by boiling in alcohol, which dissolves the latter,
and leaves the former behind.  On mixing the alcoholic liquor with
water, the gluten is precipitated, and may be collected and dried.
Vegetable Gluten so obtained is pale yellow, and forms, when soft, an
adhesive mass, very extensive and elastic.  Its solution in alcohol is
thick-fluid when concentrated; insoluble in ether; it dissolves in acetic
acid, and in alkaline solutions. It combines with the mineral acids,
forming bodies very sparingly soluble in water, which are precipitated
by adding the acid to the solution of gluten in acetic acid or in potash.
If these solutions be mixed with solutions of earthy or metallic salts,
precipitates are formed, which are compounds of the gluten with the
metallic oxide.
In all these reactions, the gluten is accompanied by a slimy material,
termed /lIucin, which it is difficult to remove perfectly from the gluten;
it is best effected by boiling with water, when the mucin remains dissolve
ed. Its solution is precipitated by sulphate of iron and infusion of galls,
but not by acetate of dead or corrosive sublimate.
Vegetable Albumen remains behind after the rough gluten has been
boiled in alcohol. It is destitute of elasticity when softened, and dries to
a hard white mass; it is moderately soluble in water, and its solution is
coagulated by heat; it dissolves in alkaline liquors.  Its solutions are
precipitated by acids, except the phosphoric and acetic, and by all earths
and metallic salts; these precipitates are white or coloured, according to
the nature of the metallic oxide; with ferro.prussiate of potash and.with
Yyy




538           LEGUMIN. —NATURE  OF  YEAST.
infusion of galls, the solution of vegetable albumen in acetic acid gives
white precipitates.
Legunmin. —'This substance, which exists in pease tand beans, possesses
properties intermediate to those of the gluten and albumenr  of wheat.
When powdered pease are diffused through water, tile starch settles to
the bottom, but the legumin is dissolved, and separates by evaporation,
on thie surface of the liquor, in mucous transparent pellicles. Its solultion
is not coagulated by heat; it is insoluble in alcohol.  It dissolves in solutions of the vegetable acids, and is precipitated on the addition of a
mineral acid.  It dissolves in alkalies, and gives, with tile earthy and
metallic salts,. compounds insoluble in water.
All these substances differ from most vegetable bodies, in containing
a large quantity of nitrogen, and, in the latter case, sulphur, as a constituent.  They leave behind, when burned, an ash consisting of' phos.
phates of lime, magnesia, and iron, similar to the ashi of animal substances.  Indeed, an almost perfect simnilarity of properties exists be.
tween these bodies, and fibrine, albumen, and casein among animal prod.
ucts; in the case of casein and lululine probably amounting to identity.
In contact with air and water, these bodies enter spontaneously into
decomposition, evolving carbonic acid and ammonia, and forming new
products'; and in this state of decomposition they superinduce the alco.
holic ferlnentation on those particles of sugar which lie in contact with
them.  Hence, in fruits, the sugar may lie in contact with these vegetoanimal substances without any change occurring, as long as the investing
membrane of the fruit-cells remains perfect; but if the fruit be crushed,
so that the air have access, then oxygen is absorbed, the vegeto-animal
body begins to putrefy, and the sugar is sooii engaged in the decomposition.  It is remarkable, that the necessity for oxygen is at the corn.
mencetnent of the decomposition: when the putrefaction of the albu.
men or gluten has once begun, it extends itself throughout its whole
mass without requiring any farther action of the air.
The principles of the conservation of vegetable juices, by enclosure in
vessels from which the air is excluded, can easily be understood from
this, as well as the utility of such agents as sulphurous acid or sulphite
of potash, which absorb any traces of oxygen that may be present, and
prevent it fiom acting on the organic substance.
The general characters of these naturalferments being thus sketched,
it is necessary to add the important facts of the history of artificial ferment, or yeast.  This is nothing more than the decomposing mass of
vegetable gluten or albumen produced in a previous fermentation. If
the yeast be too old, that is, if all the vegeto-animal matters be already
decomposed, its power of exciting action is destroyed; it is also destroyed
by boiling, by alcohol, by many salts and acids, and, generally, by all
those means which give to the albumen and gluten an insoluble form, and
prevent their farther putrefaction.
When a solution of pure sugar is fermented by contact with a certain
quantity of yeast, this last is found to be very much diminished in quantity, and to have totally lost its activity. On the contrary, if, in place of
pure sugarl, grape or currant juice, or an infusion of malt, be used, the
quantity of ferment is found to be much increased, and to preserve all
its power. In this case the albumen and gluten of the vegetable juices
are themselves brought into the same train of decomposition as the added




ALCOHOLIC  FE RiMENTATION.                       539
portion of yeast, and thus form a new and larger quantity of active fernenting material.  Thus, in a brewery, the quantity of yeast continually increases.  lf yeast be''examined with the microscope, it is found to
contain a vast number of minute globular bodies, possibly animalcules,
which derive their nutriment from it; but recently sone very uilounded
attempts have been made to connect these globUies essentially with the
process of fermentation, by the idea that, in the process of nutrition, they
absorbed the sugar, and that the products of fermentation were excreted
subsequently by them.  But this is shown to be absurd by the simple
fact that the weight of the alcohol and carbonic acid is greater than the
weight of tlhe sugar.
The phenomena of the alcoholic fermentation are best observed on the
clear-expressed grape-juice, kept at a temperature between 700 and 80~;
in a lightly covered vessel.  After a few hours a slight effervescence is
observed, and the liquor becomes turbid, as it' pipeclay were diffused
through it. As the effervescence increases, the liquor becomes warmer,
and the precipitate forms flocculi, on which the gas-bubbles are evolved,
being thereby carried to the surface of the liquor, and falling down again
when the gas.bubbles have broken. This circulation continlues until the
fermentation has ceased, when the precipitate collects at the'bottom.
TI'he liquor no longer tastes sweet; it contains no sugar, but in place of
it an equivalent quantity of alcohol.  An infusion of malt does not so
readily ferment as the grape juice, unless some yeast be first added. In
its spontaneous fermentation, most of the gum and sugar which it con
tains passes into the mucous fermentation, while but little alcohol is
formed.  In the practical manufacture of malt-drinks and spirits, therefore, the worts are always set to ferment by the addition of a suitable
quantity of the yeast formed in a preceding operation.
Although the essential character of sugar is to be capable of alcoholic
fermentation, yet the diffirent kinds of sugar enter on that process with
unequal facility.  The sugar of' milk requires the presence of a very
active ferment, and of an acid, by the influence of which it is changed
into sugar of grapes.  Thus milk does not ferment until it has become
clotted and sour; the casein then acts as yeast, in superinducing the alcoholic fermentation. Indeed, no matter what kind of sugar is employed
in this process, it is changed into grape-sugar before fermenting, as is
shown by the action of the liquor upon polarized light. The grape-sugar,
as dried at 212~, contains exactly the elements of two atoms of alcohol
and four of carbonic acid, as 2(C,4H602) and 4C.O02 arise from C12H,2,02.
As cane-sugar takes an atom of water to form grape.sugar, it follows that
cane-sugar, in fermenting, should yield more than its own weight of carbonic acid and alcohol; and it has been ascertained by experiment that
100 parts actually give 104, while by theory 105 should be produced,
consisting of 51'3 of carbonic acid and 53'7 of alcohol.  This coincidence of numbers proves that these bodies are the only products. The
influence of the yeast is, therefore, strictly what Berzelius terms catalytic, but its action becomes much more definitely intelligible by consid.
ering it as a case of the general principle expressed by Liebig, that motion (decomposition) may be communicated from the particles of one
body (yeast) to those of another (sugar) by virtue of proximity, as described more fully in p. 235-237.
As farther details of the circumstances of the alcoholic fermentation




540           CONSTITUTIO N  OF  ALCOHOL.
would vary with the nature of the liquor to be produced, whether it be
for immediate drinking, as wine, ale, or porter, or fobr distillation, and
as these lead to purely technical descriptions of the arts of brewing,
&c., I shall not enter on them.
Of Alcohol and the Ethers derived from it.
When any saccharine liquor, which has undergone the alcoholic.fermentation, is distilled at a gentle heat, a very volatile liquid passes over,
which, by successive rectifications, may be deprived of most of the water
which had been mixed with it.  In various degrees of strength, and contaminated by minute traces of essential oils, characteristic of the plants
from which the saccharine liquor has been obtained, it constitutes the
potato-.sirit, brandy, malt-whiskey, arrack, runt, &c., of commerce.  In
a still stronger form it constitutes the spirit of wine, or rectified spirit,
the term alcohol being applied to it only when it is chemically pure.
By mere distillation alcohol cannot be freed fiom all the admixed water,
for which it exerts a strong affinity.  When its specific gravity is reduced to 0-81.3 at 60~, in which state it still contains 8'2 per cent. of
water, or exactly half an equivalent, its boiling point remains constantly
at 172~, and it distils over unchanged.  In the form of proof spirit of
commerce, its sp. gr. is about 0-920, and it contains 48 per cent. of ab
solute alcohol; the rectified spirit containing about 83 per cent., and
having the specific gravity 0-839 at 60~ F'.
To obtain real alcohol, or absolute alcohol, as it is generally termed,
rectified spirit is to be distilled at a moderate heat from some substance
having a stronger affinity for water; as lime, caustic potash, carbonate
of potash, or chloride of' calcium.  Of these the last named should be
preferred.  The water of the spirit combines with the body used, and,
forming a hydrate, the real alcohol distils over.  The rectification
should be conducted in a water-bath.
A singular mode of concentrating alcohol is founded on the fact that
alcohol does not moisten the animal tissues, but corrugates, and rather
abstracts water from them.  Hence, if a bladder be filled with spirit of
sp. gr. 0-820, containing 90 per cent. of alcohol, and if it be left for a
few days in a warm room, the spirit will be found to have its sp. gr.
reduced to -0800, containing 97 per cent. of real alcohol. The water
permeates the bladder, and evaporates from the outer side, but, as the
alcohol does not moisten the bladder, it cannot get through, and conse.
quently remains behind, freed from water.
The very ingenious way of obtaining alcohol, devised by Graham, by
evaporation in vacuo with quicklime, has been described in p. 87.
Alcohol, thus obtained anhydrous has a sp. gr. of 0-7947 at 60~; it
boils at 1680; tne specific gravity of its vapour is 1601; it does not
become solid even in the most intense cold; its taste is burning and dry
upon the tongue. owing to its abstracting water from its tissue.  It is
highly inflammaole, and burns with little light.  From  its volatility, if
some drops of it are poured into a jar of oxygen gas, its vapour forms a
powerfully explosive mixture.  It does not conduct electricity.  It mix.
es with water in every proportion, contracts in volume, and evolves heat.
The sp. gr. of spirituous liquors is therefore always above the mean sp.
gr. of the alcohol and water they contain. The greatest condensation
occurs with 54 volumes of alcohol and 50 of water; the mixture occu



U S E S OF  A       H O L.                  541
pies only 100 volumes, and its sp. gr. is 0'927, being a little denser
than proof spirit.
The formula of alcohol is C4H602, and its composition is,
4 equivalents of carbon,  =242... 5266
6  "   "    hydrogen, = 6 0...  12'90
2  "   "    oxygen, =16'0...   3444
The equivalent of alcohol, =-46-2...  1000
This is enfirmed by the products of its decomposition, and by the specific gravity
of its vaporsc; for,
4 volumes of carbon vapour. (843 X 4)-3372'0
12   "     hydrogen..  (68:8x12)= 8256
2    "     oxygen.. (1102'6X2)=-2205'2
Give four volumes of alcohol vapour.  6402'8
Of which one volume Weighs..   1600.7
It will be bnown, however, that alcohol consists of ether united to water, and that
its formula is C4H5O.+Aq. Its vapour is then formed by the union of
i volume of vapour of ether, =1290 6 [ 16007.
i volume of vapour of water, - 310 1
The uses of alcohol in chemistry and pharmacy are numerous and
important.  It dissolves the caustic alkalies and most deliquescent salts,
combining with them to form alcoates, which resemble very remarkably
the hydrates.  Thus, if dry chloride of calcium be dissolved in alcohol,
the alcoate crystallizes by cooling in large transparent plates.  By heat,
these are decomposed, and also by contact with water, which expels the
alcohol, and takes its place.- The- permanent and efflorescent salts are
generally insoluble in alcohol, and may be even precipitated by it from
their solution in water, the alcohol seizing on the water.
An important pharmaceutic use of alcohol is for the solution of the
resinous principles of plants, in. the preparation of tinctures and alcoholic
extracts.  The strength of the alcohol must in these cases be regulated
by the nature of the substances to be dissolved.  Sometimes rectified
spirit, at other times proof spirit being more effectual.
The manufacture of alcohol is itself one of the most important arts;
it is the basis, also, of the manufacture of vinegar, of the making of resinous varnishes, and various other processes.  To the chemist it is
specially of interest as the type of a very interesting group of organic
bodies, and yielding by its decomposition a very numerous series of
products, which are of great importance in science, in pharmacy, and
in the arts.
When alcohol is exposed to the air it gradually absorbs oxygen,
aldehyd and acetic acid being formed. It is then said to undergo the
acetous fermentation.  Under the influence of acids it loses an atom of
water, compounds being formed which are termed ethers, into the com.
position of which the acid employed generally enters.
Of Su7lhuric Ether. Ether. Oxide of Ethy7e.
This substance may be-prepared by any process which deprives alcohol of the equivalent of water which it contains. Thus, if potassium be
placed in contact with absolute alcohol, hydrogen gas is evolved, and a
compound of ether and potash crystallizes, C4HO.+H.O. and K. giving
C4,HO.+K.O. and free H. If a current of gaseous fluoride of boron




542              PREPARATION  OF  ETHER.
(p. 326) be passed into alcohol, it is absorbed, and boracic acid separates
in crystals, while the liquor contains ether; here, also, the water of the
alcohol is decomposed, fluoric and boracic acids being produced, and
ether liberated.  By distillation with chloride of zinc, also, the water
may be abstracted from alcohol, and ether obtained; but the affinity of
thie other deliquescent salts is not sufficiently intense to decompose it.
It is by the action of sulphuric acid upon alcohol that ether is, for
practical purposes, always obtained.  Equal weights of rectified spirit
and of oil of' vitriol being well mixed, and avoiding any considerable rise
of temperature, are to be introduced into a glass globe, to which heat
may be applied by a sand.bath, as represented in the figure.  To this
may be attached  the form  of condenser devised by Liebig for the
distillation of very volatile liquids.  It consists of a glass tube three
fourths or one inch wide, and twenty-four or thirty inches long, d d, to
which is attached at one end by a good cork a narrower tube, passing
to the globe, and to the other end is soldered a smaller tube, bent at an
o_)tuse angle, and conducting to the receiver e.  The tube d d fits watertight by corks into a tinned cylinder c, the proportions of which may be
judged from the figure; this is kept full of cold water.  When the distil.
lation commences, the hot vapours entering the condensing tube at d,
give out their latent heat to the surrounding water, and that part of the
condenser would soon get hot, were not the water constantly changed;
by the funnelf, a stream of cold water flows fiom the reservoir i into the
lower part of' the tube c, and presses up betfore it the warm and lighter
water, until this is expelled by the tube h, when it is collected at b
The supply of cold water should be so proportioned to the supply of va
pour, thai, flowing away at ih, it should not be sensibly warm  to the
hanrd.  With this precaution, most volatile liquids may be pertectly condensed even in the midst of sumtmer.  The mixture of acid and spirit in
the rlobe being brougrht to a temperature of about 2600 as rapidly as
possible, it begins to boil, and the ether distilling over, accompanied by
sr-Ie water and unialtered alcohol, collects ii tilte receiver.
Since the quantity of sulphuric;lcid contilninnlly increases in the globe
as the distillatiron proceeds, its'actionl on 1tn,l-, il i.ir! alcohol chlanges,




CONTINUOUS  FORMATION  OF  ETHER.    543
the mixture becomes dark coloured, an oily substance distils over (oil of
wine). alnd the quantity of ether formed diminishes rapidly. SulphuMous
acid anid olefiant gases are then evolved, and finally the mixture becomes
thick anid black, and fioths up very much.  When the object is only the
preparationu of ether, these reactions may be prevented, and a much larger product obtained, by admitting  to the globe, by meanls of' the bent
funnel, a continual but minute stream of rectified si)irit.  The action of
the sulphuric acid is thus exercised upon successive quantities of' spirit,
and the liberation of the ether continues until the acid becolmes so weak
as to be nro longer able to decompose the alcohol, which occurs wvhen the
Whole quantity of rectified spirit used is about twice the weight of' the oil
of vitriol, which is tllen reduced to the strength of' S.03+4 Aq.
Altllougrh we may represent the results of this reaction by contsidering
the sulphuric acid to take water directly fiom the alcohol, and set tlle
ether free, such is by no means really the case; on the contrary, whlen
the alcoulol acts on the oil of vitriol, tihe water of' both is disengnged,
and the sulphuric acid and ether unite to fornm Sulpthate of Ether, (C41Ft5
O.+Aq.). and S.()+Aq. giving C4H50.-+S.03 and 2 Aq.  Th'is body,
which resembles very much sulphate of amlmonia in its tendency to comrbination, unites with an atom of oil of vitriol to form Bisuliphate of Ether,
or, as it is generally termed, Sulphovinic Acid.  T'he two atoms of sulphuric acid thus engaged change very much in properties, fornming salts
with barvtes and oxide of lead, which are very solr.ble in water.  The
two equivalents of water, which, as above described, are set fiee, dilute
the reniailning sulphuric acid to such a degree as that it cannot. decompose more alcohol; hence, if absolute alcohol be used, 3(C4Hs0. + Aq.)
with 8(S.03. H.O.) produce 3(C4F150.. S.03+H.I.. S.03) and 2(8.
03+4 Aq.). one fourth of the sulphuric acid remaining over; if a weaker alcohol be used, the quantity of dilute sulphuric acid fIormed becomes
proportionally greater.  An acid which already contains four atoms of
water, fobrns no sulphate of ether when put in contact even with absolute
alcohol, except the temperature be very high.
The ether obtained by distilling a mixture of alcohol and oil of vitriol
results, therefore, not fiom the water being seized on by the oil of' vitriol,
but from the decomposition of its compound with sulphuric acid, the sulphate of' ether; the ether being a base not much superior in energy to
water, is expelled by it in turn under favourable circumstances, especially
when the water is present in excess.  In this respect it resembles, as
Rose has remarked, the sesquioxides of iron, antimony, and bismuth,
which form  salts with sulphuric acid that are totally decomposed by a
large quantity of water, especially if their solutions be boiled; the acid
then combines with the water, and the metallic oxide precipitates.  Before deciding on this view of the production of ether, it is necessary to
describe some collateral phenomena.
If absolute alcohol and strong oil of vitriol be employed in the prepara.
tion of ether, it is found that the distilled product consist.s of ether and
water, forming two distinct layers in virtue of their diffIerent specific
gravities, but in quantity identical with those which constitute alcohol;
100 parts of the mixed liquids consisting of 19'5 water and 79'5 ether,
when separated from a quantity of alcohol which had escaped decoinp),.
sition.  The oil of vitriol remains in the retort in its original state of
concentration, and hence might be applied to etherify an infinite quantity




544   THEORY OF THE FORMATION OF ETHER.
of absolute alcohol, introduced in a continuous stream.  To explain this
very remarkable result, Mitscherlich advanced that the action of the
sulphuric acid on the alco!hol is mnerely catalytic; that it splits it, as it
were, into ether. and water, and these pieces not being able to reunite,
come over in vapour, merely mixed with each other; this idea is, however, quite inadmissible, as the whole quantity of ether is proved to be
united with the sulphuric acid in the first place, and to distil over only
after the decomposition of the compound that'had been so formed.  The
observations of' Liebig and Rose have removed the difficulty which this
simultaneous evolution of water and ether presented to the adoption of
the theory which supposes the ether to be'expelled from its combination
with the sulphuric acid by the water.  In fact, it is only at a particular
temperature that the ether and water come over in atomic prop.ortions,
and this then results fiom the identity of the boiling points of the solution
of sulphovinic acid and of the dilute sulphuric acid.  Thus, when we
heat together sulphate of ether, (C4HOF0. +S.O0), and the dilute sulphuric
acid, S.03+4 Aq., the former is decomposed, bihydrate of sulphuric
acid, S.03+2 Aq., being formed, and ether set free; but at this temperature the sulphuric acid begins to abandon its second atom of water,
which then distils over with the ether.  If we conduct the distillation
very slowly, and retain the temperature below 2120, the ether comes
over, almost perfectly free from water; but at a higher temperature,
the ether, when liberated, is immediately converted into elastic vapour,
which bubbles through the liquid like a gas, and the water evaporates in
the space thus afforded, as it should evaporate in a current of air forced
to bubble through the liquid in the same way.
The production of ether depends, therefore, upon the facts, that when
alcohol and oil of vitriol are mixed, sulphate of ether is formed and wa.
ter is set free; but on the application of heat, this action is inverted, and
the ether is expelled from the acid, with which the water recombines.  If
the distillation be conducted so that the mixture boils, the dilute sulphuric
acid concentrates itself, at the same time, by giving off an atom of water,
which condenses mixed with the ether, but had its origin in a perfectly
independent action.
If we heat alcohol in contact with glacial phosphoric or arsenic acids,
it is similarly acted on, and the ether forms a phosphovinic or arseniovinic acid, which is decomposed by boiling, the ether being set free.  These
acids would be too costly to admit of their employment in the prepara.
tion of ether on the great scale, and, besides, they do not act as powerfully as oil of vitriol.  Although this ether does not contain any sulphuric
acid, it is very generally called Sulphuric Ether, and I shall often use that
name, but the distinction between it and the compound ethers formed by
its union with acids must be carefully kept in mind.
The ether formed by the process now described is rendered impure by
admixture with alcohol and water, and sometimes oil of wine and sulphurous acid.  It is freed from these by rectification, from  a water.
bath, over some dry carbonate of potash.  It is then a colourless liquid,
of an agreeable penetrating odour, and a pungent taste.  Its sp. gr. is
0'720 at 60~; it does not conduct electricity; at — 47  F. it freezes
into a crystalline mass; it boils at 960; the sp. gr. of its vapour is
2581'3.  In evaporating it produces great cold, of which numerous ap.
plications have been noticed under the head of vaporization. (Sec. IV.,
Chap. III.)




CONSTITUTION  OF  ETHER.                         545
Ether is very combustible; its vapour, diffused through air or oxygen,
forms powerfully explosive mixtures.  Exposed to the air, it gradually
absorbs oxygen, forming acetic acid.  Its flame is brighter tha-n that of
alcohol, but it gives no smoke; it dissolves sulphur and pho.sphlorus in
small quantity; iodine and bromine are abundantly dissolved, but they
soon act on the ether; most bodies that are soluble in alcohol (are dis.
solved by ether, except salts, of which only very few, as the perecilorides
of gold, of platina, and of iron, are taken up by it.  Ether- conbilles with
almost all acids, forming well.-defined neutral salts, the compounld ethers,
which have a remarkable similarity to the ammoniacal salts. t i. tierefore, an organic base; its composition is expressed in the formula C4-IjO
giving the numbers by weight:
4 equivalents of carbon... 24'20... 65.31
5   "    "  hydrogen..  5'00... 1333
1   "    "  oxygen...  8'00... 21'33
37'20       o10000
and by volume,
4 volumes of carbon vapour,  (843X4)-:3372.0
10    "      hydrogen  (68-8X10)= 6880.
1    "      oxygen  "....       11026
Produce two volumes of vapour of ether. 5162'6
Of which one weighs, therefore.... 2581 3
In chemistry and pharmacy ether is of importance as a vehicle for the
solution of many resinous and other bodies, and from its action on the
animal economy.  By the action of reagents it yields a great number
of' derived compounds, of which the most important will be described in
their proper place.
The question of the intimate constitution of ether has been very much
discussed, and opinions have followed precisely the same course, with
regard to the theory of its compounds, as for that of the combinations
of ammonia; thus it has been looked upon as an oxide of a compound
(metallic'?) radical, Ethereitm or Ethuleu, as the salts of ammonia were supposed to contain a compound metal, Ammonium.  The formula of ethyle
should be CH15, and its symbol Ae.  On the other hand, it may be considered to consist of olefiant gas, C4H4, united to water, and the latter
then takes the place of the ammoniacal gas in the theory of aimmonia.
I shall frequently employ for ether the symbol Ae.O., and speak of it and
other bodies as compounds of ethyle, as oxide, chloride, &c., but without
any other present object than convenience of language, for it would be
impossible to discuss the comparative merits of these theories, without
knowing the properties of the compound ethers, of olefiant gas, of al.
dehyd, acetic acid, and many other bodies, which are involved in the re.
actions by which we may endeavour to test their value, and hence I shall
postpone all details of the principles of the ether-theories until the end of
the present chapter.
Compounds of Ether with Sulphuric Acid.
Suiphovinic Acid. Bisulphate of Ether, C4H50.. S.0 3+H.O.. S.03, is produced by
mixing alcohol with oil of vitriol, as described for the preparation of ether, or by
passing vapour of ether into oil of vitriol as long as it is absorbed. By heat this
solution is decomposed. The sulphovinic acid cannot be obtained in a solid form.
if a solution of sulphovinate of lead be decomposed by sulphuret of hydrogen, a col.
Zzz




"546          SULPHOVINATE   OF  POTASH) ETC.
ourless and very-acid liquor is obtained, which, when concentrated, evolves ether,
blackens, and is totally decomposed.  Its salts are all soluble, and generally deliquescent; when boiled with muriatic acid, alcohol is evolved, and sulphuric acid
set free.  By a high temperature they are decomposed, oil of wine, ether, olefiant
gas, and sulphurous acid being given off, while a metallic sulphate or sulphuret remains behind, mixed with some charcoal.  By distilling a sulphovinate with a potash salt of any volatile acid, a compound of ether with that acid distils over, and
sulphate of potash remains.  By fusing a sulphovinate with a caustic alkali, water
and olefiant gas are expelled, and all the sulphuric acid remains combined with the
alkali.
Silphovinate of Potash, Ae 0.. S.03,-K.0.. S.0, crystallizes in colourless rhomboidal plates, which are anhydrous; it is very soluble in water, but sparingly soluble in alcohol. Sulphovinate of Barytes, Ae.O.. S.03+Ba.0.. S.03,2 Aq, crystal.
lizes in oblique rhomboidal prisms unalterable in the air; it tastes strongly acid
in vacuo it abandons its water, and is then not altered by a heat of 212~, but if the
hydrated salt be heated to 2120, alcohol is given off, and sulphuric acid set free.
Sullphovinate of Lime crystallizes in thin hexagonal plates, which are very deliquescent; it is soluble in less than its own weight of cold water.  Sulphovincate of Lead
forms large rhombic crystals, deliquescent; very soluble in water and in al-ohol;
it is gradually decomposed at ordinary temperatures.  Sulohomvinate of Copper,
Ae.O0. S.,0+Cu.0.. S.03-4 Aq., forms large blue octagonal plates, permanent
in the air, and very soluble in alcohol and water; heated to 2120 it is totally decomposed.
Elhionic and Iscthionic Acids.-These substances are formed by acting on alco
hol or ether with the vapours of anhydrous sulphuric acid; the liquor, neutralized
by barytes, gives the insoluble sulphate and the soluble ethionate of barytes, which
last separates from the concentrated liquor as a crystalline precipitate on the addition of alcohol.  A solution of this salt, when decomposed by sulphuric acid, gives
free Eth/ionic Acid, which, by boiling, is decomposed into sulphovinic acid and isethionic acid, of which, indeed, Liebig considers it to be, in reality, only a mixtulre.
The isethionic acid is formed more characteristically by the direct union of anhydrous sulphuric acid and olefiant gas, and will be described as a compound of that
body.
Allhionic and Methionic Acids.-When the mixture of alcohol and oil of vitriol,
for naking ether, has been distilled so far as that it has become black and begun to
froth, it produces, when neutralized with bases, a series of salts, which, though
having the same per cent. composition as the sulphovinates, differ very much from
them in properties; thus the Althionate of Lime does not crystallize; the Althionate
of Barytcs crystallizes in fine needles, in place of the large plates of tile sulphovinate; the Althionate of Copper is still more distinct, as its crystals are thin, acute
rhombs, of a pale green colour.
If the ether, into which the vapours of sulphuric acid are passed, be allowed to
grow hot, it becomes black, sulphurous acid is evolved, and an acid is formed different. from any of the preceding; it is called the Methionic Acid, and is characterized by its barvtes salt being totally insoluble in alcohol, and but sparingly soluble
in water.  When its salts are filsed with caustic potash, merely sulphite of potash
remains; the formuli of the acid contained in the barytes salt is CH13. S207.  It
evidently does not contain any simple combination of alcohol or ether.
iHeavy Oil of Wine.  Sciphate of Ether and Etherol.-CsHI90. —.2S.Q3, or Ae.O..
S.0,-+C4H4. S.03.  WVhen one part of rectified spirit is distilled with two and a
half parts of oil of vitriol, a little ether passes over, followed by an oily yellow liquid
and water, with much sulphurous acid. The oil is to be washed waith a little water,
and then dried in vacuo under a bell-glass, beside two cups, one of oil of vitriol and
the other of caustic potash; the first absorbs the water and ether, and tle last the
sulphurous acid. This substance is then a thin oil, sometimes green and sometitmes
yellow; its odour aromatic and pungent; its specific gravity 1.133; when heated
it begins to boil, but is rapidly decomposed, blackening and evolving sulphurous
acid, and but little distilling over. It is scarcely soluble in water, but abundantly
so in alcohol and ether.  WVhen boiled with water, or with an alkaline solution,
Sulphovinie acid is formed, and Etherol (light oil of wine) set free, which floats upon
the surface.
The composition of this body is not absolutely constant.  I consider it to lhe a
mixture, in variable proportions, of true Sulphate of Elher, Ae.O.. S.O3, with Sulphate
of Etem ol, C4H4. S.O.  I have found that when distilled with oxalate or acetate




COM POUNDS  OF  ETHER.                             547
of potash. with chloride or sulphuret of potassium, oxalic and acetic ethers, muriat.
ic ether, &c., are generated, and, at the same time, etherol remains indifferent to
these re-agents.
Another process for obtaining this heavy oil of wine consists in mixing dry sul
phovinate of lime with its own weight of quicklime, and distilling at a heat not ex-.
ceeding 5200. The oil which comes over mixed with alcohol is to be purified as
already noticed.
Ethsrol annd Etherine.-C4H4.  The oil which is separated fiom the foregoing
substance by hot water or by alkalies, divides itself generally, after some time, into
a liquid and a solid portion; the first constitutes the light oil of wine, Etherol.  It is
pale yellow, and thick, like olive oil; its odour is aromatic; its specific gravity
=0 92L; it boils at 500~; at — 350 it freezes. The Etherine forms hard, brittle, colourless prisms'; it is tasteless; its specific gravity 0-980; it melts at 2300, and
boils at 4640; it is soluble in alcohol and ether.  The composition of both these
bodies is the same, consisting of equal numbers of atoms of carbon and hydrogen,
but their atomic weights are not known. It is very probable that the etherol is really a mixtume of two other bodies; for when a saturated solution of chloride of zinc
in alcohol is distilled, an oily liquor is obtained, which, by rectification, may be separated into two fluids, of which one, boiling at 212~, has the formula CsH7, and the
other, which boils only at 570~, has the formula CsH5. A mixture of equal quantities of the tawo should have the composition assigned to etherol.
Liebig and Itegnault have found the etherol obtained by alcohol and sulphuric
acid to have the foirmula C4H.3, so that it must he looked upon as an irregular mixture of several oils, which have not yet been obtained pure. The etherol, or Ethereal Oil, is employed to prepare HToffman's Anodyne Liquor, being dissolved in a mixture of one part of ether and two of spirit of wine.
Compounds of Ether with the Phosjwhoric anzd Arselic Acids.
l'hosphovinic Acid. -Ae.O.. P.O —+2H.O.  WVhen concentrated tribasic phosphoric acid is dissolved in alcohol, great heat is evolved, and one atom of water re.
placed by an atom of ether. The acid salt thus formed may be obtained crystal.
lized, but when its solution is heated strongly it is decomposed. It coibines with
two atoms of base to fobrm the Pho.phovinates, of which few are as yet well knowin.
The barytes salt, P.05+Ae.O.. 2Ba.0.+-12 Aq., crystallizes in brilliant colourless
plates, and is remarkable for being equally soluble in water at 32~0 and 2120, but
three times more soluble in water at l04~.
Arseniovinic Acid, As.O-+Ae.O.+2H.O., is formed with arsenic acid and alcohol,
like the body last described. Its salts have been but very slightly examined.
Compotunds (f Ether with the other illineral Acids.
liauriatic Ether.  Chloride of Ethyle, C41-15CI. is prepnred by distilling
a mixture of three parts of' oil of vitriol, ti'lmr of fuised common salt, and
two of absolute alcohol.  The retort should be connected with two two.
necked bottles, of whichl tlhe first should be immoursed in a vessel of water
at 600, and the second be surrounded by ice, or a freezing mixture.
Some alcohlol and common ether, which pa:ss over. are condensed in the
first bottle, wliile the iriuriatic ether is rediced to the liquid state only
in the second.  By digestion with sorme chloride of calcium it is rendered
quite pure.
It is a. colourless liquid, of a pungent garlic odout'; its specific gravity
— 0874; it boils at 52~; is neutral; sparingly soluble in water; it
burns with a bright flame, green at the edges, andl gives off muriatic acid
gas.  By passing through a red-hot tube, it affords equal volurnes:f
olefiant and nmuriatic acid gases, or by hieating with potash, it gives ole.
fiant,as and chloride of potassium.  Heated with alkiline salts, it yields
compound ethers and alkaline chlorides.  Whe n rnuriiatic ether is heated
with potassium, LUxvig states that chloride of potassium  is formed and a
ligTht oily substance separates, which has the formula C4IL1.  It should be
lthyle, but so important an observation has need of verification.  This




548            HYDR OBRO MIC ETHER, ETC.
body is often called light Muriatic Ether, to distinguish it from  heavy.liuriatic Ether, which results from the action of chlorine on weak alco.
hol.
Hydrobromic Ether..Bromide of Ethyle, C4IoBr., is obtained by dis.
tilling together. two parts of bromine, one of phusphorus, and six of alco.
hol.'T'here is first formed bromide of' ph,,sphorus, wlIich instantly decomposes the water of the alcohol, and the nascent hydrobromic acid
acting on the ether forms the hydrobromic ether.  In properties it per.
fectly resembles the following body:
Hydriodic Ether.  Iodide of Ethyle, C4HI., is formed by distilling
iodine, alcohol, and phosphorus.  It is a colourless liquid, of a pungent
ethereal smell; its. specific; gravity = 1'92; it boils at 161~; it is abundantly soluble in alcohol.  Heated with potash, it gives pure olefiant gas
and iodide of potassium.  The theory of its formation is the same as in
the fortmer case.
Hydrosulphuric Ether.  Sulphuret of Ethyle, C4H5S., may be formed
by acting on muriatic ether with an alcoholic solution of sulphuret of,potassium.  It boils at 187~; it combines with sulphuret of hydrogen to
fobrnl the following very remarkable substance:
Sulphur-alcohol, or Mercaptan, C4H6S2, or Ae.S. + —I.S., which is obtain.
ed directly by distilling in a water.bath conrcentrated solutibns of sulphovinate of lime and of' potash saturated with sulphuret of hydrogen, K.S. +
H.S. and Ae.O.. S 03+K.O.. S.0a producing 2K.O.. S.O03 and Ae.S.
+H.S.; the mercaptan distils over, and sulphate of potash remains in
the retort; it is a colourless, thin liquid, of an insupportable smell of
onions; it boils at 960~; its sl)ecific gravity is 0-84; it dissolves in alcohol; is perfectly neutral; burns with a bright blue flame; and by cold,
freezes into a crystalline mass.  In constitution, it is perfectly analogous
to alcohol, the oxygen being replaced by sulphur..When placed in con.
tact with metallic oxides, water is formed, and a double sulphuret of ethyle
and the metal produced. This occurs remarkably with oxide of mercury,
whence the barbarous name given to this body by Zeize, from Mercurium
Captans, and to its compounds of ]M ercaptides.  rhat of mercury is a
crystalline solid, fusible at 110', and soluble in alcohol.
The properties of this body induced its discoverer, Zeize, to look upon
it as a compound of hydrogen with a compound radical, which he called
Mercaptum, which should be really the following compound.  Its formula
then became C4HS,2+-H.  Hte extended this view also to common alco.
hol, which he considers as CH,502,H.; but his theory has met with
very few supporters.
Thiall.  Bisuiphuret of Ethyle, Ae.S2, is formed by distilling a mix.
ture of sulphovinate of lime and persulphuret of potassium.  It is a lim.
pid, oily fluid, with a strong garlic smell; it boils at 1240~.  Its solution
in alcohol precipitates the salts of lead and mercury.  By the action of
nitric acid on these sulphurets of ethyle, acids are produced analogous to
the sulphovinic, but which are not, as yet, accurately known.
The Seleniuret and Telluret of Ethyle have been formed, but do not require description.
Nitrous Ether.  Hyponitrite of Ethyle.-Ae.O.. N.03.  When alcohol and nitric acid are directly mixed, the action is very violent; heat
is evolved, red fumes are copiously given off, and acetic, oxalic, and carbonic acids formed.  Even when the acid is dilute, its action is very




NITROUS'ETHER   ETC.                          549
complex; giving up two atoms of oxygen to one portion of the alcohol,
it produces aldehyd, and acetic and oxalic acids, and it is only the hyponitrous acid thus produced that acts on the remaining alcohol, and, combining with the ether of it, formns the proper nitrous ether.  To avoid
these oxidized products, the best plan is to generate red fumes of hyponitrous acid, by acting on starch by nitric acid in a retort, and to conduct
these fumes by a bent tube to the bottom of a two-necked bottle contain.
ing alcohol.  They are copiously absorbed, and combine directly with
the ether.  From the second neck of the bottle a tube should pass to a
condensing apparatus and receiver; enough of heat is evolved by the ab.
sorption of the red fumes to distil over the nitrous ether formed, which
may be thus obtained quite pure.
Another process, which may now be considered as obsolete, consisted
in distilling a mixture of oil of vitriol, nitrate of potash, and rectified
spirit, by the heat of a water-bath, into a receiver cooled by snow.  The
nitric acid acted very violently on the alcohol, and the product was im.
pure, and small in quantity.
Nitrous ether is a liquid, colourless or pale yellow, of a pungent odour
of apples; it usually reacts acid from slight decomposition, but is neutral
if quite pure; its specific gravity is 0'947; it boils at 61" Fah.  Exposed
to the air, it absorbs oxygen rapidly, and forms aldehyd, acetic and formic
acids; at the same time, nitric oxide is given off.  By contact with any
strong base, it is decomposed, alcohol being set free, and a hyponitrite
formed.  A solution of this nitrous ether in spirit (spiritus nitri dulcis)
is employed in pharmacy.  It is prepared by distilling a mixture of one
part of nitric acid and ten of rectified spirit, collecting the first seven.parts which come over, and digesting them  on a little dry carbonate of
potash, to remove any traces of free acid.  Its specific gravity should be
0-850.  It may be prepared directly by dissolving one part of'real nitrous
ether in eight parts of spirits of wine.
Cyanogen Compounds of Ether.
Hydrocyanic Ether.  Cyanide of Ethyle, Ae.Cy., is prepared by distilling a mixture of sulphovinate of' potash and cyanide of potassium at a
moderate heat.  It is a colourless liquid, of a strong garlic odour; it
boils at 179~, and is lighter than water; it is very poisonous.
Cyanuric Ether,; 3Ae.O.+2CysO3+6 Aq., is formed when the vapours of hydrated
cyanic acid are passed into ether, as long as they are absorbed. After some time,
the new compound separates in crystals, which are colourless prisms, destitute of
taste and smell, soluble in water, and but sparingly soluble in ether.
Hydrosulphyoc/anic Ether appears to be formed by distilling sulphocyanide of potassium with sulphovinate of potash. It is a liquid heavier than water.
Compounds of Ether with the./lcids of Carbon.
Carbonic Ether. Ccarbonale of Ethlle. —Ae.O..C-02. This ether can only be produced by an indirect process, the theory of which is not well understood. Metallic
potassium or sodium is added, in small pieces, to oxalic ether, as long as a disengagement of-carbonic oxide gas occurs; a thick brown mass is firmed, which is to
be distilled, the excess of metal being first destroved by the addition of water; the
carbonic acid distils over. It is a colourless liquid, of an aromatic smell, lighter
than water. It boils at 260; it is insoluble in water, but dissolves in alcohol; its
alcoholic solution is decomposed by potash, alcohol and carbonate of potash being
formed.
Carbonate of Ether and ITater. GCrbovinic Acid.-Ae.O.. C.02+H..O..02. At
one time it was considered that anhydrous sutgar was actually bicarbonate of ether,
C6H505=CIi50.+2C.02, and that the alcoholic fermenitation consisted in the sep;




:550                 OXAL I'C  ETHERx ETC.
aration of these bodies, the nascent ether combining with water to form alcohol;
but that idea is now inadmissible. The true carbovinic acid is prepared by dissolving caustic potash in absolute alcohol, and passing dry carbonic acid gas through
the liquor as long as it is absorbed. A crystalline mass is formed of carbonate and
Carbovinate of Potash, which last is dissolved out by cold alcohol; and this solution,
being mixed with ether, deposites the salt, whose formula is Ae.O.. C.02+K.O.. C.
0Q, in pearly plates, which are immediately decomposed by water into alcohol and
bicarbonate of potash. The carbovinic acid is not known in an isolated form.
Oxalic Ether. Oxalate of Elthyle, Ae.O.. C203, is prepared by distilling one part
of alcohol with one of binoxalate of potash and two of oil of vitrio'.. At first alcoho.
and common ether come over, but then a heavy fluid, which sinks to the bottoms of
the receiver. The portions last distilled are richest in product. It-is rectified by
another distillation from off a little litharge. It is a colourless oily liquid, denser
than water, of a heavy but aromatic smell; it boils at 370~. In contact with water
or bases, it is gradually decomposed into alcohol and oxalic acid. The sp. gr. of its
vapour is 5077.
Oxalovinic Acid.-Ae.O.. C203+H.O.. C203. This acid is not known except in
combination. It is produced by adding to a solution of oxalic ether in alcohol half
as much potash as would suffice to decompose it. The Ox.alovinate of Potashi separates as a crystalline powder, being insoluble in alcohol. By an excess of base it
is decomposed into alcohol and an oxalate. Its other salts do not require special
notice.
Oxamethan.-Ae.O... C203+C202Ad. When oxalic ether is acted on by water
of ammonia, it is totally decomposed, alcohol and oxamide being fobrmed, as already
noticed. If a solution of ammonia in alcohol be used, but one half of the oxalic
ether is decomposed, and the oxamide produced unites with the other half; forming
a substance soluble in alcohol and water, and crystallizing in brilliant prisms and
plates. It melts at 2120, and sublimes unchanged at 430-. Its solution in cold water does not precipitate lime-water, but if it be boiled alcohol is expelled, and the
solution contains binoxalate of ammonia. By water of ammonia it is totally changed into oxamide.
Chloroxycarbonic Ether.-Ae.O.. C.02+C.O.C1. This substance is formed by the
action of chlorocarbonic acid gas on absolute alcohol. It is a colourless liquid,
perfectly neutral, heavier than water, and boiling at 2010; sparingly soluble in wa-.
ter. It consists, or, at least, contains the elements, of an atom of carbonic ether and
an atom of phosgene gas. When put in contact with water of ammonia, it is dissolved violently, and heat evolved, sal ammoniac and a peculiar substance termed
Urethan being formed. The liquor is to be dried down, and the residue distilled in a
dry retort with an oil-bath. The urethan passes over, and solidifies in the receiver
to a crystalline mass resembling spermaceti. In it the chlorine of the preceding
substance is replaced by amidogene, its formula being Ae.O.. C.02+C.O.Ad.; it
consists thus of carbonic ether and carbamide in the proportion of one atom of each.
Sulphocarbonic Ether. Hydroxanthic Acid, Ae.O.. C.S2+I.O.. C.S2, is prepared
by decomposing the xanthate of potash by dilute sulphuric acid. A milky liquor is
obtained, from which, after some time, a heavy oil separates; it is to be rapidly
washed with water, and dried by chloride of calcium. It is then pale yellow, slightly acid, inflammable, and burns with a blue sulphurous flame; it is decomposed by
warm water into alcohol and sulphuret of carbon; it decomposes the alkaline carbonates, expelling the carbonic acid. Of its salts, that of potash is obtained directly, and from it the others. Xanthate of Potash, Ae.O.. C.S2+K.O.. C.S2, is formed
by adding sulphuret of carbon to a warm solution of caustic potash in alcohol. On
cooling the liquor, it deposites the salts in crystals, which are to be collected on a filter, washed with ether, and dried between folds of bibulous paper. The salts of
lead, copper, &c., may be prepared by double decomposition; they are all yellow,
whence the ordinary name of the acid.
Mucate of Ether is solid and crystalline. It is formed by dissolving mucic acid in
cil of vitriol, and gradually adding an equal weight of alcohol. The liquor yields,
after some time, the mucic ether in crystals, which are to be dried on a porous stone,
and recrystallized from alcohol.
The remaining compounds of ether with acids will be described along with the
other salts of those acids.
Of Olefiant Gas and its Compounds.
This gas has been firequently mentioned as one of the products of the ac.
tion of sulphuric acid on alcohol. The usual process to obtain it consists




PREPARATION  OF  ODLEFIANT  GAS.                      551
in heating one part of alcohol with six of oil of vitriol in a flask, b, from
which a tube passes to the water pneumatic trough, as in the figure; the
nmass becomes dark;
ether, water, and oil
of wine collect in the
interposed globe, a,
and clefiant gas is co-.
piously evolved, mix.
ed with an equal vol.
ume  of sulphurous           C 
acid, which, however,
being absorbed by the
vwalter, thie other gas 
remains pulre.  To. A= 
wards the end of the
process the materials
in the flask swell up very much, and might boil over if not carefully attended to.  T'he theory of this action appears, at first sight, very simple;
the alcohol losing an atom of water, is first converted into ether, which,
by the influence of the excess of sulphuric acid. is deprived of the elements of another equivalent of water, and olefiant gas remains, C4HO.
giving C,4H4 and H.O.; but we cannot by this process generate the olefiant gas, without, at the same time, more complex products appearing,
as etherol, sulpliurous acid, and the black matterswhich remains in the
retort.  This last, which had been considered formerly as charcoal, appears to consist of C27H804+S.03; it combines with bases, and is termed
the Thiomelanic Acid; it evidently results fiomn the sulphuric acid, giving
up oxygen to the hydrogen of a portion of the alcohol.
Olefiant gas is generated on the large scale by the decomposition of
coal, pitch, oil, &c., at a red heat, and is employed for the purpose of illumination, being the most valuable constituent of the gas which is burned in our streets and shops.  To this source of it I shall have occasion
to return.
We may obtain this gas, however, by much more definite and simple
processes.  Thus, if vapour of muriatic ether be passed thrbugh a redhot porcelain tube, it is resolved into equal volumes of olefiant and muriatic acid gases; also, if muriatic ether be heated with ammoniacal gas,
sal ammoniac is formed, and olefiant gas evolved; the same decom'posi.
tion is caused by caustic potash.  If vapour of alcohol be passed into oil
of vitriol so far diluted as to boil at 320~, and heated to th'at degree, it is
totally resolved into water and olefiant gas.  In a theoretical point of
view, these sources of olefiant gas are peculiarly of interest.
Olefiant gas, when pure, is colourless; its odour is very slightly ethereal; it is sparingly absorbed by water; it burns with a brilliant white
flame, producing much sCnoke.  When mixed with twice its volume of
chlorine, and set on fire in a tall narrow jar, a brilliant flame descends
rapidly, muriatic acid being formed, and charcoal, smelling strongly of
napthaline, separating in dense flocculi.  Its specific gravity is 980'8, as
one volume of it contains a volume of carbon vapour and two volumes of
hydrogen (843('0+13766=980'6).  It consists of an equal number of
equivalents of hydrogen and carbon, but chemists are not unanimous as
to its real atomic weight.  Berzelius, who looks upon it as an organic




552            COMPOUNDS' OF  E THERENE.
radical, and the basis of a series of compounds with oxygen, chlorine,
&c., has p roposed for it the name Elzayl, and the foirmula CH2,. The name
Olefant Gas being very inconvenient, I shall, in speaking of its como
pounds, term it, for the present, Ethercne.  The principal support of the
theory, which considers this gas to be the radical of the ethers and of alcohol, is derived f'rom the great simplicity of their constitution by volume,
in the state of vapour, on that view.  Thus, two volumes of olefiant gas
combine with two of vapour of water to form alcohol; with one of vapour
of water to form ether; with two of muriatic or hydriodic acid gases to
form the hydriodic or muriatic ethers, and so in similar simple propor.
tions of volume in other cases.  But this' evidence is very insecure, as
we might show nearly as simple gaseous relations upon other and very
improbable points of view.  Its combinations are generally formed indirectly, as from alcohol or ether, but it combines immediately with iodine,
chlorine, and sulphuric acid.
Anhydrous sulphuric acid absorbs etherene in large quantity, form.
ing white crystals, which, when dissolved in water, constitute Isethionic
Acid, identical in every respect with that formed as described p. 546.
When dry, its composition is S20-+C,4H4; but. when in contact with
water, it combines with two atoms thereof; and becomes isomeric with
sulphovinic acid.  That it difibrs from  it essentially in constitution is
shown by its salts giving a mixture of sulphate and sulphite when fused
with potash; the sulphurous element is therefore as hyposulphuric, and
not sulphuric acid, and its rational formula is SO5+C4,HO0.  This ise.
thionic acid is much more energetic than the sulphovinic; it decomposes
all salts of.organic acids; its own salts are all soluble and crystallizable,
and sustain a heat of 450~ without decomposition.
If a jar of olefiant gas, c, be inverted in the pneumatic trough, over a
capsule, b, as in the figure, and bubbles of chlorine be-.passed up into it,
both gases disappear, and a heavy oily liquid collects
in the capsule, the fornation of which gave to the gas
its common name of Olefiant Gas.  In this process
a quantity of gas is totally decomposed, and inuriatic
acid is evolved in great quantity, but the oil results..... "-    from the direct union of the chlorine'and etherene,
its formula being C4H4,C12.  I will name it Chlor.
1ft~  - I etherene, but it is called the Oil of the Dutch Chemists,
as it was first formed by the members of a scientific
association in Holland.  When quite pure it is col.
ourless, of a sweet ethereal odour.  Its specific gravity =-125; it boils
at 180~; it burns with a greenish/flame, giving off muriatic acid; the
specific gravity of its vapour is 3421. Exposed to an excess of chlorine,
it is decomposed, hydrogen being removed, and replaced by chlorine; a
volatile oily liquid, C4H2C14, and ultimately sesquichloride of Carbon, C4
C16, are produced.,
The chlor-etherene is not decomposed by a watery solution of potash;
but if it be dissolved in an alcoholic solution of that alkali, and gently
warmed, chloride of potassium is formed, and a peculiar body produced,
whose composition is expressed by the formula C4HCI.  This substance
is gaseous, of a garlic odour, burning with difficulty with a smoky red
flame; its specific gravity is 2166.  It is evident that the chlor-etherene
May be considered as a compound of this gas with muriatic acid, C4H




PREPA:RATION  OF  ALDEHYD.                          553
CI.+H.CI., in which case the action of the potash is easily explained.
This gas itself is supposed to be a chloride of' the same carbohydrogen
as is the basis of acetic acid and aldehyd, (C4H3), or Acetyl; and the olefiant gas, on this view, is HIydruret of Acetyl, C4H3+- H., or Ac.H.  The
farther discussion of this opinion will be reserved for another place.  If
the gas, C4-3C,1., be passed over perchloride of antimony, it combines
with more chlorine and forms:a liquid, which boils at 2400, and consists
of C4H3ClI; by an alcoholic solution of potash this is decomposed into
muriatic acid, and another body, also liquid, but boiling at 86~, and having the formula C4H2C12.  By contact wvith chlorine. this produces the
liquid C4H2CI4, noticed in the, preceding paragraph, as obtained directly
fiom chlor.etherene, and, as the next stage, the sesquichloride of carbon.
If a mixture of olefiant gas and vapour of ether be acted on by chlorine, an oily
liquid is obtained, which boils at 3500, and consists of 04H4. Cl.O.; it is called Chlorethcral, but is properly a compound of aldehyd and the chlor-etherene, C4H4C12+
C4H402.
Bromine combines with olefiant gas, with the same phenomena as chlorine, and
gives rise to a similar series of compounds, which it is consequently unnecessary
to detail.
Iodine absorbs olefiant gas abundantly, and forms a white crystalline substance,
which melts at 180~, and may be sublimed if air be not present. It is soluble in
alcohol, insoluble in water; its formula is C4H412, but the products of its decomposition are not similar to those of the chlorine compound.
IWhen bichloride of platinum is dissolved in alcohol, a very complex reaction occurs, and a substance is produced consisting of Pt.Cl.-+-C2H2. This body combines
with the chlorides of the alkaline n-etals to form double salts. On Berzelius's view,
the C2H.2 being a compound radical (Elay/l), may be supposed simply to replace the
second atom of chlorine, and thus form an Elayl-chloride of platinum, which has
the same power of forming double salts as the ordinary bichloride. They are'thus
(Pt.+EI. C.)+K. C. and (Pt.+-EI.Cl.)+Na. C., &c.
Of the Products of the Oxidation of A lcohol, Aldehyd, Hypoacelous
Acid.-Eq. 555'6 or 44'2.
It has been mentioned, in speaking of nitrous ether, that by the ox.
idation of alcohol we obtain a crowd of products, as aldehyd and acetic
acid, formic, malic, and oxalic acids; these last. are secondary products
of the too violent reaction, and the result of the true oxidation of alco.
hol is found to be aldehyd or acetic acid, according to the point at which
the process stops.  The formation of acetic acid thus directly from al.
cohol constitutes the aceticfermentation.
Although aldehyd is formed when nitric acid acts on alcohol, yet, from
the other products being difficult to separate, it is not so prepared; a
large quantity of it is generated in the destructive distillation of wood,
and it may be obtained in the rectification of the pyroxylic spirit.  The
most ordinary process is that given by Liebig; six parts of oil of' vitriol
with four of water, four of spirit of wine, and six of black oxide of manganese, are to be distilled with a very gentle heat, and the product col.
lected in a receiver surrounded with melting ice.  The apparatus de.
scribed for preparing ether (p. 542) should be employed.  The process
is completed as soon as the materials in the retort cease to froth up. I
have found a purer product to be obtained by distilling, at a very gentle
heat, two parts of spirit of wine with three of bichromate of potash, three
of oil of vitriol, and six of water; the last two being previously mixed
and allowed to cool.  To obtain the aldehyd absolutely pure, it is to be
combined with ammonia, and the crystallized aldehyd.ammonia decom.
4 A




554       PROPERTIES OF ALDE IYD.-AC E TAL.
posed by dilute sulphu-ric acid, distilled in a water-batll at 1200 with the
greatest care, and rectifed over fused chloride of calcium.
Aldehyd is a colourless liquid, of an agleeable but suffocating odour;
it boils at 71~; it is lioghte  titarn water; it nmixes wvith water, alcohol,
antiether; it is neutral alid inflammable, bIul nilg with a blue fllam e; in
contact with oxidizing agents, it is changed into acetic acid, passing
through an intermediate state of Aldehydic Acid.  On this fact is found.
ed its most characteristic property; if' any liquor contaiiing alcdliyd be
added to a solution of.the amnmonliacal niti'atc of silver, and gently heat.
ed, the silver is deposited as a brilliant mnetallic film, lining the sides of
the vessel like a mlirror, and in the liquol? is found aldehydate of' silver;
if to this potash be added, oxide of' silver precipitates, and on boiling fbr
a moment, it is reduced to the state of metallic silver, and acetate of
potash is formed.  From the composition of aldehyd, these chanlges are
at once explained.  It is formed by hlle abstraction of two atoms of hy.
drogen fiom alcollol, which are carried away, as water, by the oxygen
supplied; its formula is hence C(41402: now, in contact with Ac.O., it
forms, first, aldehydic acid, C4[-41O0, and metallic silver, and then C4H403
with Ag.O. gives hydrated acetic acid, CX4-1404, and another quantity of
silver.  The formation of acetic acid from alcohol consists, therefbre, in
two stages; first, the abstraction of hydrogen, by which} aldeliyd is formed, and, second, the addition of oxygen, by which acetic acid is produced.
When aldehyd is heated in a solutionr of potash, this becomes brown,
and by an acid a solid brown substance separates,  which is fusible, and
possesses many properties of a resin.  Tliis also is a very distinctive
character of aldehvd.
When long kept, aldehyd undergoes an isonmeric change into two
bodies, one liquid, Elaldehyd, the other solid, IMetaldehyd; they have the
same formula as aldehyd, C41i402, but differ in all tileir properties.
The general characters of' aldehyd show that it contains the same rad.
ical as acetic acid, Acetyl, C,[I3 or Ac., combined with oxygen; it is,
therefore, Hydrated Oxide of Acetyl, Ac.O. — Aq.-=Cj14O2; it has been
called, also, Hypoacetous Acid, for it is capable of perfectly neutralizing
ammonia.  Its compound with ammonia is, indeed, very remarlikable;
it is best prepared by dissolving aldehyd in ether, and passing ammoniacal gas into the liquor; the aldehlyd-amnmonia, being very sparingly
soluble in ether, crystallizes as it forms in large hexagonal plates, which
are very brilliant and colourless.  Their solution in water soon decom.
poses, becoming brown, and exhaling an animal smell. The dry crystals
may be fused and sublimed without alteration; their
forminila is C4H30O.+H.O.. N.H3.
Aldehyd is formed also by the direct action of the
air on alcohol; this may be facilitated very much by
means of spongy platina, which contains much oxy.
gen condensed in its pores, but the process is of more
interest in consequence of another body which then
forms, and which cannot be otherwise generated; it
is Acetal.  To prepare it, a large bell.glass is taken, open above, and standing in a basin, so sup.
b: polrted as to allow tile air inside to be fi-equently ire
newed, as in the figure; through the top passes the
tube of a small funnel, a, under which is a watch.




FORMATION  OF ACETIC  ACID.                         55
glass, b, with a layer of p7atina  black (p. 407).  Into the funnel strong
alcohol is poured, so that from time to time a drop falls into the wrtchglass; being thus presented to'oxygen in a favourable condition, it is
decomposed, and aldehyd, acetic acid, and acetal are Ifbi-ned.  T'Iese
liquids are vaporized by the heat evolved, but condense on tLe sides
of the bell-glass, and, flowing down, collect in the basin undllrnl!th.
By processes detailed in the systematic works, the acetal is purified.
It is a colourless liquiid, boiling at 200O; its odour is agreeable; its formula is C8H903, and it appears to be a compound of aldehyd and ether,
Ct-1.102 + C4 { 0.
The A ldehydic Acid —Acelous Acid-as already noticed, is formed by
the partial oxidation ofaldehyd; but it appears to be produced also under
the circumstances of slow combustion, described in i). 179, alonig with
acetic and formic acids.  It is obtained pure by decomnposilg its silver
salt by sulphuret of hydrogen, forming a liquor of an agreeably acid
taste.
Of Acetic Acid.  Vinegcar.-Eq. 75'5-6 or 51-2.
As all alcoholice iquors are liable to undergo spontaneous decomposi.
tion, and form vinegar, this acid has been known from the earliest ages
as produced by the acetous fermentation; its origin was, however, long
wrapped in obscurity, for the complex constitution of the fermented
liqulos, in which it was ordinarily produced, prevented the simple nature of the change fiom being understood.  It is now fully established,
that the change from alcohol to acetic acid consists simply in tilhe remo.
vat of two atoms of the hydrogen of the alcohol, and addition of two
atoms of oxygen; these actions not being simultaneous, but successive,
and aldehyd being the intermediate product, thus:
Alecohol, C4H602,        and            Aldehyd, C4H402,
gives by — H2,                           gives by +02,
Aldehyd, C4H402.              Hydrated Acetic Acid, C4H1404By means of chromic and nitric acids, but especially by the platinum
black as described just now, this reaction may be carried on with perfect
accuracy and distinctness.
But if we place ourselves in the actual condition of practice, the the.
ory of the acetous fermentation becomes much more difficult; for exactly
as a pure solution of grape.sugar will not break up into alcohol and car.
bonic acid, and a cause of disturbance is necessary in order to enable
the new arrangement of its particles to occur, so do we find it to be in
changing alcohol into acetic acid.  Pure alcohol, whether weak or
strong, absorbs no oxygen by mere exposure to the air, and thence forms
no vinegar; it is necessary there should be another body more liable to
decomposition (ferment), which, abstracting oxygen from the air for the
purpose of its own decomposition, may confer upon the molecules of alcohol' such instability of structure as will admit of; and cause the similar
absorption of oxygen by them.  The ferment, in decomposing, evolves
water and carbonic acid; the alcohol evolves water only, but absorbs
the oxygen from the air.  The platinum  black, in the process that has
been described, supplies the place of the ferment.  In making vinegar
from malt liquors or fr'om wine, they are placed in hogsheads partially
full, and left more or less exposed to the air, according to circumstances.
To supply oxygen, the air must have access; but if the air were very




556            MANUFACTURE  OF  VINEGAR.
rapidly renewed, a large quantity of the volatile aldehyd would be car.
ried off.  These solutions contain abundance of organic matter,:proper
for acting as ferment; and when the fermentation is complete, the prod.
ucts of their decomposition collect upon the bottom  and sides of' the
vats, ill a gelatinous mass, termed mothers.
T'he manufacture of wine or malt vinegar by the old process of mere partial exposure to the air in vats consumed much time, and is almost superseded by the
German method, by which excellent vinegar may be made in thirty-six hours. A
cask is to be filled, as in the figure, with wood shavings, and
closed at the top by a pan, b, the bottomr of which is perforated
-   with a number of small holes, through which short threads are
/F lyt\ -''-: passed, to bring down the liquid more rapidly. The shavings,
before being used, are well steeped in vinegar, which is itself
one of the most active ferments. Below, at c c, is a circle of
holes about half an inch in diameter, by which the air may enter,.. = ig,  which then escapes above by a number of tubes, which pass
eI.c l!i'ii-t through the pan, and are left white in the figure. If now we take
i!ll[,,a spirit containing about one part of proof spirit to four of water,
~ ~:___.5~     and, having mixed with it T-vwxth of honey or yeast, pour it
into the pan above, it trickles down the orifices by the threads,.and, spreading over the shavings, has its surface enormously extended. It absorbs
oxygen very rapidly, and, having been warmed to about 750 before being poured in,
its temperature soon rises to 1000; the interior being so hot, a current of air is established through the vessels, by which a constant supply of oxygen is kept up.
According as the liquid passes down, it escapes through the pipe at the bottom, and
is collected in the vessel a; when it has passed through three or four times, it is
found to be converted into excellent vinegar, and the whole time occupied is only
between twenty-four and thirty-six hours.
The manufacture of vinegar by the distillation of wood will be described in another place.
The vinegar of commerce has frequently its pungency and acidity increased by the addition of acrid herbs, as capsicum, and by sulphuric
acid. To obtain it fi-ee from these impurities, it is redistilled. As, how.
ever, its volatility is about the same as that of water, it cannot be concentrated in that way, and hence the strong acetic acid must be obtained
by the decomposition of its salts by a stronger acid.  For this purpose,
one part of acetate of soda, which has been dried at a gentle heat, is to
be distilled with two parts of oil of vitriol; so much heat is evolved by
the mixture, that a quantity of the acetic acid distils over spontaneously,
and to complete the decomposition only a very moderate heat need be applied. In this process, S.O+ Aq. and Na.O. +C4HO, give S.O,+Na.O.
and CjHO,0+Aq.  The acid which passes over generally contains some
sulphurous acid, arising from  its secondary action on the oil of vitriol;
in order to separate this, it is rectified over some peroxide of lead, with
which the sulphurous acid forms sulphate of lead.  The liquid acetic
acid which distils is then to be exposed to a cold of about 23~, and the
crystals which form  are to be separated from the liquid portion; these
crystals are the Protohydrate of Acetic Acid, and in its most concentrated
form.
Acetic acid may be prepared also by distilling acetate of lead with oil
of vitriol, or by the destructive distillation of acetate of copper: by this
last method an acid is obtained (radical vinegar) of an agreeable aromatic odour, from an admixture of Acetone.  The acetate of potash is pre.
scribed by the Dublin Pharmacopoeia; but, as acetate of soda is found
abundant and cheap in commerce, it is now exclusively employed.
The Hydrated Acetic Acid, when free from any excess of water, crvs.




