085704 
 
 CfarngU MtttuBraitg Uibtarg 
 
 THE LIBRARY OF 
 
 EMIL KUICHLING, C. E. 
 
 ROCHESTER. NEW YORK 
 
 THE GIFT OF 
 
 SARAH L. KUICHLING 
 
 1919 
 
Cornell University Library 
 QD 151.E46 
 
 A manual of Inorganic chemistry, arranged 
 
 3 1924 004 974 436 
 
^2t 
 
 IT 
 
 K 
 
 E46 
 
The original of tliis book is in 
 tine Cornell University Library. 
 
 There are no known copyright restrictions in 
 the United States on the use of the text. 
 
 http://www.archive.org/details/cu31924004974436 
 
MANUAL 
 
 INORGANIC CHEMISTRY, 
 
 ARRANGED TO FACILITATE THE 
 
 EXPEEIIENTAL DEMONSTEATION 
 
 FACTS AND PEINCIPLES OF THE SCIENCE. 
 
 BY 
 
 CHARLES W. ELIOT, FRANK H. STORER, 
 
 PKOFESSOR OF ANALYTICAL CHEMISTRY I PBOFEBSOR OF CrENEBAL AND INDUSTRIAL 
 AND METALLURGY, I CHEMISTRY, 
 
 IX THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY. 
 
 SECOND EDITION. 
 
 (revised.) 
 
 NEW YORK: 
 
 IVISON, PHINNEY, BLAKEMAN, AND CO., 
 
 47 & 49 GREENE STREET. 
 
 1868. 
 
Entered according to Act of Congress in the year 1866, by 
 
 P. H. STOEEE AHB C. W. ELIOT, 
 
 In the Clerk's Office of the District Court of the District of Massachusetts. 
 
 LONDON 
 
 PRINTED BY TAYLOR AND FRANCIS, 
 llED LION OOUET, FLEET STREET. 
 
THE AUTHORS 
 
 INSCRIBE THIS BOOK TO THEIR TEACHER IK CHEMI8TKT, 
 
 PROF. JOSIAH P. COOKE, 
 
 OP HARVARD COLLEGE, 
 
 IS TOKEN OF 
 
 GRATITUDE AND FRIENDSHIP. 
 
TABLE OF CONTENTS. 
 
 PAGE 
 
 Introduction — Subject matter of Chemistry. Chemical change. Ana- 
 lysis and synthesis. Fact and theory . . . . 1-4 
 
 Cliap. I. — Air. Atmospheric pressure. Properties. Analysis. Air a 
 mixture. . Composition of air . . , 4-10 
 
 Chap. II.— Oxygen. Preparation and properties of oij-^gen. Oxygen sup- 
 ports combustion. Oxides. Oxidation. Wide diffusion of oxygen . . 11-15 
 
 Cliap. III. — Niti'ogen. Preparation and properties of niti'ogen . 16-18 
 
 ClXap. I V. — Water. Properties of water. The gramme. Specific gravitj'. 
 Specific heat. Ice. Steam. Analysis, electrolysis, and synthesis of.water. Hy- 
 drogen. At-oms and molecules. Molecular hypothesis. Atomic weights. Che- 
 mical combination. The chemical force. Water in nature. Distillation. Pre- 
 paration of pure water. Solution. Solution and chemical combination compared 18-39 
 
 Chap. V. — Hydrogen. Preparation and properties of hydrogen. Symbols. 
 Diffusion of gases. Diffusive power and infiammability of hydrogen. Heat 
 fifom burning hydrogen. Unit of heat. Oxyhydrogen blowpipe. Formof gas- 
 flames. Explosive mixtures of hydrogen and oxygen. Oxygen bums in hydrogen 
 as well as hydrogen in oxygen . .... 39-50 
 
 Chap. VI. — Compounds of oxygen, hydrogen, and nitrogen. Peroxide of 
 hydrogen. Mtric acid. One of the meanings of the terms acid and alkaline. 
 Ifeutralization. Nitrous oxide. Composition of nitrous oxide. Atomic weight 
 of nitrogen. Properties of nitrous oxide. Nitric oxide. ■ A test for free oxygen. 
 The terminations ous and ic. Hyponitrio acid. Nitrous acid. Analysis of nitric 
 acid. Synopsis of the oxides of nitrogen. Law of multiple proportions. Definite 
 and obscure chemical action. Air a mixture. Anhydrous and hydrated nitric 
 acid. Oxidizing and reducing agents. Atomic weights and combining weights. 
 Molecular formulfe. Combining weight of nitric acid. Nitric acid reactions. 
 Nitrogen and hydrogen. Ammonia. Analysis and synthesis of ammonia, 
 ■ Nascent state. Composition of ammonia. Ammonium. Salts of ammonium. 
 Sources of ammonia. Ammonia-water. Empirical and rational formulee. Dua- 
 listic formulsB. Typical formulae. Uses of symbolic formulee . . . 50-91 
 
 Chap. VII,— Chlorhydric acid. Properties, analysis, and composition of 
 chlorhydric acid. Atomic weight of chlorine. Synthesis of chlorhydric acid. 
 Manufacture of chlorhydric acid. Practical application of chemical equations. 
 Chemical affinity. Preparatioii and uses of ohiorhydric acid. Aqua regia . 91-105 
 
X CONTENTS. 
 
 Cna.p. vIII. — Chlorine. Preparation and propertiea of chlorine. Chlo- 
 rine-water. Metals bum in chlorine. Chlorine burns in hydrogen, and hydro- 
 gen in chlorine. Combustion in chlorine. Ueea of chlorine. How chlorine acts 
 in bleaching and disinfecting. Action of chlorine on ammonia. Chloride of 
 nitrogen. Oxides of chlorine. Hypochlorous acid. Chlorous acid. Hypo- 
 chloric acid. Chloric acid. Perchloric acid . . . 105-119 
 
 dia^p. IX. — Bromine. Bromhydric acid. Bromic acid. HypobroraouB 
 acid. Chloride of bromine. Bromide of nitrogen . . 119-123 
 
 dlSip. X, — Iodine. Extraction and properties of iodine. Testa for iodine, 
 lodohydrie acid. Iodic acid. Periodic acid. Iodide of nitrogen. Chlorides of 
 iodine. Bromides of iodine. The chlorine group of elements . - 123-135 
 
 Chap. XI.— Fluorine. Flnorhydric acid. Etching glass . . 135-139 
 
 Cliap. XII. — Ozone and Antozone. AUotropism. Frepax'ation and pro- 
 pei'ties of ozone. Tests for ozone. Ozone a disinfectant. Ozone in the atmo- 
 sphere. Preparation and propertiea of antozone. The antozone cloud. Ant- 
 ozone formed in all processes of combustion. Antozone oxidizes water. Differ- 
 ences between ozone and antozone .... . 139-154 
 
 Cliap. XIII. — Sulphur. Crystallization of sulphur. Crystalline structure. 
 The six systems of crystallization. Sulphur a dimorphous element. Change of 
 prismatic into octahedral sulphur. Methods of obtaining crystals. Soft sulphur. 
 Milk of sulphur. Metals burn in sulphur as in oxygen. Uses of sulphur. Sul- 
 pbydrio acid. Preparation, analysis, and properties of sulphydric add. Sul- 
 phuretted-hydrogen water. Sulphydi'io acid as a reagent. Ready decomposition 
 of sulphydric acid. Persulphide of hydrogen. Greek and Latin numeral prefixes. 
 Oxides of sulphur. Sulphurous acid. Preparation, properties, and composition 
 of sulphurous acid. Liquid sulphurous acid. Bleaching-power of sulphurous 
 acid. Oxidation of sulphurous acid. Bulphitea. Sulphuric acid. Manufacture 
 and properties of sulphuric acid. Its behaTior towards water and ice. Hydrates 
 of sulphuric acid. Sulphates. The terms monobasic, bibasic, &c Fuming sul- 
 phuric acid. Anhydrous sulphuric acid. Preparation and properties of anhy- 
 drous sulphuric acid. Hyposulphurous acid. Hyposulphites. Chlorides of 
 sulphur ..... ... 154-19S 
 
 Chap. XIV. — Selenium and Tellurium. Propertiea of selenium. Iso- 
 morphism. Atomic volume. Tellurium. Compounds of tellurium. The sulphur 
 group of elements .... 198-203 
 
 Chap. Xv. — Combination by volume. Synopsis of the gaseous compounds 
 previously studied. Condensation ratios. Combining-weight and volume -weight. 
 Double or product volume. Molecular condition of elementary gases. Mole- 
 cular formulae ... , . . 203-209 
 
 Chap. XVI. — Phosphorus. Allotropic modifications of phosphorus. Fric- 
 tion matches. Phosphorescence. Solutions of phosphorus. Poisonous pro- 
 perties of phosphorus. Manufacture of phosphorus. Red phosphorus. Amor- 
 phous and crystallized red phosphorus. Safety-matches. Phosphorus with 
 oxidizing agents. Phosphuretted hydrogen. Preparation and analysis of phoa- 
 
CONTENTS. xi 
 
 phuretted hydrogen gas. Composition of phosphui-etted hydrogen as compared 
 with that of ammonia. Unit-Tolmne weight of phosphorua twice its atomic 
 weight. Liquid and aohd phosphuretted hydrogen. Compounds of phosphorus 
 and oxygen. Bed oxide of phosphorus. Hypophoephorous acid. Phoephoroua 
 acid. Spontaneous combustion. Phosphoric acid. Hydrates of phosphoric 
 acid. Meta- and pyi-o-phosphoric aoids. Chlorides of phosphorus. Dissociation. 
 Bromides, iodides, and sulphides of phosphorus ... . . 209-241 
 
 Cnap. XVII — Arsenic. Sources and properties of arsenic. Arseniu- 
 retted hydrogen. Oxides of arsenic. Manufacture of arsenious acid. Iso- 
 merism. Properties and uses of arsenious acid. Beduction of arsenious acid. 
 Solubility of arsenious acid. Arsenic acid. Salts of arsenic acid ; their analogy 
 to the phosphates. Detection of arsenic in cases of poisoning. Diffusion of 
 liquids. Dialysis. Crystalloids and colloids. Destroying the organic matters. 
 Precipitation and reduction of sulphide of arsenic. Marsh's test. Chloride of 
 arsenic. Sulphides of arsenic. Sulphur-salts. Sulpharsenites and Sulphar- 
 
 Chap. XVIII. —Antimony. Sources, properties, and alloys of antimony, 
 Antimoniuretted hydrogen. Testing for antimony. Distinguishing between 
 arsenic and antimony, Teroxide of antimony. Antimoniate of antimony. An- 
 timonic acid. Metantimonic acid. Chlorides of antimony. Chloridizing agents. 
 Sulphides of antimony. Sulphur-salts . 266-281 
 
 Cnap. XIX. — Bismuth. Sources and properties of bismuth. Fusible 
 metal. Teroxide of bismuth. Bismuthio acid. Chloride of bismuth. Sulphide 
 of bismuth. The nitrogen group of elements . . 281-287 
 
 Chap. XX. — Carbon. AUotropio modifications of carbon. Diamond. 
 Graphite or plumbago, G-raphitic acid. G-as-carbon. Coke. Anthracite. 
 Charcoal. Preparation of charcoal. Distillation of wood and of coal. Illumi- 
 nating gas. Lampblack. Properties of charcoal. Beducing-power of charcoal. 
 Deflagration. Stability of charcoal. Charcoal absorbs gases. Induces combi- 
 nations. Disinfects. Decolorizes. Compounds of carbon and hydrogen. Or- 
 ganic chemistry. Homologous series. Marsh-gas or light carburetted hydrogen. 
 Atomic weight of carbon. Typical hydrogen compounds. Composition of illu- 
 minating gas. Carbonic acid. Preparation and properties of carbonio acid. 
 Ventilation of wells. Diffusion of gases. Solubility of carbonic acid. Carbonic 
 acid produced in the processes of fermentation, respiration, decay, and combus- 
 tion. Liquid and solid carbonic acid. Decomposition, analysis, and synthesis of 
 carbonic acid. Carbonates. Carbonic oxide. Preparation and properties of car- 
 bonic oxide. Carbonic oxide a deoxidizing agent. Heat evolved in the com- 
 bustion of carbonic oxide. Dissociation of carbonic oxide. Composition of car- 
 bonic oxide. Combustion. Luminosity of flames. The Btmsen burner. Quantity 
 and intensity flames. All flames gas-flaraes. Formof luminous flames. Blast- 
 lamps and blowpipes. Oxidizing and reducing flames. Chimneys. Indestructi- 
 bility of matter. Kindling-temperature. Flames and fires extinguished by wire 
 gauze and other good conductors. Safety-lamps. Flaming fires. Loss of heat 
 from incomplete combustion. Chlorides of carbon. Compounds of carbon and 
 nitrogen. Bisulphide of carbon .... 287-364 
 
 Chap. XXI.— Boron. Sources of boron compounds. AUotropism of boron. 
 Boracicacid. Chloride of boron. Fluoride of boron. Fluoboric acid. Sulphide 
 and nitride of boron . . 365-'172 
 
Xn CONTENTS. 
 
 Ulia,p. XXII. — Silicon. Abundance of silicon. Preparation of ailicon. 
 Modificafciona of ailicon. Silicon and hydrogen. Oxide of ailicon. Silicic acid. 
 Soluble silicicacid. Varieties of silicic acid. Silica in natural waters. Silicates, 
 ormulffi of silicates. Decomposition of silicates. Composition and formula of 
 silicic acid. Chloride of silicon. Composition of chloride of ailicon. Compound 
 of ailicon, hydrogen, and chlorine. Fluoride of ailicon. Muoailicic acid. Fluo-' 
 silicates. Sulphide of silicon. The carbon group . 372-391 
 
 Cha.p. XXIII. — Sodium. Sources of sodium salts. Chloiide of sodium. 
 Salt-works. Properties and uses of salt. Bromide and iodide of sodium. Sul- 
 phate of sodium. G-lauber's salt. Supersaturated solutions. Bisulphate of so- 
 dium. Carbonate of sodium. Leblanc's process. Soda-ash. Soda-crystals. 
 Bicarbonate of sodium. Yeast powders. Sulphidea of sodium. Metallic sodium. 
 Hydrate of sodium. Caustic soda. Bases and acids. Keplacement. Direct com- 
 bination. Phosphates of sodium. Borax. Borax as a blowpipe test Silicates 
 of sodium. Waterglasa. G-lass. Devitrified and colored glaaa. Hyposulphite 
 of sodium . . . 391-414 
 
 Oh^p. XXIv. — Potassium. Sourcea of potassium. Carbonate of potas- 
 sium. Bicarbonate of potassium. Hydrate of potassium. Caustic potash. 
 Strength of bases. Alkalimetry. Volumetric analysis. Valuation of potash and 
 soda-ash. Metallic potaasium. Cream of tartar. Chloride of potassium. Bro- 
 mide of potaasium. Iodide of potassium. Cyanide of potassiiun. Sulphides of 
 potaasium. Liver of sulphur. Sulphates of potaasium. Nitrate of potasaiimi. 
 Refining of saltpetre. Saltpetre not explosive. G-unpowder. Chlorate of potas- 
 sium . . . 414^-436 
 
 Clia.p. XXv. — Ammonium-salts. The hypothetical metal ammonium. 
 
 Hydrate of ammonium. Chloride of ammonium. Sulphate of ammonium. Ni- 
 trate of ammonium. Carbonates of ammonium. Sulphides of ammonium . . 437-443 
 
 C]ia.p. XX vl. — Lithium. Spectrum analysis. Kubidium and Csesium. 
 
 Thallium . ... . . 443^43 
 
 Cll£ip. XXVII. — Silver. Occurrence of silver. Extraction of silver. 
 Metallic silver. The terra metal. Acids and bases. Silver coin. Nitrate of 
 silver. Indelible ink. Oxides of silver. Fulminating silver. Photography. 
 The daguerreotype. Photography on glass. Photography on paper. Chloride 
 of silver. Atomic weight of silver. Bromide of silver. Iodide of silver. Cyanide- 
 of silver. Sulphide of silver. Sulphate of silver. The alkali group. Quanti- 
 valenee. Atomicity . . 448-466 
 
 Clia^p. XXVIII. — Calcium — Strontium — Barium — Lead. Calcimn. Car- 
 bonate of calcium. Calcareous petrifactions. Calc-spar and aiTSgonite. Oxide 
 of calcium. Hydrate of calcimn. Milk of Hme. Slaked lime. Mortar. Caustic 
 lime. Uses of lime. Sulphate of calcium. Plaster of Paria, or calcined gyx>aum. 
 Plaater eaata. Incruatation of steam-boilers. Hai-d water. Testing water. Phos- 
 phates of calciimi. Chloride of calcimn. Hypochlorite of calcium. Bleaching- 
 powder. Preparation of chlorine and oxygen from bleaching-powder. Chlori- 
 metry. Nitrate of calcium. Siilphydrate of calcium. Sulphite of calcium. Me- 
 tallic calcium. — Strontium and barium. Peroxide of barium. Making oxygen 
 with peroxide of barium. Strontium salts. Barium salts. Uaes of strontium 
 
CONTENTS, XUl 
 
 and barium salts. The calcium group. The alkaline earths.— Lead. Extraction 
 of lead. Separation of silver from lead. Oxides of lead. Corrosion of lead by 
 water. Leaden wafcer-pipes. Suboxide of lead. Protoxide of lead or litharge. 
 Cupellation. Peroxide of lead. Hed lead or minium. Sesquioxideoflead. Sul- 
 phides of lead. Chloride of lead. Sugar of lead. White lead. Silicate of lead . 467-500 
 
 CllSip. XXIX. — Magnesium — Zinc — Cadmium. Metallic magnesium. 
 Oxide of magnesium. Calcined magnesia. Hydraulic magnesia. Chloride of 
 magnesium. Sulphate of magnesium, or Epsom salts. Carbonate of magnesium. 
 Citrate of magnesium. Phosphate of magnesium and ammonium, — Zinc. G-ra- 
 nulated zinc. Chilvanized iron. The galyanic current. Correlation of forces. Re- 
 placement of one metal by another. Oxide of zinc. Chloride of zinc. Sulphate 
 of zinc. Alloys of zinc. — Cadmium, Sources and properties of cadmium. Unit- 
 volume weight of cadmium half its atomic weight. The magnesium group. . 501-511 
 
 Cll£Lp. XXX. — Aluminum — G-lucinum— Chromium — Manganese — Iron — 
 Cobalt — Nickel— TTranium. Metallic aluminum. Alloys of aluminum. Alumi- 
 num bronze. Atomic weight of aluminum. Oxide of aluminiun. Hydrate of 
 altmiinum. Aluminates. Mordants in dyeing. Lakes. Chloride of aluminum. 
 Sulphate of aluminiun. Alum. Acetate ' of aluminum. Silicates of aluminum. 
 Clay. Earthenware, bricks, and pottery. Glazes. Hydraulic cement. Concrete.— 
 G-lucinuin. — Chromitmi. Oxides of chromium. Chlorides of chromium. Sul- 
 phate of chromium. Chromic acid. Chromates. Photolithography. — Manganese. 
 Protoxide of manganese. Sesquioxide of manganese. Alums. Binoxide of 
 manganese. Manganic acid. Manganates. Chameleon mineral. Permanganic 
 acid. Permanganate of potassium. — ^Iron. Ores of iron. Extraction of iron. 
 The bloomary process. The blast furnace. Fluxes. Cast iron. Impurities of 
 iron. Wrought iron. The puddling process. SteeL The Sessemer process. 
 Protoxide of iron or ferrous oxide. Sesquioxide of iron or ferric oxide. Oxidation 
 by iron-rust. Ferric hydrate. Sulphide of iron. Iron pyrites. Chlorides of 
 iron. Ferrous sulphate or copperas. Ink. Dyeing. Ferric sulphate. Nitrates 
 of iron. Silicates of iron. Cyanides of iron. Prussian blue. Oxidizing ferrous 
 and reducing ferric salts. — Cobalt and nickel. The terminations ous and ie. — 
 Uranium. Salts of the sesquioxides. The sesquioxide group. Atomic volume of 
 the alums. Rare elements allied to aluminum and iron . . . .512-561 
 
 OKstp. XXXI. — Copper— Mercury. Extraction of copper from its ores. 
 Properties of copper. Alloys of copper. Dioxide of copper. Protoxide of copper. 
 Hydrate of copper. Sulphides of copper. Chlorides of copper. Sulphate of 
 copper. Nitrate of copper. "Verdigris. — Mercury. Its extraction and pro- 
 perties. Unit-volume weight of mercury half its atomic weight. Oxides of 
 mercury. Red oxide of mercury as a source of oxygen. Sulphides of mercmy. 
 Vermilion. CalomeL Corrosive sublimate. Mercuric iodide. Sulphates and 
 nitrates of mercury. Amalgams. Detecting mercury . . . ,562-577 
 
 Ch£tp> XXXII. — Titanium. Tin. Its ore. Its extraction and properties. 
 Tinning. Protoxide of tin. Binoxide of tin. Stannic acid. Metastannic acid. Btan- 
 nates. Sulphides of tin. Protochloride of tin. Its reducing-power. Bichloride 
 of tin. Alloys of tin. The tin group. ,. 577-585 
 
 Chap. XXXIII Molybdenum. Bisulphide of molybdenum. Oxides 
 
 of molybdenum.— Vanadium. Its occurrence. Its oxides.— Tungsten. Its occur- 
 rence and properties. Oxides of tungsten. Wolfram. Tungstale of aodium . 585-587 
 
XIV CONTENTS. 
 
 Clia.p. XXXIV. — Gold. Its wide diffusion. Its physical properties. In- 
 destructibility of gold. Eefining of gold. Chloride of gold. Gilding. Alloys 
 of gold. — Platinum. Chlorides of plafeiniun. Platinum sponge. Platinum black. 
 The platinum group . . ... . . 587-596 
 
 Clia,p._XXX V. — Atomic weights and symbols of the elements. Claasiflca- 
 tion. Natural groups. Atomic heats of the elements. Atomic heats of compounds. 
 Value of specific heats. Two sets of atomic weights in use. Barred symbols. 
 The student's view of discuaaions concerning theories . ... 597-605 
 
 Appendix. — Glass tubing. Gutting and cracking glass. Bending, drawing, 
 and closing glass tubes. Blpwing bulbs. Lam.pa. Blast-lamps and blowers. 
 Caoutchouc stoppers, tubing, and sheets. Corks. Cork-cutters. Patting tubes 
 through corks. Supports for vessels — iron stand, sand-bath, wire gauze. Pneu- 
 matic trough. Collecting gases. Safety-tubes. Gas-holders. Deflagrating- 
 spoons. Platinum foil and wire. Filtering. Filters. Drying of gasea. Drying- 
 tubes. Chloride- of-calcium tubes Spring clip. Screw compressor. Water- 
 bath. Iron retort. Self-regulating gas-generator. Glass retorts. Flasks. Beakers. 
 Test-tubes. Test -glasses. Measuring-glasses. Burettes. Eeading-off Burettes. 
 Pipettes. Wash-bottle. Porcelain dishes and crucibles. Eings to support round- 
 bottomed vessels. Crucibles. Tonga. Pincers. Mortars. Spatulse. Thermome- 
 ters. Furnaces. The metrical system of weights and measures. Table for the 
 couTereion of degrees of the centigrade thermometer into degrees of Fahrenheit's 
 thermometer. Table for the conversion of grammes into grains, and centimetres 
 into inches , i-xlii 
 
PREFACE TO THE SECOND EDITION. 
 
 The authors have thoroughly revised this second edition of 
 their manual. Practical experience in using the book with tvro 
 classes in the laboratory, the questions of students, and the 
 suggestions of friends have enabled them to improve some of the 
 detailed directions for experiments, and to make a few other 
 changes and additions calculated to smooth difficulties or supplj' 
 defects. Special pains have been taken to make the printing of 
 this edition as accurate as possible. 
 
 Boston, December 1867. 
 
PREFACE TO THE EIRST EDITION. 
 
 In preparing this manual, it has been the authors' object to 
 facilitate the teaching of chemistry by the experimental and 
 inductive method. The book wiH enable the careful student to 
 acquaint himself with the main facts and principles of chemistry, 
 through the attentive use of his own perceptive faculties, by a 
 process not unlike that by which these facts and piineiples were 
 first established. The authors believe that the study of a science 
 of observation ought to develop and discipline the observing 
 faculties, and that such a study fails of its true end if it become 
 a mere exercise of the memory. 
 
 The minute instructions, given in the descriptions of experi- 
 ments and printed in the smaller t3^e, are intended to enable the 
 student to see, smeU, and to^ph for himself; these detailed 
 descriptions are meant for laboratory use. In order to mark as 
 clearly as possible the distinction between chemistry and chemical 
 manipulation, the necessary instructions on the latter subject 
 have been put in an Appendix. In cases in which it is impossible 
 for every student to experiment for himself, the authors hope that 
 this manual wiU make it easy for the teacher, even if he be not a 
 professional chemist, to exhibit to his class, in a familiar and 
 inexpensive manner, experiments enough to supply ocular demon- 
 stration of the leading facts and generalizations of the science. 
 Judging from their own experience, the authors venture to hope 
 that even professional chemists may find it convenient to have 
 
TL PBEFACE. 
 
 always at hand the details of several hundred experiments, 
 covering the ground of an extensive course of chemical lectures. 
 
 The student of this manual is supposed to be already acquainted 
 with the rudiments of physics. The chemist must often depend 
 upon physical properties for his means of characterizing the 
 numerous substances with which he deals, and he is nearly con- 
 cerned with the physical properties of gases and vapors ; but 
 chemistry has now so wide a scope and so great an importance as 
 to deserve to be studied by itself, and not merely as an appendix 
 to the subject of molecular physics. 
 
 Like all elementary text-books, this manual is a mere compila- 
 tion ; it embodies in a somewhat new form previously existing 
 statements of weU-recognized facts and principles which have 
 become the common stock of the science. There is little original 
 in the book, except its arrangement and method, in part, and its 
 general tone. The authors have, of course, drawn largely from 
 the invaluable compilations made by GmeUn, Otto, and Watts, 
 and they have also availed themselves freely of the text-books of 
 Stoeckhardt and MiUer and the writings of Hofinann. 
 
 The book is not written in the interest of any particular theory 
 or system of notation, but is intended to exhibit, so far as is pos- 
 sible within the limits proper to an elementary manual, the present 
 state of the science. 
 
 The authors wiU feel very grateful to any one who will com- 
 municate to them errors, detected in using the book, or suggestions 
 for its improvement. 
 
 Boston, June 1867. 
 
MANUAL 
 
 OF 
 
 mOE&AIIC CHEIISTEY. 
 
 INTRODUCTION. 
 
 1. The various objects vMcli constitute external Nature pre- 
 sent to the observing eye an infinite variety of' quality and cir- 
 cumstance. Some bodies are hard, others soft ; some are brittle, 
 others tough or elastic ; some natural objects are endowed with 
 Hfe, — ^they grow ; others are lifeless, — they may be moved, but 
 never move themselves ; some bodies are in a state of incessant 
 change, while others are so immovable and unchangeable that 
 they seem everlasting. In the midst of this infinite diversity of 
 external objects, where lies the domain of Chemistry ? "What is 
 the subject-matter of this science ? 
 
 When air moves in wind, when water moves in tides, or in the 
 fall of rain or snow, the air and water remain air and water still ; 
 their constitution is not changed by the motion, however frequent 
 or however great. A bit of granite, thrown off from the ledge 
 by frost, is still a bit of granite, and no new or altered thing. If 
 a solid piece of iron be reduced to filings, each finest morsel is 
 metaUic iron still, of the same substance as the original piece, as 
 will appear to the eye if a morsel be sufficiently magnified under 
 the microscope. The melted, fluid lead in the hot crucible, and 
 the soUd lead of the cold bullet cast from it, are the same in 
 substance, only differing in respect to temperature. In all these 
 
CHEMICAL CHANGE. 
 
 cases the changes are external and non-essential, not intimate 
 and constitutional ; they are ealledjohysical changes. 
 
 2. Wien iron is exposed to the weather, it becomes covered 
 with a brownish, earthy coating which bears no outward resem- 
 blance to the original irOn ; and, if exposed long enough, the 
 metal completely disappears, being wholly changed into this very 
 different substance, rust. A piece of coal burns in the grate, 
 and soon it vanishes, leaving nothing behind but a little ashes. 
 Dead vegetable or animal matters, buried in the ground, soon 
 putrefy, decay, and disappear. So, too, the fragment of granite 
 which frost has broken from the ledge, exposed for centuries to 
 the action of air and rain, becomes changed ; it " weathers," and 
 after a time could no longer be recognized as granite. All these 
 changes involve alterations in the intimate constitution of the 
 bodies which undergo them ; they are called chemical changes. 
 
 Experiment 1. — Mix thoroughly 3 grammes (for Tables of the 
 Metrical System of Weights and Measures, see Appendix) of coarsely 
 powdered sulphvir with 8 grammes of copper filings, or fine turnings. 
 Put the mixture into a tube of hard glass, No. 3, p- n 
 
 about 12 centimetres long, and closed at one 
 end. (Tor the manipulation of tubing, see 
 Appendix, §§ 1-4.) Hold the tube by the 
 open end, with the wooden nippers, as in 
 Pig. 1, and heat the mixture over the gas-lamp 
 (Appendix, § 5), until both copper and sulphur 
 have disappeared. 
 
 Before heat was applied, the mixture of the 
 two substances was simply mechanical, ani the 
 copper might have been completely separated 
 from the sidphur, by due care and patience; 
 but during the ignition the copper and sulphur 
 have united chemically, and there has been 
 formed a substance which, while containing both, has no external 
 resemblance to either. In the new body, the eye can detect neither 
 copper nor sulphm-. 
 
 If 10 grammes of metallic iron he allowed to rust away completely 
 in moist air, the pile of rust which remains when the metal has disap- 
 peared, will weigh much more than 10 grammes. The iron has com- 
 bined with two of the constituents of the atmosphere, the gas called 
 oxygen and the vapor of water. The weight of the rust is the sum 
 
ANALYSIS AHJ) STNIHBSIS. 3 
 
 of the weights of the metallic iron, and of the water and oxygen with 
 which the iron has comhiaed. 
 
 Processes by which the whole character and appearance of the 
 bodies concerned are changed, as in these experiments, so tha;t 
 essentially new bodies are formed from the old, are chemical 
 processes. It is the function of the chemist, on the one hand, to 
 investigate the action of each substance upon every other, to take 
 note of the phenomena which attend this action, and to study the 
 properties of the combinations which result from it ; and on the 
 other, to contrive the resolution of compound bodies into their 
 simpler constituents. He further seeks the general laws by 
 which the intimate combinations of matter are controlled. With 
 these ends in view, the chemist endeavors to puU to pieces, or in 
 technical language, to analyze, every natural substance on which 
 he lays hands. Having thus found out the composition of the 
 substance, he seeks to put it together again, or to recompose it 
 out of its constituent parts. By one or both of these two pro- 
 cesses, analysis (unloosing) and synthesis (putting together), the 
 chemist studies all substances. 
 
 3. There are two qiiestions which the chemist asks himself 
 concerning every natural substance. First, Of what is it com- 
 posed ? With the means at his disposal the chemist may, or may 
 not, be able to resolve the substance into simpler constituents. 
 If he succeeds in decomposing it, he obtains the answer to this 
 first question ; if the body cannot be decomposed by any known 
 method of analysis, the substance must be regarded as being 
 already at its simplest. Such simple bodies are called elements. 
 Secondly, the chemist asks. Sow does this new substance com- 
 port itself when brought into contact with other substances already 
 familiar 1 There are sixty-five substances which are, at present, 
 admitted to be simple, primary substances, or elements. Of com- 
 pouna jodies, formed by the union of these elements with each 
 other, we find a series, numbering many thousands, in the inor- 
 ganic kingdom of Nature, comprising all the diversified mineral 
 constituents of the earth's crust ; while another series, far more 
 complex in composition, and almost innumerable in multitude, 
 exists in the vegetable and animal world. The task of tlie 
 chemist in thoroughly answering his second question would 
 
 b2 
 
4 TACI AND XHEOBT. 
 
 clearly be endless, were it not for the existence of general pro- 
 perties common to extensive groups of both elementary and 
 compound bodies, and of general laws which chemical processes 
 invariably obey. 
 
 WhUe, therefore, the chemist seeks the answers to the two 
 fundamental questions above stated, he is at the same time 
 inquiring what relations exist between the properties of a body 
 and its composition, and he is also studying that natural and 
 invariable sequence of chemical phenomena, which, when fuUy 
 known, will constitute the perfect science of chemistry. 
 
 4. Generalizations from observed facts, so long as they are 
 uncertain and incomplete, are called hypotheses and theories ; 
 when tolerably complete and reasonably certain, they are caUed 
 laws. The attention of the student should be constantly directed 
 to the keen discrimination between facts and the speculations 
 founded upon those facts — between the actual evidence (rf our 
 trained senses, brought intelligently to bear upon chemical phe- 
 nomena, and the reasonings and abstract conclusions based upon 
 this evidence — between, in short, that which we may know, and 
 that which we may believe. 
 
 CHAPTEE I. 
 
 5. We are everywhere surrounded by an atmosphere of invisible 
 gas, called air. All objects upon the earth's surface are bathed 
 with it. In motion, it is wind, and we recognize its existence 
 by its powerful effects; but in the stillest places it exists as 
 well. 
 
 The presence of air in any ordinary bottle, flask, or other 
 hollow vessel which is empty, in the sense in which this word is 
 ordinarily applied, can be shown very simply by attempting to 
 put some other substance into the vessel, under such conditions 
 that the air cannot pass out from it. Or the aix can actually be 
 
AIltOSPHERIC PEESSUEE. 5 
 
 pumped out of tke bottle ; and it can. be removed by other means, 
 both, mechanical and chemical. 
 
 Exp. 2. — Wrap around the throat of a funnel, -with narrow outlet, 
 a strip of moistened cloth or paper, so that the funnel shall 
 fit tightly into the nech of a bottle. After the funnel has Fig. 2. 
 been fitted to the bottle, as is shown in Fig. 2, fill it with 
 water, and observe that this water does not run into the 
 bottle. The bottle which we have called empty is in reality 
 fiUed with air, and it is this air which prevents the water 
 from entering the bottle. If, now, the funnel be lifted slightly, 
 so that the mouth of the bottle shall no longer be completely 
 closed by it, the air vsdthiu the bottle will pass out, and the 
 water in the funnel will instantly flow down. 
 
 6. In order to pump the air out of any hollow vessel, an appa- 
 ratus known as the air-pump is commonly employed. Descrip- 
 tions of this machine may be found in the text-books on physics. 
 For J)urposes of illustration, a portion, of the air can always 
 be removed by suction, or by mechanically displacing the air by 
 some other substance, as when the finger thrusts the air out of a 
 thimble. 
 
 Exp. 3. — Fit to any small flask or phial a perforated cork (for the 
 manipulation of corks, see Appendix, § 8), to which has been adapted 
 a short piece of glass tubiug. No. 7. Tie upon this glass tube a short 
 piece of caoutchouc tubing. Suck part of the air out of the flask, and 
 then nip the caoutchouc tube with thumb and flnger, so that no air 
 shall reenter. Immerse the neck of the flask in a basin of water, and 
 release the caoutchouc tube. Water will instantly rise into the flask 
 to take the place of the arc which has been sucked out. 
 
 7. The water, in this experiment, is forced into the flask by 
 the pressure of the superincumbent atmosphere. Air has weight. 
 It is subject to the law of gravitation, and is attracted towards 
 the earth's centre iu the same way as other ponderable matter. 
 It has' been found by experiment that a litre of dry air, at the 
 temperature of 0°, and under a pressure of 760 mUlimetres, 
 weighs 1-2932 gramme. It has also been determined by the 
 physicists that the force with which the air is attracted to the 
 earth is on an average equal to a weight of 1-033 kilogramme 
 to the square centimetre of surface. That is to say, the ocean 
 of air above us presses down upon every square centimetre of 
 the earth's surface with a force equal to that which would be 
 
PEOPEETIES OP AIK. 
 
 exerted by a bar of metal, or other substance, a centimetre square 
 in section, and long enough to weigh 1'033 kilogramme. 
 
 If such a bar were constructed of iron, it would be 1-3 metre 
 long ; if of water (and a bar of this substance can readily be 
 made by enclosing the water iu a tube), it would be 10'33 metres 
 long ; if of mercury, 76 centimetres long. A clear conception of 
 the atmospheric pressure is important to the chemist, because of 
 its bearing upon the mechanical collection, manipulation, and 
 measurement of gases. 
 
 8. In addition to the qualities already mentioned, we find au- 
 to be tasteless, and odorless, colorless when in small depths, but 
 exhibiting a blue tint when seen in large masses, as when in the 
 absence of clouds we look at the sky, or at a distant mountain. 
 Several of its properties are not peculiar, but are common to all 
 gases. Dry air obeys precisely the law of Mariotte up to a pres- 
 sure of several atmospheres ; that is to say, its volume diminishes 
 or increases in proportion to the pressure to which it is sub- 
 jected ; but it has never yet been condensed to a liquid. Upon 
 being heated one degree centigrade, it expands -^-fj, or in other 
 terms 0-003665, its volume at 0° At the temperature of 0°, air 
 is 773 times lighter than water at 4° ; that is, than water at its 
 maximum density. 
 
 These physical properties of air have been enumerated in order 
 to a distinct acquaintance with this gas, and that we may more 
 clearly comprehend its chemical properties as we now proceed to 
 study them. 
 
 9. Of what is air composed^ When a bar of iron is heated 
 in the air, as at a blacksmith's forge, it becomes covered vrith a 
 coating, which flies off in scales when the iron is beaten upon the 
 anvU. If a bit of tin be melted in a shallow crucible, its surface 
 soon becomes covered with a white earth, or ashes. At a high 
 temperature both iron and tin slowly bui~n hi the air, and are 
 converted into earth or ashes. With the exception of gold, silver, 
 platinum, and a few other exceedingly rare metals, aU the metals 
 bum, or rust, when heated in the air. If no air be present, this 
 rust or ashes will not be formed, however long or intensely the 
 metal may be heated. But in what manner is the rust formed ? 
 Is something driven out of the metal into the air, or does some- 
 
AKAITSIS OP AIE. 7 
 
 thing come out of the air and unite with the metal ? Experi- 
 ment shall answer. 
 
 Exp. 4. — Place 20 grammes of tin-foil in a porcelain dish, 4 or 
 5 cm. in diameter. Counterbalance the dish, with its contents, upon 
 scales which will turn promptly with 0-5 grm. when thus loaded. 
 Heat the dish, placed upon the wire gauze of the iron-stand (see Ap- 
 pendix, § 9), over the gas-lamp moderately and continuously for two 
 or three hom-s, or until a large part of the metal has been converted 
 into ashes. To facilitate the change, move the dish frequently, so 
 that a new surface of metal shall be often exposed to the air. Replace 
 the dish, when perfectly cool, upon the pan of the balance, and observe 
 that the weight of the dish and its contents has very decidedly in- 
 creased. 
 
 A more rapid demonstration may be obtained by substituting for 
 the tin-foil a piece of magnesium wire or ribbon. This metal takes 
 fire when touched with a lighted match. 
 
 10. It is possible that during the heating the metal may have 
 lost something, but it is certain that it has gained more. This 
 additional matter has not come from any alteration in the dish, 
 for it is made of materials expressly adapted to resist such treat- 
 ment, and a little cleaning will restore it to exactly its original 
 condition. "We have, then, taken something out of the air, 
 which, gaseous in the air, has become solid in the white ashes of 
 the tin. 
 
 If this something with which the tin has united can be sepa- 
 rated again from the metal, and restored to the gaseous condition, 
 it will be easy to compare it with common air, and so learn 
 whether the matter which combined with the heated tin is air 
 itself, or only a part of the air. It is quite possible to recover 
 the gas which enters into the composition of the rust of iron, or 
 copper, or tin ; but the processes required are too circuitous for 
 the present purpose. From the rust of other common metals, 
 such as lead, manganese, or mercury, the absorbed gas can be 
 very easily expelled. The rust of mercury is the most easily 
 decomposed. Mercury-rust may be prepared by the long heating 
 of the metal in the air, in a manner strictly analogous to the 
 method already applied to the preparation of tin-rust. 
 
 Exp. 5. — Put into a tube of hard glass, No. 3, about 12 cm. 
 long, and closed at one end as in Exp. 1, 10 grammes of the rust of 
 
AlfAlTSIS OF ATB. 
 
 mercury, a substance which is sold under the name of red oxide 
 of mercury. Such tubes of hard glass will be hereafter designated 
 as " ignition-tubes." Attach to this ignition-tube, by means of a per- 
 forated cork, or caoutchouc stopper, a 
 delivery-tube of glass. No. 8, of such ^^S- ^• 
 
 shape and length that it shall reach 
 beneath the inverted saucer in the 
 pan of water, as represented in Fig. 3. 
 The point of departure, for the con- 
 struction of the apparatus, is the top 
 of the gas-lamp placed upon the foot 
 of the iron-stand ; the end of the ig- 
 nition-tube should be about 4 cm. r-Hh^^ 
 above the top of the lamp. The ^^^^^^^. 
 other details of the apparatus maybe ^^ 
 
 learned from the figure. 
 
 Upon lighting the lamp, the air within the ignition- tube will ex- 
 pand, and a portion of it will pass out through the delivery-tube. This 
 air should be collected in a small bottle by itself, and thrown away. 
 The volume of air thus thrown away should of course not be much 
 greater than that of the tubes. (For a desaiption of the pneumatic 
 trough, see Appendix, § 10.) 
 
 As the ignition-tube becomes hot, gas will be freely given off from 
 the red oxide of mercm-y contained in it. It is necessary to avoid 
 heating intensely a single small spot of the ignition-tube, lest the glass 
 soften, and, yielding to the pressure from within, blow outward, and 
 so spoil the tube and arrest the experiment. The gas-flame should be 
 so placed and regulated as to heat 3 or 4 cm. of the tube at once. 
 Collect the escaping gas in bottles of 100 to 150 c c. capacity. 
 
 As soon as the disengagement of gas slackens, lift the iron-stand up, 
 and take the deli very- tube out of the water, taking care that no water 
 shall remain in the end of the tube. Then, and not tiU then, extinguish 
 the lamp. (See Appendix, § 10.) In the upper part of the ignition- 
 tube, and sometimes in the delivery-tube also, metallic mercvuy will be 
 found condensed in minute globules. The liquid metal is volatile at 
 the temperature to which it has been subjected, and has distilled away 
 from the hot part of the tube, and condensed upon the cooler part. 
 
 Thus is recovered the metallic mercury from which the red 
 
 mercury-rust was originally prepared by long heating in contact 
 
 with air. Is the gas, which the mercury originally took from the 
 
 atmosphere, air itseK, or something different ? 
 
 Exp. 6. — Introduce a lighted splinter of soft wood into a bottle of 
 
AlB A MIXItTEB, 9 
 
 the gas collected in the last experiment. It will burn with much 
 greater hrilliaacy than in the air. Attach a bit of wax taper to a 
 piece of wire ; light the taper, blow it out, and while the wick still 
 glows, introduce it into a second bottle of the gas of Exp. 5. The 
 glowing wick will Ijurst into flame, and the taper will burn with ex^ 
 traordinary brilliancy. 
 
 11. It is very obvious, from these experiments, that the gas 
 which enters into the composition of mercury-rust is not air 
 itself. But since it came originally from the air, if it is not the 
 whole of air, it must be a part or constituent of air. This gas, 
 which causes combustible substances to bum with such intensity, 
 is indeed a constant constituent of the air, and a thorough study of 
 all its properties will hereafter convince us that it is a chemical 
 element of very various powers and great importance. It is called 
 oxygen, and under this name it wiU form the subject of the next 
 chapter. 
 
 12. But if oxygen be not air itself, but only a constituent of air, 
 it follows that air must have other constituents, or at least one 
 other constituent. If mercury be long heated in contact with a 
 certaiu confined portion of air, it wiU abstract from this air, as we 
 have seen, one of its ingredients, namely, oxygen, and there will be 
 left behind whatever of air is not oxygen. This experiment, the 
 original one by which the illustrious chemist Lavoisier demon- 
 strated that air is a constant mixture of two different gases, 
 deserves carefal study, both for its philosophical value and its 
 historical importance. The actual experiment lasts several days, 
 and is therefore unsuitable for repetition by the student. A 
 description of it will suffice. 
 
 Into a flask, provided with a long neck, some metallic mercury was 
 introduced ; the neck of the flask was then bent, as shown in Fig 4, 
 the flask placed upon a furnace, and the end of the neck plunged into 
 a basin of mercury; a jar was then placed over the end of the tube, 
 and a portion of the air within the jar was sucked out by means of a 
 bent tube ; the mercury thereupon rose in the jar, and the point at 
 which it stood was accurately noted. The thermometer and barometer 
 were also simultaneously observed. Fire was then lighted in the 
 furnace, and the heat maintained for twelve days at a point just below 
 that required to make the mercury boil. The mercury became gra- 
 dually covered with red scales, and the air in the jar, which at first 
 expanded from the action of the heat, slowly decreased in bulk until 
 
10 
 
 COMPOSIirOK OF AIR. 
 
 tvesk scales were no longer formed. From these red scales Lavoisier 
 obtained, by tie method already exhibited (Exp. 5), the element oxy- 
 gen. The residual air in the jar proved, on examination, to be unfit 
 for the support of combustion and 
 of animal life ; a candle was in- 
 
 Fig. 4. 
 
 stantly extinguished by it, as if 
 plunged in water, and small ani- 
 mals, thrust into the gas, died in 
 a few seconds. The gas is, in 
 reality, a second elementary sub- 
 stance, distinguished by marked 
 chemical and physical peculiari- 
 ties. It is called nitrogen, and 
 under this name will be more 
 completely studied in another chapter. 
 
 13. The experiment of Lavoisier not only affords the means of 
 separating the two different gases of which air is composed, but 
 also determines the proportions in which they are mixed in air. 
 If the diminution in bulk which the air in the jar undergoes 
 during the whole progress of the experiment be accurately 
 measured, it wiU be found that the bulk of the residual gas, the 
 nitrogen, is only four-fifths of the original volume of air. The 
 lost fifth is the oxygen which has combined with the mercury. 
 The air, then, is not an element, but is compound, and its two 
 principal ingredients are the elementary bodies oxygen and 
 nitrogen, mixed in the proportion of four measures of nitrogen 
 to one of oxygen. It is quite possible to prove by synthesis 
 what analysis has thus taught. On putting together four mea- 
 sures of nitrogen and one measure of oxygen, a mixture is ob- 
 tained, which, except by very refined experiments, is not to be 
 distinguished from pure air. Aqueous vapor is another normal 
 constituent of the actual atmosphere, and small traces of other 
 gases than nitrogen and oxygen are always present in it, as will 
 be set forth hereafter. 
 
OSTREN. 11 
 
 CHAPTEE IT. 
 
 OXTG E N. 
 
 14. Oxygen gas may be prepared by heating red oxide of 
 mercury, as described in Exp. 5 ; or, far more conveniently, by 
 heating a mixture of chlorate of potassium and black oxide of 
 manganese. For the present we have to regard these substances 
 merely as materials suitable for the preparation of oxygen. Their 
 constitution will be studied hereafter. 
 
 Exp. 7. — Mix intimately 6 grms. of chlorate of potassium with 
 5 grms. of black oxide of manganese, which has been previously well 
 dried. Place the mixture in a tube of hard glass, No. 1, 12 or 15 cm. 
 in length. Attach to this ignition-tube, by means of a perforated 
 cork or caoutchouc stopper, a delivery-tube of glass. No. 7, as repre- 
 sented in Fig 3, and described upon page 8. Heat the mixture in the 
 ignition-tube and collect the gas which will be given off, in bottles or 
 jars of the capacity of about 250 c. c. The first 100 c. c. or so of gas 
 should be rejected, since it wiU be contamiaated with the air origi-' 
 naUy contained in the apparatus. 
 
 It is easy to determine the moment at which the evolution of oxygen 
 commences, by noting the increased size of the bubbles of this gas as 
 contrasted with those of the expanded air, and the greater rapidity 
 with which the bubbles of oxygen come over. For every grm. of 
 chlorate of potassium taken, about 230 c. c. of oxygen gas should be 
 obtained. 
 
 Besides the general precautions described under Exp. 5, the follow- 
 ing should here be observed. 1. Both the chlorate of potassium and 
 the oxide of manganese should be perfectly dry and pure— that is, free 
 from moisture, dust, or particles of organic matter. 2. So soon as the 
 oxygen begins to be delivered, the heat beneath the ignition-tube 
 should be diminished, if need be, and so regulated that the evolution 
 of gas shall be tranquU and imiform. 3. The uppermost portions of 
 the mixture should be heated before the lower. 4. An ignition-tube 
 should never be filled to more than one-third its total capacity, lest 
 portions of its contents be projected into the delivery-tube. The 
 chief danger to be guarded against in using ignition-tubes is the stop- 
 page of their outlets with soUd matter. 5. The ignition-tube shoitld 
 
12 
 
 PEOPEETIES OF OXTeEN. 
 
 always be inclined as represented in Fig. 3, and never placed upright 
 in the flame. 
 
 The oxygen thus obtained is to be employed in the experiments 
 shortly to be described. In case large quantities of oxygen are needed, 
 a similar mixture of equal weights of chlorate of potassium and black 
 oxide of manganese is heated in a retort of iron or copper, and the gas 
 is collected in large metallic vessels, called gas-holders, such as are 
 described in § 11 of the Appendix. 
 
 Besides the methods above described, there are many other 
 ways of preparing oxygen. Several of these methods mil be 
 described hereafter, when the materials employed can be intelli- 
 gently studied. 
 
 15. Oxygen is a transparent and colorless gas, not to be dis- 
 tinguished by its aspect from atmospheric air. Like air, it has 
 neither taste nor smell. It is, however, somewhat heavier than 
 air. If the weight of a measure of air be taken as 1, then the 
 weight of the same measure of oxygen is found to be 1-1056. 
 At 0°, and a pressure of 760 m.m. of mercury 1 litre of oxygen, 
 gas weighs 1-4298 grm. 
 
 Since oxygen is thus heavier than air, it is not absolutely necessary, 
 in collecting it, or transferring it from one vessel to another, that we 
 should operate over water, as has been directed. When a gas is much 
 heavier, or much lighter, than atmospheric air, it may often be con- 
 veniently collected by displacement. A l^ottle can readily be filled 
 with oxygen fi.-om the gas-holder by carrying the delivery-tube to the 
 bottom of the upright bottle, and allowing the gas to flow in slowly, 
 as if it were water. In a short time the air will be wholly displaced, 
 and the bottle tilled with oxygen. The progress of the operation can 
 be followed by testing the contents of the upper part of the bottle ii'om 
 time to time, with a glowing match ; when this bursts sharply into 
 flame the gas may be assumed to be pm-e enough for aU ordinary 
 pui-poses. 
 
 16. Oxygen has never yet been reduced to the liquid condition. 
 Of all known substances it exerts the smallest refracting power 
 upon the rays of light. Compared with that of atmospheric air, 
 its refractive power is as 0-830 to 1-000. The specific heat of 
 oxygen, compared with that of an equal weight of water taken as 
 unity, is 0-2182 ; it has a lower capacity than other gases for 
 absorbing and radiatipg heat. Water dissolves it in smsill pro- 
 portion J 100 volumes of water dissolve, at the ordinary tempera- 
 
OXTSEN STJPPOETS COMBITSTIOlf. 13 
 
 ture, about 3 volumes of oxygen. It extibits decided magnetic 
 properties. A glass tube filled witb oxygen and suspended by a 
 fibre of sUk between the ends of a strong horse-shoe magnet soon 
 comes to rest in such a position that its long axis is parallel to a 
 line drawn between the two poles. As with iron, its susceptibi- 
 lity to magnetization is diminished, or even temporarily suspended, 
 by a sufficient elevation of temperature. Its magnetic force, com- 
 pared with that of the air, is as 17'6 to 3-4, that of a vacuum being 
 taken as 0. 
 
 17. A striking characteristic of oxygen is its power of sup- 
 porting combustion. This has already been illustrated in Exp. 6, 
 and may be further exhibited by a great variety of experiments. 
 
 Exp. 8. — Place in a deflagrating spoon (see Appendix, 
 § 12), a bit of sulphur as large as a pea. Light the sul- 
 phur, and thrust it into a bottle of oxygen. It will bum 
 with a beautiful blue flame, and much more brilliantly 
 than in air. An acid, suffocating gas is produced. 
 
 Exp. 9. — Place a piece of charcoal, that of bark is 
 best, in a deflagrating spoon. Kindle the charcoal by 
 holding it in the flame of a lamp, and then introduce it 
 into a bottle of oxygen. It will bum vividly, throwing 
 off brilliant sparks if bark charcoal has been employed. 
 
 In this experiment, as in the preceding, the products of the com- 
 bustion are obviously gaseous, no solid substance being formed. 
 
 Exp. 10. — A piece of phosphorus, the size of a small pea, having 
 been well dried between pieces of blotting-paper, is placed in a defla- 
 grating spoon, touched with a hot wire or a lighted match, and then 
 thrust into a jar of oxygen. It will bum with intense brilliancy and 
 the formation of a dense white smoke. 
 
 It should be observed that phosphorus is a substance which inflames 
 very readily in the air, when subjected to friction or any slight eleva- 
 tion of temperature. It is hence so dangerous that it must always be 
 kept under water. It should also be cut under water. 
 
 18. Many substances commonly called incombustible, because 
 they do not bum readily in ordinary air, bum vigorously in 
 oxygen. Of these, metaUie iron may be taken as an example. 
 
 Exp. 11. — Convert two-thirds of a piece of fine piano-wire 20 or 
 30 cm. long into a spiral, by winding it tightly around a glass rod, 
 No. 6, or lead pencil, and then withdrawing the rod or pencil. Thrust 
 the straight end of this wire into a cork or piece of thin board large 
 
14 OXIDES. 
 
 enough to cover one of the bottles of oxygen obtained in Exp. 7. 
 Upon the lower end of the wire coil tie a small piece of waxed 
 thread, or touch with a bit of melted sulphur the end of the spiral, so 
 that a small bead of sulphur shall adhere to the wire. Kindle the 
 thread or sulphur, and quickly place the wire in a bottle of oxygen, at 
 the bottom of which has been spread a layer of sand. 
 
 The burning sulphur heats the iron to redness, which then burns 
 brilliantly, with scintillation. From time to time, glowing balls of 
 molten matter fall off from the wire, and bury themselves in the sand 
 at the bottom of the bottle, or even melt into the glass. 
 
 If an abundance of oxygen be at hand, this experiment had better 
 be performed in a jar of 2 or 3 litres capacity, — a watch-spring which 
 has been rendered flexible by igniting it, and then allow- 
 ing it to cool slowly, being the best material with which to F'?- 6. 
 form the spiral coil. In this case it is well to tie a bit of 
 tinder upon the end of the coil as the kindling material, or 
 to attach a piece of twine to the wire, and soak this in 
 sulphur. But the experiment succeeds weU even in very 
 small bottles of oxygen, provided the wire be fine, and 
 that the quantity of sulphur, or other matter, employed 
 for kindling be not too large. 
 
 19. This experiment clearly proves what has been already 
 stated, that iron, when red-hot, combines with oxygen. It is 
 the burnt or oxidized iron which falls in globules to the bottom 
 of the bottle. This substance is called oxide of iron. The com- 
 pounds which are formed by the union of oxygen with other 
 elements are called oxides. The substances which have been 
 heretofore mentioned under the more familiar name of rust, like 
 iron-rust, tin-rust, mercury-rust, are called in chemistry oxides 
 — as the oxide of iron, oxide of tin, and oxide of mercury. 
 
 20. It wiU have been observed that the combinations obtained 
 in the foregoing experiments are of very various quality. Some 
 of these compounds are soHd, others gaseous ; some are acid and 
 caustic, while others are tasteless and innocuous. They agree 
 only in this, that they all contain oxygen. AH these bodies wiH 
 be studied in detail hereafter. It concerns us now more particu- 
 larly to realize the number and variety of the bodies into which 
 oxygen enters as an essential ingredient. In fact, the most 
 important quality of oxygen is that, with a single exception, it 
 unites with all the other elements to form compounds. 
 
OXIDATION. 15 
 
 This act of combination is often accompanied by development 
 of light and heat, as in the foregoing experiments ; in the 
 affairs of common life we daily witness similar effects . All the 
 ordinary phenomena of fire and light depend upon the union of 
 the body burned with the oxygen of the air. Indeed, the term 
 combustion may for all ordinary purposes be regarded as synony- 
 mous with oxidation. 
 
 Combustion is less vivid in air than in pure oxygen, because 
 of the nitrogen with which the oxygen of the air is diluted. If 
 a substance combines slowly with oxygen, it may often happen 
 that no evolution of heat or Hght can be detected. Thus, when 
 a small piece of iron rusts at the ordinary temperature of the air, 
 there is perceived neither light nor heat, although a combination 
 of iron and oxygen has been formed, as in Exp. 11. Heat is 
 really disengaged in the slow rusting of iron, as in every act of 
 chemical combination, but it is taken up and carried away by the 
 circumambient air at the moment of its formation, so that it can- 
 not usually be perceived. Slow oxidation, such as. this, is often 
 spoken of as slow combustion. 
 
 21. Many of the compounds of oxygen are very familiar 
 bodies. Indeed, oxygen is the most widely diffused and the most 
 abundant of all known substances. Not only does it occur in 
 the air, of which it constitutes about one-iifth the volume, as has 
 been already remarked, but at least one-third of the solid crust 
 of the globe is composed of it. It is the chief ingTedient of 
 water, as will appear in a subsequent chapter. It enters largely 
 into the composition of plants and animals. Silica, in all its 
 varieties of sand, flint, quartz, rock-crystal, &c., contains about 
 half its weight of oxygen, and the same is true of the various 
 kinds of clay, and of chalk, limestone, and marble. Oxygen is 
 absolutely essential to the maintenance of animal and vegetable 
 life. The chemistry of the respiration of animals depends upon 
 the absorption of oxygen from the air respired. In the absence 
 of oxygen suffocation ensues. 
 
16 
 
 CHAPTEE in. 
 
 NITEOGElf. 
 
 22. The common modes of obtaining nitrogen depend upon 
 the removal of oxygen from the air. 
 
 Exp. 12. — Fill a tube of hard glass, No. 2, about 36 centimetres 
 long, with bright, not too coarse, copper turnings; place this tube 
 upon a semicylindrical trough of sheet iron, and support it upon a 
 ring of the ii-on stand, as shown in Fig. 7. It is well to interpose a 
 thin layer of asbestos between the tube and the iron trough, in order 
 to prevent the glass from adjiering to the metal when it becomes soft 
 by heat. By means of corks, attach to one end of this tube a delivery- 
 tube leading to the water-pan, as shown in the figure, and connect the 
 
 Fiff. 7. 
 
 T 
 
 other end with a gas-holder iilled with air. Light the lamps (for a 
 description of these, see Appendix, § 5) beneath the tube which con- 
 tains the copper turnings, and wait until the copper has become red- 
 hot ; then allow air to flow slowly out of the gas-holder over the hot 
 metal. The heated copper wUl combine with the oxygen of this air, 
 and retain the whole of it, so that nothing but nitrogen will be delivered 
 at the water-pan. This nitrogen maybe collected in small bottles and 
 tested with lighted splinters of wood, which should be instantly ex- 
 tinguished on being immersed in it. 
 
 23. A still simpler method of preparing nitrogen is to burn 
 out the oxygen from a confined portion of air, by phosphorus, or 
 by a jet of hydrogen. 
 
PKOPEETIES OF NTTKOOEIT. 17 
 
 JExp. 13. — Float a small porcelain capsule upon the surface of the 
 water-pan ; a large cork must be placed beneath the capsule if the latter 
 win not float of itself. In the capsule put about a cubic centimetre of 
 phosphorus, and set it on fire. Invert over the whole a wide-mouthed 
 bottle, of the capacity of a litre or more, and hold this bottle so that 
 its mouth shall dip beneath the surface of the water. During the first 
 moments of the combustion, the heat developed thereby wUl cause the 
 air within the bottle to expand to such an extent that a few bubbles 
 of the air will be expelled ; but after several seconds water wiU rise 
 into the bottle to take the place of the oxygen which has united with 
 the phosphorus. 
 
 The dense white cloud, which fills the bottle at first, is a compound 
 of phosphorus and oxygen which is soluble in water. It will, there- 
 fore, soon be absorbed by the water in the pan, and will disappear, so 
 that at the close of the experiment nearly pure nitrogen will be left 
 in the bottle. But, as the phosphorus ceases to bum before the last 
 ti-aces of oxygen are exhausted (compare § 180), the nitrogen obtained 
 by this method is never absolutely pure. 
 
 As soon as the phosphorus goes out, the bottle should be shaken in 
 such a way that the porcelain capsule may be upset, and sunk in the 
 water- pan. The properties of the nitrogen may now be examined. 
 
 24. Nitrogen is a transparent, colorless, tasteless, odorless, 
 incondensable gas. It is not quite so heavy as air. If a mea- 
 sure of air weigh I gramme, then an equal measure of nitrogen 
 vriU weigh 0-9714 gramme. At 0°, and a pressure of 760 milli- 
 metres of mercury, 1 litre of nitrogen weighs 1-256 gramme. 
 The specific heat of the gas is 0-244, that of an equal weight of 
 water being 1-000. A litre of water at 0° dissolves only 20 cubic 
 centimetres of nitrogen. Its refractive power in regard to light 
 is to that of atmospheric air as 1-034 to 1-000. 
 
 25. In its chemical deportment towards other substances, nitro- 
 gen is remarkably different from oxygen. Whilst oxygen is 
 active and, as it were, aggressive, nitrogen, at least when in the 
 condition in which it exists in air, is remarkably inert and 
 indifferent as regards entering into combination with other 
 bodies. It is marked rather by the absence of salient character- 
 istics than by any active properties of its own. Many of the 
 metals, sulphur, phosphorus, and numerous other substances, may 
 be kept unchanged for any length of time in vessels filled with 
 nitrogen. A burning candle wiU instantly be extinguished when 
 
18 
 
 WATEE. 
 
 tkrust into a jar of nitrogen gas, for with the nitrogen the con- 
 stituents of the candle have no tendency to combine. 
 
 As it extinguishes flame, so it destroys life. Animals cannot 
 live in an atmosphere of pure nitrogen. It may, indeed, be 
 breathed for a short time with impunity, but it does not support 
 respiration. It is not poisonous ; if it were, it could not be 
 breathed in such large quantities as it is in air. An animal im- 
 mersed in it dies, simply from want of oxygen. 
 
 26. As a diluent of the oxygen in the air, nitrogen is essential 
 to the existing balance and order of Nature. AU animal and 
 vegetable life — most inanimate matter, even — stands in harmo- 
 nious relations with the chemical composition of the atmosphere. 
 The presence of so large a proportion of nitrogen in the air pre- 
 vents the too rapid action, as regards combustion and respiration, 
 that would take place in an atmosphere of unmixed oxygen. 
 
 Nitrogen is widely difiPused in nature. Besides occurring in 
 the air, it is a constituent part of all animals and vegetables, and 
 of many of the products resulting from their decomposition. 
 Notwithstanding the indisposition of nitrogen in the free state to 
 enter into combination, a very large number of interesting and 
 important compounds can be formed by resorting to indirect 
 methods of effecting its union with other elements. 
 
 CHAPTEE IV. 
 
 WATER. 
 
 27. Another natural substance, quite as common as air, is 
 water. Three-fourths of the earth's surface is covered with it. 
 It is diffused through the atmosphere in the form of vapor, and 
 is a constituent of all animal and vegetable substances, and of 
 many minerals. "We take up next this familiar substance, in 
 order that we may gain, through the study of it, a deeper insight 
 into chemical principles, and enlarge our experience by making 
 acquaintance with a new element. Let us first define with pre- 
 cision the external and physical properties of water, and then 
 
PEOPEBTIES OE WATBE. 19 
 
 apply the two chemical methods, of analysis and synthesis, to the 
 closer investigation of its essential nature. 
 
 28. At the ordinary temperature of the air, pure water is a 
 transparent liquid, devoid of taste or smell. In thin layers it 
 appears to be colorless, but large masses of it are distinctly blue, 
 as seen ia mid-ocean, in many deep lakes of pure water, and in 
 masses of ice, such as icebergs and some glaciers where it is pos- 
 sible to look through the ice from below. 
 
 This color can be seen upon the small scale by looking down through 
 a column of pure water, 2 metres long, upon pieces of white porcelain. 
 The water may be held in a glass tube, 5 cm. wide, which has been 
 blackened internally with lamp-black and wax to within 125 cm. of 
 the end, which is closed by a cork. Fill the tube with chemically 
 pure water, throw into it a few pieces of porcelain, and place it in a 
 vertical position, on a white plate. On now looking through the co- 
 limm of water at the bits of porcelain, which can only be illumined by 
 light reflected from the white plate through the rim of clear glass, it 
 will be observed that they exhibit a pure blue tint, the intensity of 
 which will diminish in proportion as the column of water is shortened. 
 The blue coloration may also be recognized when a white object is 
 illuminated through the column of water, by sunlight, and seen at 
 the bottom of the tube through a small lateral opening in the black 
 coating. 
 
 29. At 4°, the temperature at which it is densest, water is 
 773 times heavier than air at 0° ; at 15° it is 819 times heavier 
 than air of the same temperature. A cubic centimetre of water 
 at its greatest density, that is, at 4°, weighed in a vacuum, is our 
 unit of weight — a gramme. One litre of water, which measures 
 1000 cubic centimetres, therefore, weighs a kilogramme. Water 
 is compressible and elastic ; by the pressure of one atmosphere it 
 can be reduced to the extent of about 47-mitlionths of its original 
 volume, and this is true for every added atmosphere of pressure 
 so far as experiment has extended. "Water expands upon being 
 heated, though at a less rate than other liquids ; the rate of ex- 
 pansion increases with the temperature. Notwithstanding the 
 fact that water expands when cooled below 4°, as well as when 
 warmed above that temperature, its refractive power on light 
 continues to increase regularly below 4°, as though it contracted. 
 The refractive index increases continuously between -|-5-2° 
 
 c2 
 
20 
 
 PROPEEirES OP WATER. 
 
 and —1-3°, the direction of the variation not changing in the 
 passage through the point of maximum density. At 0° the index 
 is 1-333. 
 
 30. Pure water at 0°, a temperature always to be obtained by 
 melting ice, is taken as a standard to which the weights of equal 
 bulks of other substances, liquid or soUd, are referred. In other 
 words, the sp&Afio gravity of water is taken as 1 ; and in terms 
 of this unit the specific gravities of all other liquid and soUd sub- 
 stances are expressed. The specific gravity of gold, for example, 
 is 19-3 ; that is to say, the weights of equal bulks of water and 
 of gold are to one another as 1 to 19-3. 
 
 31. Water is also the standard of speciflc heat. By specific 
 heats are meant the relative capacities for heat of the same 
 weights of different substances, at the same temperature. For 
 example, to raise 1 kilogramme of mercury from 0° to 1° requires 
 only one-thirtieth of the quantity of heat necessary to raise 1 kilo- 
 gramme of water from 0° to 1°. Water having been made the 
 ■standard of specific heat, its capacity for heat is denoted by 1, 
 and that of mercury will accordingly be 0-033. At the same 
 temperature, and for equal weights, water has a greater capacity 
 for heat than any solid or liquid known. Hence it results that 
 the speciflc heats of all sohd and liquid substances are expressed 
 by fractions. 
 
 Water conducts heat very slowly; it may be boiled many 
 minutes at the top of the test-tube, which is held aU the while 
 by the lower end, in the fingers, without inconvenience. 
 
 32. When exposed to a certain degree of cold, water crystal- 
 lizes, with formation of ice, or snow, according to circumstances ; 
 and upon being heated sufficiently it is transformed into an 
 invisible gas, called steam. Both these changes, however, are 
 purely physical, and therefore do not fall within the province of 
 this manual. The chemical composition of the water is the 
 same, whether it be liquid, soM, or gaseous. The temperature 
 at which ice melts is one of the fixed points of the centigrade 
 thermometer, numbered 0°, and the temperature at which water 
 boUs, under a pressure of 76 cm. of mercury, is the other fixed 
 point, numbered 100°. Water evaporates at all temperatures 
 and is therefore a constant ingredient of the atmosphere. Even 
 
STEAM. 21 
 
 ice slowly evaporates, at temperatures far below 0°, without first 
 passing iato the liquid condition. 
 
 In crystallizuig, that is to say, in assuming the soKd form, 
 water increases in volume. The specific gravity of ice is only 
 0"916, which is equivalent to saying that, in the act of freezing, 
 916 c. c. (cubic centimetres) of water will be changed iato a Htre 
 of ice. From this fact result many familiar phenomena, such as 
 the floating of ice, the upheaving and disintegrating action of 
 frost, and the bursting of pipes' and 'other hollow vessels when 
 water is frozen in them. The crystals of ice belong to the so- 
 called hexagonal system ; they are six-sided prisms, with regular 
 faces ; by agglomeration they produce stellar and fernrlike forms 
 of infinite variety and great beauty. Ice is a slow conductor of 
 heat, and a non-conductor of electricity. It becomes electric by 
 friction. 
 
 Steam is a colorless, transparent gas, as invisible as atmo- 
 spheric air. It is lighter than air, the weight of any given 
 volume of steam, at the ordinary temperature, being to that of 
 the same volume of air as 0-622 to 1, a ratio deduced by calcula- 
 tion from the composition of steam. At 100°, the boihng-point 
 of water, the ratio of the weights of equal volumes of steam and 
 air is 0-455 to 1, and one volume of water furnishes about 1700 
 volumes of steam of 100°. When steam is heated by itself, vdth- 
 out the presence of any liquid water, it is called superheated 
 steam; but when there is water present, so that no excess of 
 heat can accumulate in the steam, above the quantity needed for 
 its formation under the pressure at which it exists, the steam is 
 called saturated, meaning saturated with water. When steam 
 escapes into the air, there is formed a multitude of little bubbles 
 or vesicles, composed of a film of water filled with air, precisely 
 s imil ar to the vesicles seen in clouds and fogs. This steam-cloud 
 is sometimes improperly spoken of as steam or vapor, an error 
 against which the student should be upon his guard. Similar 
 fogs of air-filled vesicles are formed whenever the atmosphere is 
 cooled to a temperature so low that the aqueous vapor contained 
 in it can no longer exist in the gaseous state. 
 
 33. Let us pass now to the analysis of water. Of what is 
 water composed? We can determine this point by methods 
 
22 ANALYSIS OF WATEK. 
 
 similar to those which were adopted in the examination of air. 
 There are several metals which, upon being brought into contact 
 with water, wiU abstract from it one of its ingredients, in the 
 same way that we have seen them abstract oxygen from the air. 
 Some metals can abstract this ingredient even at the ordinary 
 temperature. Thus the metal called sodium, on being brought 
 into contact with water, decomposes it, and, uniting with one of its 
 constituents, sets free another as a gas. This new gas is called 
 Hydrogen. 
 
 Exp. 14 — Make a small cylinder of wire gauze by rolling a piece of 
 fine gauze, about 6 cm. square, arovmd a thick piece of No. 6 glass 
 tubing. Twist fine wire around tbe cylinder in order to preserve its 
 form, then slip the cylinder ofi' the glass, and close one end of it by 
 pressure with a stout pair of pincers. Within this cylinder of wire 
 gauze place a piece of metaUio sodium as large as a small pea, and 
 then close the upper end of the cylinder by pressure with the pincers, 
 as before. Quickly place the wire gauze cyhnder under the mouth of 
 a small bottle of 100 or 200 c. c. capacity, which has previously been 
 filled with water and left inverted in the water-pan. 
 
 As soon as water comes in contact with the sodiimi, bubbles of gas 
 will issue from the wire gauze cage, and, rising through the water, 
 will collect at the top of the inverted bottle. If no gas is generated 
 during the first moment after the wire gauze has been placed in the 
 water, move the bottle to and fro, in such manner that the gauze 
 cylinder may be shaken about, and water forced through its interstices. 
 As soon as the evolution of gas has ceased, close the mouth of the 
 bottle with a small plate of glass, turn it mouth uppermost, remove the 
 plate, and touch a lighted match to the gas. The gas will take fire 
 with a sudden flash. 
 
 34. At a low red heat water can be decomposed by several of 
 the metals, such as iron, tin, zinc, and magnesium. Iron is well 
 adapted for this experiment. 
 
 Exp. 15. — Provide a piece of iron gas-pipe, about 35 cm. long, and 
 1 cm. or more in internal diameter ; fill it with small, bright iron- 
 turnings, and support it upon a ring of the iron stand over one or two 
 wire-gauze gas-lamps. By means of perforated corks, connect with 
 the iron tube, on the one hand, a glass delivery-tube leading to the 
 water-pan, as shown in the figure, and, upon the other, a delivery-tube 
 coming from a thin-bottomed glass flask, half full of water, and sup- 
 ported upon a ring of a second hon stand. Light the lamps beneath 
 
ELBCTROLTSIS OP WATEE. 
 
 23 
 
 the iron tube, and wait until its contents have become red-hot ; then 
 heat the water in the flask until it boils slowly. As the aqueous 
 
 e=>=0 
 
 vapor passes over the hot iron-turnings it will be decomposed, one of 
 its constituents will unite with the iron, and hydrogen will pass oif 
 through the delivery-tube and may be collected in bottles at the 
 water-pan, so soon as the air originally contained in the tubes and 
 flask has all been expelled. 
 
 If, at the close of this experiment, and after the tube has become 
 cold, the iron be removed from the tube, it will be found to be co- 
 vered with a black coating similar to that which forms on iron heated 
 in the air. 
 
 35. By these experiments it has been proved that one of the 
 components of water is a gas called hydrogen. But with the 
 exception of the coatuig upon the iron of Exp. 15, we have as 
 yet nothing to indicate what other ingredients the water may 
 contain. Such evidence can, however, be readily obtained by 
 resorting to another method of analysis. If a galvanic current is 
 caused to flow through water, the force by which the constituents 
 of the water are held together will be overcome, and the water 
 wiU be resolved into the elements of which it is composed. On 
 immersing the platinum poles of a galvanic battery in water, to 
 which a little sulphuric aeid has been added for the purpose of 
 increasing its conducting-power, minute bubbles of gas wiU im- 
 mediately be given off from these poles, and will be seen rising 
 through the liquid. We have here abundant proof of the power- 
 ful action exerted by the battery upon the water. But the ex- 
 periment will be much more satisfactory if it be made in a 
 vessel so arranged that the evolved gases may be collected for 
 examination. 
 
24 
 
 EtECTBOLTSIS OF WAISB. 
 
 For tMs purpose the apparatus shown in Kg. 9 can be Fig. 9. 
 conveniently employed. The test-glass, nearly full of 
 water which has been mixed with from ij to |^ of sul- 
 phuric acid, carries two platinum wires cemented with 
 shellac into the glass. These wires terminate above in 
 thin plates of platinum ; over each of these plates there 
 is inverted a long, narrow test-tube fuU of water, acidu- 
 lated in the same way as that in the test-glass. Upon 
 connecting the wires with a galvanic battery, — two , 
 Bunsen's cells of medium size will be sufficient, — the 
 water will be decomposed, and the resulting gases, as 
 they are given off at the platinum plates, vfiU rise, trans- 
 parent and colorless, into the test-txibes. On comparing 
 the bulks of the two gases, it wUl be found that twice as 
 much gas has collected in the one tube as in the other. 
 If the test-tube containing the larger volume of gas be i 
 now closed with the thumb, turned mouth uppermost, 
 and the gas within touched with a lighted match, it will take fire 
 and bum with the characteristic flame of hydrogen. It is, in fact, 
 hydrogen. 
 
 If the smaller volume of gas in the other tube be examined in the 
 same way, it wiU not inflame, although it gives intense brilliancy to 
 the combustion of the match. If a splinter of wood, retaining but a 
 single ignited spark, be immersed in the gas, it instantly exhibits a 
 vivid incandescence, and in a moment bursts into flame. This gas is 
 oxygen. It is thus proved that out of water may be unloosed two 
 volumes of hydrogen and one volume of oxygen. 
 
 K now the platinum plates be pressed so near together that a single 
 large test-tube, full of acidulated water, can be placed over both, the 
 gas obtained by passing the galvanic current will exhibit properties 
 differing from those of either hydrogen or oxygen. It is in fact a 
 mechanical mixtiire of these gases in the proportions in which they 
 would unite chemically to form water. The mixture is precisely 
 similar to that which would have been obtained if the two volumes of 
 hydrogen and one volume of oxygen, previously collected in two sepa- 
 rate tubes, had been mixed in one. On touching a lighted match to 
 the mixed gas it instantly explodes with great violence, the hydrogen 
 burning suddenly, so that for a moment a flash of flame Alls the whole 
 interior of the tube. Incited by the burning match, the hydrogen and 
 oxygen have combined chemically to form water, a portion of which 
 is deposited as dew upon the inner walls of the tube. 
 
 At the temperature of the air, and under ordinary cireum- 
 
SYNTHESIS OF WAIEB. 
 
 25 
 
 stances, oxygen and hydrogen do not combine chemically. Upon 
 being brought together they simply mis with one another mecha- 
 nically in conformity with the physical laws which govern the 
 diffiision of gases. But under the influence of heat, of electricity, 
 and of certain other agents, the two gases will- unite chemically, 
 and will thus again be converted iato the water from which they 
 were derived. 
 
 36. It remains to be investigated whether hydrogen and oxy- 
 gen, during their conversion into water, undergo any change of 
 volume, or merely combine to produce a measure of gaseous 
 water exactly equal to the sum of the measures of the consti- 
 tuents. To determine this point it is necessary to compare the 
 joint volumes of the constituents of the water with the volume of 
 the product formed, at a temperature high enough to maintain 
 the latter in the purely gaseous condition known as dry steam. 
 
 Through the closed end of a U-tube (Fig. 10) two platimmi wires are 
 passed, and welded tightly to the glass wallfl of the tube. The outer 
 ends of these wires are formed into loops for the attachment of appro- 
 
 Fig. 11. 
 
 Fig. 10. 
 
 priate battery wires ; their irmer ends are separated by a distance of 
 two millimetres. The general arrangement of the apparatus to be 
 employed is shown in Fig. 11. The U-tube is first completely filled 
 with mercury, and then the screw-compressor (Appendix, § 16) at a 
 is opened so as to afford a gradual exit to the metal in the open limb. 
 By means of a delivery-tube reaching down the open limb to the bend 
 
26 
 
 SYNTHESIS OF WATER. 
 
 of the tube, we introduce from a gas-holder (see Appendix, § 11) a 
 quantity of a mixture of oxygen and hydrogen, made in the propor- 
 tions in which they form water, — namely, two-thirds hydrogen, and 
 one-third oxygen, — in such a manner that the gas shall bubble up 
 through the mercury into the sealed limb, from which, of course, the 
 mercury escapes as the gas enters. A column of gas 25 or 30 cm. 
 high is thus admitted. 
 
 It must be borne in mind that this mixture of hydrogen and oxygen 
 is very explosive ; fire should be carefully kept away from the Ticinity 
 of the gas-holder which contains it, and any remnant of the mixture 
 which is not used should be thrown away at the end of the experiment. 
 
 The gas-filled limb of the U-tube is next siirrounded by a high glass 
 cylinder, h c, the ends of which are fitted with corks ; through the 
 lower cork pass the TJ-tube, and a small glass tube, which is connected 
 with a condensing worm, d, kept cool with water ; through the upper 
 cork pass the wires which are to carry the electric current to the pla- 
 tinum points at the top of the U-tube, and a bent glass tube coming 
 from the flask, e. The top of the cylinder h c rises about 5 cm. above 
 the sealed extremity of the U-tube. In the flask e, fusel oU, a liquid 
 which boils at 132°, a point much higher than the temperature at 
 which water becomes a gas, is kept in constant ebullition. The vapor 
 rising from the flask penetrates the annular space between the U-tube 
 and the enclosing cylinder, and quickly raises the tube to its own tem- 
 perature. These strong-smelling vapors are not allowed to escape into 
 the atmosphere, but are carried out from the bottom of the cylinder 
 b c, into the condenser d. 
 
 When thus heated, the column of mixed oxygen and hydrogen in 
 the tube expands, and its heighWs marked by a caoutchouc ring, pre- 
 viously slipped over the cylinder h c. Care must be taken, before doing 
 this, to bring the mercury to the same level in both limbs of the U- 
 tube, by adding or vrithdrawing mercury as may be required. A few 
 centimetres of mercury are next poured into the open limb, which is 
 then closed with a good cork. Between this cork and the mercury 
 intervenes a column of air, 8 or 10 cm. in length, which will act as a 
 spring, and break the shock caused by the explosion of the mixed 
 gases. This mixture is now to be inflamed by causing an electric 
 spark to pass between the platinum points within the tube. This 
 spark may be obtained from a Euhmkorfi' coil, or fi-om an electrical 
 machine. The gases instantly rush into combination, with an intense 
 energy which produces the phenomena called explosive, and at the 
 high temperature which exists within the tube (132°) the water 
 formed retains the gaseous condition. On removing the cork and 
 
STNIHESIS OP ■VTATEE. 
 
 27 
 
 allowing tlie mercury to flow through the screw-compressor until it 
 is level in both limbs of the U-tube, it becomes obTioua that the ori- 
 ginal volume of the gaseous mixture is diminished by one-third; the 
 residuary two-thirds are dry steam. If the U-tube is allowed to cool, 
 this steam will condense into liquid water. 
 
 Figs. 12 and 13 represent another form of apparatus for performing 
 this important experiment. In Fig. 12 the U-tube of Fig. 11 is replaced 
 Fig. 12. 
 
 Fig. 14. 
 
 Fig. 13. 
 
 by an iron U, such as is used in connecting parallel steam-pipes, into 
 which two straight glass tubes are fitted by means of caoutchouc 
 stoppers. One of these tubes is closed at one end, carries two platinum 
 wires, and may be graduated with advantage ; the other is a plain 
 tube open at both ends. The iron U is fastened to a solid iron foot, 
 and into its side a small iron tube is inserted, to which is attached a, 
 caoutchouc connector with a screw compressor, as in the other appa- 
 
28 
 
 STUTHESrS 01' WATBE, 
 
 ratus, The jacket- tube (Fig. 13) is a large tube, open at the bottom 
 and closed at the top with a caoutchouc stopper carrying the delivery- 
 tube for the hot vapor ; near the bottom an exit-tube for the vapor is 
 ■welded into the glass. This jacket-tube, when in position, slips 
 tightly over the same caoutchouc stopper through which passes the 
 graduated tube. The advantages of this apparatus are that its parts 
 are not rigid, that it may be taken apart for cleaning, and that it may 
 be made with greater ease and fewer resources than the other appa- 
 ratus. It is, moreover, capable of very general application in the 
 analysis of gases. Fig. 14 shows the ease with which the closed limb 
 of the U-tube in this apparatus may be charged. The closed Umb and 
 the iron U being fuU of mercury, and the apparatus placed in an iron 
 pan suited to catch the overflow of mercury, the long open tube is 
 taken away, and the bent gas-delivery tube is inserted beneath the 
 closed limb through the iron U. The iron U acts simply like the 
 water-pan or pneumatic trough. When the required amount of gas 
 has been introduced, the open glass tube is replaced, and the level of 
 mercury in the two tubes is adjusted at wiU. For the experiment 
 now under consideration, it is well to employ the actual mixture of 
 gases obtained by the electrolysis of water ; and Fig. 14 represents a 
 simple bottle provided with two platinum plates and a single deliveiy- 
 tube for this purpose. The gas evolved is dried by passing over an 
 absorbent called chloride of calcium in a "drying- 
 tube" (Appendix, § 15). The only noticeable feature 
 in this apparatus for electrolysis is the maimer in which 
 the wires from the battery are connected vrith the pla- 
 tinum plates. This is more clearly shown in Fig. 15. 
 There passes through the caoutchouc stopper a short 
 piece of glass tubing, open at the top and drawn to a 
 point at the lower end, so as to enclose and hold tightly 
 a piece of platinum wire, as large as a common knit- 
 ting-needle, previously placed within it. With the wire 
 thus welded to the glass is connected a thin plate 
 platinum, which hangs in the liquid to be decom- 
 posed; this plate may be folded or roUed up. A little 
 mercury is poured into the glass tubes, and the battery- vpires are 
 simply placed in the mercury when the operator desires to start the 
 decomposition. 
 
 This experiment demonstrates that two volumes of hydrogen 
 and one volume of oxygen are compacted, when chemically 
 united, into two volumes of steam. 
 
 37. We have thus established the composition of water by 
 
 Fig. 15. 
 
1 
 
 • + 
 
 
 
 
 J 
 
 
 
 = 
 
 HgO 
 
 H 
 
 
 
 
 ■Atoms ahd molecules. 29 
 
 analym, having, through the agency of the dectric current, re- 
 solved water into two gaseous constituents, hydrogen and oxygen, 
 anid we have also demonstrated, by the converse or synthetical 
 method, that hydrogen and oxygen are its only constituents, 
 since we have reproduced water by effecting the chemical union 
 of these two elementary materials mixed in due proportion. 
 
 If equal volumes of hydrogen and oxygen be represented 
 by equal squares, having the initials of the elements inscribed 
 therein, the composition of water by volume, and the condensa- 
 tion which occurs when the chemical union of the elements takes 
 place, may be thus expressed to the eye : 
 
 Each smallest possible or 
 greatest conceivable volume of 
 steam will invariably yield, on 
 decomposition, its own volume 
 of hydrogen, and half its vo- 
 lume of oxygen. 
 
 38. It has been agreed to call by the name " atom'' the smallest 
 quantity of an element which can be conceived to exist in com-- 
 bination; this technical term is applied only to the chemical 
 elements, and to certain chemical knots, or groups, of elements, 
 which, under conditions hereafter to be studied, play the part of 
 an element. 
 
 It has further been agreed among chemists to call by the 
 name "molecule," the least quantity of a compound, or of an 
 element, which can exist by itself uncombined, or take part in 
 any chemical process; a molecule always contains more than 
 one atom, but these atoms may be either of one, two, or of 
 several kinds. 
 
 39. Physical experiments upon the expansion and contraction 
 of numerous gases, simple and compound, have proved that all 
 gases comport themselves in sensibly the same manner under 
 like variations of temperature and pressure ; whence it has been 
 inferred that the intimate mechanical structure of all gases, com- 
 pound as weU as simple, is the same. This theoretical concep- 
 tion is expressed in the following propositions, of which the 
 second is the more general and includes the first : — 
 
30 MOLECUXAB HTPOIHESIS. 
 
 The elementary gases contain, under like conditions of tem- 
 perature and pressure, equal numbers of atoms in equal vo- 
 lumes. 
 
 Equal volumes of aU gases, whether simple or compound, con- 
 tain under like conditions, the same number of molecules. 
 
 The idea of an atom is complete and independent in itself ; the 
 idea of a molecule is partly a consequent of the idea of an atom, 
 and partly of the physical facts which the definition helps to 
 formulate. 
 
 These definitions and hypotheses have found acceptance, partly 
 on the strength of experimental evidence, partly because of their 
 adaptation to the mathematical mode of investigating physical 
 problems which border on the domain of chemistry, but chiefly 
 on account of the clearness and formal consistency which they 
 have imparted to chemical language and modes of thought. 
 Chemical symbolization and nomenclature are mainly based on 
 the above definitions and hypotheses, which therefore justly de- 
 mand the student's closest attention. Let us apply them to the 
 chemical compound, water. 
 
 40. The molecule of water, or least quantity of water which is 
 conceived to exist by itself, must yield, like any other quantity 
 when resolved into its elements, twice as large a volume of hydro- 
 gen as of oxygen. In accordance with the physical hypothesis 
 above explained, the molecule must consequently contain twice 
 as many atoms of hydrogen as of oxygen. The bulk and weight 
 of the molecule and atom are not absolute quantities, on account 
 of their assumed infinitesimal character. None but relative facts 
 can be known touching these hypothetical quantities, which are 
 both less than any assignable quantity, although one must be 
 smaller than the other. "We shall express in the simplest terms 
 all our actual knowledge of the matter, and shall at the same time 
 conform to our definitions, in saying that a molecule of water 
 contains two atoms of hydrogen and one atom of oxygen. The 
 symbol H^O which we have already used to indicate the volume- 
 tric composition of water (§ 37) will now receive an added mean- 
 ing ; the H will represent for us an atom of hydrogen, and the 
 an atom of oxygen. 
 
ATOMIC ■WEIOHTS. 31 
 
 When th.e proportions in whicli two bodies combine by volume, 
 and their specific gravities, or equal-volume -weights, are known, 
 it is a matter of easy calculation to determine the proportions in 
 which they combine by weight. The specific gravity of oxygen, 
 or its density compared with that of air, has already been given, 
 namely, 1-1056. The specific gravity of hydrogen likewise referred 
 to £iir as the term of comparison, has been found by the most exact 
 experiments yet made to be 0'06926. Oxygen is therefore 16 
 times heavier than hydrogen. If hydrogen be made the standard 
 of specific gravity for gases, its specific gravity wUl be denoted 
 by 1, and that of oxygen will be 16. Now any measure of dry 
 steam is, as we have seen, resolvable into its own measure of 
 hydrogen and half that measure of oxygen ; the weights of equal 
 measures of hydrogen and oxygen are as 1 to 16 ; but there is 
 twice as much hydrogen as oxygen in bulk, therefore the weight 
 of the hydrogen generated from any quantity of water, small or 
 great, is to the weight of the oxygen simultaneously produced, as 
 2 to 16. In 18 parts by weight of steam, water, or ice, there are 
 then 2 parts by weight of hydrogen and 16 of oxygen : and it 
 matters not what the absolute weight of these parts may be ; the 
 proposition is as true of kilogrammes as of grammes, of the milli- 
 gramme as of the millionth of the milligramme of water, in either 
 of its physical states. 
 
 Applying these facts of observation to our abstract definitions 
 of molecule and atom, it wiU appear that the molecule of water, 
 the least proportional weight in which it is conceived to exist 
 uncombined, must be composed, like any other mass of water, of 
 2 parts by weight of hydrogen, and 16 parts by weight of oxygen; 
 but in conformity with our definitions and hypotheses we conceive 
 of the molecule as consisting of two atoms of hydrogen and one 
 of oxygen ; one proportional part by weight of hydrogen is then, 
 in chemical language, synonymous with one atom of hydrogen, and 
 16 of the same parts by weight is the relative quantity of the 
 atom of oxygen. As for volume, so for weight, absolute quantities 
 are entirely unattainable ; the numbers express proportions only. 
 The numbers 1 and 16 are called the atomic weights of hydroge;^^ 
 and oxygen respectively ; <Kyjexpress the proportions by weight 
 
32 
 
 CHEMICAI, COMBINATIOH'. 
 
 in whici these two elements enter into combination. If thes» 
 numbers be borne in mind, the symbol of water, H^O, will always 
 remind us that water consists of 1 part by weight of hydrogen 
 and 8 parts of oxygen. 
 
 That any given weight of water, as for example one gramme, 
 is one-ninth hydrogen and eight-ninths oxygen, is a fact capable 
 of experimental demonstration. It is not difficult to decompose 
 a convenient weight of water, and to actually weigh separately 
 the hydrogen and the oxygen which are produced; the weights 
 of the two gases wiU invariably be to each other as 1 to 8 or as 
 2 to 16. The great value of the symbols used in chemistry may 
 be weU illustrated by the amount of information condensed into 
 the concise expression H^O : we learn from it the number and 
 names of the elements entering into the composition of water, and 
 the ratios in which the elements are united by volume and by 
 weight. 
 
 41. This discussion of the constitution of water rests upon two 
 soM facts of observation, namely the composition of water by 
 volume and its composition by weight ; aU else is plausible hypo- 
 thesis and convenient theory. The strong chemical compound, 
 water, admirably illustrates the essential changes which the ele- 
 ments undergo, when they are joined together by that peculiar 
 force whose play it is the object of chemistry to study. Nothing 
 can be more striking than the contrast between the properties of 
 hydrogen and oxygen gases, or of a mechanical mixture of these 
 elements, and those of the liquid water which is produced by their 
 chemical union ; even in dry steam, a prominent property of 
 hydrogen (inflammability) and a marked characteristic of oxygen 
 (power of supporting combustion) entirely disappear. In mecha- 
 nical mixtures the constituents may be mingled in any propor- 
 tions ; in chemical compounds the elements are forcibly united 
 in definite volumetric and ponderal proportions, and the indivi- 
 duality of the elements is lost in the formation of a new sub- 
 stance with new properties. The Chbmioai, Foece is a peculiar 
 power, distinct from, though akin to, the forces of Light, Heat, 
 and Electricity ; it is the province of chemistry to investigate the 
 conditions, modes, and effects of its action. 
 
W^TBE IN NATTJEB. 33 
 
 42. Having thiis succeeded in determining the constituents of 
 air and water, we are naturally led to inquire whether it be not 
 possible to resolve oxygen, nitrogen, and hydrogen themselves 
 into simpler forms of matter. To this question but one answer 
 can be made — the result of the accumulated experience of many 
 philosophers of this and former generations — ^namely, that oxygen, 
 nitrogen, and hydrogen are incapable of decomposition by any 
 means as yet at our disposal. They resist the most powerful influ- 
 ences of electricity and heat, and they issue unchanged from every 
 variety and form of chemical reaction hitherto devised in the 
 hope of resolving them into simpler forms of matter. We are, 
 therefore, justified in regarding these gases as simple bodies, or 
 elements, in contradistinction to decomposable bodies, such as air 
 and water. 
 
 43. The water which occurs in nature is never absolutely pure. 
 In the form of ice, and as it faUs from the clouds as rain or snow, 
 it is, indeed, tolerably free from foreign substances ; but after 
 having once soaked into the ground, it becomes charged with a 
 variety of mineral and other substances, whifih, being soluble in 
 water, are dissolved by it as it trickles through the earth. 
 
 Where the proportion of soluble matter contained in the water 
 is unusually large, and particularly if it possesses marked medi- 
 cinal properties, the water is called mineral water, and the springs 
 from which it issues are known as mineral springs. Sea- water 
 may be regarded as a variety of mineral water. 
 
 44. For the conduct of chemical investigations it is often neces- 
 sary to purify natural water. This is done by a process called 
 distillation. As a general rule distilled water is employed in aU 
 delicate chemical operations. 
 
 Exp. 16. — Into a retort of 500 c. c. capacity, put 200 or 800 c. c. of 
 well-water. Thrust the neck of the retort into a half-litre receiver 
 placed in a pan of cold water. Cover the receiver with a cloth, or with 
 coarse paper, and upon this pour cold water fi'om time to time, or pile 
 upon it fragments of ice. Place the retort upon wire gauze, on a i-ing 
 of the iron lamp-stand, and adjust the distance of the retort from the 
 lamp as described in Exp. 5, Fig. 3. Light the lamp beneath the re- 
 tort, and bring the water to boiling. As fast as the water m the re- 
 tort is converted into steam, this vapor will pass over mto the cold 
 
 r 
 
34 
 
 DISTILLATION. 
 
 Fig. 16. 
 
 receiver, and will there be condensed again to the liquid condition. 
 Continue to hoil until about three-quarters of the water in the retort 
 has evaporated. 
 
 The earthy and saline ingredients of well-water are for the most 
 part not volatile; very few of them are 
 capable of accompanying the water as it 
 goes off in vapor ; hence the greater part of 
 the original impurity of the water will re- 
 main behind in the retort. 
 
 Besides the non-volatile impurities, there 
 are often contained in well-water certain 
 volatile substances, such as ammoniacal salts 
 and organic matter, which pass over into 
 the receiver with the aqueous vapor ; but 
 since it has been found that most of these , 
 volatile matters go over with the first por- 
 tions of the steam, it is only necessary to throw away that portion of 
 the distillate which is first condensed, in order to obtain thereafter 
 water of a high degree of purity. 
 
 This experiment must not only be so regulated that the retort shall 
 not boil over, but care must be taken that vapor alone shaU pass off. 
 The ebullition should be so moderate that none of the particles of 
 water which are thrown up mechanically from the surface of the liquid 
 can be projected into the neck of the retort, or carried thither by the 
 current of steam. 
 
 45. In the operation of distillation the substance to be distilled 
 must in the first place be converted into the condition of vapor, 
 this vapor must next be transferred to another vessel, and there, 
 by refrigeration, be again condensed to the liquid state. As will 
 appear from the foregoing experiment, the vaporization is effected 
 in the retort or stiU, and the refrigeration in the condenser. In 
 the experiment above given the receiver acts at once as receiver 
 and condenser ; but a far more efficient apparatus can be con- 
 structed by interposing a long tube between the retort and the 
 receiver. This tube may be wrapped with cloths upon which 
 bits of ice are laid, or water is poured ; or better, the tube may 
 be enclosed in a larger tube, or a metallic pipe, through which a 
 current of cold water is made to circulate. The water, which 
 may be iced if need be, is poured iu through the funnel at the 
 lower end of the tube, and passes out at the top (Mg. 17). This 
 
DISTIILATION. 
 
 35 
 
 exceedingly convenient and valuable form of condenser was in- 
 vented by Weigel j it is, however, commonly called Liebig's. 
 
 JExp. 17. — Place a few drops of the distilled water obtained in the 
 preceding experiment upon a piece of platinum foil (Appendix, § 13). 
 Hold the foil with iron pincers above the gas-iiame in such a manner 
 that the liquid may slowly 
 evaporate without boiling or ^' 
 
 spirting. After the water has 
 disappeared, no residue will 
 be found upon the foU. Take 
 out of the retort the same 
 number of drops of water, and 
 evaporate them upon the foil 
 as before. A very decided 
 residue of earthy matter will 
 be left upon the foU. 
 
 46. In this country, where ice can be had in abundance at all 
 times, it may often be employed as a convenient substitute for 
 distilled water. In freezing, that is, in crystallizing, water re- 
 jects a great part of the foreign substances which were dissolved 
 in it. Hence, by collecting ice and remelting it, there can be 
 obtained water which is nearly pure. 
 
 Rain-water, also, especially that which has been collected in 
 the open country, is often pure enough to be used for chemical 
 purposes. 
 
 47. But even after all the mineral and all the organic matters 
 have been removed, the water is not yet absolutely pure. It still 
 contains oxygen and nitrogen in solution. Both of these gases 
 are soluble in water to a certain extent; and since the water 
 upon the surface of the earth is all the while in contact with air, 
 it must necessarily become charged with the constituents of the 
 air. A method of collecting these gases for examination will be 
 described in a subsequent chapter ; we are here more particularly 
 concerned with their removal. This may be effected by long- 
 continued boiling. 
 
 &p. 18. — In a common long-necked medicine-phial of thin " blown" 
 glass, and of the capacity of about half a litre, place 300 or 400 c. c. of 
 recently distilled water. Draw out and bend the neck of the phial, as 
 
 d2 
 
36 
 
 SOLrrllON IN WATBE. 
 
 Fig. 18. 
 
 sliown in Fig. 18, and tie upon its point a short piece of caoutchouc 
 tuhing. BoU the water steadily during half 
 an hour. Finally, nip the open end of the 
 caoutchouc tube, at the same moment remove 
 the lamp from beneath the flask, and instantly 
 seal the neck of the phial by directing the 
 flame of a blowpipe against the narrow spot. 
 This water can now be preserved for an in- 
 definite length of time, without undergoing 
 change. Upon inverting the phial, the water, 
 which has been thus thoroughly freed from 
 air, will fall about as if it were a solid body, ^ 
 and will strike against the glass with a sudden ^ 
 shock. The apparatus is in fact nothing else 
 than the so-called water-hammer of the physicists. 
 
 It foUows, then, that whenever absolutely pure water is needed 
 for chemical investigations, natural water must first be distilled, 
 with the precautions above indicated, and this distilled water 
 must sul jquently be thoroughly boiled, in order to expel the 
 gases w'h jh it holds in solution. "Water so purified, though 
 neoessa- ; for chemical purposes, is unfit to support the life of 
 fishes or other animals which breathe in water, and is not suitable 
 for drinking. It is not only insipid and unpalatable, but is not 
 refreshing like ordinary water. Even if only a part of the dis- 
 solved gases have been removed, as is the case with water which 
 has been recently distUled, the taste of the water is stiU flat, and 
 repugnant. Hence, on board vessels where fresh water is pre- 
 pared by distilling sea-water, the distillate should be left for 
 some time in contact with air, in order that by absorbing the 
 constituents of the air it may become fit for drinking. 
 
 48. As might be inferred from the foregoing, water has the 
 property of dissolving many substances, solid, liquid, and gaseous. 
 Sugar, for example, dissolves readily in water ; but sand is in- 
 soluble therein. 
 
 A substance is said to be soluble when it is capable of being 
 divided in, and dispersed through watbr so intimately and com- 
 pletely that its particles become invisible, and can no longer be 
 separated by filtration; the result of this coalescence, or the 
 
soLtriioN. 87 
 
 solution as it is termed, is a transparent jliquid, as a general rule 
 scarcely less mobile than the water itself. 
 
 Of the various substances soluble in water, some dissolve in 
 far larger proportion than others. With some liquids (as alcohol, 
 for example) water can be mixed in any proportion ; but of ether 
 it dissolves but little, and of oil none. The proportion of any 
 substance that can be dissolved in a given quantity of water is 
 usually limited, and under fixed conditions is definite and peculiar 
 for each substance. When a given quantity of water has dis- 
 solved as much of a substance as it is capable of dissolving at the 
 temperature and pressure to which it happens to be exposed, the 
 solution is said to be saturated. Generally speaking, solid sub- 
 stances dissolve in far larger quantity in hot than in cold water, 
 though with gases and some exceptional solids the contrary 
 obtains. From the saturated hot solution of any saline sub- 
 stance, crystals are usually deposited during the process of cool- 
 ing. But so long as a solution is neither exposed to variations 
 of temperature, nor changed by the addition of another substance 
 or by the abstraction of either of its parts, it will usua ty deposit 
 nothing, and will remain unaltered during an indeiiL- "s period 
 of time. 
 
 During the act of solution, the iirst portions of the solid dissolve 
 with comparative rapidity, the subsequent portions dissolving 
 more and more slowly, until complete saturation is attained. In 
 preparing a solution of any solid, at the ordinary temperature of 
 the air, it is therefore inadvisable to add a large quantity of water 
 all at once ; a much more satisfactory result wiU. usually be ob- 
 tained if the substance be rubbed in a mortar with repeated 
 small portions of water, the several portions of the solution being 
 poured off into a common receptacle as fast as the water becomes 
 nearly saturated. 
 
 There are many other liquids besides water which are com- 
 monly used as solvents ; but as water is the commonest solvent of 
 all, and the most universally applicable, ^ome of the general prin- 
 ciples o:if solution may here be appropriately set forth. 
 
 49. Solution, though in many cases closely allied to chemical 
 action, is usually treated of as a distinct process. Prom the best-_ 
 marked chemical action it differs in several particulars. In true 
 
38 soLiTiioir. 
 
 chemical combination the union of the several ingredients is so 
 close and intimate, that their properties are merged and lost in 
 those of the compound; while in the solvents proper, such as 
 water, alcohol, and benzine, the particles of the dissolved matter 
 appear to be merely mechanically divided and diffused through 
 the liquid. The chemical properties of the dissolved matter 
 undergo no essential change during the act of solution, but re- 
 main unimpaired. When common salt is dissolved in water, the 
 brine retains the peculiar taste of the salt, and behaves Kke salt 
 itself towards most chemical agents ; moreover the salt can 
 readily be recovered unchanged by evaporating the water. But 
 if a piece of chalk be placed in muriatic acid, chemical decom- 
 position and combination wiU immediately occur, the first sig- 
 nalized by a violent etfervescence, the second resulting in the 
 formation of a liquid which contains neither chalk nor muriatic 
 acid, if the materials have been mixed in due proportion, but 
 which yields, on evaporation, a solid chemical compound, con- 
 taining one of the constituents of each. 
 
 Chemical combination, as usually defined, occurs in fixed pro- 
 portions only, whereas solution takes place in indefinite propor- 
 tions ; not only may many substances, as alcohol and glycerine, 
 be mixed with water in every proportion, but where the solubility 
 of a substance is limited in one direction, as that of common 
 salt, of which only about 0-355 part is dissolved by one part of 
 water at 15°, the substance can nevertheless be dissolved in every 
 possible proportion below this maximum. Chemical action is 
 most marked between substances of unlike character ; but with 
 solution the rule is different. In general, solution occurs most 
 readily when the solvent is not far removed in composition and 
 properties from the body dissolved. 
 
 Extreme cases of chemical action upon the one hand and of 
 solution on the other, are readily distinguishable. But there is 
 a wide range between these extremes, and it is well nigh impos- 
 sible to find a point at which the line of demarcation shall be 
 drawn. Many cases which at first sight seem to be examples of 
 simple solution can readily be shown to depend in part upon 
 chemical force. 
 
 The majority of chemists are now inclined to regard most 
 
HYDEOSBSr. 
 
 39 
 
 instances of solution as feeble exhibitions of the chemical force, 
 or at aU events as intermediate between purely chemical and 
 merely mechanical action. Solution, facilitates chemical action 
 between heterogeneous materials, both by overcoming the force 
 of cohesion by which the particles of homogeneous solids are held 
 together, and also by bringing the particles of the unlike bodies 
 into intimate contact with one another through the vehicle of 
 the common solvent. Cohesion resists chemical action as it does 
 gravity ; but solution overcomes cohesion, frees the particles from 
 the bonds which held them, and, as we may imagine, leaves them 
 free to enter into other combinations. 
 
 CHAPTEE V. 
 
 HTDBO&EN. 
 
 50. The commonest method of preparing hydrogen is by treating 
 zinc or iron with dilute sulphuric or muriatic acid. Unless very 
 large quantities of the gas are needed, this method is cheaper and 
 more convenient than either of those heretofore mentioned. 
 
 £xp. 19.— To a bottle 18 or 20 cm. high, and of 500 or 600 c. c. 
 capacity, the mouth of which has an internal diameter of 2'5 to 3 cm., 
 fit a caoutchouc stopper or a 
 
 sound cork, furnished with a 
 thistle-tube (Fig. 19) and a gas 
 delivery-tube, of No. 6 glass. 
 Within the bottle put 15 or 20 
 grms. of granulated zinc, or small 
 scraps of the sheet metal, and as 
 much water as will cover the zinc 
 and close the end of the thistle- 
 tube. Replace the cork in the 
 bottle, taking care to press it in 
 tightly, and gradually pour in 
 common muriatic acid through 
 the thistle-tube. The thistle- 
 
 Fig. 19. 
 
40 PEEPARATIOX OP HTDEOGEN. 
 
 tube must reach nearly to the bottom of the bottle, so that its point 
 may dip beneath the water ; and the muriatic acid must be added by 
 small successive portions, not more than a large thimbleful at a time. 
 
 On the addition of the first portions of the acid, chemical action 
 •will ensue, the contents of the bottle will become warm, and gas will 
 be seen to escape from the liquid. This gas is hydrogen. 
 
 After all the air has been expelled from the bottle the hydrogen may 
 be collected oyer the water-pan, in inverted bottles filled with water, 
 or it may be passed into a gas-holder (Appendix, § 11). The rapidity 
 with which the gas shall be evolved is easily controlled by regulating 
 the supply of acid ; and the moment at which the hydrogen ceases to 
 be contaminated with air can be determined by collecting small por- 
 tions of the escaping gas, in wide-mouthed bottles of about 50 c. c. 
 capacity, and testing its quality by means of a lighted match. In 
 doing this the small bottle tilled with gas must not be turned over, but 
 should be carefully lifted from the water without changing its vertical 
 position, and the lighted match should then be applied to the mouth 
 of the bottle. If the hydrogen be pure, it will bum tranquilly at the 
 mouth of and within the bottle ; but in case the gas is still mixed 
 with much air, a sharp explosion will occur at the moment when the 
 match is applied to it. In order to avoid these explosions, which 
 would be exceedingly dangerous if the volume of mixed gases were 
 large, it is indispensably necessary, in preparing hydrogen, to take care 
 that none of the gas shall be admitted into the gas-holder untU all the 
 atmospheric air has been expelled from the bottle in which the gas is 
 generated. So, too, in experimenting with hydrogen, no light should 
 ever be brought into contact with the contents of the bottle into which it 
 is generated, or with any large quantity of the gas, until the purity of 
 the sample, or rather its non-explosive character, has been demon- 
 strated by applying to a very small volume of the gas the test above 
 described. 
 
 This experiment, which has here been executed with zinc, can be 
 equally well performed with iron-filings, and with several other of the 
 less common metals. 
 
 Muriatic acid, or, in chemical nomenclature, chlorhydrie acid 
 is a compound of hydrogen and another element, called chlorine, 
 which will shortly be described. The chemical composition of 
 this substance can be represented by the symbol H CI, ia which 
 H represents, as before, the least proportional weight of hydro- 
 gen which exists in combination, and CI the least proportional 
 weight of chlorine. "We may likewise abbreviate the word zinc 
 
PEOPERTIBS 01' HTBKO&EN. 41 
 
 to the symbol Zn ; and the chemical process, or reaction, by 
 which the hydrogen is liberated may then be symbolized by the 
 
 2HCl+Zn=ZnCl,+2H. 
 Since hydrogen is a gas, it escapes as such, and there remains 
 dissolved in the water within the bottle a compound of the ele- 
 ments chlorine and zinc, called chloride of zinc (Zn Cl^). The 
 zinc which was free, enters into combination, and the hydrogen 
 which was in combination, is set free ; in other words, the zinc 
 has been substituted for, or has replaced, the hydrogen. It may 
 here be stated that chemists of ail nations have agreed to repre- 
 sent each of the elements by a symbol, which consists either of 
 the initial letter of the Latiu name of the element, or, when the 
 names of two or more elements begin with the same letter, of 
 the initial letter together with the first of the succeeding letters 
 in the Latin name which is distinctive. Thus Pe (Ferrum) is the 
 symbol of iron, W ( Wolframium) of tungsten, C of carbon, Ca of 
 calcium, Cd of cadmium, CI of chlorine, and Cr of chromium. 
 
 51. Hydrogen is a transparent, colorless, and tasteless gas, 
 odorless when pure. It is not poisonous, though animals die 
 from suffocation when immersed in it, as they do in an atmosphere 
 of nitrogen. It has never been condensed to a liquid. It is the 
 lightest substance known, being about 14J times as hght as air. 
 If 1 volume of air weighs 1 gramme, an equal volume of hydrogen 
 wiU weigh only 0-0693 grm. It is 11,160 times as light as 
 water, 151,700 times as light as quicksilver, and 236,000 times 
 as light as platinum. 1 litre of hydrogen at 0°, and a pressure 
 of 76 cm. mercury, weighs 0'089578 grm. Hydrogen is the 
 most suitable standard of specific gravity for gases, as water is for 
 liquids and solids ; when thus used as the standard, its specific 
 gravity is, of course, unity. The student should, however, be in- 
 formed that air is used by many writers as the standard of specific 
 gravity for gases. 
 
 52. The exceeding lightness of hydrogen can be illustrated in 
 various ways. From an inverted bottle, even though it be open 
 below, hydrogen wiLL escape but slowly ; but if a bottle of hy- 
 drogen be opened in the air, with the mouth upward, the gas wiU 
 
42 
 
 LIGHTirBSS OP HTDROGEN. 
 
 qiiickly escape. Hence it can readily be poured or decanted up- 
 wards from one vessel to another. 
 
 Exp. 20. — Lift from the -water-pan a thick, strong, wide-mouthed 
 bottle, of 200 to 300 c. c. capacity, full of hydrogen, taking care to 
 hold it in a perpendicular position, with the mouth downward. With 
 the other hand place another bottle of equal size and strength, but 
 containing only air, beside the hydrogen-bottle, so that the mouths of 
 the bottles shall touch at one end. Gradually turn down the hydro- 
 gen bottle, and at the same time push its mouth beneath that of the 
 air-bottle va. such manner that the bottle which originally contained 
 the hydrogen shall at last stand upright beneath the inverted bottle. 
 During this operation, the lighter hydrogen flows up into the upper 
 bottle, while the heavier air sinks into the lower. If a burning match 
 be now thrust into the upper bottle, the hydrogen within it will take 
 fire ; but upon applying the match to the lower bottle, originally full 
 of hydrogen, there will be found in it nothing but air. 
 
 In like manner, hydrogen may be collected by displacement — an up- 
 right delivery-tube being carried from the bottle in which the gas is 
 generated, to the top of an inverted recipient. The student wiU do 
 well to remember as a general rule, that in manipulating with hydro- 
 gen we must operate in a manner precisely opposite to that which 
 would be adopted if we were at work with water. Where water would 
 flow down, hydrogen will flow up. 
 
 Owing to its Ughtness, hydrogen is well adapted for filling 
 balloons ; and it is still sometimes employed for this purpose in 
 military operations, being prepared by means of hot iron, as in 
 Exp. 15. For purposes of Hlustration, soap-bubbles filled with 
 hydrogen will serve as well as balloons of more costly construc- 
 tion. 
 
 Exp. 21. — By means of a caoutchouc tube, attach an ordinary to- 
 bacco pipe to a gas-holder containing hydrogen. (See Appendix § 11, 
 Fig. xvii.) Dip the pipe in a solution of soap for a moment, then turn 
 it mouth uppermost, and slowly open the stopcock of the gas-holder so 
 that hydrogen may flow out and inflate the flhn of water upon the 
 mouth of the pipe. The bubble will soon break away from the pipe 
 and rise rapidly through the air. If a burning match be applied to 
 the bubble the hydrogen within it wiU, of course, burst into flame. 
 
 53. There is another noticeable peculiarity of hydrogen which 
 is directly connected with its extreme lightness. It possesses in a 
 
DIPFTTSION OF (JASBS. 43 
 
 high degree the power of difiiision. This diffusive po-wer is a 
 physical property common to all gases and yapors ; in the _. 
 ease of hydrogen it is only the intensity of the diffusive p?^ " 
 power which is remarkahle. 
 
 When different gases, which have no chemical action 
 upon each other, are brought into contact, they will not 
 remain separate, but will commingle. This tendency of 
 the gases to intermingle is so strong that it will not only 
 overcome the greatest differences of specific gravity, but 
 even cause the spread of gases directly against powerful 
 currents of air or vapor. If a bottle of oxygen, standing 
 upright, be connected with an inverted bottle full of hy- 
 drogen, by means of a tube a metre in length, and no more 
 than 8 or 10 m.m. in diameter, both the bottles will be 
 found to be fiUed with a uniform mixture of the two gases 
 after the lapse of a very few hours. Upon now touching 
 a lighted match to the open mouth of either bottle, the 
 gaseous mixture wiU explode. As a precautionary measure 
 it is best in this experiment to employ the thick, strong 
 bottles in which soda-water is kept — or, in lack qf these, strong 
 wide-mouthed bottles enveloped in thick towels. 
 
 The velocities with which gases diffuse are in the inverse ratio 
 of the square roots of their specific gravities. Hence it happens 
 that hydrogen being the most attenuated of all gases, diffuses with 
 the greatest rapidity. Compared with that of oxygen, its rate 
 of diffusion is as 4 to 1 ; that is to say, the relative _. ^ 
 rates of diifusion of the two gases are inversely as 
 the square roots of the numbers 1 and 16, which 
 represent the specific gravities of hydrogen and oxy- 
 gen respectively. 
 
 Exp. 22. — ^A glass tube, 3 or 4 cm. in diameter, and 30 \ 
 or 40 cm. long, is closed at one end with a plug of plaster 
 of Paris 1 or 2 cm. thick. The tube is then set aside for 
 a day or two, in order that the plaster may become dry. 
 When the plug is dry, fill the tube with hydrogen by 
 displacement, and set it upright in a glass of water. Water 
 wiU rise rapidly in the tube, since hydrogen escapes 
 through the plaster more rapidly than air can enter the tube through 
 
44 
 
 HTBBOeEir ryPLAMMABLB. 
 
 tliis porous plug. That some air does enter, however, can he shown 
 by exploding the contents of the tube by applying a lighted match, 
 after the lapse of some time. Of course, if the tube be left to itself, air 
 will slowly enter through ithe plaster, so that the water within the 
 tube will in due time sink to the level of the outside lic[uid. 
 
 On account of its high diffusive power, hydrogen can be kept 
 only in perfectly tight vessels. It has been found that it will 
 leak rapidly under a pressure of 27 or 28 atmospheres through, 
 stopcocks that are perfectly tight for nitrogen at a pressure of 
 even 50 or 60 atmospheres ; from the same cause it cannot be 
 kept for any length of time in bladders or rubber bags. If a 
 sheet of paper be held a short distance ia front of the opening of 
 a gas-holder from which hydrogen is escaping, the current of gas 
 will pass directly through the paper, and can be inflamed upon the 
 other side of the sheet. The high diffusive power of hydrogen, 
 which is to some extent shared by its compounds also, is an 
 obstacle to be overcome before ballooning can be made practicable. 
 
 Sound is propagated in hydrogen but little better than in a 
 vacuum. The specific heat of hydrogen is 3*4046, that of an 
 equal weight ^f water being 1-000 ; it is 0"2356, that of an 
 equal volume of air being 0-2377. It refracts light very power- 
 fully. 
 
 54. Hydrogen is exceedingly iaflammable, as has been already 
 seen ; that is to say, the temperature at which it takes fire is 
 comparatively low. But, as a matter of course, it extinguishes 
 any burning body which is immersed in it, since oxygen is neces- 
 sary for the support of combustion. 
 
 XJxp. 23. — Carefully lift from the water-pan a bottle of 200 or 300 
 c. c. capacity, completely full of hydrogen, slowly carry the bottle, the 
 mouth of which is of course held downward, to a burning candle or 
 splinter of wood, and depress the bottle over this flame. The hydro- 
 gen will take fire and burn, below, at the mouth of the bottle where it 
 is in contact with the oxygen of the atmosphere ; but the flame of the 
 candle will be extinguished the moment it becomes completely en- 
 veloped by the hydrogen. The caudle can easUy be relit by slowly 
 lifting the bottle until the wick is brought into contact with the air 
 and the burning hydrogen. 
 
 JExp. 24. — ^FiH a bottle of the capacity of 400 or 500 c. c. with hy- 
 drogen, close the mouth with a cork or a plate of glass, stand the bottle 
 
TTNII OP HBAI. 45 
 
 upon the table with the mouth upward, remove the stopper, inflame 
 the hydrogen, and immediately pour out of a pitcher into the bottle a 
 large quantity of water. The flame will instantly be increased, since 
 the water wiU force the gas out of the bottle into the air. Within the 
 bottle the hydrogen can only bum gradually, since it takes time for the 
 outside air to enter; but if the gas be pushed aut of the bottle into 
 the air, it will burn at once. 
 
 In the familiar instances where water extinguishes fire, it does so by 
 reducing the temperature of the combustible — that is to say, by cooling 
 it to below the temperature at which it wiU take fire. It would act 
 thus in this case, were it not for the lightness and mobility of the 
 hydrogen, by virtue of which this gas immediately escapes from con- 
 tact with the water. , 
 
 55. It has been seen that the hydrogen-flame aifords only an 
 exceedingly feeble light ; but it would be a grave error to infer 
 that but little heat is developed by the combustion. 
 