.PROPERTIES  OF  ACETIC  ACID, ETC.                    557
talhzes at 50~ in large white plates, which do not again become liquid
until heated above 60~;- it is hence called Glacial Acetic Acid; its odour
is very characteristic and pungent; its taste caustic; it blisters the skin;
it mixes with water, alcohol, and ether, and dissolves camphor and essential oils, which solution constitutes the aromatic vinegar of the shops.
When liquid, its sp. gr. is 1'063; but its specific gravity does not indi.
cate its strength, as it increases according as water is added until it becomes 1'078, which is that of an acid containing 34 6 per cent., or three
atoms of water; being a definite compoun(d, C4H3,0+ H.O. +2 Aq. On
farther dilution, the sp. gr. again diminishes, and an acid containing 64
per cent. of water has a sp. gr. of 1'063, the same as that of the most
concentrated acid.  The strength of any acetic acid may, however, be
very simply found by immersing in it a weighed piece of white marble,
and weighing it again when the acid has been completely neutralized;
the loss of weight gives pretty accurately the quantity of acetic acid, as
the atomic weight of Ca.O. - C.02 (50'5) is nearly the same as that of
CJH03 (51'2); of course, if the acetic acid be not pure, this method
cannot be employed.
The formula of hypothetic dry acetic acid is C4H303, and its equivalent =51'2.  The acetate of water, C4t1-303+Aq., consists of
4 equivalents of carbon,  =24'20.. 40 20
4     "      hydrogen, - 400..  6'64
4     "      oxygen,  =3200.. 53!6
60'20     100.00
The hydrated acetic acid boils at 2400.  The specific gravity of ts
vapour is 2278, and is anomalous as showing that its equivalent volume
is 3, in place of 4 or 2, as occurs with almost all other organic bodies.
The products of the decomposition of acetic acid by chlorine and by
bases will be hereafter noticed;'with powerfully oxidizing bodies it yields
formic, oxalic, and carbonic acids.
Acetic acid is recognised by its peculiar odour and its volatility; it
reddens litmus powerfully; its solutions are precipitated by the nitrates
of silver and of black, oxide of mercury, giving white crystalline salts,
sparingly soluble in cold water.  But even strong solutions are not af.
fected by the salts of lead or barytes.  It combines with all bases form.
ing salts, of which none are quite insoluble in water, but generally very
soluble and easily crystallized.  Thie most important of these acetates
will now be described.
Acetate of Potash, K.O.. CI4H,3, is formed by neutralizing acetic
acid by means of pure carbonate of potash.  The solution is generally
evaporated at once to dryness, and the salt fused at a dull red heat, in
order to obtain it quite white.  It forms, on cooling, a foliated mass,
greasy to the feel.  From  its concentrated solution it may be obtained,
also, in delicate crystals. It is very deliquescent, and dissolves copiously
in alcohol.
Acetate of Soda, Na.O.. C4H40,,+  Aq., may be obtained in the
same way as acetate of potash, but is made on the large scale in purify.
ing the rough wood-vinegar.  The impure acetate of lime, obtained by
neutralizing the pyroligneous liquors with chalk, is decomposed by 62
times its weight of crystallized sulphate of soda. These are in the proportion of two equivalents of Glauber's salt, as but one half of the quantity added is decomposed by the acetate of lime.  It answers still better




558        ACETATE  OF  BARYTES, LI IME   ETC.
to neutralize the acid liquors by sulphuret of sodium, prepared by roast.
ing Glaubel's salt with small coal, as' fbr making soda-ash (p'. 488).
When purified by successive crystallizations, the acetate
of soda forms oblique rhombic prisms, as i, u, in the figure,
with many secondary planes, as a, e, o.  These contain six
atoms of water.  It is permanent in the air; soluble in
three parts of cold and in one of boiling water;  at a red
heat it melts.  Its principal use is in the preparation of
acetic acid.
Acetate of Barytes, Ba.O.. C4Ha03, is formed by neutralizing acetic acid with
carbonate of barytes or sulphuret of barium. It crystallizes in oblique rhomnbic
prisms; ~by heat it is completely decomposed into carbonate of barytes and acetone
(Ba.O.. C.02 and C3H30.).
Acetate of Lime is made on the large scale, but in a very impure form, as one
stage in the process of purifying the wood-vinegar. When pure, it crystallizes in
needles, which do not deliquesce. It is decomposed by heat in the same way as
the preceding salt.
Acetate of Alumina is of considerable technical importance, fiom  its
use as a mordant in dyeing. It is formed by mixing solutions of' alum
and of acetate of lead when to be employed in the arts.  The solution
then contains much acetate of potash.  To obtain it pure, the simple
sulphate of alumina should be decomposed by acetate of barytes.  Evaporated at a very gentle heat, it dries into a transparent gummy mass;
but if boiled, acetic acid passes off, and a basic acetate of Alumina is deposited as a white powder. This effect is produced also by contact with
linen or cotton cloth, the acetic acid becoming free.  A piece of calico
is thus mordanted uniformly by immersion in a bath of acetate of alumina,
and then dried at about 80C, or it is mordanted partially, so as subsequently to fbrm a coloured pattern, by being printed with the solution of
this salt, thickened with gum or starch, in order that it may not spread;
on being then dried by passing over warm  cylinders, the acetic acid
passes off, and the alumina fixes itself upon the tissue.
Acetate of Zinc, Zn.O.. C4H1303+-3 Aq. Metallic zinc dissolves in acetic acid,
evolving hydrogen; but this salt is generally prepared by mixing
solutions of acetate of lead and sulphate.of zinc, and separating
/'-'..- \ the sulphate of lead which is formed by filtration.  On evaporax/'i ['"x,'   ting the solution, the acetate of zinc crystallizes in brilliant, soft,
hexagonal rhombic tables, as in the figure, of which i, u are pri-': —N./;7  mary, and m a secondary face. They are unalterable in tile air,
-I  -t     but very soluble in water. When boiled with alcohol, a Ibasic
acetate of Zinc precipitates, 3Zn.O.-+C4H303. A solution of this
salt is completely decomposed by sulphuret of hydrogen.
Proioacetate {if Iron. —Fe.O.. C4H303. This salt, which may be prepared by dissolving protosulphuret of iron in acetic acid, forms a colourless solution, which
yields, when evaporated in vacuo, pale green prisms, which attract oxygen with
great avidity  It cannot be formed by decomposing protosulphate of iron by acetate of lead, as only a portion of the lead salt precipitates until the iron becomes
peroxidized.
Se sqtiacetate of Iron, Fe2Oa + 3(C4HO33), is [)repared by dissolving red
oxide of i ron in acetic acid, or by detcornmposing red sulphate of iron with
ncetate of barytes.  It forms a brownish red solution, which, when boil.
ed, gives off acetic acid. and oxide of iron separates.  By very cautious
eval}o)ratiotn, a dark red gummy nmass may be obtained, which redissolves
in cild water.  It tlhus resembles closely acetate' of alumina, and, like it,;(rv(es in dyeing as a rordant, to fix upon the cloth oxide of iron, with
wiich the colouring matters may combine; being roughlly prepared by




ACETATE S  OF  LEAD.                            559
diestilng old iron in the impure acetic acid from  wood, it is commonly
termed Pyrolignite of Iron.
A  tincture of Acetate of Iron is emnployed in medicine, which, as
directed by the Dublin Phlarm;acopmia, is formed by trituritting togetlher
protosulphal-ite of iron and acetate of potash, and digestinr in alcohol; in
ordel that the solutioh shall have the rich wine red colour which is required, the mixture of the salts should be left for a little time pasty, so as
to absorb oxygen, and there should be present an excess of acet-ate, of
potash.  The iron is present in these tinctures as black oxide.  If' too
much sesquioxide be formed, the solution decomrposes very easily, red
oxide of iron separatingl, and acetic eher and aldehllyd being producced.
If the protoxide be present in excess, the colour is a brownish ytllow,
and the preplaration is liable to spoil when oxygen has subsequently access to it.  Although the acetate of potash does not formr a true double
salt in this case, yet it gives much  greater stability to the acetates
of iron.
Acetates of Lead.-r-Acetic acid forms, with oxide of lead, four wellcharacterized salts.
Neutral Acetate of Lead.  Sugar of Lead, Pb.O.. C4H1-303-3 Aq.,
is prepared by dissolving lith-arge, or  wlite lead, in acetic acid, of which
a slight excess should be used.'lhlle liquors yield by evaporation rigllht
rhombic prisms with dihedral summits, as in the
/-, "'.     figure, which are very bright and colourless;
their taste is sweet and astrintgent;   the solution
iin water reddens litmus, but turns sirup of vio~' lets green.  In very dry air they effloresce;
\.... - when heated to 136~ they undergo aqueous fusion, but, having lost their water of crystallization, becolmie solid again.  The dry salt thus
obtained fuses again at a higher temperature, and without blckening,
is decomposed into carbonic acid, acetone, and sesquibasic acetate of
lead, which remains, 3(Pb.O.. C4H303) giving C.O. with Cs3[  (;. aind
3Pb 0. +-2C4H303.
This neutral salt dissolves easily in alcohol; it is very pois.ous; the
antidote to it is Glauber's or Epsom salt, which forms insolu.e sulphate
of lead.
Sesquibasic Acetate of Lead. —3Pb. O.  2C4H303.  This salt, which
is fortned as just described, dissolves in water, and the sirupy solution
crystallizes in pearly hexagonal plates; its solution reacts alkaline.
Tribasic Acetate of'Lead. —3Pb.O. +C4HO30.  When  ammonia  is
added to a solution of neutral acetate of lead, so as to render it strongly
alkaline, it does not combine with it as with most other metallic salts,
but acetate of ammonia and tribasic acetate of lead are fornmed; it may
also be prepared by boiling together six parts of crystallized acetate of
lend, seven of litharge, and thirty of water.  This solution, known in
pharmn-acy as Extractum Saturni, gives, by evaporation, a mass of fine
crystallilne needles; it reacts powerfully alkaline; it is insoluble in
alcohol.
Sexbasic Acetate of Lead, 6Pb.O.+C4H1303, is precipitated when a
solution o:f neutral acetate is added to a great.excess of water of ammno.
nia; it is fo>rmed, also, when acetic acid acts on metallic lead with acces.s
of air, and is hence generally present in the Ceruse of' commerce.  (See




.560   ACETATr ES OF COPPER,  IERCUR,    ETCr C.
p. 491.) It forms minute feathery crystals when deposited fiom boiling
water, in which it is slightly soluble.
All these basic acetates of lead are decomposed by carbonic acid,
giving neutral acetate and carbonate of lead.
Acetates of Copper. —The acetate of the suboxide of copper is not
Important; there are four acetates of the black oxide.
Neutral Acetate of Copper. Distilled Verdigris, Cu.O.. C4HO33+Aq.,
is prepared by dissolving verdigris in acetic acid. It fobrms. —-— "..   oblique rhombic prisms, as in the figure, where i, u, u are
primary, and e, e secondary faces of a firne deep green colour.  It cryvstallizes in another form with five atoms of
water: these crystals are blue, like sulphate of' copper,
and when heated to 86~, give off 4 Aq., and clhange into;J >  the common green crystals; it effloresces gradually in
the air; when heated in close vessels, it gives a mixture
of acetic acid and acetone; in the air it takes fire, burning with a bright
green flame.
If a solution of this salt be mixed with sugar or honey, and heated, it
deposites a green powder of carbonate of copper, which changes into
minute crystals of the orange-red suboxide: the liquor contains then
abundance of formic acid.
Bibasic Acetate of Copper.  Verdigris. - 2Cu.O.+C4H3,+6 Aq.
This salt is manufactured in wine countries by stratifying plates of
copper alternately with the residual stalks and pulpl of tile grapes that
have passed into acetous fermentation; oxygen is absorbed, ar:d the mass
being occasionally turned over and moistened, to give access to air, the
plates of copper become covered with a crystalline crust of basic acetate;
this is scraped off, made into a paste with vinegar, and put into moulds,
where it is allowed to dry; the mass so formed contains all the basic
salts mixed together..- In this country it is prepared by stratifying copper plates with cloths steeped in pyroligneous acid.  When pure, the
bibasic acetate is of a fine blue colour; it is decomposed by water into
the insoluble tribasic acetate, and the soluble sesquibasic acetate of cop.
per, which forms a pale blue solution, whence it may be precipitated in
crystalline scales by alcohol.
Tribasic Acetate of Copper, 3Cu.O.+C4HO303+2 Aq., remains as an
insoluble residue when verdigris is treated with water, or by digesting a
solution of neutral acetate with oxide of copper.  It is a clear green
powder, which detonates feebly when heated.  For Emerald Green, see
p. 456.
Acetate of Black Oxide of Mercury, Hg.O02+C4H1303, may be formed
by mixing boiling solutions of acetate of potash and subnitrate of mercury, and filtering rapidly. On cooling, it is deposited in brilliant white
crystalline scales, which are very sparingly soluble in cold water, and
insoluble in alcohol.  The Acetate of the Red Oxide is very soluble in wa.
ter, and does not crystallize.
Acetate of Silver, Ag.O.. C4H130, is formed by mixing boiling solu.
tions of nitrate of silver and acetate of potash, and filtering the liquor
while very hot. On cooling, it crystallizes in pearly white needles,
which are but very sparingly soluble in cold water.  These last salts
serve as tests for the acetic acid in liquids.
Acetate of Ammonia, N.H,O.. C4H30,, is prepared by passing ammo.




A.CETATE  OF  ETHE R.-A C E T O N E.                    61
niacal gas over the crystalline hydrate of acetic acid, or by heating
moderately a mixture of equal parts of acetate of potash and *of sal
ammoniac.  The acetate of ammonia sublimes mixed with a little free
acetic acid; it crystallizes in needles, which are very soluble in alcohol
and in water; by exposure to the air it loses ammonia, and appears to
form an acid salt; its solution in water, prepared by neutralizing distilled
vinegar with carbonate of ammonia, is used in medicine by the name of
Spirit of Mlzindererus; in its original form, when the carbonate of ammonia, obtained by the distillation of bones (salt of hartshorn), and which
contained empyreumatic animal oil, was used, it was a much more pow.
erful medicinal agent than when prepared, as now, with pure carbonate
of ammonia.
Acetate of Ether.  Acetic Ether, C4H50.+C4H,03, is prepared by
distilling 16 parts of dry sugar of lead, 4- of alcohol, and 6 of oil of
vitriol; the product should be rectified over some lime to remove free
acetic acid.  This ether is colourless, and very inflammable; it boils at
165~; it is lighter than water; it is remarkable for being isomeric with
aldehyd, their per cent. composition being the same, but the sp. gr. of
the vapour of acetic ether (3063) is double that of aldehyd (1531).
Products of the Decomposition of Acetic Acid by Heat.
A. Of Pyroacetic Spirit.  Acetone.
When acetate of lime or barytes is heated to redness, the acetic acid
is completely decomposed, an earthy carbonate remaining, and a volatile
inflammable liquid, of an agreeable aromatic odour, distilling over, C4
H303 separating itself into C.0, and C03H30.  The metallic acetates are
similarly decomposed, but the products are not so pure.  This liquid,
for which I shall retain the name Acetone, is formed also abundantly
when the vapour of acetic acid is passed through a tube containing
charcoal, at a temperature just below redness.
Acetone is colourless, and lighter than water; it burns with a luminous flame; it boils at 132~; the specific gravity of its vapour is 2022.
When heated with hydrate of potash, it is totally converted into carbonic
acid and marsh gas, C,HO0. and H.O. producing C1H4 and C.02O.  When
treated by oxidizing agents, as permanganate of potash, or bichromate of
potash and sulphuric acid, it is totally converted into acetic acid.
~With sulphuric acid, acetone yields a series of products closely analogous to those
derived from alcohol, but still presenting such characteristic differences as induce
me to look upon them as not simply extracted from acetone, but derived from its
total decomposition. Thus it gives a hydrocarbon, Mesitylene, whose formula is
C6H4, and also, an ether, Mesitic Ether, CoH50. With sulphuric acid, this forms the
Sulphomesitic and Persulphomesitic Acids, which are remarkable, as the sulphuric
acid retains all its power of saturating bases. With phosphoric acid, it produces
Phosphomesitic Acid, and with hypophosphorous acid a very remarkable compound,
whose barytes salt has the formula C6HO..+2Ba. O.. P.O. The series of wine-alcohol contains no similar body. The mesitic ether combines also with protochloride
of platinum.
When acetone is treated with chloride of phosphorus, it gives phosphoric acid
and Chloromesitwc Ether, C6H5C1.; with iodide of phosphorus it produces Iodomesitic
Ether, CoH6I.; and, when acted on by chlorine, it fbrms, first, the Mesitic Chloral, of
which the formula is C3H2. ClO., and subsequently another body, also a heavy,,
oily liquid, C3H.. C120.
When red fumes of hyponitrous acid are passed into acetone, and the vessel is
kept cool, they are copiously absorbed, and, on adding water, a dense fluid' separates, which is Nitrous Mesitic Ether, C6H50O.+N.03.
By acting on mesitylene, C6H4, with nitric acid, a heavy liquid is produced,
-4 B




562    BODIES  OF  THE  KACODYL  SERIES..wlich is termed Mesitic Aldehyd; its formula is C6H30.+Aq. Its solution in alkaline liquors becomes brown after some time, and precipitates most salts of the
heavy metals. By chlorine, the mesitylene is converted into a crystalline body,
soluble in etlier, and separating from it in brilliant colourless prisms. Its formula
is C0H3Cl. I have termed it Chloride of Plelcyl. 
In my origin'l examination of this series of bodies, I looked upon acetone as an
alcohol (Mesitic Alcohol), C6H602_(C61HjO.+Aq.), from which they were all derived;
but I do not now consider that either mnesitylene or mesitic ether pre-exists in acetone. The intimate nature of' that body remains yet to be examined.
B. Of the Bodies of the Kacodyl Series.
When equal weights of acetate of potash and arsenious acid are mix.
ed and distilled at a dull red he-at, a dense colourless liquid is obtained,
which had been long known to chemists as the Fuming Liquor of Cadet.
The admirable researches of Bunsen have showna that it is an oxide of'
a compound radical, which he has succeeded in isolating, and which, in
the variety of its combinations, and the influence their discovery will
doubtless exercise on science, ranks with cyanogen.  Nevertheless, as
-they are not of practical importance, a short notice of them will suffice.
The Fuming Liquor of Cadet, or Alkarsine, when purified fi'om acetone
and other. accidenltal products of' the distillation, is colourless; much
heavier than water.:It freezes at -9~, and boils at 300~.  The specifice
gravity of its vapour is 7180; its odour is excessively disagreeable, prbvoking weeping and nausea; it is actively poisonous; in contact with
the air it fumes very much, and absorbs oxygen so rapidly, that if a large
surface be exposed, it takes fire spontaneously, and burns with a large
wlhite flame, throwing off much arsenious acid.  Its composition is ex.
pressed by the formula C4jT6. As.O., and in all the combinations which
it gives, the oxygen alone is replaced.  Thus, when distilled w\ith strong
muriatic acid, a dense liquid of an insupportable odour is produced, wllich
gradually changes into a crystalline mnass, consisting of C4o6. AsCI.
By digesting this liquid with zinc and water, in a vessel kept full ot pure
carbonic acid, chloride of zinc is fiormed, and the radical C41I6As. is set
free; this is an oily-looking, heavy liquid, insoluble in water, and tiking
fire immediately on contact wvith air.  This is the liacodyl, and as its
symbol I shall adopt that used by Bunsen, Kd.=C4H6As.  T}ie alkarsine is therefore oxide of kacodyl, Kd.O., and the body formed by muriatic acid is the chloride, Kd.Cl.  The iodide, bromide, sulphluret, amid
cyanide of kacodyl, may be formed by the simple process of distilling al.
karsine with the corresponding hydracids, or the chloride of kacodyl with
the iodides, &c., of potassium.
When alkarsine is distilled with dilute muriatic acid, or when chloride
of kacodyl is treated with water, this is decomposed, and an oxycllloride
obtained, the formula of which is Kd.O.+3Kd.CI.  In a similar man.
ner, a corresponding oxybromide, Kd.O.+3Kd.Br., may be produced,:
and an oxviodide.
If alcoholic solutions of oxide of kacodyl and of corrosive subli mate be
mixed, a brilliant white precipitate is obtained, which is soluble in water, and crystallizes therefrom in large but delicate rhombic. tables, of a
satiny lustre.  It is a direct combination, its formula being: Kdll.O.-t
2Hg.Cl.  A precisely similar compound is formed with the bromide of
mercury.
When alkarsine is exposed to the air, so that it may absorb oxyger,
but not burst into flame, it is changed totally into a white crystalline
mass; at the same time, arsenious acid and some volatile products are




SOUR CES  E TC., OF M ARSH  GAS.                    563
termed.  The crystals beiring dissolved in a small quantity of water, this
liquor is evaporated to dryness, and the residue dried by blotting-paper,
and recrystallized from alcohol.  The substance thus obtained is termed
J.dlkargene; it f'orms large oblique prisms, wlhich are inodorous and taste.
less; it deliquesces in moist air; it combines with alkalies and metallic
oxides, forming very instable compounds; it melts at 3900, and is decomposed by a stronger heat.  By deoxidizing agents, as protochloride
of tin or phosphorous acid, it is reduced to the state of alkarsine; it is
not poisonous.  Its composition is expressed by the formula C4F17. As.
04, or Kd.03+-Aq.; its proper name is therefore Kacodylic Jcid.
C. Of light Carburetted Hydrogen.  Marsh Gas.
T'his gas is fortned by the decomposition of almost every organic sub.
stance at a high temlperature.  Thus it exists always mixed with olefi.
ant gas, in. the coal or oil gas used for illumination.  It may be formed
by passing olefiant gas through a red-hot tube, when half of its carbon is
deposited and its volume doubled.'It is produced, also, by passing the
vatours of alcohol, of ether, or of acetic acid through bright red-hot
tubes in a similar manner.
A very interesting source of this gas is the decomposition of vegetable
matter in contact with water, but excluded fiorn the air.  By assimnila.
ting the elements of' four atoms of water, the lignine breaks up into car.
bonic acid and this gas, C12H808 with 4H.O. giving 6GC.0) and 6C.I12.
As the origin of the great deposites of coal is to be found in the slow de.
composition of submerged forests of high antiquity, this gas was thel
generated in large quantity, and, being subjected to enormous pressure
under the mineral strata, which gradually settled on the vegetable mass.
es, it remaine(l infiltrated through the coal, probably in a liquid condition.'During the o[perations of mining. when this great pressure is re.
moved, it reassumes its gaseous condition, and, mixing with the air of
the mine, creates the danger of explosion, against which the genius of
H-Jumlpphrey Davy provided by the construction of his safBet-lanmp (see p.
183).  Under thte name of Fire.damp, this gas is known and dreaded
by thle miners, while the carbonic acid, which results simultaneously from
the decomposition of the wood, and is known, also, from its fital effects
when breathled, is terme d Choke-damp.
T'his decomposition of wood goes on in every muddy ditch.  If the
mud be stirred. numerous gas bubbles will be seen to ascend, and when
collectted will be found to consist of fire.damp mixed with carbonic acid;
hence this gas has got the name of Pond or Marsh Gas.  It is obtained,
hlowever, most pure by the decomposition of acetic acid by hlydrate of
potash.  About equal parts of' acetate of potash and caustic potash are
to be well mixed, and heated in a hard glass retort nearly to redness.
T'he acetic acid an(c water are simultaneously decomposed, C4t1303 and
11.0. producing 2C.H2 and 2C.02.  This last remains combined with
the potash, while the gas which passes off may be collected over Wrater.
It is colourless and transparent.  It burns with a yellow flamen, pos.
sessincg but little illuminating power; its sp. gr. is 559; its forr.mula be.
int C. Hf, and consisting of
One volume of carbon vapour....       =843'0
Four volumes of hydrogen.=... -    =275'2
Forming two volumes of marsh gas...    1118 2
Of which one weighs, therefore....    559-1




564          c  H I, O RAL.-C H L O R O ACE T I C  ACID.
Or it may be considered as containing one volume of olefiant gas and two of hydrogen, condensed to two, (980-4+1376) — 2-559.
The real atomic weight of the marsh gas is difficult to determine, as
it does not foCm  any well.defined combinations.   rhere is reason to
suppose it to be C2H4.  When acted on by chlorine, it gives muriatic
acid gas and bichloride of carbon (p. 498), which has been already noticed.
Of the Action of Chlorine on Alcohol, Aldehlyd, Acetic Acid, and the va.
rious Kinds of Ethers.
When chlorine gas is passed into alcohol not absolutely anhydrous, a heavy
oily liquid is obtained, known as heavy Muriatic Ether or Chlorine Ether. It is a
mixture of several substances in indeterminate proportions.
When the alcohol is anhydrous and the gas qulite dry, the action.is definite, and
gives rise to a remarkable result.  Five sixths of the hydrogen of the alcohol are
removed, and are replaced by three of chlorine, and, after the evolution of a large
quantity of muriatic acid gas, a dense oily liquid is obtained, to which the name
of Chloral has been given; its formula is C4-H.I.. C1302. The first operation of the
chlorine is'to remove two equivalents of hydrogen, and thus to reduce the alcohol
to the state of aldehyd. just as any other oxidizing agent should have done; but
then it acts on the hydrogen of the radical, acetyl, and, expelling it, takes its place,
generating a new compound radical, Acechloryl, C4C13. This is combined with oxygen and water in chloral, as acetyl is in ordinary aldehyd; the rational formula of
chloral is therefore C4ClsO.+Aq.
Chloral combines with water, forming a crystalline hydrate.  It gradually chan
ges into an isomeric porcellaneous-looking substance. The equivalent change of
common aldehyd has been described (p. 554). When chloral is acted on by a
solution of potash, it yields formic acid and chloroform, C4H.. C1302. and H.O. giving C2H.03 and C2H.Cls.
By the action of chlorine on aldehyd, chloral is directly formed.
When the crystallized acetic acid is exposed to the action of chlorine in bright
sunshine, a substance is formed which crystallizes in brilliant rhombs, and possesses strong acid properties; its formula is C41H.. C1304. It is formed by the
replacement of the hydrogen of the radical acetyl by chlorine, forming thus the
Chloroacetic Acid, C4C1a30- +Aq. Its salts crystallize with facility, and have great
similarity to the acetates. When the chloroacetate of potash is heated with an ex.
cess of potash, it is decomposed into carbonic acid and chloroform; C4Cl303 and.
H.O. giving 2C.02 and C2H.C13. This reaction is exactly similar to that of the
common acetate of potash, the chloroform replacing the pond gas.
When chlorine acts upon sulphuric ether, a remarkable series of bodies is produced; the first formed is a dense oily liquor, having the formula C4H3. C120.,
which, by contact with water or an alkali, is decomposed into hydrochloric and
acetic acids, 3(C4H3. C120.) and 6H.O. producing 6H.0C1. and 3(C4H303). This
body is properly, therefore, Oxychloride of Acetyl; it is decomposed by sulphuret of
hydrogen, muriatic acid being given off, and an Oxysulphur-et of Acetyl being formed,
which resembles it in properties.
In presence of a great excess of chlorine, this oxychloride is totally decomposed,
the chlorine entering into the place of the hydrogen in the acetyl, and forming the
same radical as exists in chloral and chloroacetic acid. The substance thus pro
duced is solid and crystalline; it bears a very simple relation to sulphuric ether,
as its formula is C4C150., being apparently ether, in which all hydrogen is replaced
by chlorine. It may be termed Chloryl Ether.
The action of chlorine on the acetic and oxalic ethers has thrown much light on
the theory of these bodies.
Acetic ether combines with two atoms of chlorine and loses two atoms of oxy
gen, thus giving from C0411303+C4H50., the Chloroacetic Ether, C41H303+C4H3. C120.,
an oxychloride of acetyl, containing twice as much acetic acid as that just now
described, and its rational formula being, therefore, Ac.Cl3+2Ac.03; with potash
it gives chloride of potassium and acetate of potash.
By a stream of dry chlorine gas oxalic ether is totally converted into a mass of
crystalline plates, which are tasteless and perfectly neutral; this body contains no
hydrogen, its formula being C0C1504_C4C150.+-C 203.   It is, therefore, a combina



ACTION  OF  CHLORINE  ON  M]URIATIC  ETHER. 565
lion ol oxalic acid with chloryl ether, and is termed Chloroxalic Elther.'With water
of ammonia it gives oxamide; by the action of dry ammonia it forms a substance
also crystalline, which is soluble in alcohol and ether, sparingly Soluble in water,
and the formula of which is Cs-H2Cl. N.06; at the same time, chloryl ether and
water are evolved; the rational formula of this body, Chloroxamethan, is at once
seen by comparing it with the oxamethan, formed by ammonia on oxalic ether
(p. 550). Thus,
2 atoms of oxalic ether. C12HloOs, give an atom of oxamethan, CsH7. N.06.
1 atom of ammonia, N.H3, gives an atom of alcohol, C4H60.+Aq.
In like manner,
2 atoms of chloroxalic ether, C12ClloOs, give 1 of chloroxamethan, CCIH2. N.O6.
I atom of ammonia, N.Hs, gives I of chlorine alcohol, C4C150.+Aq.
The rational formula of the chloroxamethan is therefore C4C150.. C203+C202Ad.
When chloroxamethan is dissolved in water of ammonia, and the solution evaporated, crystals are obtained, which are Chloroxalovinate of Ammonia, their formula
being CsH4Ct5. N.Os, or, in its rational form, C4C150.:. C2033+C203. N.H40.
identical in constitution with the ordinary oxalovinate of ammonia, except that it
contains chloryl ether in place of common ether; the Chloroxalovinic Acid itself has
been isolated; it crystallizes in long needles, which react acid, and combines with
all bases to form well-defined salts; its formula is C4C150.. C203 —C203Aq.
A crystallographie examination has rendered the isomorphism of the ordinary
oxamethan with the chloroxamethan exceedingly probable.
The results of the action of chlorine on the light muriatic ether have led to remarkable results. Regnault considered this body as affording a test experiment
for the actual presence of olefiant gas in ether; for if olefiant gas be Ac.H., and
muriatic ether be Ac.H.. 1H.C1., the result of the action of chlorine should be the
same on both bodies, as the muriatic acid in the latter could not influence such a
reaction Now, by acting on muriatic ether with chlorine, a series of bodies is
obtained, isomeric with those arising from olefiant gas, but quite different in properties. Thus there is first formed a liquid, C4H4C12; this has the composition of
Dutch oil; next, a liquid forms whose formula is C4HCI13; afterward, bodies consisting of C4H2C14 and C4H CI5, and ultimately C4C16, SesqTichloride of Carbon. Now
the bodies C4H4C12 and C4H3CI3, as derived from olefiant gas, are separated by potash into C41T3CI. with H.C1., and into C4H2C1I with H.C1.; but the bodies C4H4C12
and C4H3C13, from muriatic ether, are not decomposed by that alkali. - I do not,
however, believe in the indefinite replacement of hydrogen by chlorine, which
Regnault assumes, and look upon the relation of these series of bodies as being the
following:
From Olefiant Gas.               From Muriatic Ether.
C4H4C12=C4H3Cl.+H.CI.            C4H4C12=(C4H3Cl.+C4HsCl.
C4H3C13:=2(C2H.C1.) and H.CI.    C4H3C13.
C4-I2C14=2(C2H.C12).              C4H2C14=C4Cl5C.1. 2(C4H3C13).
C4H.C15=C4H3C13-+2(C4ChC1..).
Both these give, finally, sesquichloride of carbon, C4ClbCI.  The bodies from
olefiant gas, which contain chloride of hydrogen, are decomposed by an alcoholic
solution of potash, but thaos  in which the chlorine is combined with an organic
radical are not affected by that reagent.
By the action of chlorine on mercaptan, a similar series of products is obtained,
of which the terminal body is C4H.. C14S., consisting of C4H3S33+2(C4C15C1.).
On the Theoretical Constitutioz of Alcohol, and the Bodies derivedfrom  it.
The theory of alcohol and the ethereal combinations is of the more
importance, as the principles of it regulate our ideas, not merely concern.
ingr the bodies that have been now described, but a vast number of others;
for the ordinary, or wine-alcohol, is but one example of a numerous family
of bodies, which resemble it in all its general laws of reaction, with, of
course, peculiarities characteristic of each; thus wood-spirit, oil of potato-spirit, and ethal are alcohols.
Thle generic properties of an alcohol are, that its composition may b'




566.THi.EORY OF  THE  ETHERS.
represented by a hydrocarbon isomeric with olefiant gas, united with.two atoms of water; that it gives an ether, which contains an atom of
water less, and acts as a base; and that, by combining the hydrocarbon
with four atoms of oxygen, an acid is formed.  Thus we have;
Wine-Alcohol.  Wood-Alcohol.  Oil of Polato-Snirit.  Ethal.
Alcohol, C4H4+2H.O.   C2H2+2H.O.   C,o1H,+2Ht.O.   C32H32+2H.O.
Ether,   C4H4+H.O.    C2H2+H.O.    Clo10-lo+H.O.    CT-2H32+-H.O.
Acid,    C4H40.       C2H204         CloHlo04        C32H3204.
Such being the connexion of the bodies of this class, the propositions
in which:I shall now proceed to imbody the principles of the constitution
of the substances derived from wine-alcohol, may be hereafter immedi.
ately applied to illustrate the history of the other alcohols.
1. From the action of sulphuric acid, of chloride of zinc, of fluoride of
boron, of potassium, and of chlorine on alcohol, it results that it contains
an atom of water ready formed, united with sulphuric ethler; its formula:is:therefore C4H,0.+ Aq.
2. The sulphuric ether is a base, neutralizing the strongest acids, and
producing both oxy-salts and haloid salts, perfectly resernbling those of
an alkali.  The oxygen in ether may be replaced by all other electro.
negative bodies, while the carbohydrogen, C4H5, remains constant. By
the conditions laid down in p. 467, this, therefore, is a compound radical;
it is called Ethyl, and its.symbol is written Ae. Ether is oxide of ethyl,
and its symbol is Ae.0.:3. By the action of oxidizing agents, hydrogen may be removed from
ethyl, and a new radical-, C413, produced, which, by combining with oxy.
gen, forms aldehyd and acetic acid, its symbol being Ac.  Aldehyd is
protoxide, Ac.O., and acetic acid, peroxide of acetyl, Ac.,03, both being
considered free from water.
4. From olefiant gas, by-the action of oxidizing agents, we cannot, in
any case, pass to the series of bodies containing acetyl; nor can we,
by bringing olefiant gas in contact with water or acids, produce any
form of alcohol or ether.  On the contrary, the isethionic acid is essentially distinct from these acids, which cc:dain ether, and yields none by
any form of decomposition; olefiant gas, on the other hand, gives, by
the action of chlorine, a series of bodies, which are quite different from
those given by muriatic ether, but which indicate that it is itself a radical, having laws of combination peculiar to itself, and independent, as
Berzelius had. already suggested, both of the alcohol and acetic series.
Its formula is therefore C2H,; its symbol El.; and the Dutch oil is truly
Chloride of Elayl. The ethyl may change itself readily into elayl by loss
of hydrogen, since C4H5=2C2H2 and H., and it is thus broken up when
the hydriodic or muriatic ethers are decomposed by heat, or by potash,
or ammonia; or when sulphuric ether is acted on by an excess of sul
phuric acid.
5. Although firom the decomposition of ether we obtain olefiant gas,
or light oil of wine, yet as ether cannot be in any way regenerated from
these bodies by the influence of water or otherwise, neither can the other
products derived from ether, as acetic acid, be produced from them, we
must abandon the theory which considered ether to be a hydrate of CiH4,
and consider it simply as an organic base, the oxide of ethyl.
6. By the action of chlorine on the ethereal compounds and on ole.
fiant gas, radicals are generated, which are precisely -equivalent to the




THEORIY  OF  THE  ETHERS,.ETC.                        567
tarce, ethyl, acetyl, and elayl, but w hich contain chlorine in place of hydrogen. Their formulm are C4Cl,, C14C,, and C.C12. This last is the pro.
tochloride of carbon, already described; the first, Acechloryl, exists in
chloraldehyd and in chloroacetic acid; the second, Ethchloryl, exists
combined with oxygen in chloryl ether, which acts as a base similar to
common ether towards the oxalic and acetic acids.  In contact with an
excess of chlorine, it breaks up, as ethyl does, into olefiant gas and hy.
drogen, into the protochloride of carbon and chlorine, and thus the ulti.
mate result is the sesquichloride of carbon, C2CI3.
7. The series of bodies formed by the action of chlorine on elayl and
on chloride of ethyl, are double combinations of bodies containing the
lhydrog(en and chlorine radicals, and hence results their isomerism.'hus
the body (C4H12C1), from  elayl, consists of CH,2CI-+C2CICICI., while the
body (C,HMC14), from the muriatic ether, is really 2(C4H13CI) +C4CICI3.
The body, C4HCI., from  elayl; is 3(C0H.2)+CIC12.
8. Thne relation of acetyl to ethyl is simply that of internal constitution, described in p. 467. For as benzoic acid contains benzoyl, C14H502,
while this, again, contains, as radical, the carbohydrogen, C,4Hs, so ethyl,
CH15, contains within it, ready formed, the radical acetyl, and-its formula
might be still more correctly written as Ac.H2.  This is simply shown
by the action of chlorine on ether, -where C4[-I3. H20. becomes first
CJ4-3. C10., and subsequently changes to C4CI,. C120.; the intermediate
compound, Ac.C1,, relating itself to the oxygen, as the sulphurous acid,
S.02, or the benzoyl, C14H,5Q2, in the sulphuric and benzoic acids.  Al.
though the connexion of these two radicals is thus analogous to that of
amidogen, Ad., and ammonium, Ad.HI2,-Am., yet a broad line of distinc.
tion is drawn between the ammonia and ether theories, by the very defi.
nite character of ether, oxide of ethyl, as contrasted with the hypothetic
oxide of ammonium; and, on the other hand, there does not appear to
be any acetylide of hydrogen corresponding to ammonia, the arnidide of
hydrogen, for the assumption of olefiant gas as being that body is not
based upon sufficient evidence.
Secondary Products of the Alcoholic Fermentation.
I have already noticed that, besides the carbonic acid and alcohol which are derived from the sugar, other bodies are evolved in minute quantities, and by their
odour and taste characterize the spirit obtained from particular vegetables. Thus,
in the fermentation of grape-juice, (Enanthic Ether is produced; in the spirit distilled from potatoes, a peculiar oil is found; and in the fermentation of malted corn,
both of these bodies are generated, besides a third, to which the name of Oleum
Sitictm, or Corn Oil, has been given.
The fEnanthic Ether is a thin, colourless liquid, of an almost stupifying odour of
wine, as to it the peculiar bouquet of wine is due; its specific gravity is ()862; it
boils at 4450; when heated with caustic soda, it evolves alcohol, and forms aenanthate of soda, from which the (Enanthic Acid may be separated by muriatic acid.
This is a white crystalline solid, which melts at 88~, and distils over at 5600 unchanged; its formula is Ci4Hn302; it combines with water, forming a thick oil,
which solidifies only at 550, is tasteless and inodorous, but reddens litmus sensibly.
The formula of the ether is Ae.O.-+C-I4IO302; it is remarkable as the only ether
that exists as a natural product, but it may also be formed artificially by means of
alcohol and cenanthic acid.
The Corn Oil, of which the formula is C42H3504, is lighter than water, of a very
penetrating odour, a biting taste, and cannot be distilled without partial decomposition.
The Oil of Potato-spirit has become of much interest, from the discovery that it
gives rise to a series of ethereal combinations similar to those of wine alcohol; the
name of Amilic Alcohol may be applied to it; it is colourless, oily, its odour at first




568                   AMILIC  ETHER, ETC.
pleasant. but subsequently nauseous; its taste acrid; it burns with a blue flame
its sp. gr. is 0 812; it freezes at 40, and boils at 2940; it dissolves in alcohol and
ether; its formula is CloH1202. In this alcohol a compound radical is assumedl to
exist, termed Armilyl, CloHI,; its symbol is Ayl., and it is combined with oxygen
and water, Ayl.O.+Aq., as ethyl is in wine-alcohol.
The Amilic Ether, Ayl.O., is not known except in combination with acids; its
bisulphate, or Sulph-amilic Acid, is obtained by acting on amilic alcohol with oil
of vitriol; its formula is Ayl.O.. S.03+-S.03. H.O.; its barytes salt crystallizes in
pearly plates, colourless, very soluble in water and alcohol. This salt is decomposed when its solution is boiled. The salts of lead and lime are completely similar in properties.
Chloride of Amilyl, CloHCI1. or Ayl.Cl., is prepared by acting on amilic alcohol
with chloride of phosphorus; it is a colourless oil, which boils at 217~. By the
action of bromine or iodine and phosphorus on the amilic alcohol, the bromide and
iodide of Amoiilyl are prepared; they possess properties similar to those of the chloride.
Acetate of Amilyl, Ayl.O.+Ac.03, is easily formed by distilling acetate of potash,
oil of vitriol, and amilic alcohol; it is a volatile, colourless liquid, which boils at
257~. The Oxalate of Amilyl may be similarly formed.
By distilling amilic alcohol with glacial phosphoric acid, a colourless aromatic
liquid is obtained, having the formula CloHlo. It is in this series what olefiant gas
is in that of the wine-alcohol; it is termed Amilcne; the sp. gr. of its vapour is 4918.
Valerianic Acid.-C,0H1004. When the amilic alcohol is exposed to the air, it absorbs oxygen, but its oxidation is more rapidly effected by. heating it with caustic
potash. By a loss of hydrogen and absorption of oxygen precisely similar to that
by which wine-alcohol forms acetic acid, it produces a volatile, oily acid, remarkable
as naturally existing in the roots of the valeriana officinalis, and being extracted
therefrom by distillation; it is lighter than water; it boils at 347~, and neutralizes
bases, forming soluble sweet-tasted salts; it must be considered as containing a
radical analogous to acetyl, valeryl, =-CoHs or VI., and its formula becoines V1.03
+-Aq.
IWhen valerianate of lime is heated, carbonate of lime is formed, and a volatile
liquid like acetone distils over; it is termed Valeron, CloH903 giving C.02 and
CgH90. The roots of the.valerian contain, besides the valerianic acid, another oil
destitute of active properties.
By cautiously treating amilic alcohol with sulphuric acid and chromate of potash,
an oily liquid is obtained, which is Valerianic Aldehyd, Co0H0o02 or Al.O.+Aq.  By
an excess of chromate of potash it is changed into valerianic acid.
Treated with chlorine, the amilic alcohol, and the various amilic ethers, as well
as the valerianic acid, give new products, which contain chlorine, and are constituted according to the same principles as have been fully described for wine-alcohol
CHAPTER XXII.
OF THE ESSENTIAL OILS, CAMPIIORS, AND RESINS.'rHE bodies now to be described constitute thrqe groups, very closely
allied in composition, in properties, and in origin.  For the most part
they exist ready formed in plants, as secreted by their proper organs, or
they are derived, by reactions of a very simple kind, from substances so
circumstanced. They are employed in medicine for their aromatic and
stimulant properties, and in the arts for the manufacture of a variety of
perfumes, varnishes, lacquers, &c.
A. Of the Essential or Volatile Oils.
These oils are so named from their solubility in alcohol, such solutions
being called essences, and from their volatility.  In virtue of this last prop.




PREPARATION, ETC., OF:AMYGDALINE.    569
erty, they are generally obtained by the distillation of the plants with water.
If the oil were extracted by the distillation of the dry plant, the heat would
rise so high as to destroy its odour and alter its composition; but, by
using a large quantity of water, the mixed vapours of the oil and water
pass over at a much lower temperature, as at 212~; for, although the
boiling point of the oil may be 400, yet it forms a quantity of vapour at
2120 proportional to its tension at that degree.  (See p. 78.)  To pre.
vent even the injurious heat which might arise from the plant touching
the sides of the still, when fragrant flowers or leaves are operated on,
they are suspended in a cage in the centre of the still, and allowed only
to come into contact with the vapours. These oils are somewhat solu-.,le in water, and, giving to it their odour and taste, form the various
medicated waters.  Hence often the same quantity of water must be
distilled with fresh quantities of the plant before the oil is in such pro.
portion as to separate.
Most essential oils, as those of turpentine, lemon, peppermint, &c.,
exist actually in the plant, as secretions from peculiar glands; but oth.
ers are produced only at the moment of distillation, by the decomposition of substances which did exist in the plant, and which undergo
a kind of fermentation.  This is the case with the oils of bitter al.
meonds, of spiresa, of mustard, and these oils possess much more active
chemical properties than those of the former class.  Another important difflrence among essential oils is, that some, by absorbing oxygen
directly, produce well-characterized acids, as occurs in the oils of bitter
almonds, of cinnamon, and of cloves; while others, as the oils of turpentine, citron, and copaiva, by a much more indirect action of oxygen,
give origin to resins.  On these principles I will arrange the oils in two
classes, for convenience of description.
1ST CLAss.-Oils forming Acids not pre-existing in the Plant.
Of Amygdaline and Oil of Bitter Almonds.
All plants which yield prussic acid on distillation produce, at the same
time, a volatile oil, which is known as the Oil of Bitter Almonds, it being
most abundantly obtained from that fruit.  The leaves of the cherry.lau.
rel, peach.kernels, &c., also yield it.  The oil and the acid both arise
from the decomposition of another substance, Amnygdaline.  This is pre.
pared by bruising bitter almonds, and pressing them strongly between
plates of hot iron, to force out the fixed oil; the residue is treated by
alcohol of 93 per cent., and the solution evaporated in a water.bath to
the consistence of a sirup; this is then diluted with water, and a little
yeast added, which, by inducing fermentation, destroys a quantity of
sugar.  When this is over, the liquor is to be again evaporated to a
sirupy consistence, from  whieh the amygdaline is precipitated by the
addition of cold strong alcohol, in which it is scarcely soluble; being
dissolved in boiling alcohol, it is finally obtained pure by crystallization.
The formula of amygdaline is C40H27. N.022; it forms short silky needles, which are anhydrous, tasteless, and inodorous; it is very soluble in
water, and crystallizes therefrom in large colourless pri-isms, containing
6 Aq.  By contact with nitric acid it produces ammonia, oil of bitter
almonds, benzoic and formic acids, and by caustic alkalies it is decomposed into ammonia and Amygdalic Acid, C40H26024,,,,+Aq.
When bruised bitter almonds are distilled with water, all amygdaline
4 C




5'70             OIL  OF  BI TTER  ALMONDS.
disappears, and a number of l)roducts, as prussic acid and volatile oil,
are evolved.  Pure amygdaline li-jay howvever, be boiled:in water without beingr altered.  It i. thle anirno-vegetal principle which constitutes the
imAss of tile cttelydot;  oi tle alinond that inlduces the reaction; it has
been called Emtl.sine, and appears very simnilar in properties and con-.
stitultion to thle ve getable alt)bumen or legumine, described as the active
principle in tile alcoholic fermentation.  (See p. 538.)'The emulsine
is: soluble in water, but insoluble in.alcohol.  It' solutions of ten parts of
amy daline in 100 of water, and 1 of emulsine in 10 of water, be mixed,
ihnleudiate decomposition occurs; the liquor becomes milky, smells of
bitter almonds; it contains sugar, prussic acid, formic acid, and volatile
*3il, arnd the emnulsine coagulates.  It is most probable thait tihe emlulsine
s itself also decomposed in this reaction, but we mnay explain tie origin.f tlhese bodies frlun the amygdaline alone thus:
1 equivalent of prussic acid, C21-I.N., )
2      "     volatile oil, C-0sH204,
~ c "     ~suar,  C6Hr,0O.,
2      "     f ormic acid, C4Ho0, 3     lent of alliygdaline.
7      i"    water,       1707,   )
In the cotelydon of the almond, the amygdaline and emulsine are in
distinct cells, and have no means of acting on each other, but when bruised in water both dissolve, and decomposition immlediately occurs.  The
preparation of the oil by distillation can hence be fully understood.
The mixture of arnygdaline and emulsine has been employed as a
means of producing a prussic acid of standard strength for medicinal
purposes.
Oil of Bitter- Almonds.  Hydruret of Benzyl.
Prepared by distilling bruised bitter almonds with water.  In this
rough state it contains a great quantity of prussic acid, from which
it is freed by distillation with some water, chloride of iron, and lime.
It is then colourless, of a strong peculiar smell, sp. gr. 1-043; it boils
at 356~; when exposed to the air it absorbs oxygen, and forms crystals
of benzoic acid; when heated with hydrate of potash, hydrogen is evolved, and benzoate of potash formed.  Tile formula of this oil is C,4H02;
but, from the series of compounds to which it gives rise, it is believed to
contain an organic radical, C,,4H502, termed Benzyl, and its rational formula is therefbre Bz.H.  (See p. 471.)
Chloride of Benzyl, Bz.CI., is formed by acting on the hydruret with
chlorine.   It is a liquid heavier than water; it boils at 3830; when
heated with water, it gradually changes into benzoic and muriatic acids.
By heating chloride of benzyl with iodide of potassium, Iodide of jBenzyl
is formed; and by using the bromide, sulphuret, or cyanide of potassium, compounds of benzyl with these electro-negative bodies may be
formed.
Amidide'of Benzyl.  Benzamide, Bz.Ad., is formed by acting on
chloride of benzyl with dry ammonia, 2(H.Ad.) and Bz.Cl. give Bz.
Ad. and Ad.H.. H.CI.; it forms -rhomboidal prisms, which melt at
240~, and may be distilled unaltered; heated with potash, it gives am.
monia and benzoate of potash.
Oxide of Benzyl.  Benzoic Acid.-Bz.O.- Aq.  This acid is found:ready formed: in the resin of benzoin and in dragon's blood; it some.




COMPLEX  BENZ O I C  COMI POUNDS.                       571
times appears in the urine of herbivorous animals, and is formed by the
oxidation of oil of bitter ulmonds and of amygdaline.
The following process for obtaining it pure was devised at the same
time by Mohr and Hennell: 1 lb. of benzoin resin, in powder, is to be
spread on the bottom of a metal dish, eight or tine inches diameter, and
two inches deep, which is to be covered with a drum  of blotting papler,
pasted to the edge of the dish; the whole is to be covered with a. cvlindrical cap of stout packing paper.  To render the heat unifobrm  the dish
is to be placed on a metal plate, covered with sand, resting on a furnace;
heat being cautiously applied for three or four hours, the cap is found
full. of splendid crystals of benzoic acid; the empyreumatic oil, which
usually contaminates the sublimed product, being arrested by the\ dcum
of blotting paper, through which the vapour of' the acid passes freely.
it may also be extracted from the resins by boiling these with lime; a
soluble benzoate of lime is produced, fiom which the benzoic acid is precipitated by tile addition of' muriatic acid; it is then to be dissolved in
boiling water, and allowed to crystallize by cooling slowly.
Benzoic acid crystallizes in hexagonal needles; when pure, it is -inodot'bus; it reddens litmus feebly; melts at 248~; the fuised acid boils first
at 462~, but it sublimes freely at 2930; it dissolves in 25 parts of boiling
water, but requires 200 partse of cold water for its solution; it is soluble
in twice its weight of alcohol or ether; it forms a very extensive series
of salts, of which few require special notice.
Benzoate of Lime, Ca.O.. Bz.O.+ Aq., crystallizes in brilliant prisms;
at a. dull red heat it is decomposed into carbonate of lime and. Benzone,
the formu;a of which is C131-150.  Another liquid, Benzin, C,2[6, is at the
same time formed by viritue of a much more complex process, napthaline,
carbonic acid, and carbonic oxide being evolved.
Benzoate of Ammonia. Ad.HO.. Bz.O., crystallizes in brilliant plates.
This salt is employed in mineral analysis to separate iron from manganese; a solution of peroxide of iron, not containing any excess of acid,
being completely precipitated by neutral benzoate of ammonia, while the
salts of manganese are not affected by it.
Benzoate of Silver, Ag.O..  Bz.O., is obtained by double decomposition; crystallizes from a boiling solution, on cooling, in brilliant colourless
needles.
Formobenzoic Acid.-H.Bz.+Fo.03. If water, saturated with the impure oil of
bitter almonds, be mixed with muriatic acid and evaporated, this substance crystallizes. The prussic acid is decomposed into formic acid and ammonia (p. 5t7), and
the nascent formic acid combines with the hydruret of benzyl; in this body all the
saturating power of the formic acid is preserved.
If a current of chlorine be passed through a solution of impure oil of bitter al
montls in water, a similar body is formed, consisting of benzoic acid and hydruret
of benzyl, Bz.H.+Bz.O.
Sulphobenzoic Acid.-C 4HsO0+S205+2 Aq. This body is formed by the action
of dry sulphuric acid on benzoic acid. A viscid mass results, which, when neutralized by barytes, yields a salt permanent in the air, crystallizing in rhomboidal
prisms, and having the formula C14H1803+-S20+2B.a.O.3 Aq.  From this the
pure acid may be obtained; it is decomposed if its solution be boiled, but when
evaporated in vacuo it crystallizes. The sulphobenzoate of copper crystallizes in
large rhombs of a rich blue colour.
B1romobenzoic Acid, C2sH9. Br.Os+2 Aq., is formed when benzoate of silver is de,
composed by broniine. It is a crystalline solid, very soluble in water, fuses at 2120.
and sublimes at 4820; its salts are all soluble, and contain two atoms of base.
Of the liquids produced by the distillation of benzoate of lime, Benzene, Cl3H50O.0
does not form any compounds; but Bezzin, C12H6, produces with sulphuric acid,




572                    OIL OF CINNAMON.
nitric acid, and chlorine, a series of bodies, of which the formule alone need be
here given; they are,
Sulpnobenzide,     C12H-5. S.02.     Chlorbenzin, C12H6C]6.
Sulphobenzidic acid, C,2H5. S205.    Chlorbenzid, C12H3(13.
Nitrobenzide,      CI2H5. N.04.      Azobenzid,  C12H5N.
I shall have occasion to refer to benzin as a product of the distillation of resin
and coal. It is colourless, of an agreeable ethereal odour; it boils at 187~; its
specific gravity is 0'85; that of its vapour is 2378; at 32~0 it freezes into a crystalline mass, which melts first at 430~
Oil of Bitter Almonds with Ammonid.-By the action of water of ammonia on hydruret of benzyl, all oxygen is removed, and a crystalline body, Hydrobenzamide,
produced; its formula is C42H16N2. It is soluble in alcohol, and by boiling the solution is decomposed into ammonia and hydruret of benzyl. The nitrogen here entersjnto the constitution of the radical, replacing the oxygen, and the body is Hydruret of Azobenzyl (Clr4H5 -N)+-H. This azobenzyl is itself also formed in the
same process as the former, and also the Azobenzoilic Acid (CI4H5.;N.)+-N., which
is benzoic acid, in which all oxygen is replaced by nitrogen. The origin of these
bodies is explained, by the constitution of the radical benzyl, as described in p. 471
In the impure oil of bitter almonds a substance exists, termed Benzoine, which is
isomeric with the oil, its formula being C14H602; it crystallizes in colourless prisms.
By potash it gives benzoic acid and hydrogen; by ammonia it forms a substance
isomeric with I-ylydrobenzamide.  By chlorine it gives muriatic acid, and in place of
chloride of benzyl, a crystalline body, which is isomeric with that radical, its formula being C14H1502; this is termed Benzo'l: when heated with potash it gives the
Benzoilic Acid, which has the formula C24H,,O1+Aq.
By acting on oil of bitter almonds with a solution of sulphuret of ammonium in
alcohol, Laurent has obtained a series of bodies, in which the oxygen of the radical
benzyl is replaced by sulphur, and in some cases partly by sulphur and partly by
azote; there should thus be Sulphobenzyl (C,14H5S2), corresponding to the azobenzyl. It is unnecessary, in an elementary work, to enumerate the individual substances, but I look upon their formation as corroborating very much Berzelius's
idea, that the true radical of the benzoic series is the carbohydrogen, C14H115, and
that the chloride, &c., of benzyl are really oxychlorides, &c. (See p. 471.) Certainly the element which remains truly constant in those reactions (and hence satisfies the definition of a radical, p. 467) is C14H1, and not C14H502.
Oil of Cinnamon and the derived Compounds.
This oil is found in the bark and flower-buds of the laurus cinnamomum and laurus cassia. It is heavier than water, and possesses the odour of the plant in the
highest degree. It boils at 4280; its formula is CoH11002, and for distinction I shall
term it the a oil. When exposed to the air it absorbs oxygen, and forms another
oil, which is that generally found in the shops, the P oil, the formula of which is
C0sHs802. Two resins, a and P, are at the same time produced.
~ atoms of a oil, =C60H   r06,
36resin, =CH50-.,
absorbing          produce    resoil,  =s-CsH50
6 atoms of oxygen, =0                 5 atoms water,-H802,
X  5 atoms water, =-H5O0.
The  oil of cinnamon, although thus only a product of the decomposition of the
true oil, is very important, from the variety of compounds it gives rise to. It is
heavier than water; it dissolves in water of potash or of barytes, a cinnamate of the
base being formed, and an oil lighter than water separating, 2(C8sHe02) and H.O.
giving C0sH1002 and C18H:03. The properties of this oil indicate that it contains
an organic radical, Cinnamyl, CSH702, united to hydrogen. It is Hydruret of Cin
namyl, Ci.H., and the oil lighter than water is Ci.H3.
Cilnamic Acid, Ci.O0.+Aq., is formed by exposing the hydruret of cinnamyl to
the air; it absorbs two atoms of oxygen, and forms crystallized cinnamic acid. It
forms colourless groups of plates of an acid taste; it is almost insoluble in water
but easily soluble in alcohol and ether. It melts at 264~, distils over at 5540 un
changed. Its salts are exceedingly similar to the benzoates.
Hydruret of cinnamyl combines directly with muriatic acid, with nitric acid, and
with ammonia, forming compounds which are solid and crystalline. Their formulae
are Ci.H. H.CI., Ci.H.. H.Ad., and Ci.H.. H.O.+N.Os. By chlorine one half
of the hydrogen of this 3 oil is removed, and a white crystalline body formed, C14
H4.  C1402. The chlorine here enters into the constitution of the radical.




OIL  OF  CLOVFS  AND  SPIRAA.                           573
Oil of cinnamon combines with iodide of potassium  and iodine to form a substance which crystallizes in large needles of a brilliant bronze colour, like permanganate of potash.  Its formula is Ci.H.s13+K.I.  Once formed, it is decomposed by
water. It was discovered by Moore, of Dublin, and analyzed by Apjohn.
The origin of the Balsams of Perl-i and Tolu is closely related to the oil of cinnamon. They consist of resinous substances (the a and 3 cinnamnic resins 1), and of
an oil which may be obtained pure by distillation.  It is called Cinnanzeine; its formula is CisHsOf being isomeric with the S oil of cinnamon. It is neutral; but
when its alcoholic solution is boiled with potash, it forms cinnamate of potash; or,
by simple boiling of its alcoholic solution, Cinnanlic Ether is produced, and another
oil, Peruvine, is separated, the fbormula of which is ClsIlsO2.   In these cases three
atoms of cinnameine and two of water produce two atoms of dry cinnamic acid
and one of peruvine.
These researches on the nature of the balsams are due to Fremy; but Richter
has advanced that the balsam of Peru contains two oils, which he terms JIqyriospermine and Myroxyline, the relation of which to peruvine and cinnameine is not
yet established.
By the action of an excess of nitric acid, both oil of cinnamon and cinnamic acid
are converted into oil of bitter almonds and benzoic acid.
Oil of Cloves, Eugenic Acid, 4-c.
The oil obtained by distillation from the undeveloped flower-buds of the eugenla
caryophyllata is a mixture of several bodies.  By the action of potash, it is separa
ted into a volatile oil which does not possess active properties, is lighter than
water, and consists of CjoHs, while a eugenate of potash dissolves.  From this
solution the Eugenic Acid is precipitated by any strong acid.
Eugenic Acid. Heavy Oil of Cloves, C24H,505, is a colourless oil, sp. gr. 1'079'; it
boils at 470~; its taste and smell are those of cloves. It forms, v with the metallic
oxides, well-defined salts, most of which are soluble and crystallizable.
When the common oil of cloves is kept for some time, it deposites a crystalline
substance, Caryophylline, C2oHI602; it is soluble in alcohol, insoluble in water. It
is volatile. From water distilled with cloves a different body separates in pearly
scales, having the formula C20Ht.204. It is called Euo'enine.
The eugenic acid and eugenine are rendered blood-red by contact with nitric acid.
The Lioght Oil of Cloves has sp. gr. =0'918; it boils at 287~'.
Oil of Spircra Ulmaric.  Salicide of Hydrogen.
The oil distilled from the flowers of the meadow-sweet is a mixture of a light
and of a heavy oil, with a solid body like camphor.  The heavy oil is of much interest, from the number-of compounds which it forms, and from our being able to
form it at will, although from a body, salicine, which has not been found to exist in
the spirea.  The impure oil of spirea is purified by adding potash, by which the
lighflt oil is separated, and Salicide of Potassium formed, which, when acted on by
sulphuric acid, yields the Salicide of Hydrogen pure.
To form it artificially, equal parts of salicine and bichromate of potash are to be
distilled with 21 parts of oil of vitriol and 20 of water. There is heat evolved and
much gas disengaged; on then distilling, the heavy oil passes over. Two atoms
of dry salicine (C42H2101s), Without any oxygen, might yield three atoms of oil,
3(C04H604), and six of water; but the reaction is far more complicated in reality,
as four parts of salicine yield but one of oil.
The properties of this oil show it to be a compound of a radical (C141a104), Salicyle, Syl., with hydrogen; it acts as a hydracid in combining with metallic oxides;
its specific gravity is 11'73; it boils at 380~. The specific gravity of its vapour is
4260. In this and in composition it agrees with crystallized benzoic acid, with
which it is isomeric. The alkaline Salicides are soluble and crystallizable; those
of lead, zinc, and mercury are insoluble. If a solution of any salicide be mixed
with a solution of a sesqui-salt of iron, the liquor assumes a fine purple colour; by
which the oil is well characterized.
When salicide of hydrogen is heated with caustic potash, hydrogen is evolved,
and Salicylic Acid, Syl.O., tbrmed; the potash salt being dissolved'in water, and
muriatic acid added, the new acid is precipitated, and is purified by recrystallization; it dissolves in boiling water; it may be sublimed, and condenses in long
needles, like benzoic acid; it possesses the usual acid properties; its salts are
generally soluble, and resemble closely the benzoates.




574                  OIL OF MUSTARDI ETC.
By the action of chlorine on salicide of hydrogen, Chlorzide of Salicyle Is fbrme.t,
Syl.C(l.; it crystallizes in rhomboidal tables, which melt and sublime undecoirr.
posed; bromine and iodine give similar compounds; with nitric acid it produces
Nitrosalicylic Acid, Syl..N.04, which crystallizes in long prisms, and unites with
bases forming salts.
The connexion of salicyl with benzyl is very remarkable; they contain the same
hydrogen and carbon, Cl4H5, hut it is combined in salicyl with 4, and in benzyl with
but 2 atoms of oxygen. By the action of ammonia on the chloride of salicyl and on
the oil, this relation is more clearly shown, for the oxygen in the radical may be
brought to the composition of benzyl. Thus the Chlorosalicamide is C42H,1Cls.
06N2, or, properly, 3(C14Hz150. -N.)CL.; that is, (Bz.2N.)CI.  By the direct action
of ammonia on the salicide of hydrogen, the corresponding (C14H502. ~-N.)+H.
may be formed. To this new radical, which, is evidently Nitruret of Benzyl, the
name Azosalicyl might be given (see p. 572).
Essential Oil of Mustard.
The oil obtained by distilling the seeds of the sinapis nigra with water is remarkable for a'n unusually complex constitution, as it contains five elements; its formula being C3aH20N4. S;05.  When pure, it is colourless; it boils at 2890; its
specific gravity is 1'015; that of its vapour is 3370; when acted on by nitric acid,
it yields sulphuric acid and an organic product; with caustic potash it forms sulphuret and sulphocyanuret of potassium, and organic products which have not been
examined.  With ammonia it forms a substance in large white crystals, the formtula of which is C32H20N4 ~ S505+4N 113. Our knowledge of the chemical nature
of this oil is vet imperfect. It has been only established that it does not exist in
the seeds, being, like oil of hitter almonds, formed at the moment of distillation.
Tile seeds of mustard contain two crystalline substances.  Of these, Sulphosinapisine is obtained by a process similar to that used lbr preparing amygdaline. It
is, when pure, white; soluble in alcohol and water; it contains the same five elements as the oil, which is probably formed from it by the action of the emulsin of
the seed, as is the case with amygdaline. The principle of the mustard seed to
whichl it appears to owe most of its pungency has been termed Sinapisine; its
preparation is complex; it does not contain any sulphur, and hence can act but
indirectly in the formation of the essential oil. Fremy considers the essential oil
to be formed by the action of the. albumen of the seed on a peculiar acid body,
which he terms Myronic Acid; but this has not been analyzed, and we do not know
its relations to sinapisine, with which it may possibly be identical. The formula
given above for the oil is that of Durnas; L6wig has since analyzedit, and denies
tlhat it contains oxygen, assigning to it the formula N.Cs. H1S2. Accurate res
searches (on the constitution of these bodies are very much to be desired.
2u CrLAss.-)Oils pre-existing in the Plant.  Properties not Acid
These oils are very numerous, and so similar in properties that aspe.
ci.al descripltion is quite unnecessary for each.  They are characterized
bv not dissolving in solution of potash, by being lighter than water, (and
by a less energetic action on the animal system  than the oils of the first
class.  They combine with muriatic acid to form  heavy oily substances,
in somne cases crystalline.  When put in contact with iodine, they fre.
qelntly combine Mvil.il it so energetically as to produce a feeble explosion.
By chlorine, hydrogen is removed, and an oily liquid, heavier than water,
is produced.' The oil, as yielded by the plant, consists of two substances, one s,lid (Stcaropten), the other liquid (Elaopten); the former gener.
ally cryst:lllizes when the oil is long kept.  I prefer to term  the liquid
simr ply thet oil, and the solid portion the camphor of the plant.  We some.
tinrit:s o)bserve these oils forming thle carnphor artificially, by contact with
W  a.lt l'.'rihse, oils may he very naturally divided into two groups, accordi:g
as lthvyv conltaitl oxygen or not.  The fIllowing table includes all the im.
portamnt hots of the history of the oils (elaoptens) containing oxygen'




NEUTRAL  ESSENTIAL  O ILS) ETC.                             57 5
Plant yielding the oil.  Fs iimr.   It'illu  For Vllula.
asli id.  Piift.      a ipour.?,ajeput.......  0'927  3470 C-toli — -
l,avender.....   0896  397c CI11H,40,
[tosemary......           0'897  3650 C4;I-IHs()
Pennyroyal....       0925  3950 CotSiI()
Camphor-tree..      0.910..    02uH160.
Valerian..... 5180 C2Otl,0.
Spearmrrint..   091.. 0 4.    035I0S().
Mlarjoram....               0 8ti7  3540 G0o010 ).
Asarum..  C 6Hf,( 
FenneI.........    0:997..  C2o0t1iz20,
-Anse....2()
Peppermint0 902. 0.902. 092               21C10-I1o(
[tue........ 0837  4460  C2jH23 7690
Olibanum..... 0866  3230 C3-I,3()
Cumin.         0.8610  418~ C(,oi1, )5094
F roem the recent experimtents of Gerhardt and Cahou rs, it alti))ear  tihat,
by the action of fused hydrate of potash, most essential  oils co )ntainintg
oxygen may be separated into an acid, and an oil destitute of oxvgen.
Sotmne of the results obtainedl byr those chemists are of great interest;
thus, from  the oil of valerian, C.20EIO., vaierianic acid is olbtainmed, anld
an oil which absorbs oxygern  vilth g'reat rapidity and generates comirnn
camphor.  Tile oil of charnmomile also yields valorianic acid.
TPhe oil of cumin- (curminurm cyminum), of which the chtracters have
been given in the table, yields, when treated with hydrate of potash, a peculiar acid, Cunmenic Acid, whose ftrmnula is C20,I,,O-l-Aq.; it is perfectly white, crystallizes in finle prismatic tables, tastes souI, fuses at
197~, and may be distilled unchaonged.  If cumeiate of barytes be distilled at a dull red heat, a colourless liquid oii is obtained, whichl boils at
2920; it is terined Cymnen; its firmula is C,-H12, b Zilig -iorneri e with
mn-esitylene; with sulphuric acid cym-nen unites, fortmiing Cymensu/ptu)1hric
Acid, Cls,2. S206, which forms well-characterized s,lttble salts.  By t ie
action of chlorine and of bromine on the oil otf ctlnii, hueavy oily  oirnpounds are obtained, whose formrul'e are C201H,,. 02CI,  CI.,  tC,,-1, ~. 01...
It is evident that in these comtjioullds a radical (Cuty,!), C,0[I,,O,, exactly analogous to benzyl, may be assumed. and the cyiLnll has thie pIl;ce,
of benzin.  The carbohydrogen of the oil of cumin is termed by C;hours Cumen; its formula is CQHi4; its specific gravity (086(0; it boils
at 330~; it may be prepared artificially also fromr  common ca;ll)hor;
with sulphuric acid it forms Cumensuiphuric Acid, which resembles comrl.
pletely the other acids of that class.'The stearoptens, or camphors containing oxygen, will be described by.
and-by.'T'he following table contains a similar view of the most important oils
not containing oxygen:
Sp. g   oili  For    SP. gr. as    Circular'olarizing
Plants yielding the ()il.  as  liquid. ] Point.  Form l a  our.  C lr  i
Citron......    087'30  -.                   +80~ 9', right
Copaiva.. 0878 4730'                +340 3', left.
Parsley..           4t010.
Juniper.               0839  3110~. 3 3             30 5', left.
Savine......315 
COhebs                  0929.40) 1', left.
Black Pepper.......                              - ~  l
Bergamotte.....  +29~ 3',,:lt.                               t
Turpentine.... 0861  3150~   -                 -43 3'. et.K




576        ISOMERIC OILS OF  TURPIENTINE.
Although these oils have all the same per cent. composition, they dif.
fer in the formula of their atom, that of turpentine being C20[-16, that
of cubebs, C,5H,2,, and all the others being C,0EIH.  Although, even as given in the table, they constitute a remarkable group of isomeric bodies,
yet each one is capable of changing its molecular condition in various
ways, and thus generating other bodies, still more closely isomeric, as
they differ only in their action on polarized light.  Of these changes
I shall describe only those of oil of turpentine, which will serve as an
example.
By contact'with oil of vitriol, oil of turpentine changes into another
liquid, which has the same specific gravity both in the state of liquid and
of' vapour, the same boiling point, and the samne atomic weight:, but is totaily without action on polarized light.  This new liquid is called Terebene.  If the oil of turpentine be acted on by muriatic acid gas, it combines therewith, forming a dense liquid, which is muriate of terebene. and
which has no action on light; but another portion of the turpentine unites
with the muriatic acid unchanged, and forms a solid, which crystallizes
in fiiie white prisms, and, from its remarkable odour, is called artificial
Camphor.  In this solid the oil of turpentine preserves all its action upon
light, and, for convenience, it mav obtain the name Camphene, tand the
solid is then ]Muriate of Camphene.  Now if this solid be distilled with
lime, the muriatic acid is removed and an oil obtained, which differs
fiom camphene only in having no action on light, while it differs from
tereberne in forming with muriatic acid a solid product.  This oil is
termed Camnphilene, and the Muriate of Camphilene is distinguished from
the muriate of camphene in being quite destitute of rotatory power.
From none of these products can the true oil of turpentine,or camphene,
be regenerated.  There are thus three forms of oil of turpentine, of
which two give solid compounds, and the third a liquid, with muriatic
acid; two are without action on light, but the camphene rotates powerfully to the left: with chlorine they all give heavy liquids, all of which
have the formula C20H,2C14, but are distinguished friom each other by their
action upon polarized light; the Chlorcamnphene presenting the anom.
alous character of a rotatory power to the right.
When oil of turpentine is mixed with nitric acid and gently heated, a
thick and heavy oily substance is produced, apparently by their direct
union, and may be separated by the addition of cold water.  If; however,
the materials be left to themselves, after some time, violent, almost explosive action sets in, copious red fumes are given off, and a resinous ma.
terial formed, which, by boiling with more nitric acid, dissolves, and the
solution, on cooling, yields crystals of Turpentinic Acid. Its composition
was found by Bromeis to be C,,H,O,60Aq. The exact theory of its for.
mation has not been as yet ascertained.
The other oils of this class are capable of similar metamorphoses,
which need not be specially detailed.
The type C5H4 exists probably in all essential oils, for it will be seen,
by reference to the former table of oils containing oxygen, that their for.
mule consist in multiples of CH,, combined with oxygen, or'with the
elements of water.
B. Of the Camphors or Stearoptens of the Oils.
The most remarkable substance of this class is the common camphor,




CAMPHOR. —-CAMPHORIC  ACID.                        577
whichl is extracted from the wood of the laurus and dryabalanops camphora by distillation with water.  In the plant it is mixed with the camrn
phor-oil (C23H,60.), from the gradual oxidation of which it appears to be
prod uced.
Caml)phor forms a white semitransparent mass, crystallized in irregular octohedrons.  It is very tough and difficult to powder; its specific
gravity is 0'986; its taste is bitter; its odour is well known; it Inelts at
3470, and boils at 390~, subliming unaltered; it is sparingly soluble in
water, but easily so in alcohol and ether; its formula is C20LH602.  The
specific gravity of its vapour is 5317, which might be considered as form.
edi by one volume of vapour of camphene and half a volume of oxygen
(4776+551'3).  Hence camphor and camphor-oil may be looked upon
as oxides of' an oil of the turpentine family.
When camphor is heated with lime, water, and an oil, Camnphron
(C,,0HI2O.), are produced.  With muriatic acid it unites, forming a col.
ourless liquid, whose formula is C20H,7. OaC1.  By boiling with strong
nitric acid, it is completely converted into Camphoric Acid.
This acid crystallizes in small rhomboidal tables, which taste sour and
bitter; it melts at 1450, gives off water, and leaves the anhydrousacid,
which melts at 423~, and distils over at 518~ without alteration.  The
formula of the anhydrous acid is C,0H703; the crystals contain an atom
of water. The-salts of camphoric acid are not important, and appear to
differ in properties according as the dry or hydrated acid was etnployed
to formn them.  The Camphorate of Ether is a dense liquid, wlhich, with
camphoric acid, forms the Camphovinic Acid, a thick, heavy liquid, which
is decomposed by heat, and forms unimportant salts.
When camphor is distilled with glacial phosphoric acid, water is form-.
ed, and a volatile oil passes over, having the formula C2NH,4, and identical
in every respect with the Cymen obtained from oil of cumin, as described in p. 575.
When camphor in vapour is passed over hydrate of potash, heated to:
about 700~, an acid is formed, which has the formula C201H,70+Aq.
This Camphoric Acid fuses at 1760~, and boils at 4820; it may be distil;
led unchanged.  It is insoluble in water, but dissolves abundantly in alcohol and ether, and crystallizes firom these solutions on cooling. When
it is heated with phosphoric acid, a volatile oil is produced, Campholein,
having the formula C,sH,6. When campholeate of lime is distilled, an.
other oily fluid is formed, whose formula is C9,H170.,
Of the camphors of the other volatile oils, only a few require any de.
tailed notice. The characters of most of them are given in the follow.v
ing table:
Pan gtng the o Sp. Or.!Melting    Boiling    Sp. Gr. t orn 
Plant giving the Camphor. as Liquid.   Point.  Po  nt.  of Vapour.  aormsa.
Rose (Otto).770 5500... C.H.
Parsley                          700  5520..C1H704
Iris Florentina......... C4H40.
Elicampane.                    1080~...... 071-C0.
Asarum..                      104   53)0....C16H,,14
Fennel.....    1'014   68~  428..  CoH20.20
Anise......     640  4300  5680 ('2011:202
Peppermint.910  4060  5455 C2l1:I2002
Cubebs...                          1. C6H140.
Turpentine  1....   1057  3020~  311 I....CoH00o4
4D