 The temperature of the hydrogen-flame is in reality very 
 high. Indeed it has been found that when a given weight of 
 hydrogen enters into chemical union with oxygen, more heat is 
 developed than in the burning of the same weight of any other 
 substance. 
 
 In order to determine the amount of heat which is developed 
 in any act of combination, this heat can be transferred to water, 
 and there estimated either by the quantity of water heated, or 
 the amount of steam produced. A unit of heat is that amoimt 
 of heat which will raise 1 gramme of water from 0° centigrade 
 to 1°. 
 
 The amount of heat evolved during the combustion of a body 
 is as constant and unvarying as any other direct consequent of 
 its properties, and the quantity of heat evolved is absolutely the 
 same, no matter whether the combustion occurs in air or pure 
 oxygen, or whether it be slow or rapid. The actual amount of 
 heat developed during the most vivid combustion is no greater 
 than when the same combustible combines with oxygen, by gra- 
 dual oxidation, without visibly burning. From 1 gramme of 
 hydrogen, as it unites with oxygen, there are evolved 34462 units 
 of heat. 
 
 Although the same amount of heat is developed, in the aggre- 
 gate, when a litre of hydrogen bums in the air, as when it burns 
 
46 
 
 OXT-HTDEOGEN BLOWPIPE. 
 
 in pure oxygen, it is none the less true that a far hotter flame 
 is obtained by burning the hydrogen in oxygen than in air. If 
 the combustion be complicated by the presence of nitrogen from, 
 the air, a great deal of heat wiU expand its energy in expanding 
 this useless nitrogen. Moreover, since the nitrogen occupies much 
 room, it wiU, as it were, keep asunder the particles of hydrogen 
 and oxygen ; the flame wiU thus be made longer and more dis- 
 persed, or, in other words, the heat evolved by the union of the 
 hydrogen and oxygen vrill be spread over more space than if the 
 nitrogen were absent. Where nothing but hydrogen and oxygen 
 are present, and in the precise proportions in which these gases 
 unite to form water, the flame produced by their union wiU be to 
 all intents and purposes soKd, and the heat will be concentrated 
 in the smallest possible space. 
 
 Exp. 25. — Provide two gas-holders (see Appendix, § 11), one full 
 of hydrogen, the other full of oxygen, also a metallic jet so constructed 
 that the tube which carries the oxygen shall pass through the 
 centre of the hydrogen tube as shown in Fig. 22. Screw the jet on 
 to the oxygen gas-holder, and connect the other opening with the 
 hydrogen gaa-holder by means of a caoutchouc tube. Open the cock 
 of the hydrogen gas-holder, and inflame the gas at the point of the jet, 
 then slowly open the cock of the oxygen gas-holder until the flame of 
 the burning hydrogen has been reduced to a fine pencil. This appa- 
 ratus is known as the compound, or oiy-hydrogen blowpipe. In order 
 to insure a steady flame, care must he taken that a constant and suffi- 
 cient pressure be maintained upon the contents of the gas-holders. 
 
 Kg. 22. 
 
 Eacp. 26. — In the flame of the oxy-hydrogen blowpipe, described in 
 the foregoing paragraph, hold the end of a piece of platinum wire, 
 about 10 cm. long and less than one m.m. in diameter. The platinum 
 will melt and fall down in drops. 
 
 The intense heat of the oxy-hydrogen flame is thus admirably illus- 
 trated j for platinum is an exceedingly infusible metal, which can 
 
POEM OP GAS-PLAMBS. 47 
 
 scarcely be softened in the hottest furnace. The drops of platinum 
 should be caught upon sand, or in water. In case the melted platinum 
 falls into water, a portion of the water wiU be decomposed into hydro- 
 gen and oxygen, bubbles of which wUl be seen issuing from the water. 
 Some of this gas can easily be collected, by an assistant, in an inverted 
 ignition-tube filled with water, and its explosive character demon- 
 strated by applying a lighted match. 
 
 £xp. 27. — If a piece of chalk or lime, scraped to a fine point, be held 
 in the flame of the oxy-hydrogen blowpipe, it will quickly become 
 white-hot and evolve light of great briUiancy, almost comparable with 
 that of the sun. K the bit of lime be long exposed to the intense heat, 
 it will undergo incipient fusion, and afford less light than at first. 
 
 Where a constant light is desired, cylinders or plates of chalk are 
 kept continually moving before the flame by mechanical power, so that 
 fresh portions shall continually be brought into the flame. This is the 
 so-called Drummond or Calcium light, often employed for night signals 
 and optical experiments. 
 
 56. No matter in what way hydrogen is burned, whether in 
 the pure state or in combination with other materials, whether in 
 pure oxygen or in the air, the product of the combustion is always 
 water. At the high temperature of the flame, this water must of 
 course remain in the condition of a gas, but it can readily be 
 brought to the liquid state by reducing the temperature. 
 
 JExp. 28. — Over a jet of burning hydrogen, best obtained from a 
 gas-holder, hold a dry, cold bottle. The glass soon becomes covered 
 with a film of dew, as the water generated by the union of hydrogen 
 and oxygen condenses in droplets upon the cold sides of the bottle. 
 
 57. As the burning jet of hydrogen is the simplest instance of 
 combustion with flame, some exact knowledge of the form and 
 quality of flames may here be gained. 
 
 As hydrogen, or any other gas, issues from a small orifice into 
 the air by force of pressure from behind, the escaping gas 
 assumes a certain definite shape in accordance with the physical 
 conditions to which it is exposed, just as a fountain of water 
 takes form in accordance with the size and shape of the orifice 
 from which the water is expelled, the pressure by which it is ex- 
 pelled, the gravity of the water, the resistance of the air, and the 
 force and direction of the wind, and so forth. 
 
 If a lighted match be brought into contact with the column or 
 
40 EXPLOSIVE MIXIT7EE OF HTDROGEN AND OXYGEN. 
 
 fountain of gas, the gas will take fire and bum ; that is to say, 
 the hydrogen wiU enter into combination with oxygen as fast as 
 the latter can be furnished from the air. But, in any event, the 
 column of gas wiU burn only upon the outside, for there alone 
 can the oxygen of the air come into contact with the hydrogen. 
 Neither the interior of the flame nor the contents of the reservoir 
 from which the gas is flowing can bum ; for they consist of pure 
 hydrogen, which, as has been shown in Exp. 23, wiR by itself 
 immediately extinguish combustion. 
 
 All ordinary gas-flames are, of necessity, hollow. They are 
 visible to us through the evolution of light which is an accom- 
 paniment of the chemical action. But even if no combustion 
 were going on upon its surface, the escaping column of gas could 
 still be made visible by causing it to pass through a quantity of 
 dust or other fine powder before coming into the air. A portion 
 of the solid matter would be transported by the current of gas, 
 and the form assumed by the latter would be made manifest. 
 
 The shape of the unignited gas-column would of course be 
 somewhat different from that of the burning flame ; in the latter, 
 not only is the outer edge of the column sharply defined by the 
 zone of combustion, but the actual form of the column itself is 
 modified through the expansion of the gas as it becomes heated by 
 the enveloping fire. 
 
 58. If, instead of burning pure hydrogen as it flows into the 
 air, as in the foregoing experiments, the gas be first mixed with 
 air or oxygen and then ignited, a very different result will be 
 obtained. The hydrogen being now in contact with oxygen at aU 
 points, the entire mass of gas will bum with a violent explosion 
 the instant a hght touches it. 
 
 JExp, 29. — Introduce 2 volumes of hydrogen and 5 volumes of air 
 into a strong round-bottomed bottle such as is used for soda-water. 
 Close the mouth of the bottle with a cork, and shake violently in order 
 that the gases shall be mixed. A small quantity of water should be 
 left in the bottle to act as a stirrer. Grasp the bottle firmly in one 
 hand, remove the cork with the other, and apply the open mouth of 
 the bottle to a lighted candle. An explosion wiU immediately ensue. 
 
 Rvp. 30. — Into a gas-holder, bladder, or rubber bag, introduce a 
 mixture of 2 vols, hydrogen and 1 vol. oxygen. Connect therewith, 
 
EXPLOSITB MlXTTmE OF HTDBOSElf AND OXTSEN. 49 
 
 by means of caoutchouc tubing, a tobacco-pipe, or bit of glass tube. 
 Press the gas through the pipe into a dish of soap-suds, in such manner 
 that there shaJl be formed upon the surface of the suds a mass of foam 
 as large as an egg. Close the gas-holder and remove it from the vici- 
 nity of the suds. On now touching the foam with a long, lighted 
 stick an exceedingly violent explosion will occur. 
 
 It is well to avoid the formation of a large quantity of foam in this 
 experiment, since the concussion is in any event deafening. In this 
 experiment the explosive mixture is purposely confined in an ex- 
 ceedingly flimsy envelope, in order that no harm may be done by the 
 fragments. 
 
 Care should be taken to throw away any remnant of the mixture of 
 hydrogen and oxygen which may have been left in the gas-holder at 
 the close of the experiment, and upon no account should flre ever be 
 brought into its vicinity. 
 
 59. The cause of these loud explosions is twofold. By the 
 act of comMnation water is foniied, and at the same time intense 
 heat is emitted ; the water, or rather steam, is thereby enormously 
 expanded, so that for a moment there is violent motion outwards 
 in aU directions. This outward motion would scatter about ia a 
 most dangerous manner the fragments of any vessel in which, 
 through carelessness, a mixture of hydrogen and oxygen might 
 be ignited — unless, indeed, the vessel were very strong, small, 
 and of large aperture. But in the next instant, as the steam 
 condenses, there is an even more violent motion inwards^. 
 
 The original mixture of hydrogen and oxygen occupies about 
 2000 times as much space as the liquid water which results from 
 the combination of these gases. Hence a partial vacuum is 
 formed, into which air rushes from aU sides ; and it is the heavy 
 and sudden undulations thus communicated to the air which 
 occasion the noise. The outward and inward shocks follow one 
 another so quickly that the ear cannot distinguish between them. 
 
 Mixtures of hydrogen and air produce less violent explosions 
 than mixtures of hydrogen and oxygen, because of the inert 
 nitrogen in the air, which acts as an elastic pad, or CushioB, td 
 break the force of the shock. 
 
 60. Since air is everywhere about us, and since aU ordiMiy 
 combustions occur in it, it has become customairy to speak of it 
 and of oxygen as supjaorters of comhmtion, in contradistinction to 
 
50 OXTGEN BUBNS IN HTDEOGBlf. 
 
 tte so-called combustibles, such as hydrogen. These terms are 
 often convenient, but, as will appear from the following experi- 
 ment, they have only a relative, and no absolute significance. 
 
 Hxp. 31.— Provide a tube of thin glass, the neck of a broken retort, 
 for example, 30 or 40 cm. long, and 3 or 4 cm. in diameter ; fix it in 
 a vertical position, so that the lower opening shall be 20 or 30 cm. 
 above the table, and connect the upper opening with a gas-holder filled 
 with hydrogen. 
 
 To a second gas-holder, containing oxygen, attach a caoutchouc 
 tube, and to the end of this fit a piece of glass tubing, No. 7, 25 or 30 
 cm. long, bent at a right angle at 5 or 10 cm. from the end which is 
 attached to the caoutchouc tube, and drawn out to a fine open point 
 at the other. The caoutchouc tube must be long enough to reach as 
 far as the lower mouth of the wide vertical glass tube above 
 mentioned. 
 
 Open now the stopcock of the hydrogen gas-holder so that the 
 vertical tube shall be filled with the gas, then apply a lighted match 
 to the mouth of this tube, and regulate the flow of gas so that the 
 latter may continue to hum slowly at the lower edge of the tube. 
 Finally, open the stopcock of the oxygen gas-holder, so that a cur- 
 rent of this gas shall flow through the pointed delivery-tube, and thrust 
 this tube up into the middle of the wide vertical tube which has been 
 filled with hydrogen. 
 
 As the stream of oxygen passes through the burning hydrogen at 
 the bottom of the vertical tube, it takes fire, and afterwards continues 
 to bum in the atmosphere of hydrogen within the tube. 
 
 CHAP TEE VI. 
 
 OTHER COMPOTTNBS OE THE ELEMENTS ALREADY STTTDrED. 
 
 61. Oxygen and hydrogen do not unite directly in any other 
 proportion than that in which they form water ; but by indirect 
 means, too complex for profitable study at this stage, a molecule 
 of water can be made to combine with an atom of oxygen forming 
 a new substance, known by the name of peroxide of hydrogen. 
 Its formula is, in accordance with this statement, H,0 , and it 
 
PESOXIDE OP HTBKOGEN. 51 
 
 would yield, if completely decomposed into its elements, equal 
 volumes of hydrogen and oxygen ; its composition by weight 
 must be 2 parts of hydrogen to 32 of oxygen ; it contains just 
 twice as large a proportion of oxygen as water. The best method 
 of preparing this substance does not yield the pure thing itself, 
 but only a concentrated solution of it in water ; the specific gra- 
 vity of this solution is 1-45 ; it is colorless, transparent, and some- 
 what syrupy, has a metallic taste, corrodes the skin, and bleaches 
 vegetable colors. 
 
 How different a substance this is from water, appears at once 
 from this enumeration of some of its properties. It is very un- 
 stable, being readUy decomposed by heat, and by contact with 
 various substances at the ordinary temperature, into oxygen and 
 water. Its instability and the intense chemical activity of which 
 it is capable, emphatically distinguish this, as yet obscure, body 
 from the neutral, stable, inactive compound of hydrogen and 
 oxygen, common water. 
 
 62. But though the peroxide of hydrogen is not water, it is 
 nevertheless a true chemical compound of the same elements which 
 are united in water ; it is definite and constant in composition, 
 and its properties are as unlike those of its elementary consti- 
 tuents as are those of water. A new fact of great significance 
 here comes plainly into view. Two of the elements are evidently 
 capable of combining in two definite proportions to form two 
 chemical compounds, each differing from the other and from its 
 primary constituents. The study of the compounds of nitrogen 
 and oxygen wiU bring into clearer view the general principle of 
 which this fact is a single illustration. These compounds form a 
 series of five members, all derived, more or less directly, from 
 common nitric acid. 
 
 63. Nitric Add. — Two abundant sources of this material are 
 found in nature, and are familiar as articles of commerce. Salt- 
 petre or nitre, a whitish, saline, crystallized substance, now 
 maioly brought from India, is one of these sources ; a similar 
 substance, known as ChiU-saltpetre, or soda-nitre, is collected on 
 a desert tract in ChUi and Peru, and forms a valuable article of 
 export from those countries. These two substances only differ 
 from each other in thisj — that the first contains the metal potas- 
 
 e2 
 
52 PKEPARATIOW OP NITKIC ACTD. 
 
 slum, the second the very similar metal sodium, in either case 
 combined with definite proportions of the elements nitrogen and 
 oxygen. By the reaction of snlphiiric acid (oil of -ritriol) on 
 either of these two substances, nitrio acid is obtained. On a 
 small scale, for laboratory purposes, saltpetre, or, as it is called 
 in chemistry, nitrate of potassium, is generally employed ; on a 
 manufacturing scale, soda-aaltpetre or nitrate of sodium is used, 
 because this salt costs less than nitrate of potassium, and also 
 contains a larger proportion of nitric acid, which it yields np with 
 greater facility, 
 
 &p. 82.— Into a tubulated, glass-stoppered retort of 250 c. c. capa- 
 city put 40 grammes of powdered nitrate of potassium, or, better, 
 84 grammes of powdered nitrate of sodium if it can be obtained, and 
 through the tubulature pour 60 grammes of strong sulphuric acid, 
 which has been weighed out in a bottle previously counterpoised upon 
 ■the balance with shot or coarse sand. Imbed the bottom of the retort 
 in sand, contained in a small iron pan placed over tbe gas-lamp on a 
 ring of the iron-stand. Thrust the neck of the retort into the receiver 
 with two tubulatm'es ; the retort-neck should fit the tubulature of the 
 receiver with tolerable accuracy. The second tubulature of the re- 
 ceiver should be left open, or loosely covered with a bit of glass, in 
 order to avoid the possibility of any pressure being created within the 
 retort during the operation. Place the receiver in a pan of cold water, 
 and cover it with cloth or bibulous paper, which must be kept con- 
 stantly wet during the distillation. (See Fig. 16, p. 34.) Apply a mode- 
 rate heat to the sand-bath ; reddish vapors will appear for a moment, 
 then disappear, and a yellowish fuming liquid will begin to condense 
 in the receiver. Towards the end of the operation the red vapors 
 reappear ; after this has happened, and the saline matter in the retort 
 has attained a state of tranquil fusion, while very little liquid passes 
 over into the receiver, the lamp may be put out, for the process is 
 finished. 
 
 The very acid, corrosive, and poisonous liquid in the receiver is 
 nitric acid; its faint color is not its own, but is due to the presence of 
 a compound of nitrogen and oxygen shortly to be described. Transfer 
 the liquid to a glass-stoppered bottle, and keep it for future use. In 
 all manipulations with nitric acid it is necessary to avoid getting it 
 upon the skin, since it produces rather permanent yellow stains. 
 
 As the retort cools, the residue solidifies into a white, saline mass, 
 which must be dissolved out of the vessel by heating it with water after 
 the apparatus has become thoroughly .cold. It will be observed that 
 
ACID AJSD AT.KALTKE REACTIONS. 53 
 
 the liquid sulphuric acid which was used has disappeared, though the 
 saline tesidue is still intensely acid. 
 
 64. Pure nitric acid is colorless, and is about half as heavy 
 again as water. It may he mixed with water in all proportions. 
 
 .Erp. 38.-^To one-third of the nitric acid obtained in the last experi- 
 ment add an equal bulk of water. The solution thus obtained wiU be 
 still intensely acid, as may be proved by its action on vegetable colors. 
 Litmus is a blue coloring-matter, prepared from various lichens, and 
 used in dyeing. Unazed paper, colored with a solution of litmus in 
 water, is a convenient test for many acids, which, as a rule, change 
 the color Of the paper fifom blue to red. K the acidity of this diluted 
 nitric acid be now destroyed or neuti-alized by the addition of some 
 other substance of opposite quality, the point at which the liquid 
 ceases to be acid may be determined by observing when the blue paper 
 remains blue on immersion in the liquid. 
 
 To the diluted nitric acid, placed in an evaporating-dish, add cau- 
 tiously ammonia-water (the Liquor Ammoniae of the apothecaries), 
 which has been previously diluted with its own bulk of water, until 
 the liquid no longer turns the litmus-paper red. The ammonia-water 
 must be added, slowly at first, and at last drop by drop, and the mix- 
 ture must be constantly stirred with a glass rod. The ammonia- water 
 has the property of turning litmus-paper, which has been reddened by 
 an acid, back again to blue, as direct experiment may prove ; this 
 property is possessed by a class of bodies called alkalies, and this reac- 
 tion with Utmus is termed the alkalme reaction, in contradistinction to 
 the change from blue to red, which is the reaction characteristic of 
 acids. When mixed with nitric acid, ammonia^water produces a 
 compound which, when fresh and pure, has no action on vegetable 
 colors, and being soluble in water is not visible at this stage of the 
 experiment. Place the evaporating-dish on the wire gauze over the 
 gas-lamp, and evaporate the liquid, taking care to avoid actual ebulli- 
 tion, until a drop of the solution taken out on a glass rod becomes 
 almost solid on cooling. Extinguish the lamp, let the dish become 
 perfectly cold, separate the semitransparent crystals which have 
 formed during the cooling from the fluid, if any, which remains in the 
 dish, allow them to drain, dry them by gentle pressure between folds 
 of bibulous paper, and reserve them for use in the next experiment. 
 Besides water, these crystals are the sole product of the reaction ; 
 they must therefore contain both aU of the nitric acid and all of the 
 ammonia which is not water. The chemical name of the substance is 
 nitrate of ammonium. 
 
54 
 
 MAKING HTTEOTJS OXIDE. 
 
 65. We find in this experiment a striking illustration of what 
 is meant by chemical combination. From two fuming liquids, 
 of very intense but opposite properties, there has come forth a 
 neutral solid, as unlike its constituents ia taste, smell, and aU 
 physical attributes, as could well be imagined. The idea of neutra- 
 lization, well exemplified in this experiment, has in the history 
 of chemistry been very fruitful both of names and hypotheses. 
 Bearing in mind the fiery constituents of the cooUng, harmless 
 salt which we have thus synthetically prepared, we proceed to 
 learn by experiment whatever its decomposition may teach. 
 
 Exp. 34. — Introduce into a Florence oil-flask, or other suitable flask 
 of thin glass, and of about 300 c. c. capacity, the nitrate of ammonium 
 obtained in the last experiment. From the mouth of the flask, placed 
 upon the wire gauze on the iron-stand, carry a gas deliveiy-tube. 
 No. 6, beneath the saucer in the water-pan ; but interrupt the tube, at 
 some convenient point to interpose (by means of a cork or caoutchouc 
 stopper with two holes) a small bottle which can be kept cool with 
 water, as shown in the figui'e. 
 
 Fiff. 23. 
 
 Heat the flask moderately and cautiously, to avoid breakinf it. 
 The nitrate of ammonium will melt, and little bubbles wiQ soon begin 
 to escape from the fused mass. The heat must now be so controlled 
 that the evolution of the gas shall not be tumultuous. The gas is to 
 be collected in bottles of 300 to 400 o. e. capacity. In the cooled 
 bottle, through which the gas passes, a clear and colorless liquid will 
 condense, which will be found on examination, if the process has been 
 successfully conducted, to be neither acid nor alkaline, to have neither 
 taste nor smell, and to be wholly volatile when heated on platinum 
 
COMPOSITION OF NITKOUS OXIDE. 55 
 
 foil, — in short, to possess all the properties of water, and none other. 
 When two bottles of gas have been filled, and enough water for testing 
 condensed, the delivery-tube may be withdrawn from the water and the 
 lamp extinguished, altliough the nitrate of ammonium be not all decom- 
 posed. The nitrate of ammonium may be entirely resolved into water 
 and the gas which now awaits examination, but it is difficult to push 
 the decomposition to actual completion without breaking the flaslc in 
 which the operation is performed. That the nitrate leaves no residue 
 behind, when sufficiently heated, may be proved by heating a crystal 
 of it on platinum foil over the gas-lamp. 
 
 66. Nitrous Oxide. — It is obvious that the colorless and trans- 
 parent gas, which is the most voluminous product of the decom- 
 position of nitrate of ammonium just accomplished, must contain 
 all the elements, besides those of water, which enter into the 
 composition of nitrate of ammonium, and therefore of its consti- 
 tuents, nitric acid and ammonia-water ; much interest, therefore, 
 attaches to the determination of the composition of this gas. 
 
 Exp. 35. — Insert a glowing sphnter of wood into a bottle of the gas. 
 It will reinflame with almost as much energy as in oxygen. 
 
 If oxygen be really a constituent of this gas, it may be possible to 
 mix the gas with hydrogen, and efiect the chemical combination into 
 water of the oxygen in the gas and the added hydrogen, by heating the 
 mixture, or passing through it an electric spark (see pp. 24, 26). If 
 just enough hydrogen can be added to exactly convert all the oxygen 
 contained in a given volume of the gas into water, the constituents 
 other than oxygen vrill be left behind for separate examination, and 
 we shall have determined how much oxygen a given volume of the gas 
 contains by observing how much hydrogen has been necessary to con- 
 vert it into water, the volumetric composition of water being already 
 known. Now it has been found that when any volume of this gas is 
 mixed with an equal volume of hydrogen, in a strong tube, provided 
 with platinmn points, like those of the U-tube already used (p. 25), 
 and the mixture is fired by the electric spark, a violent explosion takes 
 place, a dew of water condenses upon the walls of the tube, and there 
 remains a volume of colorless gas, precisely equal to that with which 
 the hydrogen was originally mixed. On studying the properties of 
 this residual gas, it is found to be tasteless, odorless, a little lighter 
 than air, and to be neither inflammable, nor yet a supporter of com- 
 bustion ; it is recognized as the pure element, nitrogen. 
 
 It follows from this experiment, and the knowledge of the 
 composition of water previously gained, that any measure of the 
 
N 
 
 
 
 
 N 
 
 
 KO 
 
 56 ATOMIC WEIGHT OF NITEOGEN. 
 
 gas obtained from nitrate of ammonium contains its own measure 
 of nitrogen and half that measure of oxygen. The constitution of 
 this gas is strictly analogous to that of steam ; as two volumes of 
 hydrogen and one volume of oxygen are compacted into two 
 volumes of steam, so two volumes of nitrogen and one volume of 
 oxygen are condensed into two volumes of this transparent gas. 
 As the chemical formula or symbol of water is H,0, so the 
 formula of this new gas is NjO, and its volumetric composition 
 may be represented by a diagram 
 similar to that by which we con- 
 veyed to the eye the composition , , , 
 pf water. i 1 | | 
 
 67. As has been already said, 
 a combination of oxygen with 
 another element is called an oxide ; the name of the second ele- 
 ment is given either by an adjective which precedes the word 
 oxide, as in the case of this gas N^O, whose name is nitrous oxide, 
 or by connecting the name of the second element with the word 
 oxide by the preposition of, as in case of oxide of iron. 
 
 From the above composition by volume, and from the known 
 specific gravities of nitrogen and oxygen, the composition of 
 nitrous oxide by weight is readily deduced. The specific gravity 
 of nitrogen, referred to hydrogen, is 14 ; that of oxygen 16 ; 
 since there are two volumes of nitrogen for each volume of 
 oxygen, the two elements must, in any given weight of the gas, 
 be combined in the proportion of 28 parts by weight of nitrogen 
 to 16 of oxygen. The molecule of nitrous oxide, N^O, must be 
 composed, like any other quantity of the gas, of 28 parts by 
 weight of nitrogen and 16 of oxygen ; but precisely as in the case 
 of water, we conceive of the molecule as made up of two atoms 
 of nitrogen and one atom of oxygen, and we have already learned 
 that if the atomic weight of hydrogen be represented by 1, that of 
 oxygen must be 16. It follows, from the constitution of nitrous 
 oxide, that, if 16 represent the smallest proportional weight of 
 oxygen which exists in combination, 14 must be the corresponding 
 smallest weight of nitrogen when thus united with oxygen. Ni- 
 trous oxide contains 16-44th8, or 36-36 per cent, of oxygen. 
 
 68. Mtrous oxide is almost without odor, but has a distinctly 
 
PBOPEKIIES OF iriTKOTrs OXIDE. 67 
 
 sweet taste ; its specific gravity referred to hydrogen is 22 ; it is 
 quite soluble in water, which at 0° dissolves more than its own 
 volume of the gas, and more than half its volume at 24°. Owing 
 to this solubility there is a trifling loss incurred by collecting it 
 in the usual manner over water; this loss may be partially 
 avoided by using warm water in the pan. Nitrous oxide may be 
 obtained in the liquid state by submitting it to a mechanical 
 pressure of about 30 atmospheres in an apparatus cooled to 0°. 
 The liquid is very mobile, boils at —88°, and crystallizes at 
 about — 100° when allowed to evaporate spontaneously under the 
 exhausted receiver of an air-pump. It is noteworthy that the 
 permanent gases, such as nitrogen, oxygen, and hydrogen, are 
 but slightly soluble in water, while all the soluble gases axe liquifi- 
 able, and often the more readily liquifiable in proportion to their 
 solubility. A drop of liquid nitrous oxide blisters the skin like a 
 hot iron. By mixing the solid, snow-like nitrous oxide with the 
 volatile liquid called bisulphide of carbon, and evaporating the 
 mixture in a vacuum, the lowest temperature which has hitherto 
 been attained is produced ; it is estimated at — 140°. 
 
 Small animals immersed in gaseous nitrous oxide die after 
 some time, but it may be respired for a few minutes with entire 
 impunity by the healthy human being. The physiological eifects 
 of this gas, when respired, vary somewhat, according to the 
 quality of the gas and the mode of administration ; sometimes it 
 produces a lively intoxication, attended with a disposition to 
 muscidar exertion and violent laughter, whence its trivial name 
 of lavghing-gas ; sometimes, on the contrary, it produces a com- 
 plete insensibility, during which surgical operations may be per- 
 formed without pain. "When intended for respiration, great atten- 
 tion should be paid to the purity of the gas ; carefully prepared 
 and judiciously administered, it is advantageously used as an anae- 
 sthetic agent, especially for operations lasting but 'a few seconds. 
 
 As the gas contains nearly twice as much oxygen as atmospheric 
 air, it does not seem strange that it should make common com- 
 bustibles bum with great intensity ; it forms explosive mixtures 
 with many inflammable gases ; it causes glowing charcoal to burst 
 into flame, and sulphur and phosphorus bum in the gas with 
 great brilliancy, if well on fire when immersed in it. 
 
58 
 
 PEEPAEAIION OP NITBIC OXIDE. 
 
 Exp. 36. — ^Place a bit of sulphur in a deflagrating spoon, and ignite 
 it witli the least possible application of heat ; then thrust it into a 
 bottle of nitrous oxide. It will be extinguished. Yet it would con- 
 tinue to bum in the air. Heat the sulphiu: much hotter, and again 
 introduce it into the bottle of nitrous oxide. It will now bum far 
 more brilliantly than in the air. 
 
 The air is not a chemical compound, but only a mechanical mixture 
 of nitrogen and oxygen ; so that a body burning in the air has only to 
 take oxygen, which is perfectly free to join it. The case is entirely 
 different when the substance at whose expense the oxygen is furnished 
 is a chemical compound ; to dismember the compound will require a 
 force superior to that which binds its elements together. Before the 
 sulphur, in this experiment, can unite with oxygen, it must detach 
 the oxygen from the nitrogen with which it is combined. To accom- 
 plish this, the sulphur must be hotter than it need be for simple biirning 
 in the air. We shall soon learn that there are many chemical com- 
 pounds, much richer in oxygen than either the air or nitrous oxide, 
 which nevertheless cannot support combustion at all, in the ordinary 
 sense of the term, and this simply because the common combustibles 
 are quite unable to detach the oxygen from the elements with which 
 it is ah'eady combined. 
 
 69. Nitric Oxide. — The nitrous oxide which we have thus 
 studied, is a derivative of nitric acid, or, more exactly, of the 
 compound of nitric acid with ammonia-water, but it is only one 
 of several such derivatives. We proceed to investigate another 
 substance still more directly obtained from nitric acid. 
 
 Exp. 37. — Place some copper 
 tm-nings or filings in a bottle ar- 
 ranged precisely as for genera- 
 ting hydrogen (see Exp. 19), and 
 pour upon them one half of the 
 nitric acid still remaining from 
 Exp. 32, previously diluting this 
 portion of acid with twice its 
 bulk of water. Brisk action will 
 immediately occur. The bottle 
 becomes filled with red fumes, 
 but when the gas disengaged is 
 collected over water, it is found 
 to be colorless. Collect four bot- 
 tles, of 300 to 400 c. c. capacity, 
 
 Fig. 24. 
 
NITKIC OXTDB. 59 
 
 of this gas. Save the Hue solution (nitrate of copper) which remains 
 in the generator for futiu'e use. 
 
 Sxp. 38.^Dip a lighted candle into a bottle of the gas. It goes 
 out. Into the same hottle thrust a glowing splinter of wood. It wiU 
 not inflame. 
 
 Exp. 39. Lift a bottle of the gas from the water so that the air may- 
 enter the bottle, and the gas may escape into the air. Red fumes, of 
 very disagreeable smell, and very irritating when inhaled, are abun- 
 dantly produced. Bring in contact with these fumes a piece of mois- 
 tened litmus-paper. It will be immediately reddened. 
 
 Exp. 40. — Thoroughly ignite a bit of sulphur in a deflagrating- 
 spoon, and introduce it into a bottle of the gas. It will not bum. 
 
 Exp. 41. — ^Into the same bottle thrust a piece of phosphorus as big 
 as a pea, burning actively. The combustion will be continued with 
 great brilliancy. 
 
 70. The new gas is transparent and colorless, and that it is 
 sparingly soluble in water may be inferred from the fact that 
 bottles of it may stand indefinitely over water without appre- 
 ciable loss. It differs from nitrous oxide, and from all the other 
 gases thus far studied, in its relation to combustibles. The com- 
 monest combustibles will not burn in it at all ; phosphorus may 
 be melted in the gas vrithout inflaming ;»but when its combustion 
 is once started, phosphorus bums with a vividness which recalls 
 its burning in oxygen. 
 
 "When the gas touches the air, a new compound, red, acid, and 
 irritating, is immediately produced; the question arises. Is it 
 the nitrogen or the oxygen of the air which gives rise to this 
 new combination ? Experiment would answer this question in 
 favor of oxygen. If into a' bottle of this new gas nitrogen were 
 introduced, the result would be simply negative ; no visible 
 change and no chemical combination would take place. The 
 introduction of oxygen into a bottle of the gas would, on the 
 other hand, produce the red vapors in question, only more 
 vividly than air, because dilution with the inert nitrogen of the 
 air would have been avoided. So visible and trustworthy is this 
 reaction, that the gas we are studying may be used to exhibit 
 the presence of free oxygen in gaseous mixtures. For example, 
 both oxygen and nitrous oxide reinflame a glowing splinter, and 
 we cannot distinguish between these two gases by this test ; but 
 
60 ANALYSIS OP NITBIC OXIDE. 
 
 tlie gas -we are now studying supplies us with a means of disori'- 
 mination, since it produces no red fumes with nitrous oxide. 
 
 If a sufficient quantity of the metal potassium be heated in the dry 
 gas till it bums, and the experiment be so executed as to allow the 
 volume of gas to be measured both before and after the combustion, it 
 will be found that one half of the volume of gas used has disappeared, 
 and that the half which remains possesses few or none of the qualities 
 of the original gas ; a slight examination would convince us that we 
 had set free the well-known element nitrogen. The other half of the 
 original volume of gas has united with the potassium to form a body 
 which we shall hereafter be familiar with under the name of oxide of 
 potassium. The other half of the gas is then oxygen, and we have 
 found the elements which enter into the composition of this gas, and 
 the volumetric proportions in which they are united. One volume of 
 nitrogen is combined with one volume of oxygen to form two volumes 
 of the compound gas. 
 
 We meet here the first case of chemical combination betweesn 
 two gases unattended by any condensation of the ingredients. 
 The molecule of the gas will be represented by the formula NO) 
 and its elements are united by weight in the proportion of 14 
 parts of nitrogen to 16 of oxygen, because equal volumes of 
 nitrogen and oxygen ■weigh respectively 14 and 16 times as 
 much as the same volume of hydrogen. The gas is another oxide 
 of nitrogen, and is distinguished by the name nitric ocdde. 
 
 When there are two or more oxides of one element, the terini- 
 nation ous implies less oxygen than the termination ic, as in this 
 case ; nitrovs oxide contains half as much oxygen for its nitrogen 
 as nitric oxide. 
 
 Nitric oxide is one of the permanent gases ; it has never been 
 liquified. It is a very stable compound, and if perfectly dry is 
 not decomposed by a red heat or by the action of electric sparks. 
 Owing to its rapid union with oxygen and the formation of acid 
 products, its taste, gmeU, and respirability cannot be ascertained. 
 Bearing in mind the fact that certain red acid fumes, the like of 
 which we remember to have seen in making nitric acid are 
 formed by adding oxygen to nitric oxide, we proceed to a further 
 study of still other oxides of nitrogen. 
 
 71. Hyponitrie Aeid. — When a mixture of two volumes of 
 nitric oxide and one volume of oxygen, thoroughly stirred to- 
 
HTPONITEIC ACID. 61 
 
 gether and perfectly dried, is submitted to the action of a freezing 
 mixture of salt and ice, transparent, colorless crystals are con- 
 densed from the mixed gases ; but if the least trace of moisture 
 has been present, the product ■will he an almost colorless liquid. 
 The vapor of this new substance has a brownish red color; from 
 a mixture of two measures of nitric oxide and one measure of 
 oxygen, two measures of the new vapor are produced. Since 
 two measures of nitric oxide contain one measure of nitrogen and 
 one of oxygen, the compoedtion of the new substance may be 
 represented by the accompanying diagram ; the molecide will be 
 represented by the formula 
 
 N 
 
 + 
 
 
 
 
 
 NO, 
 
 NOj, and the composition of 
 the substance by weight wiE 
 be 14 parts of nitrogen to 32 
 of oxygen. The name of this 
 new body is Hyponitrio acid, 
 a name derived from nitric acid by prefixing the Greek icro, 
 "below." The term is used to indicate that the substance to 
 which it is applied contains less oxygen than the other substance 
 from which the name is derived. Thus hyponitric acid contains 
 less oxygen than nitric acid, hyposulphurous acid less than sul- 
 phurous, and so forth. It remains to justify this assertion re- 
 specting the comparative oxygen-contents of hyponitric and 
 nitric acids. 
 
 Exp. 42. — ^Add to the nitric acid which remains from Exp. 32, pre- 
 viously diluted with twice its bulk of water and wanned over the 
 lamp, finely powdered litharge in small portions so long as it readily 
 dissolves. The operation may he best performed in an evaporating- 
 dish, which should he only very moderately heated. The substance 
 sold under the name of litharge is a simple combination of the two 
 elements, lead and oxygen; the formula of its molecule is PbO, in 
 which Ph represents the least proportional weight of metallic lead 
 (plumbum) ; its composition by weight is accurately known. When 
 the litharge no longer dissolves with promptness, no more should he 
 added, and the liquid in the dish should be evaporated to dryness, at 
 first on the wire gauze over the lamp, but towards the end of the 
 operation on a water-bath. 
 
 During this evaporation there escape into the air unchanged, water 
 and the excess of nitric, acid which was not neutralized by the oxide 
 
62 HTPOKITRIC ACID. 
 
 of lead. There remains a white, saline substance, which has resulted 
 from the combination of the oxide of lead with a portion of the nitric 
 acid ; it is called nitrate of lead. Experience has proved that it is a per- 
 fectly dry substance, containing no water whatever ; it is the raw mate- 
 rial, 80 to speak, of important experiments shortly to be described. 
 
 Exp. 43. — Heat one or two teaspoonfuls of the nitrate of lead, of 
 Exp. 42, in an ignition-tube, and observe that the compound decom- 
 poses ; deep red fumes are produced, and oxide of lead (litharge) is 
 left behind. If these red vapors be carried through a U-tube immersed 
 in a mixture of ice and salt, a portion of the vapors condense into a 
 liquid, while an uncondensable gas passes through the cold tube, and 
 may be collected by a suitable arrangement beyond the U-tube. The 
 condensed liquid is hyponitric acid ; the gas is oxygen. If the com- 
 plete absence of moisture has been secured, crystals of hyponitric acid 
 may often be obtained by replacing the first U-tube by a second to- 
 wards the end of the distillation. In fact, this is by far the most con- 
 venient method of preparing hyponitric aQJd. Into the U-tube con- 
 taining the liquid hyponitric acid drop a bit of ice or a little snow ; 
 the color of the solution changes from reddish to a greenish blue, and 
 two layers become visible in the liquid. The explanation of this 
 change will be found in the next section. 
 
 The name of hyponitric acid is now justified; for it is apparent 
 that when the litharge was dissolved in nitric acid, it found there, 
 and combined with, an oxide of nitrogen containing more oxygen 
 than hyponitric acid does, since when this oxide of nitrogen is 
 decomposed by heat, as in the experiment just described, hypo- 
 nitric acid and oxygen are evolved, the litharge remaining behind 
 unaltered. Keserving the further discussion of the composition 
 of nitric acid, we may here speak of the properties and products 
 of hyponitric acid. 
 
 72. Hyponitric acid occurs in. the solid, liquid, and gaseous 
 states; at — 9° it crystallizes; above that temperature and below 
 22° it is a mobile liquid of sp. gr. 1-451, and of various colors at 
 various temperatures ; it boils at 22°- The liquid acid gives off 
 red, acid, irrespirable vapors at the ordinary temperature. If to 
 liquid hyponitric acid, cooled by ice and salt, a proportionally 
 small quantity of ice-water be added, two layers of liquid are 
 formed, as has been above illustrated, the upper and least-colored 
 of which consists principally of nitric acid, the lower and darker 
 of a fluid which yields, on cautious distillation at a low tempo- ■ 
 
ASTALTSIS OP NITRIC ACID. 63 
 
 rature, a very volatile blue liquid. This blue liquid is so unstable 
 that its composition and qualities are not certainly known ; but 
 it is supposed to be, or to contain, an oxide of nitrogen differing 
 from all those heretofore studied, — an oxide capable of direct 
 derivation from nitric oxide by adding, to any volume of this last 
 one-fourth that volume of pure oxygen, and therefore answering 
 to the formula ^fi^, and being composed of 28 parts by weight 
 of nitrogen and 48 parts of oxygen. This obscure substance is 
 known by the name of nitrous acid; though itself but imper- 
 fectly known, some of its compounds are not unfamiliar bodies. 
 
 73. We have already learned that the white, saline substance 
 called nitrate of lead can be made from oxide of lead and nitric 
 acid, that it contains no water in its composition, and that when 
 heated it is decomposed into oxygen, an oxide of nitrogen, and 
 the original oxide of lead. On the basis of these facts, a method 
 has been constructed of determining the composition of nitric acid 
 hy weight. 
 
 To 10 grammes of oxide of lead add something more than enough 
 nitric acid to transform it completely into nitrate of lead ; evaporate 
 the excess of acid, dry the residual nitrate of lead 'completely, and 
 weigh it. If W represent this weight in grammes, W— 10 is the 
 weight of the unknown oxide of nitrogen which has combined with 10 
 grammes of oxide of lead to form W grammes of nitrate of lead. From 
 these data the percentage composition of nitrate of lead can be calcu- 
 lated ; 10 grammes of pure nitrate of lead invariably contain 
 
 Oxide of lead .... 6-738 grammes. 
 
 Oxide of nitrogen . . 8'262 „ 
 If now 10 grammes of pure nitrate of lead be decomposed by heat 
 under such conditions that the vapors which it yields shall pass over 
 some substance capable of abstracting all the oxygen from the vapors 
 without affecting the nitrogen, it will be possible to collect all the 
 nitrogen contained in 3'262 grammes of the unknown oxide of nitro- 
 gen, and so to determine its volume and thence its weight. 
 
 This determination is actually made by heating the nitrate of lead in 
 a long glass tube, in such a manner that aU the vapors evolved from it 
 pass over a large surface of red-hot copper. The copper absorbs the 
 oxygen, the mtrogen passes over it unaltered and is collected in a suit- 
 able vessel and accurately measured. As the specific gravity of nitro- 
 gen at any given temperature and pressure is known with precision, 
 the exact weight of the nitrogen can be deduced from this volume. 
 
64 COMPOSITIOJf OF NITRIC ACID. 
 
 Suet experiments often repeated have led to the conclusion that the 
 oxide of nitrogen, which with oxide of lead makes up nitrate of lead, 
 contains 
 
 Nitrogen; 25'98 per cent. 
 
 Oxygen 74-07 „ 
 
 If these two numhers be divided by the specific gravities, or unit- 
 volume-weights, of the two gases respectively, the quotients will 
 express the composition by measure of the oxide of nitrogen ; the 
 quotients are 1-862 and 4-63, numbers which are to each other as 1 to 
 2-5 or, avoiding fractions, as 2 to S. 
 
 The molecule of this compound is' therefore considered to contain 
 two volumes of nitrogen and five volumes of oxygen, and is represented 
 by the formula N^O, ; the weight of this molecule will be 108, of 
 which 28 parts will be nitrogen and 80 oxygen, — a composition pre- 
 cisely corresponding, of course, to the percentage composition abovei 
 given. This new oxide of nitrogen may be called for the present nitric 
 add, though we shall soon learn to distinguish between this body and 
 common nitric acid. 
 
 74. The combining proportions of nitrogen and oxygen in this 
 oxide have been experimentally determined by weight, and not 
 by volume, as ,was the case with all the preceding oxides of 
 nitrogen. The reason of this different treatment is to be found 
 in the fact that nitric acid cannot be converted into vapor with- 
 out suffering decomposition — not indeed into its elements, but 
 into oxygen and a lower oxide of nitrogen. It is therefore in 
 the present state of science, impossible to obtain a volume of 
 nitric acid gas capable of experimental resolution into nitrogen 
 and oxygen. 
 
 Since a large majority of the elementary bodies are non-volatile 
 under any treatment in our power to employ, and since the greater 
 number of chemical compounds either are non-volatile, or are 
 like nitric acid, decomposed by a temperature high enough to 
 volatilise them, the proportions in which the elements unite by 
 weight are of much more general value than the proportions in 
 which they unite by volume ; and the methods of determining the 
 atomic weights of the elements have been studied with a thorough- 
 ness, and brought to a perfection commensurate with the funda- 
 mental importance of these proportional numbers. 
 
 75. Nitric acid completes the series of oxides of nitrogen ; no 
 
OXIDES OF NITROGEN. 
 
 65 
 
 higher oxide is known. We are now prepared to exhibit this 
 series in a diagram which shall present to the eye at once the 
 volumetric composition of the oxides, the resultant volumes after 
 the condensation of the ingredients, the atomic weights of the 
 elements, and the combining weights of the compounds. Since 
 the atomic weights of the gaseous elements are at the same time 
 their specific gravities referred to hydrogen, it will he easy to 
 deduce the specific gravities, or equal-volume weights, of the 
 compound gases, N^O, NO, and N02,from their combining weights 
 by dividing these weights by two. As the resultant volumes 
 after condensation are not known for the two members of this 
 series N^Og and N^Oj, we abstain from figuring hypothetical 
 volumes which analogy may point to as probable, but which ex- 
 periment has never demonstrated as fact. 
 
 The Oxides of Nitrogen. 
 Nitrous Oxide. Nitric Oxide. 
 
 N 
 14 
 
 
 
 
 
 + 
 
 
 
 16 
 
 = 
 
 NjO 44 
 
 
 14 
 
 
 
 
 
 N 
 14 
 
 + 
 
 
 
 16 
 
 = 
 
 NO 30 
 
 Nitrous Add. 
 
 Hyponitric Acid. 
 
 
 
 ■ + 
 
 O 
 
 16 
 
 N 
 14 
 
 
 
 
 
 16 
 
 
 
 N 
 34 
 
 
 
 
 
 16 
 
 
 
 .N^O, 
 
 " 76 
 
 
 
 
 
 16 
 
 
 
 N 
 14 
 
 + ■ 
 
 
 NOs 46 
 
 
 z= 
 
 
 
 16 
 
 
 
 
 
 
 N 
 14 
 
 
 + ■ 
 
 
 
 N 
 
 14 
 
 
 Nitric Add. 
 
 
 
 
 16 
 
 
 
 
 16 
 
 
 
 
 
 16 
 
 
 
 
 
 
 
 16 
 
 
 
 
 16 
 
 
 
 _NA 
 
 108 
 
66 
 
 LAW OF MtTLTIPLE PEOPOfiTIONS. 
 
 76. These five bodies are all chemical compounds ; they are 
 definite and constant ia composition; and all differ essentially 
 from their elementary constituents and from each other, as the 
 experiments we have performed with them have abundantly de- 
 monstrated. It is, therefore, obvious that two of the elements 
 are capable of combining in several proportions to form definite 
 chemical compounds; and what is here proved of two of the 
 elements we shall hereafter find to be true of all, though not of 
 every couple ; so that the series of oxides of nitrogen is but one 
 illustration of a most comprehensive law. The difference between 
 a mechanical mixture and a chemical compound does not on this 
 account become less marked. The possible mixtures of nitrogen 
 with oxygen are innumerable ; the known combitutiions of these 
 two elements are only five, — two volumes of nitrogen combining 
 chemically either with one, two, three, four, or five volumes of 
 oxj'gen, and with no other proportions whatsoever. As for 
 volumes, so for weights ; the proportional weight of oxygen in 
 these oxides rises by definite leaps from the first member of the 
 series to the last. 
 
 This definite, step by step mode of forming chemical com- 
 pounds is one of the most characteristic, as it is one of the most 
 general facts of chemistry ; no other science offers a parallel to 
 it ; but long experience and patient labor with the balance and 
 measuring-glass have established it as the habitual mode in which 
 the force called chemical ordinarily acts. The abstract results 
 of observation and experiment may be expressed iu the following 
 proposition, often called the Law of Multiple Proportions : If two 
 bodies comhine in more than one proportion, the ratios in which 
 they combine in the second, third, and subsequent compounds are 
 definite multiples of those in which they combine to form the first. 
 
 While the mode of action of the chemical force set forth in 
 this proposition is that which has long been uppermost in the 
 minds of chemists, most prominent in chemical treatises, and 
 perhaps most important to the progress of the science in the 
 direction in which it has thus far been cultivated, it should be 
 remembered that in the phenomena of solution, in the formation 
 of metallic aUdys by fusion, and in the crystallization of minerals 
 and other substances with constant forms but variable composi- 
 
AIK A MIXTUEB. 67 
 
 tion, the chemical force has a part to play which, if more ohscure 
 than its ordiaary manifestations, is not less real. 
 
 77. -Air a mixtwre. — All that has been said of the distinction 
 between a mechanical mixture and a chemical combination finds 
 perfect illustration in the differences between air and the definite 
 oxides of nitrogen which have just been studied. Air is not, like 
 these, a chemical combination. The evidence that it is a mecha- 
 nical mixture merely may here be appropriately presented. 
 
 The statement that air contains 1 volume of oxygen to 4 volumes 
 of nitrogen is not absolutely true. These proportions are never 
 actually found ; the gases are not combined in any simple ratio 
 either by volume or weight ; they are always mixed in the pro- 
 portion of 20-81 measures of oxygen to 79'19 measures of nitro- 
 gen, or 23-10 parts by weight of oxygen to 76-90 parts of nitrogen. 
 The experimental processes by which these numbers have been 
 fixed are so perfect, that it is impossible to entertain the idea 
 that the gases are really mixed in the ratio of 20 measures to 80, 
 or 1 volume to 4 volumes, or the proportion of 20 parts by weight 
 of oxygen to 70 of nitrogen, as the formula N^O would require. 
 When 20-81 parts of oxygen are mixed with 79-19 of nitrogen, 
 there is no development either of light, heat, or electricity, such 
 as usually attends the formation of a chemical compound ; and 
 the specific gravity, magnetism, and refractive power of the mix- 
 ture are such as calculation would directly deduce from the num- 
 bers expressing these properties for the two constituents. 
 
 We have seen that when nitric oxide is added to nitrous oxide 
 no red fumes are produced (§ 70), but that when the nitric oxide 
 is brought in contact with air these suffocating fumes are abun- 
 dantly formed, though the air contains only half as much oxygen 
 as the nitrous oxide. These experiments go to show that while 
 in nitrous oxide the oxygen is held in chemical combination, in 
 air it is free. 
 
 Strong positive evidence that air is a mere mixture is afforded 
 by its behavior towards water. All gases are soluble in water 
 to a greater or less extent, each one dissolving in a certain fixed 
 and definite proportion at any given temperature and pressure. 
 Thus at 15° and a pressure of 76 cm. of mercury, 1 volume of 
 water dissolves 0-0193 volume of hydrogen and 0-7778 volume 
 
 f2 
 
68 
 
 AIE A MIXTTTEE. 
 
 of nitrous oxide. As a general rule, the pressure to which the 
 liquid is exposed being constant, the quantity of gas dissolved by 
 water is less in proportion as the temperature of the water is 
 high ; in many cases boiling water is altogether incapable of re- 
 taining gases in solution, particularly those which are only spa- 
 ringly soluble at any temperature. 
 
 Hence, by prolonged boiling, many gases can be completely 
 expelled from the water which held them in solution. Por ex- 
 ample, if a solution of nitrous oxide be boiled, and the gas be 
 collected as it escapes, this gas will be found to exhibit the cha- 
 racteristic properties of nitrous oxide. The nitrous oxide has not 
 been altered by the act of solution. It still remains a definite 
 chemical compound as before. But a result very different from 
 this is obtained upon boiling water which has become charged 
 with the ingredients of atmospheric air. The gas collected in this 
 case is composed of oxygen and nitrogen, it is true, but not in 
 those proportions in which the elements are united in air. 
 
 Water does not dissolve air directly as such, as it should do 
 were air a chemical compound; but it dissolves out from it a 
 quantity of oxygen, just as if no nitrogen were present ; at the 
 same time it dissolves nitrogen in accordance with the solubility 
 of this element, and to precisely the same extent that it would 
 absorb it if there were no oxygen in the air. Oxygen is dis- 
 solved by water in larger proportions than nitrogen ; 1 volume 
 of water at 15° and under a pressure of 76 cm. of mercury 
 dissolves 0-02989 volume of oxygen, but only 0-0148 volume 
 of nitrogen. 
 
 Exp. 44. — By means of a sound perforated cork or caoutchouc 
 stopper, adapt to a flask of the capacity of 1 or 2 litres a gas-delivery 
 tube, No. 6, long enough to reach to the water-pan in the usual way. 
 Upon the outer end of the delivery-tube tie a short piece of caoutchouc 
 tubing, to which a stopper, made of a bit of glass rod or a wooden plug, 
 has been fitted. FiU the flask completely with ordinary well or river 
 water; fill also the delivery-tube with water, and close it by putting 
 the stopper in the caoutchouc tube. Careftdly place the cork of the 
 delivery-tube in the neck of the flask in such manner that no air shall 
 be entangled by the cork ; at the same moment remove the plug from 
 the delivery-tube, and finally press the cork firmly into the flask. Both 
 flask and tube will now be completely fiill of water. Place the dried 
 
NIIKIC ACID. 69 
 
 flask upon a ring of the iron stand, and invert a small bottle filled with 
 water over the end of the delivery-tube. Then slowly bring the con- 
 tents of the flask to boilinsf. 
 
 As the water gradually becomes warm, numerous little bubbles of 
 gas will be seen to separate from the liquid and to collect upon the 
 sides of the flask ; these subsequently coalesce to larger bubbles, which 
 collect in the neck of the flask. As soon as the water actually boils, 
 the steam will force this air out of the flask, and it will collect in the 
 inverted bottle at the end of the delivery-tube, the steam being mean- 
 while condensed as fast as it comes in contact with the cold water in 
 the pan. By continuing to boil moderately during ten or fifteen mi- 
 nutes, nearly aU the air can be swept out from the flask by means of 
 the escaping steam. The gas delivery-tube may then be lifted fr'om 
 the water-pan and the lamp extinguished. 
 
 From a litre of ordinary water about 50 c. e. of gas can usually 
 be obtained. This contains, of course, besides oxygen and nitro- 
 gen, a certain amount of carbonic acid ; but careful analyses 
 have shown that it is much richer in oxygen than ordinary air, 
 the proportion of oxygen to nitrogen in the gas from water being 
 as 32 to 68 in 100 volumes, instead of 20'81 to 79'19 as in air. 
 
 78. Nitric Acid. — ^The nitric acid above referred to (§ 73), 
 whose composition is represented by the formula N^O^, is an un- 
 stable solid which melts at 30° ; the liquid produced boils at 47° 
 and is decomposed at 80°. The crystals of this substance are 
 transparent and colorless ; they undergo spontaneous decomposi- 
 tion into hyponitric acid and oxygen, even when preserved in 
 closed tubes. It is obvious that this is not the common nitric 
 acid with which we are already familiar. It remains to demon- 
 strate that commercial nitric acid contains water and the oxide of 
 nitrogen N^O,. A single experiment may be made use of to 
 demonstrate the presence of water in common nitric acid, and at 
 the same time to determine the proportion in which it enters into 
 the composition of the sample of acid examined. 
 
 By adding to a known weight of common nitric acid (10 grammes, 
 for example) a weighed quantity of the oxide of lead much larger than 
 the acid is able to dissolve (100 grammes, for instance), and then 
 heating the mixture, with suitable precautions against over-heating, in 
 a weighed flask, the vapor of water, and nothing else, is given off'; 
 this vapor may of course be condensed, and proved to be common 
 water. Since the oxide of lead contains nb water, and the nitrate of 
 
70 HYDRATED NITEIC ACID. 
 
 lead is also anhydrous, it follows that whatever water escapes from the 
 flask during the heating must be derived from the 10 grammes of nitnc 
 acid, and, further, that if the heating be long enough maintained, all 
 the water which the acid contained will be expelled. By weighing the 
 flask and its contents after all water has been thus driven out, the loss 
 of weight win be the quantity of water contained in the 10 grammes 
 of acid. 
 
 It has been already proved (Exp. 42) that the nitrate of lead, 
 which, with a quantity of unused litharge, constitutes the residue 
 in the flask, yields the oxide of nitrogen N^Oj. If this oxide of 
 nitrogen be called nitric acid, then is the common acid hydrated 
 nitric acid ; but if the shorter name, nitric acid, be applied to the 
 commoner substance the commercial acid, then the oxide "Nfi^ 
 must be distinguished as anhydrous nitric acid. 
 
 79. Anhydrous nitric acid unites with water in at least two 
 definite proportions ; its molecule combines with one molecule of 
 water, or vrith four, to form the two hydrates represented by the 
 formulae Jlfi, N^O^, and 4II2O, ^fi. respectively, wherein the 
 symbols of one and four molecules of water are simply placed 
 beside the formula of the molecule of anhydrous nitric acid. 
 Ponderal analysis has given us this knowledge of the composition 
 of these two hydrates, by actually weighing the proportion of 
 water combined with the oxide of nitrogen in the two cases. 
 
 When pure nitric acid is spoken of, the acid containing one 
 combining proportion of water to one of the oxide of nitrogen is 
 generally referred to. This acid is often called the monohydrated 
 acid, an adjective which may be applied to any substance which 
 is coupled with a single molecule of water. The monohydrated 
 acid is a colorless, transparent, mobile liquid of specific gravity 
 1-52, which boils at 86° and freezes at about —60°. Light 
 slowly decomposes it, and a very moderate heat resolves it, not 
 indeed into its elements, but into less complex compounds. It 
 exerts a highly corrosive action on organic bodies, and stains 
 tissues containing nitrogen of a bright orange colour. It should 
 be handled with great care, as it burns the skin Kke a hot iron. 
 It absorbs water from the air. When mixed with water, heat is 
 developed from the mixture, and the second definite hydrate is 
 formed, ^B-fi, N^Oj, — a colorless, strongly acid liquid, having a 
 
THE TEEM OXII)IZIlf& AGENT. 71 
 
 specific gravity of 1-42, and containing 60 per cent, of anhydrous 
 nitric acid. To this last hydrate all weaker and stronger acids 
 are alike converted by boUiag. The ordinary nitric acid of com- 
 merce has a specific gravity of either 1-40 or 1-42, and therefore 
 contains either 56 or 60 per cent, of anhydrous nitric acid. 
 Sometimes its specific gravity is as low as 1-33 or 1-28. What 
 is known in commerce as aqua fortis is a still weaker nitric acid 
 containing some nitrous acid and other impurities. 
 
 80. Nitric acid, especially when hot, gives up a part of its 
 oxygen with great facihty to substances capable of combining 
 with oxygen. When a substance habitually and readily imparts 
 oxygen to other bodies with which it is brought in contact, it is 
 called an oxidizing agent ; and, on the other hand, a substance 
 which habitually and readily takes oxygen out of other substances 
 with which it is brought in contact, is called a reducing agent. 
 When concentrated, nitric acid acts with more energy than when 
 diluted with water ; and when mixed with strong sulphuric acid 
 (a substance which tends to take water from other compounds), 
 it becomes an oxidizing agent of intense power. We have seen 
 liquid nitric acid yield a part of its oxygen to copper with evolu- 
 tion of nitric oxide, a lower member of the series (Exp. 37), and 
 we have also learned that the vapor of anhydrous nitric acid will 
 give all its oxygen to red-hot copper, nitrogen being set free 
 (§ 73). Most of the metals are dissolved by nitric acid, with 
 evolution of one or other of the lower oxides of nitrogen ; and 
 sulphur, phosphorus, arsenic, carbon, and many other less familiar 
 elements are converted by it into oxides. Organic substances 
 are oxidized by nitric acid to very various degrees and with very 
 various products, according to the strength and temperature of 
 the acid employed. 
 
 81. Combining Weights of Chemical Compounds. — The atomic 
 weight of oxygen, or the weight of the least proportional quan- 
 tity of oxygen which enters into combination, is the same when 
 it unites with nitrogen as with hydrogen. It is a general fact, 
 that each element has but one least combining weight with each 
 and all of the other elements. The atomic hypothesis is based 
 upon this important fact. This hypothesis attributes to the 
 imagined atom of each element a constant proportional weight. 
 
72 
 
 COMBINING -WEIGHTS. 
 
 expressed by the same number which, experiment proves to be 
 the combining proportion by weight of the element taien in 
 finite, ponderable quantities. In this sense the atom of oxygen 
 is said to be 16 times as heavy as the atom of hydrogen, and the 
 atom of nitrogen 14 times as heavy as the atom of hydrogen. 
 The combining weight of a chemical compound is always equal 
 to the sum of the atomic weights of the elementary atoms con- 
 tained in its molecule. Thus the combining weight of water, 
 HjO, is 18=2+16; of anhydrous nitric acid, N^Og, is 108 
 =2x14+5x16; of monohydrated nitric acid, H^O, N^Oj, is 
 126=2+2x14+6x16. 
 
 It must never be forgotten that these combining weights are 
 . not absolute weights, but simply express the proportions by 
 weight in which the elements and their compounds invariably 
 unite. The combining weight of a compound is directly deduced 
 from the composition of the molecule, or least quantity of the 
 compound which can exist by itself uncombined, or take pari; in 
 any chemical process. To correctly determine this least propor- 
 tional quantity often requires a large accumidation of facts, and 
 a just coUation of these facts, such as is possible only when a 
 wide experience is added to a keen insight into the principles of 
 chemical philosophy. 
 
 82. The discussion of the true molecular formulse of chemical 
 compounds presents difficulties which render it entirely unsuit- 
 able for our present stage of progress ; nitric acid, however, wiU 
 enable us to illustrate one of the difficulties appertaining to the 
 subject. When nitric acid dissolves oxide of lead (Exp. 42) the 
 reaction which occurs may be thus symbolized : — 
 
 PbO + H,0, N,0, = PbO,N,0, + H,0 
 Litharge. Nitric acid. Nitrate of lead. Water. 
 
 The resulting molecular formulae of nitrate of lead is not divisible 
 by any number but unity, and therefore cannot be made simpler 
 and stiU express the same proportional combination of its ele- 
 ments. 
 
 If instead of the oxide of lead we employ the oxide of silver, 
 we shall find it possible to express the resulting molecule of 
 nitrate of silver by two formulse, either of which will represent 
 
COMBININO WEIGHT OF NITKIC ACID. 73 
 
 correctly the proportions by weight in which the elements have 
 combined : — 
 
 Ag,0 + H,0, N,0, = Ag^O, N,0, + H,0 ; or 
 Oxide of silver. Nitric add. Nitrate of silver. Water. 
 
 Ag^O + H,0,N,0, = 2AgN03 + H,0. 
 Now there is a class of metals which enter into reactions in the 
 manner of silver in the above equations ; and there is another class, 
 of which lead may be taken as an example ; and the diiference 
 between these two classes is put into the form of a definition by 
 the statement that silver and its analogues are wni-valent or 
 mono-atomic, and that lead and its analogues are bi-valent or 
 bi-atomic, — terms which are intended to express the fact that 
 one atom of any metal of the lead class is capable of uniting with 
 twice as many atoms of oxygen, chlorine, or any other element 
 as one atom of any metal of the silver class. 
 
 The use of the common algebraic signs in these formulae re- 
 quires no explanation. The sign of equality denotes the equality 
 of the sum of the atomic weights on either side of it ; a numeral 
 on the left of a group of symbols is intended to multiply the whole 
 group, unless a comma divides the group, in which case the nu- 
 meral multiplies that part of the group on the left of the comma ; 
 brackets are sometimes used, as in algebra, to mark the extent 
 of the multiplication. The formula of nitric acid itself admits of 
 simpler expression : 
 
 H,0,N,0, = HAOe = 2HNO3. 
 The first formula reminds us that the nitric acid, of which we 
 speak, may, by indirect means, be made to yield anhydrous nitric 
 acid and water ; from the second we easily learn the proportions 
 in which the three elements are united by weight ; but the third, 
 IINO3, expresses these same proportions with precision, and is 
 the most concise of the three. Now, although the two formulae 
 H^NjOj and HNO, express precisely the same compound of the 
 same three elements in the same fixed proportions by weight, the 
 combining weight of nitric acid is 63 if the last formula be cor- 
 rect, and 126 if the first represents the real molecule of the acid. 
 In the great majority of chemical processes in which nitric acid is 
 involved, that proportional weight of nitric acid is necessary which 
 
74 NITKIC-ACID EEACTIOIfS. 
 
 is implied by the molecular formula H^N^Oj ; but there are not a 
 few cases in which the proportional weight represented by the 
 simpler formula SNO^ completely accomplishes the actual reac- 
 tion, and is capable of representation in the algebraic form. 
 
 To illustrate the first class of cases we have the formula, just 
 given, of the reaction which occurs when oxide of lead is dis- 
 solved in nitric acid ; a less proportional weight of nitric acid 
 than HjNjOj or 2HNO3 wiU not answer the conditions of the re- 
 action. Let us draw from the preceding sections some further 
 illustrations of this class of nitric-acid reactions. When copper 
 (whose symbol is Cu, from cujarum) is used to set free nitric 
 oxide from nitric acid (see Exp. 37), the reaction is symbolized 
 as follows : — 
 
 3Cu -I- 4H,]Sr,0, = 2N0 -f- 3CuN,0, + 4H,0. 
 Copper. Nitric acid. Nitric oxide. Nitrate of copper. Water. 
 
 When nitrate of lead is decomposed by heat iato litharge, hypo- 
 nitric acid, and oxygen, the following equation represents the 
 chemical change : — 
 
 PbN,0„ = PbO + 2N0, 4- 0. 
 
 In these two reactions the nitrates of copper and lead contain two 
 combining weights of nitrogen and six of oxygen for each one of 
 the metal. 
 
 To illustrate the second class of nitric-acid reactions, we have 
 only to explain more fully the nature of some of the substances 
 with which we have already experimented. As the nitrate of 
 lead may be made by bringing together oxide of lead and nitric 
 acid, water being eliminated, so the nitrates of potassium and 
 sodium, from which we originally prepared nitric acid (see 
 Exp. 32), may be formed by an analogous, though not identical, 
 reaction.' The composition of common caustic potash, or caustic 
 soda, may be expressed in two ways. Some chemists represent 
 these substances as consisting of oxide of potassium, or sodium, 
 and water, and therefore prefer the formula E^OjH^O; while 
 other chemists divide this molecular formula by two, and repre- 
 sent caustic potash by the briefer formula KHO, and caustic soda 
 by the corresponding symbol NaHO. In these formulsB K stands 
 for Kalium, the Latin name of potassium, and Na for Natrium, 
 
KTTO + 
 
 HNO3 
 
 Caustic potash. 
 
 Nitric- acid. 
 
 NaHO + 
 
 HNO3 
 
 Caicstic soda. 
 
 Nitric acid. 
 
 NITROGEN AND HYDROGEN. 75 
 
 the Latin name of sodium. If we adopt for the moment these 
 shorter formula, which of course express precisely the same pro- 
 portional composition by weight as the longer, the reaction by 
 which nitrate of potassium, or sodium, may be prepared wUl be 
 written as foUows : — 
 
 = KNO3 + H,0 
 
 Nitrate of potassium. Water. 
 
 = NaNO, + H,0 
 
 Nitrate of sodium. Water. 
 
 From this nitrate of potassium, or sodium, nitric acid is prepared 
 (see Exp. 32) by treating it with sulphuric acid, a substance whose 
 composition by weight, as we shall hereafter learn, may be cor- 
 rectly expressed by the formula H^SO^. This reaction may be 
 thus symbolized : — 
 
 KlSrO, + H^SO^ = KHSO4 + HNO3 
 Nitrate ofpotas. Sulph. acid. Acid sulph. ofpotas. Nitric acid. 
 By substituting Na for K the reaction with nitrate of sodium 
 would be represented. It thus appears that the molecule of nitric 
 acid, which wiU represent in the simplest way its reactions with 
 caustic potash, will not represent at all its reactions with oxide 
 of lead, unless two molecules are assumed to enter into every re- 
 action with this latter substance. The formula H^N^^e ^ ^^® 
 more comprehensive, because nitrate of potassium can be repre- 
 sented by the formula K^^aOe ^ accurately, if not as simply, as 
 by the formula KNO3. 
 
 It is noteworthy that, iu the reactions above formulated, one 
 atom or combining proportional weight of potassium, or sodium, 
 changes place with one atom of hydrogen, while one atom of lead 
 or copper replaces two atoms of hydrogen. These different capa- 
 cities of the other elements to replace hydrogen are of great im- 
 portance in chemical philosophy, and will be more fuUy treated of 
 hereafter. 
 
 83. Nitrogen and Hydrogen. — ^Ammonia-water, such as we 
 made use of in Exp. 33, when gently heated, evolves a very 
 pungent, colorless gas, which now claims our attention. 
 
 This gas may readily be prepared as follows : — Fill a flask of 250 to 
 500 c. c. capacity about half full of the strongeist ammonia- water to ba 
 
73 ASIMONIA. 
 
 had at the druggist's. Close the flask by a cork provided with a 
 funnel-tube and an exit-tube ; carry the delivery-tube to the bottom 
 of a taU bottle, having a capacity of at least a Utre and filled with 
 fragments of quick-lime. -p- ng 
 
 When the ammonia- water 
 in the flask is gently boiled, 
 the gas which passes off 
 will be deprived of mois- 
 ture by the quick-lime and 
 win issue dry from the 
 bottle ; it may be collected 
 either over mercury, or by 
 displacement, as shown in 
 the figure (Fig. 25). The 
 gas is so extremely soluble 
 in water that it cannot be 
 collected over the ordinary 
 water-pan ; as it has little 
 more than half the density 
 of atmospheric air, it can 
 be readily collected by displacement. When thus collected, the gaa 
 should be allowed to pass into the very loosely corked bottle, until a 
 piece of turmeric paper, held at the mouth, is immediately turned 
 brown ; the delivery-tube is then vrithdrawn, and the mouth of the 
 bottle is tightly closed with a caoutchouc or glass stopper. 
 
 The gas thus obtained is transparent and colorless, possesses 
 an extraordinarily pungent odor which provokes tears, and has an 
 acrid, alkaline taste. It will be found to be uninflammable, and 
 is, of course, irrespirable. It turns red litmus to blue most ener- 
 getically. Its specific gravity as deduced from actual experiment 
 is 8'62 ; a litre of the gas weighs 0-7625 grm. One measure of 
 water at 0° dissolves 1049 measures of the gas. 
 
 The ready solubility of ammonia gas may be exhibited as follows : 
 — Fill a stout glass tube, an ignition-tube for example, over mercury 
 with the gas ; grasp the tube by the top, and, holding it upright, dip 
 its mouth into a vessel of water. The water wUl rush up the tube, if 
 the gas be pure, with a force which might break the tube, if too thin. 
 
 84. The solution of ammonia exposed to the air, or placed in a 
 vacuum, or simply boiled, loses all its gas. As its ready solubi- 
 lity in water suggests' (compare § 68), the liquefaction of the gas 
 
^ALTSIS OF AMMONIA. 
 
 77 
 
 is not only possible but easy ; the gas becomes a colorless, trans- 
 parent, mobile liquid at 0°, under a pressure of 4J atmospheres, 
 or at — 40° at the ordinary pressure. This liquid freezes at 
 about — 80°. An excellent freezer, apphcable on both the large 
 and smaU scale, is now constructed, in -which the cold is produced 
 by the rapid evaporation of liquefied ammonia-gas. It is the low 
 pressure at which ammonia becomes a liquid which renders this 
 machine possible. 
 
 85. But of what is this gas, whose properties are so strikingly 
 unlike those of any gas previously studied, composed? The 
 question may be answered by the following experiment : — 
 
 With the exit-tube of pj~ £6 
 
 the drying-bottle of an ap- 
 paratus fitted for the gene- 
 ration of ammonia gas as 
 shown in the figure (Fig. 
 26), connect a tube of hard 
 glass, in which a bidb has 
 been blown (see Appendix, 
 § 4). Thrust into this bulb 
 a piece of the metal potas- 
 sium ; cause ammonia gas 
 to fiow through the bulb 
 by heating the contents of 
 the flask, and then warm 
 the glass bulb. As soon as 
 the potassium melts, it be- 
 comes covered with a brownish-green film, and a gas begins to escape 
 which we recognize as hydrogen by lighting it at the mouth of the 
 tube. The burning gas is certainly not ammonia, for ammonia is not 
 inflammable, but, as the odor proves, it is mixed with some ammonia 
 which has escaped decomposition by the potassium. 
 
 To separate this ammonia, and collect the pure hydrogen, fill a test- 
 tube, about 14 cm. long, three-quarters ftdl of mercury ; pour water 
 upon the mercury tUl the tube is full, close the tube vrith the thumb, 
 and invert it into a cup of mercury ; with the outer end of the bulb- 
 tube (Fig. 26) connect a suitable delivery-tube which shall dip into the 
 cup of mercury and deliver the gas into the test-tube, whose upper 
 quarter is full of water. The gas must pass through this water, which 
 frees the hydrogen from intermixed ammonia. 
 
78 
 
 ANAITSIS OF AMMONIA. 
 
 It is absolutely necessary to use mercury in this experiment, because 
 if the delivery-tube were allowed to dip into water, the extreme solu- 
 bility of ammonia in water might cause the water to suck back into 
 the bulb containing- the heated metal, whereupon an explosion would 
 inevitably ensue. 
 
 86. Having thus learned that potassium will set free hydrogen 
 from ammonia, just as the analogous metal sodium eliminates 
 hydrogen from water, we shaU be inclined to try upon ammonia 
 the same powerful agent by which we resolved water into its 
 elements — the galvanic current. 
 
 A glass tube (No. 1), 60 to 80 cm. long, open at one end and closed 
 at the other, is bent into the form of a V ; the closed limb is provided 
 with a platinum-wire fused into the glass, through which the wii'e 
 passes, to terminate near the bend of the V, in jnj„_ 27. 
 
 a slip of platinum foU. Fill the whole of the 
 closed limb and nearly half of the open limb of 
 this tube with ammonia- water, to which has 
 been added a teaspoonful of a strong solution 
 of sulphate of ammonium in order to increase 
 its eonducting-power ; support the tube as 
 shown in the figure (Fig. 27), and connect with 
 the platinum-wire iu the closed limb of the 
 tube the negative or zinc pole of two medium- 
 sized Bunsen cells, at the same time inserting 
 a platinum-wire and plate, attached to the po- 
 sitive or, carbon pole, in the open limb. Gas 
 quickly collects iu the closed limb. Discon- 
 nect the battery-wires, fill the open limb vpith water, close it with the 
 thmnb, and by inclining the tube transfer the gas to the open limb. 
 On applying a match to the gas, it proves to be iniiammable, and we 
 recognize it without difficulty as hydrogen. 
 
 The experiment is now repeated with the electrodes reversed ; the 
 positive pole is connected with the sealed, and the negative with the 
 open limb. The hydrogen, which is disengaged at the negative pole, 
 now escapes through the open end of the tube into the air, while a 
 transparent and colorless gas, previously evolved at the positive pole 
 in the open limb and consequently lost, is now collected in the sealed 
 end of the apparatus. The quantity of gas evolved at the positive pole 
 is comparatively small, but in half an horn- enough for examination 
 will probably have been collected. By the same manipulation as before, 
 
SYNTHESIS OF AMMONIA. 79 
 
 transfer this gas to the open limb, and thrust into it a lighted match. 
 It is neither inflammable nor will it support combustion, and has in 
 itself neither taste nor smell ; it is the inert nitrogen. 
 
 A cheaper and perfectly effective form of the apparatus used in this 
 experiment may be made by closing one end of a common U-tube with 
 a good caoutchouc stopper, through which the conducting wire is 
 thrust. 
 
 87. These experiments have conclusively proved hydrogen and 
 nitrogen to be constituents of ammonia; and it now becomes 
 desirable to prove synthetically that these two gases are the only 
 constituents of ammonia ; which would be done, if ammonia 
 could be experimentally produced by the direct union of the two 
 gases. Unfortunately, no process has been discovered whereby 
 ammonia can be directly reproduced from free hydrogen and 
 free nitrogen. The following experiments, however, will demon- 
 strate that ammonia is actually produced from materials which 
 are known to generate a mixture of hydrogen and nitrogen — or, 
 more strictly, which are known to be capable of generating both 
 hydrogen and nitrogen :— 
 
 Hxp. 45. — ^Place in an ignition-tube an intimate mixture of 3 
 grammes of fine iron filings with 0'2 gramme of caustic potash ; adapt 
 a delivery-tube (No. 7) to the ignition-tube, heat the contents of the 
 tube over the gas-lamp, and collect the gas which escapes in a test- 
 tube over the water-pan. Examine this gas, which will prove to be 
 the infiammable hydrogen. Caustic potash, as we have already 
 learned (p. 74), consists of potassium, hydrogen, and esygen ; at a high 
 temperature, metallic iron is able to seize upon a portion of the oxygen 
 in this compound, setting free hydrogen, which finds no place in the 
 new combinations. 
 
 Exp. 46. — Heat in a second ignition-tube, similarly disposed, a 
 mixture of 3 grammes of fine iron filings and 0-2 gramme of nitrate 
 of potassium, and collect the gas as before, over water. This gas has 
 neither taste nor smell, and when tested with a lighted splinter it is 
 found to be uninflammable, and in &ct to extinguish the taper. It is 
 nitrogen. Nitrate of potassium contains, as has been already stated 
 (p. 75), potassium, nitrogen, and oxygen ; at the high temperature 
 employed the salt is partially decomposed, the metallic iron combines 
 with the oxygen of the nitrous vapors formed, and their nitrogen is set 
 free. 
 
 Exp. 47. — In a third ignition-tube, heat the same quantities of the 
 
80 THE NASCENT STATE. 
 
 same materials which have been used in the last two experiments, at 
 once and together. A delivery-tube is not necessary in this case ; the 
 tube may be held in the wooden nippers by the open end. Neither 
 hydrogen nor nitrogen will be evolved as before, but instead of them 
 we have ammonia, whose presence may be manifested by holding a 
 bit of reddened Utmus-paper at the mouth of the tube. The intense 
 alkaline reaction of the gas, and its odor, sufficiently distinguish it from 
 both hydrogen and nitrogen. 
 
 88. It is to be observed that the hydrogen and nitrogen, -which 
 refuse to unite when once actually in the free state, will form a 
 chemical compound, as in the last experiment, at- the precise in- 
 stant when they issue from other compounds of which they formed 
 part. This fact is expressed by saying that these two gases will 
 enter into combination when in the nascent state — that is, at the 
 moment of birth. 
 
 There are numerous cases in which bodies which do not unite 
 under ordinary conditions are capable of chemical combination at 
 the instant when they are disengaged from other compounds ; and 
 the phrase " in the nascent state " is one of some convenience, 
 though it must not be supposed to explain, or in any way to 
 account for, the phenomena with reference to which it is used. 
 
 89. The exact quantitative analysis of ammonia gas will afford 
 proof that hydrogen and nitrogen are the sole constituents 
 of this gas, and will further show the proportions in which 
 they are combined. Ammonia is completely decomposed 
 into its elements by heat — the heat of a furnace or the 
 heat produced by a continuous discharge of electric sparks. 
 When, therefore, 50 c. c. of the gas are placed in a eudi- 
 ometer (gas-measure) (Fig. 28), and sparks are passed 
 between the platinum points by means of a Euhmkorff 
 apparatus, the gas is finally resolved into its elements ; 
 its volume increases until it reaches 100 c. c, or double its ori- 
 ginal bulk, when it remains constant. We know that a part, at 
 least, of these 100 c. c. of gas is hydrogen, and that this hydro- 
 gen can be eliminated from the gaseous mixture by introducing 
 oxygen in sufficient quantity to convert the hydrogen into water, 
 and then exploding the mixture. Were the 100 c. c. of gas all 
 hydrogen, 50 c. c. of oxygen would convert it into water. That 
 we may be sure of having enough oxygen, let us introduce into 
 
COMPOSITION or AJSIMONIA. 
 
 81 
 
 the eTidioineter 50 c. c. of oxygen, and then pass a spark to explode 
 the mixture. 
 
 After the explosion, only 37'5 c. c. of gas will remain ; 112-5 
 c. c. have disappeared, having heen converted into water. But 
 of these lost 112-5 c. c. we know that 75 c. c. must have been 
 hydrogen and 37'5 c. c. oxygen, in accordance with the known 
 volumetric composition of water ; consequently, the 100 c. c. of 
 gas, into which the original 50 c. c. of ammonia were dilated, 
 contained 75 c. e. of hydrogen. After the explosion, there re- 
 mained 37'5 c. c. of gas, and since we used only 37-5 c. c. of 
 oxygen out of 50 c. c. added, we may infer that 12-5 c. c. of 
 oxygen stiU remain in the residue from the explosion. On intro- 
 ducing into the eudiometer a little pyrogaUic acid (an acid used 
 in photography) dissolved in water, and a few drops of a solution 
 of caustic potsish, these 12-5 c. c. of oxygen wiU aU be absorbed 
 by these liquids, and there wiU remain 25 c. c. of a colorless gas, 
 which may readily be recognized as pure nitrogen. The original 
 50 c. c. of ammonia have therefore yielded 75 c. c. of hydrogen 
 and 25 c. c. of nitrogen, and the composition of ammonia, both 
 by weight and measure, may be fully expressed by the diagram : 
 
 H 
 
 1 
 
 H 
 1 
 
 H 
 1 
 
 V + 
 
 N 
 14 
 
 NH, 17 
 
 This composition of the gas is verified by its specific gravity as 
 
 determined by experiment, namely, 8-62. 
 
 Three volumes of H weigh . . . . 3 
 One volume of N weighs ... 14^ 
 
 Two volumes of NH, should weigh . . 17 
 One volume of NH3 should weigh . . 8-5 
 
 a number sufaciently near the result of direct experiment. 
 
 90. The knowledge, thus acquired, of the composition of am- 
 
 monil will enable us to recur with advantage to some of the ex- 
 
 G 
 
82 THE SBOUP AMMONItTM. 
 
 periments performed in the first part of this chapter. Ammonia 
 gas, when dissolved in water (as in the Liquor Ammoniae), must be 
 considered to be in combination with one molecule of water, in 
 the form of the compound NHjjH^O or NH^O. This compound 
 may be supposed to be dissolved in the water present in excess, of 
 what is necessary to form the compound. When this water of 
 anunonia combines with nitric acid, as in Exp. 33, to form the 
 compound we have called nitrate of ammonium, a reaction occurs 
 precisely similar to that which takes place where caustic soda 
 combines with nitric acid (p. 75) ; but in order to bring out the 
 resemblance, the elements of the compound of ammonia and water 
 must be so arranged as to exhibit its analogy with caustic soda, 
 whose formula is NaHO. Por that purpose its formula must be 
 written (NH^)HO, so that the group of elements NH^ shall stand 
 in the formula of water of ammonia where the element sodium 
 stands in the formula of caustic soda. The combination of water 
 of ammonia with nitric acid may then be represented by the 
 equation 
 
 (NH,)HO + HNO, = (NH,)N03 + H^ 
 Ammonia-water. Nitric acid. Nitrate of ammonium. Water. 
 
 just like 
 
 NaHO + HNO3 = NaNO, + H^O. 
 
 The student may write both of these reactions in the typical 
 
 manner ; the simple type water, -□- t 0, is the only one needed to 
 
 represent all these substances, whether before or after the reac- 
 tions which take place between them. 
 
 91. Ammonia-water combines with nearly aU the acids with 
 which soda is capable of combining, forming a series of compounds 
 in which the group of atoms NH^ plays the same part which the 
 single atom Na plays in the corresponding compounds of sodium. 
 For this reason it has been found convenient to give to this group 
 of atoms a name bearing some resemblance to the names of 
 metals, and it has therefore been called ammonium. Ammonium 
 is known only in its compounds ; many attempts have been made 
 to obtain it in a free state, but hitherto in vain ; as soon as the 
 group of atoms escapes from combination, it is resolved into am- 
 monia and hydrogen. 
 
SALTS OF AMMONItTM. 83 
 
 The important compounds into whioli ammonium enters, com- 
 monly called the salts of ammonium, will be studied hereafter in 
 immediate connexion with the analogous salts of sodium and 
 potassium. Already, however, it wiU be possible to verify the 
 statement of § 66, to the effect that nitrous oxide contains " aU 
 the elements, besides those of water, which enter into the compo- 
 sition of nitrate of ammonium, and therefore of its constituents, 
 nitric acid and ammonia-water." The reaction last given shows 
 that a molecule of nitrate of ammonium contains all the elements 
 of a molecule of nitric acid and a molecule of ammonia-water, 
 less one molecule of water. If the formulae of ammonia-gas and 
 nitrate of ammonium have been correctly determined, it will be easy 
 to exhibit in an equation the actual result of Exp. 34, as follows : — 
 
 (NH,)N03 = N,0 + 2H,0. 
 We thus link together several distinct experiments, and confirm 
 the determinations previously made of the composition of nitric 
 acid, nitrous oxide, ammonia, and water, by showing that the 
 representative formulae of these substances exhibit with perfect 
 precision reactions already well known to us, hut other than those 
 from which the formulae in question were originally derived. 
 
 92. Ammonia exists in very minute quantity in the atmo- 
 sphere, and hence in rain-water, fog, and dew. The proportion 
 of ammonia in rain-water has been variously given by dififerent 
 observers, from 3-49 parts to 0'744 part of ammonia in 1,000,000 
 parts of water. The water of fog and dew contains a larger 
 proportional quantity of ammonia; on account of the high solu- 
 bility of the gas, the proportion of ammonia in water derived 
 from the atmosphere is greater, the smaller the fall of water. 
 Ammonia is given off by putrefying animal and vegetable sub- 
 stances containing nitrogen ; and almost every process of slow 
 oxidation in the presence of air and moisture is attended with the 
 formation of ammonia or ammonia salts. Moistened iron-filings, 
 if exposed to the air, become rusty; and this rust is found to 
 contain a smaU quantity of ammonia. When some of the metals, 
 by preference tin, zinc, or iron, are dissolved in dilute nitric 
 acid, the oxidation of the metal is frequently accompanied, to a 
 greater or less extent, by the production of ammonia. But the 
 chief source of ammonia and its compounds is the decomposition, 
 
 e2 
 
84 SOTJECES OF AMMONIA. 
 
 either by putrefaction or destructive distillation, of nitrogenous 
 organic matter. The distillation of bones and animal refuse, for 
 the purpose of making bone-black, yields a large amount of am- 
 moniacal liquor, •which was formerly the principal source of the 
 compounds of ammonia ; the horns of deer used to be thus dis- 
 tilled, whence the name '•' hartshorn." At present, the destruc- 
 tive distillation of coal in gas-works furnishes the great bulk of 
 ammonia compounds used in the arts. The ammoniacal liquor 
 of the gas-works is water contaminated with tarry matters, and 
 holding in solution a small proportion of very volatile ammonium 
 salts. These volatile salts are distilled off, by application of heat, 
 into dilute sulphuric or mxiriatic acid, and the sulphate, or chlo- 
 ride, of ammonium thus formed is obtained from the dilute liquid 
 by evaporation and crystallization. These salts will be studied in 
 detail hereafter. 
 
 93. The solution of ammonia-gas in water is a reagent con- 
 tinually required, as a test, in the laboratory, and much used in 
 the arts. The solution is colorless, intensely alkaline, has a 
 caustic taste, and, when concentrated, blisters the skin. The solu- 
 tion is lighter than water, and so much the lighter in proportion 
 to the amount of ammonia it contains ; for this reason its strength 
 may be accurately determined by its specific gravity. Tables of 
 the relation of strength to specific gravity may be found in che- 
 mical dictionaries. The applications of ammonia-water are nu- 
 merous and various ; it is an ingredient in many pharmaceutical 
 preparations ; applied to the skin, it is an irritant, and, when 
 very strong, even a caustic; its pungent odor is reviving and 
 stimulating; in veterinary practice it is a useful medicament; 
 on account of its alkalinity it is used in removing grease from 
 cloth, and in restoring colors which have been changed by acids. 
 The solution is ordinarily prepared from a mixture of chloride, or 
 siilphate of ammonium, with slaked lime. 
 
 Exp. 48.— Mix intimately 25 grms. of chloride of ammonium, a sub- 
 stance generally sold under the name of sal-ammoniac, with about the 
 same weight of cold freshly slaked lime. Introduce the mixture into 
 a flask of 600 c. c. capacity, and place the flask on a sand-bath over 
 the gas-lamp. If a smaller flask be used, the quantities of the mate- 
 rials must, of course, be proportionally diminished. Close the mouth 
 
MAKING AMMONIA-WATER. 
 
 85 
 
 of the flask with a good cork, provided with a delivery-tuhe so bent as 
 to connect conveniently, by means of a caoutchouc connector, with the 
 first of the series of small three-necked bottles ("Woulfe's bottles) re- 
 presented in Fig. 29. 
 
 Fig. 29. 
 
 The first of this series of bottles is smaller than the rest, and is not 
 filled so full of water as the others ; it should be kept cool by immer- 
 sion in cold water ; the delivery-tube coming from the flask into this 
 bottle must not dip into the water at all, so that it will be impossible 
 for any water to suck back into the flask, should the gas suddenly 
 cease to come off from the dry mixture. The construction of the 
 apparatus is easily to be understood from the flgure ; the open tube 
 which dips beneath the water in each bottle is a safety-tube, which, by 
 admitting air into any bottle in which a partial vacuum may happen to 
 be created by rapid absorption, prevents the contents of the succeeding 
 bottle from flowing back into it. In order to show the action of the 
 safety-tubes, the open tube in the first bottle may be closed for a 
 moment with the finger and the bottle shaken very gently. Water 
 will immediately be forced back from the second bottle through the 
 connecting-tube to fill the vacuum caused by the absorption of the 
 ammoniacal gas ; but the moment the finger is removed from the safety- 
 tube air will enter through the latter to fill the vacuum, and the water 
 in the connecting-tube will fall back into the second bottle. 
 
 The ammonia-gaB cannot avoid four separate contacts with water as 
 it passes through the apparatus, so that all the gas is sure to be ab- 
 sorbed ; the contents of the first bottle will not be as pure as those of 
 the succeeding. This apparatus, or modifications of it, is used on the 
 large scale as well as the small, in operations which involve the absorp- 
 tion of a gas by a liquid capable of dissolving it. When a large quan- 
 tity of gas is continuously delivered from the generating vessel, the 
 absorption can be made equally continuous by successively removing 
 
86 EMPIEICAI FORMXTLS. 
 
 the bottle nearest the flask as soon as the liquid in it is saturated, and 
 adding a fresh bottle at the other end of the series. On heating the 
 flask, the ammonia-gas wiU be set free from the mixture, and in this 
 experiment will be mostly absorbed in the first and second Woulfe- 
 bottles. It ia evident that the Woulfe-bottles in this experiment might 
 be replaced by common bottles with mouths wide enough to admit 
 corks pierced with three holes. 
 
 The reaction between the chloride of ammonium and the 
 slaked lime is represented by the following equations : — 
 
 2KH:,C1 + CaH^O, = 2NH3 + CaCT, + 2Hp 
 Chloride of Slaked lime. Ammonia. (Jldoride of Water, 
 ammonium. calcium. 
 
 Chloride of ammonium is a compound which may be obtained by 
 bringing together dry ammonia, NH^, and dry muriatic acid gas 
 HCl (see Exp. 65). 
 
 NH3 + HCl = NH3H:C1 = NH.Cl. 
 It may obviously be regarded as a compound of the group called 
 ammonium, NH^, vfith the element chlorine ; from this view is 
 derived the name chloride of ammonium. Slaked Ume is pre- 
 pared from water and quicklime, a substance which is chemically 
 the oxide of the metal calcium, 
 
 CaO + H,0 = CaO,H,0 = CaH,0,. 
 94. In each of the last two chemical equations, two expressions 
 are given for a single substance ; in the first case, chloride of 
 ammonium is formulated in two dififerent ways, and in the second, 
 slaked lime. We may now inquire into the meaning of this 
 diversity of expression for one and the same substance. A for- 
 mida which simply represents the number of atoms of each ele- 
 ment in one molecule of any substance, as determined by its 
 analysis, is called an empirical formula. The truth of such a 
 formula depends solely upon the correct performance of the ana- 
 lytical process, and upon the accuracy with which the atomic 
 weights have been determined. Concerning such formulae there 
 is little room for difference of opinion ; they express aU. that we 
 actually know of the elementary composition of any compound 
 body. But chemists have endeavoured to contrive formulae which 
 should express something more than the mere elementary com- 
 
EMPIRICAL AND EATIONAL FOEMTJI^. 87 
 
 position by weight — which should recall the materials from which 
 the formulated substance was made, and prophesy the products of 
 its decomposition — which should not only name and number the 
 atoms of the substance, but should also suggest such a grouping 
 or arrangement of those atoms as might serve to interpret its 
 known reactions. Such formulse are called rational formula. 
 Thus NaHO is the empirical formida of caustic soda, while 
 NajO.HjO is a rational formula of the same substance, which 
 recalls the facts that it may be made from anhydrous oxide of 
 sodium and water, and that it enters into many reactions in 
 which the Na^O goes one way and the H^O another. 
 
 Another rational formula of the same substance is tt^ I 0, 
 
 which suggests many reactions in which caustic soda is involved 
 either as product or ingredient — for example, the decomposition 
 of water by metallic sodium (see Exp. 14), which may be thus 
 written : — 
 
 g}0 + Na = g^}0 + H. 
 
 We shall hereafter meet with many such reactions, in which an 
 
 atom of sodium replaces an atom of hydrogen ; the formula 
 
 Na 1 
 
 TT \ suggests this large class of reactions by implying that 
 
 caustic soda is itself constituted as water in which an atom of 
 sodium has replaced an atom of hydrogen. Such formulae as 
 H,0,N,05, PbO,]Sr,0,, lira,0,N,0,, and Na,0,H,0, are caHed 
 dualistie, because they represent these bodies as of a dual nature 
 — as being made up of two oxides which were distinct before 
 they were brought together to form the compound, and will be 
 distinct when separately extracted from it ; in a dualistie formula 
 these two distinct parts are conventionally represented as having 
 some separate existence within the compound itself. The sup- 
 position is not unnatural ; thus, for example, common plaster of 
 Paris is a substance containing the metal calcium and the ele- 
 ments sulphur and oxygen in the proportions by weight which 
 are correctly expressed by the formula CaSO^ ; but this substance 
 may be made by methods which suggest another formula. If we 
 put together quicklime CaO, and anhydrous sulphuric acid SO, in, 
 
OO DUALISTIC FOKMTTliE. 
 
 due proportions, under suitable conditions, plaster of Paris, or, as 
 its chemical name is, sulphate of calcium, results — 
 
 CaO + SO3 = CaO,S03; 
 or if we mix slaked lime CaOjH^O with strong sulphuric acid 
 HjOjSOj, in proper proportions, at a suitable temperature, we 
 shall again obtain sulphate of calcium, and water wiU be elimi- 
 nated : — 
 
 CaO,H,0 + H,0,S03 = CaO,S03 + 2Kfi. 
 
 Accordingly we find that the great majority of chemists have 
 hitherto written the formulae of sulphate of calcium, hydrated 
 oxide of calcium, and hydrated sulphuric acid, in conformity with 
 the suggestion of these reactions, CaO,S03, CaOjH^O, and 
 HjO,S03 respectively. Of positive knowledge conoeming the 
 actual grouping of the imaginary atoms which are supposed to 
 make up the hypothetical molecule of a compound body, we have 
 absolutely none, and it must never be forgotten that a rational 
 formula is merely a suggestion of some of the chemical processes 
 in which the substance formulated is capable of taking part. In 
 some cases the rational formula may point to the majority of all 
 known transformations of the substance ; but generally it suggests 
 only a few of the possible changes. Since a rational formula 
 never represents a fact, but only an hypothesis or opinion, it is to 
 be expected that a great diversity of rational formulae should be 
 in use among chemists ; and this is really the case. 
 
 The dualistic view, above illustrated, has long been, and still 
 is, the prevaUing view of the proximate composition of inorganic 
 compounds ; but in the chemistry of the very numerous com- 
 pounds which the element carbon forms with oxygen, hydrogen, 
 and nitrogen, a different view, called the doctrine of types, widely 
 obtains, and has been adopted by not a few chemists as affording 
 the best theoretical representation of aU chemical combinations, 
 whether in the inorganic or organic kingdom. According to 
 this doctrine every possible chemical combination may be ima- 
 gined to be bmlt upon the plan, or framed upon the type or model, 
 of some one of the four substances, chlorhydric acid, water, am- 
 monia, and marsh -gas. These will aU shortly be to us well-known 
 substances ; but the most important of these types is water, a 
 
• 0=one molecule. 
 0„=one molecule. 
 
 TYPICAL rOKMTJLiE. 89 
 
 body with whose composition we are abeady familiar ; we are 
 therefore competent to write upon the type of water the formulse 
 of several substances with which we have already dealt, and which 
 are classified under this t3fpe : — 
 
 Water=j|- I 0=one molecule; -g.^ I o^=two molecules. 
 
 Caustic Soda=-rr* I 0=one molecule. 
 
 HydratedOxideof Calcium, slaked lime,=^^| 02=1 molecule. 
 
 Monohydrated Nitric acid= -o- ^ ^ 0=one molecule. 
 
 Nitrate of Potassium ^ = 
 
 Nitrate of Lead=^ (p^^) 
 
 SO 1 
 Sulphuric acid= jt^ > 02=one molecule. 
 
 SO \ 
 Sulphate of Calcium p ^ [■ O^^one molecule. 
 
 In these formulse it is to be observed that K, Na, and NO^ re- 
 place one atom of hydrogen in one molecule of water, while Ca, 
 Pb, and SO^ replace two atoms of hydrogen in two molecules of 
 water. Facts of this class will accumulate as we advance, and 
 wiU be the subject of future discussion. The typical notation is 
 doubtless capable of expressing, in a logical and consistent system, 
 the greater part of the reactions of inorganic as well as of organic 
 chemistry ; but at present it finds its best application in the che- 
 mistry of the compounds of carbon, and has gained but little foot- 
 hold in the great departments of mineral and industrial chemistry. 
 
 The need of rational formulse is much more urgently felt in 
 that department of chemistry, called organic, which treats of the 
 chemistry of carbon, than ia the wider field of mineral and inor- 
 ganic chemistry. Among the very numerous compounds of car- 
 bon there are many cases in which one empirical formula repre- 
 sents not one compound, but several ; hence it becomes of con- 
 sequence to determine, or to guess, how the atoms of a compound 
 are arranged, as well as to know what and how many the atoms 
 are. The diversity of opinion concerning this arrangement of 
 
90 
 
 ITSES OF JOEMTJL^. 
 
 atoms is so great, and the possible modes of grouping the nume- 
 rous atoms which often enter into organic compounds are so many, 
 that the number of rational formulae proposed for any organic 
 substance is commonly large in proportion to the thoroughness 
 with which the substance has been studied. For acetic acid, for 
 example, one of the best-known of the compounds of carbon with 
 oxygen and hydrogen, no less than nineteen different rational 
 formulae have been proposed. 
 
 Eemembering that a rational formula is never to be regarded 
 as the expression of an absolute truth, but only as a guide ia 
 classification, an aid to the memory, and a help in. instruction, 
 and holding fast to the empirical formula as containing all the 
 results of actual observation and experiment, we shall endeavor 
 to familiarize the student with both the dualistic and typical 
 guesses at the hidden mysteries of chemical processes and the 
 unknowable structure of chemical compounds, giving the prefe- 
 rence rather to the dualistic view, as being that which at the 
 present moment prevails in the great bulk of chemical literature, 
 and has become incorporated into the language of the chemical 
 arts. 
 
 Lest any doubt should suggest itself to the student's mind as 
 to the value of symbolic formulae, let it be observed that they 
 express the elementary composition of a compound much more 
 tersely than words can, that they are written and read more 
 rapidly than the sentences of the same signification would be, 
 and that by their brevity, clearness, and precision they greatly 
 facilitate the comparative study and comprehensive classification 
 of chemical compounds. Again, the chemical equations, of whose 
 construction we have already had several examples, enable us tc 
 set forth with precision the changes which accompany complicated, 
 as well as simple, reactions. Thus the somewhat complex de- 
 composition of nitric acid by copper takes definite form in the 
 appropriate equation which has been given above (p. 74), and the 
 very simple reaction by which nitric oxide yields red fumes of 
 hyponitric acid in contact with air or oxygen is concisely stated 
 by the simple equation NO + 0=]SrOj. 
 
 The chemistry of the analysis of nitric oxide by potassium 
 (§ 70) is aU condensed into the equation N0 + K2=K O-t-N. 
 
CHLOKHYKKIC ACID. 91 
 
 When a little ice-cold water is added to liquid hyponitric acid 
 
 (Exp. 43), the reaction which occurs is very concisely set forth 
 
 in the equation ; — 
 
 Empirical: 2N0, + H,0 = HNO, + HNO3 
 
 Hyponitric -r^ . JSydrated „.^ . . , 
 
 "-^ ■ 7 Water. .. " ., Nitnc acid, 
 
 acid. nitrous acid. 
 
 Dualistic: 4N0, + 2H,0 = H,0,N,03 + H^O.N^,. 
 
 But hesides having all the advantages of a short hand, chemical 
 symbols are susceptible of another application of hardly less im- 
 portance ; they often direct the chemist beforehand to the most 
 perfect experiment among many similar, or point out in anticipa- 
 tion the possibility of certain methods of research, and the in- 
 evitable fruitlessness of others. Thus the equation 
 N^Oj -I- 5Cu = N, -1- 5CuO 
 
 actually directs the chemist to the due proportion of copper for 
 the exact decomposition of anhydrous nitric acid (§ 73) ; neither 
 four, nor six, nor any other number than five, parts of copper, 
 would give a perfect reaction without excess of either ingredient. 
 Practically, an excess of copper does no harm, and is always 
 used to make sure of the decomposition. 
 
 The student should endeavor, from the beginning, to familiarize 
 himself with the use of chemical symbols and equations, and to 
 this end he should invariably write the formula of every reaction 
 described or actually witnessed in the execution of an experiment. 
 
 CHAPTEE VII. 
 
 CHLOEHTDRIC ACID. 
 
 95. Muriatic (sea-salt) acid, called in modern nomenclature 
 chlorhydric acid, is a liquid which has been known for centuries, 
 and is to-day an article of commerce, largely employed in the 
 useful arts. The pure acid is a gas, as ammonia is ; the liquid 
 muriatic acid of commerce is only an aqueous solution of this 
 
92 
 
 MAKING CHLO'RHTBBIC ACID GAS. 
 
 gas, and gives it up when heated, precisely as ammonia- water 
 yields ammonia-gas. 
 
 This operation may be conveniently performed in the apparatus 
 shown in Pig. 80. About . . 
 
 250 c. c. of the commercial °' 
 
 acid is poured into the flask, 
 which is then moderately 
 heated ; the gas disengaged 
 is charged with aqueous va- 
 por, which needs to be re- 
 moved before the gas is col- 
 lected. For this purpose 
 the delivery-tube is carried 
 to the bottom of a bottle 
 filled with pieces of pumice- 
 stone saturated with strong 
 sulphuric acid ; the moisture 
 of the gas is greedily ab- 
 sorbed by the large surface 
 of acid with which the gas 
 comes in contact, as it is forced upward through the acid-soaked stone. 
 The dry, colorless, transparent gas must be collected over mercury, for 
 it is extremely soluble in water. 
 
 96. The gas is strongly acid in taste and reaction on vegetable 
 colors, provokes violent coughing, and is wholly irrespirable. It 
 is neither combustible nor wiU it support combustion. The gas 
 is somewhat heavier than air; its specific gravity referred to 
 hydrogen, as determined by experiment, is 18'12, its theoretical 
 density being 18'25 ; it is possible, though not convenient, to 
 collect it by downward displacement. It forms opaque, white 
 fumes in the air, owing to its union with, and condensation of, 
 atmospheric moisture. Under a pressure of 40 atmospheres, at a 
 temperature of 10°, chlorhydric acid gas is condensed into a color- 
 less liquid. Its great solubility in water would lead us to expect 
 that it could be readily reduced to the liquid state ; but, on the 
 contrary, it can be condensed only with difficulty. At 0°, one 
 volume of water dissolves about 500 volumes of chlorhydric 
 acid gas ; at common temperatures, something more than 400. 
 The specific gravity of the solution is greater than that of water 
 and the more concentrated the solution the higher the specific 
 
PEOPEEIIES OF CHLOKHTDRIC ACID. 
 
 93 
 
 gravity; so that the strength of any sample of the commercial acid 
 may be ascertained by taking its specific gravity. Tables for this 
 use will be found in chemical dictionaries. 
 
 The avidity of water for chlorhydric acid gas may be neatly 
 shown by thrusting a bit of ice into a small cylinder of the dry 
 gas standing over mercury ; the ice instantly melts, and the gas 
 as quickly disappears. A solution of the acid containing 20-2 
 per cent, of the gas, and having a specific gravity of 1-104, distils 
 imchanged at a temperature of about 111° ; stronger solutions 
 than this, on being heated under the ordinary atmospheric pres- 
 sure, lose gas untU reduced to this strength ; weaker solutions 
 lose water until raised to this degree of concentration. This 
 stable solution, which distils unchanged, is supposed to be a defi- 
 nite compound of the dry gas and water, whose composition the 
 formula HCl+SHjO would correctly represent. 
 
 97. We propose to answer the question — of what is chlor- 
 hydric acid composed — by a partial analysis and a complete 
 synthesis. 
 
 One of the elements of this gas can be isolated by a method which 
 we have already applied to the analysis of ammonia. It is only neces- 
 sary to remove the delivery-tube from the apparatus already used to 
 generate the dry gas (Fig. 30), and to fix in its place a bulb-tube of 
 hard glass, containing a 
 
 Fig. 31. 
 
 piece of potassium. As 
 soon as the acid gas reaches 
 the potassium, the metal 
 becomes covered with a 
 white incrustation ; and if 
 the bulb be now very gently 
 heated (Fig. 31), the potas- 
 sium fuses, and taking fire, 
 burns with a violet light. 
 During the reaction the 
 chlorhydric acid is decom- 
 posed, an inflammable gas, 
 easily recognized as hydro- 
 gen, is evolved, and may 
 be lighted at the end of 
 the tube. 
 The metal sodium produces similar results, but at a much higher 
 
94 ANALYSIS OF CHLOEHTDRIO ACID. 
 
 temperature. A solution of sodium in mercury, known amongst clje- 
 mists as sodium-amalgam, will however bring about the decomposition 
 of the acid at the ordinary temperature. This solution is best pre- 
 pared by very gently heating some mercury in a glass flask, and gra- 
 dually adding the sodium, cut into fragments not bigger than a grain 
 of wheat; the fragments dissolve with evolution of light and heat. 
 Why the sodium-amalgam should act at a lower temperature than the 
 sodium itself, is not clear, unless it be that the minute subdivision of 
 the sodium in the mercury gives the gas a freer contact with the metal. 
 
 Instead of potassium or sodium, as above described, metallic iron 
 could be employed for analyzing chlorhydric acid. To this end iron 
 turnings should be heated to redness in a glass tube such as is shown 
 Ln Fig. 8 ; a wide delivery-tube should be visei. 
 
 Hydrogen is, then, one ingredient of chlorhydric acid ; the other, or 
 others, have combined with the potassium or sodium-amalgam. The 
 isolation of these unknown ingi-edients may be -p^ 32 
 
 accomplished by means of the V-tube already 
 used for the analysis of ammonia. Into this 
 tube liquid chlorhydric acid of specific gravity 
 I'l, colored with indigo solution, is introduced, 
 so as to fill the whole length of the sealed, and 
 about half the length of the open, limb ; the 
 negative pole of the battery is connected vsdth 
 the wire of the sealed limb, while the positive 
 pole is inserted into the open limb. Gas ra- 
 pidly collects at the negative pole in the closed 
 limb, but at the positive pole the disengage- 
 ment of gas is so slight that it would hardly 
 attract attention but for its intensely disagree- 
 able odor and powerful bleaching action upon the blue liquid. The 
 gas in the sealed limb has no such bleaching power. When enough 
 gas for examination has collected in the sealed limb, it is transferred 
 to the open limb by the manipulation previously described (§ 86) ; the 
 gas is inflammable, and is, in short, hydrogen. 
 
 The poles are now reversed, and immediately hydrogen escapes in 
 abundance from the open mouth of the tube, while the liquid in the 
 closed limb becomes decolorized. In the course of fifteen minutes the 
 bleached liquid in the sealed limb begins to assume a yeUowish-gi'een 
 color, and the evolution of gas becomes gradually more and more 
 copious, so that in three-quarters of an hour the greater portion of the 
 tube is filled with a transparent, yellowish-green gas. As the gas is 
 transferred to the open limb of the tube for examination, it maiiifests 
 
ANALYSIS OF CHXOEHTDBIC ACID. 
 
 95 
 
 its powerful bleaching property by decolorizing, as it passes, the por- 
 tion of the acid which had retained the blue color of the indigo. The 
 tube is no sooner opened to admit a burning taper than the sulfocating 
 odor of the gas becomes oflFensiTcly perceptible ; the gas proves to be 
 uninflammable, and it supports combustion but imperfectly, as is evi- 
 denced by the sooty cloud which is produced. 
 
 This pecidiar gas, so difierent in properties from any gas heretofore 
 studied, is an element; it has been named, on account of ifa color. 
 Chlorine, from the Greek word for yeUowish-green. This element is 
 the subject of the next chapter, where it will be fully studied. As will 
 there be seen (Exp. 51), chlorhydric acid, when heated with a sub- 
 stance called black oxide of manganese, yields chlorine in abundance, 
 with great facility ; in fact, this acid is the soiirce of chlorine when- 
 ever large quantities of this gas are required. Chlorine is soluble in 
 about one-third of its volume of cold water, — a property which ex- 
 plains its apparently slow evolution at the outset of the foregoing 
 experiment, and the more rapid disengagement of the gas when the 
 liquid has become saturated therewith. Chlorine is heavier than air, 
 and consequently very much heavier than hydrogen ; the best experi- 
 mental determination of its specific gravity has given the number 35-66 : 
 but there can be no doubt that the true specific gravity of the gas is 
 35 '5, or in other words that it is 85 J times as heavy as hydrogen. 
 
 98. We have tlitiB learned that the electric current sets free 
 from chlorhydric acid two essentially different gases — ^hydrogen 
 and chlorine, — and that each of these gases may be separately 
 evolved from muriatic acid — the hydrogen by potassium, and the 
 chlorine by oxide of manganese. It remains to prove that chlor- 
 hydric acid contains no other than these two con- 
 stituents, and to demonstrate the proportions in 
 which they are united. To this end the first step 
 shaU be to make a partial quantitative analysis 
 of chlorhydric acid gas. 
 
 The instrument employed is a glass U-tube, about 
 50 cm. long by 1-5 in diameter, having one sealed 
 and one open limb ; communicating with the latter is 
 a small outlet-tube which may be closed by a spring- 
 clip on a piece of caoutchouc tubing. The apparatus, 
 mounted on a convenient stand, is represented in 
 Fig. 33. The U-tube is first filled with mercury, and 
 then, the spring-clip being open, the delivery-tube of 
 the apparatus used to generate dry chlorhydric acid gas is passed 
 
 Fig. 33. 
 
yt) COMPOSITIOSr OF OHLOEHYBKIC ACID. 
 
 down the open limb to the bend of the tube in such a manner that the 
 gas bubbles up through the mercury into the sealed limb, from which 
 the mercury escapes as the gas enters. When the closed limb is two- 
 thirds full, the outlet-tube is closed, the gas delivery-tube withdrawn, 
 and mercury is poured into the apparatus imtil it stands at the 
 same level in both limbs. The space occupied by gas in the tube is 
 then marked by a caoutchouc ring slipped over the tube. That por- 
 tion of the open limb which is not occupied by mercury is then filled 
 with sodium-amalgam. By closing the orifice of the tube with the 
 thumb, and inclining the tube, the gas may be transferred from the 
 sealed limb to the other, there shaken up with the amalgam, and re- 
 transferred to the sealed limb. This thorough contact with the sodium 
 decomposes the gas. On removing the thumb from the mouth of the 
 open limb, the mercury therein falls a little, and must be further 
 lowered by opening the spring-clip until the mercury stands at one 
 level in the two limbs. When this is the case, it wiU be observed 
 that the gas is reduced to half its original volume. The gas which 
 remains, is, of course, hydrogen. The experiment proves that any 
 given bulk of chlorhydric acid contains half that bulk of hydrogen. 
 
 By availing ourselves of the known speoiiic gravities, or like- 
 volume weights, of chlorhydric acid and chlorine, referred to 
 hydrogen, we may establish a strong presumption in favor of 
 'the supposition, that that half of any bulk of chlorhydric acid 
 which is not hydrogen is chlorine without admixture of any 
 other substance. 
 
 From the relative weight of any volume of chlorhydric acid gas 18-12 
 Subtract the relative weight of half that volume of hydrogen. . -50 
 
 And the remainder 17'62 
 
 is very nearly equal to 17-83, the relative -weight of half the 
 same volume of chlorine, according to the best experimental de- 
 terminations. If we assume, for the moment, that any volume of 
 chlorhydric gas is really composed of half that volume of hydro- 
 gen and half of chlorine, and if we use the theoretical specific 
 gravities, which are doubtless the true ones, instead of the above 
 approximate determinations, which are the best which experi- 
 ment has hitherto furnished, the numerical statement will be as 
 follows : — 
 
ATOMIC WBISHT OF CHLORINE. 97 
 
 From the relative weight of any volume of chlorhydric acid gas 18-25 
 Subtract the relative weight of half that volume of hydrogen. . -50 
 
 And the remainder , 17-75 
 
 is the relative weight of half the same volume of chlorine 
 17-75=-2-. The very close coincidence between the first nume- 
 rical statement, which is based wholly upon experiment, with the 
 second, which is based on the theory that chlorhydric acid is, by 
 volume, half hydrogen, half chlorine, is evidence enough, when 
 taken in connexion with the preceding experimental isolation of 
 chlorine from chlorhydric acid, to convince us that in any two 
 volumes of chlorhydric acid gas, one volume of hydrogen and one 
 volume of chlorine are united without condensation. 
 
 The formula of the molecule of the acid will therefore be HCl, 
 in which CI is the symbol of chlorine. The following diagram 
 represents the composition of this important compound, both by 
 volume and weight: — 
 
 H 
 
 1 
 
 + 
 
 CI 
 35-5 
 
 = 
 
 HCl 36-6 
 
 99. The atomic weight of the new element, chlorine, is hereby 
 determined. Hydrogen and chlorine unite by equal volumes to 
 form this single stable compound, chlorhydric acid ; and the pro- 
 portions in which the two elements unite by weight are directly 
 deducible from the proportions in which they unite by volume 
 and the known specific gravities of the two gases. Indeed it also 
 admits of direct proof, bj' appropriate experiment, that 36-5 
 parts by weight of chlorhydric acid gas invariably yield 35-5 parts 
 by weight of chlorine and 1 part by weight of hydrogen ; and, 
 siace it matters not what the absolute weight of these parts may 
 be, millionths or millions of grammes, the molecule of chlorhydric 
 acid, the least proportional weight in which it is conceived to 
 exist uncombined, must be composed, like any other quantity of 
 the acid, of 35-5 parts by weight of chlorine to 1 of hydrogen. 
 But we conceive of this molecule as consisting of one atom of 
 chlorine and one atom of hydrogen ; the chlorine atom, therefore, 
 weighs 35-5 times as much as the hydrogen atom. 
 
 100. If it were entirely inconceivable that another substance, 
 
 H 
 
SYNTHESIS OF CHLORHTBEIC ACID. 
 
 not identical with, chlorine, should have precisely the same specific 
 gravity as chlorine, the reasoning by which we have just arrived 
 at the composition of chlorhydric acid would be not only con- 
 vincing, it would be entirely conclusive ; it would do more than 
 establish a very strong presumption, it would furnish a complete 
 demonstration. But it is not inconceivable, though in the highest 
 degree improbable, that there should exist a body, different from 
 chlorine, yet possessing the same specific gravity, and not to be 
 detected by the qualitative tests to which we subjected the acid ; 
 and we therefore welcome the perfect demonstration with which 
 the synthesis of chlorhydric acid supplies us. 
 
 This synthesis is readily effected ; but as the experiment involves the 
 preparation of clolorine, the actual performance of the experiment will 
 be best postponed until chlorine has been prepared and studied in the 
 next chapter. The method is as follows: — Into one of two glass 
 cylinders, standing full of mercury upon the mercury trough, introduce 
 a certain volume of dry hydrogen, not so large as to fill more than 
 half the cylinder, and into the other cylinder bring precisely the same 
 volume of dry chlorine. Cover one of the cylinders from the light 
 with a towel, and deliver the contents of the other cylinder into the 
 protected one. The mixture of equal volumes of the two gases having 
 been thus effected, withdraw the towel, and leave the cylinder for 
 several hours in diffused and not too bright daylight, but sheltered 
 from the direct rays of the sun, which would cause an explosive imion 
 of the two elements. Under the influence of the light the two gases 
 gradually combine ; when the yellowish tint of the mixture has nearly 
 disappeared, the cylinder may be exposed to the direct influence of 
 the solar rays, in order to complete the reaction. Throughout the ex- 
 periment there is no change in the volume of the enclosed gas ; if the 
 temperature were constant the mercury would neither rise nor fall in 
 the cylinder. The chemical union of one volume of hydrogen with 
 one volume of chlorine is attended neither by condensation nor ex- 
 pansion. 
 
 That there has been chemical action, resulting in the disappearance 
 of the properties of the original materials, is evident from the fact that 
 the contents of the cylinder will no longer taie fire, or bleach vege- 
 table colors. In contact with air the new gas forms white clouds; 
 blue litmus paper it turns red ; and if a little water be passed up into 
 the cylinder, the gas is rapidly absorbed-; the taste and smell also, 
 and, in short, all the properties of this gas are those of chlorhy- 
 dric acid. 
 
MANTTPACTUKE OF CHLOBHYBIIIC AOIB. 99 
 
 By the synthetieal method we therefore prove that chlorine 
 and hydrogen are the only constituents of chlorhydric acid. On 
 this fact is based the chemical name of this compound. Summing 
 up our previous and present results, we now possess a complete 
 demonstration that chlorhydric acid is composed solely of hydrogen 
 and chlorine, united in equal volumes without condensation. 
 
 101. The muriatic acid of commerce is made from the most 
 abundant and cheapest of all the natural compounds of chlorine, 
 common salt, whose chemical name is chloride of sodium, and 
 formula NaCl. This substance supplies the chlorine ; the neces- 
 sary hydrogen is obtained from common sulphuric acid (oil of 
 vitriol), whose composition, as expressed in. its formula H^SO^, 
 we have already become familiar with. 
 