578              RE SINS OF  TURPENTINE.
On comparing these formulme  with those of the corresponding oils
(p. 575), it is seen that the camphors arise from various causes; in some
cases they are isomeric with the oils, in others oxides of thenil, and in
others hydrates; thus the camphor of turpentine may be fotrmed at will,
by agitating the oil with water, and then exposing it to cold; the hydrate
crystallizes out in colourless prisms, sometimes of great size.
The peppermint.camphor has been found to yield, by the action of re.
agents. a series of compounds.  Thus, by the action of,glacial phIosphlor ic
acid or of oil of vitriol, a light oil was obtained, having the formnlula C2,
I1,,, which is termed Menthen.  By the action of' chlorine, a thick, heavy
liquid is produced, C2, H4. C1602.  By nitric acid, menthen yields a heavy
oily liquid, C2AHsO9, which possesses,acid properties; and with chlorine,
menthen yields a sirupy yellow liquid, having the formula C2,H,CI15.
The anise-camphor yields with bromine a crystalline substance, CJE-9.
Br302, and with sulphuric acid an oily substance, Anisoine, isomelic with
itself.  By nitric acid it is converted into a body which crystallizes in
long needles, Anisic Acid, C,6 6Os60+Aq., whicll forms salts with nmetallie oxides, and gives b)y Nfarther action the Nitranisic Acid, C,615. N.0-.+
Aq., and ~Nitranisid, C20H,0. N20o,.
C. Of the Resins.
The bodies of this class approach closely to the camp'hors in composition and properties, but are distinguished by not being volatile without
decomnposition, and being generally capable of acting as acids.  The most
important will be first specially noticed, and the properties and formulke
of the remaining expressed in a table.
Resins of Turpentine.-The ordinary white resin coexists, in the dif.
ferent species of pine, with oil of turpentine, and is obtained bv making
incisions through the bark, when the thick, tenacious turpentine flows
out.  This, when distilled with water, gives off the oil, while the resin
reinains, and is called Colophony.  It is a mixture of two resins, which,
though having the same composition, differ in properties, arnd are termned
the p)ilic and sylvic acids.
T'he Pinic Acid is obtained by digesting colophony reduced to fine
powder, in cold spirit of sp. gr. 0'865, which does not dissolve sylvic
acid.   The solution is to be mixed with a spirituous solution of acetate
of copper as long as a precipitate forms.  This Pinate qf Copper is
to be dissolved in4 strong boiling spirit, decomposed by a little muriatic
acid, and then mixed with water; the pinic acid precipitates as a resin.
ous powder, which may be dried at a moderate h'eat.
When quite pure, pinic acid is colourless; it melts at 257~, bat be.
comes soft at 149~: its solution in alcohol reacts acid.  It ex.pels car.
bonic acid from bases; its alkaline salts are soluble; its earthy and me.
tallic salts insoluble in water, but many of them soluble in spirit; its for.
mula: is C4013004....
When a solution of pinic acid in alcohol is long exposed to the air, it
abso!rbs oxygen and forms Oxypinic d.cid, the formula of which is C40FHI
Os; it is a stronger acid than the pinic.  When heated with lime, pinic
acid is decomposed, and three differeeit volatile oils obtained, which need
not Ie specially noticed.
The Sylvic.cid remains when the pinic acid is dissolved by weak al.
coliol.  As it is not pure, the residue is to be dissolved in two parts of




COMPOSITION  OF  RES INS.                         579
boilingf spirit of 0O835; on cooling, the sylvic acid separates.  By a sec.
ond solution, all the traces of pinic acid may be removed. The pure sylvic acid crystallizes fiom  its alcoholic solution in colourless rhombic
prisms; it melts at 212; it is easily soluble in strong alcohol and in
ether,' but insoluble in water; its formula is C0H3O,.  Its salts are exactiv similar to those of pinic acid.
WVTien either pinic or sylvic acids are kept melted for some time, they
become brown, and ciange into a resin very sparingly soluble in alcohol,
and possessed of stronger acid properties than either; it is termed Colo.
phonic 5.cid; it exists in small quantity in common resin.'The resin of the spruce fir has been found by Johnstone to be a mixture of two resins, whichi are separated by means of alcohol.  The more
soluble, or A resin, has the formula C,40H1,O6; the less soluble, or B resin, that of' C40H3900; they both possess acid characters.
For the mnanufacture of tar and pitch, the pine wood containing turpentine is exposed to a kind of destructive distillation, in kilns hollowed
out in the ground.  Although a large quantity of the resin flows out undecormposed (as colopholic acid), yet the important components of the
tar are bodies belonging  to a ditFerent series, which will be described
hereafter.
A great variety of resins, of important use in medicine and in the arts,
exude from trees, either pule, or mixed with oils, or with gums (Gum
Resins), sometimes with benzoic or cinnamic acids, constituting Bal*7tms.
Frequently there are many kinds of resins mixed together, but they all
possess the characters of fusibility, insolubility in water, and of being
dissolved by alcohol, ether, essential oils, and alkaline solutions.  Their
comnposition is given in the following table:
Anime Resin.  C                  B. Sandarach.          43
Elemi Resin.                     A. Euphorbiumn.
Fossil Copal.... C40H3.20.    Asphaltene.....  0
B. Ma'stic Resin.    C. C4913lO2    A. Olibanumn...
Antiar Resin.      C4O03oa02    Labdanurn..... C483301
B. Copal Resin.      C40HoO3103  Pasto Resin.....  C40H30
Birch Resin..         C40H303      Sagapenu..... C40H909
A. Mastic Resin..                 Scammony..... C4H0
Copaiva Resin  J..                 alap Resin..         C40Ho340
A.  lemi Rcsin... C4020        Galbanum...         C40H2707
B. Olibanum Resin                   Dragon's Blood... C40H2Os
C. Sandarach.... 0o3006    Gamboe.....  C,1H08
Amimoniac Resin.      C40I2')09    A. Assafcetida.... C40 609
B. Assafmtida.... C4H2O         Acaroid Resin... CoH0o)l2
Guiacur......  C4H30i         Opoponax..... C40Ho50o
Bdelliurn Resin.'., O        B. Benzoin Resin       C40oHz20O
A. Sandarach...                A. Benzoin Resin.     C40H2607
In all this series of resins, it is evident that the carbon remains unal.
tered, and Johnstone has shown that they may all be considered as derived from  oils having the turpentine constitution =C40H32.
A substance wvhich is connected with the preceding in many ways is./mnber.'This body is fobund in rounded: pieces, mixed with or attached
to fragments of decomposing wood, in the lignite beds of the north of Europe.  It is also found, cast on shore by the waves, along the coast of
the Baltic.  It is yellow. transparent, and often contains imbedded in it
insects anid parts of plants, so as to prove it to have been perfectly liquid
when first formed.  It is, in flact, the turpentine of unknown trees, belonging to a forier geological epoch; its specific gravity is 1'067;




580            A MB E-Ri:SU:C:CINIC ACID, E TC.
when heated it melts, and is then totally decomposed; its. relations to
electricity have been fully noticed, p. 108.  Amber is found to be a mix.
ture of fwo resins, which are soluble in alcohol and ether, a bitumen insoluble in those liquics, a volatile oil, and a peculiar acid, the Succinic.icid.  It is used very extensively in the arts as a material for varnishes, but to chemists its principal interest is its electrical properties, and
as a source of its acid.
Succinic./cid is obtained by the destructive distillation of amber; it
partly sublimes into the neck of the retort, in discoloured crystals, and
partly dissolves in the water which comes over; by solution in nitric
acid it may be freed from the resinous colouring matters.  It may also
be obtained from  the amber by digestion with alcohol or solution of
potash; it hence pre.exists in the amber, and is not produced by the
heat.  It is found in small quantity also in colophony, and is abundantly
produced by the action of nitric acid on the fatty acids, as the stearic or
margaric.
Succinic acid crystallizes, from  its solution in water, in
colourless right rhombic prisms, as m, t, a in the figure, which
/i;i a  have the formula C4H203+Aq.; when heated to 3500 it melts,
-      t  abandoning half its water, and at 450~ sublimes in an anhydrous state; its solution in water is markedly acid; when
heated with lime, a volatile liquid is produced, Succinone, the
exact formula of which is not established.
The salts of succinic acid are mostly soluble and crystalli.
zable.
The Succinate of Soda, prepared by neutralizing the acid by carbonate of soda, crystallizes in doubly oblique rhombic prisms, of which i, u, v
are primary, and z, n secondary faces in the figure; it is per-, manent in the air, and very soluble in water. The Succinate
In: \    of d.lmmonia, which is much used in mineral analysis for the
separation of iron from manganese, clrystallizes in nearly the
same form  as the soda-salt figured above.  The succinates
of barytes, lime, and lead are white powders, insoluble in
water.  The Succinate of Manganese forms rose-red, four-sided prismatic crystals, permanent in the air, and soluble in ten parts of cold
water.  The Succinate of the Peroxide of Iron is precipitated when an
alkaline succinate is added to any salt of iron not containing an excess
of acid; it forms a pale brownish-red powder, insoluble in cold water,
but decomposed by boiling water, which dissolves out the acid with a
small quantity of the iron; it dissolves readily in acid liquors.
The Bisuccinate of.Ammonia gives off water when heated, and a white
crystalline solid sublimes, which is termed Suqcinamid.  Its formula is
CaH,5. 04N.
The rare mineral, Mellile (see p. 498), is only found accompanyi;lg
amber in the deposites of lignite.
Caoutchouc.  Indian Rubber.-This substance, now so much used in
the laboratory for connecting pieces of apparatus, and so extensively em.
ployed in the arts, possesses much similarity to the resins.  It dissolves
but imperfectly even in ether, its proper solvent being the volatile oils,
into which it is converted by distillation.  One of these is the lightest
liquid known, its specific gravity being but 0.654; it boils at 92~; it has
been termed Faradyn.  Another, known as Caoutchene, has a spe-:ifie,




CONYSTITUTION  OF  FATTY  BODIES'.                    81
gravity of 0.842; it boils at 3400.  The composition of these liquids,
or of caoutchouc itself, is not well known, as they have not been, as yet,
obtained absolutely pure; but, so far as 1 can judge, they appear all to
have the same composition as oil of turpentine.
CHAPTER XXIII.
OF THE SAPONIFIABLE FATS AND OILS.
THE substances of this class are found both in the animal and vegetable kingdoms very extensively distributed.  In anirnals, the various-fats
are deposited in the cavities of the cellular tissue, but often also diffused
through the mass of the glandular organs.  In plants, the oils or fats are
generally found in the investing membranes of' the seed, or in the cellu.
lar texture of the fruit.  The leaves or roots seldom contain any fatty
matter.  The fiats and oils, as they exist in nature, are mixtures of-a
few simple fatty and oily bodies in variable proportions, their degree of
consistence depending on the relative preponderance of the solid or ii.
quid constituent.  The greater number of fats consist of two simple fats,
Stearine and  Jlargarine, and a simple oil, Olein; but these three bodies,
which may be considered as the bases of all fats and oils, are accompa.
nied generally by smaller quantities of solid or liquid fats, which are
often peculiar to a particular animal or plant.  These fatty bodies are
all fixed; that is, they cannot be distilled without decomposition; but
they are totally converted by heat into volatile bodies, undergoing, in
some cases, singular metamorphoses, which will be described in the his.
tory of the individual fats.
Exposed to the air, the fatty bodies gradually absorb oxygen, and
evolve carbonic acid; they at the same time obtain an acid reaction, and
a smell well known as rancid.  Most of this change appears to result
from minute quantities of azotized organic tissues, which remain inter.
spersed through the fats.  A great number of oils, however, absorb oxygen very rapidly, and, evolving carbonic acid, change into a soft resin.
ous body; they are hence termed Drying Oils, and are used so in paint.
ing.  rThis drying quality is increased by combining the oilwith a small
quantity of a base, as oxide of lead.
The most important fact in the history of the fixed oils and fats: is,
that, by the action of alkalies, they are converted into soaps; 7whence
the name of saponfiable given to the class. By means of the: alkli, the
fat or oil is decomposed into an acid, which combines with the base, forming a true salt, which is tile Soap, and a substance soluble in water, of
a sweet taste, which is the same, no matter what kind of fat had been
employed.  This substance, the sweet principle of the oils,: or- Glycerine,
is united in each fat with a different acid, and hence, as the fats' are best
described as salts of glycerine, I shall first notice the composition and
properties of the base itself:
Of Glycerine. -C[l705+Aq.  Eq. 1157'4 or 92.3.  To obtain glycerine, any fatty matter is to be saponified by a caustic alkali.  The
solution being decomposed by tartaric acid, which -precipitates the fatty




82t3    GLYCERINE' STEARINE~ AND  STEARIC ACID.
acid,: is to be evaporated, and the glycerine dissolved out by strong alco..
hol.  It may also be obtained by saponifying, the fat by oxide of lead,
and treating the watery solution with sulphuretted hydrogen to precipi.
tate some oxide of lead, which dissolves; tile glycerine may then be obtained by evaporation.
Glycerine cannot be obtained solid.  When brought to its greatest
degree of consistence by evaporation. in vacuo over sulphuric acid, it is
a colourless sirup, sp. gr. =1'26; it dissolves in water and alcohol, but
is insoluble in ether; it is decomposed by heat.  With nitric acid it
produces oxalic and fobrmic acids. Boiled with solutions of copper, it
precipitates metallic copper.  With chllorine it fbrms a wlhite flocculent
solid, having the formula C,2H1,,. O,CI3, and with bromine it gives a
dense oily liquid, whose formula is C,2H,,. O,Br3.
When glycerine is mixed with oil of vitriol, they unite without black
ening, and form an acid compound, Sulphoglyceric Acid, the formula of
which is C6H70. 2S.0. 1H.O.  With bases this acid forms soluble
salts, havinf considerable analogy to the sulphovinates.  The Sulphoglycerate of Lime crystallizes in long delicate needles, whose formula is
C6H705. S.03+S.03. Ca.O.  The compounds of glycerine with the
fatty acids constitute the various kinds of faits and oils.
Of Stearine and Stearic Acid.
Stearine is the essential constituent of all solid fats, and preponderates in proportion to their consistence. It is best obtained from muttonsuet, either by washing it with ether, as long as anything is dissolved,
or by mixing up melted suet with six times its volume of ether, and sub.
jecting the mass, when cold, to strong pressure. In both cases the stea.
rine remains behind; it is generally crystalline like spermaceti, not at
all greasy between the fingers, and is easily powdered; it melts at 1430~;
it is insoluble in water and in cold ether; it dissolves in boiling alcohol
or ether, and crystallizes out as it cools.  The formula of stearine is
C1,H14,017, consisting of
1 atom of glycerine,   =C6H705,   1
2 atoms of stearic acid, =C136H]32010, =C142H114107.
2 atoms of water,    =H202,
By the action of strong bases or of strong acids, it is separated into
these constituents.  A similar decomposition is effected by heat.
Stearic Acid is obtained pure by saponifying stearine by potash, and
decomposing the solution by means of warm dilute muriatic acid. The
stearic acid which precipitates is to be washed with water and dissolved
in boiling alcohol, whence the pure acid crystallizes, on cooling, in brill.
iant white plates.
When mutton.suet is directly saponified, very troublesome operations
are necessary to free the stearic acid from the other fatty acids whicht
accompany it.
Pure stearic acid is tasteless and inodorous. It does not melt below
1580; the melted acid forms a crystalline mass on cooling; it is appa.
rently volatile, and may be distilled unaltered in close vessels; it is insoluble in water, but dissolves in hot alcohol; the solution reddens litmus; its composition, when crystallized, is C6.H660-+2 Aq. When heated in contact with lime, carbonic acid is formed, and a volatile liquid,
teitcarn, whose formula is Cw6H60.




MARGARINE AND MARGARIC ACID.    583
Stearic acid is but feeble in its action: it expels the carbonic acid
from the alkalies only when the solution is boiling.  It is bibasic, forming two classes of salts, the Bistearates, which contain one atom of water
and one of fixed base, and the Neutral Stearates, which contain two atoms
of fixed base. The alkaline stearates are the only salts soluble inllwater;
they dissolve also in alcohol.  If neutral stearate of potash be mixed
with a large quantity of boiling water, it is decomposed, one half of the
potash becoming free, and the Bistearate of Potash precipitating in minute
crystalline scales. A solution of soap precipitates all earthy and metallic salts, producing insoluble stearates.
The Stearic Ether is exceedingly remarkable, as it corresponds exactly
to stearine in composition, the glycerine being replaced by ether. Thus
its formula is
1 atom of ether,    -=C4HO0.,
2 atoms of stearic acid, =C136HI32010, Cl40H3903=-1 atom of stearic ether.
2 atoms of water,    =H1202,
Stearic acid is now very extensively used for making candles.  The
tallow is saponified by boiling with a thin paste of lime.  The glycerine
is washed out, and the soap being decomposed by muriatic acid, tile oleic
acid is removed from the stearic acid by violent pressure between folds
of cloth. The pure stearic acid, when solidifying, assumes a crystalline
structure, which would spoil the appearance of the candle, and this ten.
dency is removed by the very improper addition of one part of arsenious
acid to about 2000 of stearic acid.
Of Margarine and Mllargaric Acid.
Margarine exists along with stearine in most fats, but is most characteristic of human fat. It is prepared from the ethereal solution, which
has left the stearine undissolved.  This liquor is to be evaporated, and
the residue dissolved in boiling alcohol, fiom which the margarine crystallizes as the solution cools; it melts at 118~.  In all other properties
it resembles stearine, but is much more soluble in ether and alcohol; it
consists of C741H7402.
1 atom of glycerine,    =C61705, 
2 atoms of margaric acid, =C6sH6606, =C-,4H74012, 1 atom of margarine.
1 atom of water,     -H.O.,
By the action of bases it is separated into glycerine and margaric acid.
The preparation of Margaric Acid is precisely similar to that of the
stearic acid, which it resembles very closely, being most different in its
melting point, which is 140~.  On solidifying, it crystallizes in white
needles.  When carefully heated, it volatilizes without alteration. The
formula of margaric acid is Cj4Hs0a,+ Aq. If it be mixed with lime and
distilled, carbonic acid is produced, which combines with the lime, and
a volatile substance is obtained, which is termed Margaron. Its formula
is C[lU33O.  It is a white solid, of a pearly lustre, which melts at 170~,
and forms, on cooling, a crystalline mass like spermaceti. By repeated
distillation with lime, all oxygen is removed as carbonic acid, and a volatile oily substance obtained, having the composition of olefiant gas.
The experiments of Redtenbacher have indicated a remarkable source
of margaric acid in the distillation of stearic acid. The distilled product,
though in appearance unchanged stearic acid, yet does not in reality




584              OLEIN  AND  OLEIC  ACID.
contain any trace of it, being a mixture of margaric acid, of margarone
and of the volatile oily carbohydrogen.  The reaction being that
(6 atoms of margaric acid, C204H200o4,
4 atoms of hydrated       1 atom of water,     1 0.,
stearic acid,    produce 1  "   margarone,   C3H30O.,
C272H27202s,   )      1  "   carbonic acid, C 02,
kThe oily carbohydrogen, C34H34.
Redtenbacher doubts the real existence of stearone, as none of it is
produced in this reaction.
The salts of margaric acid resemble perfectly the stearates in their
properties, but the acid being monobasic, there is but one class of margarates.  The pearly lustre of the crystalline scales of the margarate of
potash gave occasion to the name of this acid, from the word uapyapt-rq, a pearl.
If we compare the formulae of the bodie-s now described, we find them
capable of being expressed by a very simple theory: thus, indicating an
hypothetic carbohydrogen, C34Hn3, by R., the stearic acid becomes R2+ 
05, and the margaric acid, R.+0, being related as hyposulphuric and
sulphuric acids. Also, as Redtenbacher has remarked, all the results
obtained might be accounted for by ascribing to margarone the formula:C,4H30., in which case it becomes R.+O., and the volatile oil may be
R.~ +H. Farther researches are, however, wanted to give experimental
evidence on these points.
Of Olein and Oleic Acid.
Olein exists in small quantity in the various solid fats, but constitutes
the great mass of the liquid fixed oils which are not drying oils. It
holds dissolved, more or less, stearine and margarine, of which the greatest part may be separated by exposure to cold, when they crystallize.
Olive oil contains a large quantity of margarine, and hence freezes very
readily. The expressed oil of sweet almonds is the purest native olein;
next to it is rape oil.
To obtain pure olein, almond oil is dissolved in hot ether, and the so.
lution exposed to great cold; the traces of margarine crystallize out
completely, and by evaporation the ether is removed.  Olein remains,quald at ~0 Fah. In constitution it resembles the solid fats, containing
a peculiar acid, Oleic Acid, combined with glycerine and water.
1 atom of glycerine, C6H705,,
2 atoms of oleic acid, C88H7808, produce 1 atom olein, Cs4H87015.
2 atoms of water,   H202,
Oleic Acid is obtained by saponifying olein with a strong solution of
potash, then decomposing the oleate of potash by muriatic acid, washing
the oil which separates, and drying it with chloride of calcium; when
cooled below 200 F., it congeals as a mass of needly crystals.  Its specific gravity at 60~ is 0'898; it is tasteless and inodorous when pure;
it is insoluble in water, but abundantly soluble in alcohol and ether;
these solutions react strongly acid; its composition has been determine
ed by Varrentrapp to be C44Ha1904+Aq.; its alkaline salts are soluble,
and form soft masses, destitute of tendency to crystallize; they are still
more soluble in alcohol.  The earthy and metallic salts are white, plastery substances, insoluble in water.  The Oleate of.Lead is soluble in
ether, by which it may be perfectly separated from the stearate or mar.




SE BACIC  ACID, ETC.                          585
garate of lead. The Oleic Ether was formed by Varrentrapp by passing
muriatic acid gas into a solution of oleic acid in alcohol. It is a colour.
less liquid, sparingly soluble in alcohol, lighter than water, but heavier
than alcohol, from  which it is deposited as it forms; its formula is
Ct4L13904+ Ae.O.
When oleic acid is distilled, a portion of it passes over unaltered, but
the greater part is decomposed, and some charcoal remains in the retort.
The distilled products are Sebacic Acid and a liquid carbohydrogen,
isomeric with olefiant gas; sebacic acid is not produced by the distillation of any other fatty substance than oleic acid, and hence may be con.sidered as characteristic of it.  The decomposition consists in that
1 atom of sebacic acid,  C oH904,
2 atoms of hydrated oleic acid,     f 3 atoms of carbonic acid, C306,
C(8H: 00 o,         produce  carbohydrogen,          C71H71,.residual charcoal,    C4.
Sebacic Acid had been considered as a product of the destructive dis.
tillation of all fatty bodies; but it has been shown by Redtenbacher to
arise only fiom oleic acid; the distilled product is to be washed with
boiling water, which dissolves the sebacic acid; on the addition of ace.
tate of lead, a white precipitate is obtained, which, being decomposed by
sulphuretted hydrogen, gives sulphuret of lead, while the pure sebacic
acid dissolves, and may be obtained crystallized by the evaporation and
cooling of its solution.
The crystallized sebacic acid closely resembles the benzoic acid in
properties and appearance; its solution reddens litmus; its alkaline
salts are very soluble; its lead, silver, and mercury salts are insoluble
in water; from a strong solution of an alkaline sebacate, the acid is precipitated in voluminous crystalline flocks on the addition of a stronger
acid.  When completely pure, the sebacic acid is totally without odour,
the strong smell of' heated oil being due to llle formation of a totally different substance, Acroleon.  The dry sebacic acid has the formula
C,OH 03; when crystallized it becomes C,0ISO8,+Aq.
Of the Action of Nitric Acid on Stearic, Margaric, and Oleic Acids.
By the gradual oxidation of those fatty acids, a series of bodies result, which
have so much connexion with each other as to be most conveniently studied in relation to their origin.
A. If stearic acid be digested with two or three times its weight of common
aquafortis at a moderate heat, a very lively action commences after some time, and
copious red fumes are given off. When the mixture has ceased to froth up, and
the action of the acid ceases, the only product forms a colourless layer on the surface of the acid liquor, and is found to be pure Ma.?garic Acid. The change here is
evidently a simple oxidation, as RI2+05 and 0. give 2(1.-+03), as described in p."584
If the fatty acid be acted on by successive quantities of the nitric acid until it
disappears, the watery liquor deposites, on cooling, abundance of crystallized Succinic Acid, and the mother liquor of these crystals being evaporated to one half,
forms, on cooling, a thick mass of crystals, which may be washed with cold water,
and being purified by recrystallization, are found to be identical with the acid formned by the action of nitric acid on the peculiar woody tissue which exists in cork,
Suberine, and which will be hereafter described. This acid is termed the Suberic
Acid; it is white, inodorous, and of a feebly. acid taste; easily soluble in alcohol
and water; the crystals melt at 2480, and when heated more strongly, are decomposed in great part; it precipitates solution of acetate of lead; its alkaline salts are
soluble and crystallizable; when crystallized, the formula of the acid is CsH603+
Aq. The Suberic Ether was prepared as described above for the oleic ether; it
is liquid, and its formula is CsH603+Ae.0. By the distillation of the suberate of
lime, a volatile liquid, Suberone, is obtained, whose formula is C7H160.
4E




86        I-IMELIC. ADIPIC9  LIPIC  ACIDS,   ETC.
The artificial formation of the succinic and suberic acids in this way is exceedingly curiouts; but Bromeis and Laurent, to whom the observation is due, have not
been able to trace the precise reaction in which they originate.
B. The action of nitric acid on oleic acid is mluch more violent than on the stearic
acid. Among the products of the reaction are fiound the succinic and suberic acids,
but in addition, four other acid bodies, of which, however, a very slight notice will
suffice.
The Pimelic Acid forms white crystalline grains, which melt at 2730, anrid subiline
easily in brilliant needles; its alkaline salts are soluble, but its earthy and metallic
salts insoluble in water; the formula of the acid is C7-I603+Aq.
Adipic Acid resembles closely the former; it dissolves in water, alcohol, and
ether; melts at 2230; it sublimes in very beautiful crystals; its formula is C414H9
07+2 Aq., it being a bibasic acid.
The Lipic and Azoleic acids are still less important, and our knowledge of their
constitution very imperfect.  All these bodies are obtained fiom the mother liquors,
from which the succinic and suberic acids have crystallized.
The most important products of the action of nitric acid on oleic acid, or on olein,
are Elaidine and the Elaidic Acid; these bodies are of pliarmaceutic interest, firom
their constituting the Citrine Ointment, or Ungaentum  Nitralls Hydrargyri of the
Dublin and Londoin pharmacopoeias.
Elaimdine is prepared by the action of nitric acid, or, still better, of the red fumes
of the nitrous acid on olein; the oil gradually becomeg thick, and finally congeals
into a butyraceous mass of a deep yellow colour.  By digestion with warm alcohol,
a deep orange-red oil is dissolved out, and the pure elaidine is obtained perfectly
white; it melts at 97~0, is insoluble in water, and but sparingly so in alcohol; it
dissolves readily in ether; with caustic alkalies, it saponities completely, glycerine
being set free.  The whole action of the nitric acid in this reaction is exerted on
the oleic acid, and the elaidine is a true fat, consisting of ela'idic acid united to
glycerine.
Elaidic acid may be prepared by saponifying elaidine, and decomposing the alkaline elaidate by a stronger acid, but it is obtained in a mnuch purer form by passing
nitrous. acid fuimes, generated by heating nitrate of lead (p. 276) into pure ole'ic acid,
prepared from oil of sweet almonds; after some time, the liquid becomes a nearly
solid mass of crystalline plates, of a fine yellow colour; this mass is to be boiled in
water to remove adhering nitric acid; then dissolved in boiling alcohol, and allowed
to cool. The orange-red oil remains in solution, while the ela'idic acid crystallizes
in large, brilliant, white rhombic tables.  This body, when pure, fuses at 113~; it
dissolves readily in alcohol and in ether; these solutions redden litmus; when
boiled with a solution of carbonate of potash, carbonic acid is expelled, and elaidate
of potash formed; its earthy and metallic salts are insoluble in water. The crystallized elaidic acid has the formula C72116605+2 Aq.; it is a bibasic acid.  The
Elaidate of Silver is hence C72H660- 2Ag.().; and the Elaidic Elher, which is a
colourless fluid lighter than water, consists of C72-H6605n+H.O.. Ae.0.
The orange-red oil, which is formed simultaneously with the ela'idic acid, has not
been, as yet, accurately examined, and hence we cannot explain by precise formulae
the mode in which these bodies are generated.  It is this oil which gives to the
Citrine Ointment its characteristic colour and smell; it is lighter than water, and
dissolves in alkaline liquors, but does not form true soaps.
In the formation of citrine ointment, the conversion of the olein into elaidine is
effected by the nitrous acid which the solution of the mercurial salt always contains, it being formed by the deoxidation of the nitric acid, and there being nio heat
used to expel it.  The subnitrate of mercury is then mechanically mixed with the
elaidine and with the yellow oil. Some of the mercurial salt is often decomposed,
however, as metallic mercury may usually be detected interspersed through the
ointment.
Both oleic and elaidic acids give origin, when heated with fused hydrate of potash, to a peculiar fatty acid, discovered by Varrentrapp; it is white, solid, and crystalline; melts at 1440, and has the formula C32H13003+Aq.  There is formed, at the
same time, a large quantity of acetic acid.  Another point of connexion between
the oleic and ela'idic acids is, that by distillation both furnish sebacic acid.
The Acroleon, to which is due the exceedingly sharp and disagreeable smell of
highly heated oil or fat, is generated by the decomposition of the glycerine, and in
such exceedingly small quantity, that its isolation has not yet been successfully attempted. According to the observation of Brandes, it is a colourless oil, of sp. gr




ACTION OF SULPHURIC ACID ON MARGARINE, ETC. 587
0'578, which, when distilled with caustic soda, becomes inodorous, while the soda
combines with a fatty acid; no analytical investigation of it has been as yet made.
Action of Sulphuric Acid on _Margarine and Ole'ne.
When ole'in is mixed-with oil of vitriol, the sulphuric acid combines with both
the glycerine and the oleie acid, forming sulphoglyceric and sulphole'ic acids.  This
last is soluble in water, but insoluble in dilute sulphuric acid, and hence, by adding
water gradually to the mixture of oil of vitriol and oleine, it separates, floating as a
thick sirup on the surface, while the sulphoglyceric acid and the excess of sulphuric
acid dissolve.  The sulphole'ic acid thus obtained forms. with lime and harytes,
soluble salts, which are analogous to the sulphovinates; when its solution in water
is heated, it is decomposed, sulphuric acid becoming free, and the oleec acid being
converted into two acids, which. have been named the _letaoleic and the Hydroleic
Acidls.
These acids are both liquid like oleic acid; they are principally distinguished, as
to properties, by the sparing solubility of the former in alcohol, and are thus separated. The constitution of these bodies had been examined by Fremy at a time
when the true constitution of the oleic acid had not been established, and the forminula he assigned to them are not now admissible. They are isomeric with each other;
when distilled, they produce carbonic acid, and two volatile liquids, Olen and Elaen,
which are isomeric with olefiant gas.  From the circumstances of the formation of
these acids, the change must consist in the fixation of the elements of water, as no
other body containing carbon is produced; but, from his analysis, the anhydrous
metaole'ic acid has evidently the same composition as the hydrated ole'ic acid, and
its formula is therefore C44H4005 when in combination, and C44H4106 when free. Its
decomposition by heat consists in the separation of 3C.02, and C411H41 remaining,
which contains the elements of the two volatile oily liquids.
Withll margarine, oil of vitriol does not combine directly; but if margarine and
olein together, as they are in olive oil, be mixed with oil of vitriol, union occurs,
and a sulphomargaric acid is produced, which, being treated similarly to the sulpholeic acid, gives two other acids, the Melamargaric and Hydromararic.  These
are soluble in alcohol, from which they crystallize by cold, so combined as to produce distinct salts, and to affect all the characters of an independent acid, called by
Fremy the Hydromarngaitic.
If the mnixed solutions of sulphomargaric and sulphole'ic acids be left to decompose without heat, in place of being boiled, the metamargaric and metaoleic acids
separate and float on the top, but the hydromargaric and hydroleic acids remain
dissolved, and separate only by bringing the solution to boil. Each of the products
thus obtained is to be dissolved in alcohol, and the modified margaric acids crystallize on cooling, while the modified ole'ic acids remain dissolved.  The metamargaric acid is polymeric with the margaric acid; its formula is C6sH6606+2 Aq., but
the hydromargaric acid contains the elements of four atoms of water more, its
formula being C6SHo10010+2 Aq.
Ole'n of the Drying Oils.
The oils which possess the property of rapidly absorbing oxygen and evolving
carbonic acid, thereby being changed into a kind of transparent resinous varnish,
consist of glycerine united to a liquid acid, quite distinct from the ordinary oleic
acid; treated with nitric acid, it yields first a resinous substance, and then oxalic
acid. The drying properties of these oils is known to be much increased by boiling
on litharge, of which a quantity dissolves; in this case, however, Liebig has shown
that no saponification occurs; the litharge serving only to combine with, and coagulate a quantity of vegetable mucus, which, being diffused through the oil, prevented
its acting as rapidly on the air as it does when pure.
Of Cocoa-tallow and Cocoa-stearic Acid.
The albumen of the cocoa-nut contains a solid fat, which is extracted from it,
and imported largely into these countries, to be used in the manufacture of candles.
it is a mixture of ordinary olein with a stearine, which contains a peculiar acid.
The olein and stearine are separated by pressure or by ether, or by solution in boiling alcohol, from which the stearine crystallizes on cooling, exactly as described for
ordinary stearine.
The cocoa-stearine is white and crystalline; its specific gravity is 0 925; insolu



588          PAL M ITINE; PALMITIC I ACID,  ETC.
ble in water; it dissolves but sparingly in alcohol, except when boiling; it is moro
soluble in ether; it melts at 77~. The products of its decomposition by heat have
not been well examined. With caustic alkalies it forms soaps, from which, by a
stronger acid, the ocoa-stearic acid is separated.
This acid, purified by repeated crystallizations from alcohol, is brilliant white; it
fuses at 950, and cannot be distilled without total decomposition. Its formula was
found by Bromeis to be C7HZ2603+Aq.; its alkaline salts are soluble, but the earthy
and metallic, salts are insoluble in water. By the process described for oleic ether,
the cocoa-stearic ether was prepared by Bromeis; it is a clear oil, lighter than wi
ter; its formula is C27H2603-+Ae;O.
Palm Oil and Pai7mitic Acid.
This solid oil, which is now extensively employed in the manufacture of yellow
soap, is prepared in Africa, by.pressing and boiling the fruits of the cocos butyracea
or of the avoira elais; it is of the consistence of butter, reddish-yellow colour, and
an aromatic odour. When kept, it acquires a rancid smell, and becomes white;
the colour results from a small quantity of a substance which may be decomposed,
and the palm oil bleached by chlorine or any: oxidizing agents.  Besides ordinary
oleine, this oil contains a peculiar stearine, Palmitine, which has been accurately
examined by Fremy and Stenhouse.
Pure Palnmitine melts at 1180, and is crystalline. It is insoluble in water, very
sparingly soluble even in boiling absolute alcohol, but abundantly soluble in ether.
It is quite neutral; when saponified by potash, and the soap decomposed by an
acid, palmitic acid is set free. The palm oil of commerce usually contains a large
quantity of free palmitic acid, and hence is more easily saponified than any other
fat; it also contains free glycerine, so that the palmitine would appear to undergo
a spontaneous decomposition.
Palmitic Acid melts at 140; it dissolves in hot alcohol, and crystallizes therefrom
by cooling. Its formula in crystals is C64H6206+2H.O.; it is a bibasic acid; its
silver salt is C64Hs62062Ag.O. The Palmitic Ether, which may be prepared by
heating palmitic acid with alcohol and oil of vitriol, is solid, and crystallizes in fine
prisms, which melt at 70~, and have the formula C64HOs06+2Ae.O.  By distillation, the palmitic acid is not altered; by the action of chlorine, hydrogen is removed
from it, and an acid containing chlorine produced, the formula of which appears to
be C64H54 ~ C1806The constitution of palmitine was found by Stenhouse to be expressed by the
formula Co0H660s, from which should follow, that the substance united with the palmitic acid is formed of C6H402, and hence differs from common glycerine, C6H705,
in having lost the elements of three atoms of water. This would be a very important fact to reinvestigate.
Nutmeg Butter.  Myristic Acid.
This substance is a mixture of an aromatic volatile oil, with three fats, of Mwhich
two are easily soluble in alcohol, and are thus simply separated from the third,
which has been termed by Playfair Myristicine. Of the fats soluble in alcohol, one
is liquid and the other solid; but we do not know whether they are peculiar, as the
analyses of Playfair have been confined to the third.
Pure myristicine is obtained by crystallization from its ethereal solution; it lias
a silky lustre, and melts at 880. When saponified, it yields glycerine and Myristic
Acid. This substance is snow-white and crystalline, easily soluble in hot alcohol
and then reddening litmus; it melts at 1200; its composition is expressed by the
formula C28H2703Aq.; its salts are very well characterized and crystallizable.
The Myristic Ether is analogous in constitution to the stearic ether (583), consisting of
Two atoms of myristic acid, =C56Hs406, 
One atom of ether,        =C4HI50.,   One atom of myristic ether, C60H6008.
One atom of water,       — H.O.,
The myristicine was found by Playfair to have the formula C1sHs130jO, consist,
ing of
Four atoms of myristic acid, =C112Hl00sl2, f
One atom of dry glycerine, =-6H402,      ClsH13015.
One atom of water,       =-H.O.,
By distilling myristicine, much acroleon is generated, but no.sebacic acid.




BUTYRINEE   CAPROINEn  ETC.                             589
Ordinary Butter.  Butyric, Caproic, and Capric Aczds.
(ILttef is a mixture of six different fats, viz., common stearine, margarine, and
0leine, with butyrine, caproine, and caprine; by inciting the butter, and keeping it for
some days at a temperature of 68~, the stearine and margarine crystallize, while
the others remain liquid.  By means of alcohol, the ole'ine is then separated from
the other fats, which are more easily soluble in that menstruum; their farther purification depends on successive solutions in alcohol, but none of them can be considered as having been obtained completely pure.
Butyrine is a colourless oil, with the odour of heated butter.  It solidifies at 32~0;
with alkalies, it gives a soap, and sets glycerine fiee.  Its elementary composition
is not known.
Capro'ine and Caprine cannot be obtained sufficiently free from butyrine, or from
each other, to be described.
When butter is saponified, and the soap decomposud' by tartaric acid, stearic,
inargaric, and oleic acids separate, while the other acids remain dissolved. On distilling this liquor, the butyric, capric, and caproic acids pass over along with the
water, and, being neutralized by barytes, the three barytic salts are separated by
repeated crystallizations.  Of these acids, the history of the Butyric Acid is most
complete. It is a clear, oily liquid, of a penetrating, sour smell of rancid butter;
tastes pungent and acid, and leaves a white mark on the tongue.  Its specific
gravity is 0'976; its boiling point is above 2120; it burns with a brilliant white
flame, and is abundantly soluble in water, alcohol, and ether.  Its formula is
C7H603+Aq.; when distilled with lime, it gives a neutral volatile liquid, Buttyrone,
whose formula is C6H60. The Caproic Acid agrees in properties closely with the
butyric acid, but has a characteristic odour of sweat; its formula is C,2H903=-Aq.
The Capric Acid crystallizes in fine needles, which melt at 660, and have the formula ClsH1403+Aq.
Of Fish Oils, Delphinine, and Delphinic Acid.
These oils are generally composed of ordinary margarine, stearine, and oleiine,
but some, as whale oil and dolphin oil, contain a peculiar fat, Delplhinine, whiclh
yields Delphinic Acid. From the fish oil the delphinine is extracted by cold alcohol,
which dissolves it more readily than the other oils; it is liquid, of specific gravity
0'954; it is not acid, but becomes so by exposure to the air; it saponifies readily.
From the soap, the delphinic acid is separated by tartaric acid, And may be obtained
pure by distillation. It is a thin oil, of specific gravity 0'932; it boils above 2120,
and distils unchanged; it has a peculiar aromatic smell; tastes acid, and reddens
litmus strongly; it dissolves in twenty parts of water; its formula is CoH90sO3Aq.,
and when distilled with lime, it gives a volatile neutral liquid, Delphinon, (G9HsO.
Ths3:lphinic acid has been found in the berries of the viburnum opulus, and its
composition being the same, and its properties very closely resembling those of the
valerianic acid, I think it verv likely that a re-examination of it would demonstrate
its identity with that remarkable vegetable acid.
Of Castor Oil and its Products.
The oil of the ricinus communis (castor oil) is, according to lecanu and Bussy,
a mixture of three fats, ricino-stearine, ricino-oleine, and ricine, which are all easily
soluble in alcohol. ILike the fats of butter, they can be but imperfectly separated;
but, when saponified, they yield acids, which can be more accurately examined:
the soap, being decomposed by muriatic acid, yields an oil, from which, by cooling,
the Ricino-stearic Acid crystallizes, and the remaining oil, when distilled, separates
into the Ricinic Acid, which passes over, and the Ricin-oleic Acid,,which is not volatile.
Purified by recrystallization from alcohol, the ricino-stearic acid forms pearly
scales, which are easily soluble in alcohol, redden litmus, and do not melt below
266fi0. The ricin-olei'c acid freezes a few degrees below 320. The ricinic acid is
solid and crystalline, melts at 71~, and distils unchanged at a temperature but little
higher.
When castor oil is acted on by nitrous acid, it is converted into a solid substance, termed by Boudet Palmine; it is white, of a waxy appearance, and melts at
1510; it is easily soluble in alcohol and ether; with alkalies, it yields glycerine
and Palmic Acid. We do not possess any knowledge of the elementary composition of these bodies.




590                MANUFACTURE  oF  SOAP.
The products of the complete oxidation ot castor oil by nitric acid have been accurately examined by Mr. Tilly. The action is violent, and much nitrous acid
fumes are given off. Besides suberic and lipinic acids, a peculiar fatty acid is
formed, which is colourless, of an agreeable smell, and a sweet, stimulating taste;
it boils at 300~, but cannot be distilled without being in great part decomposed.
Its formula was found to be C,4H1303+Aq.; he formed the ether of this acid in the
way described for oleYc ether, and ascertained its foirmula to be C,41-1303+Ae. 0. This
body is termed the Pcercnanlhic Acid, as it contains the same carbon and hydrogen
as the oenanthic acid which exists in wine, as described in page 567, but combined
with an atom more of oxygen.
Oil of Tiglium. Crotonine. Crotonic Acid.
The experiments that have been made on this oil have not given very satisfactory results: by saponification, it yields an acid which is exceedingly volatile; but
whether the active properties of the oil reside in this crotonic acid is not established, nor have any analytical results been obtained as to its constitution.
Of the Manufacture of Soaps and Plasters..
Although the general principles of the constitution of soaps have been
frequently alluded to in the description of individual fattv substances, and
a detailed account of their manufacture would be out of place in the pres.
ent work, yet it may not be uninteresting to notice briefly some cir.
curmstances of the processes employed, which could not be deduced from
the mere theory of their nature, and yet are essential to practical success.
There are found in commerce three varieties of soap: 1st, hard white
soap, which is made from tallow and caustic soda; 2d, hard yelloue soap,
which is made fiom soda with tallow, palm oil, and resin; 3d, soft soap,
in which the alkali is potash, combined with whale or seal oil, and some
tallow.  The difference of consistence depends principally upon the alkali; as the fatty salts of sodaunite with water to form  true hydratcs,
which are completely solid, while the potash salts absorb water, and form
a semitransparent gelatinous mass, such as is the ordinary soft soaip.
For the preparation of the hard white soap, a solution of caustic soda
is prepared, of specific gravity 1'050, by decomposing sodal-ash by the
proper quantity of lime; the soda ley being brought to boil, the t;allow
is added in small portions at a time, until the free alkali has been all
combined with fatty acids, and the ley will saponify no more.  The liquor contains then free glycerine, and the fatty salts of soda, all dissolved
together in the water; and as the soap scarcely crystallizes, a peculiar
method is necessary to separate it from  tie solution.  This is founded
on the fact that soap is insoluble in a solution of common salt.  If to a
solution of' soap in water, as much common salt be added as the water
can dissolve, the soap is separated, and floats on the surface of the li.
quor comrnletely deprived of water.  But this is not the state in which
the manufacturer wishes it to be.  Hence the salt is added but gradually
to the soap-ley, and the water then diviling itself between the salt and
the soap, a point is obtained at which the soap is in its proper }hydrated
condition, and this being recognised by the appearance of thee boil and
the texture of the layer of soap, the latter is run into wooden boxes, where
it congeals, and is then cut by a wire into the forms it has in cornmerce.'rhe hard white soap thus made gen'erally contains from forty to firtv
per cent. of vater.  When very hard it still retains above thirty, and
maylv hold seventy per cent. without being very soft.
Thie forimation of the Yellow. or Resin Soap. depends on the direct
combitmation of an acid resin (cololhony, p. 578) with soda.  In this




S P E R.RA C E T I.-E T HA L.                     591
case no glycerine is set fiee, as there is no proper saponification. I A
mere corrmpound of' resin and soda would be, howe ver. too soft, anl-d also
act too powerlully on clotbles; and hence there is always a quantity of
fat added, generally tallow, and sorime palm oil, which brightens the col.
our, and lmalsks the disagrceable odour of' tile resin.  A good soap should
contain tlwo parts of' fatty matter to one of resin.'1'he Soft Soap is mantlufictured by heating the oils hi shallow pans,
and Igradually addting a strollg solution of. caustic potash, boiling and con.
tinuailly agitatitng thie mass until the milkiness produced by the oil va;lnishes, the nmass becolnes transpuarelt, and the froth subsides..As this
soap cannot be separated fromt the liquor by the addition of' cornmiln salt,
which would decompose it, folrming a soda.soap and chloride of' petassi.
urn, the liqulor is evaporated until the operator recognises that it htas at..
tained the proper strengttl, and it is tlihe  cooled as rapidly as possi)ble.'The glyceritne of the oils exists, threfore, mixe(l through tile substatice
of tile soap.  To give it ogreater consistence, sonie tallow is generally
employed; and tle stearate of potasll crystallizing gradually, forms the
white p)oints which are seen in most sp)ecimens of soft soap.
Pltasters are metallic soaps.  Of these, tile only one of' pharnlaceutic
importance is the Littarge' Plaster, preparted by boiling lith;rge. olive toil,
and water together; oleate and margarate of' lead are firnmed, and float
upon tlhe surface; when the miass has obtained tlhe proper consistence,
it is removed, and formed into rolls for use.  The watery solution contains glycerine and a large quantity of oxide of lead dissolved.  If lith.
arge plaster be digested in ether, oleate of lead dissolves, and the mrargarate of lead is left behind.
Of Spermaceli, Ethal, and the derived Bodies.
Spermaceti exists in the cavities of.the head of the physeter macro.
cephalus, and sortime allied species of  whales, dissolved in thle sperlmalccti
oil, from which it separates by crystallization after the death of' tlhe anitmral.  To obtaitl it pure, it is to be crystallized repeatedly fi'om  its alcoholic solution by cooling; it is a remtarkably beautiful crystal liine lit,
melting at 120~, and volatilizing at 6800 without change, if' the air be
excluded.  By boiling with very strong alkalinr  solutions, it giradua:llv
saponifies, a margarate and an oleate being fbrmed; but. in place of
glycerine, a peculiar base, which is termed lEthal, beinlg set fret.  To
obtain it pure, spermaceti is saponified by being) lfused with hllf' its
weight of potash; the resulting nmass beiing digested witli water artd In.
riatic acid, the oily acids and the ethal separate from the liquor aind float
upon tile surface.  Being then mixed with lime, which comlbi e: s witlh thle
oily acids, and boiled in absolute alcohol, the ethal dissolves, and cryvstal.
lizes out on cooling.
It is a solid crystalline white substance, destitute of taste or smell;
neutral to test paper; it melts at 119', antd vola.tilizes rapidly mat 250 ~;
it is insoluble in water; its folmula is C32s402, 01o C32H1330+.   Aq.''he
spe rnmaceti itself consists of
2 atoms of margaric acid, =C68H66Os,  Co086Ha0O7c, one equivalent
I atom of oleie acid,  -C41t-C13()4    2    O  one equrmaceti
3 atoms of ethal,      =C9H06              of spermaceti.
The ethal is remarkable for its analogy, in composition and propertiess
to the bodies of the alcohol group; like them, it nlay be looked ul)on as




592 WAX,  CERINE) MYRICINE, AND  TARTARIC ACID.
formed of water united to a ca.rbohydrogen, isomeric with olefiant gas,
and by distilling ethal with glacial phosphoric acid, this body is actually
obtained, and has been termed Cetene.  It is an oily liquid, colourless,
soluble in alcohol and ether; it boils at 5270.  From  its reactions and
the specific gravity of its vapour, 7846, it results that its formula is
C,2H32:
If ether be heated with perchloride of- phosphorus, a heavy liquid is
obtained, having the formula C32HE1C1l.; and by fusing ethal with potassi.
um, hydrogen is evolved, and a white solid substance formed, consisting
of C32Ha330.+K.O., which, wvith water,,gives hydrate of potash and ethal.
With sulphuric acid ethl forms sulphoethalic acid, which resembles the
sulphovinic acid, and has the fiormula CQ32IT30.. S.03-S.03. H.O.
Farther, if the ethal be heated with potash, hydrogen gas is given off,
and an acid formed, the formula of which is CJ32L103+Aq.: it is termed the Etlalic Acid.
From this analogy of ethal to wine.alcohol, a compound radical, Cetyl,
similar to ethyl, may be assumed to exist in these combinations, and its
formula be written C3JHI  or Ct.  Ethal is then Ct.O.+Aq.  (See p.
566.)
Wax. —Ordinary beeswax is a mixture of two substances, which are
separated by boiling alcohol.  Cerine dissolves; it is quite white; its
specific gravity is 0'969; it is less fusible than wax; it does not combine
with bases; its formula is C~2I2002. The substance insoluble in alcohol
is Myricine, which melts' at 950 ~; its formula is C20H,200. In yellow wax a
colouring matter is present which has not been examined.  When wax
is bleached by nitric acid, oxygen is absorbed, and a peculiar substance
formed, Ceraic Acid, which has the fo'rmula C20Hi2003.  All these bodies
are probably derived from oils, isomeric wvith otto of roses, which exist
in the flowers of odoriferous plants.
When cerin is boiled with solution of potash, a soap is formed, and
from this a peculiar waxy substance (Ceraine) is obtained, as ethal is from
spermaceti: its properties are but very little known; from an analysis
by Ettling, its formula would appear to be CIsH9,07.
CHAPTER XXIV.
OF THE ORGANIC ACIDS WHICTI PRE-EXIST IN PLANTS, AND DO NOT BELT,AO4
TO ANY ESTABLISHED SERIES.
Tartaric Acid.-CH40,,,-2 Aq.
THIS important acid exists in most kinds of fruit, occasionally free, but
more usually combined with potash, forming cream of tartar, or as tartrate of lime. For the purposes of commerce, it is almost exclusively
prepared from the bitartrate of potash.  This salt exists abundantly in
grape-juice, and being but very slightly soluble in spirituous liquors, it
gradually separates as the alcoholic fermentation proceeds, and collects
in irregularly crystallized layers on the insides of the casks in which the
wine is made. It is purified, as will be elsewhere described.




TA RTARIC  ACID.-CREAM  OF  TARTAR'R.    593
~When one part of carbonate of lime is added to a solution of four parts
of bitartrate of potash, one half of the tartaric acid combites with the
lime, carbonic acid being expelled with effervescence.'artrate of lime
precipitates as a white powder, and neutral tartrate of potash renmains
dissolved. By the addition of chloride of'calcium to the liquor, this portion, also, of tartaric acid is thrown down, and chloride of potassiium is
fornied. The whole quantity of tartrate of lime being then collec1ted and
washed, it is to be digested with a quantity of oil of vitriol, half the
veighit of the cream of tartar employed, and diluted witl tfour parts of
water; sulphate of lime is formed, and tartaric acid set free. The mixture, hiaving been boiled for a shlort time, is to be strained, arid the liquor
evaporated gently to a pellicle; the tartaric acid then crystallizes on
cooling.
The tartaric acid forms colourless oblique rhombic prisms, generally
tabular, as in the figure, where i, u, u are primary, and.-..
a, c, m secondary faces; it is permanent in the air, and', i
dissolves readily in half its weight of water; it is also? — <-:-'-.
easily soluble in alcohol; its taste and reaction are  N          t 
strongly acid.  When heated, it abandons water, and
forms two acids which will be again noticed.  When a solution of' it is
long exposed to the air, it absorbs oxygen, and forms carbonic and acetic
acids. This effect may be instantly produced by boiling it with an excess of oxide of silver, metallic silver being set free.
Tartaric acid is known by its not being volatile, and by leaving a co.
pious coaly residue when heated.  If it be fused with potash, it is de.
composed, acetic and oxalic acids being produced (p. 475); with other
oxidizing agents, as black oxide of manganese and sulphuric acid, it gives
carbonic and formic acids. A solution of tartaric acid precipitates lime.
water, but the precipitate is redissolved by an excess of acid or by solution of sal ammoniac. The soluble neutral tartrates give white pre.
cipitates, which are not crystalline, with the neutral salts of lead, lime,
and silver, which all redissolve in an excess of acid.
The tartaric acid is bibasic, its formula being CJH40,o+2 Aq.; sev
eral of its salts are of considerable importance.
Bitartrate of Potash.  Credm of Tartar.-C1H,o04+ K.O.Aq.
This salt, just now noticed as being deposited from gr-ape-juice, accord.
ing as alcohol is formed, is sent into commerce under the name of Argol,
which is red oi white, according to the kind of wine it was deposited
from.  This is dissolved in boiling water, and mixed with some pipeclay, which, combining with the colouring matter of the grape, renders it
insoluble; the clear liquor is then allowed to cool slowly, and the cream
of tartar is deposited in irregular crystals on the sides of the vessel, still
containing a small quantity of tartrate of lime.  It crystallizes in right
rhombic prisms, as in the figure, p, u', u being primary,
and a, a', i, m secondary planes. It is but very sparingly    
soluble in cold water, requiring 80 parts at 60~, and 7     inZ
parts at 2120; hence an excess of tartaric acid produces
a crystalline precipitate in solutions of potash which are
not very dilute. By calcining cream of tartar either alone or with nitre,
the black or white fluxes employed in metallurgy are formed (p. 334). ~Its
4 F




594    TARTRATES  O-F. POTASH, A-M M ON I A E.T E.
calcination filrnishes also the purest source of carbonate of potash, -which
hence derives. its name of Salt of Tartar (p. 487).
Neutral Tartrate of Potash.  Soluble 7Tartar.-CH0,o+ K..O. K.O.
This salt is formed by adding cream of tartar to a ihot,.solutio ) of carbonate of potash, until this be completely neutralized.  It crystallizes
with difficulty in right rhombic prisms, which, when pure, are not (icli.
quescent.  100 parts' of water dissolve 130 parts of it at 60~, and 2268
paurts:at 212~.  Any acid added to its solution takes half the- p)tash, and
prec ipitates cream of tartar.
The  Tartrates:of Ammonia resemble closely those of potash.  The
neutral Tartrate of Soda crystallizes in large rhombic prisms like nitre;
it is very soluble ia water; its;formula is C8H401,0+Na.O.~.  Na.O.
+-4 4Aq.
Tartrate of Potash and Soda. Rorellle Salt, C81-140,o 
K.O.. Na.O.+lO Aq., is prepared by. neutralbzing. a'hot
Kie e'.!solution of carbonate of soda with cream  of tartar: by evap-..oration, and cooling it forms. large prismatic'crystals, with
many  sides, of the right rhombic  system, p, u, u being
primary,  and i, i, t, e, e being secondary faces.  These:crystals are remarkable for being often but half formed, so
as to present the aspect represented. in the lower figure.
i:'    - Its taste is mildly saline, and not very disagreeable,. whence;..J Ah  its popularity as a medicine.. It is permanent -in thle air except it be very dry, when it effloresces slighttly at the sur.
ftce; it dissolves in two parts of cold water.:
The Tartrate of Lime is very sparingly soluble in water, and is precipitated as a;
white powder,'when solutions of a neutral tartrate and of a salt of lime are mixed.
It dissolves in an excess of acidl; and if this solution be neutralized, it is deposited
in small octohedral crystals, which have the formula C8H40lo+Ca-.O. Ca.O. —8
Aq. Nalner has asserted that, when tartrate of lime is mixed with yeast, a fermentation sets in, by which a-new acid, Pseuzdo-acetzc Acid, is produced.; this requires,'
however, confirmation.
JProlotartrate of Iron, CsH400o+2Fe.0., is a white powder, very sparingly soluble in water; it is foirmed in minute crystals when hot solutions of protosulphate of
iron and of cream of tartar are mixed together. The Prototartrate of Iron and Potash, CsH4010+.-Fe.0. K.O., is formed by digesting cream of, tartar and water with
metallic iron. Hydrogen gas is evolved, and a white, sparingly soluble salt is obtained-, which, when exposed to the-air, rapidly absorbs:oxygen, and becomes greenish. brown or black. In this state it contains mhgnetic oxide of iron, and is much
more soluble;Pertartrate of Iron; formed by dissolving the freshly precipitated red
oxide of iron in a solution of tartaric acid, giveshby evaporation a brown jelly  If
the red oxide of iron be boiled with a solution of cream of tartar, it dissolves abutndantly, giving a fine brown-red liquor, firom which, by cautious evaporation, small
ruby-red crystals may be obtained; but it is generally dried, downcompletely, when
it forms a translucent brown mass, deliquescent in damp air. An excess of tartaric
acid sh1ould be avoided, as  it- acts on the peroxide of iron during the evr.poration,
reducing it to the state of protoxide, and carbonic acid being given off.  Ilnce the
pharmacopoeias direct perfect neutrality of the liquor to be secured by the aldditiao
of a small quantity of ammonia. The formula of this salt is CsH4400o+K.O...Fe"Os.
It is very soluble in water, and its soluition is not precipitated by an excess of.pot;:sh.
Tartrate of Antimoany. 3(Ca3H40o)+Sb.03.  This salt is obtained by the solution
oftihe sesquioxide of antimonhy in tartaric acid; it is colourless, and crystallizes in
short deliquescent prisms.
Tarlrate of Potash and Antimony..Tartar.Emetic.-C81C,,+ K. O.,
Sb. O3+2, Aq. - This salts, a most important compound of- antimony; is
prepared: by boiling together in water' equal weights of sesquioxide of
antimony and cream  of tartar.  In the Dublin and Edinburgh pharma



PRO PIERTIE S OF  TAR T A R-E   E T I C.                595
Colraias, the Powder of A.garotti (p, 453)is' employed:as the source of
oxide of antimony, but by the Lontdon ocollege'an impure oxideo is pre.
pared, by gently deflagrating together sullhuret odf antimony and nitre
with a little muriatic acid, and washing out the soluble products.  In
eitlier case the Oxide of antinony replaces the second atom  of base
(water) in.the cream  of tartar, and by evaporation and: cooling. it may
be obtained in crystals, which are right rhmrnbic octohedlons, with many
secondary planes, as in the figure.o  This salt dissolves
in fourteen parts of cold and in two of' boiling water.
In dry air it etfloresces, losing the 2 Aq.-Its solution is
not affected by alkalies; but the -oxide of antimony is
precipitated by sulphiuric or muriatic acids,' and by am-i
monia.  In tlhe preparation of tartar-emetic, the whole:
product, from the materials used, can never be obtained
crystallized; the mother liquor cottains a substance
which dries; down to a transparent mass, like gum Ara-'
bic.  By alcohol it is decomposed into tartar-emetic andffree ta rtaric acid.  According to Knlapp's ia'nalys;is,- this 
salt is the neutral tartrate o.f potash and an timitony,  having the formula
C4H.O1.0  K.O.-(;:3C4HO5+Sb.03)-+2 Aq.'It- may be: firmed by dissolving. tartar-emetic in  a- strong solution of' tartaric acid, and then crystallizes in minute oblique rllombi c prisms.  -In order to form:thins salt,
h6wever, fronl- creanm of tartar and: oxide:of antimnony, a quantity of
potasll must enter into some form of cornbination, which has not been
explained.
Owing, to the occasional presence -of arsenic in tile 0ores of antimony,
the tartar-emetic of commerce is not -unfiequently contaminated bby its
presence, and should, in such case, be absdlutely rejected from  medicinal use.
If tartar-emetic be exposed-to a temperature of 4803, it abandons, besides its crystal-water, two equivalents of' water, the elements:of which
are abstracted firom  the constitution of the tartaric acid as generally
assumed.  In this dried tartatr.emetic-thierefore, the organic element is
not CH4010, but C8H2Os.:  When redissolved, in water. it resumes thie
two atoms of water, forming ordinary tartaeremetic' again.. Of the other
salts:of tartaric acid, but one possesses this p:rope:rty, the boiotartrate
of potash  being also reduced' by loss' of water at 480~ to the forn mula
C8112O08+K.O.. B.03.  Chemists are not unanimous in explaining this
)peculiarity.  The:simplest idea is, that these two atoms of water exist
ready  fo rm ed in these salts, and: that tar t:aric acid is really quad ibasic
being, -in its cystallized firm,' C8H2Os+44H.O.  -the: cream  of tartar
beirig C8H,20-+K.O.  3H.O.; llochelle salt, (H. 08-+I(.O. - Na.O.  2
0-.-;-and for tartar-emetic, the oxide of antimnony rep'acing three atoms
of a protoxide, the formula is C8H2,O,+K.O.. Sb.03+2 Aq.+2 Aq., and
the two portions of watei- btei:lg'retained by;vely une-qual forces, tire given
ofTat vet)' different tetperatues.  Be rzelius considers that' in this change
the naature. of the- acid: i:is t otal y altel ed; and as opinion is so much divided
on thetsubiject,':  shill:1not' enter tallithc  ihtor its discussion.-:
Action of: feat on Tarlaric- Acid. -When: taitari:; aeid is  autiously heated, it filses
into(} a mass like. gum,.and;gives- off water.:.In-l this'state; it. combines with b'ses,
foriming' salts quite d(tiferen' t from the tartrates; it.retains its hbibasie character, but
its a(toluic weight is increased to one and a Wa'If times that of taitaric acid, its formula being Cltl60s+2 -~1 Aq. It thus constitutes Tartralic Acid; it does not crys



59 3.         RACEMIC.ACID  AND  ITS SALTS.
tallize, and in solution gradually passes back into tartaric acid. If the tartralic acid
be kept long melted at 3600, it abandons still more water, and forms Tat'relic Acid,
in which the bibasic character remains, its formula being C,6Hs02o+2 Aq. T'his
acid is characterized by fornmiig insoluble salts with lime and barytes, thereby differing fromt the tartralic acid. If the heat he still longer kept up, a porous white
mass is lbrmed, which is insoluble in water and in alcohol. It is Anhydrous Tartaric Acid; its formula is CsH4010. If left long in contact with water, it changes
successively into the tartrelic, tartralic, and common tartaric acid. This change is
produced niore rapidly by boiling with a solution of potashl: this substance appears
to hold the same relation to tartaric acid that the white sublimate does to the proper lactic acid (p. 536).
If tartaric acid be distilled at a still higher temperature, it abandons water and
carbonic acid, and forms. Pyrolartaric Acid, C-H4010 giving off 30 02 and H.O.,
and C0H303 remaining. The process succeeds best at about 40()~. This acid is
white; it crystallizes from the distilled liquors in prisms, which are to be purified
from empyreumatic oil by recrystallization and digestion with animal charcoal; it
reacts very acid; it melts at 210~, and sublimes at 3600; is very soluble in water
and alcohol. It is a monobasic acid, forming salts which, with few exceptions, are
soluble and crystallizable.
Racemic Acid.-8CH140, o+2.Aq.  This acid is found in grape.juice,
replacing tartaric acid to a greater or less extent; its formation alppears
to depend on very peculiar circumstances, as it has never been lound
except in the district about the Vosges Mountains, and only in some sea.
sons.  It is combined with potash, forming a kind of cream  of tartar,
which is biracemate of potash, and from which it is prepared by the
same methods as have been described for tartaric acid.
It crystallizes in colourless oblique rhombic prisms, which contain
water, of which one half is lost by efflorescence in warm  dry air; the
remaining hydrate is identical in composition with crystallized tartaric
acid; it tastes and reacts as strongly acid.  In its relation to salts, it
follows exactly the same rules as the tartaric acid, but their crystalline
form  is completely difiberent; it is a bibasic acid, and its formula, when
crystallized, is CsH40,o+2H.O.O.+2 Aq.   The characters by which it
is distinguished from  tartaric acid are, first. racemnic acid requires ten
times as much water for solution, and they are hence easily separated
by crystallization.  Second, that the corresponding salts are not of the
same crystalline form.  Third, the racemate of potash and soda is uncrystallizable, givilng merely a gummy mass, while the Rochelle salt
forms very large crystals.  Fourth, the racemate of lime is insoluble
in a solution of sal ammoniac.  The two acids, however, form a most
perfect example of isomerism, as not merely their composition, but their
atomic weight is absolutely the same.
When heated, racemic acid passes through precisely the same changes
as have been described for tartaric acid, abandoning water, and forming
bibasic acids, whose formulae are respectively C,2H160,5-+2H.O. and C,6
H8O20+2HI.O.. They are distinguished by their salts, which differ in
characters from each other, and from those of the bodies formed by tar.
taric acid.
By the destructive distillation of racemic acid is generated the Pyroracentric Acid, in which the isomerism  with the tartaric acid series is
broken through; its formula being C6H305.  It differs totally in proper.
ties from the pyrotartaric acid; it does not crystallize; it tastes acid(; its
salts are all soluble and crystallizable, but pass also into a gummy condition.  If a little crystal of copperas be laid in a solution of one of these
salts, it becomes coloured bright red.




CITRIC ACID AND ITS SALTS.                             597
Citric Acid. —C1,H2,0+3H.o.+2 Aq.
This acid exists in the juices of fruits, especially the lemon, orange,
currant, and quince.  It is usually p4epared fiom  lemon-juice. which is
clarified by rest, then saturated with chalk, and the neutral solution is
boiled until the citrate of lime is completely deposited; this is then wash.
ed and decomposed by a quantity of oil of vitriol, equal in weight to the
chalk employed, and diluted with six volumes of water.  After the sul.
phate of lime has been removed by straining, the liquor is evaporated,
and allowed to crystallize by very slow cooling; its form  is generally
that of a right rhombic prism, very much modified, as in the figure,
where i, u', u are primary, and n', y, r are secondary planes.
In this case its formula is that given above; but if its solu.
tion be evaporated at 212~ to a pellicle, it crystallizes while    i;l
hot in a totally diffbelent form, and its formula is then Cl2  
HoO,1+33H.O.  By exposing the hydrated crystals in vacuo
to sulphuric acid or to a gentle heat, the 2 Aq. may also be removed.
The citric acid possesses an agreeably sour taste; it dissolves in less
than its own weight of cold, and in half its weight of boiling water; it is
sparingly soluble in alcohol; when heated, it fuses, becomes yellow, and
ultimately gives the uswal pyrogenic products of organic acids.  It is a'
tribasic acid, and gives rise to three classes of salts; and, as these contain different quantities of combined water, their history was very confused until Liebig explained their true constitution.  Very few  of these'salts are, however; of practical or medicinal interest.
Citrate of Soda crystallizes in efflorescent prisms, having the formula Cs2HoO+
3Na.O.+4 Aq.+7 Aq. By exposure to a heat of 2120 the 7 Aq. are removed,' and
at 400~ the remaining 4 Aq. are driven off: Berzelius is of opinion that in this action the real constitution of the citric acid is changed, and that it is partly converted into aconitic acid; but the point is not yet experimentally decided, and Liebig's
views explain the phenomena with such beautiful simplicity, that I have no hesitation in adopting them, at least provisionally.
The Citrate of Lime is obtained by mixing solutions of a soluble citrate and of a
salt of lime; it forms a white powder, sparingly soluble in pure water, but much
more so if the liquor be acid. Its constitution is C12H501nl3Ca..+4 Aq. When
boiled with an excess of lime-water, citric acid forms a basic Citrate of Lime, which
is less soluble than the neutral salt.
The Citrates of Lead and of Barytes are white powders, insoluble in water, formed by double decomposition, and resembling in constitution the citrate of lime;
there are also basic salts, the formation of which, as in that of lime, appears to result from the crystal-water (2 Aq.) of the acid being more or less replaced by metallic oxide, in addition to that which fulfils the proper basic function.
The citric acid is easily recognised by forming no precipitate with lime-water unless the liquor be heated, Its potash salt is also very soluble, even with an excess
of acid; it is thus distinguished from the racemic and tartaric acids.
When citric acid is heated, it fuses, gives off water, and is converted into an
acid, which, from being found in the aconitum napellus, is called Aconitic Acid, but
it exists also abundantly in various species of equisetum, and is hence often called
Eqiuisetic Acid. To complete the change of the citric acid, it must be distilled until the gases which come over cease to be inflammable, and oily drops appear in the
receiver; the process is to be then interrupted, the mass remaining in the retort to
be dissolved in water, the solution filtered and evaporated to a pellicle. On cooling, it forms a crystalline mass, from which ether dissolves out the aconitic acid,
and leaves unaltered citric acid behind; the former may then be obtained crystallized by evaporation.
Aconitic acid is soluble in water, alcohol, and ether; its formula is C,2H309+
3 Aq.; like citric acid, it is tribasic; it forms well-characterized salts: the aconitate of ether had been mistaken for citric ether; for, when citric acid is put in con-,act with alcohol and oil of vitriol, it changes into aconitic acid.