 The commercial acid is obtained by heating common salt with 
 sulphuric acid in iron pans or cylinders, and absorbing the evolved 
 gas in water contained in a series of stone-ware Woidfe-bottles, 
 or soine similar apparatus. The reaction is somewhat various, 
 according to the proportion of sulphuric acid employed ; it may 
 be either of the reactions expressed in the following equations, 
 or may lie between them : — 
 
 ISTaCl + H,SO, = HCl + NaHSO, 
 Chloride of Sulphuric Chlorhydric Acid sulphate 
 
 sodium. acid. add. of sodium. 
 
 2]SraCl + H,SO^ = 2H01 -f- Na.SO, 
 
 Sulphate of sodium. 
 
 In the first reaction, only one-half of the hydrogen in each 
 molecule of suiphuric acid is replaced by sodium ; in the second, 
 both atoms of hydrogen are replaced. The first reaction requires 
 more sulphuric acid than the second, in proportion to the amount 
 of the product, but is accomplished with less wear of the appa- 
 ratus, because a less heat suffices for the first than for the second 
 reaction. 
 
 We may illustrate the practical importance of the atomic 
 weights, by taking an actual example of each of these reactions. 
 Starting with 100 kilos, of salt in each case, what quantities of 
 sulphuric acid should be employed, and what will be the weights 
 of the products in each reaction ? (See § 81.) 
 
 h2 
 
100 MAlnrFACTTJEE OF CHLOEHTDEIC ACID. 
 
 The molecular weight of NaCl is 23+35-5 =58-5 
 
 H,SO, is 2 + 32+4x16 = 98 
 „ „ „ NaHSO, i8 23+ 1 + 32+4x16=120 
 Na,SO„ is 46 + 32 + 4x16 =142 
 
 HC'l is l + 35'5 = 36-5 
 
 The weight of sulphuric acid needed in the two cases is ascer- 
 tained by solving the following proportions : — 
 
 re'^ctionl ^^'^ '■ ^^ = ^*^^.'^- " ^ (=167-52 k.) 
 J Mol. wt. of Mol. wt. of Quantity of Quantity of 
 'Sia.Ql. H^SO,. ^Mlused. B.^m^ required. 
 
 reactk)n} ^^'^ ' ^^ = ^^^^' '' ^(=83-76 k.) 
 ' Mol. wt. of Mol. wt. of Quantity of Quantity of 
 
 2NaCl. H,SO,. 'Ea.Cl used, 'a.^m^ required. 
 
 The weight of chlorhydrio acid gas produced in the two cases will 
 be precisely the same ; it is deduced from the proportions : — 
 
 reSn} ^^"^ ' ^^'^ = ^^^^- = ^(=62-39 k.) 
 ' Mol. iut. of Mol. wt. of Quantity of Quantity of 
 
 NaCl. HCl. mCl used. KCl ^produced. 
 
 rSction} 11^ = '^^ = 100^- ■■ ^(=62-39 k.) 
 > Mol. wt. of Mol. wt. of Quantity of Quantity of 
 2NaCl. 2HC1. SaCl used. KCl produced. 
 
 The weights of the residual sodium-salts in the two oases are de- 
 duced from the proportions : — 
 
 relSonl ^^'^ = ^^0 = 100 k. : ^' (=205-128 k.) 
 -• Mol. wt. of Mol. wt. of Quantity of Quantity of 
 NaCl. NaHSO,. NaCl used. mKSO^ produced. 
 
 reaction} ^^^ = ^^^ = 100 k. :«. (=121-367 k.) 
 J Mol. wt. of Mol. wt. of Quantity of Quantity of 
 2NaCl. Na,SO,. mCl used, m^^^ produced. 
 
 In each case the sum of the weights of the materials employed is, 
 of course, equal to the sum of the weights of the products. If 
 the questions suggest themselves — how much water will these 
 62-39 k. of chlorhydric acid gas saturate, and what will be the 
 bulk of the concentrated solution so obtained ? — the answers can 
 
MANUPACTTIEE OF CKLORHTDEIC ACID. 101 
 
 be easUy deduced from the following data : — The strongest chlor- 
 hydric acid has a specific gravity of about 1-20, and contains 
 about 40 per cent, by weight of the gas. 40 k. of chlorhydric 
 acid gas will then saturate 60 k. of water, and it follows that 
 62-39 k. of the gas will saturate 93-58 k. of water. The weight 
 of the solution of chlorhydric acid produced will therefore be 
 62-39 + 93-58=155-97k.; and since 1 litre of the solution weighs 
 1-20 k., the total bulk of concentrated aqueous acid produced will 
 be very nearly 130 litres. 
 
 102. If the question suggest itseK — ^why not get the hydrogen 
 wanted from water, H^O, a much simpler and cheaper substance 
 than sulphuric acid? — the only answer is, that experience has 
 taught that water has no action upon salt except to dissolve 
 it, while sulphuric acid has power to part the two elements of 
 salt, and, giving hydrogen to the chlorine of the salt, to accept the 
 detached sodium of the salt in the place of its own lost hydrogen. 
 Of the nature of the play of forces by which this new adjust- 
 ment iu definite proportions of the atoms of five elements is 
 brought about, we have no distinct conception. AU that we 
 know has been said when it is stated that water works no che- 
 mical change on salt, while sulphuric acid (and a few other sub- 
 stances of analogous composition) does bring about a very essen- 
 tial change. 
 
 In the hope of rendering these and similar facts more intelli- 
 gible, many chemists have assumed that an element like chlorine, 
 or a group of elements like sulphuric acid, may possess a supe- 
 rior chemical attraction, or a greater affinity, for some elements 
 or groups than for others. They would explain the reaction 
 between salt and sulphuric acid by saying that chlorine has a 
 greater affinity for hydrogen than for sodium, while a part of the 
 sulphuric acid has a stronger attraction for sodium than for 
 hydrogen ; and, in like manner, they would account for the ab- 
 sence of action between water and salt by saying that the affinity 
 of oxygen for sodium is no stronger than that of chlorine for 
 sodium. If the second of the equations above given be written 
 after the duaUstic theory, as follows, 
 
 2NaCl + H,0,S03 = 2HC1 + Na.O, SO,, 
 we shall perceive the basis of a still more ample explanation, 
 
102 CHEMICAL AiTIKITT. 
 
 often given, of such reactions. The reaction above written is 
 said to be determined, or caused, by three affinities : — 1. The 
 affinity of the metal for oxygen ; 2. The affinity of the hydrogen 
 for chlorine ; 3. The affinity of the oxide of sodium for sulphuric 
 acid. It will be at once perceived that the contact of water with 
 salt gives opportunity for the play of the first two affinities ; it is, 
 therefore, the third affinity, superadded to the other two, which 
 in this view actually determines the decomposition of salt by sul- 
 phuric acid. 
 
 Such speculations as these have not been altogether fruitless 
 in the development of chemistry, and to some minds they seem 
 to render the actual phenomenon more intelligible; the term 
 affinity is also sometimes convenient in expressing the varying 
 intensity with which one element grapples and holds other ele- 
 ments, or groups of elements ; the student must not faU to dis- 
 tinguish, however, between the matters of fact and the matters 
 of speculation, in whatever stands written in chemical literature 
 touching affinities and their play. The best use of the iU-chosen 
 term affinity is as a synonyme for chemical force. Phrases in 
 which the term is used in this sense may contain simple state- 
 ments of fact ; but very frequently, especially when the word 
 "elective" is coupled with it, the term is used in connexion 
 with unprofitable hypotheses. What we actually know of the re- 
 action between salt and sulphuric acid is comprehended in the 
 statement that the hydrogen of the acid and the sodium of the 
 salt change places in the definite proportions by weight which are 
 expressed in the atomic weights of the two elements. 
 
 Commercial chlorhydric acid is not pure ; its commonest im- 
 purities are sulphuric acid which gets mechanically mixed with 
 the acid, iron derived from the iron vessels, arsenic supplied by 
 the impure sulphuric acid employed, the salts contained in the 
 water which dissolved the gas, sulphurous acid, and, not unfre- 
 quentiy, free chlorine. 
 
 Exp. 49. — Melt a handM of coarse common salt in a Hessian cru- 
 cible in a coal fire, and pour out the liquid salt upon a brick or stone 
 floor. Weigh out 30 grms. of the fiised salt when it has become cold 
 and place it in a flask of a litre capacity, provided with a delivery- 
 tube which can be conveniently connected by a caoutchouc connector 
 
USES or CHLOKHrOEIC ACID. 
 
 103 
 
 with a series of small Woulfe-bottles, such as is represented in Fig. 84. 
 Pour 50 grammes of strong sulphuric acid upon the salt, and imme- 
 
 Pig. 84. 
 
 diately cork the flask, place it upon a sand-bath on the iron-stand, 
 and connect the delivery-tube with the Woulfe-bottles. The tubes 
 by which the gas enters the bottles should barely dip beneath the 
 water contained in them, inasmuch as the solution of chlorhydiic acid 
 is heavier than water ; the bottles should not be more than half full, 
 for the water becomes hot and increases considerably in bulk. As hot 
 water holds less gas in solution than cold water, it is not amiss to 
 place each three-necked bottle in a vessel of cold water. The first 
 Woulfe-bottle should contain but a small quantity of water, and the 
 tube coming from the flask should not dip into this water. The con- 
 tents of the flask must be very gradually and moderately heated, else 
 a violent frothing is liable to occur, which would spoil the experiment. 
 The process is like that of making ammonia-water, except that the 
 delivery-tube passes to the bottom of each Woulfe-bottle in making 
 ammonia-water, because the solution of ammonia-gas is lighter than 
 water, instead of heavier as is the case with the solution of chlorhy- 
 diic acid gas. As with the ammonia process, the solution will be 
 purer in the second bottle than in the first, in the third than in the 
 second, and so forth. Reserve the contents of the first bottle to make 
 chlorine from (Exp. 51). The pure acid should be preserved for use 
 in experiments which cannot be performed except with an acid purer 
 than the commercial article. 
 
 103. The uses of chlorhydiic acid are very numerous. It is 
 employed in making chlorine, chlorate of potassium, and chloride 
 of lime (bleaching-powder), in preparing chloride of ammonium 
 and chloride of tin, in the manufacture of gelatine, for dissolving 
 
104 
 
 AQUA EBGIA. 
 
 metals (either by itself or mixed with nitric acid) ; it is one of the 
 most useful reagents in the chemical laboratory. - 
 
 Chlorhydric acid dissolves most metallic oxides, and appears to 
 combine with them ; but on evaporating such a solution a com- 
 pound is obtained which contains neither hydrogen nor oxygen, 
 but only chlorine and the metal. When caustic soda, for example, 
 combines with chlorhydric acid, chloride of sodium and water are 
 the products, as exhibited by the equation 
 
 NaHO + HCl = Naa + H,0. 
 When the black oxide of copper is dissolved in chlorhydric acid, 
 the green liquid produced is an aqueous solution of chloride of 
 copper ; 
 
 CuO + 2HC1 = CuCl, + H,0. 
 
 But though the metal may exist in solution in the form of chlo- 
 ride, it is quite possible to precipitate it as oxide, if it have an 
 insoluble oxide, by adding to the solution of the chloride a soluble 
 oxide of another metal capable of displacing the &st. Thus, if 
 to a boiling solution of chloride of copper a hot solution of caustic 
 soda be added, the sodium and the copper change places, and the 
 insoluble black oxide of copper is precipitated. 
 
 CuCl, + 2NaH0 = SNaCl + H,0 -|- CuO. 
 
 Chlorhydric acid is, in fact, the chloride of hydrogen, strictly 
 analogous in composition to the chloride of a metal like sodiiim, 
 and it takes part in double decompositions Hke any other chloride. 
 104. Aqiuz Regia {Royal Water). — This name was given by 
 the alchemists to a mixture of chlorhydric and nitric acids, be- 
 cause of its power to dissolve gold, the " king of metals." 
 
 Exp. 50. — Place two square centimetres of genuine gold-leaf at the 
 bottom of a test-tube, and pour upon the gold six or eight drops of 
 strong chlorhydric acid ; put a similar piece of gold-leaf in a second 
 test-tube, and pour upon it two or three drops of nitric acid ; neither 
 acid attacks the gold, which remains undissolved. If the contents of 
 the two test-tubes be mixed together in either tube, the gold-leaf will 
 almost immediately dissolve. 
 
 Platinum, which like gold resists the action of both chlorhydric 
 and nitric acids singly applied, yields at once to the mixture of 
 the two acids. Both these precious metals are converted by aqua 
 
CHLOEHTE. 105 
 
 regia into chlorides soluble in water. Strong chlorhydric acid is 
 oxidized by strong nitric acid ; cblorine, water, oxides of nitrogen, 
 and unstable compounds containing chlorine, oxygen, and nitro- 
 gen, are the products. The decomposition is complex, but may be 
 roughly represented by the equation 
 
 HCl + HNO3 = CI 4- H,0 + NO,. 
 The presence of nascent (§ 88) chlorine explains the energetic 
 conversion of metals into chlorides by aqua regia; and the strong 
 oxidizing effect of the liquid is further explained by the presence 
 of the unstable oxygen compounds which result from the reaction. 
 Aqua regia has indeed a very strong oxidizing power ; it can 
 change sulphur into sulphuric acid, arsenic into arsenic acid, and 
 effect many other similar oxidations. 
 
 This powerful solvent is made by simply mixing the two acids, 
 though in various proportions, according to the use to be made of 
 it ; the commonest mixture is composed of one part of nitric acid 
 and three parts of chlorhydric acid. 
 
 CHAPTEE YHT. 
 
 OHIO RINE. 
 
 105. Chlorine can readily be prepared from chlorhydric acid 
 by removing the hydrogen of that acid by chemical means. 
 
 Exp. 51. — ^In a flask of about 500 c. c. capacity furnished with a 
 suitable delivery-tube, place 8 or 10 grms. of coarsely powdered black 
 oxide of manganese ; pour upon it 20 or 30 grms. of common muriatic 
 acid, and gently heat the mixture. Chlorine wiU soon be disengaged, 
 and may be recognized by its peculiar color. Being very heavy the 
 gas may best be collected by displacement in dry bottles, placed in the 
 open air, or in a case or box provided with an efficient draft. It may 
 also be collected over warm water or brine in the water-pan. It can- 
 not be well collected over water at the ordinary temperature, since it 
 is rather easUy soluble therein — ^though the difficulty may be obviated 
 in part by evolving the gas rapidly, or by passing the delivery-tube 
 to the top of the bottle in which the gas is collected. It must not be 
 
106 MAKDfd CHLOKINB. 
 
 left standing over water, since it would soon be entirely absorbed. 
 In experimenting with chlorine, care must always be taken not to 
 inhale it. 
 
 The reaotion which, occiirs in this experiment may be thus 
 formulated : — 
 
 MnO, + 4HC1 = 2Efi + MnCl, + 2C1. 
 
 Black oxide of manganese is a substance rich in oxygen, which, 
 under certain conditions, it readily yields up to other elements. 
 In the case before us, the oxygen of the oxide of manganese unites 
 with the hydrogen of the chlorhydric acid to form water. The 
 chlorine of the chlorhydric acid unites in part with the manga- 
 nese, and is in part left free. 
 
 In place of the black oxide of manganese in this experiment, 
 several other substances which readily give up oxygen may be 
 employed ; and instead of the free chlorhydric acid of the fore- 
 going experiment, the mixture of common salt and sulphuric 
 acid, which generates chlorhydric acid (Exp. 49), is often used. 
 The latter method has the advantage of eliminating the whole of 
 the chlorine from the chlorine compound used, whereas, in the 
 decomposition of the oxide of manganese by chlorhydric acid alone, 
 half the chlorine remains combined with the manganese. More- 
 over, when present in excess, the sulphuric acid has the effect of 
 drying the chlorine. The reaction may be expressed as follows : — 
 
 2NaCl + 2H,80^ + MnO, = Na.SO, + MnSO^ + 2H,0 + 2C1. 
 
 Another method, which has been carried out in practice upon the 
 large scale, is to heat a mixture of common salt and nitrate of so- 
 dium with an excess of sulphuric acid. Chlorhydric and nitric 
 acids are evolved, and, reacting upon one another, generate chlo- 
 rine, hyponitric acid, and water : — 
 
 HCl + H]Sr03 =C\ + NO, + H,0. 
 The hyponitric acid is absorbed by sulphuric acid, and subse- 
 quently employed in the manufacture of sulphuric acid, while the 
 chlorine is coUeoted apart and employed in such manner as may 
 be desired. 
 
 106. Chlorine is an abundant element, and very widely distri- 
 buted in nature. It exists chiefly in combination with sodium as 
 a chloride of sodium, which is called rock-salt or sea-salt, accord- 
 
PKOPEKTIES OF CHXOKINE. 107 
 
 ingly as it is found in beds in the earth, or dissolved in the water of 
 the ocean. Since the atomic weight of chlorine is 35-5 (§ 99), 
 and that of the metal sodium is 23, each molecule, each gramme,'or 
 each kilogramme of chloride of sodium contains j||, or 60-684 per 
 cent, of chlorine. Accordingly in a gramme of chloride of sodium 
 there exists something more than 0-6 grm. of chlorine; and a 
 kilogramme of common salt should yield 606-84 grms of chlorine. 
 Jlvery litre of sea- water wiU yield about five litres of chlorine gas. 
 Besides chloride of sodium, sea- water contains small quantities of 
 the chlorides of several other metals ; there are numerous miae- 
 rals, also, which contain chlorine. 
 
 107. At the ordinary temperature chlorine is a gas of yellowish- 
 green color, 2'5 times as heavy as atmospheric air. Its specific 
 gravity and atomic weight are 35*5. It is excessively irritating 
 and suffocating, even when inhaled in exceedingly small quan- 
 tities. Any attempt to breathe the undiluted gas would un- 
 doubtedly be fatal. Under a pressure of 4 atmospheres at 15° it 
 is condensed to a yellow mobile liquid, having a sp. gr. of 1-33 ; 
 this liquid has never yet been solidified. It is soluble to a con- 
 siderable extent in water at the ordinary temperature, 1 volume 
 of it being dissolved by half a volume of water at 16°. This so- 
 lution, which exhibits the color, odor, and general chemical pro- 
 perties of the gas, is called chloriae- water. At low temperatures, 
 water dissolves a still greater proportion of chlorine ; and at 0° a 
 definite hydrate of chlorine, Ci.,SKJ}, crystaUizes out. 
 
 Uxp. 52. — Fill with water the body of a retort of the capacity of 
 500 c. c, and without tubulature. In- 
 vert the retort and set it upon a ring, or ^^' 
 
 upon a bed of sand, with the neck 
 pointed upwards in such manner that 
 no air shall enter the body. From a 
 flask in which chlorine is being gene- 
 rated pass a long dehvery-tube down 
 the neck of the retort to the water, so 
 that the chlorine may slowly bubble 
 through the water. The absorption of 
 the gas may be promoted by gently shaking the retort from time to 
 time. As soon as the water becomes saturated with chlorine, so much 
 gas vfill collect in the retort that the liquid will be pressed out of the 
 
108 
 
 CHLOEINE-WAIEB. 
 
 body and -will flow over from the neck ; when this occurs the opera- 
 tion may be stopped. 
 
 At the beginning of the experiment, before all the atmospheric air 
 has been expelled from the flask in which the chlorine is generated, it 
 is well not to push the gas delivery-tube completely to the bottom of 
 the neck of the retort, but to simply immerse it in the edge of the 
 water, so that none of the escaping bubbles of gas shall enter the body 
 of the retort until it has become evident that nothing but pure chlorine 
 is coming over ; the tube may then be immersed more deeply. 
 
 The water saturated with chlorine should be transferred to a bottle 
 and preserved for future use. It may be employed, more conveniently 
 than the gas, to Ulustrate many of the properties of the element. 
 
 In sunlight, or even in ordinary daylight, chlorine-water sufiers de- 
 composition (see § 113), but in the dark it undergoes no change. It 
 should be kept, therefore, either in a cellar or tight closet, or in a 
 stoneware bottle, or in a bottle of black, red, or yellow glass, or in one 
 covered with black paper. Through the blackened glass no light can 
 penetrate to the chlorine-water, and through red or yellow glass few, 
 if any, of the so-called chemical or actinic rays can pass. The violet 
 rays of the spectrum are those which exhibit actinic power, and these 
 are stopped by red or yellow glass, which is red or yellow because it 
 permits the passage of only these colored rays. 
 
 108. Chlorine is a powerful chemical agent. It combines with, 
 hydrogen with explosive violence upon being heated, or even on 
 being exposed to sunlight. 
 
 Sxp. 53. — In a soda-water bottle, which must be screened from 
 strong light by wrapping it in a towel, unless direct and reflected sun- 
 light be excluded from the room, mix equal volumes of chlorine and 
 hydrogen, then remove the cork and hold the mouth of the bottle in 
 the flame of a lamp. A sharp explosion will ensue. Or the mixture 
 may be made in a phial of white glass rolled up in a thick towel and 
 flUed in a darkened chamber. The explosion can then be brought 
 about by carefully rolling the phial out of its envelope into a ray of 
 Sunlight, in a place where the fragments of glass can do no harm. In 
 this last modiflcation of the experiment the phial is, of coiirse, left 
 corked. The operator should stand behind a window-shutter or other 
 suitable screen. 
 
 Still another method is to place the bottle in a shady place, and by 
 means of a looking-glass reflect upon it a ray of sunlight. The moment 
 the beam touches it, the bottle vrill explode. 
 
 A mixture of the two gases may be kept in the dark for any 
 
CHLORINE UNITES WITH METAIS. 109 
 
 length of time without change; in diffused daylight they usually 
 unite only slowly and gradually; but in direct sunlight the union 
 is so instantaneous as to be attended with explosion. 
 
 109. Chlorine combines also very readily with many of the 
 metalsj the combination being in several instances attended with 
 evolution of light. 
 
 Exp. 54. — Fill a bottle of at least half a litre capacity with dry 
 chlorine gas, by displacement ; the gas should be dried by passing it 
 through a tube filled with chloride of calcium, as described in the Ap- 
 pendix, § 15. Gradually sift a gramme or two of very finely powdered 
 metallic antimony into the bottle. The metal will instantly take fire 
 and fall in a glowing state to the bottom of the bottle. This fire 
 attends the formation of a compound of chlorine and antimony, a por- 
 tion of which wiU be seen pervading the bottle as a white smoke. 
 
 This experiment, and indeed all experiments with chlorine, should 
 be performed only in places where there is a current of air sufficiently 
 powerful to carry away from the operator the volatile products of the 
 reaction, together with any chlorine which may escape from the bottle. 
 
 As in the case of the union of sulphur with copper (Exp. 1), 
 so here it will be seen that burning, as commonly understood, is 
 in no wise peculiar to the union of oxygen with the other ele- 
 ments. In the act of chemical combination heat is always evolved, 
 and, of course, Hght as well, if particles of solid matter be present 
 and become hot enough to be luminous. 
 
 Since oxygen is very abundant, we are more accustomed to 
 witness exhibitions of its chemical action than those of any other 
 element ; but we must not therefore lose sight of the fact that 
 among the elements there are several which possess chemical 
 power as great when brought into play, though not as frequently 
 exhibited as that of oxygen. 
 
 Exp. 55. — Into a small dry bottle throw loosely several leaves of the 
 so-called Dutch-metal (an imitation gold-leaf made from an alloy of 
 the metals copper and zinc), and invert over it a bottle of dry chlorine. 
 As the heavy gas falls into the lower bottle, the chlorine attacks the 
 metal, which becomes red-hot for a moment, shrivels up, and is con- 
 verted into a mixture of chloride of copper and chloride of zinc. Both 
 these compounds are readily soluble, the chloride of copper impart- 
 ing to the water a peculiar green tinge. The term chloride is used to 
 denote the combination of chlorine with another element, just as the 
 term oxide denotes a compound of oxygen. 
 
110 CHLORINE BtTENS IN HTDEOGrEN. 
 
 110. A burning jet of hydrogen, on being introduced into a 
 jar of chlorine, will continue to bum with a peculiar green light, 
 the two gases uniting to form chlorhydrio acid. 
 
 Exp. 56. — From a gas-holder containing hydrogen, carry a glass 
 tube, No. 6, outwards horizontally a few centimetres, then downwards 
 to reach the bottom of a wide-mouthed litre bottle fiUed with dry 
 chlorine; bend the end of the tube, previously drawn to a point, 
 sharply upward, so that the jet of hydrogen may stream upwards 
 through the chlorine. Light the hydrogen jet, and insert it into the 
 bottle of chlorine. 
 
 By reversing the experiment, chlorine may just as well be 
 burned in an atmosphere of hydrogen. 
 
 Hxp. 57. — In a small flask of 75 or 100 c. c. capacity, provided with 
 a small chloride-of-calcium tube prolonged into an upright delivery- 
 tube which is drawn out to a fine point at the top, generate a free 
 supply of chlorine. Inflame a jar of hydrogen, held mouth down- 
 wards, and press it slowly down upon the chlorine flask so that the 
 orifice from which the chlorine is issuing may be at the centre of the 
 hydrogen bottle, in the midst of the gas. In passing through the 
 burning hydrogen at the bottom of the jar, the chlorine vyill be heated 
 to the temperature necessary for its own inflammation, and it vnll con- 
 tinue to bum in the hydrogen in the same way that oxygen bums in 
 hydrogen under similar circumstances. 
 
 111. The heat evolved during the combustion of hydrogen in 
 chlorine is less intense than that produced by its union with 
 oxygen. When one gramme of hydrogen is burned to chlor- 
 hydric acid, there are disengaged 23783 units of heat, while 
 34462 units of heat are evolved when it burns to water. 
 
 112. As has been seen, chlorine is both combustible and a 
 supporter of combustion so far as hydrogen is concerned, and it 
 exhibits a strong affinity for many of the metals ; but it does 
 not unite directly with either oxygen or carbon. 
 
 Exp. 68. — If a burning taper, or a bit of flaming wood or paper, be 
 thrust into a bottle of chlorine gas, the flame will become murlty, and 
 after strugghng for a moment will go out. Much smoke is at the same 
 time given off. 
 
 Exp. 59. — A bit of paper, attached to a wire, dipped in hot oil of 
 turpentine and then quickly plunged into a bottle of chlorine, will 
 usually take fire spontaneously, and burn vsdth evolution of dense black 
 
COMBUSTION IN CELOBINE. 
 
 Ill 
 
 fumes. On account of the Tolatility and ready inflammability of oil of 
 turpentine, it should he carefully heated upon a water-hath (Appendix, 
 § 17) in a porcelain dish. If by any chance the turpentine take fire in 
 the dish, it can be instantly extinguished by covering the dish. 
 
 &p. 60. — Place an inverted tall bottle full of water upon the shelf 
 of the water-pan and flU it two-thirds full of chlorine ; then displace 
 the rest of the water with ordinary illuminating gas. Cover the 
 mouth of the bottle with a glass plate, and, removing it from the 
 water-pan, place it in an upright position upon the table. Remove 
 the cover, and touch a lighted match to the gas ; fire will be propa- 
 gated from above downwards, while clouds of smoke are evolved. 
 Hold a piece of moistened blue litmus paper in the smoke ; it will be 
 reddened by the chlorhydric acid which has been formed. 
 
 The wax, wood, paper, turpentine, and gas of the foregoing 
 experiments, and indeed most of the substances ordinarily used 
 as combustibles, contain hydrogen and carbon. The hydrogen of 
 these things wiU burn in chlorine, will unite chemically with the 
 chlorine to form chlorhydric acid; but the carbon wQl not thus 
 unite with chlorine. Hence it is that, in the experiments in 
 question, the combustion is at the expense of the hydrogen ; the 
 hydrogen of the candle, turpentine, and so forth alone unites with 
 chlorine, while the carbon is set free as lampblack or smoke. 
 
 113. Chlorine can even decompose water under certain condi- 
 tions, taking away its hydrogen, while the oxygen is left free. 
 This occurs, for example, when a mixture of chlorine and aqueous 
 vapor is passed through a red-hot glass or porcelain tube filled 
 with fragments of the same material. So, too, when an aqueous 
 solution of chlorine is exposed to light, the water is gradually 
 decomposed, as has been stated in § 107, oxygen being set free, 
 and chlorhydric acid formed. 
 
 2C1 -f H^O = 2HC1 + 0. 
 Hxp. 61. — Fill a narrow-mouthed bottle, of 
 the capacity of at least half a litre, with water 
 which has been saturated vrith chlorine at a 
 comparatively low temperature — such as is 
 readily obtained by immersing the receiver in 
 ice- water during the absorption of the gas. 
 By means of a perforated cork, or better, a 
 caoutchouc stopper, fit tightly to the bottle a 
 glass tube, No. 6, bent twice at right angles. 
 
 Fig. .36. 
 
112 USES OF CHXOEIITE. 
 
 one branch of wMcli shall be long enough to reach to the bottom of 
 the bottle, while the other arm, made much shorter than the first, 
 dips into an open beaker glass half full of water. 
 
 Place the apparatus in such a position that it shall be exposed to as 
 much direct sunlight as possible. After a time oxygen gas will begin 
 to collect at the top of the bottle, and in the course of several hours, 
 or days, so much will have collected that it can be tested by removing 
 the cork from the bottle and thrusting in a glowing splinter. The 
 liquid displaced by the oxygen flows over, through the tube, into the 
 beaker glass. The chlorhydric acid of course remains dissolved in the 
 water of the bottle. 
 
 114. The appKcations of chlorine in the arts depend upon that 
 readiness to combine with hydrogen which has just been exem- 
 plifled. By virtue of this affinity for hydrogen, chlorine acts 
 indirectly as a powerful oxidizing agent. It acts as a purveyor 
 of nascent oxygen, and is hence a much more efficient agent than 
 free oxygen, such as exists in the air. Its chief uses are for 
 bleaching cotton goods, paper stock, and so forth, and for destroy- 
 ing foul and unhealthy emanations. 
 
 Hxp. 62. — ^Pour into a test-glass a quantity of chlorine-water 
 (Exp. 52), drop into it a small quantity of a solution of indigo, and 
 stir the mixture with a glass rod. The blue color of the indigo wiU 
 be immediately destroyed. 
 
 In the same way the color of litmus, cochineal, aniline-purple, 
 or of flowers, calico, and the like, can be readily destroyed by 
 immersion in chlorine-water or in moist chlorine gas. The pre- 
 sence of water is essential ; perfectly dry chlorine will not bleach. 
 
 Exp. 63. — Fill a glass tube, No. 1, about 20 cm. long, with scraps 
 of coloured calico and hits of paper which have been written upon with 
 ink. Take care that the tube and its contents are perfectly dry, and 
 that the tube is closed at either end with a cork, through which passes . 
 a short piece of tubing. No. 6. Place the tube in a vertical position, 
 and pass into it, from below, chlorine gas which has been thoroughly 
 dried by means of chloride of calcium (Appendix, § 15). The color- 
 ing-matters will not he destroyed so long, as they remain dry ; but if, 
 after thf dry chlorine has been allowed to act for a few minutes, a little 
 water be poured in at the top of the tube, so that its contents may be 
 wetted, they will be bleached at once. 
 
 1 15. Those coloring-matters which are of vegetable or animal 
 origin are for the most part complex compounds of carbon, hy- 
 
HOW CHLOEINE BLKACHES AND DISINFECTS. 113 
 
 drogen, nitrogen, and oxygen. When moist chlorine is brought 
 into contact with them, a somewhat complicated reaction occurs ; 
 a portion of their hydrogen is no doubt taken out by the chlorine, 
 hut at the same time some of the water which is present is decom- 
 posed, and its oxygen assists the disorganization of the compound 
 which is to be destroyed. 
 
 Of the hydrogenized or carburetted compounds exposed to the 
 action of the nascent oxygen in the foregoing experiment, those 
 which are most complex, and of which the elements are held 
 together least firmly, will of course be acted upon, burned up, 
 and destroyed. As a rule, the coloring-matters are far more 
 easily oxidized than the cotton cloth ; hence they can readily be 
 removed by the action of chlorine, without injury to the cloth. 
 But if the action of the chlorine were to be continued .after the 
 coloring-matter had been destroyed, the cloth itself would gra- 
 dually be burned up. 
 
 In actual practice, where the duration of the exposure of the 
 cloth to the chlorine is carefully regulated, and the portions of 
 bleaching liquor which at first remain adhering to the cloth are 
 completely removed by washing and by chemical treatment, the 
 process is perfectly safe and trustworthy as regards cotton or 
 even linen ; but the animal fibres, such as wool and sUk, are of 
 more complex composition than cotton and linen; they cannot 
 be bleached by chlorine, since this gas would attack and dis- 
 organize them. 
 
 116. In destroying noxious effluvia, chlorine either acts upon 
 them as upon coloring-matters, or it simply takes away hydrogen, 
 as in the case of sulphuretted hydrogen hereafter to be studied. 
 Putrid animal matter may be rendered comparatively odorless, by 
 sprinkling it copiously with chlorine-water ; hence a solution of 
 chlorine finds some application in inquests and judicial investi- 
 gations. 
 
 The energy with which chlorine seizes upon hydrogen may be 
 further illustrated by causing chlorine to act upon ammonia- water. 
 
 I!xp. 64. — ^Into a glass tube, No. 1, about a metre long, pour enough 
 chlorine-water to fill it nine-tenths full, and then ammonia-water 
 enough to fiU the remaining space. Close the tube with the thumb, 
 invert it and place it in an upright position upon the water-pan. The 
 
 I 
 
114 ACTION OF CHLOHINE OS AMMONIA. 
 
 ammonia-water, being epeoiflcally lighter than the solution of chlo- 
 rine, will flow upwards and become mixed with the latter ; a reaction 
 will immediately ensue ; some of the chlorine will unite with the hy- 
 drogen of a portion of the ammonia, to form chlorhydric acid, and 
 nitrogen will be set free. Numberless little bubbles of this gas will 
 escape from the liquor and collect at the top of the tube, and may be 
 subsequently tested with a burning match. The chlorhydric acid 
 formed unites with the remainder of the ammonia to form chloride 
 of ammonium : — 
 
 4NH3 + 301 = N + 3NH,C1. 
 By modifying the apparatus employed in the foregoing experiment, 
 so that a cm-rent of chlorine can be passed into a vessel containing 
 ammonia-water, the evolution of nitrogen can readily be made con- 
 tinuous, and large quantities of the gas may be collected. It would 
 be an excellent and easy method of preparing nitrogen for use in the 
 laboratory, were it not that care must be taken that the ammonia 
 shall always be present in considerable excess. If this precaution 
 were neglected, there might be formed, by the action of the chlorine 
 upon the chloride of ammonium, a very dangerous compound called 
 chloride of nitrogen. As prepared by this method, the nitrogen is 
 always contaminated with a certain amount of oxygen. 
 
 In the foregoing experiment, the chloride of ammonium which 
 is produced remains dissolved in the water. It may be recovered 
 by evaporating the water, or a new portion of it may be prepared 
 by mixing chlorhydric acid with ammonia. 
 
 Hxp. 65. — Fill one half-litre bottle with dry ammonia-gas, and 
 another with dry chlorhydric acid gas. Invert the latter, and place it 
 over the former, so that the mouth of the upper bottle shall rest upon 
 that of the lower. The gases wiU immediately tmite to form solid chlo- 
 ride of ammonium, a dense white cloud of which wiU fill the bottles : — 
 
 NH3 + HCl = NH^Cl. 
 One volume of ammonia unites with one volume of chlorhydric acid, 
 and the gases are completely condensed to a white solid. 
 
 117. Chloride of nitrogen, the dangerous compound of chlorine 
 and nitrogen which has been alluded to above, is formed when 
 chlorine is brought into contact with a weak solution of chloride 
 or nitrate of ammonium at the temperature of 15° or 20°. As the 
 chlorine is gradually absorbed, yeUow oUy drops of chloride of 
 nitrogen form upon the surface of the liquid, and soon fall to the 
 bottom : — ■ 
 
 NH.Cl + 6C1 = 4HC1 + NCI3. 
 
CHLOEIDB OF MTEOGEN. 115 
 
 Chloride of nitrogen is a volatile yellow oilj of peculiar, pene-, 
 trating odor j it is insoluble in water, and does not congeal when 
 exposed to cold. Its specific gravity is 1-653. It decomposes 
 very easily. Upon being heated to nearly 100°, or touched with 
 any fat or oil, with turpentine, or with various other substances, 
 it explodes with extreme violence ; indeed it often explodes 
 spontaneously, without any apparent cause. A single drop of it, 
 exploded upon a glass or porcelain dish, shatters the vessel to 
 atoms. The preparation and handling of this body require the 
 greatest caution ; it should never be prepared by the novice in 
 chemistry. 
 
 118. We have heretofore adduced experimental proof of every 
 proposition and statement so far as was possible at such a stage 
 of the student's progress. The chemical properties of the four 
 elements, oxygen, nitrogen, hydrogen, and chlorine, have been 
 exhibited by experiment, the composition of many of their most 
 important compounds has been demonstrated by analysis or by 
 synthesis, or by both these methods, and the chemical properties 
 of these compounds have been Ulustrated by actual experiment. 
 Several objects have been thus attained : — first, experimental 
 methods of research have been illustrated by tangible examples ; 
 secondly, the foundation, scope, and application of important 
 laws of chemical combination have been explained ; thirdly, four 
 leading elements have been minutely studied — hydrogen (the 
 standard atom and the unity of specific gravity for gases), 
 oxygen, nitrogen, and chlorine (three widely diffused elements, 
 each of which is' the first member and prototype of an important 
 group of elements, many of whose properties we shaU hereafter 
 find we have already become acquainted with in studying the 
 prototypes); fourthly, three compounds of these elements have 
 been carefuUy studied — chlorhydric acid, water, and ammonia 
 — compounds which are not only interesting in themselves, but 
 of great significance as types, or models, of three large groups of 
 compounds whose properties we have reaUy been studying while 
 we studied their types. 
 
 From this point forward the student will be asked to accept 
 on trust many facts, drawn from the accumulated stores of the 
 science and resting on satisfactory evidence, the fuU exposition 
 
116 OXIDES OP CHLOEnra. 
 
 of which would he hoth tedious and inappropriate. The subject- 
 matter of chemistry is so vast and various that it will be neces- 
 sary to select from the great mass of material only the most 
 valuable portions, and to dwell only on those elements and com- 
 pounds which are of practical importance in the useful arts, or 
 which are of interest in connexion with instructive theories or 
 recognized laws of the science. 
 
 119. Compounds of Chlorine and Oxygen. — Free chlorine does 
 ot combine directly with free oxygen. But by resorting to 
 indirect methods several compounds of the two elements can be 
 obtained. As many as five different oxides of chlorine, enume- 
 rated below, have been described, though as yet some of them 
 are known only in combination with water or other substances, 
 and not in the free condition : — 
 
 Names. Composition. Formux^. 
 
 By volrane. 
 
 Chlorine. Oxygen. 
 Hypochlorous acid . 2 toIs. + 1 vol. 
 
 Chlorous acid 2 vols. +3 vols. 
 
 Hypochloric acid... 1 vol. +2 vols. 
 
 Chloric acid 2 vols. + 5 vols. 
 
 Perchloric acid 2 vols. +7 vols. 
 
 a) p 
 
 %s. 
 
 o 
 2 
 ? 
 2 
 ? 
 ? 
 
 By weight. 
 
 Chlorine. Oxygen. 
 
 35-5x2=71 16 
 
 35-5x2=71 16x3= 48 
 
 35-5 16x2= 32 
 
 35-5x2=71 16x5= 80 
 
 35-5x2=71 16x7=112 
 
 CljO 
 
 CljO, 
 
 CIO2 
 
 CLO5 
 Clio, 
 
 120. HypochlorovLS Add (Cl^O). — If a small quantity of slaked 
 lime (hydrate of calcium) be thro-wn into a bottle of chlorine gas, 
 and the mixture be then left to itself during several hours, the 
 chlorine will be completely absorbed, and there will be formed 
 two compounds, one of which -will be found to be hypochlorite 
 of calcium, the other chloride of calcium. The reaction may be 
 thus formulated : — 
 
 2(CaO,H,_0) -I- 4C1 = CaO,Cl,0 + CaCl, + 2H,0. 
 This mixture is a substance much used in the arts -under the 
 technical names " chloride of lime," and " bleaching-powder ; " it 
 wiU be again referred to hereafter. 
 
 121. Hydrated hypochlorous acid may be prepared from 
 "bleaching-powder;" the solution has a yeUo-wLsh color, an 
 acrid taste, and a peculiar sweet odor. When concentrated it 
 decomposes rapidly, even if kept upon ice. Dilute solutions are 
 
CHlOROTTS, HTPOCHIORIC, AND CHLORIC ACIDS. 117 
 
 more stable, but they decompose slowly upon being boiled. Hy- 
 pochlorous acid is a powerful oxidizing and bleaching agent. 
 Its solution produces at once effects which are only slowly ob- 
 tained when chlorine- water is employed. 
 
 Anhydrous hypochlorous acid, which may be obtained by re- 
 moving the water from the aqueous solution, is a gas of pale 
 yellow color and offensive odor, somewhat resembling that of 
 chlorine. It decomposes very easUy into 2 volumes of chlorine 
 and 1 volume of oxygen ; even the warmth of the hand is suf- 
 ficient to decompose it ; and it is difficult to preserve it unchanged 
 even for a few hours. At low temperatures, such as are pro- 
 duced by a mixture of ice and salt, the gas condenses to a dark 
 orange-colored liquid, heavier than water and very explosive. 
 
 122. Chlorous Add, Cl^Og, may be obtained by deoxidizing 
 chloric acid by means of nitrous acid. When in the anhydrous 
 condition it is a gas of a yellowish-green color, liquefiable by 
 extreme cold. It is a dangerous compound to prepare, since at 
 temperatures above 57° it decomposes, with explosion, into chlo- 
 rine and oxygen. It is readily soluble in water, and the solution 
 possesses strong bleaching and oxidizing properties. It is a 
 weaker acid than chloric acid, § 124, but resembles it in many 
 respects. With metallic oxides it unites to form compounds 
 called chlorites. 
 
 123. Hypochloric Acid, ClO^. — This very explosive compound 
 may be prepared by gently heating a mixture of chlorate of 
 potassium and concentrated sulphuric acid. The gas is of a 
 bright yeUow color and aromatic odor. Upon being exposed to 
 daylight or to a temperature somewhat below the boiling-point of 
 water, it decomposes into oxygen and chlorine, the decomposition 
 being usually attended with explosion. The preparation of the 
 gas is dangerous, and should never be attempted unless upon a 
 very small scale. At the temperature of a mixture of ice and 
 salt, the gas condenses to a yeUow, highly explosive liquid. 
 
 124. CMoric Acid, Clj^O,. — In the present state of science this 
 is the most important of the compounds of oxygen and chlorine. 
 It is not known in the free state, and in the hydrated condition 
 has never been obtained with less than 1 molecule of water, 
 H,0,C1,0,. 
 
118 
 
 PEECHLOEIC ACID. 
 
 When a current of chlorine is made to flow into a cold dilute aqueous 
 solution of caustic potash, a mixture of hypochlorite and of chloride of 
 potassium is produced : — 
 
 2(Kfi,Hfi) + 401 = Kfifilfi + 2KC1 + SH^O,— 
 the reaction heing analogous to that between lime and chlorine, de- 
 scribed in § 120. But if the conditions as to the concentration and 
 temperature of the solution of potash be changed — if, instead of using 
 a dilute solution, chlorine be passed into a moderately strong hot solu- 
 tion of caustic potash, or of carbonate of potassium, hypoohlorous acid 
 will no longer be formed, but instead of it chloric acid. The reaction 
 may be expressed as follows : — 
 
 eCKjOjHjO) + 12C1 = £30,01205 -I- lOKOl + 6H2O. 
 
 Chloride of potassium is formed as before, but the remainder of the 
 chlorine is now more highly oxidized. Chlorate of potassium is less 
 soluble than chloride of potassium ; it separates in flat tabular crystals 
 after the liquid has been concentrated by evaporation and cooled. It 
 is the substance which was employed for maMng oxygen in Exp. 7. 
 
 Chloric acid could be prepared directly from chlorate of potassium by 
 boiling a solution of this substance with fluosilicic acid. An almost 
 insoluble fluosilicate of potassium would be formed, and chloric acid 
 set free. But an easier method is to first convert the chlorate of potas- 
 sium into chlorate of barium, and to liberate the chloric acid from this 
 salt by means of sulphuric acid, with which barium forms a remarkably 
 insoluble compoimd : — 
 
 BaOjCljO^ -I- HASO, = BaO,S03 -1- Hfifilfi,. 
 The solution of chloric acid is separated from the insoluble sulphate 
 of barium by filtration, and concentrated by evaporation over sulphuric 
 acid in the exhausted receiver of an air-pump. By cautious evapora- 
 tion the acid may be brought to a syrupy consistence, but is then 
 rather easily decomposed, especially if it be heated or exposed to light. 
 At the temperature of boiling it is rapidly converted into perchloric 
 acid, water, chlorine, and oxygen. It is a strong acid, and a powerful 
 oxidizing and bleaching agent. 
 
 125. Perchloric Add, Cl^O,, is formed, as above stated, when 
 an aqueous solutioil of oHoric acid is boiled ; 'being volatile it may 
 be distilled off and collected. A coihpoimd of this acid and po- 
 tassium, perchlorate of potassium, can be obtained by heating 
 chlorate of potassium to a certain temperature. Perchloric acid 
 is a more stable compound than either of the other oxides of 
 chlorine. The dilute aqueous solution may be concentrated by 
 
BROMINE. 119 
 
 evaporation over fire, evea at high temperatures. The hydrated 
 acid HjOjCljO^ is a colorless, oily liquid, which boils at 203°, 
 and has a specific gravity of 1-782. It is a powerful oxidizing 
 agent. 
 
 The student will do weU to compare this series of oxides of 
 chlorine with that of the oxides of nitrogen, and to note the 
 points in which the two series resemble and those in which they 
 differ from each other. 
 
 CHAPTER IX. 
 
 B B M I N E. 
 
 126. Bromine is an element closely aUied to chlorine. It is 
 found in small quantities in sea-water, and in the water of many 
 saline springs. 1 litre of sea-water contains from 0-0143 to 
 0-1005 grm. of it. As it exists in nature it is combiued with 
 metals, bromide of magnesium being the compound most com- 
 monly met with. Bromide of magnesium is a constituent of the 
 uncrystaUizable residue, called bittern, which remaias after the 
 chloride of sodium has been crystallized out from the natural 
 brines ; at several saline springs this bittern contains so large a 
 proportion of the bromide that bromine can be profitably extracted 
 from it. Most of the bromine of commerce is thus obtained. 
 
 In order to obtain bromine from the bittern, the latter is mixed with 
 black oxide of manganese and chlorhydric acid, and heated in a retort. 
 Chlorine ia of course evolved from these materials in the midst of the 
 liquid ; it reacts upon the bromide of magnesium and sets free bromine, 
 which distils over into the receiver as a dark-red, very heavy liquid : — 
 MgBr^ + 2C1 = MgClj + 2Br. 
 
 An the metallic bromides are readily decomposed by chlorine, bro- 
 mine being, as a rule, a less energetic chemical agent than chlorine. 
 
 127. At the ordinary temperature bromine is a liquid of dark 
 brown-red color, about three times as heavy as water, and highly 
 poisonous. Its odor is irritating and disagreeable, whence the 
 name bromine, derived from a Greek word and signifying a 
 
120 
 
 PKOPEKIIES OP BEOMINE. 
 
 stench. It boils at about 60°, but is very volatile even at the 
 ordinary temperature of the air. 
 
 Exp. 66. — By means of a small pipette, throw into a flask or bottle, 
 of the capacity of 1 or 2 litres, 3 or 4 drops of bromine. Cover the 
 bottle loosely, and leave it standing. In a short time it will be filled 
 with a red vapor, which is bromine gas. This vapor is very heavy, 
 more than five times as heavy as air, and eighty times as heavy as 
 hydrogen. 
 
 At about 7° bromine crystallizes in brittle plates. It dissolves 
 sparingly in water, but is soluble in alcohol, and in all propor- 
 tions in ether. 
 
 In its chemical behavior, as well as in many of its physical 
 properties, bromine closely resembles chlorine. Its afiinity for 
 hydrogen, though weaker than that of chlorine, is still power- 
 ful, like chlorine, it is an energetic bleaching and disinfecting 
 agent, and it decomposes the vapor of water when passed with it 
 through a tube heated to bright redness, bromhydric acid and 
 oxygen being the products of the reaction. A lighted taper bums 
 for an instant ia bromine vapor and is then extinguished. Phos- 
 phorus, antimony, potassium, and the Kke, take fire on being 
 thrown into bromine, in the same way as in chlorine, a bromide 
 of the other element being produced. 
 
 Exp. 67. — ^Fit a thin cork to a large, wide-mouthed bottle ; perfo- 
 rate the cork, and through the hole pass a tube of thin glass (No. 2) 
 closed at one end. The tube should reach nearly to the bottom of the 
 bottle, and should project two or three inches above the cork. "Within 
 the tube place a few drops of bromine ; throw in upon this a very small 
 quantity of finely powdered antimony, and instantly cover the mouth 
 of the tube with an inverted crucible or wide-mouthed phial, in order 
 that nothing may be thrown out of the tube by the violent action 
 which attends the combination. If the tube be broken, its fragments 
 wUl be retained within the bottle. 
 
 Bromine is used to a certain extent iu medicine, and largely in 
 photography. In the chemical laboratory it is often employed, 
 not only for its own sake, but as a substitute for chlorine ; for, 
 though less energetic, it is more manageable than the latter, espe- 
 cially in those cases where a liquid is desirable. 
 
 128. Bromhydric Add (HBr). — In spite of the strong affinity 
 of bromine for hydrogen, these elements cannot readily be made 
 
BEOMHYDKIC ACID. 121 
 
 to unite directly. A mixture of equal volumes of hydrogen and 
 bromine vapor cannot be made to combine with, explosion by ex- 
 posure to the sun's rays, or by the introduction of a burning 
 lamp, though a certain amount of combination occurs in the im- 
 mediate neighborhood of the flame. But by immersing in. the 
 mixture a platinum wire, kept red-hot by a galvanic current, the 
 two elements may be made to unite slowly ; and a similar result 
 is obtaiaed by passing the mixed gases through a red-hot tube. 
 Bromhydric acid gas can, however, be readily prepared by de- 
 composing bromide of potassium with sulphuric acid, or, better, 
 with a concentrated solution of phosphoric acid. The reaction is 
 analogous to that in which chlorhydric acid is obtained from 
 chloride of sodiiun : — 
 
 SKBr -I- B.fi,m, = E,0,S03 + 2HBr. 
 
 If sulphuric acid be employed, a secondary reaction occurs; a 
 small part of the bromhydric acid suffers decomposition, and the 
 product is slightly contaminated with free bromine and with 
 sulphurous acid : — 
 
 2HBr + H,0,SO, = 2H,0 + 2Br -|- SO,. 
 
 Since phosphoric acid does not thus decompose bromhydric 
 acid, the latter can be obtained in a state of purity by distUling a 
 mixture of bromide of potassium and phosphoric acid. 
 
 129. Bromhydric acid is a colorless, irritating gas, which, on 
 coming in contact with the moisture of the air, fumes even more 
 strongly than chlorhydric acid. By powerful pressure it can be 
 reduced to the liqidd condition, and upon being exposed to intense 
 cold it may be obtained in the form of a crystalline solid. 
 
 It is readily soluble in water, forming a strongly acid solution 
 which resembles chlorhydric acid in many respects, and, like it, 
 fumes in the air. A ready method of preparing the solution is 
 to decompose a strong solution of bromide of barium with sul- 
 phuric acid diluted with its own weight of water. The solution 
 of the free acid may then be separated from the insoluble sulphate 
 of barium by filtration or by distillation. 
 
 When the solution of this acid is mrsed with nitric acid, there 
 is obtained another aqua regia capable of dissolving gold andpla- 
 
122 
 
 BBOmC ACID. 
 
 tinum, like the mixture of chlorhydric and nitric acids, though less 
 readily. 
 
 130. The gas undergoes no change ■when passed through a 
 red-hot tube ; but it is readily decomposed by metals like potas- 
 sium at the ordinary temperature, and by tin gently heated. A 
 bromide of the metal is formed in either case, and there remains 
 a volume of hydrogen equal to half that of the original gas. Ob- 
 servation has shown that the specific gravity of the gas is very 
 nearly 40-5, or half the sum of the specific gravities of bromine 
 vapor and hydrogen. From this fact and the above decomposi- 
 tion of the gas by metals, it follows that bromhydric acid is com- 
 posed of equal volumes of bromine and hydrogen united without 
 condensation. 
 
 131. Bromic Add, 'Kfi^rf)^. — Only one oxide of bromine 
 has been studied, and even this has never been obtained free from 
 water. It is bromic acid, a substance corresponding to chloric 
 acid in composition and properties. Its compounds, also, known 
 as bromates, generally resemble very closely the corresponding 
 chlorates. 
 
 Bromate of potassitun can be obtained by the action of bromine upon 
 potash-lye, in the same way that chlorate of potassium is obtained by 
 the action of chlorine : — 
 
 Q(S.f),'S^O) + 12Br = KjOjEr^Os -|- lOKBr + eHjO. 
 
 The bromate, which is less soluble than the bromide, can'suhse- 
 quently be separated by crystallization. In order to obtain the hy- 
 drated acid, bromate of baritmi may be decomposed with dilute sul- 
 phuric acid : — 
 
 BaO,Br205 + 'Rfi,BO^ = BaOjSO, + H^OjBrjO,. 
 
 The insoluble sulphate of barium is separated by filtration. The 
 acid solution can be concentrated to a certain extent by evaporation 
 at a gentle heat, but cannot readily be brought to a syrupy consistency 
 without decomposition. It decomposes, also, on being heated to 100°, 
 and in general gives up oxygen on being brought into contact with sub- 
 stances which readily combine with that element. 
 
 132. Hypohrormus Add, H^jBr^O. — There can be no doubt 
 of the existence of an oxide of bromine corresponding to hypo- 
 chlorous acid. "When bromine is added to an excess of a solution 
 of nitrate of silver, a liquid of strong bleaching-properties is 
 
lODINB. 123 
 
 obtained, from wliieh a yellowisli, acid fluid may be distilled. 
 This distillate bleaches strongly, and yields, on analysis, mimbers 
 corresponding with the above formula. , When cold dilute alka- 
 line solutions are mixed with bromine they acquire a power of 
 bleaching, and in general behave like the alkaline hypochlorites, 
 'te'hich are formed under similar conditions. So too when bro- 
 iaine-water is treated with red oxide of mercury ; a sparingly 
 soluble oxybromide of mercury is formed, together with a bleach- 
 ing liquor supposed to contain hypobromous acid. 
 
 The analogies which subsist between chlorine and bromine are, 
 however, everywhere so clearly defined that there is good reason 
 to believe that other oxides of bromine, corresponding to those of 
 chlorine, will be sooner or later discovered. 
 
 133. Chloride of Bromine. — Liquid bromine absorbs a large 
 quantity of chlorine-gas when the two elements axe brought 
 together, and there is formed a very volatile liquid called chloride 
 of bromine. It exhales a pungent, irritating odor, and is soluble 
 in water ; the solution possesses considerable bleaching-power. 
 
 134. Bromide of Nitrogen is an explosive compound analogous 
 to chloride of nitrogen, from which it may be prepared by means 
 of bromide of potassium. 
 
 CHAPTEE X. 
 
 IODINE. 
 
 135. In its chemical properties iodine bears a striking resem- 
 blance to bromine, and consequently to chlorine also. It exists 
 in sea-water and in the water of many saline and mineral springs. 
 The proportion of iodine in sea- water is exceedingly small, being 
 even smaller than that of bromine. But iodine is obtained more 
 readily than bromine ; for iodine is absorbed from sea-water by 
 Various marine plants, which, during their growth, collect and 
 concentrate the mintite quantities of iodine which the sea-water 
 
124 EXIEACTION OF IODINE. 
 
 contains, to such an extent that it can be extracted from them 
 with profit. 
 
 Upon the coasts of Scoyand, Ireland, and France, where lahor is 
 cheap, the sea-weeds which contain iodine are collected, dried, and 
 burned, at a low heat, in shallow pits. The half-fused ashes thus 
 obtained, called kelp or varec, contains, among other things, iodine in 
 the form of iodide of sodium and iodide of potassium. It is lixiviated 
 with boiling water, and the solution is then evaporated and set aside 
 to crystallize. The iodides, being much more soluble than the other 
 constituents of the ash, remain dissolved in the mother-liquor after 
 most of the other salts have crystallized out. If this mother-liquor, 
 or iodine-lye, be now mixed with a small quantity of sulphuric acid 
 and left to itself for a day or two, it maybe freed from a further portion 
 of impurity ; it is then transferred to a leaden retort, mixed with a 
 suitable quantity of powdered black oxide of manganese, and gently 
 heated. Iodine is set free, just as chlorine would be from chloride of 
 sodimn under similar circumstances, and may be collected in appro- 
 priate receivers : — 
 2NaI -t- 2(H20,S03) + MnO^ = Na20,S03 -1- MnO,S03-l- SH^O -1- 21. 
 
 136. At the ordinary temperature iodine is a soft, heavy, 
 crystalline solid of bluish-black color and metaUie lustre. Its 
 specific gravity is 4-948. It melts at a temperature (107°) a 
 Kttle above that at which water boils, and boils at a somewhat 
 higher temperature (178°-180°) ; but in spite of this high boil- 
 ing-point it evaporates rather freely at the ordinary temperature 
 of the air, and the more rapidly when it is in a moist condition. 
 It may be entirely volatDized by heating it upon writing-paper. 
 Its odor is peculiar, somewhat resembling that of chlorine, but 
 weaker, and easily distinguished from it. Its atomic weight 
 is 127. 
 
 The vapor of iodine is of a magnificent purple color, whence 
 the name iodine, derived from a Greek word signifying violet- 
 colored ; it is very heavy, indeed the heaviest of aU known 
 gases ; it is nearly nine times as heavy as air. The specific gravity 
 of the vapor is 127. 
 
 Exp. 68. — ^Hold a dry test-tube in the gas-lamp by means of the " 
 wooden nippers, and warm it along its entire leng-th, in so far as this 
 is practicable. Drop into the hot tube a small fragment of iodine, and 
 observe the vapor as it rises in the tube. If only a small portion of 
 
PEOPEKIIES OF IODINE. 125 
 
 the tube were heated, the vapor would be deposited as solid iodine 
 upon the cold part of its walls. 
 
 137. Solid iodine is never met with in the amorphous, shape- 
 less state in which glass, resin, coal and many other substances 
 occur. Kg matter how obtained, its particles always exhibit a 
 definite crystalline structure. If the iodine be melted and then 
 allowed to cool, or if it be converted into vapor and this vapor be 
 subsequently condensed, crystals wiU be formed in either case. 
 Perfect crystals can be stiU more readily obtained by dissolving 
 iodine in an aqueous solution of iodohydric acid, and exposing this 
 solution to the air in a narrow-necked or loosely stoppered bottle ; 
 the iodohydric acid will be slowly decomposed by the action of 
 the atmospheric oxygen, and, as it decomposes, well-defined crys- 
 tals of iodine wiU be deposited. 
 
 In whichever way prepared, the crystals of iodine are octahe- 
 drons with a rhombic base, belonging to the crystalline system 
 called trimetric. As commonly seen, the crystals are thin, 
 flattened tables, distorted by excessive elongation in one di- 
 rection. 
 
 138. Iodine is scarcely at all soluble in water, though enough 
 dissolves to impart a brown color to the water ; but it dissolves 
 readily in alcohol and ether. These solutions are much used in 
 medicine, particularly the alcoholic solution, which is called tinc- 
 ture of iodine. When swallowed in the solid state, iodine acts as 
 an energetic corrosive poison ; but several of its compounds, and 
 the element itself when taken in small doses, are highly prized 
 as medicaments. It is also largely employed in photography, and 
 is a useful reagent in the chemical laboratory. 
 
 139. As has been already stated, iodine, in its chemical beha- 
 vior, resembles chlorine and bromine, only its affinities are more 
 feeble. It enters into combination with less energy than either 
 of these elements, and is displaced by them from most of its com- 
 binations. Like them, it unites directly with the metals and with 
 several other elements. It gradually corrodes organic tissues, 
 and destroys coloring-matters, though but slowly. No oxygen is 
 given off from the aqueous solution when this is exposed to sun- 
 light ; but the color of the solution slowly disappears, and a mix- 
 ture of iodohydric and iodic acids is formed in it. 
 
126 
 
 TESTING FOE IODINE. 
 
 A. singular property of iodine is its power of forming a blue 
 compound with starch. 
 
 JExp. 69. — Prepare a quantity of thin starch-paste by boiling 30 c. c. 
 of water in a porcelain dish, and stirring into it 0-5 grm. of starch 
 which has previously been reduced to the consistence of cream by 
 rubbing it in a mortar with a few drops of water. 
 
 Pour 3 or 4 drops of the paste into 10 c. c. of water in a test-tube 
 and shake the mixture so that the paste may be equably diifiised 
 through the water ; then add a drop of an aqueous solution of iodine, 
 and observe the beautiful blue color which the solution assumes. If 
 the solution be heated the blue coloration will disappear, but it reap- 
 pears when the liquid is allowed to cool. 
 
 Dip a strip of white paper in the starch-paste and suspend it, while 
 still moist, in a large bottle, into the bottom of which two or three 
 crystals of iodine have been thrown. As the vapor of iodine slowly 
 difiuses through the air of the bottle it vdll at last come in contact 
 with the starch, and after some minutes the paper will be colored 
 blue. 
 
 This reaction furnishes a very delicate test for iodine. By its 
 means it has been proved that iodine, though nowhere very abun- 
 dant, is very widely distributed in nature ; traces of it have been 
 detected in land plants, and in many weU, river, and spring 
 waters, also in rain-water, and even in the air ; indeed it would 
 be difficult to say where iodine is not. 
 
 In order that it may be detected by this test, the iodine must 
 be free or uncombined. But, as has been stated, chlorine readily 
 expels iodine from most of its combinations. In case, then, we 
 have reason to suspect the presence of a compound of iodine 
 (iodide of potassium, for example) in any substance, a small quan- 
 tity of chlorine-water, or of some other agent capable of expelling 
 iodine, must be added to this substance. Once displaced from 
 its combination, the iodine may be at once detected by means of 
 starch. 
 
 Exp. 70.— Place in a test-tube 10 c. c. of water, a drop of concen- 
 trated aqueous solution of iodide of potassium, and 3 or 4 drops of the 
 starch-paste of Exp. 69. If the iodide of potassium be pure, no colo- 
 ration will occur. Add now 2 or 3 drops of chlorine-water, and shake 
 the tube. The characteristic blue coloration at once appears. 
 
 In order to illustrate the extreme delicacy of this reaction, dissolve 
 0-14 grm. of iodide of potassium in 1 litre of water, and to this aolu- 
 
DEUCACT OF THE lOBrNE-IEST. 127 
 
 tion, which, contains 1 part of iodine in 10,000 parts of water, add some 
 of the starch-paste and several drops of red fuming nitric acid, a re- 
 agent on some accounts better fitted than chlorine to disengacre iodine 
 in this experiment (see § 150). After a time the solution will exhibit 
 the blue color, though in solutions so dilute as this it sometimes 
 happens that the coloration appears only after the lapse of several 
 hours. 
 
 It follows, of course, from the foregoing experiment, that the 
 reaction of iodine upon starch can be used as a test for those 
 substances which, like chlorine or nitric acid, are capable of set- 
 ting free iodine, as well as for iodine itself. In the chemical 
 laboratory it is customary to keep on hand for this purpose a 
 store of paper upon which has been spread a mixture of starch- 
 paste and iodide of potassium, prepared as follows : — 
 
 £xp. 71. — ^Dissolve O'S grm. of pure iodide of potassium (free from 
 iodate) in 100 c. c. of water ; boU this solution in a porcelain dish and 
 stir into it 5 grms. of finely powdered starch, taking care not to bum 
 the starch, and stirring until the mass gelatinizes. Remove the lamp, 
 allow the paste to become cold, and by means of a wooden spatula 
 spread it thinly upon one side of white glazed paper. The paper is 
 then dried, cut into strips about 8 cm. long by 2 wide, and preserved 
 in stoppered bottles kept carefully closed. 
 
 £xp. 72. — Place in a test-tube a small quantity of binoxide of man- 
 ganese, pour upon it 4 or 5 c. c. of chlorhydric acid, heat the mixtui'e, 
 and hold at the top of the tube a moistened strip of the test-paper 
 which was prepared in the preceding experiment. The chlorine evolved 
 by the reaction of the chlorhydric acid upon the biuoxide of manga- 
 nese sets free iodine from the iodide of potassium upon the test-paper, 
 and the starch is thereby coloured blue. The presence of chlorine in 
 chlorhydric acid is thus made apparent. By this test we might dis- 
 criminate, for example, between dilute nitric and chlorhydric acids, 
 
 140. lodoJiydric Acid (HI). — Hydrogen and iodine do not 
 readily unite together directly. There is here nothing to recall 
 the explosive violence with which chlorine and hydrogen com- 
 bine. Sunlight has no power to bring about the union of the 
 two elements at the ordinary temperature ; but when a mixture 
 of hydrogen gas and iodine vapor is passed through a red-hot 
 tube, iodohydric acid is formed. It has been observed, also, that 
 spongy platinum will cause the union of the two elements even at 
 ordinary temperatures. Even when indirect methods are resorted 
 
128 
 
 lODOHTDEIC ACID. 
 
 to, it is less easy to prepare iodohydric acid than chlorliydric or 
 bromhydric acids. 
 
 If iodide of sodium he distilled -with sulphuric acid, there will be 
 obtained but little iodohydrioacid; for most of that which is produced 
 at first will be subsequently destroyed by the action of sulphuric acid, 
 in the same way as happens to a less extent with bromhydric acid, 
 § 128. 
 
 As fast as iodohydric acid is formed in accordance with the reaction 
 2NaI + H^SO^ = NajSOi + SHI, 
 most of it is decomposed by another portion of sulphuric acid, in a 
 manner which may be thus represented : — 
 
 2HI + H^SO^ = 2H2O + SO2 + 21. 
 Solutions of iodohydric aeid can, however, be readily obtained by the 
 action of iodine upon a compound of sulphur and hydrogen, called 
 sulphydric acid. In practice, a current of sulphydric acid gas is made 
 to pass through water in which finely divided iodine is kept suspended 
 by agitation. The sulphydric acid, the formula of which is HjS, 
 reacts upon 21, and there is formed 2HI and free sulphur, which is 
 deposited. 
 
 A solution of iodohydric acid may also be obtained by distilling a 
 mixture of iodine, phosphorus, and much water, in which case the 
 phosphorus unites with the oxygen of a portion of the water, while 
 the iodine takes the hydrogen. Or it may be prepared by decompo- 
 sing an aqueous solution of iodide of barium with an equivalent quan- 
 tity of dilute sulphuric acid, and filtering off the solution ifrom the 
 insoluble sulphate of barium. 
 
 141. The dilute acid obtained by either of these methods can 
 be concentrated, by evaporation, to a liquor of 1-7 specific gravity, 
 boiling at 127°, and composed of one molecule of iodohydric acid 
 united with 11 molecules of water. The aqueous solution has 
 a sour, suffocating odor, and pungent acid taste. When concen- 
 trated it fumes strongly in the air. It cannot be long preserved 
 when exposed to contact with the air, for the oxygen of the air 
 unites with its hydrogen, and iodine is set free. At first this iodine 
 dissolves in that portion of the iodohydric acid which has not yet 
 been decomposed ; but after the acid has become saturated, crystals 
 of iodine are deposited, as has been stated in § 137. The decom- 
 position of iodohydric acid is so rapid that the pure, colorless so- 
 lution of it becomes red from separation of iodine after a few 
 
lODOHrORIC ACID. 129 
 
 hours' exposure to the air, no matter whether it be minute or 
 concentrated. The easy decompoaiton of this acid shows clearly 
 with how much less force hydrogen holds iodine in combination 
 than it holds either chlorine or bromine. 
 
 142. The usual method of preparing anhydrous iodohydric 
 acid is as foUows : — 
 
 In the bottom of a test-tube place a mixture of 9 parts of iodine and 
 1 part of phosphorus. Cover the mixture with coarsely powdered 
 glass, and bring abou* chemical union between the iodine and the 
 phosphorus by gently heating them. Place now a few drops of water 
 in the tube, and connect with it a gas delivery-tube by means of a 
 caoutchouc stopper. Iodohydric acid will be immediately given off, 
 and may be collected by displacement. 
 
 Another method is to pack a test-tube with alternate layers of phos- 
 phorus, iodine, and moistened glass-powder, and then to gently heat 
 the tube. The operation depends upon the formation of an iodide of 
 phosphorus and the subsequent decomposition of this body by contact 
 with water into iodohydric acid and a compound of phosphorus, oxygen, 
 and water, called hydrated phosphorous acid : — 
 
 2PI3 -1- 6H2O = em -f 3H20,P203. 
 
 143. Iodohydric acid is a colorless, acid gas, of suffocating 
 odor ; it fumes strongly in the air, and is very soluble in water. 
 It can be liquefied rather easily by pressure, and solidified at — 51° 
 to a colorless mass Uke ice. The gas is more than four times as 
 heavy as air, its specific gravity having been fouud by observa- 
 tion to be 64'11. From this fact, taken in connexion with the 
 striking analogy which the compound bears to bromhydrio and 
 chlorhydric acids, it follows that the gas is composed of equal 
 volumes of iodine vapor and hydrogen united without condensa- 
 tion ; for the theoretical density of a gas thus composed would be 
 (127-1- l)-r 2=64, a number with which the observed specific 
 gravity closely agrees. The chemical effect of the small propor- 
 tion of hydrogen contained in iodohydric acid is most remark- 
 able. Only Yjg-, or less than 1 per cent, of iodohydric acid is 
 hydrogen, yet this very small proportional quantity of hydrogen 
 is competent to impart an entirely new set of properties, both to 
 the iodine and the hydrogen ; the acid bears no resemblance to 
 either of its constituents. 
 
 144. Iodohydric acid is a compound which decomposes easily. 
 
130 IODIC ACID. 
 
 When a mixture of the gas and oxygen is passed through a red- 
 hot tube, water and free iodine are the products. Chlorine and 
 bromine abstract hydrogen from it, and leave iodine free ; and 
 the same effect is produced by many oxygen compounds which 
 readily part with oxygen. With many of the metals it forms 
 iodides, while hydrogen is set free ; and it reacts upon most of the 
 metallic oxides, forming water and a metallic iodide. 
 
 Though the hydrogen of iodohydric acid is readily removed by 
 means of oxygen in numerous instances, it appears, upon the 
 other hand, that iodine can abstract hydrogen from most of its 
 combinations with the other elements. Only oxygen, chlorine, 
 bromine, and an element (still to be studied) called fluorine, ex- 
 hibit a stronger tendency than it to unite with hydrogen. Iodine 
 separates hydrogen from its compounds with nitrogen, sulphur, 
 and phosphorus, and from many organic compounds, such as alco- 
 hol and ether, iodohydric acid being formed in each case. 
 
 145. Compounds of Iodine and Oxygen. — Of the compounds of 
 iodine and oxygen, only two have as yet been carefully studied. 
 These correspond respectively to chloric and perchloric acids. 
 Compounds analogous to hypochlorous and hypoohloric acids ap- 
 pear to exist, but have not been described with much accuracy. 
 
 146. Iodic acid (ifi^) may be obtained directly by oxidizing 
 powdered iodine with monohydrated nitric acid at a moderate 
 heat. After aU the iodine has disappeared, and the excess of 
 nitric acid employed has been evaporated, iodic acid will be left 
 as a white residue. 
 
 Iodic acid is readily soluble in water, and crystallizes from an 
 acidulated solution in colorless, six-sided tables, of the formula 
 HIO3 or HjO.iPj. It has a pecuhar odor, and acid, disagTceable 
 taste. At the temperature of 170°, water is given off and the 
 anhydrous acid remains. This melts upon being heated more 
 strongly, and suffers decomposition. 
 
 Iodic acid readily gives up oxygen to many other substances, 
 or, in other words, it is easily decomposed by reducing-agents ; 
 for example, when mixed with iodohydric acid it reacts upon it 
 with formation of water and deposition of iodine : — 
 
 lOHI + 1,0, = 5H,0 -I- 121. 
 All of the metals are oxidized by it, excepting gold and platinum. 
 
IODIDE OF NITKOGEN. 131 
 
 With metallic oxides it forms compounds called iodates, which are 
 analogous to the corresponding chlorates and hromates in com- 
 position and properties. 
 
 147. Periodic acid (1,0^) may be prepared by passing chlorine 
 gas through a solution of iodate of sodium mixed with caustic 
 soda. Chloride of sodium and basic periodate of sodium will be 
 formed, and the latter, being sparingly soluble in water, will be 
 deposited in crystals : — 
 
 'Sa.fi,ljd, + 3(Ifap,H,0) + 4Cl=2Na,0,I,0,+ 4NaCl+ 3H,0. 
 If now the sodium salt be collected and dissolyed in water, and 
 the solution be mixed with nitrate of lead, a periodate of lead 
 will be obtained ; this may be decomposed by means of dilute 
 sulphuric acid into periodic acid and insoluble sulphate of lead. 
 The latter may then be separated by filtration, and the clear so- 
 lution of the acid finally concentrated by evaporation. 
 
 From the concentrated aqueous solution periodic acid separates 
 in colorless hydrated crystals, which, upon being carefully heated, 
 give off water and yield as a residue the anhydrous acid 1^0^. 
 At a stiU higher temperature, the anhydrous acid deeomposes 
 and gives off oxygen. It is decomposed also by reducing-agents 
 in the same way as iodic acid. 
 
 The other compounds of iodine and oxygen have but little in- 
 terest for us, except that they serve to increase the number of 
 analogies which subsist between iodine, bromine, and chlorine. 
 
 148. Iodide of Nitrogen (?). — There appear to be a number of 
 compoimds which have hitherto been usually classed under this 
 title. They are produced by the action of ammonia upon iodine, 
 and are mostly of a highly explosive character, though their pro- 
 perties and composition vary to a certain extent according to the 
 mode of their preparation. 
 
 Exp. 73. — Place 0-25 grm. of finely powdered iodine in a porcelain 
 capsule, and pour upon it so much concentrated ammonia-water that 
 the iodine shall be somewhat more than covered ; allow the mixture 
 to stand during 15 or 20 minutes, when an insoluble dark-brown 
 powder wiU be found at the bottom of the liquid. This powder is the 
 so-called iodide of nitrogen. It should be collected upon two or three 
 very small filters and well washed with cold water. Remove the 
 filters, together with their contents, from the funnels, pin them upon 
 bits of board, and leave them to dry spontaneously. 
 
 k2 
 
132 
 
 CHLORIDES OP IODINE. 
 
 As soon as the powder has become thoroughly dry it will explode 
 upon being rubbed, even with a feather, or jarred, as by the shutting 
 of a door, or by a blow upon the wall or table. Though incomparably 
 less dangerous than chloride of nitrogen, and therefore better suited 
 than the chloride to illustrate the explosive character of this obscure 
 class of nitrogen compounds, iodide of nitrogen must nevertheless be 
 handled with great care, and should never be prepared by the student 
 except in very small quantities. 
 
 149. Chlorides of Iodine. — Iodine combines directly with chlo- 
 rine in several proportions, a protochloride, ICl, and a terchloride, 
 IClj, being the best-known of these compounds. 
 
 The protochloride is obtained by passing dry chlorine over dry 
 iodine, the current of chlorine being checked at the moment when all 
 the iodine has become liquid. Or it may be made by distilling iodine 
 with chlorate of potassium, and collecting the product in a cooled 
 receiver. 
 
 3KCIO3 + 21 = KCIO^ + KIO3 -I- KCl -(- 20 -t- ICl. 
 Protochloride of iodine is a i%ddish-brown, oUy liquid, volatile, irrita- 
 ting, and of peneti-ating odor. It decolorizes litmus and indigo, but 
 does not give a blue color with starch. 
 
 The terchloride may be produced by treating iodine with an excess 
 of chlorine gas, or by acting upon anhydrous iodic acid with dry 
 chlorhydric acid gas ; — 
 
 Ijd, + lOHCl = 2ICI3 -I- SRfi + 4C1. 
 It is a yellow crystalline solid, melting at 20°-25°. It acts upon 
 other substances in the same manner as the protochloride ; like the 
 protochloride, it decolorizes indigo and does not turn starch blue. 
 
 150. A knowledge of the properties of the chlorides of iodine is 
 of some practical importance, since they are liable to be formed 
 incidentally in several chemical processes, which their presence 
 perturbs. Thus, in the manufacture of iodine, as described under 
 § 135, the iodine-lye almost always contains a certain proportion 
 of chloride of sodium. It is evident that if the chlorine in this 
 compound were to be evolved at the same time as the iodine by 
 the action of the black oxide of manganese and sulphuric acid, 
 there would be formed a quantity of the very volatile protochloride 
 of iodine, which would escape condensation. Whatever of iodine 
 was thus combined with chlorine would he lost to the manufacturer. 
 But, as has been repeatedly stated, iodine is an element which 
 
THE CECLOEnrE GEOUP. 
 
 133 
 
 can be much more readily expelled from its combinations than 
 chlorine ; and in the case in point it is fonnd that the iodine in 
 the mixture of iodide of sodium and chloride of sodium, which 
 the iodine-lye contains, -will all come off before the chlorine, if 
 the distillation be slowly conducted. If, through irregular heat- 
 ing, any portion of the contents of the retort should become hotter 
 than the rest, and so lose all its iodine, chlorine would he disen- 
 gaged from that portion, and would unite with the vaporized 
 iodine which fills the retort. To ensure the necessary slow and 
 equable heat, the retort is set upon a stove suitable for the 
 maintenance of a slow fire, and is provided with an agitator, by 
 means of which its contents may be continually stirred. 
 
 Again, in testing for iodine, as in Exp. 70, chlorine is a far 
 less convenient agelit for setting free the iodine from its combi- 
 nations than fuming liitric acid; for if thfl slightest excess of 
 chlorine be employed, the iodine will all be converted into chlo- 
 ride of iodine, and the starch will not be colored blue. 
 
 151. Bromides of lodine.^Theie are two compounds of bro- 
 mine and iodine, and their properties are analogous to those of 
 the chlorides of iodine. 
 
 152. Chlorine, bromine, and iodine constitute one of the most 
 remarkable and best-defined natural groups of elements. Whether 
 we regard the uncombined elements or their compounds, it is im- 
 possible not to be struck with the dose analogies which subsist 
 between them. With hydrogen, aU of these elements unite in the 
 proportion of one volume to one volume, without condensation, to 
 form acid compounds extremely soluble in water and possessing 
 thronghont analogous properties. 
 
 H 
 
 + 
 
 + 
 
 CI 
 
 = 
 
 HCl 
 
 
 
 
 
 H 
 
 Br 
 
 = 
 
 TTBr 
 
 H I + 
 
 m = 
 
 HI 
 
 With oxygen each of them forms a powerful acid containing five 
 
134 THE CHLOEHfB GEOTTP. 
 
 atoms of oxygen, besides divers other compounds of obvious like- 
 ness. The compounds famished by their union with any one 
 metal are always isomorphous (like-formed); the chloride, bromide, 
 and iodide of potassium, for example, aU crystallize in cubes. 
 With nitrogen they all form explosive compounds. Many similar 
 analogies will be made manifest as we proceed to study the other 
 elements, and their compounds with this chlorine group. 
 
 There is a distinct family resemblance between these three 
 elements as regards their physical as well as their chemical cha- 
 racteristics ; but, in all their properties, a distinct progression 
 is observable from chlorine through bromine to iodine. At the 
 ordinary temperature chlorine is a gas, bromine a Kquid, and 
 iodine a solid, though at temperatures not widely apart they are 
 all known in the gaseous and liquid states. The specific gravity 
 of bromine vapor is* greater than that of chlorine, and that of 
 iodine greater than that of bromine. Chlorine gas is yellow, the 
 vapor of bromine is reddish brown, that of iodine violet. So with 
 all their other properties, — chlorine wiU be at one end of the 
 scale, iodine at the other, while bromine invariably occupies the 
 intermediate position. 
 
 The properties of many of the compounds of chlorine, bromine, 
 and iodine exhibit a similar progression as we pass from the 
 chlorine compounds to those of iodine. For example, the specific 
 gravity of 
 
 Chlorhydric acid gas is 18'2 
 
 Bromhydric „ 40 '5 
 
 lodohydrio „ 64-0 
 
 Chlorhydric acid can be liquefied at about —80°, and has not yet 
 been solidified. Bromhydric acid liquefies at about — 60°, and 
 solidifies at about —92°. lodohydric acid liquefies at about 
 —40°, and sohdifies at about —50°. 
 
 Chlorhydric acid is a more energetic acid than bromhydric, 
 and bromhydric acid is more powerful than iodohydric. The 
 aqueous solution of chlorhydric acid can be kept without change 
 in contact with air; that of bromhydric acid becomes colored 
 after a while, from separation of bromine ; but the solution of 
 iodohydric acid decomposes rapidly, and much iodine is deposited. 
 
 As regards the relative chemical power of these elements, it 
 
FtTTOBISrE. 135 
 
 has already been shown that the intensity of this force becomes 
 less as we descend from chlorine to iodine. It is easy, for ex- 
 ample, to displace iodine from its compounds by means of bromine, 
 Nal + Br = NaBr + I, 
 
 and equally easy to displace bromine from its combinations by 
 means of chlorine, 
 
 NaBr + CI = NaCl + Br. 
 
 153. It is an important principle, borne out by most of the 
 other groups of elements, and emphatically true of the natural 
 family now under consideration, that, with kindred elements, the 
 chemical power of each is great, in comparison with that of the 
 related elements, in proportion as its atomic weight is low. 
 
 Among the members of a natural chemical group, chemical 
 energy seems to be inversely proportional to atomic weight. Thus 
 the atomic weight of chlorine is 35-5, that of bromine SO, and that 
 of iodine 127, while the chemical energy of these elements fol- 
 lows the opposite order. 
 
 154. It is noteworthy that elements of like character almost 
 always- occur associated with one another in nature. Bromine 
 and iodine are always found in company with chlorine. That 
 this should be so is in nowise surprising. Those elements which 
 are similar in character and properties must necessarily be simi- 
 larly acted upon by the natural forces to which they are exposed, 
 and must therefore inevitably tend to be gathered or deposited* 
 in like places under like conditions. 
 
 CHAPTER XI. 
 
 FLTJOKIlfE. 
 
 155. There is another substance, called fluorine, which is closely 
 analogous to chlorine. This element cannot be readily obtained 
 in the free state, and scarcely anything is known 'of it in that 
 condition. Special interest attaches to it upon this very account, 
 
136 
 
 riUORHTDKIC ACID. 
 
 and many fruitless eiforts to isolate it have been made. Of aU the 
 elements, it appears to have the strongest tendency to enter into 
 chemical combination ; at all events it is the most difficult to ob- 
 tain, and to keep, in the free and uncombined condition. 
 
 It is not only difficult to expel fluorine from the minerals in 
 which it is found in nature, but on being set free from one com- 
 pound it immediately attacks whatever substance is nearest at 
 hand, and so enters into a new combination. Hence it is weU- 
 nigh impossible to collect it. It destroys at once glass, porcelaia, 
 and metal, the materials from which chemical apparatus is usually 
 constructed. Vessels made of the mineral fluor-spar (a compound 
 of fluorine and calcium), are the only ones which have as yet 
 been found capable of withstanding its action. By operating in 
 such vessels, a small quantity of impure fluorine gas appears to 
 have been reaUy obtained ; but the process is difficult, expensive, 
 and not uniformly successful. Little or no doubt, however, is 
 entertained as to the general nature of fluorine, since its com- 
 pounds are closely analogous in many respects to the correspond- 
 ing compounds of chlorine, bromine, and iodine. 
 
 The symbol of fluorine is Fl. Its atomic weight is 19. It 
 occurs tolerably abundantly in nature as fluoride of calcium 
 (CaFlj), in the miueral known as fluor-spar. SmaU quantities 
 of fluorine are foimd also in several other minerals, in vegetable 
 and animal substances, particularly in bones; and traces of it 
 t)ccur in sea- water, and in various rocks and soils. It appears 
 to be almost as widely disseminated as iodine, though, from the 
 lack of delicate tests for fluorine, it is far less readily detected. 
 Of late years a considerable mine of a fluorine mineral called cryo- 
 lite (fluoride of sodium and tduminum) has been worked in Green- 
 land. 
 
 156. FluorJiydric Acid ('SF]).—'Witlih.yiiogen, fluorine forms 
 a powerful acid corresponding to chlorhydric acid and the other 
 hydrides of the chlorine group. It is a more energetic acid than 
 either of these, but is specially characterized by its corrosive 
 action upon glass. It may be readily prepared by distilling 
 powdered fluor-spar with strong sulphuric acid; the reaction 
 being analogous to that which occurs when common salt is treated 
 with sulphuric acid : — 
 
PLUOEHTDKIC ACID. 137 
 
 CaFl, + H,SO, =CaSO, + 2HF1. 
 Since the acid rapidly corrodes glass, the process must be con- 
 ducted in metallic vessels. Ordinarily, retorts of lead or platinum 
 are employed, and the distillate is collected in receivers made of 
 the same metals, and carefully cooled by means of ice. 
 
 157. The product of the distillation is a very volatile, colorless 
 liquid, a little heavier than water. It is strongly acid, emits 
 copious white and highly suffocating fumes in the air, boUs at 
 15°, and remains unfrozen at —20°. On account of its corrosive 
 power, this substance is highly dangerous ; if any of it happens 
 to come in contact vnth the skin, wounds are produced which are 
 very difficult to heal ; a single drop of it is sufficient to occasion 
 a deep and painful sore. In preparing the acid, special provision 
 must be made for carrying away from the operator any fumes 
 which may escape condensation. 
 
 The acid may be kept in bottles made of lead or silver, or of 
 gutta percha, substances upon which it has no action. It unites 
 with water with great avidity, so much heat being evolved that 
 a hissing noise is produced, as if a bar of red-hot iron had been 
 immersed in the water. In its concentrated form the acid has a 
 specific gravity of 1-061, but on the addition of a certain amount 
 of water the density increases to 1'15, a definite hydrate 
 (HFl-|-2HjO) being formed, which boils at 120°, and may be 
 distilled unchanged. The further addition of water to this hy- 
 drate is attended with a regular decrease in density. 
 
 According to some chemists, the liquid acid obtained as above 
 described is not anhydrous. It is asserted that if it be distUled 
 with an excess of anhydrous phosphoric acid (a substance which 
 has a very strong affinity for water), the anhydride will be set 
 free in the form of a colorless, extremely irritating gas. 
 
 158. Upon metals and metallic oxides, fluorhydric acid acts 
 like chlorhydric acid, only more powerfully ; but its most striking 
 peculiarity is its action upon silica and the compounds of silica, 
 such as glass or porcelain. If a drop of the concentrated acid be 
 allowed to fall upon a piece of glass, it becomes hot, boils, and 
 partially distils off as a fluoride of silicon, while the glass is cor- 
 roded and becomes covered with a white powder consisting of com- 
 pounds of fluorine and various constituents of the glass. If this 
 
138 ETCHING BY rLTTOKHTIIKIC ACID. 
 
 powder be washed away a deep impression will be found upon the 
 glass at the point where the acid has acted. 
 
 This corrosive power, which is possessed by fluorhydrie acid 
 gas as well as its aqueous solution, is made use of for etching 
 glass. The graduations on the glass stems of thermometers and 
 eudiometers may thus be made with great precision and facility ; 
 the acid is largely employed also in ornamenting glass with 
 etched patterns. 
 
 Exp. 74 — Warm a slip of glass and rub it with beeswax so that it 
 shall be everywhere covered with a thin, uniform laj'er of the wax. 
 With a needle, or other pointed instrument, write a name, or trace 
 any outline through the wax, so as to expose a portion of the glass. 
 Lay the etching, face downward, upon a bowl or trough of sheet-lead, 
 in which has been placed a teaspoonful of powdered fluor-spar and 
 enough strong sulphuric acid to convert it into a thin paste ; if the 
 glass be smaller than the opening of the dish, it may be supported 
 upon wires laid across the latter. 
 
 Cover the glass and the top of the dish with a sheet of paper, and 
 then gently heat the leaden vessel for a few moments, taking care not 
 to melt the wax ; then set the dish aside in a warm place and leave it 
 at rest during an hour or two. Finally melt the wax and wipe it ofi 
 the glass with a towel or bit of paper ; the glass will be found to be 
 etched and corroded at the places where it was laid bare by the re- 
 moval of the wax. 
 
 This experiment can be performed more rapidly by covering the 
 outside of a watch-glass with wax, tracing characters upon this layer, 
 and then placing the glass upon a small platinum crucible containing a 
 mixture of fluor-spar and sulphuric acid, which is heated over the gas- 
 lamp. The watch-glass is meanwhile kept full of water, in order to 
 prevent the wax from melting. In this way the etching can be effected 
 in the course of a few minutes. 
 
 Instead of the gas, a dilute aqueous solution of the acid may be em- 
 ployed in this experiment. The concentrated acid of § 157, diluted 
 with six parts of water, answers a good purpose. In this case the 
 etched smface will appear smooth like the rest of the glass, while in 
 case the gas is employed the etched portion of the glass will be duU 
 and rough. 
 
 159. No compounds of fluorine with chlorine, bromine, iodine, 
 nitrogen, or oxygen have yet been discovered, though a sulphur 
 compound has been obtained, as a fuming liquid, by distilling 
 fluoride of lead with sulphur. Fluorine is the only element of 
 
OZONE AND ANIOZONE. 139 
 
 which no oxygen compound is known ; this fact, however, will 
 appear less remarkable if it be remembered that, in order to ob- 
 tain oxygen compounds of chlorine," bromine, and iodine, it is 
 necessary first to isolate these elements, and to have them in the 
 free and uucombined condition. Analogy would therefore teach 
 that a practicable method of preparing free fluorine must be dis- 
 covered before we can hope to prepare oxides of fluorine. 
 
 160. The fact that fluorine forms a powerful acid with hydro- 
 gen, connects this element with the three elements (chlorine, 
 bromine, and iodine) which have last been studied. Many of its 
 compounds with the metals are analogous in composition to the 
 compounds of chlorine, bromine, and iodine, and not a few of 
 these compounds are isomorphous with one another. It is cus- 
 tomary therefore to study fluorine in. connexion with the chlorine 
 group ; but the student should remember that in several respects 
 it differs widely from chlorine, and that its connexion therewith 
 is, in any event, less intimate than that of either bromine or 
 iodine. 
 
 CHAPTEE XII. 
 
 OZONE AND ANTOZONE. 
 
 161. Besides ordinary oxygen, such as is found in the air and 
 has been prepared in Exps. 5 and 7, two other kinds or forms of 
 this element are known to chemists. These new modifications of 
 oxygen have received special names, and are called ozone and 
 antozone respectively. 
 
 162. Several other elements, notably sulphur, phosphorus, and 
 carbon, occur, as oxygen does, in very unlike states, or with very 
 different attributes, whUe the fundamental chemical identity of 
 the substance is preserved. The word allotropism is employed to 
 express this capability of some of the elements; it is derived 
 from Greek words signifying of a different habit, or character. 
 This word serves merely to bring iuto one category a considerable 
 number of conspicuous facts, of whose essential nature we have 
 
140 
 
 OZONE. 
 
 no knowledge ; there is, of course, nO Yirtue in the word itself to 
 explain or account for the phenomena to which it refers. 
 
 163. Ozone is an exceedingly energetic chemical agent, which 
 resembles chlorine in some respects ; it can therefore he advan- 
 tageously studied in connexion with the chlorine group. More- 
 over, since ozone and antozone were for a long time confounded 
 with one another, and since they are really intimately related, 
 they should, of course, be studied together. The most natural 
 connexion of these somewhat obscure bodies is with oxygen ; but 
 we are better able to appreciate what is known of the properties 
 of ozone and antozone now that we have become acquainted with 
 a number of the elements, and have made ourselves familiar with 
 a considerable variety of chemical processes and reactions, than 
 we were at the very outset, when common oxygen was neces- 
 sarily studied. 
 
 164. It had long been noticed that when an electrical machine 
 was put in operation a peculiar, pungent odor was developed; 
 but it is only at a comparatively recent period that it has been 
 observed that the same odor is manifested during the electrolysis 
 of water (§ 35), and that this odor resembles that evolved by 
 moistened phosphorus when exposed to the air. It has gradually 
 been made out that the odor in each of these cases is due to the 
 presence of a peculiar modification of oxygen, called ozone from a 
 Greek word signifying to smell. This modification of oxygen was 
 at one time erroneously supposed by some to be a high oxide of 
 hydrogen, of composition HjO^, or H^Oj ; but this view has lately 
 been completely disproved. 
 
 Of the methods of obtaining ozone above suggested, that by 
 phosphorus will usually be found most convenient. 
 
 Exp. 76.— In a clean bottle, of 1 or 2 litres capacity, place a piece 
 of phosphorus 2 or 3 cm. long, the surface of which has been scraped 
 clean (under water) with a knife ; pour water into the bottle until the 
 phosphorus is half covered; close the bottle with a loose stopper and 
 set it aside in a place where the temperature is 20° or 30°. 
 
 In the course of ten or fifteen minutes a column of fog will be seen 
 to rise from that portion of the phosphorus which projects above the 
 water, the original garhc odor of the phosphorus will soon be lost, and 
 the peculiar odor of ozone will gTadually pervade the bottle. After 
 
OZONE BT ELECTEICITT. 141 
 
 five or six hours, the bottle wiE be found to contain an abundance of 
 ozone for use in the subsequent experiments. 
 
 The chemical changes' -which occur during this experiment are 
 complicated ; it will be enough to say of them that the phos- 
 phorus unites with oxygen from the air in the bottle to form an 
 oxide of phosphorus, which will be studied hereafter imder the 
 name of phosphorous acid ; that during this process of oxidation 
 a portion of the oxygen in the bottle is changed into ozone and 
 antozone, and that some of the ozone remains, even after many 
 hours, diffused in the air of the bottle. 
 
 165. It must be distinctly understood that no very large quan- 
 tity of ozone is obtained in the foregoing experiment. At the 
 best, only a very minute proportion of it will be found in the air 
 of the bottle. But ozone is a substance possessing great chemical 
 power, and but little of it is needed in order to exhibit its cha- 
 racteristic properties. 
 
 If it be desired to prepare ozone by passing electric discharges 
 through air or oxygen, either of these gases may be sealed up in nar- 
 row glass tubes, through the centres of which are passed platinum 
 wires, welded tightly into the glass, as shown in Fig. 37, and a series 
 of sparks from an electrical machine is thrown through the gas in the 
 tube, during ten or twelve hours. If the experiment be continued 
 longer than this, nothing is gained ; for the sparks after this time appear 
 to destroy the ozone previously produced. 
 
 To avoid the difficulty last named, a slow current of oxygen may be 
 forced through a tube open at both ends, and electrical discharges may 
 be passed through the gas in its transit ; a constant stream of ozonized 
 air will be thus obtained. 
 
 Instead of the sparks, the gas within the tube may be sub- 
 jected to silent discharges of electricity obtained by con- -f 'g- •>'• 
 necting one of the platinum wires with the ground, the •(~-X-= 
 other with the prime conductor of an electrical machine, 
 and slowly turning the crank of the latter. By using a tube 
 having wires near the top, as in Fig. 37, and closing the 
 lower end of the tube by immersing it in a bath filled with 
 an aqueous solution of iodide of potassium, so that the ozone 
 may be absorbed as fast as it is formed, it has been found 
 possible, by some experimenters, to transform and remove ^^ 
 aU the original oxygen contained in the tube. 
 
 166. Ozone is produced not only during the slow oxidation of 
 
142 OZONE BY OXIDATION. 
 
 phosphorus, and by the actioa of electricity upon air or oxygen ; 
 a certain quantity of it appears to be produced also during other 
 processes of oxidation. It is readily formed, for example, during 
 the slow combustion of ether and of various other volatile liquids ; 
 it can be at once produced by plunging a heated glass rod or iron 
 wire into a mixture of air and ether vapor. 
 
 Into a wide-mouthed bottle, a small quantity of ether is poured ; the 
 bottle is shaken for a moment, that the air within it may become 
 charged with the vapor of ether ; the liquid ether, if any remain, is 
 then poured away, and a large glass rod, or thick iron wire, heated to 
 about 250°, is thrust into the bottle. The rod must not be too hot, lest 
 the ozone formed be reconverted into ordinary oxygen ; if it be insuf- 
 ficiently heated no ozone is produced. 
 
 During the slow oxidation of oil of turpentine, oil of cinnamon, oil 
 of lemons, and others of the so-caUed essential oils, at the ordinary 
 temperature of the air a considerable quantity of ozone is produced. 
 This may be seen in oil of turpentine which has been kept for a long 
 time in half-filled bottles, exposed to sunlight, and frequently opened 
 and shaken. The formation of ozone imder these circumstances ex- 
 plains the familiar fact that the corks employed to close bottles con- 
 taining oil of turpentine and the analogous oils are soon bleached and 
 corroded. At the same time, antozone is also produced in large quan- 
 tity, as win be explained hereafter. 
 
 If quicksilver, to which a little water and a few drops of a solution 
 of indigo have been added, be shaken up violently in a large bottle fall 
 of air, the indigo wiU soon be bleached as if by the action of ozone. 
 
 167. One of the best methods of preparing ozone is by treating 
 a compound known as permanganate of potassium with sulphuric 
 acid. It should be observed, however, that in this process, as in 
 all the others, the ozone obtained is mixed with common oxygen ; 
 no available method of isolating ozone in a condition of purity 
 has yet been made known. 
 
 A small quantity of concentrated sulphuric acid is placed in the 
 bottom of a bottle, and a quantity of pure, dry permanganate of potas- 
 sium, in fine powder, is added ; the proportion of acid to permanganate 
 should be three parts to two, by weight. A strong smell of ozone will 
 be at once perceived, and the pasty mass will continue to give off 
 ozone for a long time. 
 
 In this case it is conjectured that a portion of the oxygen of the per- 
 manganate of potassium, the empirical formula of which is KjMnjOj, 
 
PBOPERTIES OP OZONE. 143 
 
 actually exists in the compound as ozone, and is given off as such when 
 the compound is decomposed. 
 
 168. As has been already mentioned, the chemical behavior of 
 ozone is analogous to that of chlorine ; it bleaches and destroys 
 vegetable coloring-matters, and is a powerful disinfectant. Like 
 chlorine it instantly decomposes the iodides of the metals ; upon 
 this property is based a ready method of testing for its presence. 
 
 Exp. 76. — Into the bottle of ozonized air (Exp. 75), thrust a mois- 
 tened slip of the test-paper, saturated with starch and iodide of potas- 
 sium, which was prepared in Exp. 71 ; the paper wiU instantly acquire 
 a deep blue tint. As in the case where the test-paper was, employed 
 for detecting chlorine (Exp. 72), so here, the reaction depends upon 
 the displacement of the chemically feeble iodine by the more powerful 
 ozone : — 
 
 SKI -1- = EjO + 21. 
 
 The ozone here acts as oxygen, in one sense ; at all events the oxide 
 of potassium formed is not to be distinguished from oxide of potassium 
 prepared with common oxygen ; but this in nowise contradicts the fact 
 that ozone is an extraordinarily active and energetic variety of oxygen, 
 inasmuch as common oxygen will not effect this decomposition. 
 
 169. Ozone is an irritating, poisonous gas ; air which is highly 
 charged with it is irrespirable, and produces effects on the human 
 subject similar to those produced by chlorine. Its odor, which 
 has been compared to that of weak chlorine, is so powerful that 
 it can be recognized in air containing only one millionth part of 
 the gas. Its oxidizing power is intense. When moisture is pre- 
 sent it oxidizes all the metals excepting gold, platinum, and the 
 platinum metals ; even silver is oxidized by it at the ordinary 
 temperature, and becomes covered with a brown coating of per- 
 oxide of silver. It destroys many hydrogen compounds, such as 
 those of sulphur, phosphorus, and iodine, the hydrogen being 
 oxidized as well as the element with which the hydrogen is 
 associated ; iodohydric acid, for instance, is converted into water 
 and iodic acid. In the same way, free iodine is oxidized by 
 ozone, and if test-paper which has become blue by exposure to 
 ozone, as in Exp. 76, be left long in ozonized air, it wiU become 
 white from oxidation of the iodine. Ozone will even oxidize 
 nitrogen, at the ordinary temperature, when in contact with 
 water and such alkaline oxides as caustic soda, caustic potash, 
 
144 TESTING FOE OZONE. 
 
 or caustic lime ; thus, if lime-water (a solution of caustic lime in 
 water) be left exposed to ozonized air, a certain quantity of 
 nitrate of lime will be formed. Ammonia is oxidized by it also, 
 and it converts nitrous and sulphurous into nitric and sulphuric 
 acids. 
 
 Many salts of the metals are oxidized by it— for example, the 
 sulphates of iron and of manganese. A valuable test for the 
 presence of ozone is furnished by its behavior towards sulphate 
 of manganese. 
 
 Exp. 77. — Dissolve a gramme or two of sulphate of manganese in 
 water ; soak in this solution strips of thin white blotting-paper ; dry 
 the paper, and preserve it in a bottle. If a slip of this paper be mois- 
 tened, and then hung in Ozonized air (Exp. 75), it wiU quickly become 
 brown from the formation upon it of black oxide of manganese. 
 
 In like manner, most organic substances are quickly oxidized 
 by ozone ; when substances such as sawdust, garden-mould, 
 powdered charcoal, mUk, or flesh are thrown into a bottle of 
 ozonized air, the odor of ozone instantly disappears ; corks and 
 caoutchouc tubes are attacked by it, and must not be used in 
 experimenting with the gas. It destroys the color of indigo, and 
 bleaches litmus without first reddening it. Some organic bodies, 
 on the other hand, become colored when exposed to its action ; 
 thus, the cut surface of an apple becomes brown, and fresh sur- 
 faces of certain mushrooms become blue. Gum guaiacum also 
 becomes blue. Papers soaked in a dilute alcoholic solution of 
 gum guaiacum, indeed, are often employed as a test for ozone. 
 
 Exp. 78. — Dissolve one part of gum guaiacum in thirty parts of 
 ninety per cent, alcohol ; add a few drops of this solution to 2 c. c. of 
 ordinary eighty per cent, alcohol ; dip in this dilute solution strips of 
 thin white blotting-paper, and dry them in the dark. By exposure 
 to ozonized air this test-paper acquires a bright blue color. 
 
 170. By virtue of its strong oxidizing-power, ozone is of great 
 importance as a disinfecting agent. It destroys instantly a mul- 
 titude of offensive gases, such as arise from decaying animal and 
 vegetable matter, and has been frequently recommended of late 
 as a substance weU fitted for the purification of sick-rooms and 
 hospital- wards. Where ozone is employed for purposes of disin- 
 fection, it must be borne in mind that the action of the gas 
 
OZONE A DISINFECTANT. 145 
 
 depends solely upon oxidation. A given quantity of ozone can 
 destroy only a certain definite amount of tte offensive organic 
 matter; wherever these emanations are incessantly generated, 
 ozone must be as constantly produced in order to destroy them. 
 This disinfecting-power of ozone is interesting ia connexion with 
 the observed facts, that ozone is abundant in the air of pine 
 forests, where turpentine abounds, and that pine forests are, as a 
 general rule, remarkably free from malaria. The weU-known 
 disinfeeting-power of tar is supposed in like manner to be partly 
 due to the formation of ozone during the oxidation of some of its 
 ingredients. 
 
 Coal-tar, mixed with plaster-of-Paris, coal-ashes, or dry earth, in 
 quantity sufficient to destroy its stickiness, has been found to be a very 
 efficient disinfectant. The dry powder obtained as above, is simply 
 scattered freely about the offensive locality. The coal-tar, of course, 
 evolves a shght odor, peculiar to itself, which tends to mask or conceal 
 other odors, and also acts as an antiseptic, or arrester of putrefaction ; 
 but its chief merit does not appear to depend upon either of these pro- 
 perties ; it seems really to destroy the gases which are evolved from 
 putrescent matter, and probably does so by generating ozone. 
 
 171. It is supposed that a minute proportion of ozone exists 
 in normal atmospheric air : at all events, there is usually present 
 in air a substance which exhibits the various reactions of ozone, 
 and behaves as ozone would if it were there. This atmospheric 
 ozone, which is supposed to be formed in the processes of oxida- 
 tion which are always going on in nature, varies in quantity with 
 the locality, the season of the year, the hour of the day, and many 
 other circumstances. 
 
 172. Ozone is seldom found in the air of thickly inhabited loca- 
 lities ; it often happens that it cannot be detected in the air of cities 
 at the very time when it is abundant ia the neighboring country. 
 It is often found to be abundant on the windward side of a city, 
 and altogether absent from the air upon the leeward side, the in- 
 ference being that it is destroyed by the exhalations which arise 
 from a dense population. Ozone appears to be more abundant 
 in the air in winter than in summer, in cloudy than in clear 
 weather, and by night than by day ; it has been observed to be 
 specially abundant at times when dew was falling heavily. As 
 might be expected, comparatively large quantities of it are found 
 
146 OZOND IN THE ATMOSPHEKB. 
 
 during thunder-storms, and its odor has been recognized in the 
 neighborhood of objects struck by lightning. Ozone is abundant 
 during snow-storms ; and it is probable that upon its presence de- 
 pends the well-known bleaching-power of newly fallen snow. 
 
 In searching for ozone in the air, test-paper containing iodide of po- 
 tassium and starch, such as was prepared in Exp. 71, is usually em- 
 ployed. Dry slips of the prepared paper are exposed, during from six 
 to twenty-four hours, to a free current of air, in a place well sheltered 
 from light and rain. By exposure the dry paper becomes brown, and 
 when wetted acquires shades of color varying from pinkish-white and 
 iron- gray to blue. The shade of color obtained in this way is then 
 compared with a standard chromatic scale, which includes all the 
 shades possible under the circumstances ; and the proportion of ozone 
 present in the air is thus roughly estimated. 
 
 Although observations of this Hnd are far from possessing that 
 degree of accuracy and certainty which is desirable, they have never- 
 theless been considered trustworthy by numerous observers, and have 
 given rise to much speculation concerning the functions of atmospheric 
 ozone, more particularly with regard to its probable influence upon 
 health and disease. If there be ozone in the atmosphere, it will, on the 
 one hand, oxidize and destroy many volatile organic substances which 
 are supposed to be prejudicial to health. Hence many physicians are 
 of opinion that the atmospheric ozone plays an important part in con- 
 trolling or preventing epidemic diseases through its power of remo- 
 ving infectious matter from the air ; and it has been noticed that with 
 the advent of an ozone-bearingwind such diseases have abated or ceased. 
 But, on the other hand, ozone is a highly irritating gas, and in the 
 opinion of some physicians occasions many diseases of the respiratory 
 organs. Numerous statements are upon record to the effect that epi- 
 demics of catarrh, colds, sore throat, and influenza have been coinci- 
 dent with the beginning of a spell of ozoniferous wind. 
 
 173. Ozone is usually considered to be completely insoluble in 
 water ; but it has been recently ascertained that water can take 
 up a small quantity of it, and so acquire some of the properties of 
 ozone. When ozonized air is passed through a solution of caustic 
 soda or caustic potash, a certain amoTint of ozone is absorbed at 
 first, perhaps by combination- with some oxidizable impurity of 
 the solution, but after a little time the ozone will pass through 
 without apparent alteration. Acids do not absorb ozone. It is 
 readily absorbed, however, by aqueous solutions of iodide of potas- 
 
ANIOZONE. 147 
 
 slum and of pyrogallic acid, with the constituents of which it enters 
 into combinations not to be distinguished from those made with 
 oxygen. 
 
 174. At moderately high temperatures ozone loses its peculia- 
 rities and changes into ordinary oxygen ; if ozonized air, such as 
 was obtained in Exp. 75, is made to pass through a narrow glass 
 tube heated to 250°, its peculiar odor, and its power of decom- 
 posing iodide of potassium will entirely disappear. The same 
 change occurs gradually if the tube is heated only to 100°, — or 
 instantly if steam be thrown into the ozonized air, so that the 
 whole of it can be heated at once to 100° ; hence it may be stated, 
 in general terms, that ozone is converted into ordinary oxygen at 
 temperatures greater than 100°- 
 
 175. Ozone is supposed to exist as such in several of the oxides. 
 Black oxide of manganese, for example, is thought to contain it 
 as a constituent ; and a method of obtaining it from perman- 
 ganic acid has been already given, § 167. The oxygen com- 
 pounds which are supposed to contain ozone are called ozonides. 
 The formulae of the following compounds, recognized as ozonides, 
 are here given for the sake of reference ; — 
 
 PbO, CrO, MnO, Co^, N,0, 
 Ag^O, MnO, MnA Ni^ Bi,0, 
 
 176. Antozone (the opponent or opposite of ozone) appears 
 to be produced simultaneously with ozone whenever the latter is 
 formed, whether by electrical action or during processes of oxida- 
 tion. It may even be that, as some chemists believe, ordinary 
 oxygen is in a certain sense a compound, substance, and that 
 when in contact with phosphorus, and in the other circumstances 
 under which ozone is produced, the neutral oxygen is split or de- 
 composed into two opposite and dissimilar modifications — we had 
 almost said elements — one of which is ozone, the other antozone. 
 It is thought that while the greater part of the ozone thus engen- 
 dered enters into combination with the phosphorus, or other 
 substance, undergoing oxidation, a certain portion of it, together 
 with some of the antozone, becomes mixed with the surrounding 
 air, and so escapes combining with the body which is being oxi- 
 dized. 
 
 Only a comparatively short time has elapsed since antozone 
 
 l2 
 
148 PKEPAEATION OF ANTOZONE. 
 
 has been recognized as a distinct substance ; hence its properties 
 have been less thoroughly studied than those of ozone. Many of 
 its characteristics and properties are stiU involved in great ob- 
 scurity, very various and even conflicting statements having been 
 published concerning them. 
 
 177. Of the methods devised for preparing antozone, the fol- 
 lowing deserve notice : — 
 
 By passing dry electrized air (§ 166) through a concentrated aque- 
 ous solution of iodide of potassium, or of pyrogallic acid, all the ozone 
 contained in the air will be at once absorbed, and the antozone left 
 behind, iree from any admixture of ozone. 
 
 During the slow oxidation of oil of turpentine and other volatile or 
 essential oils (§ 166), a considerable quantity of antozone is produced, 
 as well as of ozone. While most of the ozone at once combines with 
 the constituents of the oil, to form resins and other products of oxida- 
 tion, the antozone, which does not oxidize the oil, is dissolved by it. 
 In what state the antozone exists within the oil is still tmcertain ; but 
 it is, in any event, very loosely held, and is readily given up to other 
 substances. 
 
 In the same way that ozone maybe prepared, by chemical decompo- 
 sition, from permanganate of potassium, a compound supposed to con- 
 tain ozone (§ 167), antozone may be obtained by decomposing certain 
 compounds which are beheved to contain this variety of oxygen — such, 
 for example, as peroxide of barium, BaOj. A little concentrated sul- 
 phuric acid is poured into a small bottle, and into this acid are thrown 
 a number of small fragments of peroxide of barium (free from any ad- 
 mixture of nitrate of barium) ; so soon as an evolution of gas ensues, 
 the air of the bottle will be found charged with antozone. This re- 
 action is sometimes capricious. Usually it occurs at the ordinary 
 temperature of the air ; but it is often necessary to place the bottle in 
 a water-bath heated to 60° or 60°, in order to start the evolution of 
 gas ; and, on the other hand, the violence of the reaction must some- 
 times be allayed by immersing the bottle in cold water. 
 
 In the preparation of ozone by means of phosphorus in moist air 
 (Exp. 75), or by the electrolysis of water (§ 35), the antozone which 
 is formed at the same time with the ozone, unites with the water 
 present, and must there be sought. (See § 181.) 
 
 Antozone has been found in nature in a dark-blue variety of fluor- 
 spar from Wolsendorf, in Bavaria. Upon being rubbed, this mineral 
 emits a peculiar odor, which was formerly thought to be that of chlo- 
 rine or of hypochlorous acid. More recent investigations have shown 
 
PKOPBMIES OF ANTOZONE. 149 
 
 that the odor is that of aiitozone, and that by grinding the mineral 
 with water the antozone can be transferred to the water. 
 
 178. Antozone is a gas, the odor of which, somewhat resembles 
 that of ozone ; there is, however, a decided difference between 
 the two odors, that of antozone being disgusting, while that of 
 ozone is merely pungent and irritating. Antozone changes at 
 once to ordinary oxygen on being heated. Even at the ordinary 
 temperature it reverts to common oxygen very readily — much 
 more readily than ozone. Most of the antozone usually disap- 
 pears from dry electrized air in the course of an hour, or an hour 
 and a half; and if the air be moist, the change is still more rapid. 
 Ozone, on the contrary, is comparatively permanent, under the 
 same conditions ; and although when a mixture of ozone and anto- 
 zone is left in contact with water in a glass-stoppered bottle, some 
 ozone is destroyed during the reversion of the antozone, the 
 larger portion of it will remain almost, if not quite, unaltered 
 for months. Antozone, whether moist or dry, also reverts to the 
 condition of ordinary oxygen on being brought in contact with 
 black oxide of manganese, peroxide of lead, or finely divided 
 platinum. 
 
 179. A very remarkable characteristic of antozone is its power 
 of forming fogs and clouds with water. It may even be found, 
 after the matter has been more thoroughly studied, that all the 
 fogs and clouds which occur in nature are dependent for their 
 existence upon the presence of antozone. 
 
 If air, charged with antozone, be made to bubble through water, it 
 wiU emerge from the water in the form of a thick white mist, similar 
 to that formed by the cooling of steam. The same thing occurs when 
 electrized air, or electrized oxygen, issues into a moist atmosphere, 
 though the effect is less marked when ozone is present than when it 
 has been removed by means of iodide of potassium. The mist pro- 
 duced by slowly passing antozonized air through water is heavy ; it 
 remains hanging over the surface of the liquid, and may be readily 
 poured from one vessel to another. By conducting it through a tube 
 to the bottom of a dry, tall bottle, it displaces the air, all the while 
 preserving a sharply defined boundary ; by gentle agitation it is easily 
 broken up into cloud-like masses. 
 
 When a large, dry bottle is nearly fiUed with this antozone mist, 
 then closed and left to itself, the mist gradually becomes thinner and 
 
150 
 
 THE ANTOZONE CLOXTD. 
 
 less opaque, and in the course of half or three-quarters of an hour 
 vanishes altogether. As the cloud thus disappears, water is deposited 
 upon the sides of the hottle, at first as a mere dew, but afterwards 
 accumulating in droplets, which finally flow together to the bottom of 
 the vessel. When the air in the bottle has become clear, no antozoue 
 can be detected in it. 
 
 It thus appears that antozone has the property of taking up water 
 in such a manner that the water assiunes the peculiar physical condi- 
 tions of a cloud or mist. While the antozone lasts the cloud is per- 
 manent ; but the antozone is soon transformed into ordinary oxygen, 
 and as fast as this change occurs the water of the cloud is deposited 
 in droplets. 
 
 By passing the antozone mist through tubes filled with desiccating 
 substances, such as chloride of calcium (Appendix, § 15), the water 
 may be removed, and transparent antozonized air obtained, capable of 
 again producing a mist on being brought in contact with water. Many 
 strong saline solutions likewise deprive antozone of water ; hence the 
 non-appearance of the cloud when electrized air is passed through a 
 strong solution of iodide of potassium ; the cloud does appear, how- 
 ever, when the solution is sufficiently dilute. 
 
 It has been proved by experiment that electrized air can sup- 
 port or carry nearly twice as much moisture as ordinary air or 
 oxygen at the same temperature, and that this air is much more 
 difficult to dry than the gases with which chemists usually have 
 to deal. This explains how it happened that, before the disco- 
 very of the cloud-forming property of antozone, so many obser- 
 vers had been led to consider ozone an oxide of hydrogen. One 
 experimenter would pass recently electrized air through an ordi- 
 nary drying-tube, such as long experience had shown to be 
 capable of drying common air perfectly, and would then heat the 
 gas ; by this treatment both the ozone and the antozone would 
 be changed to ordinary oxygen, and the water which had been 
 carried through the drying-tube by the antozone would be made 
 visible. The remarkable capacity of antozone for moisture being 
 unknown, the water thus obtained was naturally enough supposed 
 to have been derived from some compound of hydrogen and oxy- 
 gen other than water, and capable of passing unabsorbed through 
 the drying-tube. Other chemists, performing, as they supposed, 
 the same experiment, but in reality operating upon air less recently 
 electrized, and so containing no antozone, were, of course, unable 
 
ANTOZONB FORMED DtTEING COMBTTSTION. 151 
 
 to obtain any water at the point where it had been observed by 
 their predecessors ; hence arose a series of controversies which 
 have only recently been composed. 
 
 180. As has been already mentioned, antozone, like ozone, is 
 formed in all processes of oxidation and combustion. During 
 combustion most of the ozone produced enters into combination 
 with the substance burned, while the antozone is left free, or 
 enters into combination with water to form peroxide of hydrogen. 
 "When the combustion is slow or smouldering, antozone appears 
 in large quantities, and in presence of moisture forms the cha- 
 racteristic mist or cloud. Tobacco-smoke, the gray smoke of 
 chimneys and of gunpowder, and all such smokes are antozone 
 clouds, — facts which support the idea that aU clouds, fogs, and 
 mists are caused by the presence of antozone in the atmosphere. 
 
 The oxidation of phosphorus affords a ready method of exhibiting 
 the antozone cloud. During the oxidation of phosphorus in moist air, 
 white fumes are formed, which were long a great puzzle to chemists. 
 Whether the phosphorus he allowed to oxidize slowly, as in Exp. 75, 
 or burned rapidly, as in Exp. 13, there is always produced a white mist 
 of very considerable permanence, which remains long after the oxides 
 of phosphorus, which are also formed, have been taken up and removed 
 by the water. This mist is the antozone cloud; it is nothing but water 
 held suspended by antozone. 
 
 In the rapid combustion of phosphorus, little or no ozone is left free; 
 all of it seems to unite directly with the phosphorus ; hut much more 
 antozone is produced when the combustion is rapid than when it is 
 slow. The formation of antozone in this connexion explains the fact 
 already alluded to (Exp. 13), that phosphorus burning with flame, m 
 a coniined volume of air, does not wholly exhaust the latter of oxygen. 
 The phosphorus cannot combine with antozone, but only with ozone ; 
 hence, when no oxygen other than that in the form of antozone re- 
 mains, the combustion must cease. 
 
 During the bvuning of a jet of hydrogen under a bell-glass through 
 which a stream of air is drawn, antozone is formed, as is proved by 
 passing the issuing stream through water ; the antozone cloud is pro- 
 duced without difficulty, and peroxide of hydrogen appears as a pro- 
 duct. The formation of the antozone mist, and of peroxide of hydro- 
 gen, may be observed with any other flame if care be taken that the 
 air which streams over the flame be not too strongly heated. A high 
 temperature destroys the antozone as fast as it is formed. 
 
152 
 
 AJfTOZONE OXIDIZES WATEB. 
 