598             MA.LIC ACID AND ITS SALTS.
If aconitic acid be heated until it boils, it gives off carbonic acid, and forms ita.
konic Acid, which distils as an oily liquid, and forms a -crystalline mass as it cools;
by solution in alcohol and slow evaporation, it may be obtained in long prismatic
needles; its lsalts, of which there are two classes (it being bibasic), generally crys-,tallize-very-well.; its formula is:C0oH06+2 Aq.; foirme:l by the aconitic: acid lpsing
C204, ibut ani atom of waterj previously basic, entering into the organic. element.
When.the IltakoniG Acid is redistilled, it is converted into water and a heavy oily
liquid, Citrakonic Acid, the formula of which is C0oH1130-j-Aq  In contact with water, it forms a crystalline mass containing 2 Aq.
-All these products are-simultaneously and;successively formed in the distillation
of common citric: acid.'Acetone;isa.lso generated, CI.H,20:u1 giving 3(C3H30.),. with
3H.O. and 3(C.02).
Malic.lcid.-C8H08+Os  2H.O.:This. acidexists in most fruits, associated with citric and tartaric acids,
but is. found purest and most abundant in the berries of the mountain ash
and in.the houseleek.: The. best mode of extraction is the following, devised by Liebig.  The juice of the berries of the mountain ash (sorbus
aucuparia) is to, be nearly, but not completely, neutralized by. line, and
the liquor then boiled for some hours, during which the. malate of limee
precipitates as a sandy white powder; when no more falls down, the
neutralization is completed by adding a little more lime, and on cooling,
the remainder of the salt is obtained.  This m~atte of lime is to be dies.
solved by boiling in the smallest possible quantity of very dilute nitric
acid,  On cooling, the. acid malate of lime crystallizes, and is to be:purified by recrystallization.  This salt being then decomposed by acetate of lead, malate of lead is formed, which, being acted on by sulphuretted hydrogen,  gives sulphuret of lead and free malic acid; by evapo
ration of the liquor and cooling,:a sirup-thick liquid is obtained, which,
after long repose, forms a white crystalline mass.
Malic acid is deliquescent, and very soluble in water.  It tastes and
reacts.strongly:acid; its relations to bases are very curious; thus mag.
nesia is the only earth by whose carbonate it can be completely neutral-;zed.' This arises from its tendency to form salts, in which one atom of
basic water is preserved, it being a bibasic acid.  Another peculiarity
pointed out by Hagen is, that it forms with many bases two neutral salts,
of which one retains water with obstinacy at 212~, at which tempera.
ture the other at once abandons: it. When crystallized it appears to con.
tain only basic water; its formula is hence C8H408+2 Aq.  None of its
salts are:of technical.o'r medicinal interest, and hence require but brief
notice.
-..The lalkaline malates are very soluble in water, scarcely crystalliza.
ble, sparingly soluble in alcohol.'The Malate of Lime forms as a granular white precipitate when malic acid is
neutralized by lime. Its formula is C8H408+2Ca.O.; it separates in hard, brilliant
crystals, which contain 5 Aq., when the-following salt is neutralized by an alkaline
catbonate. Bima.late of'Lime,' CsH4Os+Ca.O.. H.0. —6 Aq., crystallizes in large
right, rhombic octohedrons. Water dissolves it abundantly when boiling, but very
sparingly when cold..The Malate of Lead,' CsH840s2Pb.O., precipitates, on mixing solutions of a soluble malate with. acetate of lead, as a white curdy mass, which, after' some time,
changes into minute but brilliant crystalline scales. By boiling in water, a small
quantity of it is dissolved, which separates in brilliant plates on cooling. It fuses
below 212~, and is then nearly insoluble in water.
Malic acid is distinguished both from tartaric and citric acids by not giving any
precipitate with lime-water either by heat or when cold.
*When mealic acid is heated to a temperature of about 4000, it abandons water and




MECO NIC  ACID'A-ND  IT'S  SALTS.                          599
~*gtves origin to two.acids, of which 6ne. is remarkable as being found- naturally existi.ng-in several plants.  They are the Maleic Acid and the Famaric Acid, the latter
-.so called firomnl having.been first discovered in the fumnaria officinalis. These acids.are. isomeric,- the reaction being in both cases that CsH408 produces. 21.0. and
*CsH.206.: Both acids may be formed in the same process;'the maleic acid passes
over with the water, and crystallizes from the condensed liquor; the less volatile.fumiaric acid constitutes the residue in the retort, which solidifies into a crystalline
mass as it cools.  From the plants which contain this acid, it may be obtaihed by
precipitating the clarified juices by acetate of lead, and decomposing the salt of lead
by sulphuretted hydrogen.  The liquors yield the acid by crystallization when concentrated to the necessary degree.
Tlie Mdlcic Acid, which had been thought identical with the Aconitic Acid, already noticed,:forms crystals of a sour, bitter taste, soluble in water, alcohol, and
ether. When heated, it abandons water, and the anhydrous acid:remains, which,
if the water be allowed to flow back, gradually changes into fumaric acidi. This
anhydrous acid melts at 167~, and sublimes at 350~. Of its salts, that of harytes
alone is remarkable; it is a white precipitate, which changes soon into a mass of
brilliant plates.
The Fumnaric Acid, which exists also in Iceland moss, crystallizes in fine long
prisms, which fiuse with difficulty, and volatilize first at 400~.  It requires 200 parts
of water for its solution. When heated, it is decomposed' into water and anhydrous
maleic acid. The fumarate of silver is so insoluble, that one part of the acid, dissolved in 200,000 parts of water, is precipitated by nitrate of silver, but the precipi*tate dissolves in nitric acid. The salts, with copper, iron, and lead, are also very
sparingly soluble.
When muriatic acid gas is passed into a solution.of malic acid.in absolute alcohol, Hagen fbund that the ether formed contains fumaric, and not malic acid. It is
a liquid, heavier than water, of an agreeable smell. With potash it gives alcohol
and furnarate of potash. - Its formula is C4H.O3+Ae.O.  On adding water of, amnmonia to this ether, a substance is deposited in brilliant white scales, insoluble in,cold water.and in alcohol, but dissolved by boiling water.- It is Fl'uzrrnia.mid, its
formula being C4H.. 02Ad. By potash, ammonia is set free, and fumarate of potash
formed.
Meconic Acid.-C,4H.O,,+ 3IH.0.+ 2 Aq.'This acid is found. only in opium-; it is best extracted by adding chloride of calciuni to an infusion-of opium in cold water. A white precipitate of mixed meconate
and sulphate of lime occurs. This, being washed with hot water and with alcohol,
is to be treated with dilute muriatic acid, heated to about 180~. The meconate of
lime dissolves, and, from the liquor on. cooling, bimeconate of lime separates in'brilliant crystalline plates.  On dissolving these in warm, strong muriatic'acid, and
cooling the.solution, the pure.meconic'acid crystallizes. It may be freed from any
adhering colouring matter byocombination with potash, decomposing the crystallized
meconate of potash by muriatic acid, and recrystallization.
When pure, meconic. acid is in brilliant white crystalline scales, containing 2 Aq.,
which they give off at 212~;- it is soluble in four parts of boiling water; it is a tribasic acid,, forming, salts; of which. those -with the earths and heavy metallic bxides
are generally inso'uble in' water.  There are, three,classes of Mec'onates, according
as the quantity of fixed base is one, two, or three atoms.  Few of them are specifically of iminportance.  The most characteristic. properties of this acid are, ist, that
it produces'with solutions of the peroxidelof iron a blood-red colour, analogous to
that of the sulpliocyanide of iron, from which it is distinguished by the fact that,
on the addition:of the acetate of lead, a white precipitate is formeds whilch, when
heated to full, redness with a little sulphur and potassium, and treated With-water,
gives no red colour with the salts of iron (see page 525); 2d, that with nitrate of
silver it gives' a white precipitate, which is dissolved'by dilute nitric acid; the
liquor, however, when boiled, becomes milky, and deposites cyanidee'of silver.
~ If a strong solution of meconic acid be boiled for a long time, or if the crystallized
acid be dissolved in'strong, boiling muriatic acid, it is converted into Komenic Acid,
carbonic acid being given off. The crystallized meconic acid undergoes the same
change when heated to 400(~.; This acid forms granular crystals, which are soluble
only in sixteen parts of boiling water, and have the formula C2H20s-2H:O., as the
C14H.o01 loses 0204 and gains H.O.- This'acid is bibasic; the third atom of water,
which was basic in the' Meconic acid, entering into the radical here. It also red



600              PREPARATION  OF  TANNIN.
dens the per-salts of iron. It forms two series- of salts, which in properties resem-a
ble closely the corresponding meconates. When it is heated to 500~, it gives off
water and carbonic acid, and forms Pyromekonic Acid, of which the formula is CIO
H30j5+H.O. This acid forms crystalline plates, which fuse at 2400, and are volatilized by a heat little higher. It is very soluble in water, alcohol, and, ether; it is
a monobasic acid, forming salts, which, with the exception of that of lead, are all
soluble in water. Like the acids from which it is derived, it strikes a blood-red
colour with solutions containing peroxide of iron.
Tannic adcid, or Tannin. -CG,,s50,   3H. 0.
This important substance exists in the bark of most exogenous trees
particularly the oak and horse-chestnut, accumulated principally in the
inner lavers of bark.  It is found also in the roots of the tormnentilla and
bistort, in the leaves of roses and pomegranates; but its most abundant
source is the gall-nuf of the oak (qucrcus infectoria).
- To distinguish this from the other kinds of tannin, of which there is a
great number, it may be suitably termed Gallo-tannic./cid, and I shall
generally, though, perhaps, not uniformly, employ that name.
The method given by Pelouze for its extraction, and which serves for
the preparation of a variety of other vegetable principles, is as follows:
Into a globular funnel, b, which can be closed at the top by a
stopper, and rests in a bottle, a, as in the figure, is to be intro-:,   duced a quantity of nut-galls in powder, moderately compress.
-       F:_ -  ed, after the tube of the funnel has been stopped with a little
cotton. The upper empty part of the funnel is to be then filled
with ether, as it is usually in the shops, containing about one
tenth of water dissolved in it, and the apparatus allowed to stand
for some days.  The bottle is then found to contain two lay.
ers of liquid.  The inferior, sirap-thick, is a concentrated solution of tannic acid in water, with very little ether.  The
1 upper is ether, containing but a trace of tannic and gallic
acids.  Being separated, the lower layer is to be washed once
or twice with a little ether, and then evaporated in vacuo with
a capsule of sulphuric acid.  A faintly-yellowish white mass remains, of
a distinctly crystalline structure, which is pure gallo-tannic acid.  The
theory of this process is, that the tannic acid is so greedy of water as to
withdraw it from the ether, and to dissolve it to the exclusion of every
other constituent of the gall-nut.
The watery solution of gallo-tannic acid reddens litmus; it is probably
insoluble in absolutely anhydrous alcohol and ether; its taste is intense.
ly astringent, but not bitter.  The most characteristic property of tannic
acid is, that it combines with the animal substance Gelatine, and forms a
compound insoluble in water, which is the basis of most kinds of leather;
hence any tissue, as skin, which contains gelatine, removes gallo-tannic
acid- from its watery solution, on which is founded the art of Tanning.
It is a tribasic acid, and forms three classes of salts, which are of inter.
est from the colours of precipitates it gives with metallic solutions, being
often useful as a test for the presence of certain metals.  Hence an in.
fusion, or tincture of Galls, is always found in the laboratory as a reagent; it does not affect the solutions of Zinc or Cadmium, or the proltox.
ides -of Iron and Manganese, nor any of the alkaline or earthy salts.
With the other metals it gives precipitates which, with Lead and SAnti.
nony, are white; with Copper, gray; with Tin, Nickel, Cobalt, Cerium,
Tellurium, and Silver, are various shades of yellow; with Tantalum and




PREPARATION  OF  GALLIC ACID.                       601
Bismutlh, are orange; with Titanium, blood.red; with Platinum, green,
with Chrome, Molybdenum, Uranium, and Gold, are brown; and with Osmium and peroxide of Iron, are rich bluish purple.  This last is the most
important of all, from its great delicacy and distinctness.  If the solutions be very strong, the liquor appears absolutely black, and constitutes
the mnaterial of ordinary writing ink.
The insolubility, and consequent inactivity of tartrate of antimony, is
taken advantage of in medicine, infusion of oak-bark or galls being employed as an antidote in poisoning by tartar-emetic.  I shall have occa
sion hereafter to notice its use in the detection and neutralization of the
vegetable alkaloids.
The galio-tannic acid is not the only kind of tanning material employ.
ed in the manufacture of leather; yet, as the others will hereafter come
under notice, I shall give Humphrey Davy's estimate of the comparative
power of such substances as contain true tannic acid.  He found the
quantity of active material in 100 parts of the following bodies to be,
Gall-nuts........ 24    White inner oak bark.      16'0
Oak bark entire...3    White inner horse-chestnut. 15"2
Hiorse-chestnut bark entire.. 43    Sicilian sumach....   16.32
Elm bark entire......   2'7    Malaga sumach.....   10'4
These numbers are but approximative, and such as are given'by very
rough processes, the true quantity of tannic acid present being much larger; thus'the gall-nuts easily yield, by Pelouze's method, forty per cent
of pure product.
When a solution of tannic acid is exposed to the air, it is decomposed,
absorbing oxygen and evolving carbonic acid, the liquor becomes colour
ed, and a large quantity of gallic acid is found to be produced.
Gallic -.cid.-C,H. 03+ 2I-. O. + Aq.
This remarkable substance does not appear to exist naturally formed
in plants, but is generated by the decomposition of gallo-tannic acid.
Powdered galls are to be made into a thin paste with water, and exposed
to the air for some weeks, at a temperature of about 80~, water being
supplied according as it evaporates  away; the resulting mass is to be
boiled with water, and the gallic acid crystallizes out of the liquor as it
cools.  By digestion with ivory black and recrystallization, it is obtain.
ed completely pure.
In this process the reaction is very simple, as an atom of tannic acid,
ClbHSOl2, absorbing from the air eight atoms of oxygen, produces 4C.O0
and 2(C7H.0q-3 Aq.).
The conversion of gallo-tannic acid into gallic acid may occur, howev.
er, without the access of air, and, indeed, be effected almost instantane.
ously; thus, if tannic acid be boiled in a strong solution of potash for a
few minutes, and an excess of sulphuric acid be then added, a copious
product of gallic acid is obtained crystallized on cooling; or, if sulphuric acid be added to a strong solution of gallo-tannic acid, and the pre.
cipitate thus formed be washed with a small quantity of water, and then
added gradually to. boiling dilute sulphuric acid, it dissolves, and on cool.
ing the gallic acid crystallizes.  In these reactions, which succeed also
perfectly with infusion of galls, some other substances must be simrnulta.
neously formed, which are as yet not known.  Gallo-tannic acid contains
exactly the constituents of gallic acid and acetic acid, as C,8H615092(07
4G




602   PYR OG'ALLIC,    I-ELANGALL.IC  ACIDS, ETC..:I.O03)+Ct-1O303; but Liebig has: determined that acetic acid is not pro.
duced.
rLThis change. may occur in the nut-gall itself, whi(' h it is very probable
-contains a: principle analogous to yeast, which, under fiavo urable circumstances, induces this kind of decomposition in the gallo.taninic acid.  This
idea, first suggested by Robiquet, has derived tmuch support frotri -the ex
perirnerits of -Larocque, who tound that. the matter of the nut-gall which
remains after the extraction of. the tannin has the power of exciting the
alcoholic:fermentation in solutions of sugar.  As yet, however, we pos.
Hsess no, accurate knowledge of the- theory of this interesting transmutation.
Pure gallic acid crystallizes in colourless oblique rhombic prisms, as
u, z in. the figu re, where i is a seconda y -plane; it tastes bitter, and slightly:acid, and requires 100- parts of cold, but much less of boiling
water for its solution; it is less soluble in alcollol; its crys.:  tals contain three atoms of' water, of which one is expelled at'a:  I   temperature of 2300, but the remaining two are only removed when replaced by bases.  It is a bibasic acid, forming two
classes of salts; those with the alkalies are very soluble; the
-earthy and metallic salts are. insoluble in water.' With a
per-salt of iron, gallic acid gives a blackish-.blue precipitate, which dif-..fers fiom  the tannate of' iron in becoming gradually colourless, the acid
being decomposed, and the iron reduced to the state of protomxide; this is
effected instantly by boiling, carbonic acid gas being evolved.  The gal.
lic acid is farther distinguished from  the tannic by not precipitating gela.
title nor any of the vegetable alkalies.
Products of the Decomposition of Gallic Acid.
Pyrogallic Acid.-When gallic acid is carefllly heated to about 4000, it is totally
decomposed into carbonic acid and pyrogallic acid (C7H3a0=CsHs603+C.02), which'subllimes in brilliant white plates; it is easily soluble in ether, alcohol, and water;.it reacts feebly acid; it fuses at 240~, and sublimes at 4000. If a solution contain-.ing peroxide of iron be added to a solution of pyrogallic acid, a black colour is
struck,.but the iron is rapidly reduced to the state of protoxide, and the liquor as-'
sumes a rich red tint: If, however, a salt of pyrogallic acid be used, the solution
remains permanently blue.
M: tclangallic Acid. —If, in. the distillation of pyrogallic acid, the.temperature be al-.lowed to rise beyond 450~, it is decomposed, water is given off; and a shining, jetblack mass, like coal, remains in the retort, which is this body; its formula is
C, H303, being formed from 2(C6Ha303) by loss of 3H.O.; it is insoluble in water,'alcohol; and. ether; at a temperature of 500o it is totally decomposed into the ordinary'-pyrogenic products; it dissolves in alkaline solutions, forming salts of a black
colour, which do not crystallize; these salts give black precipitates with solutions
of the earthy and metallic salts.
If gallo-tannic acid be heated to about 400~, it is resolved totally into pyrogallic,
melangallic, and carbonic acids and water.
Ellagic Acid.-Inr the formation of' gallic acid by the:slow fermentation of tannic:acid, a' certain, quantity.:of ellagic acid generally, though not constantly, appears.
-Being insoluble in water, it remains when the gallic acid has been dissolved out;
and, by digesting the. residue.with a weak solution of potash, it is taken. up, and
may then be precipitated by muriatic acid.
It for-s minute crystals; whose forimlais C7H0aH.0.+Aq,:.The Aq::is driven
~-off by a; heat- of 21-20, and the dry acid is then-isomeric with the gallic acid, but it is:monobasic; it is very feebly-acid, not expelling carbonic acid from its salts; the:.earthy and metallic Ellagates are all. insoluble, and all white or yellow.
If gallic acid be heated to 2800 with oil of vitriol, it dissolves, and on cooling,
brilliant crystals of a dark scarlet colour are deposited, which constitute Parellafgz;Acid. -This body is isomieric w ith ellagic acid; it forms with bases salts which are




C AT E C HU, I C  AND.-. C A, T E C LI U T AN.N I C  A C:I D.S.  603
generally red. It is worthy of notice,.that:ellagic acid acted on by oil: of vitriol
gives:   o parellagic acid.' 
lt i.s hl ere p)ro baUbly best to notice the formation of what has been termed
Arlt/cial Tannin.; it is produced by mixilng one part of' almost any kind
ot-;vegetable substance with five parts- of oil of vitriol, letting the mixture
stand ttr some days, and then heating it as long as atiy sulphurous acid
gas is evolved.  A. black. mass, remains, firom which the rellainling acid
is to be washed with water, and then the tannin disslved out by alcuilol
ihe: solution is dark brown, and when evaporated gives a black extracti-ve matter, which tastes astringent, smells of burned sugar, and dissolves
in water; it precipitates gelatine, but does not affect the salts of iron
like true tannin.
Another and a very singular manner of producing artificial tannin
consists in boilingr pure charcoal in nitric acid as long as any reaction
occurs; the liquor is then brown n; being evaporated to thle consistence
of a sirup and mixed with water, a brownish.yellow substance faills, and
the filtered:solution gives, by evaporation, a hard black mass, whict reddens: litmus, tastes astringent, is soluble in water and alcohol, ant copi.
ously precipitates gelatine; when heated, it smells like horn, and containo
nitrogen; it precipitates most metallic salts brown.  The true nature c~f
these bodies is not well known, as they have not been much studied sin(,e
the methods.of organic.chemistry acquired their present exactness; they.
are probably mixtures of'many bodies, as ulmnine in its various,forms
with crenic and aprocrenic acids.
Catechuic Acid and Catechutannic Acid.
The Catech-u, or Terra Japonica, a, brown extract prepared from the wood of the
mimosa catecbhu, appears to.contain at least four acids, the precise composition and
connexion of which have not.yet been definitely established. The rough catechu,
as imported, is of extensive use. in medicine, and in the arts for tanning and:for giving a rich permanent brown dye. Davy estimated that 100 parts of Bengal catechu
contain forty-eilght, and of Bombay, catechu about fifty-four per cent. of' useful tanning material.
If catechu be treated with ether, by the method of displacement as described for
tannic acid, the liquor does not separate into two layers, but a strong solution of
Catcchutannic Acid in ether.is obtained, which, by evaporation, yields it as a pale
yellow, scarcely crystalline mass,:in taste and appearance similar to tannic acid;
its solution in water precipitates gelatine, but- not tartar-emetic; with the salts -of
peroxide of iron it strikes an intensely olive-green colour, which is best marked with
the perchloride, being somewhat. purple with the persulphate;..exposed to the air,
its solution rapidly absorbs oxygen, becomes red, and.finally brown, depositing a
brown. insoluble matter... This.change is instantly:effected by any oxidizing agent.
The catechutannic acid.has b.een analyzed by.Pelouze, who ascribes to, it the
formula C18HsOs+Aq.;  it would thus appqar to be formed by the abstraction of four
atoms of oxygen from tannic acid.
When catechu has been deprived of the catechutannic acid by ether or continued
washings with cold water, the residual mass is to.be, boiled in alcohol,.and: the filtered liquor evaporated to one third of its volume; on cooling, Catechuic Acid crys-.
tallizes.  If coloured, it'is to be dissolved in boiling water, precipitated by.acetate'
of lead, the catechuate of lead diffused through boiling water, and decomposed lby
sulphuretted hydrogen; the liquor being filtered, gives, on cooling, a perfectly:whiteo.
and pure catechuic acid;. it forms satiny flakes, indistinctly crystallized; it -is very
little soluble in cold water,. but abundantly in boiling water and in alcohol;.. it is insoluble in ether; its solution is not acid; it appears to exist.in very.different states
of hydration, or, possibly, different kinds of catechu contain substances:which are-:
totally distinct, for the formulae assigned to it are quite discordant, and.chemists
are not agreed. quite as to its properties.. Svanberg, who. examined.the catechu
from the mimosa catechu, gives as its formula COH5sOsqAq.. Zwenger, who states
the substance he worked with to be the produce of the nauclea gambir, gives




604 CINCHONATANNIC AND CINCHONIC ACIDS, ETC.
C20HgOs+- Aq.; and Hagen, who used Bengal catechu, found the catechuic,,acid to
be C14H606+3 Aq., and its lead salt Ci4H60-6+2Pb.O. Additional researches are
required to clear up this confusion.
When catechuic acid is heated, it fuses, gives off water, and, finally, a white crystalline sublimate, Pyrocatechin, which has the formula C6H2O.+-Aq., its characteristic property is that of forming a bright green solution with alcohol.
If a solution of either of the acids now described be exposed to the air, oxygen is
absorbed, and much more rapidly in presence of an alkali. The substance formed
is termed Japonic Acid; it makes up the mass of the coloured portion of catechu
it is almost insoluble in water; soluble in caustic, but not in carbonated alkalies.
Svanberg gives for it the formula CI2H204+Aq.  If catechuic acid be boiled with a
solution of carbonate of potash, Rubinic Acid is formed, whose formula is said to be
ClsHO69. By farther absorption of oxygen it forms japonic acid. None of'these results, however, can be considered as definitely established.
Cinchonalannic Acid and Cmznchonc Acid.
These substances exist in the barks of various species of cinchona, combined with
quinia and cinchonia. The first is extracted by digestion in dilute muriatic acid and
precipitation with magnesia. The precipitate is to be dissolved in acetic acid and
precipitated with acetate of lead, which leaves the alkaloids dissolved; the cinchonatannate' of lead being decomposed by sulplluretted hydrogen, the filtered liquor.yields, on evaporation, the Cinchonatannic Acid pure, and of a very pale yellow colour, -not crystalline. In properties it resembles closely ordinary tannic acid; it
precipitates gelatine and tartar-emetic. An infusion of cinchona is hence recommended as an antidote in cases of poisoning by tartar-emetic.  It colours solutions
of the per-salts of iron green. By exposure to the air, it is converted into a rustcoloured substance termed Cinchona Red. Nothing is known of the composition of
these bodies.
The Cinc'ionic Acid, which Berzelius believes to exist in the inner bark (albumen)
of fir and of most trees, is obtained by adding lime in small quantity to a cold infu-'sion of cinchona bark. The alkaloids being thus separated, the liquor is filtered and
evaporated very carefully to the consistence of a sirup. On standing for a few days,
the cinchonate of lime crystallizes in needles, which are to be decomposed by an
exact equivalent of sulphuric acid. The gypsum being removed by the filter, the
solution is concentrated, and the cinchonic acid crystallizes. It forms small acid
needles; is very soluble in water; its salts are all soluble in water; it affects neither gelatine, tartar-emetic, nor the per-salts of iron; its formula appears to be
C14HsOs8+4 Aq. When it is heated, a substance sublimes in brilliant yellow nea.
dies, which is termed Chinoyl, and consists of C3H.O.
Kfinoic Acid, or Coccotannic Acid.
The substance known in pharmacy as Gum Kifno, which is an extract of the
wood of the coccoloba uvifera, is to be dissolved in cold water, the solution precipitated by sulphuric acid, the precipitate washed, dissolved in boiling water, and solution of barytes added until the sulphuric acid is all removed; the liquor is then carefully evaporated to dryness. The kinoic acid forms a crimson transparent mass,
soluble in alcohol and water, but not in ether; its taste is astringent, but not bitter.
The salts of this acid are not known, nor has its composition been examined. It
does not precipitate solution of tartar-emetic.
Of the following acids we possess little more than a knowledge of their probable
existence.
Lactucic Acid is said to exist in the lactuca virosa. The expressed juice is precipitated by acetate of lead, and the lactucate of lead decomposed by sulphuretted
hydrogen. From the liquor the acid crystallizes by evaporation and cooling, like
oxalic acid; it tastes acid, and gives with protosalts of iron a green, and with salts
of copper a brown precipitate.
F'R7agic Acid exists in most mushrooms; their expressed juice is boiled, and the
coagulated albumen removed by filtration; the liquor is then evaporated-to a sirup,
and treated with alcohol. Fungate of potash remains undissolved, from which the
acid is obtained by acetate of lead and sulphuretted hydrogen. The fungic acid is
colourless, sour, deliquescent, and not crystalline.
Boletic Acid is obtained from the boletus ignarius, in the same way as the last acid
is. from other mushrooms. It crystallizes readily, and sublimes without decolnpio
sition.




KRAMERIC  ACID, ETC. —PECTIN.                           605
Krameric Acid exists in rhatany root (krameria triandria). The watery infusion
is precipitated, first by. gelatine, and then by copperas. The filtered liquor is concentrated, neutralized by lime, precipitated by acetate of lead, and the kramerate of
lead decomposed by sulphuret of hydrogen; it crystallizes irregularly, and tastes
strongly acid and astringent; its fblrmula is probably COHs05, by Lieblg's analysis.
Caincic Acid exists in the root of the chiococca racemosa. Its mode of extraction
resembles that of the krameric acid; it crystallizes in needles; is but sparingly soluble in water; its solution reacts acid; it appears to have the same formula as kra
meric acid, and perhaps they are really identical.
Verdoeus and Verdic Acids exist in a variety of plants of the families dipsacea,
composita, and eupatoriae; it is best prepared from the roots of the scabiosa succisa. They are to be digested in alcohol, and the solution mixed with ether. Impure
verdous acid is thrown down; it is to be dissolved in water, and the liquor precipitated by acetate of lead; the verdite of lead being collected and decomposed by
H.S., gives the pure Verdous Acid, which remains after evaporation as a clear yellow mass, wtich is not altered by the air; it reddens litmus strongly. If it be neutralized by an alkali, it then absorbs oxygen rapidly, and the solution becomes deep
green; from this, acids throw down a brown-red powder, which is Verdic Acid.
Runge, who observed these facts, considers that the two acids are different, oxides
of the same radical,. but no exact researches have been made about them.
Other acids, of which the existence has been only indicated, will be notided in de,
scribing the more important bodies with which they are associated in the plants.
CHAPTER XXV.
OF THE NEUTRAL ORGANIC SUBSTANCES AND TIIE PRODUCTS OF TIIE1R
DECOMPOSITION.
TImI  bodies to be described in this chapter are distinguished by the
absence of distinct acid or basic characters, and also that they are at
least so destitute of colour as not to be included in the list of colourinng
matters.  In other respects they possess no direct connexion with each
other, and are united only for convenience of arrangement.
Pectin, or TV/egetable Jelly.
This substance, which is to be carefully distinguished from  animal
jelly, or Gelatine, to which it by no means bears the relation that the
albumen of plants does to that of animals, is very extensively diffused,
being found in almost every kind of plant, and distributed through all
their parts.  It is very easily prepared fiom the expressed juice of white
beet, celery, parsley, currants, cherries, or plums.  It is sufficient to
filter the juice and mix it with alcohol; after some hours, the pectin
separates as a consistent jelly, which is to be collected on a filter, washed with alcohol, and dried by a very moderate heat.  It forms a transparent mass, like isinglass, and is almost insipid.  When immersed in
water, it swells up; one part gives a firm jelly with 100 parts of water.
When acted on by nitric acid, it produces pectic and the mucic acid.  It
precipitates the salts of barytes, lead, copper, and sesquioxide of iron, but
does not affect solutions of silver, of protosulphate- of iron, of tartaremetic, of tannic acid, or of silicate of potash.  Its formula, as from the
experiments of Fremy, is C24H,O22.  By long boiling,-or by contact with
any powerful acid or base, it changes into the following substance;




606  P E (, T I C; AND  I- M E T A P'E C'T I C - AC-I-D S. —SA -AL I C I N E.
P~Gctic Ac'd: appears to exist naturally combined with lime in many plants, and is
precipitated tirom their juice on the addition of muriatic acid.: The precipitate is to'
be boiled with a; little lime, and the solution again decomposed' by muriiatic acid.
The pectic acid, which then separates pure, is to be washed xwith distilled water and
dried.'It does not crystallize, but forms white transparent'scales, tastes distinctly'
acid,:and reddens litmus.  It dissolves very sparingly in cold, -hut more copiously
in boiling water; the solution is colourless, and does not gelatinize on cooling, but
is coagulated to a transparent jelly by acids, by lime-water, alcohol,' and many
salts. Sugar gradually converts the solution into a firm jelly; and is thus usefull in
the manufacture of the: preserves of juicy fruits.:The pectic acid is isomeric with pectin, its formula being C024HI7022z. It appeals
to be bibasic, the pectate of lead being C2HI1o,0.21,2Pb. h.O. Its alkaline salts aresoluble in water, but the others are insoluble,: and ibrm transparent jellies whili
moist.:.
If pectin or pectic acid-be' boiled in a solution of potash, the alkali being in excess, until the liquor: ceases to give any precipitate on the addition of muriatic acid,
Metapectic Acid is formed.  On the addition of sugar of lead, metapectate of lead is
thrown: down, which, being decomposed by sulpliuretted hydrogen, the'metapectic
acid dissolves, and: is obtained by cailtious evaporation to dryness, Its'taste and
reaction are strongly acid; it deliquesces, and dissolves easily in alcohol and water;it is not volatile.  When'dry, it is isomeric withlthe preceding' bodies, its formula
also being C24H7022; but its salts contain five atoms of base: Those of the alka-:
lies are soluble and uncrystallizable, but those of the earths and heavy metallic oxides are insoluble in water.
Of Salicine, and the Bodies derivedfrom it.
This substance exists in the leaves and bark of a great variety of
trees, but is particularly abundant in those species of salix wthich have a
bitter taste.  The bark is to be boiled three or four times with water,
the decoction evaporated till it amounts to but three times the weight of
the bark employed, then digested fbr.twenty-fbur hours with oxide of
lead, and the clear liquid evaporated to the consistence of a sirup,. After
a few days this becomes a mass of crystalline fibres,' which, separated
by, pressure from the mother. liquor, are.to be purified by solution, diges.
titon with animal charcoal, and recrystallization.
When pure, salicine is in the form  of small white rectangular crystalline plates or prisms; its taste is very bitter.  It dissolves in eighteen
parts of cold and in one of boiling water; it is soluble in alcohiol, Iut
not in ether; at 2120 it melts, and on cooling solidifies into a crystalline
mass.  The compositionof salicine has been very accurately determin.
ed; its formula is, when crystallized, C2 1]1209+2 Aq.; it precipitates ihle
basic acetate of lead, forming a white compound,' the. formula of which is
C2, Hi.209+3Pb. 0.
-The products- of the decomposition of salicine are' exceedingly remarkable.
When it is' boiled with dilute sulphuric acid,,it is decomposed into grape-sugar, and,
a resinous substance termed Saliretine.  Three atoms of salicine, Ce3Hs11Os:, giving
saliretine, C51H24()01, and sugar, CH12,H120'.  VWhen quite pure, this body is white or
pale yellow,  It is insoluble in water, but soluble in alcohol and ether.
With sulphuric acid and chromate of potash, salicine gives hydruret of salicyl
(oil of. spiraea), as described page 573. - Although the evolution of forimic and carbonic acids, whlich occur in this reaction, show that it is in reality complex, yet its;
result may be expressed by the simple abstraction of water from the salicine, as
2(C_,,H o09)-6H.O.- 3(C14H604).
When salicine is b(oiled with nitric acid, it is totally converted into picric acid.
As this body is, however, more closely connected with indigo, it will be tlhere fully
described.
By the. action of chlforine on salicine,two bodies are prlroduced:l. one:crystalline,
whose fortmula is-G C!H-2 C1209, and the other a hea`v.y oil, consisting of': C.2,s1
(CO40s. They'are iboth soluble in'alcohol, but sparingly soluble in water.
If strong oil of vitriol be-poured on salicine, it is decomposed intO water and a




P H L O R ID ZINE -AND  ITS  PRODUCTS.                          607
deep olive-green powder, Olivin, the fiormula of which is C2H9Os. This action is
accompanied by the disengagement of nmuch heat.  Olivin is crystalline, insoluble
in water, alcohol, and et;her.  If the oil of vitriol be in great excess, it becoines
red-coloured, and the salicine dissolves.  The red substance thus formed is termed
ItafiL; it is obtained Imore simply from phloridzine.  If a large quantity of salicine
be acted on by sulphuric acid, it forms a tenacious mass. which, when~ treated with
water, and the liqui.ior neutralized by lime, gives a brown resinous b1)o0y, wlicl( is
telrmed IRtaldin.  TifhiS contains sulphuric acid, its fornmula being C2sHI120-S0a.3
Of Phloridzine and its Products.
This remarkable substance exists in the hbark of the roots of the various species
of apple. pear, piutn, aind cherry trees.  It is prepared by infusing the root-burk in
weak spirit fbr eight or ten hours at 120~.  The greater part of the spirit irnay then
be distilled off; and on cootling, the pliloIidzine crystallizes f-oni tile remliaining liqutor.
It foirms brilliant silky plates and needles, perfe(-tly white when pure.  It is easily
soluble in alcohol, ether, and in boiling water, but requires 1000 parts of cold wate)
for its solution.  Its taste is bitter and astrintgent.  The forinmula of the crystals is
CsDi03,Os-4 Aq.  At 2120 it gives off 2 Aq.; it melts at 226~, and boils at 350~,
but.is decomposed, water beiing evolved, and a new substance produced.  The solution of phloridzine precipitates some rmetallic salts.'The persulphate of iron gives
a brown precipitate, but the perchloride of iron produces a blood-red liquor and no
preci pitate.
T'1'e decomposition of phloridzine by heat is not complete until the temperature
rises to 4500~; it then forms a deep red mass of RuJin, the same substance as is
prolduce  by the action of oil of vitriol on salicine;'it is very soluble in alcohol, insoluble in ether; boiled in water, it dissolves, but loses its red colour, and the liqiior,
onl cooling, becomes milky.  It dissolves in water ofamnmonia or potash with a rich
red colour, and is precipitated on the addition of an acid; its formula is CI4 170.;
it combtines with oil of vitriol, forming RKufin-sulphutl ic Acid, which unlites with the
metallic oxides, forming red or brown salts, which possess considerable analogy to
the suliphovinates.
I:hlwui phloridzine is dissolved in dilute sulphuric acid, and the liquor boiled, a
white crystalline substance separates, which is, termed Phloretine; the liquor then
contains much grape sugar.  The formula of phloretine is C1H,0%i7; its taste is
sweet; it is sparingly soluble in water, but very soluble in alcohol; it melts at 3000;'
whllen heated with nitric acid, it forms Phloretic Acid, the firunlda of which is C511H.24.
NT0.);; it is a yellow-brown powder, of a velvety aspect, but not crystalline; insol.
lble in water, and soluble in alcohol.
lThe most remarkable action on phloridzine is that exercised by ammonia with
access of air.  Over a capsule containing water of ammonia are arranged several
capsules containing phloridzine in very thin -layers, andi the whole is so covered
with a large bell-glass as that the air shall have free ac, ess;  after a few. days the
contents of the capsules. are changed into a thick sirlipy liquor, nearly b)la(c.k; tlhe
excess of ammonia being removed by exposure in va(uo witll sulphuric acid, the
excess of phloridzine is dissolved out by:alcohold, and thie residue then being dissolved in water, gives a magnificentblue liquor, firom whlic  the colouring sulbstance,
Phloriidzcin, is precipitated hy the cautioius addition of acetic acid; it is not crystalline;:it fJorms a transparent resinous mass of a richcrirnson colouri;: its taste is
bitter; boiling water dissolves enough. of it to be coloured red, but cold water, alcohol,.or ether appear scarcely to act upon it.
llhe fiormula.of phlorizein is C21HI4. 013N.-Aq.; it is formed, therefore, by the
combination of phloridzine with five atoms of oxygen and one, of ammonia,; it is
not, however, a salt of ammonia, for the alkalies dissolve phloridzein' Withllut alteration, fiorming magnificent blue solutions; friom metallic solutions it precipitates
purple or blue lakes, the compositi ol. of. which renders. it probable that the equivalent of phloridzein is C42H2s. 026N2+2 Aq.; then t.lhe.
Phloridzeinate of ammonia, =.C42H28. Na2026-  N.Hs3
Philoridzeinate of silver,    =C-42H2s. N206-+-2Ag, O.
Phloridzei'nate of lead,    — C'421128. N2026-+2Pb.0.
if the blue solution of phloridzeinate of ammonia be put in contact with a slip ot
zinc, protochloride of tin, sulphuretted hydrogen, or any other deoxidizing agent, il
is deprived of- colour, but by exposure to the air it rapidly reassumes its tint; wilb
fchlorine the colour is instantly and permanently destroyed.




608    ASPARAGINE1  CAFFEINEn  AND  PIPE-RINE.
Asparagine.  Aspartic Acid.
Asparagine is found in the young shoots of asparagus and of potatoes, in the
roots of liquorice and marsh-mallow.  From the latter it is easily prepared.  The
decorticated roots are to be digested in cold water for folty-eight hours, and the liquor then strained and evaporated to the consistence of a sirup.  By standing foi
some time, the asparagine gradually crystallizes, and the crystals are to be purified
in the ordinary manner by animal charcoal.  It forms rectangular octohedrons and
prisms; it is colourless and tasteless; it requires about sixty parts of cold, butmuch
less of hot water foir solution; it is insoluble in alcohol; it contains nitrog)-en, its
formula being N.C4. H403s-Aq.; the water goes away by a heat of 2300;
WChen asparagine is boiled with a strong solution of barytes, ammonia is expelled, and aspartate of barytes formed; by cautiously adding sulphuric acid, the barytes may be precipitated, and the liquor yields, on evaporation and cooling, crystallized aspartic acid. In this reaction 2(N.C4. H403) produces N.H3 and N.C8. H506,
which is the formula of aspartic acid. This substance is tasteless, sparingly soluble'in cold, but abundantly in boiling water, and is deposited as a white crystal
line powder as the solution cools; it reddens litmus. Its salts are generally soluble, except those of lead, silver. and black oxide of mercury.
It is not easy to decide whether the ammonia exists ready formed or not in the
asparagine; if so, the remaining organic element may be aconitic acid (see p. 597),
and then there should be,
Asparagine=anhydrous, aconitate of ammonia=-C4H.03+N.H13.
Aspartic acid=anhydrous binaconitate of ammonia=2(C4II.0)-)+N.H3.
In the case of the anhydrous compounds of ammonia with the mineral acids, it is
rDtained with the same obstinacy as in asparagine (see p. 508).
Ccaffeine or Theine..Caffeic Acid.
This has been found only in the coffee-berry, the tea-leaf, and the paulinia soiballs (guarana).  To prepare it, raw coffee is to be boiled in water, and the decoction treated with subacetate of lead as long as the precipitate which forms is coloured. The caffeine crystallizes from the filtered liquor by evaporation and cooling;
if it be coloured, it is to be boiled with oxide of lead and ivory black, and again
crystallized; when pure, it forms brilliant long needles of a rich satiny lustre; its
taste is purely bitter; it dissolves in fifty parts of cold, but in much less of boiling
water; it is very soluble in proof spirit, but insoluble in absolute alcohol; its solutions react neither acid nor alkaline; it is not precipitated by any metallic salt.
Caffeine is remarkable for the large quantity of nitrogen it contains (29 per cent.),
being more than any other vegetable substance; its formula is N2Cs. H502+Aq.
When caffeine is boiled with solution of barytes, cyanuric acid, ammonia, formic,
and carbonic acids are produced.
The coloured precipitate produced in the decoction of raw coffee by acetate of
lead contains two peculiar substances, which may be extracted from it by treatment with a stream of sulphuretted hydrogen gas, evaporation to the consistence of
a sirup, and digestion of the residue in strong alcohol. That which dissolves is
Caffetannic Acid; it is dark brown; tastes acid and astringent; colours the persalts of iron emerald green; it precipitates the salts of barytes and lime yellow, of
copper green, but does not affect tartar-emetic. The substance insoluble in alcohol
is a white powder, which, when heated, evolves the characteristic aromatic smell
of roasted coffee; its solution in water reddens litmus; it is termed Caffeic Acid.
These bodies have not been accurately examined.  It is not known if the tannic
acid of tea and coffee be the same.
Piperine. —N.C34 H,906.
This substance exists in white, black, and long pepper; it is prepared from white
pepper by digestion in spirit of wine, and distilling the liquor to the consistence of
an extract, from which, by digestion in a solution of caustic potash, a quantity of
resin is to be removed; the residue is then to be dissolved in alcohol, and the solution abandoned to spontaneous evaporation, when the piperine gradually crystallizes
in transparent rhombic prisms. It melts at 21.2; is tasteless and inodorous; destitute of either acid or basic properties; nitric acid colours it red; when heated
strongly, it yields ammoniacal products.




ONIN'Ei    CETRARINEn  PICROTOXINEn  ETC.'609
Canlttaridine.-CloH604. This substance is extracted from the blistering fly (various species of cantharis and lytta) by digesting a watery extract of the fies in alcohol, evaporating the solution to dryness, and treating the residue with ether,
which dissolves out the canthilridine.  By spontaneous evaporation it is obtained
crystallized; it forms colourless pearly scales, which fuse when gently heated,
and sublime unaltered at a higher temperature; it is, when pure, insoluble in water
and in cold alcohol; it is perfectly neutral, and has no affinity either to acids or
bases.
Anernonine.  Anenmonic Acid.
This substance exists in various species of anemone; it is extracted by distilling
the plant with water; it separates, after some time, from the distilled water, in
brilliant white needles; it melts and volatilizes at a high temperature, yet not without partial decomposition; its formula is C6H-304; whent it is dissolved in strong
rmuriatic acid, and the liquor evaporated to dryness, Anemonic Acid is formed; its
formula is CsH4-05Aq.  It is not important.
Cetrarine, or Lichen Bitter.
This substance is found in Iceland moss; to extract it, the lichen, being well
crushed, is to be digested in alcohol as long as this acquires a bitter taste; the liquor may then be distilled in great part off; and the cetrarine is deposited, on cooling, In granular crystals; these are to be, while still moist, washed with ether and
cold alcohol, by which they are rendered white, and then being dissolved in 200
times their weight of boiling alcohol, the pure cetrarine separates on cooling as a
white powder of a slightly crystalline aspect.  It is but sparingly soluble in any
menstruum; its only remarkable character is, that by digestion with muriatic acid
it forms a deep blue mass, but the nature of the reaction is not known, as the con
stitution of these bodies has not been accurately investigated.
Picrotoxine, or Cocculine.
This substance exists in the seeds of the menispermum cocculus (cocculus Indicus), constituting their active ingredient; to prepare it, the seeds, freed froih the
capsules, are to be digested in alcohol, and the solution evaporated to an extract;
this is to be then treated with water as long as anything is dissolved, and then
some mnuriatic acid added to the liquor; by cooling, the cocculine crystallizes in
brilliant white needles. Its reaction is neutral; its taste intensely bitter; it dissolves moderately in boiling, but sparingly in cold water.  The portion of the alcoholic extract which does not dissolve in water contains another substance, Picrotoxic Acid, which is brown, and possesses the properties of a resin; it dissolves in
alkaline liquors, from which acids throw it down unchanged.  The formula CloH604
has been assigned to picrotoxine, and that of CiH604 to picrotoxic acid.
Co'umbine.-Found in the roots of the menispermum palmatum. The coarselypowdered columbo-roots are to be digested in ether, and by the spontaneous evaporation the columbine crystallizes; or by digesting the roots in alcohol, and decolorizing the liquors by animal charcoal, it may also be prepared:; it. forms brilliant
right rhombic prisms; its taste is intensely bitter; its reaction neutral; it dissolves
but sparingly in water, alcohol, or ether; its solution does not precipitate any metallic salt; its formula appears to be C24H1207.
Cusparine.-This is the active principle of the true angustura (cusparia febrifuga).
The bark is to be extracted by alcohol, and the solution concentrated very much by
spontaneous evaporation; on cooling then below 32~, granular crystalline masses
of cusparine separate, from which the liquor is to be strained; by redissolving in
alcolhol, and precipitation of the colouring matter by acetate of lead, it is ultimately
obtained pure. When crystallized from a solution some degrees below 32~0, cusparine forms colourless but irregular needles; by a very gentle heat it mlelts and gives
off twenty-three per cent. of water of crystallization; it dissolves readily in waterz
and alcohol, but is insoluble in ether; by heat it is totally decomposed; its solutions precipitate most metallic salts. Its composition is not known.
Elatcrine is the active material of the expressed juice of the momordica elaterium;
the juice, being evaporated to the consistence of an extract, is to be digested in
strong alcohol; the solution thus formed is to be distilled to a siiall bulk, and then,
on being mixed with water, it deposites the elaterine as a white crystalline powder.
It melts at about 3200, but is totally decomposed by a stronger heat; its taste i%
4 H




610  MECONINEn PEUDEC ANINE   2E SCULINE, ETC.
intensely bitter; it is almost insoluble in water, but abundantly in alcohol; it pos.
sesses no characteristic chemical property.
Meconine.-This substance exists mixed with the more important ingredients In
opium; it is most abundant in the inferior kinds; its preparation is very circuitous,
and will be described in the general analysis of opium, under'the head of' narceine.
Meconine crystallizes in white six-sided prisms; it melts at 194~, and may be sublimed unaltered; it dissolves sparingly in cold, but moderately in' boiling water,
abundantly in alcohol and ether; its formula appears to be Ca0H907+Aq. By mitric
acid it is dissolved, and a substance crystallizes fiom the liquor in long needles,
which is termed Nitromeconic Acid; its formula is N.C'20. 1-s012; its SOlutiont) in watet
reddens litmus; it volatilizes at 370~0, but is partly decomposed.  By contact with
chlorine, meconine is coloured' red, and substances formed whose constitution is not
well known.
Peudecadnine. —This substance is found in the roots of the peudecanrum officinale,
and is extracted by digestion with alcohol and evaporation; it crystallizes in cielicate white needles of a slightly -aromatic taste; it fuses at 140~; it is insoluble in
water, and but sparingly in cold alcohol; it dissolves copiously in boiling alcohol,
in ether, and the oils.
Esculine, or Polychrome.
A great number of vegetables give, when treated with hot water, a solution which
appears yellow by transmitted, hut violet or blue by reflected light.  This phenomenon results from the presence of a body hence called Polychrome, and alsoAsctuliane,
being most abundant in the bark of the horse-chestnut.  The bark is to be digested
in alcohol, and the liquor to be concentrated by distillation to the consistence of a
sirup, in which, when set aside for some weeks, the asculine crystallizes; by washing with ice-cold water it is freed from the liquid extractive matterm the impure
crystals are to be dissolved in a boiling mixture of five parts of alcohol with one of
ether, from which, by cooling, the pure substance separates, perfectly colourless,
and generally as a light powder, like magnesia alba. It tastes bitteri it dissolves
in 672 parts of water at 50~, and in thirteen parts at 212~0; its cold, watery solution
is perfectly colourless by transmitted, but slightly blue by reflected light; if springwater be used, the blue becomes much stronger; acids destroy this property, but it
is restored to the solution by the addition of a few drops of any alkali.
The watery solution of mesculine reddens litmus, yet it does not neutralize the alkalies, nor precipitate any of the ordinary metallic salts; it dissolves abundantly in
alkaline liquors, and the solutions give a magnificent play of colours with reflected
light; its formula is C16HOIo.
Populine exists in the bark and leaves of different species of populus, along with
salicine; the latter is removed from the liquors by precipitation with acetate of
lead, and then, by evaporation, the populine is obtained crystallized; its taste is bitter-sweet, like liquorice; it is very sparingly soluble in water; when heated, it fuses, and is then decomposed; like salicine, it gives with nitric acid, picric acid, and
with sulphuric acid, rutilin; its composition is not known.
Quassine constitutes the bitter principle of the quassia amara and excelsa.  The
rasped wood is to be boiled several times with water, and the filtered decoction
evaporated down to three fourths the weight of the wood employed. The liquid,
when cold, is to be mixed with slacked lime, and, after twenty-four hours, filtered
and evaporated nearly to dryness; the residue is to be treated with alcohol, and the
solution distilled in a water-bath to dryness; it is then impure quassine; it is to be
washed with ether, and then redissolved in alcohol, and this treatment repeated
until it becomes completely white.
Quassine forms small white prisms of an intense but purely bitter taste; but sparingly soluble in water or in ether, it dissolves abundantly in alcohol; when heated,
it fuses like a resin; its solution is not precipitated by any metallic salt, but abund
antly by tannic acid; its formula is C20,11206.
Santonine.-This substance exists in the flowering tops and seeds of a number of
species of artemisia, from one of which (art. santonica) it derives its name. To
prepare it, four parts of the seeds are to be mixed with one and a half of dry lime,
and boiled in twenty parts of alcohol three times; the united decoctions are to be
distilled to fifteen parts; the residue, when cold, is to be filtered, evaporated to one
half, and, having been rendered slightly acid by vinegar, boiled for some time; on
cooling, the santonine crystallizes in large feathery crystals, which are to be purified from an adhering resinous substance by washing with alcohol.  Being then re.




SAPONINE,  SCILLITINE2 SENEGINE,  ETC.   611
dissolved, and the solution slowly cooled, the santonine crystallizes in colourless
rectangular prisms and plates; it is tasteless; it is very sparingly soluble in water;
more so in alcohol and ether; at 3380 it melts, and by a carefully-applied heat may
be sublimed without decomposition, otherwise it becomes brown, and a yellow crystalline substance is formed. Santonine appears to possess feeble acid properties; it
produces with the alkalies soluble, and with the earths and ordinary metallic oxides
insoluble compounds, but they are of instable constitution.  The formula oi santonine is C,10H602.
By exposure to light, santonine undergoes a change apparently isomeric; it becomes gold-coloured, and forms yellow solutions, which, however, soon become
colourless.
Saponine.-This substance is most easily extracted from the roots of the saponaria otficinalis by boiling in weak spirit; on cooling, the saponine separates; it is
purified by digestion with animal charcoal; it is a white powder, of a sharp, piquant
taste; very soluble in water, it is sparingly soluble in alcohol, and insoluble in ether;
its formula appears to be C2.H23016. By the action of nitric acid, saponine forms
tucic acid and a resinous substance; when dissolved in solution of caustic potash, it forms Saponinic Acid, which is precipitated as a white powder on adding a
stronger acid to the liquor.  The formula of saponinic acid is C26H122012- It is insoluble in cold, but soluble in boiling water.
Scillitine is the active principle of the squill (scilla maritima).  The fresh juice is
evaporated, and the extract treated with alcohol.  The spirituous solution is to be
dried down, and the residue, being dissolved in water, is to be precipitated with acetate of lead, and filtered; sulphuretted hydrogen being passed through the clear liquor removes the excess of lead, and then, by filtration and evaporation, the scillitine
may be crystallized.
It forms a hard, brittle mass, like resin, of an intensely bitter taste; it deliquesces and dissolves readily in alcohol and water, but not in ether.
Senegine. —This substance is extracted from the roots of the polygala senega by
boiling with water, precipitating the concentrated decoction with the acetate of lead,
filtering and removing  the excess of lead from the solution by sulphuretted hydro*gen, and evaporating cautiously to dryness; the residue is to be digested in alcohol,
and this solution being dried down, the product is to be digested in ether. The ma.terial which remains undissolved is then to be passed through the same series of
operations until it becomes a white pulverulent mass, which is pure Senegine. It is
sparingly soluble in cold, but abundantly in boiling water; it' is very soluble in alcohol, hut insoluble in ether.  With sulphuric acid it produces a curious play of col.
ours, becoming first yellow, after some time rose-red, and then dissolving;. the so.
lution gradually becomes violet, after some time grayish-blue, and finally colourless,
while a gray precipitate falls down. Senegine appears to possess feeble acid properties.
Smilacine, or Sarsalparilline.-This substance is found in the roots of the smilax
sarsaparilla and the bark of the China nova. It is obtained by boiling with alcohol,
and distilling the decoction to two thirds; on cooling, the smilacine crystallizes, and
is purified by animal charcoal and recrystallization. It is white, in very minute needles; its taste nauseous and slightly bitter; very sparingly soluble in water, more
so in alcohol, most in ether; with sulphuric acid it gives colours like those of senegine.
Absinthiine.-The bitter principle of the wormwood (artemisia absinthium).  It is
prepared by a succession of operations almost identical with those described for obtaining senegine; it- is hence unnecessary to repeat their description.  When completely pure, it is white and crystalline; its taste is intensely bitter; it fuses at a
high temperature, and closely resembles a resin; its best solvent is alcohol. It
possesses the characters of a weak acid, being much more soluble in alkaline liquors
than in pure water, and being precipitated from such solutions on the addition of
an acid. VWith oil of vitriol, it is Coloured first yellow, and then dark reddish purple.
Lactucine is obtained by digesting the inspissated juice of the lactuca virosa (lactucarium) in ether; by the spontaneous evaporation of the solution, it forms a mass
of crystalline needles, slightly coloured yellow; it has a strong bitter taste, is fusible, and may be partly volatilized; it is soluble in water, alcohol, and ether.  It is
decormposed by strong acids, and appears not to have any tendency to form salts.




6L2             APO THE M E.-EXTRAC T I  E.
Of Extractive Maltter.  Apotheme.  Extracts.
If from any plant, or portion of a plant, the soluble ingredients be
dissolved out by water, a variety of substan'ces exist in the liquor, some
acid, others basic, others indifferent; of these bodies, the majority possess the plroperty of absorbing oxygen when the solution is exposed to
the air, and often, also, of evolving carbonic acid, changing thereby into
substances' insoluble. or scarcely soluble in water.- Thus gallo-tannic
acid first forms gaillic acid, and is then converted into a brown insoluble
mass; so gum and sugar ultimately produce certain forms of ulmine;
and there are few of' the neutral principles described in the present
chapter that do not rapidly undergo a similar change.
During the evaporation of a vegetable infusion or decoction, these reattions rapidly occur, being promoted by the heat; the liquor, which had
been at first clear, becomes turbid and brown, a de-posite forms, and when,
finally, it has been evaporated to the consistence of a thick sirup, what
remains is termed an extract; it is a mixture of the constituents of' the
plant in great part declriposed.  Ift this extract be treated with water,
and the soluble portion again evaporated, the same changes' occur, so
that, no matter what may have been the original nature of the vegetable
substances, they are ultimately reduced to this insoluble and inert condition.  This brown substance is termed Apotheme; its true nature is'not known, but it is probable that its composition and properties vary in
some degree with the nature of the substance it is formed from; we do
not even know of its relations to the various kinds of ulmine; though,
from its solubility in alkaline liquors, and its precipitating metallic salts,
its being separated foi'o  these by acids, and obstinately retaining a portion of the acid used to precipitate it, its identity with ulmic acid or
humir acid is not improbable.
When the conversion of the real constituents of the plant into' apo.
theme is yet incomplete, the material, which dissolves equally in water
and dilute alcohol, but not in absolute alcohol or in ether, is termed
extractive.  Such a mixture can have no distinctive chemical properties;
it is more or less coloured, and uncrystallizable; it precipitates metallic
salts; it absorbs oxygen, forming apotheme (oxidized extractive).  The
different classes of plants are considered by pharmaceutic writers to contain different kinds of extractive matter; there are thus bitter extractive,
gitummy extractive, astringent'extractive, and so on; but, to the chemist,
these names convey only the idea of absolute ignorance of the real
nature of these bodies; the chemist recognises no such substance as
extractive matter, or Apotheme; they are merely complex products of
decomposition of other bodies, and have not, as yet, been accurately examined.  In the preparation of an extract of a plant, the ambition of the
operator should be, not to have either extractive or apotheme produced,
but, by employing the lowest possible temperature, and excluding air as
much as possible, to obtain the constituents of the plant in a concentrated
form, but not destroyed, as they too frequently are, by the operation:
accordingly, in the manufacturing laboratory of the Apothecaries' Hall
of Ireland, the greatest precautions are taken to ensure success in the
preparation of extracts; but details of the methods belong to pure pharmacy, and are unfitted for the present work.
A great number of bodies, that have been from time to time announced as the
active principles of many plants containing them, are really but such extracts, prop



COLOURING  MATTERS.                               613
eny prepared, but still not the pure chemical substances. Thus, from colocynth,
Colocynthine; from hippo, Emetine; fromn rhubarb, Rheine, &c. It is on this account
that many bodies, to which distinct names have been given by their discoverers, as
chemical species, are not noticed as such by me.
The bitter principle of the Aloes is one of these which have never been obtained
chemically pure, and yet the very remarkable products of the action of nitric acid
on it show that it is a truly distinct substance. When socotrine or hepatic aloes
are digested with hot nitric acid, red fumes are abundantly evolved, and four different acids Droduced, for the accurate examination of which we are indebted to
Schunk. They are, the Aloetic Acid, the Alo-resinic Acid, the Chrysammic Acid,
and the Chrysolepic Acid, and they are generated by successive oxidation of the bitter principle of the aloes, in the order in which their names stand.
The Aloetic Acid is a yellow powder, insoluble in water, but forming soluble salts,
of which that with potash crystallizes in ruby-red needles. The AloE-resinic Acid
is soluble in water; its potash salt uncrystallizable; its combinations with the metallic oxides insoluble, and generally brownish-red. The analyses of these bodies
are not yet published.
The Chrysammic Acid is a greenish-yellow crystalline powder; it is very sparingly soluble in water, yet tinges it purplish-red; it is more soluble in alcohol, ether,
and acids; when heated, it fuses, and is then decomposed with a slight explosion,
and a bright but smoky flame; it contains nitrogen; its formula is C15H2. N2012+
Aq. The chrysammate of barytes is a red insoluble powder. The chrysammate
of potash is the most insoluble of all the salts of potash, requiring 1250 parts of water at 600 for solution, and may hence serve as an excellent reagent for that alkali;
it is a dark red crystalline powder when precipitated, but when it crystallizes from
a hot dilute solution, it forms gold-coloured plates.
The Chrysolepic Acid is distinguished by its solubility in water; i.t crystallizes In
beautiful gold-coloured plates, closely resembling Piclic Acid, with which it is isomeric, its formula being C12H2. N303s+Aq. It is distinguished, however, by the
much greater solubility of its potash salt, and by the action of heat, as it may be
fised and volatilized without decomposition, if cautiously heated.
CHAPTER XXVI.
OF TIHE COLOURING MATTERS.
THE substances to be now described may be arranged in two classes,
according as they pre-exist in the plant, or as they are merely products
of the decomposition of other bodies which are not coloured; of these
last an example has already been given in the formation of phloridzeine
from phloridzine.
SECTION I.
OF THE PRE-EXISTING COLOURING MATTERS.
Colouring Principles of Madder.
The dried' roots of the rubia tinctor6m constitute the madder of comrn.
merce, which, furnishing the well-known Turkey red, is perhaps the
most important of the dyestuffs.  The constitution of madder is very
complex; it contains five different colouring matters and two colourless
acids, the general preparation and properties of which are as follows:
Madder Purple, or Purpurine.-Madder roots are to be well washed
with water at 80~, then boiled several times in a strong solution of alum,
and each liquor filtered while very hot. On cooling, a red-brown sub.
starea precipitates, which is impure Madder Red; it is to be separated




614      COLOURING PRINCIPLES  OF MADDER.
by the filter. Oi adding to the clear red solution some.sulphuric acid,
the madder purple is thrown down.  To obtain it quite pure, it is to be
dissolved in boiling alcohol, and the solution allowed to evaporate slowly.
It separates as a fine orange-red crystalline powder, sparingly soluble
in c'old, but more easily in boiling water.  The solution is rose-red; its
solutions in ether and alcohol are bright red.  Acids turn it yellow; al.
kalies dissolve it with a rich red colo'ur.  It is fusible, and, when more
strongly heated, a portion sublimes as a red powder, but the greater part
is decomposed.
MlIadder Red, or Alizarine, as precipitated in the preparation of purpurine, is to be purified by repeated boiling with solution of alum, and
then crystallized by solution in ether and spontaneous evaporation. It is
a brownish.yellow crystalline powder. When heated, it sublimes, forming brilliant orange needles; it is sparingly soluble in water, more so in
alcohol and ether. Ammonia dissolves it with a purple red, and potash
or lime with a violet colour.:The formula C7tI,2O,0 has been assigned
to this body.
Madder Orange.  The roots are to be digested for sixteen hours in
eight parts of water at 700; the infusion is to be filtered and set aside;
small orange crystals gradually form; these are to be collected and dis.
solved in boiling alcohol. On cooling, the madder.orange crystallizes as
a yellow powder.  When heated, it fuses, and is decomposed in great
part, some of it subliming in yellow fumes; it is most easily. soluble in
ether; it dissolves in alkaline, forming brown.red liquors.
Madder Yellow, or Xanthin.-The cold infusion of madder is to be
mixed with an equal volume of lime water.  The dark-red precipitate
is to be treated with dilute acetic acid; the lime and the yellow dissolve;
any traces of the other colouring matters are removed from the liquor
by a woollen cloth mordanted with alum. The solution is to be then
evaporated, the residue dissolved in alcohol, and precipitated by sugar
of lead; the scarlet precipitate separated, and decomposed by sulphuretted hydrogen. The liquor so obtained'gives, on evaporation, the xan.
thine pure; it is yellow, uncrystallizable, and very soluble in alcohol
and water.
Madder Brown is totally insoluble both in alcohol and water.  The
acids which exist in madder are but very little known, and do not possess
any interest either technical or scientific.
Of these colouring matters, the Red, or Alizarine, is the most important,
as it forms with an alumina mordant the magnificent Turkey Red. With
an iron mordant it gives a permanent black, and with mixed mordants
of the two, various intermediate shades of purple. The great complexity
of the process. for: dyeing Turkey red arises from the difficulty of dis.
solving away the other four bodies, so that only pure madder red may
remain.
Alikanna, Red, or Anchusic Acid.
This substance exists in the:roots of the anchusa tinctoria. They are to be well
boiled in water, and then digested in-a solution of carbonate of potash; on the addition of an acid to this liquor, the colouring matter precipitates; it may also be
obtained by digesting the roots in alcohol and evaporating; it is a dark-red resinous body, insoluble in water, soluble in alcohol,: ether, and the essential oils; it
combines with alkalies, forming blue solutions, which give blue or crimson lakes
with metallic salts. The formula C17HI004 has been assigned to this body.
Braziliine is the colouring matter of various srenies of cmsalpina (Brazil wood.




SAFFLOVWER  RED; ETC.                                615
rernambolc wood). The decoction of the wood in water is to be agitated with hy.drated oxide of lead, then filtered and evaporated to dryness.  The residue is to be
treated with alcohol, the solution mixed with water and gelatine, which throws
down a quantity of tannic acid, then filtered, again dried, mixed with alcohol, and
filtered to separate the excess of gelatine, then again evaporated, and set aside to
crystallize.
WVhen pure, braziliY'ne forms orange crystals; it is soluble in water, alcohol, and
ether; the solutions are reddish-yellow; alkalies and most metallic salts give purple, and alum a red precipitate, with the solution of brazilii'ne
Santaline exists in the red sanders wood (pterocarpus santalinus). It" extraction
and properties are exactly similar to that of the Alcanna Red. Its formula is
C16Hs03.
-I-ematoxyline.-This substance, the colouring principle of the logwood (haerna
toxylon Campechianum), is frequently met with naturally crystallized in stellated
groups of' prisms, sometimes of considerable size, in clefts of the wood; it may also
be prepared by a process similar to that described for brazililne; it is slightly bitter
and astringent; it is very sparingly soluble in water, but copiously in alcohol and
ether, forming brownish-red liquids. Acids colour its solutions yellow, alkalies
purple; with the earths and metallic oxides it forms purple or blue lakes.
Sajltower Red, or Carthamine.
The petals of the safflower (carthamus tinctorius) contain a red and a yellow ma
terial; the former alone is of technical importance. The flowers are to be washed
with water acidulated with acetic acid until all the Safflower Yellow is removed.
By digestion then in a solution of carbonate of soda, the carthamine is dissolved,
and may be precipitated by any acid, but citric acid answers best; it forms a dark
red powder, insoluble in water and in acids, and but sparingly soluble in alcohol oi
ether; it reddens litmus, and gives with the alkalies yellow solutions; its compoulnd with soda crystallizes in silky needles; with alumina it forms a beautiful
redi lake, Roug-e, used as a cosmetic and in dyeing.  This substance is much em
p.6yed for dyeing silk of various shades of pink and rose colour.; I have found in the petals of the salvia fulgens a colouring matter possessing con$iderable analogy to carthamine, and capable of being substituted for it.
Quercitrine.-This substance is extracted from the bark of the quercus infectoria
by simple decoction in water; after'some days the colouring matter separates in
crystals; or, better, by digesting the bark in alcohol, precipitating the tannin by gelatine and evaporation: when pure, it resembles very minute crystals of yellow
prussiate of potash; it is easily soluble in water and in alcohol, and appears to possess feeble acid properties.  Its formula, by Bolley's analysis, appears to be C16H9gC
+-Aq.  With metallic oxides it gives brilliant yellow lakes.
Chrysorhamnine.  Xanthorhamnine.
I have found the unripe berries of the rhamnus tinctorius (Persian berries, grains
d'Avignon) to contain a substance soluble in alcohol and ether, and crystallizing
from its ethereal solution in minute silky needles of a brilliant yellow colour; it
gives with metallic oxides yellow lakes.  When cautiously heated it fuses, but is
not volatile. In the ripe berry, this substance, to which I have given the name
Chrysorhaemnine, is totally replaced by another, which I term  Xanthorhamnine,
which is of a much less beautiful yellow, and does not crystallize; this change is
effected, also, by boiling the chrysorhamnine for a few minutes with water, or by
contact with alkalies. The xanthorhamnine is totally insoluble in ether, but easily
soluble in alcohol and water.  It is formed by the union of the elements of water
with chrysorhamnine.  Its silver salt is yellow when first thrown down, but rapidly becomes black, metallic silver separating, and a colourless organic substance
being formed. The Persian berries are much used for dyeing yellow, but, from the
processes employed, the xanthorhamnine alone is actually brought into play.
Lueioline is the colouring principle of the weld (reseda luteola), and probably of
the dyers' broom (genista tinctoria). Its mode of preparation resembles that of
quercitrilie.  It is soluble in water, alcohol, and ether; it combines with both acids
and alkalies, forming yellow compounds.  With alumina and the oxides of tin and
lead, it gives brilliant yellow lakes. with iron, a dark brown precipitate.
Morine is the colouring principle of the yellow-wood (morus tinctorius); it isPIepared like quercitrine, with which its properties accurately agree.
Orellinc.-The seed of the bixa orellana are imbedded in an orange-red colouring




616                  COCHINEAL  RED, ETC.
matter, which is separated by washings and a kind of fermentation; when deposit
ed from the liquors, so as to form a consistent paste, it is sent into commerce under
the names of Rocou, Orleans, or Anotta. To obtain the colouring principle pure, the
orange-red mass is digested in alcohol, and the solution distilled nearly to dryness;
the residue is then' treated with ether, which dissolves the orelline, and yields it, on
evaporation, as an orange-red, somewhat crystalline powder; it colours water pale
yellow; it is more soluble in alcohol, but gives with ether or oils deep red solutions;
it dissolves in alkalies, and is precipitated therefrom by acids. With alumina, oxide of tin, and oxide of lead, it gives fiery red precipitates.  Tt is extensively used
in dyeing, and also to heighten the colour of cheese and butted'.
Curcumine is found in the roots of the curcuma longa (turmeric), and is obtained
by treatment with boiling alcohol, evaporation to dryness, and digestion of the residue in ether, which dissolves the pure colouring matter, and yields it by spontaneous evaporation.  Curcumine melts at 1040; it possesses the properties of a resin;
alkalies brown it. on which its employment for a test-paper rests; acids render its
proper yellow much paler, except boracic acid, which stains it yellowish-red.
Berherine exists in the roots of the berberis vulgaris; it is prepared by boiling the
roots in water, and evaporating the decoction to the consistence of an extract,
which is to be treated with spirit of wine as long as this acquires a bitter taste.
The spirit is to be distilled in great part off, and the residue suffered to stand in a
cool place for twenty-four hours; the crystals which form are to be recrystallized,
first from water, and then from alcohol. Pure berberine forms a light crystalline yellow powder of a strongly bitter taste; it is very sparingly soluble in cold, but abundantly in boiling water and in alcohol; it is insoluble in ether. At 268~ it melts,
and, if farther heated, is decomposed, giving ammoniacal products; by chlorine
it is converted into a brown-red substance; it combines with bases, acting feebly as
an acid; its alkaline compounds crystallize; those with the earths and heavy metallic oxides are insoluble, and generally yellow; a solution of it precipitates the
iodide, cyanide, ferrocyanide, and sulphocyanide of potassium. Berberine contains
nitrogen, its formula being N.C33. HisOl2.
Cochineal Red, or Carmine.
This very remarkable substance differs from all of the other colouring matters:
here described, in being a product of the animal kingdom. It exists in many insects of the genus coccus, as the coccus cacti (the true cochineal), the coccus ilicis
(kermes), the coccus ficus (lac dye), &c. For its preparation the cochineal is to be
digested in ether to remove a quantity of fat, and then boiled in alcohol as long as
this is coloured. The alcoholic liquors, being mixed, are to be concentrated by distillation, and then cautiously dried; the impure carmine thus obtained is digested
in alcohol, and the solution mixed with ether, which precipitates the colouring mat
ter quite pure.
It is a purple red powder, easily soluble in water and alcohol, insoluble in ether.
It melts at 1220, but is decomposed by a high heat; chlorine turns it yellow; alkalies colour cold solution of carmine red, but it becomes yellow by exposure to the
air or by boiling. With alumina it forms a precipitate, which is crimson when prepared with a cold, but violet if with a hot solution. All metallic salts give lakes
-with the alkaline solution of carmine; that of the protoxide of tin is a rich scarlet.
The carmine of commerce is an alumina lake more or less pure; that called Chinese Carmine is the compound with oxide of tin.
The carmine contains nitrogen; the formula N.C32. H26020 has been assigned to
it, but cannot be considered as definitely established.
Of Indigo, and the Bodies derivedfron  it.
The blue indigo of commerce is derived from the leaves of a variety
of plants of different genera.  The genus indigofera includes a number
of productive species, also the genera nerium  and isatis, marsdelia, as.
clepias, and polygonum, galega, spilanthus, and amorpha.  Of these the
great majority are natives of the tropics; but a few, as the isatis tincto.
ria.,and the polygonum tinctorium, belong to temperate regions, the former being indigenous both to Ireland and to England.
The indigo is secreted in the cellular tissue of the leaf, in a form (white




BLUE  AND  W~HITE  INDIGO.                     61
indigo) which can also be artificially produced; it is then colourless,
and remains so as long as the tissue of the leaf is perfect. When the
leaf begins to wither, oxygen is absorbed, and, the indigo assuming its
colour, the leaves become covered with a number of blue points, the first
appearance of which shows that the period for collecting them has arrived.  The fresh leaves are thrown into large vats with some water, and
pressed down by weights.  After some time, a kind of mucous fermentation sets in, carbonic acid, ammonia, and hydrogen gases are evolved,
and a yellow liquor is obtained, which holds all the indigo dissolved.
This is separated, mixed with lime-water, and then exposed to the air until the indigo becomes blue and insoluble, and is completely deposited as
a precipitate.  The theory of this action is, that, by the putrefaction of
the vegeto-animal matter of the leaves, the indigo is kept in the same
white, soluble condition in which it exists in the plant, and a clear solu.
tion of it being thus obtained, it is precipitated, according as it absorbs
oxygen, in a much purer form than otherwise could be effected.
The putrefying pasty mass of leaves obtained from the isatis tinctoria
constitutes the woad or wad employed in the hot indigo bath for dyeing
cloth.
The blue indigo, as thus obtained, is still a mixture of several bodies,
as indigo-red, indigo-brown, indigo-gluten, which are removed by repeated treatment with alcohol and dilute acids and alkalies.  When pure, the
precipitated indigo is a rich blue powder, which, when rubbed by a knife,
assumes the colour of metallic copper; it is perfectly insoluble; when
cautiously heated, it sublimes in rectangular prisms of a dark purple colour and metallic listre; its vapour is of a rich purple; it contains nitrogen, its formula, as fully established by Dumas, being N.C,6. H502.
White Indigo. -When indigo is acted upon by deoxidizing agents, as
protochloride of tin, protoxide of iron, or sulphurous acid, it loses its blue
colour, and the white indigo, which is insoluble in water, but soluble in
alkaline solutions, is produced.  Its mode of preparation is simple: one
and a half parts of commercial indigo, two and a half parts of slacked
lime, and two parts of green copperas, are to be well mixed up with six.
ty parts of water, in a vessel from which the air is carefully excluded.
The protoxide of iron, formed by the action of the lime on the copperas,
peroxidizes itself at the expense of the indigo and water, and the white
indigo thus formed dissolves in combination with lime.  On adding mu.
riatic acid to the clear solution, the white indigo precipitates, and may
be obtained dry, as a crystalline powder, by suitable precautions to pre.
vent the access of air.
The simplest theory of this process should be, that the oxide of iron
directly abstracted oxygen from the indigo: hence the names of Deoxidized
Indigo and Indigogene were given to the white substance; but the analyses of Dumas have proved that the white indigo is a compound of hy.
drogen with the blue indigo, its formula being C,06H. N.02+H.  In its
formation, therefore, water is decomposed, the elements of it combining
respectively with the blue indigo and the deoxidizing body.
On the properties of this white indigo depend the important application
of indigo as a dyeing material.  The indigo is rendered soluble either by
lime and copperas (cold indigo bath), or, being diffused through warm wa.
ter with a quantity of woad, by the fermentation of which ammonia and
hydrogen are evolved, d soluble compound of ammonia and white indigo
41




618             SULPHAT E S  O F  I NDIGO, ETC.
is obtained (hot indigo bath); the former is employed for cotton, and the
latter for woollen. cloth.  The cloth is immersed in the bath until it has
fully imbibed the solution; it is then exposed to the air, the oxygen of
which carries off the hydrogen of the white indigo, and the blue insoluble
indigo attaches itself to the fibres of the cloth so firmly at the moment
of its formation, as to constitute the most permanent and the most beautif'ul of our blue dyes.
Sulphate of Indigo. —When blue indigo, in very fine powder, is digested with strong oil of vitriol, for which purpose the German or fuming sulphuric acid answers best, it dissolves in great part, and two acids are
formed, the Sulphopurpuric arid Sulphindylic; the former.is the principal product when the indigo is in excess, the latter when the oil of vit.
riot preponderates; they are separated by dilution with water, the sulphopurpuric acid being insoluble, while, the sulphindylic acid dissolves.
The sulphdp)urpuric acid, tl-ough insoluble in dilute acids, dissolves
readily in pure water; it forms, with the alkalies and earths, blue comrn.
pounds, which are sparingly soluble in water, but soluble in alcohol. By
the analysis of Dumas, it appears to consist of C32Ho0. N204+2S.03, and
in its potash salt to contain one atom of alkali.
The sulphindylic acid, C,6H5. N.02+2S.03, when dried from its solution in water, forms a dark blue mass.  Its salts are of' a rich blue colour; those of the alkalies are soluble, those of the earths and metallic ox.
ides insoluble in water.  They consist, according to Dumas's analysis, of
an atom of indigo, two of sulphuric acid, and one of base.  The sulpho.
purpuric and sulphindylic acids thus contain the same organic element
(indigo), but in different proportions, united to sulphuric acid.
Berzelius considers that, besides these two, there are generated, by the
action of sulphuric acid on indigo, several other acids of complex nature;
but, as we possess no exact results concerning them, and as they are
of no technical importance, it is unnecessary to describe them in detail.
This solution of indigo in oil of vitriol constitutes the Saxon Blue, or
Chemic Blue, used extensively in dyeing; on neutralizing the liquor by
an alkali (carbonate of soda), and immersing the tissue, whether wool,
silk, or cotton, the indigo combines with the fibre of the cloth, and the
sulphuric acid remains combined with the alkali.
By the gradual oxidation of indigo, a substance is formed which crystallizes in
large red prisms, and is termed by Laurent Isatine; its formula is 0C6H5. N.04. If
the process be more violently carried on, the constitution of the indigo is broken up,
and a new type formed, thus: by the action of an excess of nitric acid on indigo,
two remarkable bodies are formed, the Anilic and the Picric Acids. A mixture of
one part of fuming nitric acid and ten of water being brought to boil, indigo is to be
added in fine powder as -long as any effervescence occurs; the liquor is to be then
filtered whilehot. Both acids crystallize on cooling; the crystals are to be drained, redissolved in water, and precipitated by acetate of lead; picrate of lead falls;
anilate of lead remains dissolved-, and, being decomposed by sulphuretted hydrogen,
the Anilic Acid crystallizes in white needles; its taste is hitter and acid; it requires
1000 parts of cold, and but ten of boiling water; its salts are all soluble; its formula is C014H4.. N.O9+Aq.
The Picric Acid may be obtained by diffusing the picrate of lead through boiling
water, and decomposing it by sulphuretted hydrogen gas; on filtering and cooling,
the picric acid crystallizes. It may be obtained,'however, much purer and more
abundantly by digesting salicine in nitric acid (p. 606), and directly from the sub.
stance which exists in coal gas naptha, termed by Laurent hydrate of phenyl; it
forms yellow prisms, sparingly soluble in cold water; when heated, it explodes, as
do also its salts; its potash salt requires 260 parts of pold water for solution, and
it is hence.' sometimes used as a reagent for that alkali; its formula is C12H3. N3013
+Aq.