 181. Besides its power of forming clouds or mists with, water, 
 which is interesting rather as a physical than as a chemical fact, 
 antozone, partictilarly when newly formed, also unites with water 
 chemically, the suhstance called peroxide of hydrogen (see § 61), 
 whose composition is expressed by the formula H^O^, being the 
 result of the combination. 
 
 A simple method of exhibiting the formation of peroxide of hydro- 
 gen by the action of antozone upon water, is to place a short, narrow 
 tube, containing concentrated sulphuric acid, within a bottle 2 or 3 
 cm. in width, furnished with a ground-glass stopper, and filled with 
 water nearly to the top of the tube. Small portions of peroxide of 
 barium are now added, at intervals, to the sulphuric acid in the tube, 
 elevation of temperature being avoided as far as possible ; the stopper 
 should be replaced in the bottle after each addition of the peroxide. 
 Most of the oxygen evolved in this process appears, however, to be in 
 the ordinary inactive state, and the solution of peroxide of hydrogen 
 obtained is consequently extremely dilute. A better method of pro- 
 cedure is to pass a current of carbonic acid gas into a mixture of water 
 and peroxide of barium, 
 
 Ba02 4- HjO -I- CO2 = BaO,C02 -|- H^Oj. 
 
 In this way a highly concentrated solution of the peroxide can be 
 obtained. 
 
 Another easy method of preparing peroxide of hydrogen is by the 
 oxidation of amalgams of lead or zinc. In this case also, as in the 
 preceding, the peroxide of hydrogen is probably formed by the union 
 of antozone with water. 
 
 One hundred giammes of lead-amalgam, containing so much mer- 
 cury that it shall be fluid at the ordinary temperature, is shaken in a 
 bottle of the capacity of a litre, together with 200 c. c. of water, aci- 
 dulated with 2 grms. of sulphuric acid; the water soon becomes nulky 
 from separation of sulphate of lead, and in the course of ten or twelve 
 minutes contains enough peroxide of hydrogen to exhibit the charac- 
 teristic reactions of this substance. 
 
 So, too, if pulverulent zinc-amalgam be loosely thrown into a glass 
 funnel, with narrow throat, and a thin stream of water be allowed to 
 flow through it in such manner that the metal may be at the same 
 time acted upon by both air and water, the water will become charged 
 with peroxide of hydrogen. By repeatedly pouring back the dilute 
 solution of the peroxide upon the amalgam, it can be very considerably 
 strengthened. In order to prepare the zinc-amalgam, equal weights of 
 zinc-filings and of mercury are placed in a beaker glass, covered with 
 
riPPEEENCES BETWEEN OZONE AND ANIOZONE. 153 
 
 water acidvdated with sulphuric or chlorhydric acid, and thoroughly 
 mixed by stirring with a glass rod ; the acid is then poured away, and 
 the last portions of it remoyed from the amalgam by washing with 
 water. 
 
 This power of antozone to oxidize water distinguishes it com- 
 pletely from ozone, which has little or no action upon water. 
 
 182. Peroxide of hydrogen, like peroxide of barium, is supposed 
 to contain one atom of oxygen in the form of antozone ; the per- 
 oxides of potassium, sodium, and strontium also are placed in the 
 same category. They are all called antozonides. 
 
 183. Antozone can be distinguished from ozone by the follow- 
 ing tests : — 
 
 Strips of paper, charged with a solution of sulphate of manganese' 
 (Exp. 77), do not become brown when exposed to the action of ant- 
 ozone ; on the contrary, manganese papers which have been browned 
 by ozone are bleached by antozone. Guaiacum paper (Eip. 78) does 
 not become blue in antozonized air. The yellow compound called 
 ferrocyanide of potassium, which is converted into red ferricyanide of 
 potassium by the action of ozone, is not changed by antozone. In the 
 absence of acids, antozone has no action upon iodide of potassium. 
 
 The chemical behavior of antozone may be conveniently studied by 
 resorting to its compound with water, the antozonide peroxide of hy- 
 drogen. If peroxide of hydrogen be brought in contact with an ozonide 
 like peroxide of lead, for example, both of the peroxides wiU be re- 
 duced, and there wiU result water, protoxide of lead, and &ee ordinary 
 oxygen. Whenever an antozonide is mixed with an ozonide, a similar 
 reaction occurs; the two active varieties of oxygen disappear, and 
 common oxygen is evolved ; hence it has been assumed that ordinary 
 inactive oxygen is a sort of compound, resulting from the union or 
 neutralization of ozone with antozone. Several important tests for 
 antozone are dependent upon this fact of the decomposition of ant- 
 ozonides by ozonides. 
 
 If a liquid suspected to contain peroxide of hydrogen be shaken in a 
 test-tube with a small quantity of ether, the ether will dissolve the 
 peroxide, and will finally collect upon the surface of the liquid ; on 
 adding to it a small drop of a solution of the ozonide chromic acid, or, 
 what comes to the same thing, a drop of a solution of bichromate of 
 potassium acidulated with sulphuric acid, the ethereal solution will 
 become blue. 
 
 If a liquid containing peroxide of hydrogen be added to a dilute red 
 solution of permanganate of potassium, this solution will be decolorized, 
 
154 
 
 StTLPHTTR. 
 
 ■while common oxygen will be evolved ; and in the same way the brown 
 peroxide of lead and the red-colored salts of peroxide of iron are 
 bleached by it. 
 
 Another exceedingly delicate and characteristic test for antozone, or 
 rather for peroxide of hydrogen, the rationale of which has not yet 
 been well made out, is the following : — If to a solution containing per- 
 oxide of hydrogen there are added a few drops of dilute starch-paste 
 charged with iodide of potassium, and subsequently a very small 
 quantity of a solution of copperas (protosulphate of iron), iodine will 
 be set free, and the starch will become blue. The solution to be tested 
 must be as nearly neutral as possible. The addition of an acid, instead 
 of the copperas solution, will also bring about the same reaction, 
 though less readily. 
 
 184. We have thus set forth whatever is best known concern- 
 ing ozone and antozone, in spite of the details into which so full 
 an exposition has necessarily descended, partly because the sub- 
 ject will evidently be one of primary importance, both theoretical 
 and practical, in the near future, and partly from a desire to 
 show the student how vague and uncertain the prospect is when 
 once the narrow limits of established knowledge are past and 
 the inquirer ventures out into the obscurity which perpetually 
 separates the knowledge of to-day from that which shall be 
 knowledge to-morrow, but also because of the impossibility, 
 with so obscure a subject, of making such a just discrimination 
 between salient and unimportant points as with a well-studied 
 subject is both easy and desirable. 
 
 CHAPTEK XIII. 
 
 SUlPHtTR. 
 
 185. Sulphur occurs somewhat abundantly in nature, both in 
 the free state and in combination with other elements. Many 
 ores of metals, for example, are sulphur compounds. It is a 
 component of several abundant salts, such as the sulphates of 
 calcium, barium, and sodium, and occurs in. small proportion in 
 
THE STTLPHXJE OP COMMERCE. 155 
 
 many animal and vegetable substances. Free sulphur is found 
 chiefly in volcanic districts. Generally it occurs mixed with 
 earthy matters ; but it often forms distiuct veins, and is sometimes 
 found in the shape of weU-deflned crystals of considerable size. 
 At the present time about nine-tenths of the sulphur of commerce 
 comes from Sicily. 
 
 186. Native sulphur is usually subjected to a rough purifica- 
 tion at the place of its occurrence. This purification is some- 
 times effected by distilling the volcanic earth in retorts or jars 
 of earthenware ; the sulphur being volatile, distils over, and is 
 collected in receivers, from which it is drawn off, from time to 
 time, in the liquid state ; or if the earth be very rich in sulphur, 
 it is simply heated in large kettles and the melted sulphur dipped 
 off from above, while the earthy impurities settle to the bottom 
 of the kettle. The product thus obtained is known as crude sul- 
 phur ; it comes to us in irregular lumps of a dirty light-yellow 
 color, and is largely employed for manufacturing-purposes. 
 
 This crude sulphur is contaminated with more or less earthy 
 matter. In order to purify it, it is distilled from iron retorts into 
 large chambers constructed of masonry, in which it is deposited 
 either in the form of a light powder, known as flowers of sul- 
 phur, or in a liquid state, according to circumstances. At the 
 beginning of the operation, while the chamber is cold, the sul- 
 phur vapor condenses as an exceedingly fine, soft, powder (flowers 
 of sulphur) upon the waUs of the chamber. But heat is given off 
 as the sulphur vapor condenses, and after a while the walls of 
 the chamber become so hot that sulphur will melt upon them. 
 After this, the incoming sulphur vapor of course condenses only 
 to the liquid state, and a layer of liquid sulphur collects upon 
 the floor of the chamber. This liquid sulphur is drawn off into 
 wooden moulds, and thus cast into the sticks familiarly known as 
 roll-brimstone. It is evident that, by a little management, the 
 sulphur-refiner can obtain, at will, either flowers of sulphur or 
 roll-brimstone, or first the one and then the other. 
 
 187. At the ordinary temperature of the air, sulphur is a 
 brittle solid, of a peculiar light-yellow color. It has neither 
 taste nor smell, excepting that when rubbed it exhales a faint 
 and peculiar odor. Most of the odors which in everyday life are 
 
156 
 
 CRTSTALLIZAIION OF STJLPHTTE. 
 
 referred to sulphur are really the odors of various compounds of 
 sulphur, and are not evolved by the element itself. It is a bad 
 conductor of heat and electricity. On being rubbed it becomes 
 highly (negatively) electric, and is stiU employed as a source of 
 electricity in some cases. The symbol of sulphur is S ; its atomic 
 weight is 32, being precisely twice as great as the atomic weight 
 of oxygen. 
 
 188. Sulphur melts easily at about 112°, a temperature not 
 very far above that at which water boils. A fragment of it may 
 even be melted by heating it on writing-paper over the flame of 
 a candle. It volatilises freely at temperatures lower than its 
 melting-point, and boils at 440°- Indeed, as is the case w-ith 
 water, it is a substance which can be brought into either of the 
 three states of matter without any difficulty ; we can have it as a 
 solid, a liquid, or a gas as we please. It can readily be obtained 
 also in the form of crystals. 
 
 Exp. 79. — ^In a small beaker glass, or porcelain capsule, heat i 
 50 to 60 grms. of sulphur until it has entirely melted. Remove the 
 vessel from the lamp, and allow it to cool slowly vmtil about a quarter 
 part of the sulphur has solidified ; then pour off, into a basin of water, 
 that portion of the sulphur which is still liquid, breaking through, for 
 this pm-pose, the crust at the top of the liquid, if any such have formed. 
 The interior of the vessel will be found to be lined with transparent, 
 prismatic crystals. 
 
 Exp. 80. — In a test-tube, melt enough sulphur to fill one-quarter of 
 the tube ; place the tube in such a position that its contents may cool 
 slowly and quietly, and then watch the formation of crystals as they 
 shoot out from the comparatively cold walls of the tube towards the 
 centre of the liquid. 
 
 Exp. 79 represents one general method of obtaining crystals. 
 Crystals of many of the metals, lead and bismuth for example, 
 can be obtained by operating in this way ; it is only necessary 
 to melt the metal in a crucible of some refractory material, 
 placed in a furnace. The melted metal having then been allowed 
 to cool until a tolerably firm crust has formed upon its surface, 
 this crust is pierced with an iron rod, and the crucible quickly 
 inverted, so that the portion of the metal which still remains 
 fluid in the interior shall flow out. Upon afterwards breaking 
 
CETSTALLINE STEtTCTURE. 157 
 
 the crucible, crystals will be found lining the cayity of the metallic 
 cup which has been formed withia it. 
 
 189. Exp. 80, besides illustrating the manner in which crys- 
 tals form, teaches us something of the physical structure of solid 
 bodies. The solid mass of sulphur which is left in the test-tube 
 when it has become cold, is evidently nothing more than a com- 
 pact bundle of interlaced crystals. If the mass be removed from 
 the tube, and then broken across, it will present a glistening 
 appearance, owing to the reflection of light from the surfaces of 
 the minute crystals of which it is composed. It is said to have 
 a crystalline structure. This crystalline structure is apt to render 
 a body brittle ; substances which possess it are liable to break 
 " with the grain," or to split in certain directions determined by 
 the shape of the crystals, and called Unes of cleavage ; a stick of 
 roU-brimstone, for example, may be readily broken or cut across, 
 but not so easily in the direction of its length. The same remark 
 appHes to many samples of metal. In all cases where tenacity is 
 required, it is important to counteract, or to prevent as much as 
 possible, the tendency towards crystallization. Thus, in manu- 
 facturing wrought iron, it is the constant endeavor of the work- 
 man to render the metal stringy or fibrous, and not crystalline, 
 and he seeks to accomplish this by appropriate processes of 
 kneading, squeezing, and rolling. 
 
 190. Another easy way to crystallize sulphur is by the method 
 of solution and evaporation, such as was employed in the pre- 
 paration of nitrate of ammonium (Exp. 33). Sulphur is not 
 soluble in water, but it dissolves readily in a liquid compound of 
 sulphur and carbon, known as bisulphide of carbon, which being 
 readily volatile, quickly escapes, on exposure to the air, and so 
 deposits the sulphur. 
 
 Exp. 81. — ^Place in a test-tube a small teaspoonful of flowers of 
 sulphur, pour upon the sulphur 10 or 12 c. c. of bisulphide of carbon, 
 close the tube with a cork, and allow the mixture to stand during half 
 an hour, shaking it occasionally. Decant the clear hquid from the 
 sulphur which still remains undissolved, and pour it into a small porce- 
 lain capsule, which place out of doors, or in a draught of air, until the 
 highly ofiensive bisulphide of carbon has all evaporated. Crystals of 
 sulphur will then be found at the bottom of the dish. 
 
 This experiment might he modified by preparing, ia the first place, a 
 
158 THE SIX SYSTEMS OE CETSTAIlIZATIOIf. 
 
 saturated solution of sulphur in boiling tisulphide of carbon, and then 
 allowing the clear solution to cool slowly. Crystals of sulphur would 
 finally be found beneath the cold liquid. The method by evaporation, 
 as above described, is to be preferred. 
 
 It will be noticed that the crystals of Exp. 81 are not shaped 
 like those obtained by the method of fusion in Exp. 79. The 
 two sets of crystals belong in fact to entirely different systems of 
 crystallization. 
 
 191. The researches of crystallographers have proved that the 
 crystals of natural miuerals and artificial chemical substances 
 may all be included in six general classes of form, called systems 
 of crystallization. In every crystal, certain directions may be 
 recognized, with reference to which the bounding planes of the 
 crystal exhibit a more or less symmetrical arrangement. These 
 directions, represented by straight lines drawn through the centre 
 of the crystal, are called axes. The thousands of crystal-forms 
 which occur in nature, or are produced by art, have been divided 
 into six systems, or groups, by observation of the number, rela- 
 tive length and mutual inclination of the axes around which they 
 are symmetrically formed. These six systems are defined as 
 follows : — 
 
 I. Monometric (singh-meamre) or Regular System. — The axes are 
 three in number, equal in length, and intersect each other at right 
 angles. The cube, regular octahedron, and rhombic dodecahedron, 
 forms of perfect symmetry, belong to this system. 
 
 II. Dimetnc (two-measure) System. — The axes are three in number, 
 and intersect each other at right angles ; but one, called the vertical, 
 is either longer or shorter than the two lateral, which are equal. The 
 right square prism and square octahedron are of this system. 
 
 III. Trimetric (three-measure) System. — The axes are three in num- 
 ber, unequal in length and intersect each other at right angles. The 
 system includes the right rectangular prism, the right rhombic prism, 
 and the rhombic octahedron. 
 
 IV. Monoolinic (single-inolination) System. — The axes are three in 
 number, and unequal in length ; and one, called the vertical, is at right 
 angles with one of the other two axes, which are called lateral, but 
 obliquely inclined to the other; the two lateral axes intersect each 
 other at right angles. The right rhomboidal and oblique rhombic 
 prisms belong to this system. 
 
 V. TricUnic (three-inclination) System. — The axes are three in num- 
 
SULPHUR IS DIMOEPHOUS. 
 
 159 
 
 ber, unequal in length, and all their intersections are oblique. The 
 oblique rhomboidal prism is of this system. 
 
 VI. Hexagonal System. — The axes are four in number; three called 
 lateral, lie in one plane, are equal in length, and intersect each other 
 at angles of 60°; the fourth axis, called vertical, is either longer or 
 shorter than the other three, and crosses them at right angles. This 
 system includes the hexagonal prism and the rhombohedron. 
 
 Under these systems of crystallization, the variety of possible forms 
 and dimensions is unlimited. Thus, in systems in which the axes are 
 unequal, the inequality may be great or small, through all degrees of 
 discrepancy ; in oblique systems the inclination of the axes may vary 
 indefinitely ; rhombohedrons may occur of every angle. Thus the ac- 
 tual forms of crystallography become exceedingly numerous, although 
 they all belong to a few simple types. 
 
 If the student draws in perspective, upon paper, the axes of the 
 several systems above described, or, better, constructs the different sets 
 of axes out of bits of wood or wire, he wiU appreciate the fact that 
 forms belonging to different systems are ordioarily so unlike in general 
 appearance as to be readily distinguishable even by those who have no 
 exact knowledge of the mathematical science of crystallography. 
 
 192. As a general rule, a substance crystallizes in forms be- 
 longing to only one system, and the crystalline form of a sub- 
 stance is something so constant and characteristic as to be one of 
 the chemist's most valued means of recognition and definition. 
 But this general rule is not without exceptions. Sulphur, as has 
 just been proved, may be made to crystallize in forms belonging 
 to two distinct systems of crystallization; and there are other 
 substances, not a few, which when crystallized under different 
 conditions, assume forms of two distinct systems. 
 Substances which are thus capable of assuming crys- 
 talline forms belonging to two different systems are 
 said to be dimorphous (two-formed). Two such dif- 
 ferent forms of the same substance often Y\^. 39. 
 have quite dissimilar physical properties; 
 they are apt to differ from each other in 
 hardness, specific gravity, color, optical pro- 
 perties, and in their relation to heat; the 
 chemical properties, also, of two such dif- 
 ferent forms are seldom entirely the same. 
 The crystals of sulphur obtained by fusion (Exp. 79) are 
 
 Fig. 38. 
 
160 CHAJTGE OE PRISMATIC INTO 0CTAHBDE4X STTLPHUE. 
 
 elongated oblique rhombic prisms (Kg. 38), and belong to the 
 fourth (or monoolinic) system. The crystals of sulphur which 
 are derived from its solution in bisulphide of carbon (Exp. 81) 
 are rhombic octahedrons (Kg. 39), belonging to the trimetric 
 system. The specific gravity of the octahedral crystals is greater 
 than that of the prismatic in the ratio of 2-07 : 1-91. The spe- 
 cific heat of the octahedral crystals is 0-163, and that of the 
 prismatic somewhat greater. The melting-point of the prismatic 
 crystals is about 120°. 
 
 The prismatic crystals of sulphur (Exp. 79) cannot be kept 
 for any great length of time. They soon lose their transparency 
 and characteristic amber color, becoming opaque and light yellow, 
 like ordinary brimstone. If they be examined under the micro- 
 scope it wiU be seen that the prisms are now composed of a 
 multitude of little octahedral crystals. The change of color and 
 texture is due to a rearrangement of the particles of the original 
 crystals, though the aggregation of octahedrons which have been 
 formed within the prismatic crystal still retains the shape of the 
 prism. If the prismatic crystals be left at rest, this change of 
 form usually begins in the course of a few hours ; but it may be 
 greatly accelerated by scratching the crystals, or shaking them 
 together. Under ordinary circumstances the passage of the sul- 
 phur from the one molecular state to the other goes on very 
 slowly, several years being often required for its completion ; but 
 the change can be accomplished immediately by moistening the 
 prismatic crystals with bisulphide of carbon. A considerable 
 amount of heat is developed as the prismatic sulphur changes 
 into octahedral ; this can readily be appreciated when the con- 
 version is efieoted by means of bisulphide of carbon. 
 
 In the same way that prismatic sulphur slowly changes iuto 
 the octahedral variety at the ordinary temperature, octahedral 
 sulphur is gradually converted into prismatic sulphur when kept 
 for a long time at a temperature near its melting-point. The 
 change in specific gravity enables us to foUow the progress of this 
 conversion. 
 
 Sulphur which has been melted and allowed to solidify gra- 
 dually, is always in the prismatic condition immediately after the 
 solidification. EoU-brimstone, for example, when fresh from the 
 
METHODS OF OBTArfTIlfa CRTSTAIS. 161 
 
 moulds, is translucent, and of a dark amber or brownish-yellow 
 color, like the prismatic arystals of Exp. 79 ; but ia a short time, 
 often in the course of a few hours, the sticks become light-yeUow 
 and opaque, as we find them in commerce, and are then com- 
 posed, at least externally, of a mass of octahedral crystals. 
 
 193. There is stiU a third way of obtaining crystals of sulphur, 
 namely, by sublimation. At slightly elevated temperatures, sul- 
 phur is volatile ; and if the circumstanqes be such that the vapor 
 shall condense very slowly, crystals will form. The natural 
 crystals of sulphur found in volcanic countries, which are often 
 very large and of great beauty, have been formed in this way. 
 These native crystals are octahedral, like those obtained by means 
 of bisulphide of carbon (see Exp. 81). 
 
 194. As appears from the foregoing, there are three distract 
 methods of obtaining crystals : — I. By fusion ; that is to say, by 
 the slow cooling of molten matter. II. By solution, followed 
 either by removal of the solvent by evaporation or chemical means, 
 or by reduction of its temperature. III. By sublimation. 
 
 A familiar instance of the first method is seen in the case of 
 ice, as when a part of the water in any hollow vessel freezes 
 slowly upon the sides of the vessel ; of the second, in the manu- 
 facture of common salt; and of the third, in the formation of 
 frost upon a window-pane. 
 
 There is still a fourth general method of obtaining crystals, 
 which consists in very slowly decomposing some chemical com- 
 pound of the substance to be crystallized, either by the addition 
 of some other chemical agent, or by means of the galvanic cur- 
 rent. Crystals of sulphur may be formed in this way, and are 
 in fact sometimes found in the pipes used to convey Uluminating 
 gas through the streets of cities, under such circumstances that 
 it is evident that they have resulted from the decomposition of 
 some one of the sulphur compounds with which coal-gas is always 
 contaminated. 
 
 It must not be inferred, from the above enumeration of the 
 ordinary methods of obtaining crystals, that either fusion, solu- 
 tion, or sublimation is a necessary condition of the formation 
 of crystals. Both in nature and in art examples occur of the 
 crystalline arrangement of particles within solid masses, under 
 
 u 
 
162 
 
 SOPT STJLPHTJE. 
 
 circumstances whicli preclude the idea that either fusion, solu- 
 tion, or sublimation, in the ordinary sense of these terms, should 
 have occurred. 
 
 195. Sulphur behaves in a very remarkable manner on being 
 heated. When melted at the lowest possible temperature, 110° 
 to 115°, it forms a limpid liquid of a light-yeUow color; but if 
 this liquid be heated more strongly, it begins to become viscid 
 and dark-colored at about 150°, and at 170° to 200° it is almost 
 black, and at the same time so thick and tenacious that it cannot 
 be poured from the vessel which holds it, even if the vessel be 
 inverted. At 330° to 340° it regains its fluidity in part, though 
 the liquid is still dark-colored, and finally, at about 440°, it be- 
 gins to boil, and is converted into an amber-colored vapor. The 
 specific gravity of sulphur vapor, referred to hydrogen, is 32. 
 
 196. If melted sulphur, in the viscid state, or, better, that 
 which has regained its mobility, be suddenly cooled, a semisolid 
 modification of sulphur, remarkably different from the ordinary 
 form, will be obtained. 
 
 Exp. 82. — Place in a test-tube, of about 30 c. c. capacity, 15 to 20 
 grms. of coarsely powdered sulphur ; melt the sulphur slowly over the 
 gas-lamp, and continue to heat it until it begins to boil, noting, mean- 
 while, the changes which the sulphur undergoes — as described in § 195. 
 KnaUy pour the hot sulphur, in a fine stream, into a large dish ftJl of 
 cold water. There wiU be obtained a soft, elastic, reddish-brown mass, 
 which can be kneaded and moulded like wax, and drawn out into 
 threads like caoutchouc. 
 
 This soft sulphur cannot be preserved for any great length of 
 time. When left to itself, at the ordinary temperature of the 
 air, it slowly hardens and changes into ordinary brittle yellow 
 sulphur. This change is accelerated by kneading, and is instan- 
 taneous at the temperature of 100°. In any event, a certain 
 amount of heat is evolved as the soft sulphur changes into ordi- 
 nary sulphur. The specific gravity of soft sulphur is somewhat 
 lower than that of the prismatic crystals. 
 
 From the foregoing facts it appears that sulphur, like oxygen, 
 is capable of assuming different aUotropic states. (See § 162.) 
 
 197. In its behavior towards solvents, sulphur presents some 
 curious anomalies. Some specimens of sulphur are freely soluble 
 
MTLK OP STTlPHtnt, 163 
 
 in bisulphide of carbon, while of other samples only a compara- 
 tively small portion dissolves. We distijiguish, therefore, a soluble 
 and an insoluble modification of sulphur. 
 
 Octahedral sulphur, the bright-yellow, translucent, native crys- 
 tals for example, is completely soluble in bisulphide of carbon. 
 But of the soft, elastic sulphur, such as was prepared in Exp. 82, 
 as much as 30 or 40 per cent, is completely insoluble in the 
 bisulphide, whether this liquid be hot or cold. 
 
 No method has as yet been discovered of preparing pure in- 
 soluble sidphur directly ; but it can always be readily obtained 
 by dissolving out the soluble sulphur from a mixture of the two 
 varieties, such as the soft sulphur above mentioned. Flowers of 
 sulphur contain a considerable portion of insoluble sulphur ; roU- 
 brimstone much less, though the interior of the sticks contains 
 decidedly more than the outside portions. It may be observed, 
 in this connexion, that flowers of sulphur are prepared by sud- 
 denly cooling the vapor of sulphur, while the soft variety is 
 obtained by suddenly cooling melted sulphur. 
 
 Insoluble siillphur undergoes no change at the ordinary tem- 
 perature ; but if it be kept for a long time at 100°, or if it be 
 exposed to the vapor of water or alcohol, it is slowly converted 
 into the soluble variety. 
 
 198. For some pharmaceutical purposes^ sulphur is prepared as 
 a powder finer even than flowers of sulphur. This preparation is 
 known as milk of svUphu/r or precipitated sulpJiur. 
 
 Uxp. 83. — Place in a small flask as much fl;owers of sulphur as can 
 be taken up on the point of a penknife ; pour into the flask 10 or 15 
 c. c. of a Bolution of caustic soda, and boil the mixtture for some time. 
 Part of the sulphur will dissolve and color the liquid yellowish brown. 
 
 Pour ofi' the clear liquid from the undissolved sulphur, mix it with 
 an equal volume of water and stir in dilute chlorhydric acid, added by 
 small portions, untU a drop of the mixture placed upon litmus paper 
 exhibits an acid reaction. As the acid is added, the liquid assumes a 
 milky appearance from the separation of sulphur in the form of an 
 exceedingly flne powder. This powder is so light that, for a long 
 while, it will not subside, but remains suspended in the liquor, im- 
 parting to it a milky appearance. 
 
 Collect the powder on a small filter, wash it with watery and dry it 
 at a gentle heat. It will now appear as a pale yellowish-grey impaL-» 
 
 m2 
 
164 
 
 METAIS BTTEN IN STJLPHTJE. 
 
 pable powder. If it be heated more strongly, so that it melts, the 
 color will become distinctly yellow, the numberless smaU particles of 
 the powder being now compacted into a single mass. 
 
 It will be remarked that the color of flowers of sulphur is 
 lighter than that of roll-brimstone, while the color of the pre- 
 cipitated sulphur is far lighter than that of the flowers. Such 
 differences as these are common ; they depend upon a difference 
 of mechanical condition, upon differences in the state of aggre- 
 gation of the particles of the substances which exhibit them. 
 
 The method of pulverization by precipitation, employed in this 
 experiment, is a general method, applicable to many other sub- 
 stances besides sulphur. 
 
 199. Sulphur unites energetically with most of the other ele- 
 ments, such union being, in many cases, attended with evolution 
 of light. Most of the metals, for example, combine with it 
 directly, just as they do with oxygen. 
 
 Exp. 84. — Melt in an ignition-tube, 12 to 15 Fig. 40. 
 
 cm. long, 4 or 6 grms. of sulphur, and heat the 
 liquid until it boils ; then throw in small por- 
 tions of copper filings, or fine turnings, and 
 observe the violent action which ensues. 
 
 Or a strip of very thin sheet copper or a coil 
 of fine copper-wire may be suspended in the 
 hot sulphur vapor, in the upper part of the 
 igmtion-tube ; it will glow vividly as it unites 
 with the gaseous sulphur, much in the same 
 way as if it were burning in oxygen gas. The 
 product of the reaction, in either case, is called 
 sulphide of copper. 
 
 Eocp. 85. — Mix intimately 4 grms. of flowers 
 of sulphur and 7 grms. of the finest iron-filings. Place the mixture in 
 an ignition-tube 10 to 12 cm. long, and heat the lower end of the 
 tube over the gas-lamp. In a short time the mass will begin to glow, 
 as the sulphur and iron enter into chemical combination, and this 
 ignition will, of itself, pass through the entire length of the tube, 
 even if the lamp be withdrawn. The final product of the reaction is 
 protosulphide of iron. 
 
 200. As has been already shown (§§ 2, 109), phenomena of 
 combustion, such as are exhibited in these experiments, are 
 directly referable to chemical union. They are strictly analogous 
 
USES OP SULPHUR. 165 
 
 to the ordinary processes of combustion in which oxygen is 
 involved, though the technical term, combustion, is by custom 
 limited to the act of combination mth oxygen. 
 
 Sulphur combines mth chlorine, bromine, iodine, and phos- 
 phorus at the ordinary temperature, and with carbon at a red 
 heat. With oxygen it unites readily at a comparatively low 
 temperature. When heated in the air, it takes fire at about 
 250°, and bums with a peculiar blue light. This easy inflam- 
 mability may be readUy Ulustrated by blowing flowers of sulphur 
 into the hot air issuing from the chimney of an Argand gas-lamp ; 
 the sulphur takes fire at a considerable height above the flame. 
 The irritating, suffocating gas, which is produced by the union of 
 sulphur and oxygen, wiU be shortly described under the name of 
 sulphurous acid. 
 
 Several iflaportant practical applications of sulphur depend upon 
 this property of igniting and continuing to burn at a moderate 
 heat. It is, in fact, largely employed as a kindling material. 
 By means of it, other bodies less readily combustible, can be 
 heated to the temperature at which they continue to burn. 
 Hence its use upon matches and in gunpowder and fireworks. 
 
 201. In its chemical properties, sulphur is closely allied to 
 oxygen; like oxygen, it forms a great variety of compounds 
 with a wide range of different elements ; and the senes of com- 
 pounds thus 'obtained is in many respects parallel with, or com- 
 parable to, the series of oxygen compounds. 
 
 It is an important raw material in the chemical arts, being an 
 ingredient of numerous useful compounds, such as cinnabar, ultra- 
 marine, vulcanized caoutchouc, bisulphide of carbon, chloride of 
 sulphur, and the various compounds of sulphur and oxygen, one 
 of which, sulphuric acid, is the most important chemical agent at 
 present employed in manufacturing industry. Sulphur is largely 
 employed in medicine, in the treatment of cutaneous diseases of 
 both men and domesticated animals, and has been of late years 
 extensively used in the vineyards of Europe for destroying a 
 parasitic fungus which infests the vines. 
 
 202. Sulphydric Acid (H^S). — When sulphur is sublimed in 
 hydrogen gas, or when hydrogen is passed over melted sulphur, 
 combination takes place between the two elements, though very 
 
166 
 
 PEEPARATION OF SXTIPHTDEIC ACID. 
 
 Fiff. 41. 
 
 slowly and imperfectly, so that only a comparatively small quan- 
 tity of the compound is obtained, even if the process be con- 
 tinued for a long time. Somewhat larger quantities of it are 
 formed when a mixture of hydrogen gas and sulphur- vapor is 
 passed through a tube Med with fragments of pumice-stone 
 heated to about 500°. 
 
 When the two elements meet in the nascent state, they com- 
 bine readily; thus, when organic bodies containing sulphur 
 putrefy, and when they are subjected to destructive distillation, 
 sulphydric acid is evolved, just as ammonia is under the same 
 circumstances. In either event, the product of the union is a 
 colorless gas of highly offensive odor, like that of rotten eggs. 
 
 An easier method of preparing sulphydric acid, or sulphuretted 
 hydrogen, as it is often called, is by acting upon a compound of 
 sulphur and iron with dilute chlorhydrie acid. 
 
 Exp. 86.— In a gas-bottle (Fig. 41) put 10 or 12 grms. of protosul- 
 phide of iron, see Exp. 85; re- 
 place the cork in the bottle and 
 introduce the gas-delivery-tube 
 into another small bottle contain- 
 ing cold water, letting the tube 
 dip 5 or 6 cm. beneath the sur- 
 face of the water. Through the 
 thistle-tube, pour into the gas- 
 bottle water enough to seal the 
 lower extremity of this tube ; 
 then add, through the thistle- 
 tube, as before, 2 or 3 teaspoon- 
 fuls of muriatic acid, and observe 
 that bubbles of gas soon begin to 
 pass through the water in the absorption bottle. 
 
 Sulphydric acid is soluble in water to a considerable extent, and is 
 consec[uently taken up by the water in the absorption bottle. The 
 solution thus obtained, known as sulphuretted hydrogen-water, is 
 much employed as a reagent in chemical laboratories; it will seiTe us 
 here as a convenient source of sulphydric acid. 
 
 When the disengagement of gas slackens, a new portion of muriatic 
 acid maybe added through the thistle-tube, and this process continued 
 until the water in the absorption bottle smells strongly of the gas. 
 
 This experiment should be performed out of doors, or in a draught 
 
PEEPAKATION OF STJLPHTBEIC ACID. 
 
 167 
 
 of air so arranged that those portions of the gas -which escape solution 
 shall be carried away from the operator. 
 
 203. The reaction between the sulphide of iron and chlor- 
 hydric acid in the foregoing experiment is somewhat analogous 
 to that which occurs in the preparation of hydrogen, § 50. If 
 metaUic iron (or zinc) be treated with chlorhydric acid, hydrogen 
 is evolved, according to the equation 
 
 Fe + 2HC1 = PeCl, + 2H. 
 But if, instead of simple iron, sulphide of iron, whose formula 
 is FeS, be taken, sulphur vrill be eliminated, as weU as hydrogen, 
 by the action of the acid, and these elements, as they come to- 
 gether in the nascent state, will unite to form sulphydric acid. 
 FeS + 2HC1 = FeCl, + H,S. 
 Instead of absorbing the gas evolved in the foregoing experi- 
 ments in water, it might be collected as such, over a basin hold- 
 ing but a small quantity of water, or, better, iilled with warm 
 water or with brine, either of which absorbs less of the gas than 
 cold water. Unless absolutely dry, the gas cannot be collected 
 over mercury, since, when moist, it acts upon this metal. 
 
 204. At the ordinary temperature and pressure, sulphydric 
 acid is a gas somewhat heavier than air, its specific gravity being 
 17, referred to hydrogen; but under a pressure of about 15 
 atmospheres at 11°, it be- 
 
 comes liquid. The specific 
 gravity of this liquid re- 
 ferred to water is 0-9. At 
 — 85° the liquid solidifies 
 to awhite crysl^aUine mass. 
 205. Since the sulphide 
 of iron, employed in the 
 preparation of sulphydric 
 acid, is usually mixed with 
 a certain quantity of me- 
 tallic iron, the gas is liable 
 to be contaminated with 
 free hydrogen. For aU or- 
 dinary purposes, the gas 
 
 Fig. 42. 
 
168 AlfALTSIS OF SULPHXDKIC ACID. 
 
 thus mixed with, hydrogen serves as well as if it were piire ; but 
 in some cases a gas free from hydrogen is required. In order to 
 prepare it, sulphide of antimony is substituted for the sulphide 
 of iron. 
 
 1 part of powdered sulphide of antimony placed in a thin-bottomed 
 flask is treated with 3 or 4 parts of chlorhydiic acid of 1-1 sp. gr. and 
 the mixture gently heated. The apparatus may be arranged as in 
 Fig. 42, in which the bottle into which the gas first enters contains a 
 very small quantity of water ; this water serves to remove any particles 
 of the acid or of solid matter which may have been carried over in the 
 current of gas. In case a dry gas be needed, a chloride-of-calciuni 
 tube (see Appendix, § 15) must be interposed between the wash-bottle 
 and the mercury-trough. 
 
 206. The volumetric composition of sulphydrie acid gas is one 
 volume of sulphur-vapor and two volumes of hydrogen, condensed 
 to two volumes. Its molecule, therefore, contains one atom of 
 sulphur and two atoms of hydrogen, and is strictly analogous to 
 the molecule of water. 
 
 The composition of sulphydrie acid may be determined experi- 
 mentally by heating metallic tin in a confined volume of the gas. An 
 ignition-tube 20 or 30 cm. long, bent at an obtuse angle, within 5 to 
 6 cm. of the closed extremity, as shown in Fig. 43, should be com- 
 pletely filled with dry sulphydrie acid gas over the mercury-trough, 
 and then closed with the thumb and inverted. 
 Some granulated tin should be dropped into ^' 
 
 the tube and made to lodge in the bent part, 
 the thumb being instantly replaced upon the 
 mouth of the tube the moment the tin has 
 entered. 
 
 The tube full of gas is now replaced in the 
 mercury-trough, as shown in the figure, and 
 about one-third part of the gas is allowed to escape by inclining the 
 tube 80 that the gas may bubble out through the mercury. The tube 
 and its contents are left at rest during half an hour, in order that they 
 may acquire the temperature of the surrounding air, a caoutchouc ring 
 is slipped down the tube to mark the height of the gas, and the tin is 
 then heated with the flame of a spirit-lamp. The hot tin combines 
 with the sulphur, and hydrogen is set free. The apparatus is left at 
 rest during another half hour, and the height of the gas in the tube 
 is then noted. If the gas employed was pure, it will be found that its 
 volume has undergone no change. The hydrogen which has been set 
 
PKOPERTIES OP SITLPHTDEIC ACID. 
 
 169 
 
 free occupies precisely the same space aa the sulphydric acid did before 
 it was decomposed. 
 
 It is evident from this that 1 volume of sulphydric acid gas contains 
 1 volume of hydrogen, or multiplying these numbers by 2, in order to 
 airive at the composition indicated by our molecular formula, that 2 
 volumes of sulphydric acid contain 2 volumes of hydrogen. Now the 
 specific gravity, or unit-volume weight of sulphydric acid has been 
 found, by experiment, to be 17'19, that of hydrogen being 1 ; and if 
 
 From the weight of 2 volumes of sulphydric acid .... 34-38 
 We subtract the weight of two volumes hydrogen . . . 2-00 
 
 There wiU remain 3238 
 
 which is very nearly equal to the unit-volume weight of sulphur- 
 vapor, 31-8, as experimentally determined. 
 
 The composition of sulphydric acid, both by volume and weight, 
 may, therefore, be expressed by the diagram. 
 
 H 
 1 
 
 
 • + 
 
 
 
 
 8 
 32 
 
 = 
 
 H,S 34 
 
 ii 
 
 1 
 
 
 
 207. The gas is very poisonouB; when respired in the pure 
 state it quickly proves fatal, and it is very deleterious, even 
 thougji largely diluted with atmospheric air. Small birds soon 
 die in air which contains only -j-j^ of its volume of the gas, dogs 
 in air which contains -g^^, and horses in air which contains -^^ 
 of its volume. Men can support more of it, but in experimenting 
 with it, it is best to do so where there is a free circulation of air. 
 Nausea and headache are often produced when an atmosphere 
 even slightly contaminated with snlphuretted hydrogen has been 
 breathed for any length of time. In case the air of an apart- 
 ment become contaminated with the gas, the disgusting smell 
 can readily be neutralized by sprinkling the room with chlorine- 
 water, or by evolving a little chlorine gas by adding some dilute 
 acid to a small quantity of bleaehing-powder. 
 
 The gas exists as a natural constituent of some mineral waters' 
 which are thence called sulphurous, such as the Virginia Sul- 
 phur Springs, and the mineral springs at Sharon, N. T. It is 
 
170 
 
 STJLPHUEETIED-HTDKOGBN WATBK. 
 
 also found in the air and -water of foul sewers, and wlierever 
 animal matter is undergoing putrefaction. 
 
 208. Sulphydric acid gas is readily inflammable, and, like hy- 
 drogen, extinguishes the flame of a burning candle immersed in 
 it. It bums with a blue flame, producing water and sulphurous 
 acid gas. 
 
 H,S + 30 = H,0 + SO,. 
 In case it be ignited in contact with a quantity of air insufficient 
 to bum the whole of it, the hydrogen will bum first, and a por- 
 tion of the sulphur wUl escape combustion. 
 
 If a tall glasa cyhnder be fiUed with sulphydric acid gas, and the 
 gas be lighted at the top, the flame will pass down the cylinder as the 
 hydrogen is consumed, and a quantity of very finely divided solid sul- 
 phur wiU be deposited upon the walls of the vessel. 
 
 It has already been stated that sulphur kindles very easily, and that 
 it has a strong affinity for oxygen ; but it appears from this experi- 
 ment, that hydrogen kindles still more readily, and that its affinity for 
 oxygen is greater than that of sulphur, 
 
 "When mixed with air, in certain proportions, it is explosive ; 
 a fact which should be borne in mind by the experimenter. 
 
 209. Water dissolves about three times its own volume of the 
 gas at the ordinary temperature. This solution (see Exp. 86) is 
 transparent and colorless when recently prepared, but, when kept 
 it gradually becomes opalescent and turbid from deposition of 
 sulphur. Oxygen from the air unites with the hydrogen of the 
 sulphydric acid to form water, and sulphur is set free. After the 
 lapse of several weeks or months, it will be found that the solution 
 no longer contains any sidphydric acid ; it has lost its nauseous 
 odor, and the bottom of the bottle is covered with sulphur, the 
 result of the decomposition of the dissolved gas. 
 
 The aqueous solution of the gas reddens litmus slightly, like 
 the very weak acids. Towards metals and metallic oxides it be- 
 haves in a manner somewhat analogous to that of chlorhydric 
 acid and its congeners, while, with regard to metallic sulphides, 
 it stands in the same relation as water to the oxides, as wiU be 
 explained hereafter, 
 
 Exp. 87. — Place a drop of sulphuretted-hydrogen water (Exp. 86) 
 upon a bright piece of copper^ lead, or silver. The metal will quickly 
 
STTLPHTDEIC ACID AS A EEAGENT. 171 
 
 become black. The sulphur of the aulphydiic acid unites with the 
 metal, to form sulphide of copper, sulphide of lead, or sulphide of sil- 
 ver, aa the case may be, while the hydrogen escapes. 
 Cu + HjS = CuS + 2H. 
 
 Exp. 88. — Place in a test-tube as much litharge (oxide of lead = 
 PbO) as can be held upon the point of a penknife, pour upon it a tea- 
 spoonful of sulphuretted hydrogen-water, and observe that the yellow 
 litharge immediately becomes black. Sulphide of lead is formed, as in 
 the preceding experiment, together with a quantity of water. 
 PbO -I- H^S = PbS -I- H2O. 
 
 Exp. 89. — In place of the litharge of the last experiment, take a 
 very small crystal of nitrate of lead (Exp. 42) ; dissolve it in as much 
 water as will half flU the test-tube, and to- this solution add a few drops 
 of the sulphuretted-hydrogen water. Black sulphide of lead is thrown 
 down as a precipitate, and nitric acid is set free. 
 
 PbO,N205 -I- HjS = PbS -f H^OjNsO^. 
 
 210. Since many of the metallic sulphides are, like the sul- 
 phides of lead, copper, and silver, insoluble in water and dilute 
 acids, sulphuretted hydrogen is peculiarly well adapted for pre- 
 cipitating the metals from their solutions. After having been 
 thrown down as sulphides, as in the last experiment, they can be 
 readily sepai-ated and collected by filtration. 
 
 Though many of the metallic sulphides are black, like that of 
 lead, this is not true of all. Several of them exhibit character- 
 istic colors, by which they may be readily recognized ; thus the 
 color of sulphide of antimony is orange, that of sulphide of arsenic 
 is yeUow, and that of sulphide of zinc white. Upon this fact the 
 application of sulphuretted hydrogen as a test or reagent (that is, 
 as a means of detecting and identifying many metals) is in part 
 
 211. In the same way that sulphuretted hydrogen can be em- 
 ployed for detecting the presence of metals, so, conversely, solu- 
 tions of the metals, or, in some cases, the metals themselves, may 
 be used as tests for sulphuretted hydrogen. 
 
 Exp. 90. — Prepare a strong aqueous solution of nitrate of lead, or 
 better, of acetate of lead (sugar of lead). Wet strips of white paper 
 8 to 4 cm. wide with this solution, and dry them in air which is free 
 from sulphuretted hydrogen. This lead-paper, as it is called, should be 
 kept for use in tightly stoppered bottles. 
 
172 DBCOMPosrnoN op sttiphtdkic acid. 
 
 Moisten a bit of the lead-paper with water and expose it to some 
 source of sulphuretted hydrogen — ^the mouth of the bottle of aulphy- 
 dric acid prepared in Exp. 86, for example, or to the fetid air of a sewer. 
 The paper will immediately be blackened from formation of sulphide 
 of lead. 
 
 The blackening of silver-ware, of watches, and cards which 
 have been glazed with a preparation of lead, at many mineral 
 springs, and other localities where sulphuretted hydrogen is 
 evolved, is, in. like manner, indicative of the presence of this 
 gas. Tests like these, which are continuous and cumulative, are, 
 of course, much more delicate means of detection than the mere 
 odor of the gas. 
 
 212. Sulphydric acid is a compound which is very easily 
 decomposed. When simply heated, it breaks up into its 
 components; and it is readily destroyed by various chemical 
 agents. 
 
 Uxp. 91. — To a gas-bottle such as was employed in Exp. 86, con- 
 taining sulphide of iron, attach a chloride-of-calcium tube (Appendix, 
 § 15) and a piece of hard glass tubing, No. 4, about 20 cm. long. To 
 the end of this glass tube, attach another tube bent at right angles and 
 dipping into a bottle of water. Pour chlorhydric acid into the gas- 
 bottle, so that sulphydric acid shall be freely generated, as seen by the 
 flow of bubbles through the final bottle of water. After the lapse of 
 some minutes, when the apparatus has become completely filled with 
 the gas and the last portions of air have been expelled, heat the middle 
 of the tube of hard glass with the flame of the gas-lamp, and observe 
 the ring of sulphur which will collect upon the walls of the cold portion 
 of the tube a short distance in front of the flame. 
 
 It will be seen in subsequent chapters that several other of the 
 gaseous compounds of hydrogen are decomposed, like sulphydric acid, 
 upon being passed through hot tubes. 
 
 The influence of oxygen, in decomposing the aqueous solution 
 of sulphydric acid, has been already alluded to, § 209 ; it has 
 been observed, moreover, that air contaminated with sulphydric 
 acid soon becomes odorless of itself, oxygen uniting with hydro- 
 gen, as before, and sulphur being set free. AU the oxidizing 
 agents (that is, substances which readily give up oxygen) decom- 
 pose sulphydric acid, water being formed and sulphur deposited. 
 
 £scp. 92. — Into a test-tube containing 4 or 5 c. c. of sulphuretted 
 
PERStTLPHIDE OF HTDBOGEN. 173 
 
 hydrogen-water (Exp. 86), pour half as much concentrated nitric acid. 
 Sulphur will be deposited and nitrous fumes evolved. 
 
 Very dilute nitric acid will not thus decompose sulphydric acid. 
 
 Chlorine, bromine, and iodine vapor instantly decompose sul- 
 phydric acid, uniting with its hydrogen to form chlorhydric, 
 bromhydric, or iodohydrio acid, while sulphur is precipitated. 
 
 H,S -I- 2Ca = 2HC1 -I- S. 
 
 JEep. 93. — In place of the nitric acid of the preceding experiment, 
 pour a few drops of chlorine-water into the solution of sulphydric acid, 
 and observe that the odor of the latter is destroyed. 
 
 213. Persulphide of Hydrogen (H^S^ ?). — This is an exceed- 
 ingly unstable liquid, the composition of which is not accurately 
 laiown,though it is supposed to be analogous to that of theperoxide 
 of hydrogen. It can be prepared by adding a solution of per- 
 sulphide of calcium to diluted chlorhydric acid. The reaction 
 may be conceived to take place in accordance with the following 
 equation : — 
 
 CaS, + 2HC1 = CaCl, -|- H,S, + 3S. 
 
 Exp. 94. Mix 75 or 100 grms. of flowers of sulphur and an equal weight 
 of slaked lime with half a litre of water, place the mixture in a flask 
 and heat it to boiling, taking care to agitate the flask so that the solid 
 matter may not become impacted upon it. Continue to boU for about 
 an hour, then filter off the liquor from the undissolved portions of 
 sulphur and lime. The solution thus obtained is a mixture of several 
 sulphides of calcium, more highly sulphittetted than the protosulphide, 
 but will serve the present purpose as weU as if it were the pure quin- 
 quisulphide. 
 
 Pour the solution of sulphide of calcium into 250 c. c. of a mixture 
 of 2 parts of concentrated chlorhydric acid and 1 part of water. Per- 
 sulphide of hydrogen wiU separate in fine oily drops, producing a milky 
 turbidity in the liquid. These drops soon coalesce and settle out be- 
 neath the water. A good way of collecting the persulphide is to per- 
 form the precipitation in a large glass funnel, provided with a stopper. 
 By carefully opening this stopper, the precipitatpd oil can nearly aU be 
 drawn off without disturbing the water which floats above it. 
 
 Persulphide of hydrogen emits a pecuUar, disagreeable odor, 
 and is very irritating to the eyes and mucous membrane. It 
 tastes sweet and bitter, but disorganizes the flesh wherever it 
 
174 NOMBNOLiTUEE PEEFIXES. 
 
 touctee it. Its properties closely resemble those of peroxide of 
 hydrogen ; it is very unstable, and is decomposed by the same 
 substances which destroy the oxide. It even decomposes spon- 
 taneously when left at rest for a few days ; ordinary vegetable 
 colors are quickly bleached by it ; it decolorizes also solutions of 
 indigo. 
 
 214. In the last section we have used, for the first time, cer- 
 tain technical terms which, perhaps, need brief explanation. 
 As has been stated in § 76, many of the elements are capable of 
 uniting with other elements in several different proportions to 
 form chemical compounds. Sulphur, for example, is specially apt 
 to form more than one compound with a single element. When 
 sulphur unites with a metal, the compound formed is called a 
 sulphicZe, just as a compound of oxygen and a metal is called an 
 oxide, or one of chlorine and a metal a chloride, — ^the termina- 
 tion ide, which always indicates combination, being added to the 
 first syllable of the word sulphur, or oxygen, or chlorine, and the 
 new word ending in ide being then connected with the name of 
 the metal, as in the case of sulphide of copper, Exp. 87. But 
 when, as in the case of calcium, there are several distinct sulphides, 
 it is customary to distinguish one from the other by means of 
 various Latin and Greek prefixes. Thus the compound which 
 contains one atom of sulphur and one atom of calcium is the proto- 
 sulphide, or simply the sulphide of calcium, the prefix proto being 
 derived from the Greek word for first ; the compound which con- 
 tains two atoms of sulphur to one of calcium is the bisulphide of 
 calcium, from the Latin for twice ; and in like manner we have 
 a tersulphide, containing three atoms of sulphur to one of calcium, 
 and a quinquisulphide containing five atoms of sulphur. The 
 compound containing the highest proportion of sulphur is often 
 called the persulphide. A good custom is to designate the com- 
 pounds which contain more sulphur than the protosulpliide by 
 prefixes of Latin origin, and to distinguish those which may con- 
 tain less sulphur thaft the protosulphide by means of Greek pre- 
 fixes ; thus, if there were a compound of two atoms of calcium 
 and one of sulphur (Ca^S) it' would properly be called a di-sulphide 
 of calcium, the prefix being from the Greek Sis. The same pre- 
 fixes are used in an analogous manner in connexion with the 
 
COMPOTITOS OE STJLPHTm AND OXYGEN, 175 
 
 •words oxide, chloride, bromide, iodide, and the similar words 
 ending in ide. 
 
 215. Compounds of Sulphur and Oxygen. — No less than seven 
 different compounds of sulphur and oxygen have been discovered, 
 all of which form acids by union with water. Thus the oxide of 
 sulphur SO3 forms, by union with the elements of water, common 
 sulphuric acid H^SO^ ; the name sulphuric acid being indiscri- 
 minately applied to both bodies, although only that one which 
 contains hydrogen possesses the properties commonly described 
 by the term acid. 
 
 Two of these compounds, viz. sulphurous acid (SOJ, and 
 sulphuric acid (SO3), have long been known, and these are still, 
 comparatively speaking, of most importance, since they are em- 
 ployed upon the large scale in the arts. Subsequently there were 
 found the compounds S^Oj (hyposulphuric acid) and S^O^ (hypo- 
 sulphurous acid) ; and at a still more recent period the compounds 
 
 SsO^S.O^andSA- 
 
 As long as only two compounds of sulphur and oxygen were 
 knovm, they were distinguished as sulphurotts and sulphuric, in 
 accordance with the rule laid down in § 70 ; when the two com- 
 pounds, SjjOj and S^O^, containing respectively less oxygen than 
 sulphuric and sulphurous acids, were discovered, the prefix hypo 
 was resorted to as explained in § 71 ; lastly, for the later-found 
 acid compounds of sulphur and oxygen, the ordinary rules of 
 chemical nomenclature being inadequate, it was necessary to 
 invent a special set of names. They were aU called Thionic acids, 
 from the Greek word for sulphur, and were then distinguished 
 from one another by the prefixes tri, tetra, a,nd penta, in accord- 
 ance with the number of atoms of sulphur in each. Strictly 
 speaking, the compound S^O^, since it contains five atoms of oxy- 
 gen like the thionic acids, should perhaps foUow the new rule and 
 be called dithionic acid, but it is stUl customary to retain the old 
 name hyposulphuric acid. 
 
 The complete list of the names of the compounds of sulphur 
 and oxygen is as follows : — 
 
 Sulphurous acid SOj 
 
 Sulphuric acid SO3 
 
 Hyposulphurous acid SjOj 
 
176 SULPHUKOtJS ACID. 
 
 Hyposulpliuric acid (or Dithionic acid) . . SjOj 
 
 Trithionic acid S3O5 
 
 Tetrathionic acid S^Oj 
 
 Pentathionic acid S5O5 
 
 Of all these compounds, only sulphurous acid can be readily 
 obtained by the direct union of sulphur and oxygen. The others 
 must be prepared by circuitous methods. 
 
 216. Sidphurous Acid (SO^). — This acid is produced when 
 sulphur is burned in the air or in pure oxygen gas. 
 
 £xp. 95. — Light apiece of sulphur in a deflagrating spoon Fig. 44. 
 and suspend the latter in a half-litre bottle full of air. On 
 examining the contents of the bottle, after the sulphur has 
 ceased to bum, there mU be found an irritating, suffocating 
 gas having the peculiar odor which is familiar as that of 
 a burning match. The bottle is now full of sulphurous 
 acid gas, mixed with the nitrogen originally present in the 
 air. 
 
 217. By burning sulphur in oxygen gas, instead of in air, as 
 in the preceding experiment, a much purer product could, of 
 course, be obtained. But the experiment would be chiefly inter- 
 esting in enabling us to determine synthetically the composition 
 of sulphurous acid. 
 
 If sulphur be bmned in a confined volume of dry oxygen gas, it will 
 be found, after the combustion has terminated, and the gas has been 
 allowed to regain its original temperature, that the volume of the sul- 
 phurous acid produced is sensibly the same as that of the original oxy- 
 gen, though its weight is twice as great. Hence 1 volume of sul- 
 phurous acid gas contains 1 volume of oxygen. Now, if &om the 
 weight 
 
 Of 1 unit-volume of sulphiu-ous acid, as determined by ex- 
 periment 32-256 
 
 We subtract the weight of 1 unit-volume of oxygen . . . 15-969 
 
 There will remain . . . 16-287 
 or not far from one-half the number, 32, which represents the real 
 specific gravity or equal volume weight of sulphur- vapor. Conse- 
 quently 1 volume of sulphurous acid gas contains half a volume of 
 sulphur-vapor, besides 1 volume of oxyen. Or, multiplying these 
 numbers by 2, in order . to.avoid a fractional volume, it appears that 
 the volumetric Qomposition-jof aulphurous acid is 1 volume of sulphur 
 
PBEPARATION OT STTLPHITBOrrS iCID. 177 
 
 vapor and 2 volumes of oxygen condensed to 2 volumes of tke com- 
 pound gas. Or, expressed in the form of a diagram : — 
 
 '2 + ^ 
 
 
 
 16 
 
 
 16 
 
 8O0 64 
 
 218. An easier mettod of preparing pure sulphiiroTis acid is by- 
 depriving common sulphuric acid of part of its oxygen. This can 
 be' effected by a variety of reducing or deoxidizing agents. For 
 example, when concentrated sulphuric acid is heated with metaHic- 
 copper or mercury, there are formed a sulphate of the metal, water,. . 
 and sulphurous acid : — 
 
 Cu + 2H,S0, = CuSO^ + 2H,0 + SO,. 
 
 Exp. 96. — Into a thin-bottomed glass flask of half a litre capacity, 
 put 14 grms. of copper clippings, or turnings, and 60 grms. of concen- 
 trated sulphuric acid. Attach to the flask a delivery-tube and connect 
 this with a series of Woulfe's bottles, such as were employed in the 
 preparation of chlorhydric acid (Exp. 49) ; heat the flask over the 
 gas-lamp until the acid begins to react upon the copper, then quickly 
 ■withdraw the lamp for a moment, lest the contents' of the flask boil 
 over, and finally regulate the flame so that a steady current of sulphu- 
 rous acid shall pass through the water in the Woulfe bottles. After 
 the first tumultuous evolution of gas has subsided, the flask can be 
 slowly heated without further trouble. The current of gas shoxild be 
 kept up until the water of the first bottle has become saturated, or, at 
 the least, highly charged with the gas. 
 
 Sulphurous acid is freely soluble in water, which, at 15°, takes up 
 something like 44 times its bulk of the gas ; hence the solution obtained 
 as above may be used as a convenient vehicle for sulphurous acid. On 
 account of this easy solubility, the gas cannot be collected over water; 
 but it can be collected over mercury, or by displacement. Since the 
 gas is more than twice as heavy as air, the method by displacement ia 
 to be recommended, if an efficient ventilating flue is at command to 
 carry ofi that portion of the suffocating gas which must escape.. 
 
 Mercury is, in some respects, better than copper for use ia this ex- 
 periment. It affords a much more regular evolution of gas, and the 
 operation requires less care ; but copper is usually employed on account 
 pf its comparatively low cost. 
 
178 PKOPEETIES OF STTLPHUBOTTS ACID. 
 
 Instead of copper or mercury, as in the foregoing experiment, other 
 reducing agents, such as sulphur or charcoal, may be employed. If 1 
 part of powdered sulphur be boiled with 12 parts of strong sulphuric 
 acid, sulphurous acid is set free, as exhibited by the following equa- 
 tion : — 
 
 •S + SH^SO^ = 3SO2 + 2H2O. 
 