ACTION OF CHLORINE ON INDIGO.                              619
W'hen indigo is mixed with a strong boiling solution of caustic potash, it dissolves,
and Chrysanilic Acid is formed, which may be precipitated by muriatic acid as an
orange-red powder; it dissolves in alcohol and ether, and crystallizes by the evaporation of the solutions; its formula appears to be C2sHio. N.O5+Aq. By exposure
to the air while hot, or directly by contact with peroxide of manganese, this acid is.
converted into another, Anthranilic Acid, the properties of which are remarkable;
it is soluble, crystallizes, gives very well-marked and crystallizable salts, fuses at
2750, and sublimes a little above that temperature unchanged; if it be strongly
heated, however, it is decomposed, the sole products being carbonic acid and a volatile liquid, Alilene. The formula of the hydrated anthranilic acid is C14H77. N.04,
and it gives 2C.02 and C,2H, N.
This liquid, anilene, is a body closely analogous to the melamine (p. 526); it acts
as a powerful base, combining with the hydracids directly, and with the oxacids by~
including an atom of water; it thus resembles ammonia. These important substances, for whosediscovery we are indebted to Fritzche, are still under examination.
Action of Chlorine on Indigo. —This subject, so important in relation to the theory
of the bleaching of colouring matters, has been very minutely investigated by Erdman, of whose numerous and complex results the elementary nature of this work
will allow but a general notice to be given. Dry chlorine has no action on indigo,
but in presence of water it converts it into a yellow mass, from which is separated,
by distillation, a substance termed Chlorindoptten, which sublimes in white scales
and needles; its formula is C16H4. 02C14; it is sparingly soluble in water, copiously
in alcohol and ether. This appears to be a secondary product. The substance
which remains behind in the retort, on being dissolved in boiling alcohol, yields, on
cooling, red prismatic crystals of Chlorisatine: its formula is C16H4C1.. N.03; it is
hence indigo, in which an equivalent of hydrogen is replaced by chlorine, and united
to an atom of oxygen; with an excess of chlorine it gives Bichlorisatine, which consists of C,6H4C1. N.Os. If these bodies be treated with sulphuretted hydrogen,
sulphur is set free, and the hydrogen enters into combination; in contact with potash, the elements of an atom of water are assimilated, and an acid formed, which
unites with the potash. In this way chlorisatine gives Chlorisatyd, C,6HC1.. N.03,
and Chlorisatic Acid, CI6H5Cl.. N.O4, and bichlorisatine gives two corresponding
bodies.
If chlorisatyd be heated, it produces water, chlorisatine, and a violet powder, Chlorindine, which has the formula C6HSC1.. N.02, and is hence a compound of indigoblue with chlorine. By heating bichlorisatyd, the Bichlorindine, C16H5N.. 02C12, is
similarly formed.
By passing chlorine through a solution of chlorisatine in alcohol, all hydrogen is
removed, and a substance formed which crystallizes in pale yellow plates, and has
the formula CO0 2C1; it is termed Chloranil. By the secondary reactions of these
bodies, a number of others are generated, which it is not necessary specially to describe.
Notwithstanding the attention devoted by the most distinguished chemists to the
compounds and derivatives of indigo, the theory of that body remains very obscure.
The derivation of picric acid from the body Ci2H50.+Aq. (Hydrate of Phaenyl), discovered as a product of destructive distillation by Laurent, may serve as a connecting point for many of the bodies derived from indigo, and which otherwise had appeared totally unconnected. Thus the picric acid is evidently formed by the substitution of 3N.04 for 3H. in C12H50., and the anilene is probably C.2Hs+N.H2;
other speculative ideas might be brought forward, but I shall only mention that the
blue indigo contains exactly the elements of cyanogen and benzyl, C2N.-+C4H502,
and that, as the cyanogen is converted so easily into oxalic acid and ammonia, the
derived bodies, which contain C14, may thus have their origin.
Of the Colouring Matters' derivedfront the Lichens.
Many species of lichen contain substances which, although colourless themselves,
produce, by contact with air and ammonia, the rich purple or blue colouring matters constituting the archil and litmus of commerce. The species of lichen that
have been in this respect most accurately examined are- the variolaria dealbata by
Robiquet and Dunmas, and the rocella tinctoria by myself.
The useful substance in the variolaria is termed Orcinze; it is obtained by digesting the lichen in alcohol, evaporating to dryness, dissolving the extract in water,
concentrating the solution to the thickness of a sirup, and setting it aside to crys



6;20            ORCEINE, ERYTHRYLINE,   ETC.
tallize; it forms, when quite pure, colourless prisms of a nauseous-sweet taste; it
fuses easily, and may be sublimed unaltered; its formula is Cls8H703+2 Aq. when
sublimed; when crystallized from its aqueous solution, it contains 5 Aq.
If orcine be exposed to the combined action of air and ammonia, exactly as described for phloridzine (p. 607), it is converted into a crimson powder, Orceine, which
is the most important ingredient in the archil of commerce.  The orce'ne may also
be obtained by digesting dried archil in strong alcohol, evaporating the solution in
a water-bath to dryness, and treating it with ether as long as anything is dissolved
it remains as a dark blood-red powder, being sparingly soluble in water or ether,
but abundantly in alcohol; its formula is C18H,0. N.08. The orceine in archil is,
however, frequently found to contain less oxygen, and to be represented by the
formula CsHo. N.05. I have termed the first kind Alpha-orceine, and the secondr
Beta-orceine; in properties they are identical.
Orceine dissolves in alkaline liquors, with- a magnificent purple colour; with me
tallic oxides it forms lakes, also, of rich purple, of various shades.  In contact with
deoxidizing agents it combines with hydrogen, as indigo does, and forms Leucorceine, C,8H10. N.Os+H. When bleached by chlorine, a yellow substance is formed,
Chlororceine, the formula of which I have found to be C8sHlo. N.s-8Cl., analogous
to the other.
In the rocella tinctoria there is no orcine; the origin of the coloured substances
is a body which I have termed Erythrylinze; it is soluble in ether and alcohol. insol.
uble in water, but is gradually decomposed by it; its formula is C22111606.  By the
action of the air it is gradually changed into Erythrinze, a substance which dissolves
sparingly in cold, but abundantly in boiling water, from which it separates on cooling in brilliant micaceous plates; it is very soluble in alcohol and ether; its formula
is C22H1309. By prolonged boiling in water, erythrine is.changed into a substance
very soluble in water and in alcohol, Amarythrine, the formula of which is C22H13014;
and, finally, by the still farther action of the air, Telerythrine is formed, which crystallizes in small grains, and has the formula C22H9018.
If, however, in addition to the air, ammonia have access to these bodies, the
crimson colour is produced, and the two varieties of orceine are formed. I conceive
the oxidizing stage to proceed as far as amarythrine, and that, by combination with
ammonia and oxygen, a substance is formed, to which I have given the name of
Azoerythrine.  Its formula is C22H16. N.019 —3 Aq. By the loss of 4C.02 and
6H.O., it gives alpha-orceYne, C8Hlo. N.05, which, absorbing oxygen, gradually
forms the true or beta-orceine, C8sH1o. N.Os.
When an alkaline solution of orceine is exposed to the air, it absorbs more oxygen, and a substance is produced which constitutes a great part of the colouring
material of litmus. I have termed it Azolitmine; its formula is Cs8H10. N.Ojo; it is
a dark red powder, which is insoluble in alcohol or ether, and but sparingly soluble
in water; it dissolves better in acid liquors, which render it a pale red, and with
alkalies it gives the rich blue colour of litmus.  With the earths and metallic oxides it forms purple or blue lakes; with deoxidizing agents it is decolorized, form
ing Leucolitmine, and by chlorine a yellow substance is produced, having the foi
mula CsH1o. N.Olo+Cl.
Besides the bodies of the erythrine series, the lichen rocella contains a substance,
termed -Rocelline, which is white, fusible, insoluble in water, soluble in alcohol and
ether; its formula is C26H2406. By exposure to the air, it is converted into a fatty
substance of a rich crimson colour, which I have termed Erythroleic Acid; this body
exists in archil, and is separated from the orcei'ne by means of its solubility in ether.
Its formula is C26H228s; it is capable, under circumstances which are not yet well
understood, of being broken up into two substances, which are both found to exist
in litmus; they are Erythroleine, which has the formula C26H2204, and Erythrolitmine, which consists of Cs6H22012. The erytbroleine and erythroleic acid are, like
the alpha and beta orceines, distinguished only by their composition; they have the
same colour, are sparingly soluble in water, but copiously in alcohol and ether; they
dissolve in alkaline liquors with a rich crimson colour, and give crimson lakes with
the metallic salts. The erythrolitmine, on the other hand, is bright red, very sparingly soluble in water or ether, but soluble in alcohol. Alkalies turn it bright blue;
in a solution of potash it dissolves, but its compound with ammonia is insoluble,
and consists of U(JsH2201.2+N.H40.
The brief history of these substances now given will render intelligible the process
of manufacture of archil and litmus, and the principles of their use in the arts an:l
in the laboratory. The lichens employed are ground up with water to a uniform




, OLOURING  MATTERS  OF  LEAVES; ETC.    621
pulp, and this is then mixed with as much water as makes the whole thick-fluid.
Ammoniacal liquors from the gas or ivory-black works, or even stale urine, are from
time to time added, and the mass frequently stirred, so as to promote the action of
the air. The orcine or erythrine which existed in the lichen absorbs oxygen and
ammonia, and forms  orceine; the rocelline absorbs oxygen, and forms erythroleic
acid; these being kept in solution by the excess of ammonia, the whole liquid is of
an intensely rich purple tint, and constitutes ordinary archil.  If the oxidizing action of the air be allowed to go'too far, we have the purple colour replaced by a
shade more or less blue; the orcei'ne changes to azolitmine, and the erythroleine
gives erythrolitmnine; a quantity of chalk and plaster of Paris is then added to the
liquor, so as to form a consistent paste, and this, cut into little cubical masses and
dried, forms the Litmus of commerce. From the constitution of archil and litmus,
such must be the general principles of the manufacture, although, particularly for
litmus, the details are kept very secret by those engaged in the trade.
The use of litmus paper as a test for the presence of a free acid arises from the
blue colour belonging to compounds of the erythrolitmine and azoerythrine with an
alkali, and as this istaken by even the weakest acid, the red colouring materials
are set free.
Of the Colouring Matters of Leaves and Flowers.
The green colour of plants is due to the presence of a substance termed Chlorophyll. Even deeply-coloured plants contain but very little of it, and it has not, as
yet, been obtained in a state of such purity as that any formula can be assigned to
it. It does not contain nitrogen; it is insoluble in water, soluble in alcohol and
ether; it is dissolved by strong acids, and precipitated therefrom by dilution; it
enters into union with bases, and gives pale green lakes. With deoxidizing agents
it shows the same process of decoloration as most other bodies of this class.
Berzelius has noticed that there are really three kinds of chlorophyll: the first,
which exists in fresh leaves, dissolves in acetic acid with a rich grass-green colour; the second, formed from the first by drying, gives an indigo-blue solution with
the same acid; and the solution of the third, which exists principally in the pyrus
aria and other dark-leaved plants, is brownish-greeri  So excessive is the colouring
power of this body, that Berzelius has calculated that the entire mass of leaves of
a large tree seldom contains ten grains of chlorophyll.
It is known that in autumn the leaves of many trees, as the sorbus aucuparia,
corrals sarnguinea, &c., assume a fine red colour, while the foliage of others, particularly of ftrest-trees, becomes bright yellow.  Berzelius, who has examined the
nature of this change, found the chlorophyll to be replaced in sucel leaves by a red
and a yellow colouring matter, to which he gave respectively the names Erythrophyll and Xarthophyll.  The former is an extractive matter, easily soluble in alcohol
and water;'by the air it is gradually changed into a brown insoluble matter; with
alkalies it forms rich green solutions, and with metallic oxides, green lakes; by
acids the red colour is restored; a green leaf containing chlorophyll is, however,
not reddened by an acid. It is remarkable, that all trees in whose leaves erythropbyll forms in autumn bear red fruit, as the cherry, currant, &c.
XYanthophyll is a deep yellow, fatty substance, which melts between 1000 and
1200; it is insoluble in water, but dissolves copiously in alcohol and ether; its solution, exposed to the air and light, is rapidly bleached: alkalies dissolve it sparingly with a yellow colour, which is bleached by light.
We possess bit very little accurate knowledge of the colouring matters of flowers: they constitute a very remarkable group of bodies, closely related to each
other, and distinct from the colouring matters that have been as yet. examined. It
has been stated that the colours of all flowers result from two; one blue (Anthocyan), which is soluble in water and alcohol, reddened by acids, rendered green by
alkalies, and from these changes producing the red, and all intermediate shades of
purple and violet; the yellow substance (Anthoxanthine) is likewise easily soluble
in alcohol and water, and is coloured intensely blue by oil of vitriol. These substances possess' most analogy to hematoxylin and to safflower-yellow; but it is
highly probable that a great number of species of colouring matters exist in flowTers
as they do in woods. The quantity present in the flower is generally so excessively minute, that the accurate examination of their properties is exceedingly dif/
ficult




622            THEORY OF DYEING, ETC.
On some general Characters of Colouring Matters, and on the Principles
of Dyeing.
In addition to the detailed history of the individual colouring matters,
there are a few remarks belonging to them as a class which deserve
notice.
Under the heads of indigo and of orceine, I have described the formation of white compounds, by the action of deoxidizing agents, and that
in those, which are the only cases that have been accurately examined,
it resulted from the direct combination of hydrogen with the colouring
matter.  This character of forming a colourless compound with hydrogen appears to belong to all colouring substances.  If an infusion of log.
wood, of cochineal, of violets, of immerin, be rendered acid by muriatic
acid, and a slip of zinc immersed therein, the liquor becomes gradually
colourless, and on adding ammonia, a white lake is precipitated, consisting of the hydruret of the colouring matter combined with oxide of zinc.
With oxygen all colouring matters appear also to combine to form bod.
ies quite or nearly destitute of colour.  Thus, if the chrysorhamnate of
silver be boiled in water, metallic silver separates, and oxidized colouring matter dissolves.  This illustrates the manner in which coloursfade,
and they are more or less fugitive, according as their tendency thus to
combine with oxygen is greater. On this principle was founded the old
process of bleaching, by exposing the cloth to the conjoined agencies of
water, air, and light. The bodies whose colour injured the whiteness of
the cloth were gradually changed by oxidation into others, less coloured
and more easily removable by washing.  In the majority of cases, however, the process is not limited to simple oxidation, but carbonic acid is
evolved, and the colouring matter is totally broken up in constitution.
The colour of many substances, as logwood, archil, litmus, indigo, of
most flowers,4&c., is removed by sulphuretted hydrogen and by sulphurous acid.  In'these cases there is direct combination, and the colour is
restored by expelling the combined gas, by heat, or by a strong acid.
For commerce, many bodies, particularly those of a yellow colour, are
given a temporary whiteness by stoving or smoking with sulphurous
acid, by placing them in a room where sulphur is burned; this is done
with corn, with straw fbr hats, with sponges, &c.  The sulphurous acid
gradually goes off afterward, and the yellow colour returns.
The destruction of colours by means of chlorine is the most important
decomposition to which this class of bodies is subject, as on it the modern
processes of bleaching all our woven tissues, paper, &c., is founded.
Innumerable niceties in the application of coloured patterns on cloth
would be impossible, and the art of the calico printer restrained to very
narrow limits, were it not for the power which chlorine gives him of removing the original colour from any chosen space, and replacing it by
others of various tints.  The theory of this action of chlorine, which
had been formerly thought to depend upon a mere oxidation of the colouring matter, water being decomposed, has been shown by my results
with orceine, and confirmed by those of Erdman on indigo, to consist in
the formation of new substances containing chlorine.  The chlorine in
sotne cases replaces hydrogen; in others it combines directly with the
colouring matter; in others, nagain, water is decomposed, and the produot, besides containing chlorine, is also more highly oxidized. Tile




FIXING  OF  COLOURS  ON  CLOTH, ETC.                    623
action of chlorine on colouring matter is therefore subjected to the same
laws as when it acts upon other organic substances,, the series of bodies
derived from indigo by chlorine having much analogy to the series of
bodies formed with alcohol or olefiant gas.
In relation to the processes of dyeing, colouring substances are divi.
ded into two classes, the substantive and adjective.  The substantive
colours are those which, being very sparingly soluble in water, and
having a stronlg affinity for the fibre of the cloth, combine directly with
it; such are carthamine and indigo; the adjective colours are itcapable
of so permanently fixin g themselves, and the necessary insolubili.uy and
affinity for the cloth is given through the intervention of a base Nwith
which the colouring substance may combine.  The cloth is mor(danted
with alumina (p. 4'86), or iron (p. 558), or tin (p. 448), or mixtures of
these metallic oxides, and as the lakes so formed are of dil, relnt colours,
a great varietyof tints may be produced.  Tl'he field of application of
substantive colours, also, is greatly enlarged by the use of mordanlts;
the simple colouring matter could, of course, give but its ownatints, while
it forms, with the bases, lakes of various colours.
The resources of the dyer are by no means limited e0en by the vast
number of' coloured substances described in the present chapter.  FroIil
the mineral kingdom, some of the richest colours are now procured, as
has been already noticed in the special history of the salts of chrome, of
iron, of copper, of lead, of manganese, and of antimony.  It is remarka.
ble, that hitherto no true green colouring matter has been found capable
of application in the processBs of dyeing, the only greens which exist in
nature being the chlorophyll and the green of the stems of buck-thorn
(sap-green), neither of which is capable of being attached to cloth: all
greens are, therefore, in practice, formed by the superposition of a blue
(indigo or Prussian blue) and a yellow (chrovmlate of lead or chrysotha mmine).
The details of the processes of dyeing and printing in patterns, al.
though embracing some of the most refined applications of the properties
of the colouring matters, do not enter into the plan of an elementary and
general work, such as this should be.
CHAPTER XXVII.
OF THE VEGETABLE ALKALIES.
THIE substances now to be described constitute a very remarkable
family of bodies. They exist naturally in the plants from which they
are derived, and confer upon them their most active medicinal properties; they act as bases, forming, with few exceptions, well-characterized and neutral salts even with the strongest acids, and they
are distinguished from most substances of vegetable origin by con
tamining nitrogen. The presence of this element, indeed, has been
considered as standing in immediate connexion with the source of
their alkaline power, and has given rise to theories of their intimate




624             QUININE  AND ITS SALTS.
constitution, of which I shall notice the most important at the conelusion of their special histories.
Quinine. —(N.Co,. H2,O,) or Qu. Eq. 163.1 or 2039.
The bark of the various species of cinchona contains three vegetable alkalies, combined with the cinchonic and cinchonatannic
acids already described.  These are quinine, cinchonine, and aricine; of these, the quinine is by far the most important, and is generally extracted from the yellow bark. The coarsely-powdered bark
is to be boiled with eight or ten parts of water, to which two parts
of muriatic acid have been added.  When the liquor will dissolve
no more, it is to be allowed to cool, and strained; lime is then to
be added in very fine powder until the liquor has a marked alkaline
reaction; the precipitate is to be collected on a linen cloth, washed
once or twice with water, and then dried; from thi*, boiling alcohol dissolves out quinine and cinchonine; the solution being mixed
with water, the alcohol may be distilled off and saved; the residue
is to be then neutralized by dilute sulphuric acid, and a slight excess added to form acid salts.  On evaporating this liquor to the
proper point, the sulphate of quinine crystallizes, while the sulphate
of cinchonine remains in solution.
To obtain pure quinine, solution of sulphate of quinine is to be
decomposed by caustic potash, and the white curdy precipitate, being carefully dried, is to be dissolved in'the smallest possible quantity of spirit of wine. By then allowing it to evaporate spontaneously in a warm place, the pure quinine crystallizes with an atom
of combined water.
When heated cautiously, the quinine abandons its crystal-water,
and then fuses; its taste is intensely bitter; it requires 200 parts
of boiling water for solution, and is almost insoluble in cold water;
it dissolves easily in alcohol and ether.
The salts of quinine are generally crystallizable, and soluble in
alcohol and water; those with the oxygen acids contain an atom of
water, in which they agrde with the salts of ammonia, of melamine,
and of anilene; it combines directly with the hydracids.
rThe JIuriate of Quinine, (Qu.+H.Cl.), forms pearly needles. It
dissolves easily in water; with corrosive sublimate and with bichloride of platinum it forms double salts, soluble in water, and crystallizable.
The Basic Sulphlate of Quinine is the most important preparation
of this base; its manufacture is conducted on a very large scale,
according to the process just now given for preparing quinine, or
various analogous methods. When crystallized, it contains water,
its formula being (Qu2+S.03+8 Aq.). It effloresces when gently
heated or in very dry air, giving off six atoms of water and retaining two, which cannot be expelled without partial decomposition;
it is but sparingly soluble in water, requiring thirty parts of boiling
and 740 parts of cold water; it requires eighty parts of cold alcohol, but much less of hot; its crystals are small pearly plates or
needles, which, when heated, phosphoresce strongly and fuse; by
a strong heat it is, of course, totally decomposed.
The JVeutral Sulphate of Quinine crystallizes in rectangular prisms




SALTS OF QUININE. —-CINCHONINE.                  625:;
which have the formula (Qu.+-S.03 +-8 Aq.). They effloresce easily,
dissolve in ten parts of water at 60', and undergo aqueous fusion at
2121. It is also very soluble in alcohol; though neutral in constitution, its solutidn reddens litmus.
The sulphate of quinine of commerce is sometimes adulterated
with sulphate of lime and with boracic acid, which are known by
remaining when the organic substance is burned away, and also
with sugar and with margaric acid. The latter is detected by its
insolubility in dilute acids; the former by washing the sample with
a little water, and precipitating the quinine that is dissolved by a
drop of solution of carbonate of soda, when the taste of the sugar
is recognised.
Phosphate of Quinine crystallizes in small but very brilliant nee-:
dles, which are soluble in water and alcohol.
The Tannate of Quinine is formed by adding solution of tannic
acid or infusion of galls to any salt of quinine. A white precipitate appears, which is totally insoluble in water, but dissolves in
acetic and muriatic acids.
Ferroprussiate of Quinine is formed by boiling together one part
of sulphate of quinine and one and a half of yellow prussiate of
potash with seven parts of water. The newly-formed salt separates
as a greenish-yellow oily substance. When the liquor is cold, it is
to be poured off, and the ferroprussiate of quinine dissolved in
boiling alcohol, frorn which it crystallizes in greenish-yellow needles by spontaneous evaporation.
The action of chlorine on quinine and its salts is very characteristic. If sulphate of quinine be dissolved in a large quantity of
chlorine water, and some water of ammonia added, a deep green
precipitate is formed, and the liquor becomes also intensely green.
To the body so formed the name Dalleiochlin has been given. If
the green solution be evaporated with contact of air, it becomes
dark-red coloured, sal ammoniac is formed, and two bodies, of
which one is soluble in alcohol, and the other not; the former is
called Rusiochiin, and the latter Jlelanochin. Formulte have been
proposed for these bodies, but as no security for their accuracy
has been given, I think it better not to bring them forward. These
reactions, combined with the action of tannic acid, serve as tests
for quinine.
Cinchonine.-N.C20. Hl2O. or Ci. Eq. 155.1 or 1939.
This alkali exists most abundantly in the gray bark (cinchona
micrantha), from which it may be obtained by the same kind of process as the yellow bark is subjected to for the extraction of quinine;
but it is usually prepared from the mother liquors which remain
after the crystallization of the sulphate of quinine, as just now described; from its alcoholic solution it crystallizes in thin colourless
prisms; its taste is peculiar and bitter; it requires 2500 parts of
boiling water for solution, but dissolves easily in alcohol and in
ether. At 330~ it fuses, without losing weight.. Its salts resemble
very closely those of quinine..Muriate of Cinchonine, Ci. -H.C1., crystallizes easily in brilliant
4K




626  A R I C IN E. —--  O R P tI I A.
interwoven neetiles; it forms double salts with the: metallic chlorides, similar to those of quinine.:
Sulphate:of. C(inchonine.-The basic sulphate, Ci- +S.03+2 Aq.,
crystallizes in rhombic prisms; it requires fifty-fbur' parts of cold
water for solution. The neutral salt, Ci. — S.-03 8 Aq., is much:more
soluble, and crystallizes in:large, well-formed rhombic octohedrons.
The Tannate of Cinc/honineeis a white insoluble powder.  
In contact vwith chlorine, cinchonine forms a dark red solution,
and after some time a brown precipitate appears.  If iodine and
cinchonine be dissolved t:ogether in alcohol,: and the: liquor evap-'
orated spontaneously, a compound crystallizes in saffron-coloured
needles, which is described as Iodide of Cinchonine, which it cannot
be, as hydriodic acid is formed..aricine.-N.C20. H1203 or Ar. Eq. 171'1 or 2139.
This alkaloid is found in the bark knovwn as China de cusco, or
arica bark, with which the genuine cinchona bark is often ad-ulterated; the tree yielding it is not known. It is obtained by precisely
the same process as cinchonine and quinine are procured from the
pale and yellow barks.     - 
It crystallizes inl brilliant white needles; it. is totally insoluble in
water, but easily dissolves in alcohol and ether.: These solutions
have an intensely bitter- taste; by' nitric acid it is coloured green-;
its salts have been but very little examined, but They appear to correspond very closely in constitution and properties to the salts of
quinine and cinchonine.
Jlorpia.-N.C35,. H2,006 or MIr." Eq. 293,8 or 3673.
To this body is due, in most part, the medicinal activity of opium,as a substitute for which it is prepared upon a very large scale.;
The processes adopted in the British pharmacopeias for this purpose are very simple, and deliver a product which, although by no'
mean;s chemically pure, is yet sufficiently -so for all medicinal objects; as they are, however, -more especially applied to the preparation of the mauriate of morphia, I shall describe them under that
head.To obtain. pure morphia, the process invented by Wittstock is
perhaps the best.  One part of opium, eight of water, and two of
muriatic acid are to be digested together for six hours; when the
mixture has cooled, the brown solution is to be poured off and the
residue treated twice more:with water and acid.'The liquors so
obtained, being mixed, are tobe. saturated with common salt,: on
which they become milky, and. after a few hours, a browvn clotty
precipitate forms; this being removed by the'filter, ammonia is to
be added in slight excess, and the- vhole allowed to stand for twenty-four hours.  The: precipitate which forms in this time is to be
collected on a filter, washed' with a little water,- dried, and digested
in spirit of specific gravity 0-820,: Which dissolves out the morphia.
By distillation, the greater part of the spirit is removed, and the
morphia, being dissolved in a small quantity, of boiling alcohol, crystallizes on cooling.' In this process. the narcotine is separated by
the addition of the common salt, in a solution of which it is insolu



PROPERTIES  OF MORPIHIA.                      627
ble; the imeconic acid, codeine, and' thebaine remain dissolved; after:
the addition of the ammonia in excess,~ and the other principles
present in the opium remain in the mother liquor after the morphia
crystallize s..
The process of Merck is founded on the' insolubility of morphia.
in a solution of sal ammoniac, and' its solubility in lime-water.
Opium is to be digested in three times its weight of rwater, then expressed, and this repeated three or four times; these solutions being mixed, are brought to boil, and milk of lime added in slight excess;'the precipitate which forms'is to' be c/ollected- on a strainer
and strongly pressed; the liquor is then to be evaporated until it is
about t"wice the weight of the opium emloyed; and to be then filtered, brougoht to boil, and for each pound of opium, one ounce of
Sal amnmoniac added in powder.  The morphia separates in crystals,
and may be purified by boiling with some lime and ivory black, and
precipitation again by sal ammoniac...      -
Morphia crystallizes in right rhombic prisms, as in the fioure, i,
u being primary, and m a secondary plane, containing 
2 Aq., which they lose by efflorescence in a -gentle heat,
and' become opaque; its taste is strongly and permanent-. x
ly bitter; it is almost insoluble. in water, requiring 400
parts when boiling, and separating almost completely as 
the liquor cools. The solution reacts strongly alkaline; it'dissolves
readily in alcohol,'but very sparingly ini ether.  It dissolves in solutions of the caustic alkalies or earths.  If morphia or any of its
salts be brought into contact with nitric acid, they become coloured
red; *this property belongs also to some other vegetable alkalies,
and. appears not to be possessed by morphia when-absolutely pure.
With chlorine water, mnorphia is first coloured orange-red, and' then
dissolved.  If iodic acid be brought into contact with morphia, it is
immediately decomposed, and iodine set free.
If imorphia or any of its salts be' added to a solution of sesquichloride of iron, the solution assumes a rich blue colour, which is removed by an excess of acid, but returns on the'neutralization of it
by an alkali.  With tannic acid it gives a copious white: precipitate.
By these remarkable reactions, the recognition of morphia is rendered more simple than that of any other body of its class.
Morphia cormpletely ieutralizes the strongest acids, forming salts
which are generally soluble and crystallizable.
Jl.uriale of JIoll hia,  t-H.CI., is, for medicinal objects, the
most irnportant compound of morphia; its preparation, as directed
by th'e British pharmacopoeias,   is as followvs:' the soluble parts of'
opium having been dissolved out'by digestion in.water, the united
liquors are to be evaporated to the consistence of a sirup, and'then
cold water added, by which a quantity of feculent matter (apdtheme)
is separated; the clear liquor is to be decomposed by a slight excess of chloride of lead (London) or of. chloride of calcium (Edin.
burgh).  The meconate of morphia, which exists in the opium, being decomposed, meeonate of lime or lead is precipitatcd, and muriate of morphia  remains dissolved; the liquor is to be carefully
strained and evaporated'io apel'licle:; on cooling the salt crystallizes; this is to be pressed between folds of cloth, to remove the




628.             NARCOTI N E.-C ODE IN E.
dark mnother liquor, and then dissolved in boiling water, digested
with ivory black, and recrystallized until the. crystals become perfectly white.
The product of this method, although not chemically pure, is suf
ficiently so for medicinal uses. It contains codeine,.and sometimes
others of the opium alkaloids. To obtain the pure salt, pure morplhia should be' dissolved in dilute muriatic acid, and the solution
crystrallized.
Sulphates of Aforphia.-The neutral sulphate, which crystallizes in
groups of soft needles, and dissolves in twice its weight of water,
has the formula Mr.H.O.. S.O,3-5 Aq. The Bisulphate of.Morpl)ia
does riot crystallize.
IAcetate of JMorphia is formed by dissolving the alkali in acetic
acid, or by decomposing muriate of morphia by acetate of lead; it
is soluble in water and in alcohol, and, after the muriate, is the most
important salt of morphia.
Morphia is precipitated by ammonia and by tannic acid from solutions of any of these salts.
JV.Narcotine.-N.C46. H22,,O,, or Nr. Eq. 5230 or 418.
This alkaloid may be obtained at once from opium by digestion
with ether, or when the impure morphia is thrown down by ammonia, ether dissolves out the narcotine from it. It crystallizes in colourless rhombic prisms, which are generally larger than those of
morphia; it fuses at 3383, and remains liquid until cooled to 266~,
when it congeals as a mass of radiated needles. It is almost insoluble in Rwater, but easily soluble in alcohol and ether; its salts have
but little stability, few of them crystallize, and most are decomposed by dilution with much water. By ammonia and tannic acid they
are precipitated.
From morphia, narcotine is very easily distinguished by its solubility in ether, insolubility in caustic alkalies and earths, and its not
giving the reactions characteristic of morphia with nitric acid or
with sesquichloride of iron. But if narcotine be put in contact with
sulphuric acid, and oxygen is supplied either by the air or by a
trace of nitric acid, it becomes red. Under these circumstances,
however, morphia becomes green.
Codeine.-N.C3. H2005 or Cdn. Eq. 3573 or 285'8.
This alkali remains dissolved after the morphia, narcotine, and
other strbstances have been precipitated by ammonia. The filtered
liquor is to be evaporated to dryness, and digested in solution of
potash; a substance remains undissolved, which gradually becomes
crystalline. This is to be washed with water, and then dissolved in
boiling ether, from which, by spontaneous evaporation, the codeine
separates in colourless prismatic crystals, which contain 2 Aq.
Crystallized codeine fuses at 300~, giving off its crystal water. It
dissolves copiously in water; the solution reacts strongly alkaline;
it is insoluble in alkaline liquors, but forms with acids perfectly
neutral crystallizable salts. These are precipitated copiously by
tannic acid, but not by ammonia; it does not produce any of the
reactions described as characterizing morphia. As none of its salts




TH E BA IN E.-N A R C E I N E.-S TRY C HN IN E.    629
are employed in pharmacy or medicine, they need not be specially
noticed.
Thebaine.-N.C,. H,143 or Tb. Eq. 2542 or 203'4.
The watery infusion of opium being treated with milkl of lime, so
that the morphia smay rest undissolved, the precipitate is to be
washed with water until it becomes white, and then dissolved in a
dilute acid. From this solution thebaine is precipitated by ammonia. The precipitate being dissolved in ether, and the solution
evaporated, pure thebaine crystallizes in colourless short rhombic
prisms, which taste, sharp and styptic, and have a strong alkaline
reaction. At 300' it fuses, and solidifies then only when cooled to
230'. It is scarcely soluble in wvater, but abundantly so in alcohol
and ether.
By acids thebaine is decomposed, a resinous substance and a salt
of ammonia being formed. In its other characters it completely
resembles narcotine..carceine.-The watery solution of opium is to be heated first by
ammonia, which throws down morphia, narcotine, thebaine, and
some other bodies, and these being removed by filtrations, the meconic acid and codeine are to be precipitated by an excess of solution of barytes. The excess of barytes being then removed by a
current of carbonic acid gas, the filtered liquor is to be evaporated
to the consistence of a sirup and set aside; after some time crystals form, which are a mixture of meconine (see p. 610) and narceine.
These are separated by ether, which dissolves the meconine, and
the residual narceine being dissolved in alcohol and decolorized by
animal charcoal, crystallizes, by the cooling of its solution, in delicate needles.
It tastes bitter, fuses at 200", and forms a crystalline solid on
cooling; it dissolves in 230 parts of boiling water; it is very soluble in alcohol, but insoluble in ether; its solution does not react alkaline, and it is decomposed by strong acids; in its constitution,
however, it resembles the true vegetable alkalies, its formula being
N.C2s. H200,1.
Pseudomorphine, N.CA4. H11I04, occurs but very rarely in opium.
For its mode of preparation, when present, I shall refer to the larger systematic works; in its reactions it is absolutely identified
with morphia, from which it is distinguished, however, by its composition, by crystallizing in plates, and by not forming any wellcharacterized salts, although it dissolves very readily in dilute acids
Strychnine.-N2C44. H 1O0 or Stc. Eq. 4355 or 348.
This alkaloid exists associated with brucine in several species of
strychos (nux vomica, ignatia, colubrina, &c.), also in the substance
used by the natives of Borneo for poisoning their arrows, and termed Upas-tieuta, or Woorara; it is obtained most easily from the Ignatius's beans, which contain but little brucine; but, as these are not
often found in commerce, the nux vomica is most generally employed. The seeds are to be boiled for some time in strong alcohol, which dissolves out a quantity of fatty matter; being then dried
in a stove, they are easily reduced to powder; this powder is to be




630     ST RYCHNINE  I T S PROPERTIES,  E TC.
then boiled two or three times in alcohol, and the liquor distilled
until the greatcr part:f t-he alcohol has come over.  To the residue, acetate of lead is to be added as long as any precipitate occurs.; by:this: means more fat, colouring matter, and some organic
acids are removed.  The filtered liqu. or, is to be then evaporated so
fair,'that from  sixteen" ounces of nux vomica it.amounts to, six or
eight ounces..To this quantity two drachms of magnesia are to be
added, and the whole allowed to stand aside for some days; the
preciPitate: which forms is to be collectedt on linen, pressed, dried,
and dissolved in alcohol, from  lhich the strychnine crystallizes on
cooling,R while the brucine remains. in the mother liquor. As the
strychnine, howev.er,is not yet pure, it is to be dissolved in dilute
nitric. acid, and the s.olition evaporated to a pellicle.  On cooling,
the nitrate of strychnine crystallizes in brilliant white, soft, feathery
-prisms,. while. the. nitrate of brucine. separates. afterward in large,
hard, rhomnbic prisms.  From  sixteen ounces. of nux vomica,forty
grains of nitrate of strychnine and fifty grains of nitrate of brucine.may be obtained:; from:the solution of the pure nitrate in water,
the strychnine. maybe precipitated by ammonia, and, being dissolved ion spirit of xwine, it c-rystallizes, by spontaneous evaporation, in
small white four-sided prisms.
Strychnine has an intensely bitter, somewhat metallic taste; it
requires 7000 parts of cold:water for solution; and yet, if one part
of this be diluted with 100 parts more of wvater, this — liquor tastes
strongly bitter;i it is soluble in absolute alcohol and in ether, but
dissolves readily in. spirit         ith acids strychnine unites,
forming well-ce! d: haracterized and crystallizable salts; it differs from
the other vegetable alkalies in containing two atoms of nitrogen in
its equivale nt. With chlorine strychnine gives a white precipitate;
also: with tannin;,;when completely pure, it is not reddened by nitric
acid, but such as it exists in commerce it. generally is so, owing to
the presence of traces of brucine.:.. JMuriat eo'Lf StrychAine, iStc. +HC.,'crystallizes in crowded rhom
bic nee'dles,- which ldissolve readily in water.  With corrosive sublimate, with bichloride of platinum, and with cyanide of-mercury,
it gives insoluble double salts.: Hydrocyzzanate of Strychnine is obtained by dissolving strychnine in
prussic acid; it crystallizes it  needles, which are decomposed even
by a gpentle heat.; If solution of sulphocyanide. of potassium: be ad-,ded  _a.' solution of any salt of. strychnine, the liquor, when agitated,
deposites the Suilhocyanate of. Strychnine in fine radiated needles,
which are insoluble in water. By this means one part of strychnine
may be recognised: in. 375,h of water, and hence-Artus has proposed.this reaction as the best mnedico-legal test for strychnine.
1Sulp-ate; of Strychrtine form. s small cubic cry tals, which contain
4 Aq., and are soluble in:ten parts of water.
The characters of the eitrate of Strychnine have been described in
the: method of preparing.th'e alkaloid.
Strychniine is, perhaps, after pure prussic acid, the most- intense
of poisons. It kills by. producing tetanus.




B R U C I N E. —D E L P,-H"I-N I N.E.-V-E R A T R I N E.    631
Brucine.-N2C48.H2608 orBr. Eq. 408 or 5107.
This-substance is found associated with strychnine, as already described, and also in the bark of the false angustura, which is now
known to be the strychnos nux vomica, though formerly supposed
to be the brucia antidysenterica, whence the name of this alkaloid
is derived. Its, mode of preparation from the nux vornica has been
sufficiently described in the preceding article.
From its solution in spirit, brucine crystallizes in colourless
rhombs, containing water,'which they abandon on melting at 220~.
It dissolves in 850 parts of cold and in 500 parts of boiling water;
these: solutions react alkaline, and taste intensely bitter; it dissolves
readily in alcohol, but is insoluble in ether.
With nitric acid, brucine becomes of a rich red colour, which, on
the addition of protochloride of tin, changes to a fine violet; this
distinguishes it from  the red of morphia, which is completely
bleached by protochloride of tin and by sulphurous acid.
With chlorine, brucine gives a yellowish-red, and with iodine a
chocolate-brown precipitate.
The salts of brucine have a bitter taste, are generally. crystalliza.
ble, and give with tannin and with ammonia white precipitates.
The Curara, or Urari poison, used in the Indian Archipelago for
poisoning arrows, contains a vegetable alkaloid, Curarine, which
forms a yellow uncrystallizable mass, which dissolves easily in water and in alcohol, but is insoluble in ether; it reacts alkaline, and
combines with acids; its salts do not crystallize; its solution is precipitated by tannic acid.
The -tree from which curara is derived is not accurately known,
but is supposed to be a strychnos.
- Delphinine.-N.C2. H,,902 or De. Eq. 2659 or 212'4. This substance is extracted from the seeds of the stavesacre, delp/inium.staphisagria, by digestion in water, to which some sulphuric acid
had been added. The acid liquor is to be decomposed by a slight
excess of magnesia, and the precipitate being/washed and dried, is
to be boiled in alcohol, which dissolves the delphinine.  To obtain
it quite pure, it is to be redissolved in a dilute acid, boiled with animal charcoal, filtered,:precipitated with ammonia, and the precipitate
dissolved in alcohol, from which the delphinine separates on cooling
as a white crystalline powder.
It is soluble in ether and alcohol; almost insoluble in water; its
solution has. an intolerably sharp taste; it melts at 250~; chlorine
turns it green; oil of vitriol colours it red, and then carbonizes it;
its salts are..very soluble, but crystallize badly; Courbe states that
the stavesacre contains also a substance, Stephyscaine, (N.C32. H12304.),
which is distinguished by its insolubility in ether; it is a yellow
resinous mass, insoluble in water, but dissolving in dilute acids without neutralizing them.
Feratrzne.-N.Cs3. H2106 or Ve. Eq. 3647 or 289.
This alkaloid is found in the roots of the veratrum album, and in
the seeds of the veratrumi sabadilla; the best process for its extraction is that given by Vasmer.




632    s A B A D I L'L.I N E. —J ER V I N E. —-C OL C H I C I NE,
The sabadilla seeds are to be infused in water, containing an ounce
of oil of vitriol for each pound of seeds, as long as anything is dissolved. The filtered liquor is wine-yellow; it is to be accurately
neutralized by carbonate of soda, and evaporated to the consistence
of an extract. While yet warm, alcohol is to be poured on it, and
digested: until everything soluble is taken up.  From  this solution
the alcohol is then to be distilled off, the residue digested in dilute
sulphuric acid, and from  this liquor the veratria precipitated by carbonate of soda. The precipitate must be redissolved in a dilute
acid, digested with ivory black, and agaiin precipitated by a carbonated alkali in order to obtain it pure.
Pure veratrine appears as a white uncrystallized resinous powder;
it melts at 230~, reacts alkaline, has no smell, but produces violent
sneezing; its taste is exceedingly sharp, but without: bitterness; it
is insoluble in water, but dissolves readily in alcohol and ether; its
salts are mostly crystallizable and neutral, but if mixed with much
water they are decomposed, acid being set free, and a basic salt precipitated.  Veratrine itself is actively poisonous, and is much used
in medicine, but none of its salts are important.
Sabadilline.-IN.Co,. H130,  or Sa.  Eq. 2351 or 188'1.
This body, which accompanies veratrine, is separated from it by boiling the precipitate produced by the carbonate of soda with water. From the liquor the sabadilline gradually separates in radiated crystalline needles, of a pale rose colour, but
when purified it becomes white; its taste is intolerably sharp; it is sparingly soluble
in water or in ether, but abundantly soluble in alcohol; it reacts strongly alkaline,
and forms crystallizable salts with acids.
Jervine.-N2C6,. H0,6 or Je.  Eq. 5952 or 476.
This alkaloid accompanies veratrine in veratrum album; it is prepared by a process similar to that for veratrine, from which it is separated by the facility with
which it crystallizes from its alcoholic solution, and by the very sparing solubility
of its sulphate. When pure it is white, easily blsible, totally decomposed, at 400~,
nearly insoluble ih water, but copiously soluble in alcohol. Of its salts, the sulphate, nitrate, and muriate are sparingly soluble in water or in mineral acids; the
acetate dissolves readily. Muriate of jervine forms, with bichloride of platinum, a
very sparingly soluble double salt. Crystallized jervine contains 4 Aq.
Colchicine.-(Formula not established.)
This alkaloid is obtained from the seeds of the meadow saffron (colchicum autunlnale) by digestion in a mixture of weak alcohol and sulphuric acid. The excess
of acid in the liquor is to be then neutralized by lime, and the alcohol distilled off.
The residual liquor is to be decomposed by carbonate of potash in excess, the precipitate washed, dried, dissolved in absolute alcohol, decolorized by animal charcoal,
and gently evaporated, a few drops of water being added. The pure colchicine
crystallizes in colourless needles. Its taste is intensely bitter, but not biting, like
that of veratrine, nor does it produce the violent sneezing; it is pretty soluble in water, and very soluble in alcohol and ether; its solution reacts feebly alkaline, but
neutralizes acids perfectly. Tincture of iodine precipitates it of a rich orange colour. Nitric acid colours it'dark violet and blue. Though most abundant in the
seeds, all parts of the meadow saffron contain colchicine.
Enietine.-(Formula not established.) This substance exists in all'those plants whose roots are sent into commerce under the name
of Ipecacuanh/a, or Hippo. The roots are to be powdered and digested in ether, by which a fatty substance is taken up. They are then
to be boiled with alcohol, the decoction mixed with water, and the
spirit distilled off. The residual liquor is to be filtered, and then
boiled with magnesia; the precipitate is to be dried and digested in




S O L A N I N E. —C H E L E RY T IHR I N E, ETC.           633
al ohoi, which dissolves the emetine.  This solution is to be evapor ited to dryness, the residue dissolved in a dilute acid, the liquor
boiled with ivory black until completely decolorized, then filtered,
and the emnetine precipitated by an alkali.
When completely pure, ernetine is white and nearly tasteless; it
is very poisonous; scarcely soluble in water or in ether, it dissolves readily in alcohol; it possesses strong alkaline properties;
its salts are completely neutral, but cannot be crystallized; they
dry down to gummy masses.'Tannic acid and corrosive sublimate
produce white precipitates; iodine, bichloride of platinum, brown
ish-yellow precipitates with the salts of emetine.
Solanine.-N.C,,. H17302 or So.  Eq. 7519 or 601.
This alkaloid is found in the berries of the solanum nigrum; in the berries, leaves,
and stems of the solanum dulcamara (bitter-sweet) and tuberosum (potato).
The powdered stems of bitter-sweet are to be digested with spirit of sp. gr. 0'865,
mixed with one third of sulphuric acid. The liquid is to be supersaturated with
milk of lime, the spirit distilled off, the residue washed with water, and what remains
treated with dilute sulphuric acid. From the solution thus obtained the solanine is
to be precipitated by an alkali, washed with water, dissolved in alcohol, decolorized
by animal charcoal, and then obtdined by evaporation. It forms a white brilliant
powder, of a slightly bitter, nauseous taste; it does not brown turmeric, but restores
the blue colour of reddened litmus; it melts a little above 212~; it is almhost insoluble in water, sparingly soluble in ether, but copiously in alcohol. With acids it
forms neutral salts, which do not crystallize, and are strong narcotic poisons.
The injurious properties of unripe potatoes result from the presence of this body,
It exists abundantly in the early shoots (under ground) and buds of the tubers.
Chelerythrine.-(Formula not established.)
This substance is extracted from the roots of the chelidonium majus by digestion
with dilute sulphuric acid. The liquor so obtained is to be evaporated and mixed
with ammonia. The brown precipitate which falls is to be washed, pressed between
folds of paper, and digested in alcohol with some sulphuric acid. The alcoholic
solution being mixed with water and the spirit distilled off, the residual liquor is
precipitated by ammonia, and the precipitate being washed and dried by pressure, is
to be divested in ether, and the ethereal solution evaporated to dryness. The mass
so obtained is then digested in dilute muriatic acid, which leaves a resinous substance undissolved. The deep red liquor evaporated to dryness and washed with
ether, leaves a mixture of muriate of chelerythrine and muriate of cheledoline, the
former of which is dissolved by washing with a small quantity of water, while the
latter remains undissolved.
From the solution, of the muriate, the chelerythrine is precipitated by ammonia
as a white curdy powder. From its ethereal solution it remains as a resinous mass,
which remains soft for a long time; it is insoluble in water; its solutions in alcohol
and ether are pale yellow. WATith acids it forms salts of a rich crimson colour
which generally crystallize. Tannic acid produces in their solutions a precipitate
soluble in alcohol.
Chelidonine.-N3C40. H2006 or Ch.
The preparation of this substance has been in great part described in the preceding article. By digesting the sparingly soluble muriate with ammonia, then dis.
solving in. sulphuric acid, and precipitating with muriatic acid, it is freed from all
traces of chelerythrine, and finally the pure chelidonine, separated by ammonia. is
dissolved in boiling alcohol, from which it crystallizes, on cooling, in brilliant colourless tables. It is insoluble in water, soluble in alcohol and ether; it tastes bitter,
and reacts alkaline; its salts are colourless, and those with the mineral acids crvstallize; its solutions give with tannic acid a precipitate..qconitine.-(Formula not established.)
The fresh-expressed juice of the monkhood (aconitum napellus) is to be boiled
and filtered, and the clear liquor mixed with an excess of carbonate of potash. The
L




6S34     A T R O PI N-E.-B EL L A D O N I N E.-D A T U R:I N E.
mixture is to be agitated with ether as long as anything is taken up, and by evaporating this -solution the aCorinitine remains. Fromn the dry plant or from the seeds,
-the aconitine may be-obtained by processes similar to those described for veratrine
and colchicine..
Aconitine partly crystallizes from its ethereal; or alcoholic solution in white grains,.but fbr7 the most- part forms a colourless, vitreous-looking mass; it tastes sharp and
bitter, and is intensely poisonous: it reacts strongly alkailine, and neutralizes the
- strongest acids; alkalies precipitate its solution white; chloride of gold and tanlic
acid also give white precipitates, andl iodine throws it do wn orange.
Stropine.-N.C34. H23O06 or At.
This alkaloid exists in all parts of the atropa belladonna, but most abundantly in
the roots.'To prepare it, the fresh roots are to be powdered and digested in alcohol,
cf specific gravity 0 820. The liquor obtained is to be mixed with lime, in the proportion of one part to twenty-four parts of roots, and laid-aside for twenty-olur hours
with frequent agitation; the mixture is to be then filtered, and the deposite treated
with dilute sulphnulliC acid: the filtered solution is distilled, and the spirit being thus
removed, the residual liquor: is concentrated by evaporation until it equals one
twelfth of the roots employed. To ithis liquor, when cold, is to be added a strong
solution of carbonate of potash, until a dirty brown precipitate occurs, which is to
be removed by the Iilter, and then more carbonate of' potash added as long as any
precipitate is formed. This last, which is impure atropine, is to be washed with
waster, then dried, and dissolved in strong alcohol, the solution decolorized by boiling with animal charcoal, filtered, and gradually evaporated, whereby the atropine
separates in small white silky prisms.
The taste of' atropine is sharp, bitter, and metallic. It dilates the pupil perma-.-nently and strongly; if impure, it is brown, does not crystallize, and has a horrible
smell,Y but if quite pure it has no. smell; it requires 2000 parts of cold water for solution, but dissolves-in thirty-four parts of boiling water, from which some crystallizes by cooling, but the greater part is decomposed; it dissolves readily in alcohol
and ether.
The alkaline properties of. atropine are feeble; most of its salts are decomposed
by boiling with water into ammonia and a substance of an excessively disagreeable
smell; this decomposition is instantly effected by the caustic fixed alkalies. Most
of the salts of atropine crystallize; tannic acid precipitates their solutions white;..the chlorides of platinum and&gold, yellow; and iodine, orange-yellow.
Belladlonine.-(Formula -not established.)  The dried root of belladonna is to be
mixed with a strong- solution of caustic potash and rapidly distilled; the distilled
liquor is to be decomposed by bichloride'of platinum, and the white precipitate which'-forms being washed -and dried, is to be mixed with carbonate of potash and gently
heated. Belladonine sublimes and condenses in colourless rectangular prisms, with
a penetrating odour like ammonia; it dissolves in water; the solution reacts alkaline:; it is not very poisonous; its salts resemble closely the corresponding salts of
ammonia.
It appears to me likely that this substance is a product of the decomposition of
the atropine by the caustic potash, and does not exist in the plant.
Daturine.-This  substance is obtained from the seeds of thie thorn apple (datura
stramonium), by the-same process as has been described for the preparation of aconi-'tine.:: From its solution in spirit, it crystallizes in very brilliant colourless groups
of needles.  When perfectly pure it is inodorous, but when impure it smells disgustingly narcotic; its taste is bitter, and like that of tobacco; it'dissolves in seventy-two parts of boiling,; and in t50 of cold water, in twenty-one of ether. and in three
of alcohol; it melts below 212~, and volatilizes unchanged at a stronger heat in white
clouds..... A solution of daturine reacts strongly alkaline, and forms crystallizable neutral
~ salts, which, like pure daturine;.are! very- poisonous.  Towards reagents it acts like
atropine.
*  Ih/oscyamine.-This. alkaloid, which is the active principle of the henbane (hyos-:cyamus niger and: albus),. is best prepared from the seeds, in the same way as atropinej.except that to the' spirit in which'the: seeds are digested some sulphuric acid
should be added. It crystallizes in radiated groups of silky'needles, but is more
usually obtained as a transparent vitreous mass. In its properties it resembles so
perfectly atropine -and daturine, that they need not be specially detailed. It neutralizes'acids. perfectly.;.,its salts are intensely poisonous; they are decomposed very
easily, even by boiling with water.




.C O N'E IN E.-N I C O T IN E..                   635
Coneine.-N.C,2,. O,H. or Cn.. _Eq. 1359 or 108'7.
Thisremnarkable substance is the active principle of the hemlock (coniurn macu-.atuml), ill all parts of which it exists, btut is more easily extracted fiom the seeds.
These are to be bruised, mixed with one foburth: of a strong solution of causrid potash -and eight parts of water, and distilled as long as the water which comes over
has any smell.'This is to be neutralized by dilute sulphuric acid, and evaporated
to the consistence of a sirup. The residue is treated tuwo or three times with a mixture of one part of ether and two of alcohol, sp. gr. 0'820, wherein the sulphate of
coneine dissolves.. From this solution the ether and spirit are distilled off, then some
-water added,'and the liquor evaporated to dryness. The residue is to be mixed
with hal: its weight of strong solution of potash, and rapidly distilled to dryness..The receiver should be carefully cooled. The oily coneine should be separated.from the watery liquor, and this last distilled again with some lime. If the coneine
contain ammonia, it may be got rid of by exposure for a few hours in vacuo, beside
a capsule of oil of vitriol.
Pure coneine is a colourless transparent liquid, of sp. gr. 0 89; its odour is highly
penetrating and nauseating, partly like that of the plant; its taste is disgustingly
sharpe.; it is extremely poisonous. 100 parts of. cold water:dissolve one of coneine,
and the solution becomes turbid when heated. Coneine itself dissolves one fourth of
water, and this liquor becomes milky even by the heat of the hand; it mixes with
alcohol, ether, and oils in all proportions; in close vessels it distils unaltered at
370,:.but at a nluch lower temperature if water be.present.  When completely anhydrous, coneine has no alkaline properties, but acts very powerfully if water is
present; it saturates' acids completely, aud'has the smallest atomic weight of any
organic alkali known. Its salts crystallize but imperfectly; they are decomposed
by much water; they dissolve readily in water, alcohol, or a mixture of alcoliol and
ether,.but in pure ether they are: insoluble. Their watery solution is precipitated
by.iodine,; saffron-yellow; and by.tannic acid, white. Coneine itself is coloured by
nitric acid blood-red; by exposure to the air, especially if warm, coneine is decomposed; it becomnes brown, ammonia is evolved, and a bitter, inodorous, resinous
substance is produced, which.has no poisonous properties.
JVicotine.-(Formula not established.)
This substance is the characteristic ingredient of tobacco (nicotiana tabacuam,
and many other species). For its preparation, precisely the same process is'to be
followed as has been described for coneine, to which it has a very great similarity.
When pure, nicotine is a colourless oily liquid, of a' pungent tobacco smell, and a
sharp,:burning taste; it differs from all other organic bases in mixing with water in
all proportions; it mixes also with alcohol and ether. When anhydrous, it gives
off white fumes at 212~, and distils at 480~; but the greater part of it is decomposed.
If water be present, it distils easily at a much lower temperature.
Nicotine possesses a strong alkaline reaction, and neutralizes acids perfectly. Its
salts are generally very soluble, solme crystallizable, inodorous, but with a strong
tobacco taste. With alkalies they evolve the characteristic odour of the plant.
- Menisperm nine.-N.C s. Hi202:. This substance is found in the capsules of the cocculus Indicus, associated with:picrotoXine (page 609). - The alcoholic extract is to be
boiled. with acidulated water, -and When the picrotoxine has crystallized from the, filtered liquor, an excess, of alkali is to be: added. The precipitate is to be dissolved
in. alcohol, decolorized by.animal charcoal, and evaporated to dryness. The residue
is'to be digested with ether, -which dissolves IMenispermiqne, and leaves another body,
Para',ensisp ervtmine, undissolved.:From the ethereal solution, menispermine crystallizes in white: square prisms. -It
is tasteless, and not poisonous; it forms neutral crystallizable salts. The paramenispermine dissol'ves in acids, but does not neutralize them..Ci~ssampvelivne exists -in. the roots of the cissampelos parei-ra (pareira-brava), and is
prepared by the same kind of process that has been frequently descrilbed.: From the
evaporation of its ethereal solution, it remains- as a yellowish, transparent, vitreous.
mass, which combines with water, forming a white powder like magnesia. It is very
easily decomposed; it is. a powerful organic base; its salts form gummy masses,
but scarcely crystallize.
~ Glauscioe exists in the glaucium luteurnm(horned poppy). -Its preparation is similar to that of aconitine; it crystallizes in pearly scales;. it possesses the same range
of properties as the other vegetable bases, and forms crystallizable salts. The
horned poppy contains another crystalline principle (Glauco-picrine)i which appears
also to act as a base.




636  cONSTITUTION  OF V EGETABLE  ALKALOIDS.
A great number of plants are stated to contain organic bases, which, however,
have been as yet so imperfectly examined and described as to render their intro.
duction here useless. Of such substances, the most important are: in the croton
tiglium, Crolooniqe, which is crystalline, but is not the active principle; in the aethtisa
cynapium, Cynapine, crystalline; and in the digitalis purpurea, Dig'italine, which apnears most to resemble coneine.
Of the Constitution of the Vegetable  likaloids.
From the period of the first discovery of this class of bodies,
chemists have endeavoured to ascertain on what depended the basic properties by which they are so remarkably characterized. The
discovery, by Liebig, that each equivalent of an organic base contained an equivalent of nitrogen, suggested the very plausible idea
that they contained ammonia ready formed, and that in their salts
the acid was neutralized by the ammonia, and the organic substance
remained combined with the salt, as it had been with the ammonia
before.  This idea, however, cannot be sustained, as we cannot obtain ammonia from  any vegetable alakaloid, unless by processes
which totally destroy its constitution, and which, indeed, eliminate
ammonia from any organic substance containing nitrogen. Moreover, it is now known that Liebig's rule is not universally true; the
equivalents of strychnine and of brucine contain each two atoms of
nitrogen, and we know of other organic bases, as melanine, amiline,
jervine, and urea, in which-the quantity of nitrogen in the equivalent goes much beyond one atom.  We may hence conclude that
there is no reason to suppose that the vegetable alkalies contain
ammonia, or owe their basic properties to its presence.
Some remarkably simple relations of composition occur among
certain bodies of this class, which would at first appear to throw
light upon their constitution. Thus morphine and codeine differ
in composition only by morphia containing an atom of oxygen
more; and if we supposed (N.C35. H2004) to be a compound radical
R., then codeine should be protoxide, R.+-O., and morphia deutoxide, R.+-20. In like manner, if we take the cinchona alkalies, we
find, them to differ only in the quantity of oxygen they contain, and
making (N.C20,,H,2) a compound radical, cinchonine should be R.+
O., quinine R.-20., and aricine, R.+30.  These remarkable facts
might lend considerable support to the idea that these alkaloids are
oxygen bases, oxides of compound radicals; but a closer examination of their relations does away with all probability of its truth.
Thus, if morphia were R.+20., then by muriatic acid we should
have a bichloride formed, R.+-2CI., and water' separated; in place
of which, the morphia combines directly with one atom of muriatic
acid, and so in all other cases; we cannot find in the compounds of
these vegetable alkalies any of the laws which govern the formation
of salts by metallic oxides. In addition, the salts formed by these
alkaloids with the oxygen acids contain an atom  of water, which
cannot be expelled without decomposition. In this thbey resemble
ammonia, and I think that it is the only analogy which we can establish by the facts at present known; but whether, in these vegetable
alkalies, the nitrogen makes part of a compound radical analogous
to amidogene, remains to be decided by future investigations




ULMINE  BODIES FaROM  SUGAR.                  637
CHAPTER XXVIII.
OF THE PRODUCTS OF THE DECOMPOSITION OF'WOOD AND THE ALLIED
BODIES.
SECTION I.
OF THE SLOW DECOMPOSITION OF WOOD. CONSTITUTION OF ULMIINE
OF TURF AND COAL.
THE gradual decomposition of the woody tissues of plants gives
origin to a class of bodies which had been long confounded under
the name of Ulmine, but which are now recognised to consist of
several distinct substances, differing in their origin, and still more
essentially in their properties. From the influence which they exercise in agricultural operations, by forming an element of the soil,
and their importance as fuel, by constituting the great mass of turf,
they deserve a somewhat detailed notice. I have already stated,
that by the action of acids upon sugar (p. 532), lignine, starch, and
similar bodies (page 528), brown substances are produced, the cornposition of which was not definitely established. Mulder has, however, recently reinvestigated the history of this class of bodies, and,
from his known accuracy, his results may be looked upon as satisfactory.
When sugar is acted upon by a very dilute acid, and the liquor
not allowed to boil, two brown substances ai'e formed, of which one
is soluble in solution of carbonate of soda, but the other not. For
these bodies the names Sacchulmine and Sacchulmic.Acid may be retained. From the alkaline solution the latter may be precipitated
by any stronger acid. These bodies are insoluble in water and in
alcohol. The formula of the Sacchulmine is C40HJIO4; that of the
Sacchunlmic Acid is C401,,40,,. They differ, therefore, in the former
containing the elements of water, which, however, cannot be expelled without total decomposition.
If the sacchulmic acid be dissolved in water of ammonia and precipitated by an acid, it retains a quantity of the alkali; and if the
ammoniacal solution be decomposed by a metallic salt, the precipitate which forms is a double compound of sacchulmic acid, ammonia and the metallic oxide. It was the unsuspected existence of
ammonia in these cases which produced the discordance of former
results.
If the sugar be acted on by a stronger acid, and the solution kept
boiling for a considerable time, the ulmine bodies disappear, and are
replaced by two dark brown or black substances, possessing very
analogous properties, the Saccharo-hulmihe and Saccharo-humic acid
This change takes place more readily if the air have free access.
Both are insoluble in water and alcohol; they are separated by al.
kaline liquors, which dissolve the acid body. From this solution it
is thrown down by any stronger acid. The composition of saccha



638          UIil-INE -BODIE S' F'ROM  WOOD.
ro-humine is expressed by the formula C40,,H,50,5; that of the sac.
charo-humic acid by C,,H,,O,2. Like the former bodies, these differ,
therefore, in the elements of water.
Mulder found that access of air was not necessary for the formation of sacchulmine or its acid, but that without air no saccharohuinine nor its acid could be produced. In this action, even without access of air, formic acid appears, although but in small quantity;
at the same time, glucic acid (p. 534), and another body first described by Mulder, dpoglucic acid, are generated.
When wood remains long in contact with air and moisture, it is
gradually converted into a mixture of two brown substances, which,
from their having been originally found as a product of the decomposition of elm, are specially termed Ulmine and Ulmic Acid.  The
latter is insoluble in alcohol and water, soluble in alkaline solutions;
in its natural state it contains ammonia, which can only be expelled
by boiling with caustic potash, by which the greater part of: the ul
mic acid is itself decomposed. Its formula, as derived from  the
analysis of a specimen furnished by a rotten willow, wras C40H,1202,
being isomeric with saccharo-humic acid, but distinguished from it
by many minor characters, especially that when treated with- acids:
it retains twice as much ammonia as the artificial product.  Mulder
considers the natural ulmine to contain more hydrogen; its formula
should then be C0H,40,2, and by the continued action of the air it
should change into plmic acid.  The formation of these bodies from
the woody fibre results from the absorption of oxygen and the evolotion of carbonic acid and water: thus four atoms- of lignine,: C4,O32[,,, with fourteen of oxygen, produce 8C.02 with 18H.0O., and an
atom of ulmine, C4,HI4,O,.
Another kind of decomposition to which wood is subject is the
conversion of the ligneous fibre into a white friable substance, which
is formed abundantly in the interior of dead trees; its composition
is found to be expressed by the formula C33H21 014. It is evidently
formed by the lignine combining with oxygen -from  the air and
with: the elements of water, and then giving off carbonic acid gas,
CH,,40,4 with 30. and 3H.0. forming C33H2,024 and 3C.02.
The rotting of  wood is, however, by no means necessarily induced by the mere presence of air and water; for ]ianine may be
exposed to these aaents for centuries without being altered in any
sensible degree. Precisely as in the alcoholic and acetous fermentat;-ons, it: is necessary that an azotized substance should be present;
which, being first decomposed, and forming, probably, crenic and
apocreniic acids, communicates the action to the lignine; the albuminous. juices which exist inw the vessels of the wood act thus as a
ferment, and the decomposition of the wood may be prevented by
precisely the same methods as counteract the tendency to the fer
mentation of sugar or of`;alcohol; any deoxidizing substance, as
sulphurous acid; any met.1 ie salt, as corrosive sublimate or bluestorte, which may combine w!ith the albumen and render it insoluble, wvill thus protect wood from decomposition, and are at present
-xtensively used as preservatives against What is te I     Lhnical:ly:e med
the dry rot.
It is by a similar decomposition that the roots-and other remains




ULMINE  BODIES FROMI THE  SOIL) ETC.   639
of plants are converted into a substance which, by virtue of its di
rect absorption, or by means of the products of its farther change,
contributes powerfully to the nutrition of the.succeeding race of'
plants, and thereby constitutes the essential elemnent of every fertile
soil; but though, like ulmine, derived from the rotting of vegetable
matters, and for the most part of the same composition, the organlic
substance of the soil is by no means identical with it.  It weucld
even appear, from MlIulder's results, that the vegetable constituent
of the soil varies in composition according to the nature of the
crop. For distinction, I shall apply to the ulmic acid of the soil tile
name of Geic.dcid, proposed by Berzeiius. T'Po extract it, the soil
is washed with boiling water until this passes away quite clear, and
then boiled with carbonate of soda; the brown filtered liquor is
precipitated by muriatic acid, and the precipitate boiled with alcohol to dissolve out two organic acids, which will be shortly described. In this state the substance is really an ammoniacal salt, its
formula being C40H.20,2+N.-13+4 4H.O., and even by caustic potash
it cannot be completely deprived of ammonia. In the geic acid of
a meadow, the same organic element was found to be united with
twice as much ammonia; and in one case, where the substance had
been obtained from the soil of an orchard, the geic acid had the
formula CiHI0-,4.  The geic acid, CQ0H, O,, though isomeric with
the saccharo-humic and ulrmic acids; is proved not to be identical
by numerous minor characters, which need not be described here.
-In that decomposition of vegetable matter which gives origin to
turf, water is present in much -greater quantity than in any of the
former cases, in many instances the plants being totally immersed,
and so matted together, from their mode of' growth, that the access
of air must be very much prevented. Hence we no longer find in
turf the comparatively simple decomposition of the wvood into an
ulmine'and an ulinic acid, but, in addition to these bodies, the turf
allies itself to the varieties of coal, in containing several kinds of
fossil, resinous, and waxy substances, which are produced by secondary and more complicated reactions. Here it is necessary, however, to describe only such constituents of the turf as are analogous
to those already noticed, and for distinction I shall terim them i-lumoous and'Humic acids.  The former is found principally in the
light, pale brown turf, which is not imbedded in water; the latter,
on the contrary, in the heavy black turf, to which water has had
free access. They are prepared precisely as noticed for the geYe
acid, the turf containing in abundance the same organic acids,:soluble in alcohol, as does vegetable soil.
The iumonus d.cid resembles perfectly in its properties the sac
chulmic acid, with which it is isomeric, its formula being C,,H,O 402
but it has no tendency to retain ammonia when precipitated by an
acid from its combination with that alkali. The Humic./icid. on
the contrary, combines with ammonia so intimately thtat they c(annotbe separated by any reagent; and it even absorbs ammonina in
the laboratory, from the small quantity of the gas which' may be set
free in other operations. As extracted from the black-turf,'its formula is CH40O,J05+,N.H40.  It is, therefore, when free from amnonia, isomeric with the saccharo-humine, but differs totally in c(on



640              FORMATION  OF COAL.,position from the saccharo-humic acid, with which it is so identified
in properties.
The azotized acids which have been noticed as existing in vegetable soil and in turf, are terlnmed the Crenzic and.dpocrenic.lcids;
they derive their origin from the rotting of those elements of the
plant which contain nitrogen, as albumen, &c., and are fornled, also,
in the decomposition of animal substances under peculiar circum.
stances; thus certain soft minerals, as polishing slate and rottenstone, contain so much organic matter as to be used for food in
time of distress in the north of Europe, and Berzelius found this to
consist of crenic acid, formed from the bodies of the microscopic
animals, whose silicious skeletons constitute the mineral portion of
the rock.
These acids were first discovered in mineral springs, whence
their name (fpryvy), and are most easily obtained pure from the
ochery deposites which form on the sides of the spring, and in
which they are combined with oxide of iron and silica.  They are
separated by means of their copper salts, the white crenate of copper being soluble, while the brown apocrenate of copper is insoluble in a liquor containing free acetic acid; from the copper salts
they may he set free by sulphuretted hydrogen.
The Crenic dcid is a'pale yellow gummnry mass, of an astringent
taste, very soluble in alcohol and water; its formula is N.C,4. HE
O,2; by exposure to the air it changes into.~pocrenic scid; this
is brown, of an astringent taste, reddens litmus, and is imuch less
soluble in alcohol and water than the crenic acid; its formula is
N6C28. H1I406.
The relations of these acids, and of the several species of ulmine
to the nutrition of plants, will be hereafter considered.
The circumstances under which coal is formed have been already
noticed generally in p. 476 and 563, but it remains to examine specially the mode of decomposition to which the wood is subjected
during that change. The coal appears to require for its production
that the ligneous fibre should be in presence of water, with'little
or no access of air, and that in most cases the temperature shall be
elevated. Thus, while ulmine is produced when the woody material is on the surface, or, at least, only immersed in water, the formation of any of the varieties of coal requires the conjoined influence of moisture, of great pressure, arising from the superposition
of beds of rock or soil, of a high temperature, given by the proximity of volcanic foci, or generated by the decomposition of the
wood itself, and,* finally, that the access of air shall be much more
limited than in the former cases. Then, according to the age of
the geological formation, the nature of the superincumbent rock,
and the degree to which the temperature is raised, the coaly material varies in composition. The more recent species (Lignite or
Fossil Wood), which peculiarly belong to the tertiary formations,
are characterized by the; perfect preservation of the organized
structure of the wood, and a more or lees deep brown, but not
black colour. Their composition may generally be expressed by
f6rmulT which indicate that, without any absorption of oxygen from
an external source, the wood has given off carbonic acid and water.




COMPOSITION,  ETC., OF  COAL.                       641
In the coals of the se.'ondary strata (the proper coal formation)
great diversity of constitution fexists,- depending on local circurnstances.  It would appear that, where the conversion from  lignite
into true coal is perfect, the proportion of carbon and hydrogen becomes uniformly C3,,H,, these elements being united with s)nall
quantities of oxygen, generally amounting to from  three to five
atoms.  The cannel coal of Wigan, the splint coal of Workington,
and the caking coal of Newcastle, have been ascertained, by Johnstone, to be so constituted. Here, also, the change arises from the
elimination of the elements of water and carbonic acid from  the
wood, as CAH2402, produces exactly 4C.O2 and  12H.O., with CaO
H1204,
WVhen the mrass of decomposing vegetable matter has been subjected to a very high temperature, as by the direct contact of volcanic rocks, it becomes almost completely carbonized, and the variety of c'onl termed.tnthracite is formed.  The small quantity of
hydroger. and oxygen which anthracite contains, can only be referred to traces of the proper coal that have escaped decomposition,
and if pure, it would be a lMi/neral Coke, identical in nature with the
coke artificially prepared.
The formulae here given as expressing the constitution of the pro
ducts of the decomposition of wood, are to be considered only as
illustrative of the kind of reaction which goes on between its elements; for none of these products are pure chemical substances;
they form no definite compounds; they have no precise equivalent
number, and hence it is only for illustration that -a formula can be
legitimately employed to express their composition.
The following table contains the ordinary composition of the mo~t
mnportant varieties of coal and turf.  The numbers given were selected from those obtained in the analyses by Richardson and Rega
_ault.
Oxygen and     Economic
Kind of Fuel.  Carbon.  Hydr-ogen. On ra-n shes.  Value ono
aitrogen.     100 Parts.
Turf...... 58 09   593   31 37   46i 1    171
Lignite...      7  t71.71   4'85   21-67 - 177    208
Splint Coal... 82'92   649   10'86   0'13   262
Cannel Coal... 83 75   566   8'04   2'55    260
Cherry Coal... 84-84   5.05    8-43   1 68    258
Caking Coal... 8795   5 24   5'41   1'40    271
Anthracite... 91"98 3'92 3'16   0 94    273
At the same time that the great masses of fossil fuel are thus gen
erated: by the decomposition of wood, a great number of other products make their appearance, which, although much inferior in quantity, possess, at least in some cases, considerable interest.  Thus
the fire-damp of mines (p. 563) consists in most part of marsh; gas,
but contains in some cases, also, olefiant gas and free hydrogen.
Interspersed through the masses of coal are found small quantities of a great variety of bodies, principally carbohydrogens, resembling the oils and stearoptens of
plants closely in properties and constitution. Thus Ozocherit, or Fossil Wax, is found
in cavities in the rocks lying upon coal; it is brown, of a foliated structure; it fuses
at 1430. Paraffine, which is an important constituent of the tar produced in the
destructive distillation'of wood, is also found associated with coal. It is white,
crystallizes in brilliant plates; it fuses at 1110, and may be distilled unaltered; it
dissolves readily in ether and alcohol; it is not acted upon by any reagent, whence'
$4M




642         M ANUFAC TURE  OF  W OOD  VINEGAR.
its name (parum ailnis). Both these bodies have the same composition as olefiani
gas, consisting of C.H. Many waxy fossil substances are isomeric with oil of tur.
pentine, and one, which is interesting as being the matrix in which the native cin.
nabar of Idria is imbedded (page 402), has the formula C21H7; it is termed Ilrialine.
Others of these products are liquid, and frequently issue forth from the surface of
the ground, constituting springs, which, from their-inflammability, have been invested
in uncivilized countries with a sacred character. Such liquids are known as Rock
Oil, or Petroleum. Some specimens of it that have been accurately examined are,
like paraffine, isomeric with olefiant gas, while others are isomeric with oil of turpentine, and, absorbing oxygen, are gradually converted into a resinous substance
Asphalt, for which the formula C40oH320t has been assigned.
SECTION II.
OF THE PRODUCTS OF THE DESTRUCTIVE DISTILLATION OF WOOD, COAL,
AND RESIN.
The results of the action of heat on an organic substance are
strictly analogous to those of an imperfect combustion. A quanti
ty of carbon is removed, as carbonic acid, and a quantity of hydrogen, as water. The other products contain, therefore, relatively
less oxygen.  If the substance upon which we operate be pure, and
the heat be carefully managed, the result is in all cases perfectly
simple and distinct, as where acetic acid gives acetone and carbonic acid; malic acid gives water, carbonic acid, and maleic acid; but
if the temperature change, another set of reactions occurs, and other products are generated, which arise, properly speaking, from  the
decomposition of the first.  Thus acetic acid gives marsh gas; malic acid gives fumaric acid.  Hence, if substances be taken, through
which, either from  their mass or their non-conducting power, the
heat cannot be uniformly diffused, a number of different reactions
takes place in different portions at the same time, according to their
respective temperatures; the bodies generated in the interior are
altered according as they approach the surface, and hence a very
high degree of complexity is given to the ultimate results.
When the substances operated on are not pure, but, as common wood, coal, turf,
&e., contain various organic bodies of different natures mixed together, it becomes
quite impossible to express the precise reactions which occur, and the number ot
bodies generated becomes very great. It is to the classes of bodies thus produced
that I wish to direct attention in the present section, as in all cases where the mode
of origin of a pyrogenic product is accurately known, I have described it in connexion with the body from whence it is usually derived.
According as the object of the process is the manufacture of vinegar or of tar, the
distillation of wood is very differently managed. For the first, a cast iron cylinder,
a, is built into a furnace,
g  ~r   UP t  g bee         of which c is the gtate, d
the fire-door, and c, e, e the
ff                      flue, which winds spirally round the cylinder, so
a               as to heat it as unif3rmly
as possible. The wood, in.g.                  ~t-. |dpieces which fit accurate_@t w i                               lgt. W C B i t ly the interior of the cylin-, &   c'~        der, is introduced by an
==: X e-v opening in the top, which
is then closed by the plate
b. The volatile and gaseous products of the distillbtion pass off by the
tube g, which is bent zig..
zag, and is surrounded at i, i. by larger tubes, through which a stream of cold water
constantly passes. This water is supplied from a reservoir, ni by the tube 1, and,




PYROXYLIC  SPIRIT,  ETC.                               643
eintriing below at m, passes from one jacket to another by the cross pipes o, o, and
escapes ultimately above at p; this cooling arrangement being a form of Liebig's
condensing  tube (p. 542), convoluted, as it were, in order to occupy less room. The
liquids which are thus condensed collect in the tubs r, and the gases which come
over are allowed by the cock t to issue from'the tube s, and, being set on fire, play
on the bottoln of the cylinder, and thus economize a certain quantity of fuel.
The liquid products separate, on standing, into two layers, the upper formed of
oily andi tarry matters, the lower of water, acetic acid, pyroxylic spirit, &c. By the
connecting tube, this heavier liquid passes into the second tub, while the tar remains
in thae first. The impure acetous liquor is neutralized by carbonate of lime; the
acet*atI of lime decomnposed by sulphate of soda or sulphuret of sodium; the acetate
of soda crystallized and fused in order to expel the adhering tar, then dissolved, recrystallized, and decomposed by oil of vitriol. Pure acetic acid is thus obtained,
which is then diluted with water to the various degrees of strength required in commerce (p. 557).
WVhel the acetous liquor has been neutralized by the lime, it is concentrated by
distillation, whereby a spirituous liquid is obtained, which is termed Pyroxylic Spirit,
and has a close analogy to alcohol in its characters. In this state it is, however, a
mixture of a variety of bodies; some of these, as aldehyd and acetone, have been
already noticed, and the others will now be described. Mr. Scanlan first recognised
the various constituents of the impure pyroxylic spirit, and their history was accuratelv investigated by Dumas and Peligot, by Lxwig and by myself.
The impure pyroxylic spirit having been deprived of water by repeated rectifications over lime, as much chloride of calcium as it can dissolve is to be added to it, and
the mixture allowed to stand for a few days. Being then distilled in a water-bath,
the body to which the name of pyroxylic spirit is specially applied remains in the
retort, combined with the chloride of calcium, while there distils over a mixture of
two liquids, X~~/lit and M'sit, which are separated from each other by frequent rectification, as their boiling points differ. Besides these three bodies, there exist in the
rough liquor an oil, M7thol, and a solid substance, discovered by Mr. Scanlan, and
termed Eblani7ze.
This last body remains behind when the spirit is rectified over lime, from which
it is separated by adding muriatic acid, and being then dissolved in boiling alcohol, it
crystallizes on cooling; it forms deep orange-yellow needles; it fuses at 3500, anti
volatilizes in a current of air or of vapour, but is decomposed if heated by itself; it
is insoluble in water, but dissolves in alcohol and volatile oils; sulphuric acid colours it indigo blue; its formula is C2IH904. No combinations of it are known.
The ALt/wol contains no oxygen, its formula being C4113. It boils at 3500, and
possesses the general characters of an essential oil.
Xy/lil resembles alcohol closely in its properties.  Its odour is agreeable and ethereal; its specific gravity, 0-816; it boils at 1430; with acids it produces ethereal
compounds, which have not been closely examined; its formula appears to be
C IH 120-,
illsit can scarcely be considered as having been as yet obtained pure; in its
properties it closely resembles xylit, but has a higher boiling poinit; its formula has
been stated to he C6H62. I shall have, on another occasion, to notice tne probable
constitution of these bodies.
The proper Pyrorxylic Svir'it is obtained pure from its combination with chloride
of calcium by the additions of water and distillation; by rectification in a waterbath with dry lime it is freed from water. WThen quite pure, it is a colourless
liquidl, of a peculiar aromatic smell; it burns with a flame still less luminous than
that of spirit of wine; its specific gravity is 0'798; it boils at 1400; its formula is
C2H40O2; the specific gravity of its vapour is 1'1105; in its action upon other bodies,
this substance ranges itself completely with wine-alcohol, and it is hence frequently
termed Ai L[tlylic Alcohol, from the Greek words tteOv and v0,7. In the history;of its
combinations, it will, therefore, be sufficient to fix attention on those points which
are more specially characteristic of it, its series being in many respects nioie complete than that of ordinary alcohol.
Pyroxylic spirit combines with bases and with salts to form compounds similar to
the alcoates.  It is decomposed by the chlorides of zinc and alcohol, by the fluorides
of silicon and boron; methylic ether is evolved, the reactions being precisely as in
the case of ordinary alcohol.
When treated with sulphuric acid, the methylic alcohol produces an ether, an or.
ganic acid, and a heavy oil, precisely, similar to those formed by spirit of wine.
But the reaction is much more distinct; all the products remain properly in the series of the methylic alcohol, no gas equivalent to olefiant gas being evolved.




644    M E T H YL IC  E T.H ER  AND  ITS  CO   P O U ND. D 
The M. thylic Elier is, at ordinary temperatures and pressures,.a colourless gas,
of an ethereal odour; it burns with a blue flame. Water absorbs thirty-seven times
Wits volume'6f it;'its formula is C2H30.; it' hence is isomeric with wine-alcohol,:with tlie vapour of- which it has the same specific gravity, =1601-5, but its atomic
weight is only one half that of alcohol; it combines directly with anhydrous sulphuri'r acid, forming a heavy oily liquid, and with the other acids to form compound
ethers. Fo-r the:samne reasons as have been fully discussed under the head of winealcohol, it is assumed to be an oxide of a compound radical, M.flthyl, C2H13 or Me.,
and the tormula of thQ pyroxylic spirit is therefore Me.O.+Aq.
The SildIomlthlylirc. Avid is formed precisely as the sulphovinic acid, which it
closely resenbles in properties, except that it may be obtained crystallized in white
needles by calutious evaporation of its solution. Its formula is Me.O.. S.03+S.O3.
HI.O.; its salts are generally more permanent, and crystallize more easily than the
sulphovinates.
Stdp/i. atZ of Mlt/cyl. —Me.O.+S.03.  This substance passes over as a heavy oil
when one part of pyroxylic spirit is distilled with five or six parts of oil of vitriol,
and is formed also' by the direct union of methylic ether and dry sulphuric acid. It
has a strong garlic odour;'its specific'gravity is 1'324; it boils at 3700. By boiling
water or strong' bases, it is immediately removed into its constituents. With dry
ammonia it: forms a white crystalline mass, Sbdlpllometlylan, which consists of Me.
0.. S.03+S.O2Ad.
Chlomi/e /' MdJtl1t,' C2H3CL: or Me.Cl., is formed by heating a mixture' of common
salt, pyroxylic spirit, and oil of vitriol. A permanent gas is evolved, which may bhe
collected over water, which absorbs but twice its volume of it; it burns with a
greenish-rwhite flame.
Iodlideof:'Mdtyu!il, C21131. or Me.I., is prepared by distilling a mixture of phosphorus, itlodine, and pvroxylic'spirit.  On the addition of water to the distilled liquor,
the iodide of' methyl separates as a heavy oily liquid, of sp. gr. 2237; it. boils at
about 112'.
Flluoride of MAthYI,. C2H3F. or Me.F., is formed by heating a mixt;ure of sulphate
of methyl ard fluoride of potassium, and collecting the gas evolved over water. It
is colourless, and.burns with a whitish flame, evolving fumes of hydrofluoric acid.
MWth/?lo-n7-melrcptan.   Sulph-urel of Me3thyl.-These bodies-are prepared precisely
as the corresponding substances in the series of ordinary alcohol.
Nitrate of Methyl, Me.O.. N.05, is prepared by distilling nitrate of potash, pyroxylic spirit, and oil of vitriol, mixed together in a capacious retort. The receivers
are to be carefully cooled, and a gentle heat applied to the retort to commence the
reaction, which then continues to the end without any farther external heat. The
product,' when purified by redistillation over some oxide of lead, is a colourless liquid, neutral, of an ethereal odour; it burns with a yellow flame; its sp. gr. is 1'182;
it boils at 1510.'If a drop of it be heated to 3000, it explodes, and this takes place
much more easily if' there be a quantity; hence its distillation must be very cautiously conducted.
CCarbometlLylic Acid is formed by passing a stream of dry carbonic acid into a solution of barytes in pyroxylic spirit. Carbomethylate of barytes forms in minute
plates, which are insoluble in spirit, but dissolve easily in water. This' salt rapidly
decomposes into carbonate of barytes, free carbonic acid, and methylic alcohol.
With chlorocarbonic acid and sulphuret of carbon, the pyroxylic spirit gives coillpounds precisely similar to those already described in the series of ordinary alcohol.
Oxalate of'Methyl, Me.O.. C203, is best formed by distilling a mixture of equal
parts of oxalic acid, pyroxylic spirit, and oil of vitriol. The product crystallizes in
large rhombic plates; it fuses at 124~, and boils at 31.20; it dissolves easily in water
and alcohol. With water of ammonia it produces oxamid and methylic'alcohol;
with dry ammonia it forms a crystalline body, Me.O.. C203+C202Ad., Oxamethylan.
Acetate of /lIethyl. —Me.O.. Ac.03. Formed by distilling together oil of vitriol,
pyroxylic spirit, and acetate of soda. It. forms a colourless liquid, which boils at
136~; its specific gravity is 0'919. The substance known as Mesit may be considered as a compound of methylic alcohol and aldehvd, C2H30.+C4H30., and the
xylit is probably a mixture of that body with the acetate of methyl.
The combinations -of rmethylic ether with the other acids resemble so closely
those of vinic ether that they need not be specially described.
Products of the Oxidation of Pyroxylic Spirit.
If pyroxylic spirit be distilled with chromate of potash and sulphuric acid, it
is totally converted into carbonic acid and water. If black oxide of manganese
be used, and, after the first violent effervescence has ceased, a gentle heat be ajp




PREPARATION   OF  FORMIC  ACID: E TC.                           645
piled, a liquid distils over, which, when completely pure, has the formula C6HO04;
it boils at 1040; its sp. gr. is 0'855; it is termed,lit/iylal.
If pyroxylic spirit oe Drought into contact with oxygen by means of spongy plati.
hlum, as described for ordinary alcohol in p. 554, hydrogen is removed anu oxygen
absoroed in equivalent proportion, and the methylic alcohol is totally converted into
hydrated Formtic Acid, C2H402 and'20. giving'2H.0. and CH204-. In this reaction there does not appear to be any intermediate state equivalent to that of aldehyd,
which body appears to be without a representative in the pyroxylic series, at least,
except in combination. For practical purposes, this mode of preparing formic acid
is not had recourse to, as it may be derived more easily from the oxidatiot of most
organic bodies.'lThe formic acid derives its name from existing in a very concentrated form in
the common ant (formica rufa), and produces the pain of their sting on being injected into the puncture which the animal makes; it was formerly prepared by distilling the ants with a little water; but the process of Dbbereiner is now generally
followed. It consists in mixing one' part of starch, or sugar, or tartaric acid, with
four of black oxide of manganese, four of water, and four of oil of vitriol. Considerable effervescence occurs, owing to' the escape of carbonic acid. When this is
over, the'mixture is to be distilled until four and a half parts have passed over;
this acid liquor is to be neutralized by carbonate of soda, and the formniate of soda
crystallized by evaporation and cooling. From this salt the formic acid may be obtained in any required degree of concentration, by distillation with oil of vitriol, in
precisely the manner described for acetic acid (p. 556).
If sugar, or starch, or barley be simply heated with dilute sulphuric acid until it
becomes brown, a certain quantity of formic acid is produced, along with ulmine and
ulmic acid. The generation of this acid as a product of the decomposition of prussic acid, of chloral, and of hydrated oxalic acid, has been already noticed.
Pure hydrated formic acid is a limpid colourless liquid, which fumes slightly in
the air; its odour is intensely pungent; when cooled below 3?i, it crystallizes in
brilliant plates; it boils at 21'20; its specific gravity is 1'235. In this most concentrated fbrm it is an absolute caustic if applied to the skin, producing a sore very
difficult to heal; its formula is C2H.03+H.0., and, like acetic acid, it is supposed
to contain -a radical, Formyl, C2H. or Fo., and its rational formula to be Fo.03+H'.
O. Combining with water, it forms at least one other definite hydrate, the~formula
of which is Fo.03+'2IE.O.
The resemblance of formic acid to acetic acid is very close, but they are at once
distinguished by their behaviour to certain reagents. When heated with an excess
of oil of vitriol, it is decomposed, with lively effervescence, into water and carbonic
oxide (C2H.s0=C202 and H.O.). If a solution of formiate be mixed with a coldi solution of nitrate of silver, a white crystalline precipitate of formiate of.silver falls,
which, when heated, is totally decomposed into metallic silver, water, and carbonic
acid, C2H.03+Ag.O. giving 2C.02 with fH.O. and Ag. If formic acid be digested
on red oxide of mercury, carbonic acid is given off, and a sparingly soluble crystalline formiate of the black oxide of mercury is produced: this, when boiled, is totally decdmposed, metallic mercury separating, and carbonic acid and water being
evolved.
The alkaline formiates are soluble and crystallizable; that of ammonia crystallizes in right rhombic prisms, which melt at 2500, and sublime: without alteration.
If its vapour be. passed through a red-hot porcelain tube, it is totally converted into
prussic acid and water, C2H.03+N. H40. giving C2N.H. and 4H.O.
Formniate of Soda crystallizes in rhombic prisms, which have the formula Na.o..
Fo.03+ 2 Aq. -  hen heated, it undergoes aqueous fusion, and by-a higher temperature is decomposed. A solution of this:saltj when boiled: with the; salts of silver,
mercury, gold, palladium, or platinum, precipitates the. metal, and is hence usefullin
analysis.
~Formiate of Barytes.-Ba.O.. Fo.03. It is obtained in' laSge     __
rhombic prisms, as in the figure,:where%.,y are primary, anda i.  i a
secondary plane, which have a bitter taste, and are not altered  _y i  2y
by the ail. It is very soluble in water, but insoluble in alcohol.
Formiate of Lime is easily produced by neutralizing lime with  zit'dilute formic acid; it is equally soluble in cold and in hot water, -
so that it is only obtained crystallized by slow evaporation; it...
dissolves in ten: parts of cold water; it is insoluble -in alcohol.    - 
Fornisate of Lead.. Pb.O.. Fo.s0. If formic acid be added to a
solution of acetate'of lead, this salt separates after a,short time in stellated groups
of brilliant-needles, which are anhydrous, and require forty parts of water fcr'solu



646    PRODUCTS OF  DISTILLATION  OF  COAL.
tion; it is totally insoluble in alcohol. By the formation of this salt, the formic
acid is readily distinguished from the acetic acid, and tile two, if present together,
may be thus separated.
Eo'naiate of Copper crystallizes in large rhomboidal prisms, as in
the figure, where i, u, u are primary, and in a secondary plane,
which are very regular, transparent, and of a fine, clear blue colour.
It effloresces in dry air.
al   The F ormiates of Melrcur'y.-That of the red oxide is very soluble;
it can only exist at ordinary temperatures; by a very gentle heat it
I   changes into the formniate of the black oxide and this when boiled
gives metallic mercury, as already described among the tests for
formic acid. The formiate of the black oxide may also be prepared
by mixing solutions of formiate of soda and of subnitrate of mercury; it separates
in small pearly plates of four and six sides, which may be dried between folds of
blotting paper, and have a fine silky lustre.
Chlorides and Iodides of Forrlyl.-When, under the influence of powerful reagents,
the constitution of the compounds of acetyl or elayl is broken up, a series of bodies
is generally produced, which are supposed to contain as their radical formyl. Thus,
by the action of chlorine on the chloride of elayl, a heavy oily liquid is iormed, C2
I1.C12 or Fo.Cl2, Bichloride of Formyl; and by acting on chloral by caustic potash,
formic acid is produced, and a heavy oily liquid, which is termed Chlorofo'm, and
consists of C2H.C13 or Fo.Cl3, being Perchiloride of Formyl. This, which is the most
interesting of these bodies, is easily prepared by distilling alcohol, acetone, or pyroxylic spirit with chloride of lime; it is colourless, of an agreeable ethereal odour;
its specific gravity is 1'480; it boils at 141~; the specific gravity of its vapour is
4-116; with an excess of chlorine it gives bichloride of carbon.
Periodide of Formnyl. lodoform, Fo.I3, is produced by adding caustic potash to a
solution of iodine in alcohol until it is completely decolorized, but avoiding an excess of alkali; on then evaporating, the iodoform is deposited in brilliant gold-coloured plates'; it is insoluble in water, but very soluble in alcohol and ether; it volatilizes at 218~; with potash it gives iodide of potassium and formiate of potash.
There exist also bromides, cyanides, and sulphurets of formyl, which do not require
notice.
By acting on the methylic ether and on the chloride of methyl with chlorine,
Regnault obtained two series of bodies, which follow precisely the same principles
of constitution as have been described fully when speaking of wine-alcohol (p. 565).
Malaguti also obtained, from the oxalate and acetate of methyl, bodies similar to
those generated by chlorine with the ordinary oxalic and acetic ethers, and hence
it is only necessary to say that all the conclusions there drawn respecting the nature
of these bodies, and the theory of the chlorine radicals, may be applied to explain
the origin of the bodies derived from the methylic alcohol also.
Products of the Distillation of Coal.
The products of the distillation of coal in close vessels possess
a remnarkable analogy to those that have been now described, and,
indeed, in many instances, are identical with them.  Thus the gaseous products are marsh gas, olefiant gas, and carbonic acid.  The
liquid products consist of various bodies closely analogous to petroleum, and the solids consist of napthaline and paraffine.   The
relative proportions of these products vary with the temperature.
The lower the heat employed, the less gas, and the more solids
and liquids are produced; the higher the temperature, the greater
is the quantity of carburetted hydrogen; but, for the purposes to
which the practical process is applied, the temperature must not
be raised too high, for then the gas evolved would be mostly marsh
gas and pure hydrogen,' which possess little illuminating power,
while a great deal of illuminating power may be derived from  the
vapours of some highly volatile liquid products.  In the manufacture of coal gas for the purpose of illumination, the object is, therefore, to maintain a temperature, too high for the production of much
napthaline or paraffine, but not high enough to produce hydrogen




COMIPOUNDS  OF  NAPTHALINE.                             647
or marsh gas, and thus obtain the greatest possible quantity of a
gaseous product of olefiant gas and vapours of liquid carbohydrogens.
From the albuminous constituents of the wood, coal always contains a certain, though small quantity of nitrogen, and hence ammonia is evolved in its distillation.  The gas liquor so obtained is extensively used in the manufacture of sat ammoniac.  From  the sulphates existing in the plants, or in water which has filtered through
the bed of coal, or from iron pyrites, which is generally associated
abundantly with the rocks of the coal formation (p. 3ii3), a small
quantity of sulphur always exists in coal, which is evolved during
the distillation as sulphuretted hydrogen, and requires to be carefully separated from  the other gases, which is effected by washing
them  with the milk of lime, which absorbs also the carbonic acid.
The apparatus used for making coal gas does not differ in principle,
although very much, in arrangement, from that figured in p. 642.
The ammoniacal liquor and the tar are collected in the tubs, and
the gas, in place of being burned at the orifice of the tube s, is conducted to the purifiers, and thence to the gasometers for use.
Most of the substances produced in this process have been already noticed. It
only remains now to describe, as briefly as possible, the properties of such others as
are important.
Of NaplI/aline and its Drivatives.-This substance is a very usual product of the
decomposition of organic substances by heat; it is obtained abundantly by rectifying
coal-gas tar; it crystallizes in white silvery plates; its specific gravity is 1'048; it.melts at 13'13, and boils at 413~, but sublimes rapidly at much lower temperatures;
it burns with a strong smoky flame; its smell is powerful and very peculiar; it is
insoluble in water, but abundantly soluble in ether, alcohol, and oils; its formula is
C201-I3s; the specific gravity of its vapour is 4488. It is remarkable for the number
of compounds to which it gives rise. WV- hen digested with nitric acid, it forms two
combinations; the first, Nitronaptthalid, crystallizes in sulphur-yellow prisms; its
formula is C20-7. N.O4; the second, Nitronaphlidehyd, is a white crystalline powder,
having the formula C,0H3. N.O4. Both these bodies are insoluble in water, but dissolve easily in alcohol and ether, from which solutions they crystallize on cooling.
xVhen nitronapthalid is distilled with lime, a substance is obtained which resembles eblanine (p. 643) in properties, but consists of C201170. Laurent termed it
O.ide of Napthalese.
Chlorine forms with napthaline a heavy oily liquid, which has the formula C20oH
C12. It gradually evolves muriatic acid gas, and deposites a crystalline substance.
This change is effected immediately by heat or by a base. This solid body is termed Chlornapthelid; it consists of C20H7Cl1. If this be melted and submitted to the
continued action of chlorine, hydrogen is removed and a crystalline solid formed,
Chlornapt/odehlyd.,:(H4012.  By acting on napthaline with an excess of chlorine,
and distilling the product, a solid substance is obtained, which crystallizes in large
prisms, and has the formula C2oH6C12. All of these bodies are insoluble in water,
but dissolve in alcohol and ether.
WVhen these chlorine compounds are boiled in nitric acid, a series of substances
are obtained containing chlorine and oxygen. Thus from C2018sC12 is formed C20o
Hi. 03C12, which is a brilliant yellow crystalline matter, insoluble in water, and
melting at 2060. By farther treatment with nitric acid, the Chloronaptlmalic Acid is
formed, the formula of which is C2OH5. 06C12. This body is insoluble in water, but
dissolves in ether, and crystallizes, on cooling, in short, brilliant yellow prisms; it
melts at 4000, and may be sublimed unchanged. W-ith bases it forms well-characterized salts, which are orange or red-coloured; those of the alkalies and earths are
soluble and crystallizable; those of the heavy metals are insoluble in water. In
this process there is also formed a substance which does not contain chlorine; it resembles closely benzoic acid; it is termed Nacpthalic Acid, but its composition is not
yet decided; another product noticed by Marignac is an acid possessing the remarkable constitution of C.C1.. N.04.
The action of sulphuric acid on napthaline varies, as the acid is hydrated or anhydrous. In the latter case, sulphurous acid is evolved and a series of products




648           B O D I E S- OF  -T H E:; P H E-N E YL- S E R I E S.
formed, which have:been described* by- Berzelius as follows: Sulphlonapthldine, Car
I-I8. S.O2, crystallizes in white plates, which melt below 2120~ to a colourless liquid;
S-lIphonapthalid, C24H-,o. S.O2, is a snow-white powder, which may be separated
from the former by means of its insolubility in cold alcohol. In addition to,these
-bodies there are formned two acids, the Stlphonaptbhalic and the Sulpl.onapiltic; they
are isolated by taking advantage of the insolubility:of the barytes salt of the latter in
cold alcohol, and then, by decomposing the barytes salts by dilute sulphuric acid,
these organic acids may be obtained crystallized.  The Sulphonaplthic Acid forms
soft crystalline scales, of a soapy feel, like talc, which taste bitter and' sour. Its tbrmul.a is C22H9. S401+2 Aq..; it combines with two atoms of fixed base.  The Su-L
pnumaplhbalic. Acid forms a hard crystalline mass, which:is acid and bitter, inodorous,
fusible below 2120; it is very. deliquescent; its formula is CoHs5. S2O0.  The salts
of these acids are all soluble in water. There is still another acid product, termed
by Berzelius- Sldphoglucic Acid, the constitution- of which is not known.
Notwithstanding that few subjects have been so often- investigated as the history
of napthaline and its derivatives, there are few bodies whose theory is more obscure.
It would appear that all its hydrogen, or at least, six atoms of it, is capable of replacement by chlorine or nitrous acid, and there does not exist any distinct character by which the existence:of —a; compound -radical,-either primitive'or derived, as a
basis of these combinations,:could with. reason -be: assumed.  The hypothesis of
Marignac is, that napthaline itself is a compound of two carbohydrogens, C,6H4+
C4H4, by the diverse action of reagents upon which the various bodies maybe derived; but this idea does not afford sufficient advantages to justify its adoption.
Pas'anapthaline. —This-substan-ce is associated with napthaline in the gas-tar, and
is isomeric with it, its formula being C20Hs; it differs in its fusing and boiling p4oints,
which are very much higher; it may be distilled unaltered; it is insoluble in water,
very sparingly soluble in alcohol or ether, but copiously so ill oil of turpentine; its
relations to other bodies are not well knowvn; with nitric acid it produces a colourless crystalline body; having the formula C,5H402.The liquid products of the distillation of coal- have been- as yet studied only by
Laurent, of the most interesting of whose results, as yet, but the general nature has
been:published. - This liquid, which is-properly termed Gas-lnaptha, contains a crystalline solid, which volatilizes without decomposition, and acts as an acid; its fornmula is C,12H5O.+Aq.  Its discoverer considers it as a hydrated oxide of a-compound radical, w-hich he terms Phenyl; it combines with potash and barytes, forming
crystalline compounds. With sulphuric acid it forms Sulcphophenic Acid, C12I-50..
S.-03+S.03. H.O., which forms salts resembling the sulphovinates; *with chlorine it
forms:, first, Cdlorophenesic Acid, C12H3I. C120.+Aq., which crystallizes in rhombohedrons, and possesses a very nauseous odour; and -afterward Chlorop/he7ic Acid,
the formula of' which is C1,2E2. Cl3O.-+Aq.
With nitric acid, the hydrated oxide of phenyl produces- first, N1itrophenesic Acid,
C,2H3(N20s)O.+Aq., and by continuing the action, the Nitrophlenic Acid, C12I-I.
(N3012)O.+Aq.,: which is the Picrici  Acid described p. 618, as formed- from indigo
and salicine.  This phenyl series appears, -therefore, to be the final result of the oxidation of a great number of organic bodies. As yet, our knowledge of the properties of these bodies is - not sufficiently detailed to justify any discussion of' their nature, but: the connexion with the-bodies derived from indigo is exceedingly remarkable. If we consider the-radical as C,2H5E, then- amilene is Amidide of Phenyl, and
all the characters of:its salts are easily explained.  The substance termed by Laurent Cldoralbiine, C,12H6C12 is probably C12H5Cl.+H.Cl.
In preparing olefiant gas for the purposes of illumination, by the destructive distillation of resin, a number:of substances, some solid, others liquid,: are produced,
which.have been examined-by Pelletier and-Walter.  Those not already described
are as: follows: Retisteren, a white crystalline solid, which melts at 1520 and boils at
617. - In! its properties it resembles napthaline; its formula is C3sH14. Retinol is
a colourless liquid, tasteless and inodorous; specific;gravity =0 9;  it boils at 460~;
its formula is -C32Hi -, being isometfic with' benzi n; the specific gravity of its vapour
is 7'25. Retinaptha is a coloarless liquid, of an agreeable odour; its specific gravity is 0.86; it boils at 2260; its formula is C,4H8. Retinal, also a liquid, boils' at
300~.; it consists of ClsH,, being polymeric with miesitylene. - 
When the gas obtained. by the destructive distillation of oil is strongly compress
ed, a liquid separates, which was found by Faraday to contain three distinct substances. - Of these the most abundant was the benzin described already (page 571),
as produced in the decomposition of benzoic acid. Of the others, one is known as
Faraday's Quadricarbulret of HIydrogeit, it is also formed abundantly in the distillation
of caoutchouc; its specific gravity is 0627; -it boils below 32~; it combines with




K R E 0S O T E   KAP N O M O R  E   C.              649
chlorine, forming a heavy oil; it is isomeric with olefiant gas, its formula being C4
1-4, and the specific gravity of its vapour is double that of the gas, being 1'962. The
third liquid boils at 183~. Its formula is probably C6H4, being isomeric with mesitylene and retinyl.
During an elaborate examination of the nature of the tar produced
from the destructive distillation of wood, Reichenbach described a
number of bodies, of which one, Kreosote, has become of much interest, from its remarkable properties, but the others are still very
little known.  For the preparation of kreosote, the tar is rectified by
successive distillations, until the oil which passes over becomes
heavier than water, and then digested with a solution of caustic
potash, which dissolves the kreosote; when this liquor is exposed to
the air, it becomes brown, and being then neutralized by an: acid,
the kreosote separates.  This process, of solution in an alkaline
liquor and precipitation by an acid, is to be repeated until the solution is no longer browned by exposure to the air; the kreosote is
then pure.  It is Zan oily, colourless liquid, with a penetrating odour
of smoke; its taste is sharp and burning; its specific gravity is
1'037; it boils at 400;:it burns with a strong smoky flame; with
water it unites in two ways: 100 parts of water dissolve 1'25 of
kreosote, and 100 parts of kreosote take up ten of water; the solution is quite neutral; kreosote mixes with ether, alcohol, and acetic
acid in all proportions.  It unites with alkalies and with acids, but
without appearing to form any definite compounds, and it is not certain that it has ever been obtained really pure.  The formula assigned to it is C,4H902.
The most remarkable property of kreosote is. that it coagulates
albumen and the'colouring matter of the blood, and these bodies are
*then no longer susceptible of putrefaction.  Fibrine, or muscular
flesh, immersed in a solution of kreosote for some minutes, has no
tendency to putrefy even if exposed to the heat of the sun afterward; from this is its name derived (xpewo  oow;).  Kreosote is the
antiseptic principle in pyroligneous acid, and in turf or wood smoke.
If placed on the tongue, it makes a white mark, with violent pain.
Its use as a caustic remedy for toothache is well known.
Kapnomor accompanies kreosote in tar; it is a colourless liquid; it smells like
rum; with oil of vitriol it forms a purple solution; it boils at 3600. Picamar is
also liquid; it boils at 518~:;, it combines with bases. Ced'riret crystallizes in fine red:needles,.insoluble in: all liquids except.oil of vitriol and kreosote, the former pro~ducing a blue, and the latter a purple solution. PittaLal forms a dark blue solid
mass, which; when rubbed, assumes a golden lustre; it contains nitrogen; it is insoluble in water, but dissolves in acids, and is thrown down. again by. alkalies.
With.metallic salts, its solution gives blue precipitates, which may be attachedby:mordants upon woollen and cotton cloths. The constitution of these bodies has not
been examined.
By the action of reagents on the coal-gas naptha, Runge obtained a series of bodies, a re-examination of which would be of -the highest interest to science; they are.liquid, and appear to. possess stro ng alkaline properties, and generate salts, which
with one (Cyanol) are- of a rich blue colour. They belong apparently to the same
class of bodies as anilene.
By the destructive distillation of animal substances, a series of oily bodies is generated, of a strong odour (Animal Oil of Dippel, Oil of Hlartsho/r), which is described
by Unverdorben as a mixture of several bodies, to which he has given names; but,
as we possess no accurate knowledge whatsoever of their properties, I do not. think
it necessary to give his account of their preparation.
4aN




{i350            GE RMINATIO N. -MALTING.
CHAPTER  XXIX.
OF THE CHEMICAL PHENOMIENA OF VEGETATION.
IN the seed of a plant, the gerrne of the future individual is associated
with one or mere organs, termled cotyledons, which contain, in general,
starch and some form of azotized matter, as albumen, gluten, or legumine, which substances are so disposed in order to supply the nutriment
necessary for the development of the embry6, until its organs are fitted
for the collection of nutriment fiom external sources.
The first act of growth in the seed is termed germination, and is
accompanied by a remarkable change in the constitution of the cotyledonous mass.  For perfect germination, it is necessary that the seed be
moderately supplied with water and with air, and that it be either in the
dark, or exposed but to little light; all- these circumstances are perfectly
secured by the ordinary mode of sowing seeds in a moistened soil, which
shall be so loose as to admit air, and yet exclude the light.
A seed so circumstanced gradually swells to much beyond its original
volume, and its temperature rises; it absorbs oxygen from the air, and
evolves water and carbonic acid, and the starch of the cotyledon gradu.
ally disappears, being changed into sugar.  From the point of the seed
where the embryo is situated, two shoots spring forth, one of which, the
radical, takes its direction downward into the soil, while the other, the
plumula, strikes up towards the air, to become the origin of the stem;
according as this growth proceeds, the quantity of sugar in the seed
diminishes, and by the time that the radical is fit for the performance of
its functions, as root, in absorbing nutriment from the soil, nothing re.
mains of the seed but its ligneous husk, which in some cases completely
perishes under ground, but in others rises, and, assuming the functions of
leaves (seed-leaves), assists in providing nutriment for the young plants,
until the stem has been furnished with leaves by which it may act upon
the surrounding air.
This process of germination is artificially produced, for the purposes of
the arts, by the operation of rmalting; the grain is steeped in water until
it has absorbed the proper quantity of it; it is then spread on the
floor of the malthouse, and its temperature prevented from rising too
high by the mass being frequently spread out, and new surfaces exposed to the air.  When the seed contains the maximum quantity of
sugar, that is, when the conversion of the starch is most complete,
and yet before much sugar has been assimilated by the germe, which
is practically found to be when the radical has grown as long as the
grain, but does not project beyond it, the young plant is killed by ex.
posing the malted corn to a current of hot dry air in the malt-kiln, and
the malt is then employed as a source of sugar in the fermentative pro.
cesses of the brewer and distiller.
The saccharine fermentation which thus furnishes nutriment for the
young plant in the first stage of its existence, resembles the transformation of starch by means of sulphuric acid, described in p. 528, and is ex.




CONSTITUTION  OF  PLANTS.                      651
cited by the presence of a peculiar ferment produced by the decomposition of the vegetable albumen which the seed contains.  This active
substance is termed Diastase; it does not pre-exist in the seed, but is
itself' produced by the action of the air and water upon the albumen; it
is not identical with the ferment which induces the alcoholic fermentation, but they appear to be but successive stages of the decomposition of
the same substance.  The diastase may be obtained solid by bruising
malt with a small quantity of water, and expressing the liquor; to this
alcohol is to be added, which precipitates a quantity of unaltered albumen, and on evaporating the filtered liquor to dryness, the diastase remains, thouah by no means pure; it is a white gummy mass; it is pre.
cipitated by infusion of galls and most metallic salts; one part of it rapidly and completely converts a solution of 2000 parts of starch in water,
first into dextrine, and finally into grape-sugar.  It has been suggested
by Saussure that diastase is identical with the substance termed mucin
in p. 537, but this is doubtful; it contains nitrogen, and is most probably, as already stated, the first product of the putrefaction of the gluten
or albumen.
When the process of germination is over, the plant is found provided,
by its roots and leaves, with the means of procuring such nutriment as
its future offices require, from the atmosphere and the soil.  For the
constitution of its proper ligneous tissue, carbon, hydrogen, and oxygen
are required, and these serve also for the formation of the majority of its
excreted products, as sugar, gum, starch, resin, oils, and acids; but, in
addition, nitrogen is required; and although the proportion of nitrogen
in any plant is small, compared with that of the other elements, yet it
is of great importance as a constituent of the active principles of most
medicinal plants, as the vegetable alkalies, amygdaline, &c.; and of still
higher interest, as Bousingault has shown the nutritive power of each
plant, when used asfood, to be proportional to the quantity of nitrogen
which it contains.  In every plant there. exists also certain inorganic
elements, acids, and bases, which, though small in quantity, are yet essential to its healthy growth.  The examination of the modes, chemical
and vital, by which these various substances are supplied to the plant
and assimilated by its organs, constitutes an important branch of vege.
table physiology, which can here be but superficially sketched; and, in
its relation to practice, the manner of supplying these materials so as to
favour the growth of plants, and develop their most useful principles.
must be the basis of every system of enlightened agriculture.
Of the Assimilation of Carbon by Plants.
In describing the constitution of the atmosphere (p. 269), I have had
already occasion to notice the beautiful provision by which the two great
classes of organized beings mutually compensate for the change which
each produces in its nature, and thus retain it in the condition most
conducive to the healthful existence of both.  That while the animal, in
his respiration, throws off carbonic acid and absorbs oxygen, the plant,
from the surfaces of its green leaves, in sunlight, absorbs carbonic acid
and gives out oxygen. It only remains here to examine the circumstances of this change with reference to the other functions of the plant.
As water is abundantly absorbed by plants, both with the roots and
leaves, the assimilation of carbon from the air should, with it, supply at




652         FORMAT'ION  OF  WVOODY  TISSUE.
once the elements of the woody matter, as well as of those other bodies,
as sugar, starch, and gum, which contain oxygen and hydrogen in the
proporlions to form water.  But this respiratory function of the leaves
does not in reality possess the simplicity and uniformity of effect which
has been lust assigned to it.  It is found that the absorption of carbonic
acid and the liberation of oxygen occur only under the influence of sunlighlt, and from the green portions of the plant, while the coloured por.
tions, as the flowers and fruits, and even the green leaves during the
night, absorb oxygen and give out carbonic acid, thus tending to increase the vitiation of the atmosphere produced by animals in place of
counteracting it.  The existence of -these opposing actions had induced
some physiologists to doubt whether they did not neutralize each other,
and henice to seek for the source of the carbon of the plant in -the action
of the roots upon- the organic substances: of the soil.'But the experi.
ments- of' Daubeny have conclusively established that a healthy plant
evolves so inuch more  oxygen in the day than it absorbs during the
night, and inversely absorbs so much more carbonic acid during the day
than it evolves at night, as may satisfactorily account for the growth of
the woody material of the plant, and compensate for the influence of animal respiration and combustion upon the air.
It has been already shown, that the grains of starch, when elaborated
by the organs of the plant, possess a structure totallytdifferent from that
which characterizes bodies constituted in virtue of mere affinity, and
more analogous to certain animal organs, as the crystalline lens of the
eye.  In the different Varieties of starch, it is not difficult to trace the
gradual transition to lignine, and, as stated in page 530, ordinary wood
still retains in the tubes and cells. formed by the arrangement of the par.
tieles of lignine, a considerable quantity of unaltered starch.  In the medilla of various trees, the passage from starch to lignine is still more
evident.  Now for the formation of starch there are required but water
and carbon, its formula'being C.12H1010, and this I consider as the actual
result of the true respiratory process of the plant; carbonic acid being
absorbed, and an equal volume of.oxygen being exhaled, the carbon is
assimilated by the vital power of the plant, and, with the elements of
water, produces a substance partially organized in structure, the starch
globule.  The outer layer of this gradually increasing in density, and
water being separated' from the internal portion, should,'give a cell, or, by
the; reunion of many, a continuous fibre or tube of true lignine.  The
change being simply- the loss of water, the formula of the lignine becomes
C, l.s808.  The nature-of the starch globule, and, hence,ethe structure and
physical properties of the ligneous fibre, varies in different plants. Thus
I consider, in the adult plant, starch to be the first product of the assimilation of carbon and water, that it is already possessed of a low degree
of organization,-and is, in structure and composition, adapted for the
change (growth rather than: tiAasformation) into true wood.
By contact with the albuminous or fermentative principles, the starch,
whether accumulated in the seed or roots, or distributed' throughout the
substance of the plant, undergoes changes of an opposite kind.  Its or.
ganized character is lost; it successively forms gum and sugar.  We
cannot yet-form cane-sugar artificially from starch, but we can have no
doubt that it arises, as grape-sugar does, from the' catalytic metamorphosis
of the starch, arrested, in virtue of the vital power of the plant, at a point




SECRETION  OF  PLANTS) ETC.                        6O53
where we cannot seize it in the laboratory.  These are the truly nutritious elements of the plant, whether designed for the support of the adult
individual, or, collected in proper reservoirs, to serve for the sustenance
of the future individual in the seed.
in the conversion of the starch into the numerous secondary products,
as acids, colouring matters, oils, &c., the presence of which characterizes
the generality of  plants, we may find the source of that inverse respira.
tory action which so much masks the real and simple nutritive prucess.
Of the circumstances of the formationr of these bodies, we have an example admnirably illustrative of the point, in the conversion of lignine into
ulmine.  Here, though the change would at first appear-to require only
the loss of the elements of water, we find it to be much more )profbund;
the constitution of the lignine is totally broken up; oxygen is abundantly absorbed from the air; a quantity of its carbon is carried off as carbonic acid, and a quantity of its hydrogen as water.'rilis action, which
may be looked upon as equivalent to-the various processes of secretion
perfiormed upon the blood by the organs of animals, by. which substances
adapted to the use ol structure of-different parts are there deposited,
while others unfitted fbr the purposes of the: orgainized being are tthrown
off, is ca rried on by.the leaves, probably by all portions. of- the su rfce of
the plaint, and is tlle source of the continued exhalation of water and car.
bonic acid which occurs.  During the day, and especially in bright sunshine, th-e assimnilating power of the plant being in. full act.ioni carbonic
acid is taken in, and oxygen given out; during the niglht, wllile the plant
is in repose, this nutritive action ceases.;:Through the whole-ttirne, however, the process of the secretion is carried onl, water and carbonic,acid
given off, thoughll in such proportion only as to secure at the end of the
twenty-four hours ail excess of assimilated carbon sufficient fully to secure and account, for the rapidity of growth.
T'he changes of constitution which accompany the ripening of fruit
deserve to be considered- more in detail than those of which the general
nature has been just noticed.  If we examine the cormposition of a young
apple, we find it to be nearly tasteless, and to consist of-a loose ligneous
tissue, in which is imbedded a quantity -of ordinary starch; as its growth
proceeds, the starch diminishes in proportional amount, and the firuit be.
comes intensely sour, from the presence of tartaric acid; after some time
the acidity becomes of a much less disagreeable killd, and the tartaric
acid is found to be replaced by malic acid; and in the next and concluding. stage of maturity, this acid disappears, its place being taken by pec.
tine and by sugar.  During the whole of these actions, oxygen is absorbed from the air, and water and carbonic acid given off.  Their theory is
simply indicated: thus starch, which is C,,2HoOl, absorbing 140., produces 6 Aq. and 4C.02, with tartaric acid, C1H40o0; and of' this, three
atoms, absorbing 60., produce 8C.02 and 4 Aq., with two atoms of malic
acid, 2(C,8H40). rThe change of tartaric to malic acid may also -occur
without the absorption of oxygen from  the air, as 6(CH4010) may produce 5(C,t1140s) with. 8C.04 and 4Aq.; but as fruits do: not ripen -in close
vessels, unless when they absorb oxygen, the former is more probably
the process which actually takes place.  The formation of- tle pectine
and sugar from the malic acid may be produced by the absorption of ox.
ygen and the giving -off- of water and carbonic acid, as 8(CH40,) with
9H.0(. and 50., produce pectine, C24H170, sugar, 2(C1,2H1120,2) with 16(0




654'        SOURCE  OF  CARBON  IN  PLANTS.
02. That neither pectine nor sugar is derived originally from the starch,
is evident, as the starch abounds but in the very earliest stage, and
gives place to the tartaric acid, while the increase in quantity of the
gelatinous and saccharine matter is proportional to the disappearance
of the acid constituents of the fruit.
When our knowledge of the ultimate effect of the complex actions of
plants upon the atmosphere was still uncertain, it was considered, and
upon very rational gt-ounds, that the plant was indebted for its carbon -to
the organic substances of the soil, and the necessity for a continued supply of animal or vegetable manure to keep up the fertility of the soil, was
thus satisfactorily explained; it was considered that the roots and leaves
remaining from the preceding crop, or intentionally mixed up with the
soil, were converted, as already described, into ulmine, which, either by
itself, or in combination with inorganic bases, was taken up by the ab.
sorbing rootlets of the plant, carried into its vessels, and assimilated to
the constituents of its tissues; for, in fact, if we examine, at any moment,
any kind of fertile soil, we find it to contain abundance of a kind of ulmine (geic acid, p. 639); we find this ulmine to be a product of the decomposition of the organic substances used as manure; we find that, in
barren soils, the ulmine is either absent, or it exists in another isomeric
form (humine, &c.), and hence the vegetation appeared distinctly connected with, and attributable to the quantity of geine present.  But, notwithstanding'such plausible evidence, Liebig has brought forward very
strong proof that the action of the ulmine can be but secondary towards
the nutrition of the plant.  His arguments are derived from the facts:
first,,that the plant may fully vegetate, though totally unconnected with
the ground, as has been proved by experimnents upon cellular plants, suspended in the air, and supplied with water; second, that, from the insolubility of every kind of ulrnine, either free or when combined with earthy
bases, which alone are presented in sufficient quantity in the soil, it cannot be directly absorbed by the rootlets of the plant, which totally reject
every Ikind of' solid matter; and, third, that if we compare the quantity of
ulmine in a soil before the growth and after the collection of a crop, we
find the diminution to be so small when compared with the great quantity of carbon contained in the mass of vegetable matter that has been ob.
tailmed, as fully to prove the produce of'carbon in the crop to bear but an
indirtect, if any, proportion to the quantity of ulrmine in the soil.  The true
olfice of the organic matter in the soil appears to be, that, by its gradual
decomposition, a constant supply of carbonic acid is afl(rded to the plant,
~ by which, during the first stages of its development, and while destitute
of the expanse of leaf requisite to collect the necessary quantity of nutriyment frl'om the air, a more concentrated. and. as it were, richer food is
applied to the absorbing roots, and its healthful and rapid growth thus
provided for; it is not, therefore, the ulmine of the soil, but the organic
nhatter generally, in changing into ulmine. that may supply carbon to the
y)oung plant, the office of' the soil-ulmine (geic acid) being different, as
will be shortly shown; and, even in this action of the organic matters,
ht!e flunctions of the plant remain tile same, being the absorption of carbHonic acid and evolution of oxygen.
Assimilation of Nitrogen by Plants.
The organic substances which contain nitrogen belong to two classes;




SOURCE  OF NITROGEN  IN  PLANTS.                       655
those of the first, which constitute the active or characteristic principles
of many plants, although of much interest in relation to medicine, and to
abstract science, are of very little imnportance with reference to tile growth
of tile plant, and its use as food.  T'he bodies whose orligin anld p[roperties are here of interest, belong to that class of vegeto.amlimal substan.
ces, as albumen, gluten, legunline, of whose extruordinary powerl iti inducingt catalytic decompositions of other bodies I havt so oftemn spolkel;
they are found in all parts of' the plant, dissolved or cdliused thlrooug   its
juices, but especially collected where transfolrmations necessary frl growblh
or germiination are to be accomplished.. Although present iti but small
quantity, no function of the plant. in any stage of its existence, could be
accomplished without their aid.  The conversion of starch into suo-w   for
the nutrition of the germe; of starch or lignine into the vast variety of
secretory products in the adult plants; the elaboration of the fruil, its i-.
peninrg, and even tile ultimate destruction of the vegetable tis;ues, have
their origin in a series of actions, induced and mlaintained by comlmunication ftrom the active fermentation of these azotized materiilis.
Not mnerely'does the presence of this class of bodies regulate the prop.
er performa.nce of the functions of tlhe plant, but they play an equally ijnportanit part in favouring the assipnilation of vegetable nlutter whent used
as foiod by animals.  BLousingault has shown by experiments, to which
I shall lhave occasion again to refer, thiat in herbivorous animals, the to.
tal quanitity of nitrogen assimilated for the growth of its muscular and
other tissues is derived fiom, and equal to that contained in the vegt-table substances used as food, and that hence, to ascertain the  tiutritive
value of any organic substance, it is only necessary to determine tile quan.
tity of nitrogen which it contains.  The results so calculated anree with
the mean experimental results of the most enlighltened agriculturists,
withitu limits as narrow as could be expected in experiments of' thait kind,
and anny, by farther research, be brought to still greater accuracy.
Like the carbon, the nitrogen of plants is obtained, in great part, by
absorption from the air, but yet it is not merely gaseous nitrogen which
is assimilated.  The atmosphere always contains a quantity of ammon ia,
derived fromll the putrefaction of' organic bodies.  This is absorbed, and
p)asses into the constitution of a new set of plants, and from themn to an.
imals, to be again thrown into the air after their death, and thus circulate
from age to age, entering into the constitution of each successive race of
organized beings.  We cannot refer, however, the total quantity of nitrogen in plants to this one source; for if the produce of one year dleri.
ved its nitrogen only from the decomposition of the plants of tile previous
year, the total quantity should be constant; whereas experien(e teaches
us that, by proper mettlods, the quantity of vegetables produced otn a soil
may be continuously increased, anid for this the nitrogen must be derived
strictly by absorption from the air.
Plants vary exceedingly in the facility with which they derive nitrogen
fromn the air, whether by direct absorption of gas or as ammonia.  Thus
trefoil vegetates and thrives nearly as well when planted in pure sand,
and supplied only with water and air, as when sown in ordinary soil;
and when fully grown, the quantity of nitrogen is found to be increasedl
twenty-six per cent.; but, on the contrary, wheat grows but slowly under the samne circumstances, makes no attempt to flower, and, on anailvsis, the whole plant is found to contain even a little less nitrogen than




56        ASS I M I L A T I ON OF  H HYDROGENo ETC.
had originally existed in the seed.  Wheat has, therefore, no power to
assimilate nitrogen fiom the air, while trefoil possesses that character in
pr9bably its greatest vigour.  Yet wheat, when Fully grown, is rich in
nitrogen; its seed is more nutritious than that of any otlher corn, as it
contains more gluten; its nitrogen must, therefore, be derived friom another source: it is extracted from the organic matters of the soil.
Withbut entering here'into the question of the nature of manures,
which will require especial consideration, it may be stated that, though.
wheat is thus peculiar in deriving its supply of nltrogen exclusively from
the soil, yet all plants do so in a greater or less degree.  In the soil, how.
ever, the nitrogen is not present uncombined.  It is evolved as ammonia
from the decomposing organic substances of the manures, and hence animal manures, as producing more of it, are proportionally richer.  It
has been already noticed (p. 639) that the ulmine of' the soil is always
combined with ammonia, which it retains with exceeding force.  But in
presence of strong bases, such as lime, which all fbetile soils contain, the
ulmine is slowly decomposed, the elements of carbonic acid and of am-.
nionia are eliminated from it, and these both being in a state fit for ab.
sorption by the rootlets of the plant, are assimilated, and supply carbon,
nitrogen, and water.  Independent of the ammonia derived fr'om the or.
ganic substances actually contained in the soil, much of that diffused
through the atmosphere is carried to the roots of plants by showers of
rain, and by the direct absorption of the gas by the porous clay.  T'here
are few specimens of clay, especially if they contain iron, which do not
give out ammonia when heated, and the absorption occurs with greater
power when the clay has been strongly dried.  Hence the increased fertility often given to a soil by burning the surface to the depth of a few
inches.:4ssimnilation of Hydrogen.
I have described (p. 653) as the source of the carbonic acid evolved
by plants during the night, the conversion of the starchy substance, which
I conceive to be that first elaborated by the plant, into the various secretory products, acids, colouring matters, &c.  But there are many
classes of important vegetable products in which hydrogen so far pre.
dominates, that we must conceive for their formation water to be decomposed, and its oxygen to be evolved, either free or in combination with
carbon. Of such bodies, glycerine, all of the fixed and many of the volatile oils, wax, and caoutchouc, are examples.  The secretory action
may thus, in place of opposing that of the respiration of the plant, coin.
cide with it in result, according to the nature of the substances formed,
since, if all the carbon of the starch remains in the constitution of the
secretion, oxygen is evolved from the water which is decomposed to' supply the necessary quantity of hydrogen.
Of the Inorganic Constituents of Plants.
If we make a plant vegetate in waterwhich holds dissolved small quan.
tities of inorganic salts, we find that, as long as the plant remains in
health, it exercises upon these salts a remarkable discretionary power of
absorption, taking up some and rejecting others, which pass into its sub.
stance only when, by the death or weakness of the plant, the liquor enters
the tubes by merely physical capillarity.. If a plant, whose tissues have




RELATION OF SOIL TO PLANT.                          657
ueen thus imbibed with saline matters by its own spontaneous power ofabsorption, be -placed in a vessel of pure water,,it will be found to give
-.out (tertain of the saline matters it had taken up, but to retain othqrs.
In this matnner we may recognise the action of inorganic salts ui)on'plants
to be of three kinds: first, directly poisonous, which are rejected by the
plant as long as it is in health, and to- this' class belong most subst;ances
poisonous to mnan; 2d, those to which the plant appears indifferent, which
are taken up by it and given off again, without any apparent influence on
its growth; and, 3d, those which, when absorbed by the plant, are assimilated to its proper tissues, and are not given up by the plant to water in
which it may be irnmersed.
The bodies of this last class are all combinations of alkalies and earths,
and principally with organic acids; they form  the ashes of the plant
when the organic matter is burned away, and then always possess an al.
kaline reaction from the formation of carbonates.  As a general princi.
pie, we may say that each plant requires for its healthy growth inorganic
substances in certain quantity and of a certain nature; but replacement
of one base by another may occur in certain cases, without positive in jury
to the plant.  Thus the plants which yield soda when grown upon tile
seashore (salsola, salicornia), if transplanted to the interior, gr'diatlly
lose the soda, and acquire potash in its place; so that, after a geteration,
no trace of the former alkali remains.  The ashes of oaks or pin(rs grown
upon a granitic or basaltic soil contain abundance of maginesia and of
potash, while trees of the same species will flourish on a. limestone soil,
and in their ashes lime will be the predominant ingredient.  But these
cases of substitution of one base for the other in a plant are still but rare
exceptions to the principle, that each kind of plant requires for its vigor.
ous and healthy growth to be supplied with inorganic substances of a
specific nature and in certain quantity.
It is this principle which determines the more successful cultivation of
certain plants in certain soils.'Thus, if we examine the c imposition of
the ashes of wheat, we find abundance of silica, phosphoric acid, magnesia, lime, and potash.  If we sow wheat in a soil which contains ne-ither
potash nor phosphoric acid, some of the materials necessary for tile perfection of the plant being absent, the crop cannot be productive; but if
we previously manure the soil with bonedust, with ashes of weeds, or
other substances which may supply the necessary inorganic elements,
these will be absorbed, and the plants obtain their full development.
Even when the quantity of the required inorganic base is but exceeding.
ly minute, it will still be collected by the vital action of' the plant in the
necessary quantity.  Thus, in most sea-plants, iodide of magnesium ex.
ists in such proportion as that it affiords the universal source of iodine for
all technical and scientific objects; and. yet that salt, which is excessively soluble, is removed by the plant from  the sea-water, which.contains but minute traces of it, and is retained in the vegetable tissue by a
power which prevents its being washed out again.  It is this power of a
plant to search for and remove from the soil all traces of those inorganic
bases which it most requires, that renders many soils incapable of bear.
ing, successive crops of the same kind, without tlie intermediate application of suitable mineral manures.  But if the soil be of such nature as to
contain itself' those elements, it may become truly inexhaustible for the
growth of most species of plant.  It is hence that soils formed by the de.
-40




658             CONSTITUTION  OF  SOILS.
composition of basaltic rocks or of modern lavas are, for every kind of
crop, some of the most productive; the facility with which these rocks
are decomposed by the action of air and water, provides a constant sup.
ply of soil absolutely new, and firom the constitution of these rocks, the
great variety of their mineral components renders such soil abundant in
every element that plants in general require.
Of the Constitution of Soils and of Manures.
From what has been already said, it is easy to judge of the circum.
stances which render a soil barren or productive, but from the importance
of the subject to vegetable physiology and'to agriculture, it requires more
detailed examination.
The organic elements of the plant being derived for the most part from
the atmosphere, the office of the soil, so fair as they are concerned, is reduced to supplying to the roots, during those periods when there is not
a sificient expanse of foliage to absorb nutriment fiom tile air, the carbonic acid produced by the gradual rotting o'f the ligneous matter, and
uImnine, and ammonia from the azotized elements of the manure. For
this purpose the soil is, in respect to its mineral composition, unimportant; it should be porous, in order to admit of the easy penetration of tile
rootlets, and to allow free access of oxygen to the organic matter to form
carbonic acid; it should yet be close enough to retain moisture in the
average intervals of rain, in order that the water necessary for vegetation may not be absent.
Thlese phv ical conditions are not, however, combined in any one kind
of mineral material.  If' we take a soil of pure sand or of pure limestone,
we find them so loose and porous that the water filters off almost immediately after falling, and the plants-necessarily perish.  If a soil consist
of pure clay, its tenacity would be such as totally to prevent the access
of ail, and all growth of the absorbing filaments of the roots.  Tro combine the two proper conditions of a soil, the clay should be mixed with
the porotus material, in proportions which vary with the nature of the
plant to be cultivated; and thus the simplest soil, in order to fulfil its
physical conditions, as supplemental to the atmosphere, should contain two
mineral substances, of which one should be clay, and the other lime or
silica; and as in practice, unless for some special object, the presence of
caustic lime would prove injurious to the absorbing rootlets, this should
be present, combined with carbonic acid, as in any of the usual varieties
of limestone rocks.;The proper action of the soil, that which it exercises independently of
its office in replacing the atmosphere, is to supply to the plant those inorganic constituents, the importance of which have been already shown.
For'this purpose, a far greater complexity of constitution is required.
Thus there is no plant that does not contain both lime and silica, and
hence, in the simplest soil, both must be present.  There is scarcely a
plant -whose ashes do not contain a fixed alkali, generally potash; and
hence minerals which may yield, by their decomposition, the necessary
quantity efthat base, should be present in a fertile soil.  For most plants,
also, magnesia must be supplied; and for many, and especially the vari.
ousliinds of corn, phosphoric acid.  In average soils, most of these bodies
are naturilly present in the necessary-degree.  When the soil has origi.
nated in T4e, decomposition of granitic or of slaty rocks, the silica, the al




EXCRETIONS  OF PLANTSS  ETC.                       659
umina, and the potash are abundantly supplied from feldspar and from
mica: lime and magnesia also may be derived from associated minerals;
but, in general, it is necessary to add lime to such soils, in order that the
quantity necessary to full fertility may be present.  In purely limestone
soils, clay and silicious gravel must be added; and to make up the deficiency in potash, the ashes of other plants and cinders of coal. If the
soil be purely silicious, tile addition of clay and lime (marl) may bring it
to the proper cornposition.
In these few words are contained the theory of what are termed mineral manures, with few exceptions.  In adding lime or marl, bonedust or
cinders, to a soil, we either render its physical condition of porosity and
tenacity more suitable to the circumstances of the plant, or we supply
some ingredient which was either primitively deficient in the soil, or had
been removed from it by a previous crop of the same kind,  On this last
condition is founded also the necessity, in an economic agriculture, of
alternating crops which take up from the ground materials of difftirent
kinds. Thus, if wheat be grown upon a soil, the rocky substance of which
is rich in potash and phosphoric acid, the crops will, after a few years, be
unproductive, and the soil impoverished, because the rock decomposes too
slowly to supply materials for the wheat as fast as they a- e required; but
if we take from that soil a crop of wheat but once in three years, and in.
terpose some other plant, as trefoil, which takes up but little potash and
no phosphoric acid, the soil has time to recover its constitution, and the
series of crops,,thus arranged in rotatory order, so far from impoverishing
the soil, may bring it to a higher degree of richness, by the additions made
to its azotized organic components by the roots and rejected leaves of the
various crops which are left upon it, and the manure derived from the con.
sumption of its produce by animals..
The advantage of a rotation of crops may be thus deduced from the
necessity of the soil renewing its mineral constituents, by the gradual
decomposition of the subjacent rocky matter (subsoil). But the observations of Macaire and Decandolle indicate another and not less im.
portant reason for its use.  These physiologists have found, that from
the rootlets of a plant the same process of excretion is carried on as by
its stem and leaves, and that brown-coloured substances are exuded,
which possess much analogy with tannin, and which are poisonous to
plants of the same kind when dissolved in the water with which their
roots are supp)lied.  On tile other hand, the excretory products of one
plant may be used without injury, and even advantageously, for the
growth of another plant of a different natural family; and in this respect
the grasses and the leguminous plants are most remarka'ble. It is hence,
probably, for example, that wheat unfits the soil for the growth of an.
other celop of wheat, not merely by removing the potash and phosphoric
acid which is required for the perfection of its parts, but it also gives out
a substance poisonous to a plant of the same kind, but which acts bene.
licially upon the rootlets of a leguminous plant, favouring its growth,
while the soil has time to regain from the subsoil the inorganic mate.
rials of which it had been deprived.
The utility of manures may now be easily understood; their action is
either as bone.earth, marl, lime, cinders, or silicious gravel, to supply to
the soil some mineral ingredient in. which it had been deficient, or to
provide, as by the ordinary vegetable or animal manures, soot, &c., or



660'AC TI'N  O   OF    R GA N IC M'   A N U R E.
ganic matter, which, by its'decomposition; may give oi.-.boijor,,ld
and ammonia for the' nutrition of the young plants.  it some teor.,.aes
the'action of manures is more indirect; thus the legitnmnous Plants (tre.
foil) require but little inorganic matter, but much ammonia, and yet
there is- no manure so efficient in the promotion o teacir growth as plas.
ter of Paris (sulphate of lime).  The plant, however, contains no sul.
phate of lime; it is not absorbed-.  The action of this manure appears
to be, as was first suggested by Liebig, that, acting on those substances
of the ulmine: family which always retain a large qiuantity of ammonia
intimately united in the soil;:it forms, by double decomposition, ulrhate
of lime: and sulphate ofamnmonia, which last, being soluble, is easily absorbed' by the rootlets of the plant, and the nitrogen assimilated to its
tissues.
With' reard -to organie  manures, their great value depends on the pro.
portion of nitrogen they supply., In plants, the great mass of nitrogen is
always deposited in organs,: as the seed, the tuber, &c., which, fol that'very reason, are sought after and collected by man, either as food, or for.medicinal purposes, friom the active (azotized) principles they contain.
The roots, stem's, and leaves of plants, such as are rejected in the collection of the crop, contain little nitrogen, they being rejected as useless
for that'very reason.  Hence the residue of a former season may manure
the land abundantly so far as carbon is concerned, but be quite incapable
of: supplying nitrogen, and in providing materials fbr a future abundant
crop.  The object ofthe'agriculturist must be, so far as organic mate.
rial is concerned, to supply nitrogen,' especially for such plants as the
different species of corn, which are incapable of deriving that important
element directly'from the atmosphere. The value of an organic manure
may therefore, for practical purposes, be considered as being measured
by the quantity of nitrogen which it contains, and the directness or indirectness of the benefit derivable from it depends upon the manner in
which thi nitrogen is combined.  If mere ammoniacal salts be used, or
materials, as animal manures, urine, &c., which soon form ammoniacal
salts by their putrefaction, the whole benefit of the manure is given to
the dcrops immediately succeeding its application; but if organic substances be emploved which resist decomposition, their nitrogen is evolved
but slowly'; and though little immediate amelioration be observed from
their addition to the soil, their influence is gradually and steadily exerted,
and'becomes ultimately sensible to the full degree proportional to the
nitrogen they contain.
A mode of restoring to the soil the principles it had lost by indiscreet
cultivation, is that of fallowing.  It is a method synonymous with an
ignorant and improvident agriculture.  The soil having, by over work,
lost, on the one hand, some of its essential mineral ingredients, requires
time to gather, by the decomposition of the underlying subsoil or rock,
a- proper quantity of them to supply the elements of the succeeding crops,
and having been deprived of its organic elements, especially the nitrogen,
it must be allowed to gain from the atmosphere a suitable quantity of ammonia. or by the gradual rotting of the roots of the preceding crop, a quantity of carbonic acid suitable to the wants of that which is to follow.  But
all of these'effects may be more perfectly and nmore profitably secured by
the intervention, in a succession suitably arranged, of other props, which
exercise upon the soil actions alternately opposed.  Thus, if we arrange




ACTIVE  PRINCIPLES OF  PLANTS,                      661
that wheat, which probably removes from the soil a greater quantity and
a greater number of elements than any other crop, shall be succeeded by
sown grasses, fur forage or hay, which, as they are not allowed to mature
their seeds, exercise but little deteriorating action; these, again, by ouats,
the exlhausting power of which is but one sixth that of wheat; then peaso
or beans manured; that these be followed by barley, the exhausting power
of which is one third, and this by a manured green crop, the soil may be
brought into a condition superior to that from which we had set out, and
the series may be recommenced with wheiat, the soil being every season
economized.  This is but one of the many kinds of rotation which have
been found by experienced agriculturists to be as beneficial in practice as
theory indicates that they ought to be; and no other reason can be assignted for allowing a field to lie idle every second or third year, but ignliorance
on the part of the farmer of what could otherwise be done with it.
It remains only to notice, in relation to the theory of the-growth of
plarnts, a7 few additional circumstances connected with the forma;iion -of
some of their peculiar principles.  It is not unusual to heai from even
ilntelligent agriculturists, objections to the cut!vation of certain plants,on
the grounds of their exhausting the soil too nuclh.  A plant exhausts the
soil only in consequence of its forming in propOrtiOnal quantity some substance, the elements of which are derived from the soil, and which constitute in almost every case the valuable portion -of the plant. Wheat
exhausts the soil, because it derives therefromr the large quantity- ofnitrogen which its gtrain contains; but it is precisely that gi'eat quantity of
nitrogen which renders wheat more vadluable in the market-than oats or
barlelty.  Tobacco exhausts the soil,:tecause it takes ul abundance of
nitrogen, with which it forms its nicotine; the more of the active princi.
pie the planti produces, the more it exhausts the soil; but in the samne
proportion, the greater value does it possess when sold.'To produce
indigo, nitrogen must be supplied to the plants by abundance of rich
manure; no crop is more exhausting; but without the nitrogen no col.
ouring matter could be formned, and the plant would be completely worthless.  Examples of this kind might be adduced in any number; but these
suffice to place in a distinct, though popular aspect. the general principle,
that where a plant exhausts the soil. especially as to its nitrogen, it is for
the production of the substance which gives the plant its commercial
value and importance, and that hencethe quantity of manure necessary
for the production of an abundant crop is fully repaid by the improved
quality of the produce.'        Without seeking to enter into the geneial question of the influence of
the physical agents on vegetation, which for- its discussion would require
more extended limits, and lead to considerations too far renoved from
chemistry to justify its introduction, I shall, in eonctuding this sketci of
the cheaistry of vegetation, notice the peculiar action which light exer.
cises upon plants.  It is not merely that it acts as a general stimulus, and
thus provokes the activity of.nutrition, which determines the ultimate result of the purification of the atmosphere by plants, and tiiat:its' withd rav
al is foillowved, wvith plants as with higher beings, by a torpor and tenldency
to rest, which closes their petals, and: folds their leaves at, night.': But in
the production of the coloured parts of plants the agency of!ight is indis.
pernsable.  A plant which grows in darkness, as it the gallery of a mine,
no matter to what size its orln may reach by means of a copious supply




662  ACTION  OF LIGHT. —ANIBIIAL CHEMISTRY.
of fobod, remains soft, its wood unformed, its colour pale; the chlorophyll
not being generated, unless under the influence of light.'For culinary
purposes, precisely this effect is produced by covering up the stems of
celery and asparagus, the softness and whiteness admired upon the table
being the evidence of the sick and abortive organization of the stem.
The action of light in favouring the production of colour in plants is,
however, accompanied by a more material change.  The petals, and all
coloured parts of plants, except the leaves, absorb oxygen from the air.
This is precisely what we find a'number of bodies to ellect, when passing from their colourless condition to that in which their proper colour
is displayed.  Thus white indigo becomes blue by absorbing oxygen.
Thus rocelline, by absorbing oxygen and giving off water, formns ery.
throlitmic acid. It is thus, too, by deoxidizing agents, we may remove the
colour from lo1wood, archil, and the flowers of most plants, and restore
their tints by again admitting it. Frequently, also, the generation of the
coloured substance is accompanied not merely by an absorption of oxy.
geh, but by an escape of carbonic acid; this, which is shown in the laboratory in forming orceine from erythrine, appears to take place in the
tissues of most flowers, which rapidly give out carbonic acid for some
time after they have first opened.
In similar actions, carried on in the laboratory by means of chlorine,
the influence of light in furthering the removal of hydrogen, and even of
carbon, if water be present, is most remarkable, and, illustrates the operation of that physical agent in producing the colours of plants in a distinct
and satisfactory way.  This action has been, however, so' fully noticed
in describing the general chemical agencies of light (p. 172) and the action of chlorine on colouring matters (p. 622), that 1 deem it necessary
only to refer to what has been there said upon the subject.
CHAPTER XXX.
OF ANIMAL CHEMIISTRY
IN describing the various classes of organic bodies which have hitherto
come under our notice, I have made no distinction as to their animal or
vegetable origin, for the point of view under which they were then con.
sidered, and the properties which they manifested, were independent of
their source.  It was thus with ethal, the fatty acids, and colouring mat.
ters; and, indeed, in many instances, the same substances were found to
be products of both kingdoms of organized nature. In the present chap.
ter I purpose to describe, so far as our accurate knowledge extends, the
chemical history of those bodies which I characterized in another place
(p. 468) as being rather organized than organic; as constituting, not
merely a product of the vital operations of the being, but the mechanism
itself by which these vital operations are carried on; as making part of
the tissues essential to its proper organization and life, and as being,
while in connexion with the animal, and participating in its life, protect.




FIBRINE, ITS PROPERTIES.                       663
ed from the truly:chemical reactions of their proper elements, whih,
after the death of' the animal, especially in contact with air and water,
rapidly assume simpler fobrms of union, and, breaking up the complex animal tissue into a crowd of binary compounds, induce the change well
known as putrefaction.
In connexion with these substances, which form the basis of the tissues
and organs of the animal fiame, I will bring under survey the processes
by which, firom the atmosphere, or friom the materials of our food, the
substance of our organs is continually renewed, their growth provided
for, and the conditions necessary for the continuance of' health and life
maintained.  The functions of respiration and of digestion, so far as the
chemical phenomena which they embrace are known; the composition of
those secretions and excretions, whose agency in the furtherance of those
processes has been studied, will here be described; and, finally, the composition of those excretions which have for their office the separation of
elements. unfit for the nutrition of the beings, or which are not intended
for its support.
In each of these divisions I shall add to the description of the compo.
sition and properties of these tissues or secretions in the state of health,
such facts in reference to the modifications introduced by disease, as
have been observed with proper accuracy.
SECTION I.
OF THE COMPOSITION OF THE ANIMAL TISSUES.
A. Of the Albunzinous Materials of the Tissues.
Of Fibrine.
This substance constitutes the basis of the muscular tissue, and forms
an important constituent of the blood.  In the latter it exists dissolved
during life, but separates after death or extraction from the body, producing, with the colouring material, the phenomenon of coagulation.  In
the muscles, the fibrine is arranged in a truly organized and living condition, constituting the contractile fibres, in which it is so interwoven
with nervous and vascular filaments as to render its isolation impossible.
To obtain pure fibrine, therefore, we have recourse to blood, which, it' im.
mediately on being drawn it be briskly agitated with a little bundle of twigs,
does not coagulate, but the fibrine is deposited on the twigs in soft tenacious
masses, which, being washed to remove any adhering colouring matter,
and digested in alcohol and ether to remove some traces of fatty substances which adhere to it, constitute pure fibrine, which may be dried by a
gentle heat, and appears then as a yellowish opaque mass, hard, tasteless,
and inodorous: if it be at all transparent, this results from traces of adhering fat.  It is insoluble in water, alcohol, and ether; it absorbs, how.
ever, so much water as to treble its weight, and thereby recovers the
volume, softness, and flexibility it possessed before being dried.  This
moisture is not sensible to the hand, but by strong pressure between folds
of bibulous paper it may be removed, and the fibrine rendered completely dry.  When boiled with water for a great length of time, fibrine is de.
composed and dissolves, but it does not form any kind of gelatine.
Fibrine is remarkable for decomposing deutoxide of hydrogen rapidly
by catalytic force (p. 235, 258), evolving oxygen.  Several of the animal
tissues produce this effect, though not containing fibrine.' Albumen is,
however, totally destitute of it.




664                        A L B U M E N.
Fibrine absorbs cold oil of vitriol, and swells opli    to a yellow transpa.
rent jelly.  On the addition of water, it shrinks up and becomes, hard;
but if all the excess of acid be washed away, the residual. mass,:which is
a neutral compound of fibrine and sulphuric acid, dissolves: in pure water.
With nitiic acid, fibrine evolves nitrogen and nitric oxide, and forms a
yellow powder, xanthoproteic acid, to which I snail shortly recur.i T'ribasic phosphoric acid and acetic acid dissolve fibrine.'1lhe solution is
precipitated by the. mineral acids and by caustic potash, an -excess of
which last, however, redissolves the precipitate.  The mono, or bibasic
phosphoric acids, act as sulphuric acid towards fibrine.  If perfectly dry
fibrine be digested in strong muriatic acid, it swells up, and after a few
minutes dissolves into a rich dark blue liquio..No gas is evolved.  This
blue liquor is precipitated by yellow prussiate.of potash.
Fibrine is dissolved even by a dilute solution of caustic potash, and
appears thereby to neutralize the alkali almost completely.  This:solution is coagulated by alcohol and by acids, but not by heat.  The. precipitates given by acetic and tribasic phosphoric acids are redissolved by
an: excess.
if sulphate of soda or nitrate of potash be added to newly-drawn blood,
its coagulation is prevented; and if' fibine be digested in a strong. solution
of nitre, it dissolves, forming a thick liquid, which is coagulated by heat,
by alcohol, and acids, and is precipitated by the salts of mercury, lead, and
copper, and by yellow prussiate of potash.  This property of fibrine will
again come under notice.
The composition of fibrine is expressed by the formula CsI-I,,. N,.
O40+-P.S2.  It contains, besides, minute quantities of liine and magnesia, so that, when incinerated, it leaves 0-77 per cent. of sulphates and
phosphates of those bases.
Of Albumen.
This substance is even more extensively distributed through the animal
frame than fibrine.  Like fibrine, it exists in two conditions, one soluble,
and the other insoluble in water; but whereas the fibrine becomes insoluble almost instantly on being withdrawn from  the body, albumen may
retain: that state for an indefinite time, and its:history:is therefore more
complete. Inmits soluble form it exists in the blood, the:egg, in the serous
secretions, in the humours of the eye, &c.; in the soluble or coagulated
form, it: constitutes a portion of most of:the solid tissues.  Albumen de-rives its name from its constituting: the mass: of white of egg.
Soluble Albumen.-This is obtained in the solid form by evaporating
to dryness, at a temperature which does not exceed 1200, the serum of
blood, or; white of egg,.the membranous investments of the latter having
been torn up by triturating with some angular fragments of glass.   The
dry mass is yellow, transparent, hard, tough, and contains, besides the
albumen, the salts and some other constituents of tile blood, or white of
egg, in minute quantity.  These are extracted by digestion in alcohol
and ether, which leave the albumen pure.  When thus completely dry,
it may be heated beyond 212' without passing into the coagulated condi
tion.  If digested in cold water, it gradually swells up, and finally dis.
solves.  This solution, when heated to a temperature between 140 t:and
150~, coa:gulates.  If dilute,-the solution may even be heated to 1650
without coagulating, and when present in:very small quantity, the albu



STATES OOF AL B U M E N.-P R O T E I N E.           666
-men may not separate until the water boils.  When once coagulated in
this manner, albumen is totally insoluble in water; it is changed into its
second form.  The solution of albumen is precipitated by alcohol, by
acids, and metallic salts, exactly as the solution of fibrine in saltpetre.
The only distinction that can be drawn between the two is, that the saline
solution of fibrine is partially decomposed by the addition of a large quan.
tity of water.
The precipitates yielded by solution of albumen with metallic salts are
mixtures of two distinct substances, one a compound of albumen with the
acid, the other a compound of albumen with the metallic oxide.; the former is generally somewhat soluble, the latter insoluble; and hence results
the application of albumen as an antidote to mineral poisons, as corrosive
sublimate and bluestone.'Albumen is also coagulated by many organic bodies, as tannic acid
and kreosote,. which last acts catalytically, as a very minute quantity of
it coagulates a large quantity of albumen, without entering into combina-.
tion with it.
Coagulated Albumen is obtained by heating serum of the blood, or white
of egg, to between 140~ and 150~, so that they solidify; washing the mass
with water, digesting witlh alcohol and ether until all soluble is removed,
and then drying with care.  Thus prepared, it retains some inorganic
salts, principally phosphate of lime, from which it may be obtained free
as follows: The serum of the blood is to be coagulated by muriatic acid;
the coagulum washed-with acidulated water, and then so much pure water
added as may dissolve it.  This solution being then decomposS  by car.
bonate of ammonia, the pure albumen is separated as a flocculent white
precipitate.
When dry, it is yellow and transparent; in every chemical character
except its relation to deutoxide of hydrogen, it identifies itself with fibrine,
and it is hence unnecessary to repeat the details of these reactions; in
its composition it is very closely related to it; their organic element is
the same, and they differ only in the quantity of sulphur, the formula of
albumen being CoG0H620.* N,000240+P.S4.  The quantity of ashes remain.
ing from albumen is greater than from fibrine.
The comparative history of these bodies, as now given, leads to considerable doubt as to how far they are chemically distinct, although their
physiological characters are so different.  Mulder, to whose accurate
researches we are indebted for the greater part of our knowledge of the
zonstitution of these bodies, looks upon both as compounds of the real
*:rganic substance, -which he terms Proteine, with sulphurets of phos.
phorus.  In fact,-the sulphur and phosphorus may be removed by very
simple methods, and the body (protei'ne) which then remains deserves
attentive study.
When albumen, fibrine, cheese, or flesh is freed, by digestion in water, alcohol, and ether, from all bodies soluble in these liquids, and, by
dilute muriatic acid, all earthy salts have been removed, it is to be dis.
solved in. a dilute solution of caustic potash, and heated to 120~, whereby
the sulphlur and phosphorus form phosphate of potash and sulphuret of
potassium.  From the filtered liquor the;proteines may then be precipitated by acetic acid, which must be added only in very slight.excess,:as
otherwise the precipitate would be redissolved.
Proteine forms grayish-white gelatinous flocks, which, when dried, be.,
4P




666            COMPOUNDS OF  PROTEINE.
come hard and yellow, and give an amber-coloured powder. It absorbs
vwater, swells up, and regains the appearance it had before being dried.
By long boiling with water it is decomposed and dissolved.
Proteine dissolves in all vet'y dilute acids, forming neutral compounds
which are insoluble in strong acid liquors, and are hence precipitated on
the addition of strong acids, except the acetic and tribasic phosphoric
acids.  With oil of vitriol it combines as described under the head of
fibrine, and forms Proteosulphuric Acid.  It combines also with earthy
and metallic oxides, forming insoluble compounds, which are identical in
characters with those obtained with albumen.
The composition of proteine, as found by Mulder, and confirmed by
the analyses of its acid an(d basic combinations. is expressed by the for.
mula C40H32. N5012.  We may evidently consider albumen and fibrine
as compounds of proteine; for if we represent proteine by the symbol
Prt., albumen becomes Prt20+P.S4. and fibrine is Prt20o+P.S2. I consider,
however, that the state of combination of thfese bodies requires some far.
ther consideration.
It is found that proteine constitutes the basis, not merely of the animal
substances now under examination, but that it is obtained also from vegetable albumen, gluten, and legumine (p. 538), and constitutes the pure
caseous matter of' milk, and that the similarity of properties and compo.
sition in these bodies is such as to justify us in looking upon them as
identical.  We have seen that, between albumen and fibrine, the dis.
tinctive chemical characters are, if any, so trivial as to leave, no firm
ground r their distinction in that way; and if' we examine the evidence
of their being compounds of proteine with sulphur and phosphorus, we
shall find them quite inconclusive. First, it is not certain that such sul.
phurets of phosphorus exist as P.S2 and P S4; second, the compounds of
sulphur and phosphorus do not manifest any tendency whatsoever to
combination; and, third, in all the reactions of albumen and fibrine, the
proteine on the one hand, the sulphur and phosphorus on the other, act
as if they were totally distinct. I look upon albumen and fibrine, whileI
in connexion with the body, as organized and living substances, in whose
functions the minute quantity of sulphur and phosphorus may act an important part as a catalytic body.  The proteine I consider, not, with
Mulder, as the basis of our tissues, but as the simplest product of their
decomposition. It enters in combination with acids and with bases, as
indigo or morphia do, which I look upon as totally foreign to the char.
acter of a body possessed of vital properties.
Having thus described what I consider to he the true place of proteine,
in relation to albumen and fibrine' I shall briefly notice some of its de.
rived compounds.
Ch70oroproteic Acid is formed by passing chlorine into a solution of al.
bumen.  It is a white powder.  Its formula is C40H3,'. N501,2+CI.04.
By ammonia it is decomposed, nitrogen being evolved, and a white substance formed, OxLyproteine, the formula of which is C40H3, ~   N5015.
The formation of Xanthbproteic Acid, by the action of nitric acid on
fibrine, has been already noticed.  It is an orange.yellow powder; when
washed from adhering acid, tasteless and inodorous, but reddens moist
litmus paper.  Insoluble in water, alcohol, and ether, it unites with acids,
formning compounds which are pale yellow, and insoluble; with bases it
forms soluble salts, generally deep red coloured. Its formula is C34.Ii.'N40,2.




SOURC ES  ETC., OF  GELATINE.                      667
B. Of the Gelatinous Constituents of the Tissues.
Of Gelatine.
When the skin, cellular or serous tissues, tendons, and some forms of
cartilage, as that of bones, are boiled in water, they dissolve in great part,
and form a solulion which gelatinizes on cooling. Some of these tissues,
Us the skin, dissolve easily, and almost completely; others dissolve but
pa9rtly, and leave behind a quantity of coagulated albumen.  in most
kinds of cartilage, a very prolonged boiling is necessary to extract any
sensible quantity of gelatine.  Tlhese various tissues are thus found to
consist of albumen and gelatine, united in various proportions, and each
presenting various degrees of condensation of texture, but by boiling they
may be completely separated from each other.
Thile gelatine is known in commerce as the material of isinglass and of
common glue.  When pure it is colourless and transparent, very spa.
ringly soluble in cold water, by contact with which, however, it swells
up and softens.  In hot water it dissolves readily, and on cooling, forms
so strong a jelly, that with -i- th part it is a consistent solid. It is insolu.
ble in alcohol and ether.  When a solution of gelatine is long exposed
to the air, or frequently heated and cooled, it undergoes a commencement
of putrefaction, and loses its property of gelatinizing.  The composition, of gelatine, by Mulder's analyses, is expressed by the formula CH1,0,
N205.       --'he action of reagents on gelatine is in some cases of hi'gh interest.
By digestion with strong sulphuric acid, as with caustic potash, the same
results are obtained.  Ammonia is evolved, a white crystalline body
(Leucine) and a sweet substance (Sugar of Gelatine) are formed. They
are separated from each other, and from some less important products,
by repeated crystallizations.  From its alcoholic solution, Leucine separates in brilliant colourless plates.  It feels greasy, is tasteless and ino.
dorous; heated to 3360, it sublimes totally unchanged.  It dissolves in
twenty.eight parts of cold water, but requires 625 parts of alcohol, and is
insoluble in ether; its formula is C2H,1,2. N.O,.  It combines with nitric
acid to form Nitroleucic Acid, which crystallizes in brilliant needles, and
forms with bases neutral salts. Its formula is C,21H,2. N.04+N.OAq.
The Sugar of Gelatine crystallizes from its solution in alcohol, by sp'on.
taneous evaporation, in large prisms, which are colourless, taste sweet,
and feel gritty between the teeth.  It is decomposed by heat. At 600 it
dissolves in five parts of water, but it is sparingly soluble in alcohol and
ether.  The crystals consist of C,6H,5. N40,,+3 Aq.  It forms, with
bases, well-characterized compounds, and unites also with nitric acid.
When acted on by'chlorine, gelatine is converted into a white floccu.
lent substance, insoluble in water, but dissolved by an excess of gelatine.
Its composition is expressed by the formula C52140. N8029+CI.04, con.
sisting, therefore, of' four atoms of unaltered gelatine and one atom  of
chlorous acid.  Gelatine is not precipitated either by solutions of ordinary or of basic alum; but if a solution of common salt be also mixed, the
gelatine falls down, combined with, alumina, as it decomposes the muri.
ate of alumina which is then formed.  On this principle is founded the
manufacture of white leather, by a kind of tanning with alum.
The most important compound of gelatine is that with tannic acid,
which constitutes ordinary leather.  This reaction is so distinct, that one




668. MANUFACTUIRE  OF- LE ATHER.- CHONDRINE.
part of gelatine in 5000 of water is at once detected by the infusion of
galls.  The constitution of the precipitate varies according as one or
other of these materials is employed in excess, the tannic acid and ge.
latine being capable of uniting in at least three different proportions; 100
parts of dry gelatine combine with 136 parts of tannic acid, when the
latter is in great excess: this compound contains an atom of each ingredient.
Th'le technical applications of gelatine are numerous, and, for the most
part, well known.  For glucing together wood, paper, &c., thickening
colours, filling up the pores of writing paper, and as isinglass and calves'
feet jelly, an article of food. it is abundantly employed; but its most ir.
portant use is in the manufacture of leather.  The skins are cleaned by
digestion with lime and scraping with a knife, from the hair and epider.
mis on the one, and the loose cellular tissue on the other side, and then
steeped in pits containing an:infusion of oak bark, valonia, su.mach, or
other of the substances rich in tannic acid (p. 601)  At first the tan.
ning liquior is used ve ry weak, as otherwise the surface of the skin would
become impervious, and the interior could not afterward be.tanned; but
havsing passed through a succession of liquors gradually becoming stroiger, the skins are in the last pit interstratified with oak bark, and so, for a
considerable time, submitted to tile action of the tannic acid in its high.
est state of concentration, until the conversion into leather is complete
throughout the entire substance.  Thcy are then removed, and subjected
to finishing and cleaning processes, which I need not notice.
Many' chemists consider that gelatine is merely a product of the de.
composition of albumen or fibrine by boiling water, and nota true con.
stituent of the tissues.  I believe this idea to be incorrect on the follow.
ing grounds: First, pure fibrine, or albumen, gives no gelatine by boil.
ing; second, in the process of tanning, the tannic acid combines with ge.
latine in a skin which has never been boiled; and, third, that we can
easily understand why some tissues give gelatine more easily than others
by the different degrees of condensation in their structure; but I rather
consider that gelatine bears the same relation to the organized tissue of
the skin or cellular membrane that proteine does to tlhe fibrine of the
blood, being really a product of its death and decomposition, though the
only representative of it which we can have.
Clhndrine. —Those cartilages in which bone is not deposited, are re.
solved by boiling into a substance possessing much analogy to gelatine,
but still distinguished from it by the following properties: it precipitates
solutions of alum, sulphate of iron, and acetate of lead, and is precipita.
ted by acetic acid, none of which bodies have any action on ordinary ge.
latine, which, however, chondrine resembles in all its other characters;
in composition, however, it diffbrs, its formula being, by AMulder's anal.
ysis, C,6H,8.:NEON; -it, however, contains a trace of sulphur, its complete
formula being C,20oH-6. N400,40+S.  The physiologist Miller, to whom
the discovery of chondrine is due, considers that the skeleton of cartilas
ginous fishes yields a third variety of gelatine.
C. Of thefatty Constituents of the Tissues.
The fatty bodies already described in Chapter XXII., although con.
tributing essentially to; the support of the animal frame, are mere secre.
tions, and do not form any portion of its organized tissues.  The sub.




CEREBROTE  CEaREBRO L  CHOLESTE R:IN.E   ETC. 669
stances properly included under the present head are the constituents of
the nervous tissue, such as it is found in the brain, the  jpuinal cord, and
nerves.
In the composition of the' brain it is possible to distinguish at least
three, perhaps five, distinct substances of a tatty naature; the most characteristic and important is'termed Cerebrote: its. mode of' preparation
can easily be gathered from its'characters; it is at white powder, tasteless and inodolous,ifeeiing   not ati all geasy, but like starchi; whlen heat.
ed, it does not melt until it has:become brown, and i lgreat part decolmposed-; it is insoluble il watelr, sparingly soluble in alcohol or ether when
cold, but abundantly when hot; on cooling, it is deposited fiom its alcoholic solution as a white powder, not at all crystalline; it is not acted
upon by alkalies. -In:composition it resembles albumen, containing a
large quantity of nitroger-, with sulphur and phosphoius in milute quantity, but its precise formula cannot be:considered -as being yet established.: Cerebrol is a liquid: eddis  oil, htaving tile odour of'resh: brain, and a
disagreeable rancid- taste.: It is soluble in all proportions in ether and
-in oils, but only mode rately so- inalcohol.  itP eon'ias the sa me elements
as the cerebrote, and apparently in nearly, if not exactly, the same' pro.
portions-; but the analyses of Couerbe,. whoj alonol has examined their
composrtion, are not authentic enough to be broughit forward.'I'he cerebrol is not saponifiable, nor is it in any way altered by digestion with
caustic alkalies.:1n: addition to these two bodies, the brain contains a large quantity of
a: substance, which,;from'hiaving been first —discov;ered'- as a constituent of
biliary calculi, is termed Cholesterine: it is insoluble in water, but; dis.
solves abundantly-in boiling: alcohol, friom which- it crystallizes, on cool.
ing, in brilliant -plates:; it: melts at 290~, and- sublimes partiallly by a
stronger. heat; it dissolves readily in etIher; it is not altel ed by caustic
alkalies; *its formula is C36H300.  By treatment vwith hot nitric acid, it
is converted into a substance which crystallizes in- yellow needles, and
forms,'with bases, yellow salts.' This is Cholesteric Acid, the formula of
which appears to be C26H20. ~ N.012.
Couerbe has described as constituents of the brain two other fatty bod.
ies, Cephalot and Stearocenol.: they are brown coloured resinous bodies,
which, I consider, will most probably, on re-examination of' the subject,
be found to be impure or decomposed mixtures of cerebrote and cepha.
lol.  I hence only indicate their supposed existence.  The cholesterine
I look.upon as being deposited in the brain as ordinary fat is in the cel.
lular tissue, or in the substance of other organs, and not as making up an
essential portion-of the nervous tissue.  This idea is strengthened by the
~fact that the cholesterine frequently aggregates in the brain in masses,
forming one variety of the fatty tumotIrs of that organ.
D. Of the Saline and Extractive Constituents of the Tissues.
We find in all the animal tissues small quantities of a great variety of
salts, the same as those which will be hereafter noticed as existing in the
blood, to the presence of which in the substance of the tissues they are
probably due.:In the tissue of the bones and teeth, however, these sa.
line matters are deposited in much greater quantity, and in disease and
in old age bony deposites occur in all those tissues which yield true ge.
latine on boiling. The composition of the bones and teeth will be here.
after noticed.




670             S i I N. —E P I D E R I I S. -II O R N.
The extractive matters of the tissues, like the extractive matter of
plants (p. 612), do not pre-exist as such, but are firmed by the decom.
position, by protracted boilirg in water, of the fibrine, albumnen, gelatine,
&c., which they really contain.  Berzelius has pointed out the existence
of a great number of diffierent substances that are thus generated, of
which two need here only require notice. For the first, the name Ozmna.
zome may be retained, and the name Zomidine applied to the second.
Ozrnazome is soluble in water, and also in absolute alcohol; it cannot
be dried by heat, but forms a semifluid of an acid and salty taste, which
evolves powerfully the odour of concentrated decomposing urine.  Its
solution In water is yellow; it is precipitated by the salts of mercury,
lead, and tin.
The zomidine is insoluble in alcohol; it dries down to a brown extract,
of a strong and agreeable odour of soup.  It dissolves in water in all
proportions.  Its solutions are precipitated by the salts of lead and tin,
but not by corrosive sublimate or tincture of galls.  When heated it
gives out an odour of roasting' meat, the taste and smell of which are
indeed due to its formation.  Both ozmazome and zomidine contain nitrogen.
Of the Composition of the Tissues, and of the Secretions in Health and in
Disease.
IIaving described thus the constituents of the tissues individually, 1
shall now present such results as have been hitherto obtained as to the
quantitative composition of the organized tissues formed by their reunion,
their secretory products, and morbid alterations.
Of the Skin, Epidermis, and its Miodic.ations.-The skin of animals
is a congeries of finely-constructed organs, sensitive and secretory, im.
bedded in a peculiar tissue, which is one of those most easily yielding
gelatine, whence the process of tanning skins.  The relative proportions
of solid and liquid matter in a skin freed from adhering fat and cellular
membrane, but soft and imbibed with its natural proportions of water,
was tound by Wienhalt to be,
Proper cutaneous tissues, including blood- 32.53
vessels and nerves........
Albumen............  154 100-00
Extractive soluble in alcohol...  083 3
Do.  soluble only in water..    7-60
Water.....         57'50 J
On the surface of the skin there is secreted a substance, which,
though varying in anatomical structure and appearance exceedingly, as
it flrms the fine epidermis, the nails, proper horn, the tortoise-shell,.featheirs,- hairs, &c., is yet, throughout all their shapes, identical in chemical characler, and may be described as the same substance. The best
example of horn is that which covers the process of the fiontal bone in
the ox.  It varies in colour, is translucent, tough, and elastic.  When
heated beyond 212~, it softens without being decomposed, and may then
be bent, moulded, and soldered, on which properties many of its uses
depend.  It is scarcely farther acted on by water even after an ebulli.
tion of several days.  When treated by strong acids, horn is softened,
andl becomes soluble in water.  Heated with solution of caustic potash,
it evolves ammonia, dissolves, and the liquor contains sulphuret of potas



CELLULAR, SEROUS, AND  MUSCULAR  TISSUES. 671
slum and an organic substance, precipitable by an acid. The composi.
tion of these products, or of horn itself, has not been accurately examined.
The principal mass of hair is composed of the same substance as horn,
but the colour is due to an oil, which may be extracted by ether.  It;
by virtue of the sulphur contained in hair, a solution of litharge in lime.
water blackens the hair, nitrate of silver blackens the hair also, but
by the deposition of the metal.  When horn or hair is strongly heated,
it fuses, gives off carbonate of ammonia, and gases of a characteristic
disagreeable smell; if air be present, it burns with a brilliant flame.'rhe perspiration from the surface of the skin varies in nature, according
to the part of the body; it is generally acid, contains traces of alburnen,
fatty matter, and the salts of the blood.  It often contains a volatile
odorous principle, characteristic of the animal by which it is secreted.
Of the Cellular and Serous Tissues. —These tissues are constituted of
gelatinous material, similar to that in the skin, and hence dissolve by
boiling in water, being converted into gelatine.  In the natural condition
of these membranes their surfaces are moistened by a watery liquid,
which, accumulating in excessive quantity, gives rise to the dropsies of
the cavities or of the cellular tissue.  This serum of the cavities is clear
and colourless.  It reacts alkaline; its specific gravity 1'010 to 1'020;
its composition, though liable to fluctuate, is, in general, as found by
Berzelius,
Albumen.........  166
Substance soluble in alcohol  3-32
Free soda...              028 1
Alkaline chlorides..        091         rarly
Earthy phosphates.....  009
Water.... 987-5(
In the serum of dropsical effusions I have found stearine, elaine, and
urea.  This observation has also been made by Marchand.
The cells of the cellular tissue, in which fat is usually deposited, are
often filled up by an albuminous material, having considerable analogy
to caseum.  It is thus that the diffused hardening of the cellular tissue
and the local white tumours have their origin.  T'endons, aponeuroses,
and fibrous membranes are similar in their chemical relations to the cel.
lular and serous tissues.
Of the Muscular Tissue.-From what has been already said of fibrine,
it is evidently the essential element of the muscular tissue, and it only re.
mains here to give the numerical results of two analyses of beef muscle,
made by Berzelius and Braconnot.  They found in 100 parts,
Muscular fibre (with vessels and nerves). 1580   1818
Cellular tissue giving gelatine.....    190
Soluble albumen and colouring matter..  220.  170
Alcoholic extract with salts..    180.  1'94
Watery extract with salts......   105.  015
Phosphate of lime.........  008
Water and loss........ 7717. 7703
Composition of the Brain. —The most exact analyses of the brain tnat
we possess are those by Lassaigne.  The differently coloured portions
differ essentially in their nature, as he found in 100 parts,




072           C O P O SaITION  OF  THE  BONES.
Medlullary  Cortical
Substance.  Subs!ance
Albumen.                               7
Colourless fat...          13'9.. 1'0
Red fat...... 0'9  37
Oztnazome and organic salts    1'0..  1'4
Phosphates..          13.. 1
Water....    730.. 852
The nerves or spinal marrow have not been specially analyzed.
ComllpositionJ'eftlthe Bones.r-Miiller has fi und thatt, plio'to ossification,
the carotiLloe of the bones is in. that condition which vields chondrine, although it is afterward totally changed into the gelatine cartilage.  In
the vertebrated animals with osseous skeletons, the earthy material, in
all cases, consists principally of phospllate of lime with some phosphate
of magne;sia,: calbonates of lime and soda,. and fluoride of calcium.  By
digesting a bone in dilute mllriatic acid, all of these inolganic salts are
removed, and the carltila~ge remains, preserving, perfectly the form of the
bone.  By:burning the bone in a moderate current of air, all animal mat.
ter may be consumed, and the earthy material then remains in the form
of the bone, and perfeclily white; 100 parts of burned bone of the following animals have been fobund to contain,
-   Hman Bone. BeefBone.  Lion.  Sheep.
Phosphate of lime and fluoride  864   9070   950   800
of calcium.
Carlbonate oflime..... 103    2'16    25    19'3
Calrbonate of magnesia...   03    110 t   25      07
Carbonate of soda...  30    5'74 _
Bint these proportions vary in -the bones of different individuals of the
sanle kind. o(f animal.
Thie rluantity of animal matter in the bones varies in different classe,
of animals.  In the mammalia it is generally about thirty.three pe,
cent.  Thus human and ox bones, deprived of their marrow and perios
teum, and dried until they ceased to lose weightt, gave Berzelius,
Human Bone.  Beef Bone.
- Cartilage soluble in water. 32' 17
33'30'..
Vessels...13                          3
Phlosphate of lime and fluoride  53-04        4
ofcacum04..57'45.. 100'00.
of caiciums                               100 0.
Carbonate of lime..... 1130    385
Phosphate of mniagnesia..   1-16    285 
Soda and a little common salt.  120   3-45'The teeth present, in their constitution, the closest analogy to boi,
The principal and organized substance of the teeth is indeed true bone,
contafiinig, however, less cartilage (twenty.nine per cent.) and more
phosphate of lime (sixty-four per cent.) than the other bones.  The
enamel, which is an inorganic secretion from the upper surface of the
bony tooth, is altnosat destitute of any animal matter, the analyses of Ber.
zelius giving,
I-uman Enamel. Peef Enamel.
Phosphate of lime and fluoride of' 88-5   85o0
calcium..
Carbonate b'f lime.....    80    7100
Phosphate of magnesia,..     15    30
Soda...4. 
Animal matter and water..,    2-0. 3'5.
The proportion of fluoride of calcium is greater in.enamel than in corn
8non bone, and the animal membrane appeals to belong only to the con.
nexion of the enamel with the subjacent bony tissue of the tooth.  Ths




BLOO OD — C O A G U L U M.-S  E RUM.            673
exterior crusta petrosa of the teeth, which exists most developed in herbiferous anifmals, has the same composition as bone.
In the invertebrate animals, the internal skeleton is replaced by an ex.
ternal shell, which contains cartilage, with earthy salts, similar to those
of proper bone, but in different proportions, the carbonate of lime prepon.
derating.  Thus the shells of crabs and lobsters contain from fifty to
sixty per cent. of carbonate, and but from three to six of phosphate of
lime, the rest being animal matter.  Oyster-shells contain but a trace of
animal matter, being almost pure carbonate of lime; and the substance
termed cuttle-fish bone has the same composition nearly as crab-shells.
SECTION IT.
OF TEIE COMPOSITION OF THE BLOOD, AND THE PHENOMENA OF RESPIRATION.
Blood is, in the higher classes of animals, an opaque, thick, red fluid;
its specific gravity about 1-055; it has a salty and nauseous taste, and a
peculiar smell, resembling that of the animal whence it had been derived.
When the blood of any red-blooded animal is allowed to rest, it grad.
ually forms a soft jelly, from which, after some time, a thin yellowish fluid
(serum) sep)arates, while the red jelly or coagu!lum contracts in volume,
and acquires greater consistence.  If this coagulation of the blood takes
place slowly, the upper portion of the coagulum becomes white or pale
yellow, forming thus the buffy coat.  There is no doubt that the blood,
while in connexion with the animal, participates in its life, and the phe
nomena of coagulation are to be referred to a new arrangement of its
materials consequent on the loss of that vitality.
The serunm of the blood, When coagulation has been perfect, is of a yel.
lowish, sometimes greenish colour; its' taste is dull and salty; its spe.
cific gravity about 1'028; it is thick-fluid, like olive oil; when heated to
1400, it coagulates.
If we examine under the microscope the appearance presented by
blood, we find that it consists of a great number of minute red particles
swimming in a nearly colourless liquor.  These red particles are flatten.
ed disks, in man and the mammalia round, in other animals elliptical,
Their size is variable, being in man from x-of-,th to T —Lth of an inch in
diameter, but larger in most other animals.  In the frog they are about
l-o oth.  They consist of a central colourless nodule, and an investing
ring, which is coloured red by a material (Hematosine), which may be
dissolved out without the constitution of the globule being otherwise es
sentially altered.:The blood contains a large quantity of albumen, partly dissolved, and
remaining in the serum after coagulation, partly in a solid state, forming
the great mass of the globules.  In the living body the blood contains
also fibrine in solution, but this separates soon after extraction frown the
body; it assumes a solid form, and investing, as a sponge, the red globules, forms with them the coagulum.  The fibrine is thus the element
active in the coagulation of the blood, the globules being but passively
engaged in it.  In addition to these essential organic elements, the blood
contains a variety of salts, as common salt, phosphates of mragnesia, aem.
monia, and lime, lactates of soda and magnesia. The best analyses. of
the blood are those by Lecanu, and the results for blood and seran. are..
that they contain,
4oQ




674              SER 0 L IN E.-HE M A T OS I N E.
Blood of NMan.. Senru  of Mal.
Blood globules..13S30
Fibrine,...........      21
Albumen:......6'51. 8-12
Fatty substances...            37.      34
Extractive- matters....'0 -46
Alkaline salts..... 84'75
Earthy salts. -.....21     09
Water.0,.........78'      0      90'10
Loss...........    24               14
10000   1t00'00
ITe found these proportions liable to fluctuation, and to vary according
to the sex. The maxima and minima ofeach constituent which he found
for the human subject of each sex were,
Constituents.  lMa l.      X._i.   Fe1ma le.;Water.      C.:..805- 73 -2 184784 75-00
Albumen.-    n -.    6'3 4851:6:8  5'00
Globules...  18'6 11'05 16'71 7.14
Fibrine....   4   20i 311 *2
The fatty substance of the blood is a- mixture of cholesterine with stearic:and oleic acids, and a peculiar fatty substance, termed Seroline, the history
of Which is yet incomplete, and which differs from; cholesteririe most in
containing nitrogen.  None of the phosphuretted fats of the-brain appear
to exist inhblood.
The chemical history of fibrine and albumen having been already given,
it- remains only to describe the peculiar: colouring matter, for the most
accurate knowledge we possess concerning which we are indebted to
Lecanu's elaborate researches on the -blood.  His method of preparing
hematosine is as follows:
Blood, which has been freed from fibrine by beating with-a twig. is to
be mixed, with continual agitation, with sulphuric acid diluted with its
own weight of: water, until the whole mass solidifies to a brown pulp,
fromi which the acid liquo.r is to be then drained off onl filter'ing paper,
and'tthe last portions removed by washing with alcohol.  The mass thus
obtained,  which is a mixture of sulphates:of albu'men and of hemnatosine,
is to be boiled -in successive portions of alcohol as long as;this becomes
brown.  The liquors, being filtered when cold, are to be/neutralized by
ammonia, by which albumen and much sulphate of ammonia are. precipitated, while a compound of hematosine and ammonia remains dissol-ved.
This solution is to be then evaporated in a water.bath to dryness, and the
residue washed with water, alcohol, and ether, to remove the salts and
fatty. matters which were contained in it.  Being then redissolved in alcohol by means of amnmonia, evaporated to dryness, and. washed again
with water, the hematosine remains pure, but in its coagulated form.
It is a dark brown mass, tasteless and inodorous; wvhen heated, it does
not melt, but swells up and evolves ammoniacal products:; it is insoluble
in water;, alcohol, and ether; it forms with the mineral acids compounds
which aie insoluble in water, but soluble in alcohol.: By caustic alkalies
it is dissolved with a blood'.red colour, and these combinations aire soluble
in water, alcohol;, and ether.'Hematosine contains. neither phosphorus
nor sulphur, but iron in large quantity (6'64 pel cent.).  By: Mulder's
ianalysis, the formula of hematosine is C4,,4HN3. 06Fe.  It: hence has no.connexion with proteine or albumen.  The state in which the iron exists




-H E M AT O S I N E,. G L O B U.L I NE   E T C.;     675
in. hematosine has been, even up to the present day,: an object of much
discussion among chemists; but with the knowledge we now possess.of
hematosine in its pure form, we must'consider the iron to be an integral
part of' its organic constitution, as sulphur is in albumen, or arsenic in
alkarsine; and the opinion of its being oxidized, and combined witht the
true organic element as a kind of salt, can no longer! be supported.  If a.solution of hematosine be acted on,: by chlorine gas, a white fiocculent
precipitate is produced, and the solution contains chloride of iron...
Although hematosine is the colouring material of the globules of the
blood, it is present but in very small quantity; 100 parts of dried globules containing  but from four to five of pure hematosine.  In the blood
globule, the hematosine is in its uncoagulated state, and possesses prop.
erties somewhat different from those of its coagulated form, as prepared
by the process above given.  A solution of the coloured blood globules
in water, when exposed to the air, becomes of a brighter-red colour, be.
ing thus partially arterialized.  When evaporated at, a temperature of
120~,- it gives a dark red mass, which is completely soluble in cold water.
Its solution- coagulates at 155~, leaving, the. liquor clear yellow.  It is coagulated also by alcohol and by acids., The hematosine then passes into
tile insoluble condition already described.   
I have hitherto spoken of the colourless; ingredient in the blood glob.
ules as being albumen. with which, indeed,.it is almost identical in properties, but still differs in some points. -It,has been termed. Globuline.  In
its uncoagulated condition it cannot be separated from hematosine, and
is there distinguished from albumen principally by being insoluble even
in a very dilute saline solution, which dissolves. albumen readily.  It is
hence that the globules swim unaltered in the serum of the blood, but are
readily dissolved by pure water.  On this principle is founded a method
of isolating the blood globules.  It the blood, when extracted from the
vein, be received in a vessel containing a. solution of Glauber's salt, coag.
ulation is:prevented, as the fibrine remains dissolved, and by filtering the
liquor so obtained, the serum and water pass off, and the globules remain
mixed only with a little of the salt.  The globuline cannot, however, be
separated from the hematosine except by acids, which, as described in
the preparation of hematosine, then combine with the globuline.  Mulder
found the organic element in the sulphate of globuline to have the composition of proteine (see p. 666).
Alteration of the Blood in Disease.-The examination of the state of
the blood. in disease, although presenting important relations to pathology and to practice, has been hitherto conducted in a manner too disconnected and superficial to afford satisfactory results.  This branch of
chemical pathology has, however, been taken up by the illustrious Andral, who, in conjunction with M. Gavaret, has published the results of
the analysis of the blood in 360 cases of disease, in a memoir, from whose
publication may be dated the commencement of a true pathology of this
fluid.s..
In the method which, by the advice of Dumas, they adopted, the quantity of fibrine, of globules, of the -solid materials of the serum'(which may
be considered as albumen), and the quantity of -water in each specimen
of blood, were determined.  The pure hematosine was not isolated, and
the salts were considered as sufficiently important to necessitate their
separation only in certain cases.  As a point of comparison, they assume




676  ALTE R A TION  OF  THE  BLOOD IN  DISEASE.
as the standard of healthy blood, that 1000 parts contain 790 of water,
127 of globules, three of fibrine, and eighty of solid constituents of the
serum, of which eight are inorganic; which numbers almost coincide with
Lecanu's analysis, as already given.  Their researches have enabled
them to recognise four classes of diseases in which the composition of
the blood is essentially altered, though ill different ways.
The first class presents as a constant alteration an increase in the
quantity of fibrine; it includes diseases remarkably different in their lo.
cality and form, but all belonging to the class of acute infjammations.
In some cases of morbid deposition, as in tubercle and cancel, a similar
increase in the quantity of fibrine is found, but it may be doubted wheth.
er it be due to the abnormal growth, or to the inflammatory action which
accompanies it.
In the second class, the fibrine remains stationary, or even diminishes
in quantity, while the globules increase in proportion to the fibrine.  The
diseases which belong to this class are continued fevers without local
inflammation, and some form of cerebral hcemorrhages.
In the third class, the fibrine remaining unchanged, there is a remarkable diminution in the quantity of the globules; of these diseases chlorosis
may be taken as the example; and in the fourth class, it is no longer
the fibrine or globules which are the subject of' the morbid change, but
the quantity of albunzen in the serum is dininished.  Of this class of affections Bright's disease is the type.
Without entering into the details of these researches, which are ex.
eluded by the limited extent of this work, I shall merely present in the
following table an example of the constitution of blood in each of these
classes of morbid alteration.
constituents  Health.    Ist class.   2d Class.   3d Class.  i4th Class.
Fibrine....    3      7     2      3     3
Globules...   127   125   136    47    82
Albumen            72    78    69    75    58
Salts.....                     7     8     7
Water             790   783   786   867   850
The appearance of albumen in the urine in Bright's disease is evident.
ly connected with its diminution in the serum. The oily materials which
are usually found in the blood, and the remarkable diminution which occurs, not so much in the globules as in the hematbsine, had not attracted
Andral's attention in the memoir now described. These oily substances
are of the same nature as the proper fatty matters of the blood, but pres.
ent in excessive quantity.
It has been observed that in cholera the blood becomes so thick as to
arrest the circulation, and contains from thirty to forty-five per cent. of
solid matter; it is then, also, less strongly alkaline than healthy blood.
This is connected probably with the matters vomited and evacuated,
which are strongly alkaline, and contain a quantity of albumen.
The blood has been found occasionally, in cases of diabetes mellilus,
to contain traces of sugar; the great discordance of the results obtained
may perhaps result from the sugar being contained in the blood only for
a short time after meals, and then being rapidly evacuated by the kid
- neys.  In jaundice the green colouring matter of the bile has been observed in the serum of the blood. Other observations of morbid constituents of the blood'are too indefinite to justify me in occupying space




PHENOMtENA  OF  RESPIRATION.                      677
with them.  The observation of Barruel, that, by heating the blood of:
any animal with a little oil of vitriol, the odour of the animal is so pow.
erfilly evolved as to be easily recognised, appears well founded, and may
be useful in medico-legal questions, where, however, it should be employed with exceeding circurmspection.
Of Respiration.-ln the living body, the blood in the veins and arteries is well known to differ remarkably in colour, in the former being of
a dark purple red, and in the latter of a bright vermilion colour.  The
change from the venous to the arterial state is effected during the passage of the blood through the capillary vessels of. the lungs, where it is
exposed to the action of an extensive surfhce of atmospheric air, while
the arterial blood, in traversing the general capillary system of the body,
assumes the dark red condition in which it is returned to the heart by
the veins.  Even out of the body, this change of colour is produced
when venous blood is exposed to the air, especially if agitated therewith,
and still more with pure oxygen; even the globules, when separated
from the serum  and dissolved in water, become brighter in colour, and
partially arterialized by exposure to the air. Yet, although the vital
properties of the blood depend essentially upon this change of colour, we
are not yet able to connect it with any alteration in the composition of
the constituents of the blood, or even in their relative proportions.  Art
terial and venous blood contain sensibly the same quantity of water,
fibrine, globules, albumen, and salts; and, by analysis, the composition of
these bodies is found to be identical, no matter what kjnd of blood they
are derived fiom.  To trace the difference of nature between arterial
and venous blood, it is therefore necessary to study it under other points
of view than its proximate or elementary composition, so far as we have
yet examined it.
The air which has been employed in respiration is found to have un.
dergone an important change of constitution; its volume is but slightly,
if at all, altered; but a quantity of oxygen has disappeared, and is re.
placed by carbonic acid, in generally an equal volume.  Air which has
been once respired is found to contain from three to four per cent. of
carbonic acid; and if the same quantity of air be continually breathed,
the animal dies, with all symptoms of narcotic poisoning, when the carbonic acid has accumulated to from eight to ten per cent. The action of
the air in expiration is therefore to remove carbon from the blood. The
quantity so taken from  the system in twenty-four hours is very large,
and makes up the principal portion of that element which we take in
with our food; yet such is the activity with which its assimilation pro.
ceeds, that no perceptible change in the solid elements of the blood can
be detected.
It was at one time a much disputed point whether the carbon so separated from the system was directly secreted from the lungs, and burned
off, as it were, by contact with the oxygen of the air, or whether the
oxygen was first absorbed by the blood, and carried by the circulation to
every portion of the body, where it combined with the carbon, which
was there present in excess, and the carbonic acid'so produced, being
dissolved bythe venous blood, was thrown off, on arriving at the surface
of the atmosphere, in the lungs. The progress of science has, however,
finally decided in favour of the latter view, to which the fullest confirma.
tion has been given by the careful and elaborate experiments of Magnus,




678             T H -E 0 R        Y'-EO F   E'S PI R-A T I O'N.
He:found that- both arterial and venous blood hold dissolved quantities
of gases, oxygen, nitrogen, and carbonic acid, which amoulit to from one
tenth to-one twentieths of:the volume of the, blood;.  The proportions of
these: gases:to eachi otheri:are-different- in arterial and venous blood; ithe
oxygen in arterial blood being about one hal' of the carbonic acid,;while
in the venous blood it-seldom anmournts to more than one filth.: T',he- dif.
ference is greatest in; young animrnals, and probably is proportional to
their activity of-nut-rition.  The quantity of nitrogen appears to be the
same in: both- kinds of blood, making from one filth to one tenth of the
gaseous mixture. 
The- physico-chemical -conditions of -respitration alre simply explicable
upon these results..By the principle'of gaseous diffusion (p. 267), thefine -lining pulmonary. membrlane' being'permeable to gases when the
venous:blood' arrives at the- surface of  the  a portion of the carbonic acid which it contains is evolved, and a quantity of oxygen gas absoribed in: place of it.: These two quantities are not necessaril:y equal'at
each- roment, though ultimately they become so, and hence the volume'
of oxygen absorbed is- generally, though not uni versally, equal to that of
the carbonic -acid given- out,  There appears, from the presence -of. ni.
trogen: in -equal quantity in both kinds of blood, to be an absorption-and
evolution of t'at:gas, simply from physical laws, and independent of any
direct application of it to the nutrition of the animal; hence the volume
of nitrogen in air is sometimes increased, and at others diminished, by
respiration and an animal evolves much nitrogen when respiring an ar.
tilicial atmosphere  of oxygen and  hydrogen, while Bousingault has
shown t:he rate of nutrition of an animal to be proportional to the quan-.
tity of nitrogen it receives as food, and that none of that principle is
really assimilated fiom the air.
It is-still not by any means easy to decide upon the cause of the change
of colour which occurs in the blood during respiration; for this should
appear connected, not merely with the lpresence of certain' gases in the
blood, but upon a true change. in the constitution of the hematosine, which
analysis cannot direct.'Stevens first directed attention to the remarka.
ble influence which saline bodies have upon the colour of the blood.  If
dark vehous blood be put in contact with a solution of common salt,
Gliauber's salt, nitre, or carbonate of soda, it becomes as vermilion.col.
oured  as if it-had'been truly arterialized.'On the contrary, the presence
of carbonic acid impedes: this action, and gives to blood, so reddened by;a salt not in excess, the dark tint of venOus blood. - If we consider, there.
fore,, the arterial'tint to:be due'tothe natural combination of the colour.
fig: matter with the saline constituents of the serum, this will be: darkened when, by passing through the. capillary system, the blood takes up an
excess of Carbonic a cid; -and again, in the lungs, when the carbonic acid
is replaced:by ox;gen', the vermilion colour is restored, not by any active
agency of the'oxygen, but by the. natural tint of saline hematosine becoming evident.  Althoug,-h this theory of. the change of colour is by no
means free from objections, it appears to me to be better founded than
aiy: other thiat has, been proposed:
A- aanimal. Heat.-The phenomena of respiration consisting mainly in
the conversion of carbon: i'nto carbonic acid by union with oxygen;. the
heat: which: is developed in the body of all red-blooded animals has been
naturally referred to that source; and as we know  that the change




M:-U CJU S.'-G A S T R I:C J U IC E.           679
from the arterial' to the-venous condition of the blood occurs at every
painti of the system, the almost complete equality of temperature throughoQut- the body in health is:explained. -That the great source.of:heat
is the i respiratory: process,: is abundantly proved by the temperature being highest- in; those!animals, and in: the same:animal at those periods
when: the circulation is most rapid, and the quantity of air consumed the
greatest; but it has been calculated -that the heat evolved by the combustion of' the quantity of carbon thrown off from the body in twenty.four
hours is; not more than eight- tenths of the quantity generated in the body
durinlg that time, and the origin of the remainder must be found in the
action of the muscles and in-the nervous power, which appears of itself
to be a distinct source of animal heat.
SECTION IIH.
COMPOSITION OF THE DIGESTIVE ORGANS AND OF THEIR SECRETIONS.
CIIEBIICAL_ PHENOM'IENA -OF DIGESTION.
Mucus.r -The lining'membrane  of the alimentary canal is moistened
with a liquid possessing many characters of the vegetable mucus (tragacanthine, p. 530),but containing nitrogen.  It is a thick tenacious substance, which contains, dissolved in the water through which it is diffused,
tihe ordinary salts of-the serum of the blood; it swells up with water to
a considerable mass, but without dissolving;:it dissolves'in alkaline iiquors, and is precipitated therefrom on the addition of an acid and by
tincture of galls;: the mucu:s firom different parts of the mucous membrane
is,;however, by no means identical in properties.
T'he liquid secreted by the internal surface of -the stomach, the Gastrzc
Juice, which exercises an important influence on digestion, differs essentially- in its characters from  mucus.  When the stomach: is empty and
contracted, it contains only ordinary mnucus; but if even indigestible substances be introduced, and still more after taking proper food, a liquid is
abundantly poured out, which is colourless or very pale yellow, and contains a very small quantity of so-lid matter (two per cent.), which consists
principally of inorganic -sal'ts (common salt and sal ammoniac, with a
trace of a salt of iron);it is specially characterized by the presence of a
notable quantity of free muliatic acid,the proportions of which appear to
vary with the activity of the digestive powers at the time. This. gastric
juice possesses the remarkable -propertyof softening down and dissolving
fibrine and albumen,-and thus converts the masses of food into the uniform pulp (Chyme),: from which-tlle absorbing vessels: of the small intes.'
tines take up the nutritious' elements.
If we form an artificial gastric juice -by mixing together the  muriatic
acid and salts in the proper proportions, it is found to be -totally incapa.
ble of dissolving the materials of the food, and, indeed;, to be' quite- inac-.
tive towards digestion.  The organic material of the gastric: juice, although its quantity be so minute, is therefore essential to its powers, and
these -may be perfectly'conferred Upon'the previously inactive artificial
juice by the addition' ofa little of-the mucus of t-he stomach; or by steepiig
in the acid liquor, for a -short time, a small portion of a mucous membrane,
and filtering the liquor. -For this purpose it is not'even necessary to use
the mucous membrane ofthe'stomach, for that of the' bladderqhas been found
to act equally well. The substance which is-dissolved out of thee embrane
in these cases has'been termed Pepsine' It has not been obtained in a




680               PEPSINE,  SALIVA) ETC.
truly isolated )r pure form, but its properties are very remarkable. For
its full activity it requires the presence of a fiee acid, as the artificial gas.
tric juice becomes much less active in dissolving food, when neutralized by
an:alkali, though it retains other properties, as that of coagulating milk like
rennet.  If the artificial gastric juice be precipitated by acetate of lead,
the precipitate washed, and theni decomposed by sulphuret of hydrogen,
the solution thus obtained possesses all the digestive powers of the juice.
Hence the pepsine and muriatic acid act together in combining with oxide
of lead.  The process given by Schwann fobr preparing the best artificial
gastric juice, is to mix water with 23 per cent. of muriatic acid, of specific gravity 1-13, and digest therein the mucous membrane of a stomach
for twenty-four hours, then to filter.
Pepsine appears to be completely decomposed by contact with alcohol,
or by the heat of boiling water.  Its powers are destroyed, also, by de.
oxidizing substances.  The solution of albumen and fibrine in gastric
juice is essentially different from their solution in muriatic acid, as in the
former case the quantity of acid is very minute in relation to the quantity
of material dissolved, and after solution the acid still remains quite un.
combined.
Fremy has discovered that the peculiar fermentative process, which
sometimes spoils the manufacture of sugar, and which I have described
(p. 536) as the mucous fermentation, is capable of being induced by contact with mucous membrane (by pepsine?).  He has found that sugar of
milk may thus be converted to an unlimited extent into lactic acid, no
other product appearing.  The vegetable ferments are able to produce
the same effect, but in a different stage of decomposition from  that in
whichl they induce the saccharine or alcoholic fermentations.
The action of the stomach in digestion appears, therefore, to be, so far
as our actual knowledge extends, a purely catalytic fermentative action;
one in which the active excitant is an organic substance (Pepsine) secre.
ted by the mucous surface, and whose properties are developed by the
presence of muriatic acid, which is secreted at the same time. The new
products into which -the food, fibrine, albumen, gluten, starch, oils, sugar,
&c., are converted, and which collectively constitute the white unifbrm
pulp termed by physiologists Chyme, have not been made the subject of
accurate chemical research.
In the -mouth the mass of nutritive material is acted on by a liquid
which is secreted by the salivary glands, the Saliva.  It is alkaline, and
holds in solution not one per cent. of solid matter, which contains some
carbonate of soda and common salt, admixed mucus, a trace of sulphocy.
anid: of potassium, and a peculiar organic body termed by Tiedemann
and 3melin Salivary Matter.  This last substance is soluble in water;
its solution is not coagulated by heat, nor precipitated by tincture of galls,
corrosive sublimate, acetate of lead, nor by acids. The pancreas, though
so similar in structure to the salivary glands, has a different secretion;
it contains no salivary matter, nor any sulphocyanide of potassium, but
albumen and some salts; it is generally slightly acid.
Composition ofthe Bile. —The precise part which this remarkable se.
cretion performs in the animal economy is not yet fully known. It
has been the subject of repeated and accurate chemical examination,
although, from the facility with which its elements are transformed into
other bodies, by the action-of the reagents employed, every succeeding




ANALYSES  OF  THE  BILE.                      681
analysis has led'to different results. I shall only notice the late researches
of Gmelin, Demargay, and Berzelius.
In the elaborate work on digestion, undertaken in conjunction with
Tiedemann, Gmelin analyzed principally the bile of the ox, from which,
however, as far as observations have been made, human bile does not
appear essentially to differ.  He obtained from it a volatile body having
the odour of musk, cholesterine, margaric and oleic acids, a peculiar acid,
the Cholic Acid; colouring matters, Biliary Resin, Biliary Sugar, Taurine, a glutinous substance, caseium, salivary matter, ozimazome, and a
number of salts of organic and inorganic acids. Demariay looks upon
all of these substances as being produced by the reactions used, and de.
nies that any of them really exist in the bile.  HIe considers the bile to
be a soda-soap of a peculiar fatty acid, the Choleic Acid, that is, a Cho.
ledle of Soda.  The choleic acid is obtained by dissolving one part of the
alcoholic extract of ox.gall in 100 parts of water, and mixing the solution
with two parts of sulphuric acid diluted with ten of water.  By gradual
evaporation of the liquor, oily drops separate.  It is to be then cooled,
and these drops, which are common fat, removed.  On then standing for
eight or ten hours, the choleic acid gradually separates, and, being digest.
ed with ether to remove some adhering fat, is pure.  It is a brittle yellow-white mass, tastes bitter, softens by a heat of 250~, but does not
really melt; it is slightly soluble in water, but abundantly in alcohol and
ether.  It forms, with bases, salts which do not crystallize; its formula
was found to be C,,H,,6. N.012.
When the alcoholic extract of the gall is boiled for a long time in con.
tact with an excess of muriatic acid, the choleic acid is decomposed, and
the most remarkable products are the Taurine of Gmelin, and a new acid,
the Choloidic..dcid.  The latter is a fatty acid, not volatile, yellow, of a
bitter taste; it forms a soft mass with warm water, but without dissolving;
it dissolves readily in alcohol and ether, and these solutions redden litmus.  By Dumas's analysis the formula of this body appears to be C3s
H3007.  It does not contain nitrogen.  The Taurine, which remains in
the acid liquor from which the choloidic acid separates, is obtained by
evaporation, and mixing with alcohol, from which solution it crystallizes
gradually in six-sided prisms, which are perfectly neutral; it fuses and is
decomposed by a strong heat; it dissolves in twelve and a half parts of
cold, and in less of boiling water, but requires 573 parts of spirit of wine
for solution; it is scarcely acted on even by the strongest acids, and is
not precipitated by any metallic salt; its formula is remarkable, being
C4H,. N.Oo0, including the elements of binoxalate of ammonia and 2 Aq.
If the bile be treated with an excess of a strong alkali, the choleic acid
is totally broken up into ammonia and the Cholic Acid of Gmelin. It
crystallizes from its hot aqueous solution in delicate silky needles, of a
brilliant white colour; its taste is at once acid and sweet; by heat it is
melted and decomposed; it is very slightly soluble in water, but copious.
ly in alcohol; its solutions redden litmus; it contains no azote; its for.
mula being, as determined by Dumas, C42H-36Q,0.
Demargay's examination of the bile appears thus quite satisfactory in
showing that the cholic acid and the taurine are secondary products, and
he considered the other substances found by Gmelin to be choleic or cho.
loidic acids in an impure form,  But Berzelius, who has been occupied in
the re~examination of the subject, has decided that the choleic acid of
4R 




682'      c o LOU RiN G  MiATTER  OF  THEB I L E
Demargay is really the body which is impure, being a mixture: of the true
biliary substance (Bilin, Gmelin's Biliary. Sugar) with the biliary.lesins.'
ie. found -that when thie alcoholic extracts of the tbile is mixed with'sulphuric acidi no:precipitate appealrs for a; considerable timei-showing that
tile substance, which lreally-exists in th l bile- combined with. soda, is com-.
pletely soluble in water, and it is only by its gradual change that the pre.cipitatte (choleic acid)  occurs., By digesting this:substance with ether,
he renloved from it a resin, which,. by possessing acid properties, and by
means of combination with barytes, is shown to be a mixture of two dis.
tinctL acid resins, iFellic Acid and Cholinic-A cid.'The- material insolu.
ble in ether is the trlue Bilin; it is not acid,-of a bitter taste, soluble in
alcohol and water in- all proportions, but insoluble, in ether; when heat.
ed, it becomes soft, and. burns like a resin;- its watery solution is rapidly
decomposed,- especially if -varrned; by contact with acids o-r alkalies, it
is imnmediately changed in. constitution: the substances produced are different, according as the- degree; of alteration is more or lessi- advanced.
rhose more important are the following:' Thie Biliary Mlater, whir:h -is the state in which the -greater part of the
biliri exists.in. ordinaly: hile, being the first product of its decomposition,
is — a white, bitter: substatce, which has a marked acid reaction, and is de.
co.mlposed- by oxide of I-ead -into bilin and BiliJe!llnic Acid, which: is the
choleic acid of' Denma cay.  The formation -of taurine is accorm)anied by
that of another body, Dyslysin,  which is a colourless resinous substance,
very sparingly soluble in water.  The fellinic and cholinic acid have
been -noticed above.
-W:hen the bile; has been kept for -a long time, it is decomposed by a
kind of fermentation, and two acids formed, termed the Fellanic and
hiola-nic A: cids: they are: white earthy powders sparingly soluble: in wa.
ter; the former melts only far above 212~; the latter is very easily fu.
sible.; -The.Colouring Matter-of the Bile is present during health in but small
quantity,: but: in disease it sometimes accumulates so as to produce solid
masses. -When pure,.it is a;reddish-yellow powder, which is scarcely
soluble in, water or in alcohol,- but dissolves easily in solution of caustic
potash.  This'solution is of a clear yellow- colour, but when exposed to
the- air it becomes deep green, absorbing oxygen.  This change: is remarkably produced by  nitric acid, and it is indeed the reaction by which
the presence. of the bile in the serum of the blood, in the urine, in the sklin
and eyes, &c, -, ray be shown in cases- of jaundice.' If too much nitric
acid'be not added at once, the yellow liquor becomes-at first gireen; then
blue,:violet, and finally red, all-these changes occurr   ing in-a few seconds.
After.a moment t'the red colour. also disappears, the solution becomes yel.
low, and the colouring matter -is found to be totally decomposed.':The
solution of the: colouring matter -in potash is precipitated by murliatic acid
in, deep-green flocculi, which dissolve in nitric acid with the effect already noticed, and- are soluble in caustic- ammonia and potash, with a
rich emerald-green colour. - These reactions show that, by a process of
oxidizement from the original yellow substance,:green and red materials
may be generated, in which forms the colouring matter exists naturally
in various animals, according as their bile is yellow, green, or reddish,
and also gives rise to the concretions of various kinds that: are deposited
in disease. -The most common kind of gallstone consists, however, of
cholesterine.




N A TU Ri  O F 1CHYLE` AN D  L Y MP H.               68H3
This -yellow material Berzelius names Bilifulvin.  He considers the
green' colourilngmatter plesent in healthy bile to be identical with chlorophyll (p. 621). 
"Tmse blie contains generally about nine per-cent. of solid- matter; but in
thle present state of Our knowledge of its. constituents it it ievidently im.
possible- to assign the-numerical propurtions in which they exist.Th'lie substance fo-u'nd, in; t-he abie, and termed Erythrogfen by Bizio, is
too;'apocryphal to require any notice.    -
Tr'e exarmitnation 0f the fuLrther-processes of-digestion involves-considerations too purely physiological to be entered into.'
Chyle: and: Lymph l. -'l- e- nutritive materials extracted from the food
by the absorbing vessels of the intestine -is thrown into the-thoracic duct,
where it meets with another fluid, which is transmitted to the same vessel'
from all parts of the body by the colourless veins or lymphatics. -'the
fluid from the intestines is termed Chyle, that from the. body generally is
termed Lymph.  It is the.mixture of these that alone has been examined,
for the vessels which carry either separately are too minute to allow of
the extraction of their contents in a pure form.
WVhen taken from the-thoracic duct a few hours after a meal, when,
probably, tile chylous element prevails, it is a whitish, opaque- liquid like
milk, with generally-a: reddibh sh'ade; a' short time after separation from
the body it coagulates:; the -clot is:at-first- pale, but it soon becomes light
cinnabar red; the milkiness. of the serum is due. to the presence-of oil; it
contains albumen, and- cobagulates by heat.  Except that it is more dilute,
and that the hematosine is fobr the most part absent (not yet formed), the
chyle and lymph have the same, composition as the blood.  It appears to ~
vary, however, with the nature of the food,'as Dr. Prouit found the chyle
of dogs.fed on vegetables to contain-a -much- smaller quantity of albumen
than when they had had animal food., Dr. Prout also indicates in chyle the
existence of a substance which he terms Incipient Albumen, which is not
coagulated by heat, except after the addition of acetic acid.  The prop.
erties of' this form of albumen, however, are not fully known. -The resuits of their analyses of chyle are here given; that by Berzelius was
the chyle of a-, horse, killed- some time after having fed abundantly with
oats-; and of those- by Dr. Prout, No. 1 was- from a dog supported on
vegetable,- and No. 2 of a dog- supported on animal food.  100parts con.
tamed,. B;ieroleliu               i.....Prout.:  No. 1. -  -   No. 2
Dry Clot...    -7          Fibrine... 06        0.8
Albumen.... 449'          Incipient Albumen. 4'6      4-7
Fatty:matters.  -1671'  Albumen.... 04       46
Extrafctive matters? 1*44' Oil and Sugar.. trace   trace
and salts.;.:           Salts.             0'8     0'7
Water.... 916             Water....   936    89'2.SECTION IV.
CONSTITUTION OF THE: URINE IN HEALTH.AND IN DISEASE'.
The nature Qf this secretion has at all periods been an object- of con.
siderable interest to the physician and to the chemist, fiom:the indica.
tions which changes in its composition give of disease of important organs, and from the number and interest of the organic substances it con.
tains.  As in almost all other branches of'animal chemistry, Berzelius
first determined accurately its constitution, and lately Lecanu has ascer



b0o:        COMPOSITION  OF URI.NE.-UREA.
tained with great care the limits to which the proportions of its ingredi.
ents may vary in health, and thus established a correct basis of compar
ison for urine in the various conditions of disease.
The specific gravity of urine varies from 1016 to 1030. In general,
if the excretion exceeds in quantity thirty-two ounces in twenty-four
hours, the specific gravity falls proportionally below 1030; but if the
quantity be under thirty.two ounces, the specific gravity for a man in ac.
tive health is generally 1030, but less for women.  The important organ.
ic constituents of the urine are Urea and Uric Acid, which will require
a detailed and special examination; the other principles, though nurner.
ous, being of less moment, need be only noticed in the following state.
ment of Berzelius's general analysis of the urine. He found 100 parts
to contain,
Water............. 933'00
Urea.........                   30'10
Free lactic acid, lactate of ammonia, and!  1714
animal extract.       7..    0 11
Uric acid 1........00
Mucus of the bladder........  032
Sulphates of potash and soda.       6-87
Phosphates of soda and ammonia        4'59
Common salt........   445
Sal ammoniac......              150
Phosphates of lime and magnesia.100
Silica..............    003
Urea.-N2C2. O H4 or Ur.  Eq. 60 or 750.
The artificial formation of this remarkable substance in various ways,
has been noticed already in many places (as 511, 515).  It may be obtained from urine by evaporation to the consistence of a thick sirup in a
water-bath, and mixing the mass remaining with three times its volume
of nitric acid, specific gravity about 1'25, whlacn had been perfectly freed
from all traces of nitious acid which it might contain, as this last instantly decomposes urea. The liquor forms a crystalline pulp, which, being
kept carefully cool, may be freed from the liquor by draining and press.
ure between folds of paper. The impure crystallized nitrate of urea thus
obtained is to be dissolved in a small quantity of boiling water, and re.
crystallized by cooling.  These crystals being again dissolved in water,
are to be digested with animal charcoal to remove the colouring matter,
and then with an excess of carbonate of lead, until completely neutral.
The solution so obtained, being evaporated very carefully in a water.bath
to dryness, is to be treated with boiling alcohol, and filtered.  The pure
urea separates from the alcoholic solution, on cooling, in brilliant white
four-sided prisms.
Urea is much more simply and economically obtained by the transform.
ation of cyanate of ammonia, for which purpose the process given by
Liebig answers best.
An impure cyanate of potash is prepared by roasting yellow prussiato
of potash (as described p. 515), and this is mixed with a solution of sul.
phate of ammonia in water, and the whole then boiled with alcohol, which
dissolves out urea, and leaves the sulphate of potash undissolved. On
cooling, the urea crystallizes, and may be obtained quite pure by apoth.
er crystallization from alcohol.
The taste of urea is fresh like nitre; its reaction is quite neutral; it
is inodorous. When heated to 2200~, it melts, and at a higher tempera..




SALTS  OF  UREA.-URIC  ACID.
ture is decomposed, giving carbonic and cyanuric acids and ammonia.
It dissolves inl less'than its own weight of water at 60~, producing great
cold; it is soluble in much less boiling water. If the urea be quite pure,
its solution remains for a long time. unaltered; but if it contains any tra-.
ces of an azotized substance which putrefies, this acts as a fermrent, and
the decomposition extending to the urea, this assimilates the elemlents of
water, and is totally converted into carbonate of ammonia, N C2. OtI4
and H404 producing 2(C.0 +N.H4.0.).  It is this decomposition that
renders urine alkaline in a few hours, generally, after it is voided. Urea
dissolves in five parts of cold and one of boiling alcohol.  In ether it is
almost insoluble.
In contact with strong acids, urea is decomposed, giving off carbonic
acid, and forming an ammoniacal saft. When the acids are dilute, it unites
with them, although without neutralizing them, and forms crystalline
compounds, of which but a few have been accurately examined.  The
oxygen salts of urea resemble those of the vegetable alkalies, melamine,
ammonia, &c., in containing an atom of associated water.
Nitrate of Urea (Ur.H.O.+N.O,) crystallizes in large brilliant plates
by the cooling of its solution.  It is pleasantly acid, and is soluble in al.
cohol, but much more so in water; if' heated rapidly, it explodes.  It is
sparingly soluble in dilute nitric acid, whence the addition of a great ex.
cess of nitric acid serves as a test for the presence of urea, this salt being precipitated in bright pearly scales.
Oxalate of Urea (Ur.H.O.+COa) crystallizes in long rhomboidal
tables.  It tastes acid; it is copiously soluble in boiling water, but crystallizes almost completely out on cooling, as 100 of water retain but 4 of
the salt.  It is still less soluble in alcohol.
Lactate of Urea crystallizes in fine plates and needles; it is very solu.
ble.  There is reason to consider that the urea is naturally comnbined
with lactic acid in the urine. The other salts of urea are not important.
The quantity of urea secreted in health appears pretty regular in the
same individual, when the diet remains the same, and not to depend upon
the quantity of liquor excreted. It varies, however, very much in differ.
ent individuals, and is much more abundant in men in active age than in
women or in old men. Thus Lecanu found the quantity of urea secreted
in twenty-four hours, by men in the prime of age, to vary from 350 to
500 grains; in women it varies from  150 to 430 grains; while with
old men the limits were 80 and 180 grains. In children the quantity is
still smaller, and infants secrete scarcely a trace of urea.
Uric Acid, and the Bodies derived from it.
The uric acid exists in the urine of all carnivorous animals. In birds,
reptiles, and many insects, it is voided with the excrements, and the urine
is in such a state of concentration as to form a white mass, nearly solid,
which consists almost totally of urate of ammonia. In the small islands
of the South Sea, which are inhabited by great flocks of aquatic birds, it
accumulates in'such quantity as to be an article of commerce, being
brought to South America, and even to Europe, under the name of guano,
and used as manure. In many diseases it is generated by the system in
abnormal quantity, and constitutes, free or combined with bases, the gouty
and arthritic concretions, and many forms of vesical calculus.
For the purposes of the chemist, the uric acid is most easily obtained




686       u R IC  A C I D. —A L L A NT O I N. —A LL O.X A N.
from the white solid excrements of the larger serpents in the menageries.
This is to be boiled in a solution of caustic potash, and the filtered liquor
decomposed by the addition of muriatic: acid in excess.  The precipitate
should be boiled in water for some time, then yell washed and dried.  It
crystallizes in minute brilliant white scales, which are very slightly soluble in boiling water; the solution reddens -litmus; it is tasteless; it dissolves in oil of vitriol, forming a crystallizable compound,: which is decomposed on the. addition of water: the action of nitric acid is different.
When heated, it is decomposed, giving a great variety of products, urea,
hydrocyanic and cyanuric acids, carbonate of ammonia, &c.:Its formu.
la is N4,C,,. H06; its salts are not well characterized; those of the al.
-kalies are very sparingly soluble, and are decomposed by all acids except
the carbonic acid.  The Urate of Ammonia is the material of the white
excrement (dry urine) of birds and serpents.  The Urate of Soda is the
principal material of gouty deposites.  The uric acid is specially interesting for the number of important bodies to which it gives origin by the
action of reagents, and of which some are also products of the organiza.
tion; for our accurate knowledge of tlhese we are indebted to the recent
investirations of Liebig and Wohler.
Alantoin.-T'his substance exists in the waters of.the allantois of the
cow, being contained in the urine of the feetus, from which' it may be ex-.
tracted by evaporation and crystallization.  It is, however, much more
easily formed from uric acid. Freshly-prepared peroxide of lead is to be
added to uric acid, diffused through twenty.parts of boiling water as long
as its colour is destroyed.  The boiling liquor is to be filtered, evaporated till crystals begin to form, and then allowed to cool.  The allantoin
crystallizes, and the mother liquor contains abundance of urea.  At the
same time, oxalate of the protoxide of lead is produced, 2(N4C10. H406)
and 5H.O.. with 4Pb.02  producing 4(C20,:Pb.O.); with urea, 2(N,
C2. H402), and allantoin, N4C8. H505.  On this reaction Liebig founds
a theory of the constitution of uric acid, to which I shall have occasion
again to recur.  He considers it to contain urea ready formed, and a hypothetic substance, for which he: proposes the names of Uri!l, or Cyanoxa/ic Acid, it being oxalic acid in which oxygen. is replaced by cyanogen,
Cz02+Cy.''Thus uric acid, N4C,0. H406 —N2C. HaO2+42(C2OCy.).
In forming allantoin on this view, the urea is-set free, and the cvanox.
alic acid, with oxygenwand water, gives oxalic acid and allantoin.
Allantoin:forms rhombic prisms, which contain an atom of water.  It
is sparingly soluble in water, and perfectly neutral.  By boiling with a
strong alkali, it combines with the elements of'water, giving oxalic'acid
and amtmonia.. It does not form a definite compound with any base but
oxide of silver.
A lloxan.-The products: of.the action of nitric acid on uric:c acid present considerable interest, fromt their number and connexion. -On adding, one part of uric acid:gradually to. fbur parts of strong nitric acid, it is dissolved with much heat, and copious.disengagement of carbonic acid and nitrogen.. The- rise'of temperature' being
prevented as much-as possible, the liquor solidifies on cooling to a, mass of granular
-crystals, whichi are'to be drained, and then recrystallized from. the smallest possible
quantity of boiling water.-.This is Alloxan; its crystals are, short right rhombic
prisms, brilliant and colourless. In dry air they effloresce, losing 6 Aq.; at a higher
temperature it crystallizes in oblique rhombic prisms which are anhydrous, and have
the formula, N2Cs. H40io'; its'solution -in water reddens litmus, and:stains: the skin
purple;'when neutralized by an alkali; it strikes an indigo-blue colour.with a proto.
salt of iron; it' is'decomposed by- almost all reagents. producing a series of bodies
that will be successively examined; its origin consists, probably, in the uryl being




ALLOXANI:C  AND:MYCY OM1ELINIC   ACID:S'ETC. 687
oxidized by oxygen from the nitric acid, leaving hyponitrous acid, which, reacting
on the urea, gives the mixture of the caroonic acid and nitrogen gases. The allc.xan may thus be considered as a hydrated deutoxide of uryl.
Allo.canic Acid is Ibrmled by acting on alloxan with strong alkalies or by barytes 
when separated from its combinations by a stronger acid, it crystallizes in colourless needles, which have a strong acid reaction; its alkaline salts are soluble; those
with the earths and heavy metallic oxides sparingly soluble; it is insoluble in water; its formula is N2Cs. -H2u8 when dry, tihe alluxan having lost the elements, of
two atomn. of water.  When a solution of alloxanate of barytes is boiled, or when a
solution of alloxan is gradually added to a boiling solution of sugar of lead. another
acid is formed, Mk11soxalic Acid, which in the latter case precipitates an insoitble sailt
of lead, and the liquor contains urea; the alloxan breaking up into N.2C2. I-14() and
2C304, which is the constitution of the mesoxallc acid, which has probably, therefore, an isomneric oxide of carbon (C303) for its base, and belongs to the salne group
as the mellitic and rhodizonic acids (p. 496t). By oxidizing agents, the mlesoxalic
acid is converted into carbonic acid; thus, with a solution of nitrate of silver, it
gives a clear y-ellow precipitate, which, when boiled, is converted into carlbonic
acid and metallic silver.
Mllcomelimbic Acid. —If a solution of alloxan in water of ammonia be heated. a
brownish-yellow precipitate falls, which is mycomelinate of ammonia, by boiling
which, or by washing with dilute sulphuric acid, the ammonia is removed, and.the
mycomelinic acid remains as a yellow jelly, which dries to a coarse yellow.powdler.
It is sparingly soluble in water; its,salts are gelatinous, sparingly soluble flocks;
the formula of the acid is N4Cs. I.05, Leing isomeric with anhydrous allantoin.
Parabatnic Acid.-If alloxan be heated with an excess of nitric acid, it dissolves,
nitrogen gas is evolved, and, on cooling, the new acid separates; it is also easily
procured fromt uric acid by using an excess oft nitric acid; it forms colourless, transparent, six-sided prisms, and tastes like oxalic acid. It is partly volatilized and
partly decomposed by heat. If- the crystals he heated to 2120, they assume a reddish
colour; the formula of the crystallized acid is N2C604+~2 Aq.; hence alloxan\with
20. produces 2C.02, with 41-1.0. and N2C604. By contact with bases, this acid is
decomposed, producing the.Oxatlu'ic Acid. This is best prepared by dissolving parabanic. acid in caustic ammonia, boiling, and then letting the liquor cool; it foirms
a mass of small brilliant white crystals of oxalurate of ammonia. The oxaluric
acid is also a product of other reactions on uric acid-, some of which will be.specially noticed hereafter. It is a strong acid, and is obtained free by dissolving its ammonia salt in boiling water, adding an excess of dilute muriatic acid, and rapidly
cooling, when the oxaluric acid separates as a white or slightly yellow powder; if
long boiled in water, it is decomposed into.oxalic, acid and oxalate of urea, of which
it contains the elements, its formula being N2C6. H307+Aq.
Tibiola'ric Acid.-If. sulphurous acid gas be passed through a saturated solution
of alloxan until the liquor begins to smell strongly of the gas, and then ammonia be
added, in excess, after some time brilliant white rhombic:tables form, which are
thionurate of ammonia. By:recrystallization, this salt generally becomes; pale
rose-red, but is not altered in constitution. To obtain the acid free, a solu.tion of
this ammonia salt is to be precipitated by acetate of lead, and the thionurate of lead
decomposed by- sulphuretted-hydrogen.::By evaporation of -the liquor, the acid remains las a white semicrystalline mass; it is easily soluble in water, reddens litmus strongly; its formula is NsCs. H7014S2: it contains thus the elements of one
atom of alloxan, one of ammonia, and two of sulphurous acid;, it is a bibasic acid.
If a strong solution of thionuric acid be boiled, it becomes. turbid, and soon solidifies
to a mass of brilliant silky crystals, while the liquor contains much sulphuric acid;
the crystalline: substance being drained and washed with cold.:water, in -which it
scarcely dissolves, is termed: Uramil; it is white, soluble in dilute alkaline liquors,
and precipitated therefrom unchanged by the addition of an acid; but by strong alkalies it is decomposed: ammonia: being evolved, and uranmilic acid formed.   The
formula of uramil is NsCs.:;06;' the thionuric acid might:be considered as'bisulphate of uramil. The Urantilic Acid is formed by the. action of acids. and. alkalles
on uramil; it crystallizes in colourless:needles, which dissolve in acids and alkalies,
forming with the latter well-defined salts; its formula is N;C,6. HoO0,.
Alloxal)tian?.-This substance is fobrmed as a product of the moderate oxidation
of uric acid, or it may be obtained by acting on alloxan with deoxicdizing agents.
Uric acid is to be diffused through boiling water, and the dilute nitric -acid added
until a perfect solution is obtained. On filtering and cooling, the alloxantine gradually crystallizes.  The mother. liquor contains much urea. If sulphuretted hydro.
gen gats has been passed through'a solution of alloxan, sulphur is deposited, and alloxantine formed, and the same effect is produced by acidulating the solution of al



688          DIALURIC  ACID,    MUREXID,   ETC.:oxan, and immersing therein a slip of zinc; the alloxan is deoxidized by the nascent hydrogen. By the galvanic battery alloxan is resolved into oxygen and allox.
antine. It is sparingly soluble in cold, but much more in boiling water, and cry.stallizes in short oblique rhombic prisms which contain 3 Aq., which they lose only
by a heat above 300U. The solution of alloxantine reddens litmus, but does not
formin salts with bases, being immediately decomposed by contact with them. Its
formula is N2C8. IO,-10:
By oxidizing bodies,,s nitric acid, chlorine, or oxide of silver, it is immediately
converted into alloxan. If treated by an excess of sulphuretted hydrogen, more sulphur is set free, and the liquor becomes strongly acid. The body thus olrmed, if
mixed with alloxan, regenerates alloxantine from both. If neutralized by carbonate
of ammonia, a white crystalline precipitate forms, which is a salt of ammonia, of
which the formula is N3Cis. H-70. Liebig considers it to contain a body which he
terms the Dialctric Acid, the formula of which is N2Cs04, being isomeric with the
cyanoxalic acid or uryl already noticed. The Dialurate of AmLmonia is therefore
N28Cs0A+N.E40.+3 Aq. It may be produced by adding hydrosulphuret of ammonia to a saturated solution of uric acid in dilute nitric acid, or by acting on alloxan
with zinc and muriatic acid in excess. Though white when first produced, it becomies rose-red by drying, and at 2120~ blood-red, and loses ammonia. It is by no
means established that this body is a true ammoniacal salt as described by Liebig,
or that the dialuric acid really exists. Berzelius looks upon it as a compound of
alloxantine and alloxantine-amide.
By boiling with sal ammoniac, alloxantine is converted into uramil and alloxan,
while niuriatic acid becomes free. By the action of oxygen upon an ammoniacal
solution of alloxantine, uramil, oxaluric acid, and mycomelinic acid are generated.
Murexid.-This remarkable substance may be produced by a variety of reactions,
none of which are, however, quite constant in their result. On evaporating a solution of uric acid in very dilute nitric acid until the liquor becomes flesh-red, and
then adding dilute water of ammonia in slight excess, and cooling, the murexid
crystallizes. In this process a very slight excess or deficiency of any of the ingredients prevents success, and Gregory proposes, as the most certain method, to dissolve fbur parts of alloxantine and seven of hydrated alloxan in 240 parts of boiling water and eighty of solution of carbonate of ammonia, when the mnurexid crystallizes by gradual cooling. By the action of uramil and ammonia it may also be
generated, and is the ordinary source of the purple colours that are produced in
many of the reactions already described.
The Mzr'e.iid,, the name of which is derived from the mz'rex, the shell-fish furnishing the Tyrian purple, crystallizes in short rhombic prisms of a garnet-red colour,
and by reflected light have a green metallic lustre. It dissolves sparingly in cold,
copiously in boiling water; it is insoluble in ether and alcohol. Gregory has found
that it is sometimes soluble, and at others insoluble in water of ammonia, whence
he suggests that two different bodies have been confounded under this name. It
dissolves in caustic potash, with an indigo blue colour, which disappears by heat,
ammonia being evolved; it does not appear to combine with bases; its formula is
N5C,2. H60s. By the mineral acids and by sulphuretted hydrogen it is decomposed, ammonia, alloxantine, alloxan, and dialuric acid being evolved, besides another body termed Ju'recxan. This substance is more abundantly produced by dissolving murexid in a boiling solution of potash, and when the blue colour has totally disappeared, adding sulphuric acid in excess. It precipitates in white silky
crystalline scales; its formula is N2C6. 1H405; it dissolves in caustic alkalies without neutralizing them. If its solution in ammonia be exposed to the air, oxygen is
absorbed and murexid regenerated.
The murexid was long since described by Prout under the name of Pq'rp'rate of
Ammonia; and Fritzsche has revived the idea that it is really an ammoniacal salt
of a distinct acid, Purpyric Acid. By the double decomposition of murexid with
salts of potash, barytes, lead, and silver, he has obtained purpurates of these bases,
the formula of which shows the acid to be composed of N5sC6. H-401. The murexid is, according to this chemist, composed of N6Ce6. Hs801=NO C16. H400-. O
N.H40. The evidence brought forward by Fritzsche against Liebig's view is very
strong.
In the urine of herbivorous animals, and occasionally in children, the uric acid is
replaced by a different body, the Hiprnic Acid, which exists therein combined with
soda. The urine of horses and cows is to be. evaporated to one eighth of its volume,
and mixed with muriatic acid, which produces, after some time, a yellowish crys.
talline precipitate. This is to be dissolved by boiling with some lime;- chloride of
lime is to be added to the liquor until it is nearly decolorized, and the smell of urine
has disappeared; being thern digested with ivory black and filtered, the pure acid.is




URINE  IN  DISEASE.                          689
separated by muriatic acid. By the cooling of the liquor it crystallizes in delicate
siliy needles or rhombic prisms; its taste is very slightly bitter, but it reddens litmus strongly. When heated, it melts, and is then decomposed, giving a crystalline
sublimate of benzoic acid with ammonia and prussic acid. It is very sparingly
soluble in cold, but copiously in boiling water; very soluble in alcohol. By nitric
acid and other oxidizing agents, it is decomposed, and benzoic acid is formined. Its
salts are all soluble and crystallize; they resemble the benzoates exactly. The formula of the crystallized acid is.N.Cls. HsO-+Aq. The constant transformation of
this acid into benzoic acid has given origin-to many theories of its constitution. It
has been supposed by some to.contain benzoic acid ready formed, by others benzamid, arid by others oil of bitter almonds, but none of these views have even much
probability in their favour.
Of the Urine in Disease.  Urinary Calculi.
To the pathologist and physician, the indications of disease of the
urinary and digestive organs, furnished by changes in the comnposition
of the urine, are most valuable.  The majority of -the substances which
are taken into the circulation, but are incapable of assimilation to our
organs, are tlhrown off by this secretion, and hence a variety of medicinal
substances may be traced to it after having beeni ingested, sometimes quite
unaltered, at others modified in their nature.  Thus, if alkaline salts of or.
ganic acids be taken into the stomach, the organic material is oxidized,
probably during the action of respiration, while the alkali passes into the
urine in the state of carbonate.  If, however, the organic acid be taken
uncombined, it escapes decomposition, and, passing into the urine, pro
duces an abundant precipitate of salts of lime, in the case of the tartaric
and oxalic acids.
Iodide of potassium and iodine pass into the urine, the latter as hy.
driodic acid.  Some organic bodies, as asparagine and oil of turpentine,
are decomposed, and the products which they fbrm are excreted, giving
to the urine peculiar odours, in the latter case like that of violets.  Nitrate of potash, yellow prussiate of potash, and most other alkaline and
earthy salts, pass into the urine unchanged.  The majority of colouring
matters are thrown out of the system  by means of this secretion, while
others, as cochineal and litmus, are not so given off.
The mineral acids, alcohol, camphor, most metallic salts, do not pass
into the urine in any sensible degree.
Urine in Diabetes.-The most remarkable change in the nature of the
urine occurs in diabetes mellitus.  It is voided in great quantity.  Its
specific gravity is very high, from 1030 to 1050, and it is found to con.
tain a very large quantity of grape-sugar, and very little' urea.  It was
supposed that, in this'disease, urea ceased to be formed by the system,and was replaced by sugar; but I have shown that, although the quantity
of urea- is very small in any one specimen of the urine, yet the total
quantity is so much increased, that in twenty-four hours the natural
quantity of urea is secreted; the secretion of sugar being an act of faiulty
digestion, and totally unconnected with the urea.  These results have
been fully confirmed by Macgregor.. The diabetic urine sometimes con.
tains albumen, which arises from complication of other forms of disease..
As the average composition of urine in diabetes, the following may be
taken, analyzed by myself. Its specific gravity was 1-0363; it contained
in 1000 parts, water 913, sugar 60, urea 6'5, salts, extractive matters,
and uric acid 20'5.  This patient made in volume about four times the
healthy quantity of urine in twenty-four hours.
Urine in Dropsies.-In these diseases, particularly where associated:
4S




690       URINARY  DEP'OSITES AND  CALCULI
with disease of the kidneys, the urine is not increased in quantity; its
specific gravity is very low, 1005 to 1015, and it contains but very little
urea, but generally albumen, and sometimes caseum.  In these cases, the
urea, which is deficient in the urine, is found in the.serum of the blood
and in the dropsical effusions. In some states of the system, which do
not appear connected with any distinct disease, milk passes into the urine.
in which as well the butter as the: caseiim may be detected. Such cases
have even been met with in males.  In jaundice the colouring material
of the bile passes abundantly into the urine, and may be detected by
nitric acid. The natural elements of the urine are, however, not altered
in quantity.
Blue and Black Urine.- The urine has been observed coloured deeply
blue by a peculiar organic substance, which, however, has.niot been accurately examined.  Braconnot found that it contained nitrogen, and was
reddened by acids, and the colour restored by alkalies.  But Sprangen.
berg found, in the. case he observed, that acids dissolved the blue sub.
stance without changing itfs colour.  Moncet observed in the urine of a
child: a black matter insoluble in water, but soluble in alkalies.  Prout,
who" also observed this substance, termed it melanic acid.
In many states of the system, particularly in arthritic rheumatism,
there is a great tendency to the formation of uric acid, and the urate of
ammonia is deposited under the form of a crystalline precipitate when
the urine cools.  It is usually mixed with more or less of a yellowish-red
body, which is not'purpurate of ammonia (murexid), as Prout supposed,
but a peculiar organic substance, soluble in alcohol, which deserves more
minute examination.  The deposition of this excess of niatter in the
joints and sheaths of the tendons, produces the gouty concretions, which
consist, for the most part,: of urate of soda.
In other conditions of the system, the formation of phosphatic salts
predominates, and precipitates occur in the urine which are generally
more- crystalline and less highly coloured than those of uric acid or of
urates. As these different conditions of the secreting organs require
different modes of treatment, it is necessary to be able simply to distin.
guish between these two kinds of sediment.  It is sufficient to remark,
that the uric acid deposite is soluble in alkalies and insoluble in dilute
acids,-while the phosphatic sediments dissolve in dilute acids, but not in
alkaline liquors, even though decomposed by them.'The uric, acid and the inorganic salts of the urine are afterward de.
posited in the bladder, and form urinary calculi.
The Uric Acid Calculus is probably the most common.  It is recog.
nised by being decomposed by heat; being soluble in caustic alkalies,
and: precipitated by acids. - When dissolved in nitric acid, evaporated
and moistened with water of ammonia, it gives the rich purple colour of
mu rexid.
-The Urate of Ammonia Calculus, in addition to the characters of uric
acid, gives off ammonia when dissolved in solutions of caustic potash..
The Phosphate of Lime Calculus fuses with difficulty, or not at all,
before the blowpipe.  It is dissolved by muriatic acid, and precipitated
by caustic ammonia from this solution as a white powder not crystal.
line.
The Ammoniaco.magnesian: Phosphate Calculus is generally crystal.
line in structure; before the blowpipe it gives off ammonia, and ulti.




CYSTIC  AND XANTHIC  OXIDES, ETC.                   691
mately melts, though with difficulty. It also gives off ammonia when
boiled with caustic potash.  It dissolves in dilute acids, and is precipita.
ted as a crystalline powder on the addition of caustic ammonia.
The two latter calculi often form together, and produce the Triple
Phosphate, or Fusible Calculus. This melts readily before the blowpipe,
and it' dissolved in a. dilute acid, it gives with oxalic acid a precipitate of
oxalate of lirme, and then, with an alkali, a crystalline deposite of ammoniaco-magnesian phosphate.
All of these various deposites may occur in the bladder, either success.
ively, and form the Alternating Calculus, or together, forming the Mixed
Calculus. The recognition of these species will depend on the careful
application of the methods by which each component may be known, as
already described.
It is not very unfiequent to meet with calculi formed of materials which
do not exist in healthy urine, but are produced by the decomposition of
its natural constituents. Thus the Mulberry Calculus, so called from its
usual external form, consists of oxalate of lime.  When ignited it leaves
caustic lime, which browns wet turmeric paper strongly, dissolves in
muriatic acid, and is precipitated by adding oxalate of ammonia.  Calculi have been found also, though rarely, consisting of carbonate of lime
and of'carbonate of magnesia.
The most remarkable calculi of this class, however, are those formed
of the Cystic Oxide and Xanthic Oxide, substances of purely organic nature.  The latter body is yellow, soluble in alkalies, and is precipitated
by the addition of an acid. It dissolves in nitric and sulphuric acids, but
not in muriatic or oxalic acids.  Its formula is N4C,. H,404. It contains, therefore, the same carbon, nitrogen, and hydrogen as uric acid,
but less oxygen, whence the name Uric Oxide has been proposed for it.
The Cystic Oxide-Calculus consists of small yellow crystalline plates,
which dissolve in alkalies, and crystallize out again on the addition of an
acid, by an excess of which the cystic oxide is, however, redissolved.
WMhen heated strongly it is decomposed, evolving sulphurous acid and
ammonia.  It forms definite salts with the nitric and muriatic acids. Its
form ula is N.C6H6. 04S2.
When blood is effused into the bladder, the fibrine is occasionally ag.
gregated as a calculus, the recognition of which is very simple, from what
has been said of the properties of fibrine (p. 663).
Those who would wish for more detailed information of the properties
of calculi, and of the composition of the urine in health and disease, I
would refer to the truly classical work of Doctor Prout on the Diseases
of the Stomach and Urinary Organs.
SECTION V.
OF THE BIILK, AND OTIIER NATURAL AND MORBID PRODUCTS, -NOTINCLUDED IN THE PRECEDING SECTIONS.
Some of the most remarkable constituents of milk have been already describe:d, as lactic acid (p. 536), the sugar of milk (p. 535),
the butter, fats (p. 589). It only remains to'notice the general composition of milk, and the properties of the Caseilm or curd. It is
well known that, by standing, milk abandons the greater part of its
butter, which separates, with oth'er shtistances, as Cream. -Berzelins




692           C OMPOSITION  OF  MILK, ETC.
found the cream from  cows' milk to have specific gravity 1'0244,
and to consist, in 100 parts, of 4'5 of butter, separated by agitation,
3'5 of caseiim, with some butter, separated by coagulation, and 92
of whey.  The skimmed milk had a specific gravity of 1'0318, and
contained in 100 parts:
Caseous matter with some butter.... 2600'
Sugar of milk.                        3'500
Alcoholic extract with lactic acid...   0o600
Chloride of potassium.0 1.. 0'170 100 C0.
Alkaline phosphates.....  0'025
Earthy phosphates and a trace of iron.. 0"230
Water...92 875 
The following table presents the best results that have been as yet
3btained on the average composition of the milk of' different animals:
Human.  Mares.  Asses.  C(ows.  Sheep.  )__g.,
Specific gravity.. 1 0323 1 0395 1 0322 1 0320 1 0380
Water...        88 36  88 68  90 47  85 91  53 2  65-74
Extractive..     1-24......(Cr1ea)   290
Caseine...   3'40  1'82   1 95   7'001 15'3  17-40
Butter....    253   0'75   1 29   393    5'8  16'20
Sugar.....- 425   8 75   6 29   2 87    42
Ashes...         022..   029.    1 (S
The butter of human milk is more solid than that of the cow, and appears tc contain no butyrine.
The Caseiim or Case'ne is capable of existing in a soluble and an
Insoluble condition, like albumeen.  In milk it is principally dissolved,:ut a part insoluble, united with the butter, produces the emulsive
appearance of the milk. On adding sulphuric acid to skimmed milk,
the caseine precipitates, combined with the acid, as a white coagukum, which, being washed with water so as to remove all adhering
milk, and then digested with carbonate of barytes, the caseine dissolves in the water, and may, by filtration, be freed from all traces
of the butter, sulphuric acid, or barytes. The caseine may also be
precipitated by alcohol, and when the curd is digested with ether
to remove all traces of butter, it may be looked ipon as pure.
The solution of caseine in water as thick, like mucilage; it smells
as boiled milk, and dries down to an amber-colouied mass, which is
again soluble in water. The solution is coagulated by all acids,
even acetic acid, particularly when hot, and by alcohol. In relation
to acids, caseine is similar to albumen, except that to acetic acid;
the constitution of its precipitates being precisely similar.
The coagulated condition of caseine is not produced by boiling,
but only by the digestive principle (rennet, pepsine), as already described (p. 679).  When thus coagulated, caseine is absolutely undistinguished from coagulated albumen in its properties. It contains a considerable quantity of bone-earth (phosphate of lime),
amounting to five or six per cent.,in intimate combination. Its organic element was found by Mulder to be proteine, of which ten atoms are combined with one of sulphur, the formula of caseine being
C400H30. N500,20+S.  It contains no phosphorus, but to each atom
so, expressed, two atoms of bibasic phosphate of lime.
When coagulated caseine containing water (cheese) is kept for




EGGS. AMNIOSo CONTENTS OF THE EYE, ETC.  693
a long time, it undergoes a remarkable kind of decomposition, and
a substance, crystallizable and soluble in water, is obtained, termed
by Braconnot d4posepedine. By Mulder's experiments it appears,
however, to be impure leucine (p. 667); and the GCaseous Oxide and
Caseic d4cid of Prout appear also to be the same bodies as have been
already noticed as formed from the decomposition of the other proteire substances.
By contact with caseine, sugar of milk is rapidly converted into
lactic acid, which precipitates the caseine, without, however, really
coagulating it; hence, on neutralizing the acid, the caseine redissolves, and may react on a new quantity of sugar. In this manner
Frerw, ilas shown that the Lactic Fermentation may be carried on to
an indefinite extent.
Constitution of Eggs.-The shell of hens' eggs consists of from'
90 to 95 per cent. of carbonate of lime, one to five of phosphate of
lime, and two to five of animal matter. Internally it is lined by a
membrane analogous to epidermis. The white of egg is a concentrated solution of albumen, contained in the cells of a delicate memn
brane, in the centre of which the yolk is suspended. The nutritive
material of the yolk consists of albumen and an oil; also a yellow
colouring matter analogous to that of bile. The Oil of Eggs is ob-tained by expressing the egg boiled, and partly torrefied; it is red.
dish-yellow, thick, and solidified by cold; it soon becomes rancid;
the solid portion of it appears to be cholesterine; the liquid contain.s phosphorus and nitrogoen, and is not saponifiable.  When the
young animal is developed during incubation, the quantity of phos
phoric acid in its bones is exactly represented by the quantity of
phosphorus in the yolk and white; but as these bodies contain very
little lime, that earth must be derived from the shell, which becomnes
thin and brittle as the animal advances in growth.
Liquor of the d.mnios.-This fluid, in which the feetus is immersed
before birth, appears to be identical in constitution with the liquor
effused from serous surfaces in dropsy (p. 671). The Liquor of the.lllantoi's of the cow, which is really the urine of the foetus, is of
the same nature, but contains, in addition, a small quantity of allan.
toin; the artificial formation of which is described p. 686.
Black Pigment of the Eye.-This substance is insoluble in water
and alcohol. It is decomposed by strong acids and alkalies. Caustic potash dissolves it, forming a yellow liquor, from which acids
throw down a clear brown powder. The action of nitric acid is
nearly the same. The Cuttle-fish Ink has much analogy with the
black matter of the eye, giving, when dried, a black powder, insoluble in water, alcohol, and ether, which dissolves in nitric acid and
potash with a reddish-yellow colour, from which solution a yellowish powder falls when it is neutralized. The true nature of these
black colouring matters, and their relation to the melanic acid of
Prout, which sometimes appears in the urine, would deserve attentive study.
The Humours of the Eye consist of water, holding in solution al.
bumen in small quantity, with the salts which usually accompany
it. The crystalline lens consists of albumen, in a state of beautiful




694        CERUiMEN) PUS) AMBERGRIS  ETC.
and complex organization, amounting to about thirty-eight per cent.
of the entire mass, which contains about sixty of water.
Cerumen.  Wax- of the Ear.-This substance contains an albuminous material insoluble in water, a solid and a liquid fat soluble in
ether, and a deep:yellow matter soluble in alcohol and insoluble in
ether, to which its colour and very disgusting taste are due; another constituent, which appears to be peculiar to this secretion, is
brown, insoluble in caustic potash; it most resembles horn in its
properties, but is still quite distinct from that body.
Pus.-This remarkable morbid secretion has generally a specific
gravity of 1-030. It consists, of a clear liquor, in which float a great
number of yellow globules, of various sizes, the largest or which
are about twice the size of the globules of the blood. Pus Joses
by drying 86-1 of water in 100 parts, and hence contains 13-9 of
solid material, from which alcohol takes 5-9 of fatty and extractive
matters, and leaves 7-4 per cent. of a residue, which consists of
coagulated albumen:, the solid globules, and a substance peculiar
to pus.
The globules of pus appear to consist of coagulated albumen.
The serum contains two liquids, both coagulable by heat.  One is
albumen, the other Pyin, which is characterized by being coagulated both by heat, by acetic acid, and by a solution of alum.  Giiterbach, who has recently examined pus with great care, finds the only
certain distinction between pus and mucus to be, that the pus globules sink always in water, while the mucus swims. If the suspected liquid be dried, the extraction of the fatty substance by ether
should decide very positively..vnabergris.- This substance, which is generally found floating on
the seacoasts of tropical islands, is known to be an intestinal concretion of the spermaceti whale, analogous to the gallstones-of
cholesterine in other animals. Its principal ingredient is the A.mbreine, which is obtained by solution in boiling alcohol, whence it
crystallizes, on cooling, in fine needles. It is white, tasteless, of a
very agreeable odour'; it is not saponifiable; its formula is C3,,1320
By boiling with nitric acid it produces ambreice acid, which crystal
lizes from its solution in alcohol in small colourless tables; it red-;dens litmus, but is scarcely soluble in water; it forms -well-defined
yellow salts with the alkalies; its formula appears to be C2,H20.
N.O2.
SECTION VI.
OF THE PRESERVATION AND PUTREFACTION OF ANIMAL MATTERS.
From the greater complexity of composition of animal substances,
their decomposition is more rapid, and its products more diverse,
than in:the case of -organic bodies of vegetable origin; while the
carbon, hydrogen, and oxygen give origin to the various kinds of
ulinine and other substances of the same class, the nitrogen is generally evolved as ammonia, and the sulphur as sulphuretted hydrogen.- It is the presence of these bodies that give to putrefying sub-,stances the disagreeable odour by which that process is distinguished from mere mouldering or rotting.




PUT RE F A CTI O N.~                 695
Even during life the constituent particles of the body are in.;a
continual state of change, being absorbed and thrownout of,the
system, while others are assimilated in their place. Any part of
our constituents, liquid or solid, which becomes unfitted for this
vital function, is thereby killed, and must, if not got rid of, induce
the death of the individual. Hence precisely the same means which
give to. animal substances the fixity of constitution which belongs
to true chemical compounds, and thus preserve them from decomposition by the disturbing action of their own elements (as when
we coagulate albumen by an acid, by corrosive sublimate, or by
sulphate of copper), produce, if applied to. the living body, the
death of the part or of the whole being, by depriving the blood or
the tissue of the mutability of constitution which ismrequired for the
functions of the animal frame.
It is thus that the generality of metallic poisons act in producing
death. Being absorbed into the system, they unite with the albumen and fibrine of the blood, and, converting them into the insoluble compounds which we form in the laboratory, unfit them for the
continual absorptive and secretive offices which, as organs, while
they live they must fulfil. If the injury be local, and limited in extent, the part so coagulated may be thrown off, and, after a certain
time the functions return to their proper order. If the mass, or the
importance of the affected parts be greater, the system cannot so
get rid of the-potions which have thus been removed from  the
agency. of life to s bmit to merely chemical laws; on the contrary,
the vital powers ol the remaining portions of the animal are so much
weakened in the effort that general death is caused.
For putrefaction it is thus necessary, 1st, that the force of vitality, which governs so completely the mere chemical tendencies of
the elements of our tissues, be removed; 2d, that there shall not be
present any powerful chemical reagent with which the organized
material may enter into combination, and thus the divellant tendencies of the affinities of its elements be overcome; 3d, that water be
present in order to give the necessary mobility; 4th, that oxygen
be present, or at least some other gas, into the space occupied by
which the gaseous products may be diffused; and, lastly, that the
temperature shall be within moderate limits, putrefaction being impossible below 32~ and above 182~.
The agency of the first of these preventive powers need not be
farther noticed. The second is extensively employed in the preparation of bodies for anatomical purposes, by baths, or injections into
the arteries, of solutions of corrosive sublimate, acetate of alumina,
sulphate of iron, tannin, wood vinegar, and kreosote; this last body,
however, does not appear to act by direct combinations, but by the
complete (catalytic) coagulation it produces in all the tissues of the
body that have proteine for their base. The necessity for the presence of water is shown by the fact that, by drying the animal substances, they are completely preserved. It is thus that the bodies
of those perishing in the Arabian deserts are recovered years subsequently, dried, but completely fresh. Alcohol and common salt
act in preserving animal bodies by their affinity for water. If a
piece of flesh be covered with salt, the water gradually passes from




696              M I A S M S.-C O N T A G I O N.
the pores of the flesh, and, dissolving the salt, forms a brine, which
dogs not wet the flesh (p. 540), but trickles off/its surface; the wa
ter necessary, for putrefaction is thus removed. The mode of
strengthening alcohol in a bladder (p. 540) rests on the same principle. Fourth, by excluding oxygen, the putrefactive process is retarded, precisely as the fermentative action of the gluten in grapejuice (p. 538) cannot begin until a small quantity of oxygen be absorbed. It is thus that meat which is sealed up in close vessels,
and then boiled for a moment, is preserved; the small quantity of
oxygen of the air remaining then in the vessel is absorbed, and the
product of that minute change being coagulated by the heat, it cannot proceed farther. A high temperature stops putrefaction by coagulating the azotized materials; a temperature below 32', by freezing the water, acts as if the tissue had been dried; in both cases
putrefaction is arrested.
During putrefaction, at a stage prior to any fetid gas being evolv
ed, a peculiar organic substance is generated, possessed of intensely
poisonous properties, and the blood of persons who have died from
its effects is found to be quite disorganized and irritating when applied to wounds. The blood of over-driven cattle is found to produce effects similar to those of venomous reptiles, and the wounds
received in dissection are sometimes followed by similar fatal consequences. The communication of disease in this way has recently
been very ingeniously ascribed by Liebig to the general principle
of the communication of decomposition by contact (p. 663). The
small quantity of diseased organic matter o iginally introduced into
the system by absorption, acts as a fermenr, and reproduces itself
in the mass of blood until this becomes unfitted for the performance
of its functions, and the animal is killed; the active principle being
thus copiously present, is exuded from the skin and lungs, and gives
a contagious character to the disease, or it remains only in the
blood, or is secreted in pustules, &c., constituting infection, by which
the disease may be communicated to another person.
In the decomposition of vegetable matter in marshes, similar
maleficent products may be evolved, and throwing the blood of the
animal, by whom they are absorbed, into fe;mentative decormposition, produce the effects of JMalaria and JMarsh JMliasm.




INDEX.
Absinthi'ine, 611.                     Acid, Hippuric, 688.
Absorption of Iight, 45.                   Humous, Humic, 639.
of Heat, 96.                     Hydriodic, 315.
Acechloryl, 564.                            Hydrobromic, 318.
Acetal, 554.                           -    Hydrochloric, 307.
Acetone, 561.                               Hydrocyanic, 517,
Acetyl, 554.                           - Hydrofluoboric, 327.
Acid, Acetic, 555.                     --  Hydrofluoric, 319.
-— Adipic, 586.                          -Hydrofluosilicic, 325.
-    Aldehydic, 555.                    -  Hydroxanthic, 550.
- Althionic, 546.                      -     Hypoantimonius, 385.
Aloetic, 612.                     -    Hypochlorous, 304.
-     Anchusic, 614.                        Hyponitrous, 275.
-     Anilic, 618.                     -    Hypophosphorous, 296.
-     Antimonious, Antimonic, 385.     -     Hyposulphuric, 291.
-    Arsenic, 377.                     -     Hyposulphurous, 290.
-     Arsenious, 376.                  --  Iodic, 313.
Auric, 405.                       -     Isethionic, 546.
- Azulmic, 518.                            Kinoic, 604.
- Boletic, 604.                     -    Krameric, 605.
-     Boracic, 326.                    -    Lactucic, 604.
-  Bromic, 318.                             Lipic, 586.
-  - Butyric, 589.                      -  Manganic, 356.
-  Carbonic, 485.                        -  Margaric, 583.
-  Capric, Caproi'c, 589.               Mellitic, 496.
Catechutannic, Catechuic, 603.        ---  Metaphosphoric, 299.
- Caincic, 605.                          - Methionic, 546.
-     Chloric, 304                     — Molybdic, 451.
-     Chloroacetic, 564.               -     Muriatic, 307.
-     Chlorochromic, 450.              -    Myristic, 588.
Chlorous, 305.                      - Nitric, 277.
-   Chromic, 372.                           Nitromuriatic, 310.
-  Chrysammic, 613.                        Nitrous, 276.
-  Chrysolepic, 613.                -   Oleic, 584.
-- Cinchonic, Cinchonatannic, 604.         Osmic, 374.
Cinnarnic, 572.                   -    Oxalic, 493.
-    Citric, 597.                      -    Oxalovinic, 550.
-     Colophonic, 579.                   -  Palmitic, 588.
-   Colurnbic, 375.                     -   Paracyanic, 514.
-     Crenic, Apocrenic, 640.             - Perchloric, 306.
-     Croconic, 496.                        Periodic, 314.
-  Crotonic, 590.                    -  Permanganic, 356.
Curenic, Cumen-sulphuric, 575.         Phosphomesitic, 561.
Cyanic, 514.                          --  Phosphoric, 297.
-  Cyanuric, 516.                           Phosphorous, 296.
Delphinic, 589.                   -- Picric, 618.
- Ela'idic, 586.                    -    Pimelic, 586.
--  Ellagic, 602.                   -  Pinic, 578.
Ethionic, 546.                         Purpuric, 688.
-    Eugenic, 573.                        - Racemic, 596.
-   Formic, 645.                       --   Rhodizonic, 496.
Fulminic, 515,                         Saccharic, 532.
Fungic, 604,                           Saccharohumic, 637.
Gallic, 601.                         - Sacchulmic, 532.
Gluoic, 534,                        _  Sebacic, 585,
4T




698                             INDEX.
Acid, Selenious, Selenic, 294.       Antimony, 384.
-   Silicic. 322.                        - Detection of, 388.
-    Stanuic, 370                     --         Oxide of, 385.
Stearic, 582.                              Salts of, 453.
Succinic, 580..Sulphurets of, 386.
-    Sulphomesitic, 561.             Antimony Crocus, Glasses of, 385.
-Sulphuric, 286.                   Apotheme, 612.
Sulphurous, 284.                Aqua-regia, 310.
— Sylvic, 578.                       Arabine, 530.
Tannic, 597.                     Aricine, 625.
--  Tantalic, 375.                   Arseniate of Iron, 452.
-   Tartaric, 592.                        -- Potash, 452.
Tellurous, Telluric, 389.                   Silver, 461.
Titanic, 375.                    Arsenic, 376:
Tungstic, 374.                         - Acids of, 377.
-    Valerianic, 568.                        Antidote to, 384.
-  Vanadic, 373.                           - Detection of, 381.
- Verdous and Verdic, 605.               -  Salts of, 451.
Acids, Polybasic, 413.                ---  Sulphurets of, 379.
Acroleon, 585.                       Arsenite of Copper, 456.
Actions by Contact, 235.                        Potash, 452.
Adhesion of Solids to Liquids, 19.          -   Silver, 461.
XAroliths, 357.                      Arseniuret of Hydrogen, 378.
Affinity, Chemical, 157.             Atmosphere, 262.
Order of, 159.                  Composition of, 263.
influenced by Cohesion, 164.              Effect of Respiration oi,
- _   - Elasticity, 168.                268.
- Light, 172.                  Extent and Form of, 270.
- Measure of, 202.                         Pressure of, 269.
Aggregation, States of, 16.           Atmospheric Electricity, 125.
Air, Atmospheric, 262.               Atomic Theory, 217.
-- Expansion of, 48.                 Atoms, Physical and Chemical, 219.
Alabaster, 431.                              Specific Heat of, 66.
Albumen, Animal, 663.                 Atropine, 634.
Alcohol, Ordinary, 540.               Aurates, 405.
Alembroth, Salt of, 461.              Azote, 260.
Algarotti, Powder of, 453.           Azure Blue, 447.
Alkal;es, 330.
Alkalimetry, 489.                     Balance, Electrical, 113.
Alkaline Earths, 330.                 Barium, 342.
Alkarsine, Alkargene, 563.                    Chloride of, 429.
Allantoine, 686.                      -      Sulphuret of, 344.
Alloxan, 686.                         Barytes, 342.
Alloxantine, 687.                             Salts of, 429.
Alum, 436.                           Batteries, Constant, 136.
Aluminum, Alumina, 349.               --        Galvanic, 131.
-  ---- Salts of, 435.                Bell Metal, 393.
Amber, 579.                           Benzyle Compounds, 570.
Ambergris, Ambre'ine, 694.            Bile, Constitution of the, 680.
Amidogene, 500.                       Bileiney Bilifulvine, 682.
Amilic Alcohol, 567.                  Bismuth, 397.
Ammeline, 526. —    Oxides of, 398.
Ammonia, 498.                           --    Salts of, 458.
Ordinary Salts of, 507.              Sulphuret of, 398.
Amygdaline, 569.                      Blende, 367.
Analcime, 40.                         Blue, Azure, 447.
Analysis, Nature of, 10.              - Thenard's, 447.
- Organic, 482.                   Boiling Points of Liquids, 83.
Anatase, 375.                         Boracic Acid, Boron, 326.
Anhydrite, 431.                       Boracite, 435.
Animal Charcoal, 480.                 Borax, 428.
-------   Electricity, 138.           Boron, Fluoride of, 327.
Antimonial Powder, 454.               Brass, 394.
Anatimoniuret of Hydrogen, 388.       Bromates, 318.




I N D E X.                            699
Bromide of Sulphur, 318.              Chloride of Rhodium, 466.
Bromine, 317.                         -   --    Selenium, 311.
Chloride of, 318.                       Silicon, 323.
Bronze, 393.                                 -   Silver, 459.
Brucine, 631.                            --        Sodium, 426.
-   Strontium, 429.
Cadmium and its Compounds, 369.             -    Sulphur, 310.
Salts of, 448.                       -  Tin, 448.
Caffe'ine, 608.                               -  Titanium, 454.
Calamine, 367.                                   Zinc, 447.
Calc Spar, 345.                       Chlorine, 300.
Calcium and its Oxides, 345.          -        Compounds with Oxygen, 304
- Salts of, 430.                Chlorophyll, 621.
- Sulphuret, 347.               Chondrine, 668.
Camphene, 576                         Chromates of Lead, 458.
Cantharidine, 609.                                 Mercury, 464.
Caoutchouc, Caoutchine, 580.                       Potash, 449.
Capacity of Bodies for Heat, 63.      Chrome Alum, 449.
Caramel, 533.                         --   Iron, 371.
Carbon, Forms of, 476.                Chromium, 371.
Carbonates, 485.                                 Oxide, Acid of, 371.
Carbonic Acid, 485.                           - Salts of, 449.
Oxide, 492.                  Chrysorhamnine, 615.
Carburets, 485.                       Chyle and Chyme, 679.
Carmine, 616.                         Cinchonine and its Salts, 625.
Carthamine, 615.                      Cinnabar, 402.
Caseuim, Caseine, 691.                  --   Factitious, 403.
Catalysis, 235.                       Circular Polarization, 41.
Cementation, 360.                     Classification of Bodies, 238.
Cerebrot, Cerebrol, 669.              Cobalt, 366.
Cerium and its Compounds, 351.        -— Salts of, 446.
Chalk, 345.                           Cocculine, 609.
Chameleon Mineral, 356.               Cohesion and Affinity, 163.
Chemical Action of Galvanism, 129.    Columbine, 609.
Affinity, 156.               Columbium, 375.
Formule, 156.                        -  Salts of, 451.
- Nomenclature, 149.            Combination, Laws of, 202.
- Rays of Light, 173.           Combustion, Slow, 173.
Chemistry, Origin and Object of, 9.           --  Theories of, 185.
Derivation of, 10.         Communication of Motion, 235.
Chloral, 564.                         Conduction of Heat, 91.
Chlorate of Potash, 304, 424.         Coneine, 635.
Chloride of Aluminum, 435.            Constant Battery, 136.
Antimony, 453.             Contact, Actions by, 235.
— L. Arsenic, 452.           Cooling of Bodies, 103.
Barium, 429.               Copper, 390.
Bismuth, 458.             ---- Alloys of, 393.
Boron, 326.                 --- Oxides of, 392.
Calcium, 430.                     Pyrites, 390.
Chrome, 449.              -   - Salts of, 453.
Cobalt, 446.                     - Sulphurets of, 393.
Copper, 455.               Crystalline Forms, 23.
-    -      Gold, 465.                Crystals, Dimorphous, 227.
Hydrogen, 307.                      Isomorphous, 221.
Iodine, 317.                 --  Polarization by, 38.
Iron, 444.                     --  Systems of, 26.
______-   Lead, 457.                 Currents, Galvanic, 126, 197.
Magnesium, 434.            Cyanogen, 513...... —   Manganese, 443.
Mercury, 461.              Daguerreotype Images, 175.
Nickel, 446.               Definite Proportions, 202.
Palladium, 466.            Dew, Nature of, 104.
Platinum, 466.             Dex rine, 331.
Potassium, 421.            Diamond, 477.




700                              IND EX.
Diastase, 651,                         Fluoride of Hydrogen, 320.
Differential Thermometer, 50.              --  Phosphorus, 321.
Dimorphism, 227.                              -  Silicon. 324.
Distillation, 83.                      Fluorine, 319.
Divellent Affinities, 157.             Fluor Spar, 430.
Divisibility of Matter, 17.            Freezing Mixtures, 71.
Double Decomposition, 157.             Frost, Nature of, 104.
R- efraction, 34.                  Fulminates, 513.
Dynamic Electricity, 126.              Fusion, Liquefaction, 70.
Ebullition, 83                         Galena, 395.
Elasticity of Gases, 19.               Galvanic Batteries, Common, 134.
Vapours, 78.                   ---      -        Constant, 136.. ---- - and Affinitv, 168               - - Circles, 128.
Elaterine, 609.                            -   Electricity, 126.
Elayl, 552.                                     Intensity, 131.
Elective Decomposition, 157.           Galvanism, Contact Theory of, 133.
Electrical Attraction, 112.            Galvanoscope, 147, 195.
* —-   Balance, 113.                   Gases, Conduction of Heat by, 92.
--     Battery, 120.                    --  Liquefaction of, 20.
Induction, 118.                  - Specific Gravity of, 11.
Electricity, Distribution of, 110.                   Heat of, 69.
- Dynamic, 126.               Gelatine, 667.
-- Interference of, 112.      Glass, Composition of, 437...... Nature of, 106.                 -      of Antimony, 385.
of the Air, 125.            Glucinum, Glucina, 351.
Positive and Negative, 114.  Glucose, 533.
- ----- Statical, 107.                 Glycerine, 581.
-----   Theories of, 113.             Glycyrrhizine, 535.
Electrics and Non-electrics, 107.      Gold, 405.
Electro-chemical Theories, 187.        Gravity, Nature of, 11.
Electro-magnetism, 145.                Green, Brunswick, 455.
Electrolysis and Electrodes, 194.          - Emerald, 455.
Electrotype, 130.                             Scheele's, 455.
Elements, Nature of, 9.
Classification of, 238.      Heat, Central, of the Earth, 104.
Emetine, 632.                              - Conduction of by Solids, 92.
Epsom Salt, 434.                           - Interference of, 101.
Equivalent Decomposition, 206.             - Latent of Liquids, 70.
Ethal, 591.                                           Vapours, 76.
Ether, Luminiferous, 42.               --  of Liquefaction, 70.
- Sulphuric, 541.                 --  Polarization of, 101.
Etherene, 547.                         -- Radiation of, 94.
Ethers, Theory of the, 544. -- Reflection and Absorption of, 98.
Ethyl, 645.                                - Relation of to Light, 102.
Eudiometer, Use of the, 262.               - Repulsive Power of, 46.
Evaporation, 77.                      ---— Sources of, 105.
Spontaneous, 87.          -- Specific of Atoms, 66.
Excitation, Electrical, 106.                           Gases, 69.
Expansion by Heat, 46.                              - Solids, 63.
of Gases, 56.         -.        - Transmission of, 91.
*- --  Liquids, 58.               Heavy Spar, 342..-...     - Solids, 60.                Hematite, 362.
Hematosine, 674.
Fermentation, 539.                     Hematoxyline, 615.
Fibrine, 663.                          Hepar Sulphuris, 339.
Flame, Constitution of, 181.           Hydriodate of Phosphuretted H-ydrogeN
Flashing, 399.                             316.
Flints, 321.                           Hydriodic Acid, 315... — Liquor of,.437.                  Hydrobromic Acid, 318.
Fluidity, 70.                          Hydrochloric Acid, 307.
Fluobbrates, 327.                      Hydrofluoric Acid, 320.
Fluoride of Boron, 327                 Hydrofluosilic Acid, 324.
-------- Calcium, 430                  Hydrogen, 246.




INDEX.                                701
Hydrogen, Antimoniuretted, 388.       Manganese, Salts of, 443.
- Arseniuretted, 378.         Mannite, 535.:I —---    Oxide of, 253.             Marsh Gas, 563.
Peroxide of, 258.           Meconine, 609.
- Phosphuretted, 299.         Melam, 526.
-_ - Seleniuretted, 294.        Melamine, 526.
-   Sulphuretted, 292.        Membrane, Cellular, 671.
HIydro-oxygen Blowpipe, 251.         i Menthene, 578.
HIydruret of Arsenic, 378.            Mercury, 402.
-   Salts of, 461.
Indigo, Blue, 616.                    Mesitic Ether, 561.
Inuline, 529.                         Mesitylene, 561.
Iodine, 311.                          Metal, Bell, 393.
-- Compounds of, 313.                 --   Gun, 393.
Iridium, 409.                               Speculum, 393.
-  Salts of, 466.                 Metals, Properties of, 327.
Iron, 357.                            Methyl, Salts of, 644.
Magnetic Oxide of, 362.          Minium, 395.
- Malleable, 359.                     Molecular Cohesion, 19.
- Oxides of, 362.                     Molybdates, 373.
-  Passitivity of, 361.               Molybdenum, 373.
-   Pyrites, 363.                              -- Salts of, 451.
Salts of, 444.                   Mordants, Action of, 622.
-   Smelting of, 359.                 Morine, 615.
Sulphurets of, 363.              Morphia, 627.
Isomerism, 231.                       Mosaic Gold, 370.
Isomorphism, 221.                     Mucus, 679.
Isomorphous Groups, 223.              Multiple Proportions, 207.
Murexid, 688.
Kacodyl Compounds, 562.               Muriatic Acid, 307.
Kalium, 337.                          Myriospermine, 573.
Kermes Mineral, 386.
King's Yellow, 379.                   Napthaline, 647.
Kupfer Nickel, 365.                   Narcotine, 628.
Natrium, Natron, 342.
Lac-sulphuris, 339.                   Nickel, 365.
Lactinej 535.                              -  Salts of, 446.
Lactucine, 611.                       Nicotine, 635.
Lamp, Aphlogistic, 179.               Nitric Oxide, 273.
-- Safety, 183.                   Nitrogen, 26.
Lampblack, 479                             -    Oxides of, 272.
Lana Philosophica, 367.               Nitrous Oxide, 272.
Lanthanum, 351.                       Nomenclature, 149.
Latent Heat of Liquids, 70.
*_____ — — ____     Vapours, 76.      Ole'ine, 581.
Laws of Combination, 202.             Olivine, 607.
Lead, 394.                            Ologist Iron, 362.
Legumine, 538.                        Orcine, Orce'ine, 619.
Lichenine, 529.                       Or(anic Analysis, 476.
Light, Chemical Rays of, 173.                 Bodies, 467.
- - Wave Theory of, 42.               Orpiment, 379.
Lignine, 529.                         Osmium, 374.
Lime, 345.                                     Oxides of, 374.
- - Salts of, 430.                             Salts of, 451.
Liquefaction, 70.                     Oxamethane, 350.
Lithium, 342.                         Oxides of Aluminum, 349.
- - Salts of, 429.            - -     Antimony, 385.
Lymph, 683.                                     Arsenic, 377.
Barium, 342.
Madder, Colouring Bodies of, 613.         -     Bismuth, 397.
Magnesium, 348.                           -    Cadmium, 369.
— Salts of, 434.                  -     Calcium, 346.
Magnetism, 143.                             -  Cerium, 351.
Manganese, 352.                                Chlorine, 304.




702.I N D E X.
Oxides of Chrome, 371.               Polarization of Heat, 102.
~ —----    Cobalt, 366.                          - Light, 38.
--------  Copper, 392.               Polychrome, 610.
~- --- Glucinum, 35i.                 Populine, 610.
Gold, 405.                  Porcelain, Nature of, 437.
--------  Hydrogen, 253.             Potash, 337.
-.- hIridium, 409.           Potassium, 336.
--        Iron, 362.                     -     Oxides of, 337.
Lead, 394.                            Salts of, 421.
--       Lithium, 342.                          Sulphurets of, 339.
Magnesium, 348.  Proteine, 665.
Manganese, 353.             Puddling, 359.
- Mercury, 403. -               Purpurates, 688.
Molybdenum, 373.            Pus, 694.
Nickel, 365.                Putty, 370....-     Nitrogen, 272.              Pyrites, Copper, 390.
Osmium, 374.                   -- Iron, 363.
Palladium, 406.             Pyrometer, Daniell's, 54..... —--   Phosphorus, 296.          Pyrophorus, 339.
Platinum, 407.              Pyroxylic Spirit, 643.
Potassium,<, 337.
Rhodium, 409.               Quartation, 405.
Silver, 401.                Quartz, 322.
Sodium, 340.                Quassine, 610.
~ —--   Strontium, 344.              Quicksilver, 402.
- Thorium, 351.              Quinine, 624.
---— Tin, 369.
Titanium, 375.              Radiation of Heat, 94.
- Tungsten, 373.                          - Light, 32.
-- - --- Uranium, 390.               Radicals, Compound, 333.
Vanadium, 373.                       Nature of, 233.
Yttrium, 351.               Realgar, 379.
> —---- _Zinc, 367.                  Red Lead, 394.
Zirconium, 351             -     Precipitate, 403.
Oxychloride of Antimony, 453         Reflection of Heat, 96.
_-_-________- Bismuth, 458.            --        Light, 32.
__-_________ - Calcium, 430.         Refraction of Heat, 100.
- Chrome, 449.               --  Double, 34.
-   - -------- Copper, 455.-                   Single, 32.
c —- -------- Lead, 457.             Regular System, 26.
- Mercury, 462.          Respiration of Animals, 677.
--  - - ~Palladium, 466.      Rhodium, 409.
Oxygen, 241.                                  Salts of, 466.
Preparation of, 241.         Rutile, 375.
Oxyhydrogen Blowpipe, 251.           Rutiline, Rufine, 607.
Palladium, 406.                      Safety Lamp, 183.
Compounds of, 406.         Salop, 531.
Paracyanogen, 514.                   Salicyl Compounds, 573.
Pectine, 605.                        Salts, Constitution of, 410.
Perchlorates, 306.                       - Crystallization of, 23,
Periodates, 313.                          Isomorphism of, 221.
Permanganates, 357.                      - Solubility of, 22.
Pewter, 397.                         Salts of Alumina, 435.
Phenyl, Hydrate of, 648.                    Antimony, 453.
Phloridzine. 607.   -'                       Arsenic, 452.
Phosphates of Water, 297.                   Barium, 429.
Phosphites, 297.                     --  Bismuth, 458.
Phosphorus, 295.                            Cadmium, 448.
- ----- Compounds of, 296.           ---  Calcium, 430.
Photography, 175.                    -— Chrome, 449.
Piperine, 608.                              Cobalt, 446.
Platinum, 407.                              Copper, 455.
Polarization, Circular, 41.             --  Gold, 465.




I N D EX.                              703
Salts of Iridium, 466.                 Stibium, 384.
----  Iron, 444.                       Strontium, 344.
Lead, 457.                             O- Oxides of, 345.
- -~ Magnesium, 434.                             Salts of, 429.
Manganese, 443.                 Strychnine, 629.
Mercury, 461.                  Sugar of Liquorice, 536.
---  Molvbdenum, 451.                  Sugarcane, 531.
- --  Nickel, 446.                     Sulphites, 284.
-  Osmium, 451.                    Sulphocyanogen, 525.
-Palladium, 466.                   Sulphosinapisine, 574.
Platinum, 466.                 Sulphlr, 282.
---   Potassium, 421.                  Sulphurets of Aluminum, 350.
Rhodium, 466.                  -         - Antimony, 386.
Silver, 459.                        -       Arsenic, 379.
Sodium, 426.                           -- Barium, 344.
- ----  Strontium, 429.                        B- ismulth, 398.
--  Tin, 448.                       --       -- Cadmiuli 369.
Zinc, 447.                                   Calciumn,  347.
Santaline, 615.                                  - ChIome, 371.
Santonine, 610.                        -         - Cobalt, 367.
Saponine, 611.                         ------  Copper, 393.
Scillitine, 611.  -                                G-old, 405.;Selenium, 294.                                  - Hydrogen, 292.
Compounds of, 294.               -     -  I'on, 363.
Senegine, 611.                             -     - Lead, 395.
Silica, 322.                                     - Magnesium, 348.
Silicate of Alumina, 437.                       M- anganese, 357..-.. - ^Cobalt, 44-7.                            Mercury, 404.
Potash, 426.                       -- Molybdenum, 373.
- Soda, 429.                               - Nickel, 366.
Silicon, 321.                                   - Palladium, 407.
C- hloride of, 323.                          Platinum, 407.
--  Fluoride of, 324.            --        - Phosphorus, 299.
Silver, 399.                                       Potassium, 339.,
- - Oxides of, 401.                             - Selenium, 295.
Salts of, 459.                               Silver, 401.
Sulphurets of, 401.            _          - Sodium, 342
Simple Bodies, 9.                                  Strontium, 344.
__-_________- Tableof, 149.            --       - Tin, 370.
Skin, Nature of, 670.                              Zinc, 368.
Slacked Lime, 346.                     Synthetic Action of Galvanism, 199
Smalts, 447.                           Systerms of Crystallization, 26.
Smilacine, 611.
Soap, Manufacture of, 590.             Tantalum, 375.
Soda, 340.                             Telluret of Hydrogen, 389.
- Detection of, 340.              --     - Salts of, 454.
Sodium, 340.                           Tellurium, 389.
------ - Salts of, 426.                -       - Compounds of, 389.
Solanine, 633.                         Temperature, Nature of, 49.
Solder, 396.                           Thebaine, 629.
Solids, Conduction of Heat by, 92,     Theory, Atomic, 217.
-- Expansion of, 60.                      of Volumes, 213.
Specific Gravity of, 11.        Thermo-electricity, 139.
Specific Heat, 63.                    Thermometer, Nature of the, 49.
Speculum Metal, 393.                                Kinds of.~ 50.
Speiss, 365.                           Thermometric Scales, 53.
Spermaceti, 591.                       Thialb5. 548.
Spirit of Salts, 307.                 Thorium, 351.
Starch, 527.                          Tin, 369.
Steam, Elasticity of, 78.              -- Grain, 369.
Latent Heat ot; 76.               - Oxides of; 369.
- Motive Force of, 89.           Tincal, 429.
Stearine, 582.                        Titanium, 375.
Steel, 360.                           Transcalescence, 98.




)704                             I NDEX,
Tragacanthine, 530.                    Volta's Theory of Contact, 15,
Transfer of Elements, 194.             Volumes, Theory of, 213.
Tungsten, 373...... —-- Salts of, 451.               Water, Composition of, 253.
Types, Chemical, 234.                  Wave Theory of Light, 42.
-  -leat, 102.
Ulmine, from Soil, 637.                WVax, 592.
Uranium, 390.                          Welding, 359.
- -    Salts of, 454.                  White, Pearl, 458.
Urea, 684.                                — Vitriol, 447.
Urine, 689.
Xyloidine, 530.
Vanadium, 373.
Salts of, 451.               Yeast, 538.
Vaporization, 75.                      Yttrium, 351.
Vapours, Elasticities of, 78.                   Salts of, 443.
Latent Heat of, 76.
Volumes of, 77.               ZafTre, 366.
Veratrine, 631.                        Zinc, 367.
Ve;.milion, 404.                        -   Butter of, 447.
VitrIol, Oil of; 286.                  Zireonium, 351.
Voltaic Electricity, 126.                         s.- alts'of,.45.