 The evolution of gas, in this case, though steady and uniform, is 
 comparativelyslow, as contrasted with that of the experiment in which 
 copper is employed ; hence the process is usually less convenient than 
 that with copper. 
 
 If bits of charcoal or dry sawdust are heated with sulphuric acid, a 
 copious evolution of sulphurous acid occurs, though the gas is not, in 
 this case, pure, being mixed with half a volume of carbonic acid. 
 C + 2H2SO4 = 2SO2 + CO2 + 2H2O. 
 
 For many purposes, as in the preparation of the aqueous solution of 
 sulphurous acid, this method with charcoal is to be preferred, on the 
 ground of economy and convenience of application. In the laboratory 
 it is perhaps more frequently employed than either of the others. 
 
 Sulphurous acid may also be readily prepared by heating in an ig- 
 nition-tube a mixture of 4 parts of sulphur and 5J parts of black oxide 
 of imanganese, both in fine powder, and intimately mixed. A mixture 
 of 3 parts of black oxide of copper with 1 part of sulphur answers the 
 same purpose : — 
 
 2S + MnOj = SO2 + MnS. 
 3S + 2CuO = SO2 -I- 2CuS. 
 
 In both these cases, metallic sulphides are left as a residuum in the 
 ignition-tube; but if the sulphur and black oxide of manganese be mixed 
 in the proportion of 1 part sulphur to 65 parts of the oxide, no sulphide, 
 but only protoxide, of manganese will be formed. 
 
 S -f- 2Mn02 = SO2 + 2MnO. 
 
 219. As has been already stated, sulpliurous acid gas is trans- 
 parent and colorless. It is irrespirable and suffocating, and when 
 mixed with air, even in small proportion, occasions violent cough- 
 ing. It is not inflammable, but, on the contrary, it stops com- 
 bustion. 
 
 The flame of a taper is immediately extinguished on being immersed 
 in sulphurous acid gas, just as it is by nitrogen. A useful application 
 of this property of the gas is in extinguishing burning chimneys. A 
 handful of fragments of sulphur being thrown upon the hot coals in 
 the grate, and the openings of the fire-place being closed in such a 
 
StJIPHTJROITS ACLD SIOPS COMBTTSTION. 179 
 
 manner that no air shall enter the chimney, excepting that which passes 
 through the fire, the chimney will quickly become filled with an atmo- 
 sphere of sulphurous acid mixed with nitrogen from the air employed 
 in burning the sulphur, and the burning soot upon the walls of the 
 chimney will be immediately extinguished. 
 
 It is, of course, essential that the chimney should then be closed at 
 the top, so that air may be excluded and the chimney kept full of the 
 fire-extinguishing atmosphere until its waUs shall have cooled to below 
 the kindling temperatm-e of the soot. 
 
 The oxygen contained in the sulphurous acid gas is so firmly 
 held that combustibles are powerless to take it away under ordi- 
 nary circumstances, though at high temperatures this oxygen can 
 be removed by means of hydrogen, carbon, and easily oxidizable 
 metals like potassium. 
 
 When hydrogen and sulphurous acid gas are passed together 
 through a red-hot tube, water is formed and sulphur deposited, 
 4H -I- SO, = 2Kfi + S, 
 
 and when sulphurous acid is passed through a tube containing 
 ignited charcoal, carbonic acid is produced and sulphur deposited, 
 as before. 
 
 C -t- SO, = CO, + S. 
 
 In case nascent hydrogen, come in contact with sulphurous acid, 
 it wiU decompose it at the ordinary temperature, though in a 
 manner somewhat different from the foregoing. The sulphur, as 
 weU as the oxygen, will, in this case, combine with hydrogen, 
 and there wiU be formed sulphydric acid as well as water. 
 6H + SO, = 2H,0 + H,S. 
 
 This reaction may be made visible by putting a few drops of a solu- 
 tion of sulphurous acid (Exp. 96) into a gas-bottle from which hydro- 
 gen is being evolved (Exp. 19), and testing the hydrogen with a strip 
 of moistened lead-paper (Exp. 90) l)oth before and after the addition 
 of the sulphurous acid. 
 
 220. Sulphiirous acid can readily be condensed to the liquid 
 state. It is, in fact, one of the most easUy liqueflable of the 
 gases. By mere cooling to —10°, under the ordinary pressure 
 of the air, it is converted into a colorless, transparent, limpid 
 liquid. 
 
 In preparing small quantities of the liquid, it is suificient to lead the 
 
 N 2 
 
180 
 
 LiaXJID SULPHTJKOtrS ACID. 
 
 gas, prepared from copper and svQphiiric acid, and dried by passing it 
 through sulphuric acid or over chloride of calcium, into a U-tube which 
 is immersed in a freezing mixture of ice and salt (2 parts of pounded 
 ice and 1 part salt). 
 
 Liquid sulphurous acid is a rather heavy liquid, of 1-49 11 
 specific gravity, boiling at about — 10° and solidifying at —76°, 
 to a colorless crystalline soUd. On being exposed to the air at 
 ordinary temperatures, the liquid acid evaporates with great 
 rapidity, and consequently occasions very intense cold. By 
 means of it, mercury may be frozen, and chlorine and ammonia- 
 gas liquefied. 
 
 If a quantity of the liquid acid be poured into ■water, the tempera- 
 ture of which is a few degrees above 0°, a portion of the acid will eva- 
 porate at once, another portion will dissolve in the water, and a third 
 portion of the heavy oUy liquid will sink to the bottom of the vessel. 
 If the portion, which has thus subsided, be stirred with a glass rod, it 
 will boU at once, and the temperature of the water will be so much 
 reduced that a portion, or even the whole, of the water will be frozen. 
 
 221. The specific gravity of the gas, as determined by different 
 observers, is 32-256, or 32-443, or 32-S58, instead of 32, as would 
 be indicated by theory. This variation is explained by the fact 
 that sulphurous acid, like all the easily eondensible gases, ceases 
 to conform exactly to the law of Mariotte at temperatures near 
 to its point of condensation. Under any given pressure, its 
 volume decreases in somewhat larger proportion than is the case 
 with air and the other permanent gases. 
 
 An important property of sulphurous acid is its power of 
 bleaching vegetable colors. It is extensively employed in bleach- 
 ing articles of straw, wool, silt, &c., which would be injured by 
 chlorine. 
 
 £xp. 97. — Into a bottle in which sulphur has been burned (Exp. 95) 
 pour a few teaspoonfuls of a solution of blue litmus, and shake the 
 loottle. The litmus solution will first become red, as it would if any 
 other acid than sulphvu-ous were present, and will then be decolorized. 
 
 The same property may be illustrated by holding a red rose in the 
 fumes of burning sulphur, or by immersing the rose in an aqueous solu- 
 tion of sulphurous acid (Exp. 96), and leaving it for a few minutes 
 until it has become white. 
 
 In the same way the stains of fruit or wine can be removed from 
 
StJXPHUEOTJS ACID BLEACHES. 181 
 
 clothing. A bit of sulpkui is burned beneath a small open cone of 
 paper, which serves as a chimney, and the stain, having first been 
 slightly moistened with water, is held in the fumes at the top of this 
 chimney. The cloth should finally be carefully washed with water at 
 the place where it has been exposed to the sulphurous acid. 
 
 In the arts, the process of bleaching is usually conducted in large 
 chambers, in which the slightly moistened articles are hung while 
 sulphur is burned below. The damp goods absorb the sulphurous acid 
 and gradually become white. The presence of water is essential; 
 perfectly dry sulphurous acid will not bleach. 
 
 222. The manner in which sulphuroiis acid acts as a bleach- 
 ing agent is not clear. It is remarkable that, as a general rule, 
 it does not actually destroy the coloring-matter ; and that upon 
 many coloring-matters it has little or no action. Most of the 
 yellows, and the green coloring-matter of leaves, are in this latter 
 category, and upon litmus, cochineal, and logwood, the acid does 
 not act very readily. In the few instances where it really de- 
 stroys the color, as in the case of the garden amaranthus, it 
 appears to act as a deoxidizing agent. But in most cases it 
 appears to enter into combination with the coloring-matters and 
 to form colorless compounds. These colorless compounds of sul- 
 phurotis acid and coloring-matter can be broken up, with restora- 
 tion of color, by exposing them to the action of various chemical 
 agents capable of expelling sulphurous acid. 
 
 Exp. 98. — Bleach a rose, as in Exp. 97, and immerse it in dilute 
 sulphuric acid. Then dry and warm it, so that the volatile sulphurous 
 acid may be driven ofi: The color of the rose will again appear. 
 
 In many cases a solution of caustic soda will restore the color as weU 
 as sulphuric acid. A practical illustration of this action of alkaline 
 solutions is seen in the reproduction of the original yellow color of the 
 wool when new flannel is washed with an aLbdine soap. 
 
 Sulphurous acid is a powerful disinfecting and antiseptic agent. 
 It retards, to a remeirkable extent, the processes of putrefaction 
 and fermentation, and is largely employed for this purpose in 
 wine-making ; hops and compressed vegetables are charged with 
 it to the same end, and it has been successfully employed for 
 preserving meat. It has often been employed in medicine, in 
 the treatment of skin diseases, as a fumigation. 
 
 223. Although sulphur will not take up more than two atoms 
 
182 OXIDAIIOW or STJIPHTTKOUS ACID. 
 
 of oxygen when burned in the air, or in oxygen gas, it is never- 
 theless a matter of no very great difficulty to cause it to take up 
 a third atom. 
 
 In presence of water it gradually absorbs oxygen from the air, 
 and is converted into sulphuric acid. Hence the aqueous solu- 
 tion of sulphurous acid (Exp. 96) cannot be preserved for any 
 great length of time, unless it be kept in very tight vessels. 
 
 224. If a mixture of sulphurous acid gas and oxygen, or air, 
 be brought in contact with hot platinum sponge, the sulphurous 
 acid wUl unite with oxygen, and sulphuric acid wUl be formed ; 
 the same union occurs when the mixed gases are brought in con- 
 tact with various other substances, such as pumice-stone, clay, 
 and the oxides of chromium, iron, and copper. Several attempts 
 have been made to put these methods in practice for manufac- 
 turing sulphuric acid, but they have been found to be too slow, 
 and in the case of platinum and clay, it has been observed that 
 these substances soon lose their power and cease to convert the 
 mixed gases into sulphuric acid. 
 
 Sulphurous acid is, indeed, a deoxidizing agent of very con- 
 siderable power ; and is much employed in the laboratory as a 
 reducing agent. It decomposes iodic acid with separation of 
 iodine, and nitric acid with evolution of h3rponitric acid, sulphuric 
 acid being formed in both eases. 
 
 1,0, + 5H,0 + 5S0, = 5(H,0,S03) + 21. 
 H,0,N,0. + SO, = H,0,S03 + 2N0,. 
 
 Exp. 99. — Charge a dry bottle, of the capacity of a litre pig. 45. 
 or more, with sulphurous acid gas, by burning in it a bit of 
 sulphur, as shown in Fig. 45. Fasten a shaving, or, better, 
 a tuft of gun-cotton, upon a glass rod or tube bent at one 
 end in the form of a hook ; wet the shaving in concentrated 
 nitric acid, and hang it in the bottle of sulphurous acid. 
 Red fiunes of hyponitric acid will immediately form about 
 the nitric acid, and will gradually fiU the bottle. 
 
 In presence of a mixture of water and chlorine, sulphurous 
 acid takes up an atom of oxygen from the water, while the 
 hydrogen of the water unites with chlorine. 
 
 SO, + 2H,0 -|-'2C1 = H,0,S03 + 2HC1. 
 A similar reaction occurs between iodine and sulphurous acid, if 
 
STTIPHITM. 183 
 
 a very large amount of water 'be present; in spite of the fact, 
 already mentioned, § 140, that iodohydric acid is readily decom- 
 posed by concentrated sulphuric acid with liberation of iodine, 
 sulphurous acid, and water. 
 
 225. SulphnroTis acid, though a weak acid, forms numerous 
 well-defined salts by uniting with metallic oxides. These salts, 
 called sulphites, are of two classes, — simple or normal sulphites, 
 such as the sulphite of potassium K^SO, (or, duaHstic, Kfi,m^), 
 and double or acid sulphites, such as the acid sulphite of potas- 
 sium KHSO3 (or, dualistic, ES:0,SOJ. AU these salts are de- 
 composed Tsy strong acids, such as chlorhydric, nitric, or sul- 
 phuric, sulphurous acid being expelled ; but they are not decom- 
 posed by carbonic acid. On the contrary, the salts of carbonic 
 acid are decomposed by sulphurous acid ; and hence it happens 
 that the impure stdphurous acid gas obtained by heating a mix- 
 ture of charcoal and sulphuric acid can be used for preparing the 
 sulphites. If, for example, this gas be conducted into an aqueous 
 solution of carbonate of sodium, there will be obtained a solution 
 of sulphite of sodium, and carbonic acid will be set free. 
 
 226. Besides the solution of sulphurous acid, such as was pre- 
 pared in Exp. 96, there is a definite crystalline compound of 
 water and the acid, which can be obtained by passing a current 
 of sulphurous acid gas into ice-water. This compound is very 
 unstable, and is destroyed at temperatures but little above 0° ; 
 but by collecting it upon a cooled filter and then pressing the 
 crystals repeatedly between folds of cold blotting-paper, it has 
 been found possible to remove most of the mother-liquor which 
 adheres to them at first, and to obtain the compound in a condi- 
 tion of tolerable purity. The composition of the crystals appears 
 to be S0,+ 15H,0. 
 
 227. Sulphuric Acid. — The term sulphuric acid is applied 
 somewhat indiscriminately to three or more distinct substances — 
 namely, to a compound of one atom of sulphur and three atoms 
 of oxygen, SO3, which we shall call anhydrous sulphuric acid, 
 and to certain compounds of sulphur, oxygen, and hydrogen, 
 which have been usually regarded as compounds of the an- 
 hydrous sulphuric acid, just mentioned, and water. Of these 
 hydrates the most important are those of the composition H^SO^ 
 
184 
 
 SUtPEUEIC ACID. 
 
 (dualistic, HjO, SO3) [oil of vitriol], and H^S^O^ (dualistic, 
 HjO,2S03) [Nordhausen or fuming sulphuric acid]. The body, 
 whose formula is H^SO^, is one of the most important of che- 
 mical substances, and is usually the thing meant when sulphuric 
 acid is spoken of. We will therefore proceed to study its pro- 
 perties before touching upon those of the other substances above- 
 mentioned. 
 
 Sulphuric acid is one of the most important products of che- 
 mical manufacture, and is made in enormous quantities. In the 
 same way that the metal iron may be said to be the basis of aU 
 mechanical industries, sulphuric acid lies at the foundaltion of the 
 chemical arts. By means of sulphuric acid, the chemist either 
 directly or indirectly prepares almost everything with which he 
 has commonly to deal. 
 
 Sulphuric acid might be prepared by passing sulphurous acid 
 gas into boiling nitric acid, until aU of the latter had been re- 
 duced, and finally distilling off the last traces of the lower oxides 
 of nitrogen which would be formed. Even if sulphur itself were 
 boiled in concentrated nitric acid, it woidd gradually be oxidized 
 and converted into sulphuric acid. But neither of these pro- 
 cesses would be economical. It can be very cheaply prepared, 
 however, by the action of either of the high oxides of nitrogen, 
 nitrous, hyponitric, or nitric acids, upon sulphurous acid, in pre- 
 sence of air and moisture ; and this method is the one actually 
 followed in the preparation of sulphuric acid on the large scale. 
 A mixture of the gases above mentioned is efi5ected in enormous 
 chambers constructed of sheet lead, a metal upon which cold sul- 
 phuric acid has little or no action. 
 
 228. The essential points of the process are, first, that SO^, 
 when in presence of much moisture, can take oxygen from either 
 N^Oj, NOj, or N^Oj, and reduce them to nitric oxide, NO, while it 
 is itself converted into sulphuric acid, and, secondly, that NO can 
 take oxygen from the air and become NO^. 
 
 In practice, the sulphurous acid is obtained by burning crude 
 sulphur, or more commonly a compound of sulphur and iron, known 
 , as iron-pyrites, FeSj; the gas, together with a large excess of atmo- 
 spheric air, is then conducted into the first of a series of leaden cham- 
 bers into which steam is admitted. Nitrous fumes are supplied either 
 
MANTTFACTTJEE OP SULPHTJEIC ACID. 185 
 
 by aUo-sving nitric acid to fall in fine streams through the incoming 
 current of sulphurous acid and air, or from the decomposition of a 
 mixture of salt, nitrate of sodium, and sulphuric acid, as described in 
 § 105, or by heating a vessel charged with nitrate of sodium and sul- 
 phuric acid, by means of the burning sulphur. 
 
 In conformity with the principles above stated, the sulphurous acid, 
 as soon as it comes in contact with the steam, reacts upon the nitrous 
 fumes ; there is formed nitric oxide gas and hydrated sulphuric acid, 
 which falls to the floor. But, as there is present in the chamber an 
 excess of air, the nitric oxide immediately unites with a portion of the 
 oxygen therein contained, and is converted into hyponitric acid. 
 This hyponitric acid inmiediately reacts upon a new portion of sulphu- 
 rous acid, and the process thus goes on through a whole series of leaden 
 chambers, the very small portion of nitric acid at first taken being suffi- 
 cient to prepare a lai-ge quantity of sulphuric acid. In reality, the 
 oxygen employed in converting the sulphurous into sulphuric acid, all 
 comes from the air, excepting a very little at first ; the nitrous fumes 
 serve only as a conveyer of oxygen. The nitric oxide takes oxygen 
 from the air and transfers it to the sulphurous acid, which, as has been 
 stated in § 223, is, by itself and unaided, incapable of combining with 
 oxygen. It will, of course, be imderstood that, although we trace out 
 these reactions as if they were consecutive, they are really, so far as we 
 know, simultaneous. 
 
 Theoretically, a single portion of hyponitric acid would be sufficient 
 to efiectthe conversion of an unlimited amount of sulphm'ous into sul- 
 phuric acid ; but practically this power is qualified by a variety of cir- 
 cumstances. It is found to be impossible, for example, to mix new 
 portions of air with the mixture of sulphurous acid and nitric oxide 
 for an indefinite period ; for at a certain point these gases become so 
 loaded down with nitrogen derived from the air ah'eady consumed, that 
 they are as good as lost in it. In general the flow of gases is so regu- 
 lated that all the sulphurous acid shall be oxidized, and that nothing 
 but nitric oxide and waste nitrogen shall paas out of the last leaden 
 chamber. 
 
 229. The process of manufacturing sulphuric acid can readily 
 be illustrated upon the small scale. 
 
 A large glass balloon, or receiver, of the capacity of several litres, 
 placed in a vertical position, is closed with a cork pierced with five 
 holes, through four of which are passed small glass tubes. All of these 
 glass tubes reach nearly to the bottom of the balloon, and are bent at 
 aright angle above the cork; one of the tubes is connected at the top 
 with a flask containing copper-turnings and sulphuric acid, for the 
 
186 MANFFACTUKE OP SULPHT7KIC ACID. 
 
 generation of sulphurous acid (see Exp. 96), another with a flask 
 containing copper-turnings and furnished with a thistle- tube, through 
 which nitric acid can he poured, for the generation of nitric oxide (see 
 Exp. 37), and the third with a flask containing water for the evolution 
 of steam ; the fourth tube and the fifth hole are both left open. 
 
 Everything being iu readiness, nitric oxide is generated in the small 
 flask fitted for this purpose ; as the gas passes over into the large bal- 
 loon it unites with oxygen from the air, and red fumes of hyponitric 
 acid are formed. Sulphurous acid is now made to pass into the bal- 
 loon ; this will have no action upon the red fames, so long as there 
 is no water present, but the moment steam is thrown in from the third 
 small flask, a reaction occurs, the hyponitric acid is reduced, and the 
 sulphurous acid oxidized. By means of bellows, air must, from time 
 to time, be blown into the balloon, through the fourth glass tube, the 
 waste nitrogen passing off through the fifth hole in the cork. 
 
 If but little steam be employed in this experiment, a solid compound, 
 formed by the union of nitrous and anhydrous sulphuric acids, is liable 
 to be deposited upon the walls of the balloon ; the appeai-auce of this 
 body always indicates that the supply of steam is insufficient ; it is 
 never formed when the proper proportion of moisture is present. 
 
 230. The sulphuric acid which collects at the bottom of the 
 leaden chambers is necessarily dilute, because of the large amount 
 of water which must be present, in order that the reactions above 
 described may freely occur ; moreover it would not be advan- 
 tageoiis to allow an acid more concentrated than that of specific 
 gravity 1-4 to form in the chambers, since a stronger acid would 
 absorb and retain a considerable quantity of nitric oxide. To 
 make it fit for the purposes for which sulphuric acid is usually 
 employed, the dilute acid of the chambers must be concentrated 
 by expulsion of the water ; to this end, it is run off into shallow 
 leaden pans, and there evaporated until it is of specific gravity 
 1-71 to 1-75. The concentration cannot safely be carried beyond 
 this point in ordinary leaden vessels, since the strong, hot acid 
 begins to attack the metal, and the temperature at which the 
 liquid boils is so high as to approach the melting-point of lead. 
 This acid of 1-72 specific gravity is somewhat extensively em- 
 ployed, for a variety of purposes, at the factories where it has 
 been prepared, but is stiU too dilute for transportation. It is 
 therefore transferred from the leaden pans to large glass retorts 
 set in deep sand baths, or to platinum stills, and there evaporated 
 further, until it is nearly of the composition H SO . 
 
PBOPEKTIES OP STTLPHTJEIO ACID. 187 
 
 231. The acid thus boiled down is the concentrated sulphuric 
 acid, or oil of vitriol, of commerce ; its specific gravity is usually 
 about 1-83, that of the absolutely pure acid being 1-842. Besides 
 this sHght excess of water, it contains also, in solution, a certain 
 quantity of sulphate of lead, and a variety of other impurities. 
 For most purposes, however, it will answer as well as the pare 
 acid. Like the latter, it is a heavy, oily, colorless, and odorless 
 liquid, boUing at about 330°. 
 
 Since a comparatively small amount of heat is absorbed in the con- 
 version of the liquid acid to the condition of gas, its vapor can be very 
 easily condensed ; in distilUng the acid, the receiver need not even be 
 placed in cold water. 
 
 From the same cause, combined with the great weight of the liquid, 
 the acid is liable to boil tumultuoiisly, the act of ebullition being 
 irregular and attended with violent blows or shocks. TUe babbles of 
 vapor formed at the bottom of the retort condense almost as soon as 
 they are formed, and the heavy liquid above suddenly falls back to fiU 
 the vacuum. 
 
 In distilling the concentrated acid, it is therefore best to heat only 
 the upper portions of the liquid in the retort ; this can be effected 
 either by placing the retort upon a wire-grate so perforated that about 
 half the body of the retort can be sunk below the level of the burning 
 charcoal upon the grate, or by placing a layer of ashes, or of some 
 other bad conductor of heat, beneath the very bottom of the retort, 
 then piling sand aroimd the sides of the retort outside of the ashes, 
 and applying heat beneath the iron pan upon which the whole is sup- 
 ported. 
 
 232. The common acid usually freezes at about —34°; but it 
 has been found possible to lower the freezing-point to — 80°, by 
 adding a small quantity of water to the commercial acid. When 
 once frozen, it remains solid until the temperature rises to about 
 the freezing-point of water. Crystals of the pure acid melt at 
 about 10°. At the ordinary temperature, sulphuric acid does not 
 vaporize, but, on the contrary, greedily absorbs water from the 
 air and so increases in bulk. In moist weather, its bulk may 
 increase to the extent of a quarter or more, in the course of a 
 single day, and, by longer exposure, a still larger quantity of water 
 win be taken up ; the acid must always be kept, therefore, in 
 
 ■ tightly stoppered bottles. 
 
188 SULPHITEIC ACm ABSOKBS WATER, 
 
 Hxp. 100.— Into a shallow dish of about 200 c. c. capacity, pour 
 about 75 c. c. of concentrated sulphuric acid ; place this dish of acid 
 upon one pan of a balance, and upon the other pan put enough small 
 shot, or clean, dry sand, to exactly balance the acid. Preserve the ma- 
 terial gf the counterpoise, and place the dish of acid uncovered in the 
 open air; from day to day replace it upon the balance, together with 
 the counterpoise, and note the number of grammes or fractions of a 
 gramme that it has increased in weight. 
 
 If the acid were allowed to stand for a week or two in a damp place, 
 it might become two or three times as heavy as it was at first. From 
 ■ its power of absorbing aqueous vapor, sulphuric acid is often employed 
 for drying gases. (See Appendix, § 15.) 
 
 233. "With liquid water sulphuric acid unites with great energy, 
 much heat being evolved at the mSment of combination ; during 
 the union a certain amount of condensation occurs, the mixture, 
 when cold, 'occupying less space than was previously occupied by 
 the acid and the water. The water and acid may be mixed in 
 all proportions, being mutually soluble one in the other. 
 
 In mixing water and sulphuric acid, the acid should always be 
 poured into the water, in a fine stream, not the water into the acid, — 
 the water being meanwhile stirred. In this way the hea^y acid has 
 an opportunity to mix with the water as it sinks down through it. ■ 
 
 If, by any accident, water were to fall upon sulphuric acid, it would 
 float on top of it, and great heat would be developed at the point of 
 contact of the two liquids; if the quantities of acid and water were 
 large, sudden bursts of steam would be occasioned and serious damage 
 might arise from the scattering about of portions of the acid. 
 
 In mixing water and commercial sulphuric acid as in the following 
 experiment, it will be observed that the solution becomes cloudy, and 
 that a white powder is gradually deposited from it. This precipitate 
 is sulphate of lead, originally derived from the leaden pans in which 
 the acid was concentrated ; it is soluble in concentrated, but insoluble 
 in dilute sulphuric acid, and is consequently thrown down when water 
 is added to the commercial acid. 
 
 Exp. 101. — Place in a beaker glass of about 250 c. c. capacity, 30 
 c. c. of water ; in accordance with the directions above given, pour 
 into the water 120 grms. of concentrated sulphuric acid, and stir the 
 mixture with a narrow test-tube containing a teaspoonful of water. 
 So much heat will be evolved during the union of the water and the 
 acid that the water in the test-tube will boil. 
 
 234. If sulphuric acid be mixed with ice or snow, the latter 
 
MlXnfa 8T7LPHUKIC ACID WIIH WATEK. 189 
 
 will be immediately liquefied. If the proportion of ice in the 
 mixture be smaU, as compared with that of the sulphuric acid, 
 heat wiU be evolved much as is the case with liquid water, though 
 to a leas extent. But when a large proportion of ice is mixed 
 with a comparatively small quantity of the acid, no heat will be 
 perceived, but, on the contrary, intense cold. 
 
 Exp. 102. — Place in a beaker glass of about half a litre capacity 
 120 grms. of snow, or finely pounded ice ; pour upon it 30 grms. of 
 concentrated siJphuxic acid, and stir the mixture with a test-tube con- 
 taining a small quantity of water. The water in the tube will be 
 frozen. 
 
 Eicp. 103. — ^Repeat the foregoing experiment, using 30 grms. of 
 snow or ice and 120 grms. of siilphuric acid. A very considerable 
 evolution of heat will occur, as may be seen more clearly by inmiersing 
 a thermometer in the liquid. 
 
 The result of Exp. 102 seems, at first sight, inconsistent with 
 the general fact that heat is always set free during chemical com- 
 bination ; for though chemical union between the acid and water 
 has evidently occurred, no heat, but cold, is manifested. The 
 anomaly is only a seeming one ; a certain amount of heat is re- 
 quired, in order that the cohesive force, by which the particles of 
 the ice are held together, shall be overcome ; hence the heat which 
 is really produced by the chemical combination is all absorbed, 
 together with much more, taken from the materials and the vessel 
 which contained them, during the liquefaction of the ice. 
 
 235. Besides the indefinite mixture or solution above men- 
 tioned, several crystalline compounds of anhydrous sulphuric acid 
 and the elements of water, of fixed composition and characteristic 
 form, can be prepared. 
 
 If the commercial acid be diluted with water untU its specific 
 gravity is reduced to 1'78, and the liquid be then cooled strongly, 
 a substance of composition H^SO, (dualistic, ''IKfi,^0^ will crys- 
 tallize out in the form of large rhombic prisms. These crystals 
 are of sp. gr. 1'785 ; they melt and solidify at about 8°. 
 
 A second hydrate, of composition 3HjO,S03, can be obtained 
 by evaporating a dUute acid in a vacuum at the temperature of 
 100°, until it ceases to lose weight ; and another of composition 
 'Kp,2^0^, win be described below when we come to speak of 
 fuming sulphuric acid. 
 
190 PROPERTIES OF STJLPHTTRIC ACID. 
 
 236. Sulphuric acid is one of the most powerful acids known. 
 If one drop of it be diluted with a thousand times as much water, 
 it is stUl capable of reddening blue litmus. It expels most of the 
 other acids from their compounds, in the same way that we have 
 seen it expel nitric acid from nitrate of sodium in Exp. 32. At 
 very low temperatures, however, as at —80°, it loses its power of 
 reddening Ktmus, and has no action upon the carbonates, though 
 it acts violently upon these salts at the ordinary temperature. 
 
 It is intensely caustic and corrosive, and quickly chars and 
 destroys most vegetable and animal substances. 
 
 Exp. 104. — ^Into a test-glass pour a tablespoonful of sulphuric acid 
 and immerse in it a splinter of wood. The wood will blacken as if 
 charred by fire, and the acid wiU become dark-colored. Wood is com- 
 posed of carbon, hydrogen, and oxygen; and since sulphuric acid 
 unites with compounds of hydrogen and oxygen, rather than with 
 carbon, a portion of the latter is left free ; some carbonaceous matter 
 is, however, dissolved by the acid and darkens it. The acid of com- 
 merce is often dark-colored, from fragments of straw or other organic 
 matter having accidentally fallen into it. Sulphuric acid which has 
 been colored by organic matter may be rendered colorless by strongly 
 heating it till it becomes fully concentrated. 
 
 The action of the acid upon organic matter is more rapid when moist- 
 ure is present. Thus, if a few drops of oil of vitriol be poured upon 
 dry paper, decomposition will take place only slowly ; but if a little 
 water be added to the acid, heat will be developed by the chemical 
 imion, and the paper will be at once decomposed by the hot acid. 
 
 237. When, heated with charcoal or with any organic matter, 
 sulphuric acid gives up oxygen, as has been shown in Exp. 96, 
 and is itself reduced to sulphurous acid ; by sulphur, also, and 
 by several of the metals, such as copper and mercury, it is re- 
 duced in a similar way. (See Exp. 96.) Towards some metals, 
 such as zinc for example, its behavior is various, according as it 
 is concentrated or dilute. If zinc be treated with cold, dilute 
 sulphuric acid, the zinc simply replaces the hydrogen of the acid, 
 sulphate of zinc is formed, and hydrogen is set free. 
 
 Zn -f H,SO, = ZnSO, -1- 2H. 
 
 But if zinc be heated with concentrated sulphuric acid, a portion 
 of the latter is reduced, as it would be in. presence of copper or 
 
SULPHATES. 191 
 
 mercury, sulphurous acid is evolved, as weU as hydrogen, and 
 these gases, reacting upon each other, produce sulphydric acid and 
 a deposit of sulphur, in accordance with the foUowing formulEe : 
 
 SO, + 6H = H,S + 2Hp. 
 
 SO, + 4H = S + 2H,0, 
 As a general riile, concentrated sulphuric acid acts hut feehly 
 upon the metals in the cold, though, when boiled upon them, it 
 often behaves as an oxidizing agent. 
 
 238. With the oxides of the metals, sulphuric acid imites 
 directly to form the very important salts called sulphates, water 
 being simultaneously eliminated. Oil of vitriol, HjjSO^, may, in 
 fact, be itself regarded as a salt, in the composition of which, hy- 
 drogen fiUs the same place that sodium does in sulphate of 
 sodium, Na^SOj, and it might well be called sulphate of hydro- 
 gen, were it not that usage has assigned to it another name. 
 Besides the normal sulphates, in which all the hydrogen has been 
 replaced by a metal, as above (or, on the duahstic hypothesis, 
 in which aU the water has been replaced by a metallic oxide), 
 there is another class of sulphates, often called hi or acid svl- 
 phates, in which only half of the hydrogen has been thus re- 
 placed ; as an example of these, the student wiU recall the acid 
 sulphate of sodium, NaHSO^, mentioned in § 101. 
 
 Acids, which, like sulphuric acid, contain two replaceable atoms 
 of hydrogen, and are therefore capable of forming two series of 
 salts, are called bibasic, in contradistinction to the monobasic 
 acids, Hke nitric acid, which form but one series of salts. There 
 is but one nitrate of sodium, for example, NaNO^. It is for this 
 reason that many chemists object to the doubled formula for 
 nitric acid H^N^Oj, in spite of its convenience, because this for- 
 mula suggests, what is not true, that one or both of the atoms of 
 hydrogen might be replaced by any metal which, like sodium, 
 potassium, or silver, replaces hydrogen atom for atom. 
 
 239. Fuming Sulphuric Add. — The acid H^SO^, above de- 
 scribed, has been, for nearly a century, the most important of the 
 several varieties of sulphuric acid ; but long previous to the dis- 
 covery of the process of making it in leaden chambers, there 
 was manufactured another variety, now known as fuming sul- 
 phuric acid. 
 
192 FUMINa STTLPHTJRIC ACID. 
 
 This fuming acid, or JSTordhausen acid, as it is often called, 
 from the name of a German town in which large quantities of 
 it were formerly prepared, was at first obtained by distilling in 
 earthen retorts the salt now known as sulphate of iron, formerly 
 called green vitriol. Hence the origin of the name oil of vitriol, 
 which, in England and this country, has come to be applied 
 solely to the common acid H^SO^, though it is still used as a 
 synonyme for the fuming acid by German writers. 
 
 When dry sulphate of iron is exposed to a full red heat, it 
 suffers decomposition ; a considerable quantity of sulphuric acid 
 is given off and can be collected in receivers. The distillate 
 thus obtained, which is a dense fuming liquid of about 1-9 spe- 
 cific gravity, is the acid now in question. Though of far less 
 importance than was formerly the case, considerable quantities of 
 the fuming acid are still prepared for the purpose of dissolving 
 indigo and for other special uses, where an acid stronger than 
 the common acid is needed. It may be regarded as a solution 
 of varying quantities of the anhydrous acid SO, in the common 
 acid HjSOj ; if it be gently heated, all of the anhydrous acid will 
 be expelled, and common sulphuric acid will remain. So, too, if 
 it be exposed to the air, the anhydrous acid wiU be given off, and, 
 coming in contact with the moisture of the air, will combine 
 therewith to form common sulphuric acid, which, falling as a 
 cloud, occasions the appearance of fumes. 
 
 When the fuming acid is cooled to about — 5°, a crystalline 
 compound of composition H^S^O, (dualistic, HjO,2S03) separates 
 out. After having been freed from liquid acid, these crystals 
 melt at 35°- When pure, the fuming acid is colorless ; but the 
 conmiercial article is often brown, from having been in contact 
 with organic matter. It is an excessively corrosive liquid, and 
 destroys most organic matters, even more rapidly than the com- 
 mon acid. On being dropped into water, a noise is emitted as 
 if a red-hot bar of metal had touched the water. 
 
 240. Anhydrous Sulphuric Acid (SO3). — As has been men- 
 tioned in § 224, this substance can be obtained by passing a mix- 
 ture of sulphurous acid gas and oxygen over hot, finely divided, 
 metallic platinum, or over various oxides and other porous sub- 
 stances. 
 
MAKING ANHTDEOTTS StrLPHtTMC ACID. 193 
 
 Exp. 105.— Prepare a small quantity of platinized asbestos as fol- 
 lows : dissolve about 0-25 grm. of metalUo platinum in aqua regia (§ 104), 
 and soak in this solution as much soft, porous asbestos as will form a 
 loose ball of 1'5 cm. diameter ; heat the wet asbestos gently until it 
 has become dry, and then ignite it in the flame of the gas-lamp. The 
 chloride of platinum, which was formed by the solution of the metal, is 
 decomposed by heat, and metallic platinum, in a finely divided condi- 
 tion, is left adhering to the asbestos. 
 
 Select a tube of hard glass, No. 8, about 30 cm. long, and, at a dis- 
 tance of about 10 cm. from one end, bend it to an obtuse angle, so 
 that when the tube is supported upon a ring of the iron stand above 
 the gas-lamp the shorter bent portion can be thrust into the neck of a 
 receiver ; in the centre of the longer portion of the glass tube pack the 
 platinized asbestos loosely; then force into and through the tube a cur- 
 rent of mixed sulphurous acid and oxygen ; at the same time heat over 
 the gas-lamp that portion of the tube which contains the platinized 
 asbestos, and collect the anhydrous sulphuric acid which is formed in a 
 perfectly dry test-tube or U-tube immersed in ice, or, better, in a freez- 
 ing-mixture of ice and salt. In the course of the experiment, lift up 
 the receiver for a moment, pour out from it a little of the vapor of 
 anhydrous sulphuric acid, with which it is flUed, and observe how 
 rapidly the heavy gaa falls through the air, and the cloud which forms 
 as it imites with moisture. 
 
 The mixture of sulphurous acid and oxygen may be made before the 
 experiment in a small gas-holder, or, as well, during the progress of 
 the experiment in a bottle behind the asbestos tube. This bottle, which 
 should be of at least half a litre capacity, is fitted with a cork car- 
 rying three glass tubes, and is connected with the asbestos tube by one 
 of these tubes, which reaches no lower than the cork ; by the other 
 tubes, which pass nearly to the bottom of the bottle, and dip beneath the 
 surface of a layer of common sulphuric acid, which has been placed 
 in it, the bottle is connected with a flask in which sulphurous acid is 
 being generated (Exp. 96), and with a gas-holder containing oxygen. 
 The sulphuric acid in the bottle serves to dry the gases, and the rapidity 
 with which the bubbles of gas pass through the liquid, enables the 
 operator to judge of the proportions in which the gases are being 
 mixed ; the flow of oxygen having been fixed at a moderate rate, once 
 for all, the sulphurous acid will alone need attention. 
 
 The action of the platinum in this experiment is obscure ; it will be 
 treated of under the metal platinum. 
 
 Instead of the platinized asbestos, oxide of iron, oxide of copper, or 
 oxide of chromium, or, better, a mixture of the last two can be heated 
 
194 PROPBEIIES OP ASTHTDEOITS STTIPHTJEIC ACID. 
 
 in the tube through which the mixed gases are passing. These pro- 
 cesses of preparing sulphuric acid are interesting from a scientific point 
 of view, but, as has been already stated (§ 224)^ they do not admit of 
 commercial application. 
 
 Anhydrous sulphuric acid can readily be prepared by heating the 
 Nordhausen acid (see § 239) : — 
 
 20 or 30 grms. of fuming sulphuric acid are poured into a perfectly 
 dry, small glass retort ; the neck of the retort is thrust into a dry, cold 
 receiver, andihe acid is slowly heated until it boils moderately. The 
 vapor of the anhydrous acid wiQ condense and solidify in the receiver. 
 The anhydrous acidmay also be obtained by distilling dry bisulphate 
 of sodium. The bisulphate is prepared by heating a mixture of 3 parts, 
 by weight, of dry sulphate of sodium and 2 parts of common sulphuric 
 acid, until the mixture fuses. All the water of the acid is thus elimi- 
 nated : — 
 
 NaASOj + H20,S03 = Na20,2S03 -1- H^O. 
 The bisulphate of sodium, on being distUled in an eathem retort, will 
 give up one molecule of anhydrous sulphuric acid, and a residue of 
 normal sulphate of sodium will remain in the retort : — 
 Na20,2S03 = Na20,S03 + SO,. 
 241. As thus prepared, anliydroTis sulphuric acid is a glisten- 
 ing white solid mass of silky, crystalline fibres, somewhat resem- 
 bling asbestos ; it is tough and ductile, and can be moulded with 
 the fingers like wax. So long as no water is present, it can be 
 handled without danger ; when perfectly dry, it is not corrosive, 
 nor does it even react upon blue litmus. It unites with water, 
 however, with great avidity, and is converted into common sul- 
 phuric acid. It rapidly absorbs water from the air and deli- 
 quesces ; at the same time it forms dense fumes ; for it is volatile, 
 to a very considerable extent, at the ordinary temperature, and 
 its vapor combines with tlie moisture of the air. On being 
 brought in contact with a small quantity of water, it combines 
 with it with explosive violence, and much heat is evolved. If a 
 bit of it be thrown into a large quantity of water, the water 
 hisses as if a hot iron had been thrust into it. Owing to its 
 great tendency to deliquesce, the solid acid can only be preserved 
 in dry tubes sealed at the lamp. 
 
 The specific gravity of anhydrous sulphuric acid is 1-97. It 
 melts readily upon being heated; but it has been noticed that 
 
COMPOSIXIOIf OP ANHTDKOUS STrLPHTTEIC AC33). 195 
 
 some samples melt far more easily than others. There appear 
 to be two distinct varieties of the acid ; for in some cases a tem- 
 perature of 18° is sufficient to render the mass fluid, while in 
 others the heat must he carried even to 100°. The easily fusible 
 modification appears to change gradually, by keeping, into that 
 which is more difficultly fusible; and the latter seems to be 
 changed to the former by distillation. The melted acid boils at 
 about 35°, and evolves a colorless and transparent vapor, three 
 times as heavy as air, which, upon coming iu contact with the 
 air, imites with moisture and forms dense white fumes. When 
 brought in contact with hot lime or baryta (oxide of calcium and 
 oxide of barium), it unites with them directly ; intense heat is 
 evolved, and there is formed sulphate of calcium or sulphate of 
 barium: — 
 
 CaO + SO3 = CaSO, = CaO,SO,. 
 
 242. On being exposed to a strong red heat, the vapor of an- 
 hydrous sulphuric acid splits up into oxygen and sulphurous 
 acid — ^two volumes of it yielding two volumes of sulphurous acid 
 and one volume of oxygen. As has been shown in § 217, two 
 volumes of sulphurous acid gas contain one volume of sulphur 
 vapor and two volumes of oxygen ; hence it follows that the 
 volumetric composition of anhydrous sulphuric acid is one volume 
 of sulphur vapor and three volumes of oxygen, the whole con- 
 densed to two volumes. The specific gravity of sulphur vapor is 
 32, that of oxygen is 16, and the proportions, by weight, in which 
 sulphur and oxygen are united in anhydrous sulphuric acid, are 
 consequently 32 and 16x3=48, the combining weight of sul- 
 phuric acid being 32-1-48 =80. The combining weight of sul- 
 phuric acid can also be readily determined in a manner analogous 
 to that employed in the case of nitric acid (§ 73), by saturating 
 with the common acid a known quantity of oxide of lead, 
 evaporating off the water and excess of acid, and then determining 
 the weight of the dry sulphate of lead which is formed. By 
 subtracting from the latter the weight of the original oxide of 
 lead, we obtain the weight of the sulphuric acid which has com- 
 bined with it. Experiment wiU show that the weight of this 
 sulphuric acid is to that of the oxide of lead in the ratio of 80 
 to 223. 
 
 o2 
 
196 HTPOSULPHXTKOTTS ACID. 
 
 The facility with which sulphuric acid is decomposed at a red 
 heat (§ 242) is the basis of a very economical method of prepa- 
 ring oxygen gas in large quantities for manufacturing-purposes. 
 Commercial sulphuric acid is allowed to drop upon fragments of 
 red-hot porcelain, there to be decomposed, in accordance with 
 the formula 
 
 H,SO, = SO, + + H,0, 
 
 and the products of the decomposition are then washed with 
 water, so that the sulphurous acid may be absorbed, the steam 
 condensed, and the oxygen left free. Here again, as in our 
 earlier experiments (§ 10), the oxygen has really been, obtained 
 from the air ; and if it were desirable, the solution of sulphurous 
 acid obtained in. washing this oxygen, might be placed in the 
 leaden chambers and again be converted into sulphuric acid by 
 the addition of oxygen from the air. 
 
 243. Hyposulphurous Add (S^O,) has never been obtained 
 in the free state, nor is any compound of it with water known ; 
 but there are numerous saline compounds of which it makes 
 part, and some of these are of considerable importance in the 
 iarts. These salts, called hyposulphites, can be prepared in 
 various ways, — for example, by digesting sulphur in a hot (but 
 not boiling) concentrated solution of an alkaline sulphite. If sul- 
 phite of sodium be taken, the reaction can be thus formulated, 
 
 lTa,0,SO, + S = Na,0,S,0,. 
 
 Another method of preparing the hyposulphites is to pass a cur- 
 rent of sulphurous acid gas through the solution of an alkaline 
 sulphide, until no farther precipitation of sulphur occurs : — 
 
 2CaS + 3S0, = 2(CaO,S,0,) + S. 
 
 "When a hyposulphite is treated with a strong acid, decompo- 
 sition immediately ensues; S^O, breaks up into SO^-I-S; hence 
 our inability to isolate the acid. 
 
 Some of the hyposulphites will be more fully described when 
 we come to treat of the metals. 
 
 244. Other Compounds of SidpJiur and Oxygen. — With the 
 exception of hyposulphuric acid, S^O^, none of these compounds 
 (see § 215) have been very thoroughly studied ; any detailed 
 
CHIOEIOBES OF StTLPHnjB. 197 
 
 description of the methods of preparing them would be out of 
 place in an elementary manual. 
 
 245. Compounds of Svlphur and Chlorine. — Chlorine and sul- 
 phur combine -with one another directly and readily, forming 
 several different compounds, whose properties vary in accordance 
 with the varying proportions of chlorine and sulphur which they 
 respectively contain. 
 
 246. Bichloride of Sulphur (SCI) is the best-known of the 
 compounds of chlorine and sulphur, and is often called simply 
 chloride of sulphur. 
 
 It can be prepared by passing a current of dry chlorine through a 
 flask or tubulated retort containing flowers of sulphur. The chlorine 
 is rapidly absorbed by the sulphur, and care must be taken lest the 
 mass become too hot. The reddish-yellow liquid, obtained as the 
 result of the reaction, is a solution of sulphur in dichloride of sulphur ; 
 by distilling it the excess of sulphur can be separated. 
 
 Dichloride of sulphur is a yeUowish-brown liquid of 1'68 
 specific gravity, and boiling, without decomposition, at 144°. 
 It emits a peculiar odor, which has been likened to that of 
 sea-plants ; its vapor excites tears, and its taste is acid, acrid, 
 and bitter. It fumes strongly in the air, being decomposed by 
 the moisture of the air with evolution of chlorhydric acid. It is 
 decomposed by water, but can be mixed with bisulphide of car- 
 bon and with benzine. It is remarkable as a powerful solvent 
 of sulphur ; 100 parts of dichloride of sulphur can take up about 
 70 parts of sulphur at the ordinary temperature ; on slowly cool- 
 ing the hot saturated solution, beautiful crystals of sulphur are 
 deposited. Dichloride of sulphur is used in a process of vulcan- 
 izing caoutchouc, known as the cold process. 
 
 247. Chloride of Sulphur (.SCl^). — This compound is formed 
 when sulphur is treated with an excess of dry chlorine, or when; 
 a current of chlorine is passed into dichloride of sulphur; the 
 dichloride requires some 278 times its own bulk of chlorine gas, 
 and absorbs it very slowly. Chloride of sulphur is a red liquid, 
 of 1-625 specific gravity. 'It exhales suffocating and irritating 
 fumes of chlorine and the dichloride, since it slowly decomposes 
 when kept. The decomposition is particularly rapid in a strong 
 light ; and so much gas is evolved that a tightly-stoppered bottle 
 
198 
 
 SELBNIUlt. 
 
 containing chloride of sulphur -will explode, after a time, if it 
 be placed in sunlight. On being heated, the liquid gives off so 
 much chlorine at 50° that it seems to boil ; but the temperature 
 gradually rises to 64°, which appears to be the real boiling-poiat 
 of the liquid. It is slowly decomposed by water. 
 
 The density of its vapor has been found to be 53 ; admitting 
 that the gas is composed of one volume of sulphur vapor and two 
 volumes of chlorine, condensed to two volumes of vapor, the cal- 
 ctdated specific gravity of its vapor would be 51-5. In view of 
 the instability of the compound, the experimental result is suf- 
 ficiently near coincidence with the calculated number to make it 
 certain that the composition of the gas is reaUy as above stated. 
 
 248. The other compounds of sulphur with chlorine, and with 
 chlorine and oxygen, need not here be discussed ; and the same 
 remark applies to the compounds formed by the union of sulphur 
 with iodine, bromine, fluorine, and nitrogen. The compounds of 
 sulphur with carbon, phosphorus, arsenic, and the metals wiU be 
 treated of hereafter. 
 
 CHAPTEE XIV. 
 
 SELENITTM AND TELLTJBrtTlt. 
 
 249. These elements are rare, and of little or no industrial 
 importance ; but to the chemist they are exceedingly interesting, 
 on account of the close resemblance they bear to sulphur. The 
 three elements, sulphur, selenium, and tellurium, constitute a 
 group which is equally remarkable with that formed by chlorine, 
 bromine, and iodine. (See § 152.) 
 
 250. Selenium, Se, is never found ia any considerable quan- 
 tity in any one place. Traces of it occur in many varieties of 
 native sulphur, and in various metallic sulphides. It is now 
 obtained chiefly from the sulphides of iron, copper, and zinc. 
 These sulphides often contain minute traces of selenium, though 
 the quantity is sometimes so small that it can hardly be detected 
 
PBOPEETLES OP SELENIUM. 199 
 
 by the ordinary methods of analysis. When these sulphides are 
 burned for the purpose of manufacturing sulphuric acid, or in 
 metallurgical operations, the selenium goes off -with the sulphu- 
 rous acid produced by the combustion, and is deposited either in 
 the dust-flues of the furnaces or upon the floors of the leaden 
 chambers at the sulphuric-acid works. In this way the selenium 
 from hundreds of tons of the pyritous ores is collected and con- 
 centrated to a comparatively small bulk. The deposit taken 
 from the leaden chambers of some sulphuric-acid works contains 
 as much as from 2 to 10 per cent, of selenium. The methods of 
 obtaining pure selenium from these deposits are foimded upon 
 the facts that by treatment with nitric acid or aqua regia the 
 selenium can all be oxidized and converted into selenious acid 
 (SeOj), that selenious acid is soluble in water, and that when a 
 solution of it is treated with sulphurous acid, the selenious acid 
 is reduced and pure selenium deposited. 
 
 SeO, -1- 2S0, = 2SO3 -1- Se. 
 
 251. In its properties and in its chemical behavior, selenium 
 resembles sulphur in many respects, while in others it is like 
 tellurium. Like sulphur and oxygen, it occurs in distinct aUo- 
 tropic modifications (§§ 162, 196). The precipitate obtained by 
 mixing solutions of sulphurous and selenious acids is of a deep 
 red color, almost like that of cinnabar. But, after having been 
 fused and suddenly cooled, selenium appears as a brilliant black 
 mass, amorphous, like glass, and of 4-3 specific gravity. When 
 fused selenium has been slowly cooled, it appears as a dark-grey, 
 very brittle, crumbling mass, of crystalline or granular structure 
 and a metallic lustre like that of lead ; the specific gravity of 
 this variety is 4"81. The amorphous or vitreous modification of 
 selenium does not conduct electricity ; but the granular or crystal- 
 line variety conducts it, and the more readily in proportion as it 
 is hotter. The specific heat of selenium, at the ordinary tem- 
 perature, is 0-0746, being the same for both the vitreous modifi- 
 cation and that with metallic lustre. The vitreous variety is 
 soluble in bisulphide of carbon, but the granular variety is in- 
 soluble in that liquid. 
 
 Selenium melts readily upon being heated, and the liquid thus 
 
200 
 
 ISOMOEPHISM. 
 
 obtained boils at about 700°, being converted into a dark yellow 
 vapor, the specific gravity of which has been fovmd to be 82-3. 
 The atomic weight of selenium has been determined to be 79'5. 
 This discrepancy between the vapor-density and the atomic weight 
 is to be ascribed to the imperfection of the experimental deter- 
 minations. Of itself, selenium has neither taste nor odor. When 
 heated in the flame of a lamp, }t burns with a beautiful blue 
 flame and exhales a peculiarly offensive odor, like that of putrid 
 horseradish, — selenious acid, SeO^, being the chief product of the 
 reaction. 
 
 Selenium combines with most of the elements, usually in the 
 same way as sulphur, though not always, since it is a weaker 
 chemical agent than sulphur ; its compounds are as a rule some- 
 what less stable than the corresponding sulphur compounds. 
 With oxygen it forms selenious acid, SeO^, and selenic acid, 
 SeOj, — analogous to sulphurous and sulphuric acids respectively. 
 Besides these, there is a lower oxide, SeO (?) ; it is a colorless 
 gas, having the strong and disagreeable odor like horseradish 
 before mentioned. 
 
 252. Both selenious and selenic acids form numerous salts, 
 which closely resemble the corresponding sulphites and sulphates 
 in composition and in many of their properties. Normal seleniate 
 of potassium, for example, K2SeO_j, cannot be distinguished, by its 
 external appearance, from sulphate of potassium, K^SO^, — the 
 crystalline form of the two bodies, as weU as their texture, color, 
 and lustre, being identical. If solutions of these two salts be 
 mixed, neither of the salts can subsequently be crystallized out 
 by itself when the solution is evaporated ; the crystals obtained 
 win be composed of sulphate of potassium and seleniate of po- 
 tassium mixed in the most varied proportions. Bodies which 
 are thus capable of crystallizing together in all proportions, with- 
 out alteration of the crystalline form, are said to be isomorphous 
 (like-formed). The formulae of the two isomorphous salts, just 
 mentioned, differ only in this — that the one contains the atom 
 Se, where the other contains the atom S. It is therefore pos- 
 sible to replace 32 parts by weight of sulphur by 79-5 parts of 
 selenium, or 79'5 of selenium by 32 of sulphur, without changing 
 the crystalline form of the salts; it foUows that 32 parts by 
 
ATOMIC TOLTTME TELLTTRIirM. 201 
 
 weight of solid sulphur, and 79-5 parts of solid selenium, occupy 
 the same space. That this is actually the case may "be shown 
 by comparing the quotients obtained by dividing the atomic 
 ■weights of the two elements by their specific gravities; these 
 quotients will be found to be equal, or as nearly equal as the 
 limits of error of the physical determinations involved will per- 
 mit. The specific gravity of prismatic sulphur is 1-91, or, iu 
 other words, one cubic centimetre of solid sulphur weighs 1'91 
 gramme ; the specific gravity of crystaULne selenium is 4-81, or 
 one cubic centimetre of selenium weighs 4-81 grammes ; 32 
 grammes of sulphur will, therefore, occupy j^.gj=16-75 cuMc 
 centimetres; 79'5 grammes of selenium wiU occupy j;gj=16'53 
 cubic centimetres. What is true of grammes, is true of any parts 
 by weight, and ultimately of the atoms. This quotient, obtained 
 by dividing the atomic weight of an element by its specific gra- 
 vity, is called the atomic volume of the element ; it must be borne 
 in mind that the standard of specific gravity for liquids and solids 
 is water, for gases hydrogen, and, therefore, that the atomic 
 volume of a solid or liquid must not be directly compared with 
 that of a gas. Two elements whose atomic volume is the same can 
 be exchanged in their compounds without alteration of crystalline 
 form, precisely as a brick or stone taken out of a wall can be 
 replaced by another of the same size and shape without changing 
 the form of the wall. 
 
 253. With chlorine, selenium forms two compounds, Sed and 
 SeClj, the first of which is analogous to dichloride of sulphur. 
 With hydrogen it forms a compound, H^Se, called selenhydric 
 acid, or seleniuretted hydrogen, which is perfectly analogous to 
 sulphuretted hydrogen, H^S, but possesses a still more disagree- 
 able odor. In its action upon solutions of the metallic salts, upon 
 metals and metallic oxides, selenhydric acid behaves like sul- 
 phydric acid, a selenide of the metal being always formed. 
 
 254. Tellurium (Te) occurs in nature even more rarely than 
 selenium. Sometimes it is found in the free state, but more ge- 
 nerally in combination with the heavy metals, such as gold, silver, 
 lead, copper, and bismuth. It is one of the few elements with 
 regard to which chemists have, at times, been in doubt whether 
 
202 
 
 THE StTLPHUB GBOTJP. 
 
 or not they should be classed as metals. Many of its physical 
 properties are similar to those of the metals, and it particularly re- 
 sembles the metal antimony ; but it is so intimately related to sul- 
 phur and selenium in its chemical properties, its crystalline form, 
 and mode of occurrence in nature, that it is now almost always 
 studied as a member of the sulphur group. 
 
 255. Tellurium is of a silver- white color and glittering me- 
 tallic lustre. It is hard and brittle, and crystallizes very easily in 
 rhombohedrons. It is a bad conductor of heat and electricity. 
 Its specific gravity is 6-2 ; its specific heat is 0-04737, and its 
 atomic weight 128. It melts at a temperature somewhat above 
 the melting-point of lead, and is volatile at a full red heat, the 
 vapor being of a yellow colour, like that of selenium. When 
 heated in the air, it takes fire, and bums with a greenish-blue 
 flame, copious fumes of tellurous acid, TeO^, being at the same 
 time evolved. 
 
 256. The compounds of tellurium and oxygen (tellurous acid, 
 TeO^, and telliu:ic acid, TeOj) are analogous to sulphurous and 
 sulphuric acids. By uniting with metallic oxides, they form nu- 
 merous salts, analogous to, and isomorphous with, the correspond- 
 ing compounds of sulphur and selenium. So, too, the hydrogen 
 compound, H^Te, is analogous to sulphuretted and seleniuretted 
 hydrogen, in composition and properties. "With the metals it 
 unites directly to form tellurides. There are chlorine compounds 
 also, TeCl and TeCl^. 
 
 257. The close relationship which subsists between sulphur and 
 oxygen has been already alluded to, as well as the many points 
 of resemblance between sulphur, selenium, and tellurium; the 
 student is therefore now prepared to recognize the fact that in 
 oxygen, stdphur, selenium, and tellurium we have another group 
 or family of elements, as intimately and naturally related to each 
 other as are the members of the chlorine group. (See § 152.) It 
 will be seen at a glance that in passing from oxygen, at one end 
 of the series, to tellurium, at the other, we meet with the same 
 progression of physical and chemical properties that was so 
 noticeable in passing from chlorine to iodine. The properties of 
 the various compounds formed by the union of the members of 
 the sulphur group with other elements exhibit the same kind 
 
COMBINATION BY VOLUME. 203 
 
 of progression ; that these compounds are of analogous composi- 
 tion has been shown in the preceding paragraphs. 
 
 With hydrogen the members of the sulphur group unite in the 
 proportion of two atoms of hydrogen to one atom of the other 
 element; thus, H^O, H^^S, H^Se, H^Te. This peculiar relation 
 to hydrogen is an important characteristic of the group. 
 
 In this sulphur group, precisely as in the chlorine group, the 
 relative chemical power of each element in the family is great 
 in proportion as its atomic weight is low (§ 153) ; oxygen is, as 
 a rule, stronger than sulphur, sulphur than selenium, and selenium 
 than tellurium, their atomic weights being respectively : — 
 = 16, S = 32, Se = 79-5(80?), Te = 128. 
 
 CHAPTEE XY, 
 
 COMBINATION BY VOIUME. 
 
 258. A comparison of the formulae representing the volume- 
 tric composition of aU the well-defined compound gases and vapors 
 which have been thus far studied, wiU bring into clear view some 
 of the general facts relating to combination by volume. 
 
 It has been established, by experiment, that the following com- 
 pounds are formed by the chemical union, without condensation, 
 of equal volumes of the two elements which enter into each com- 
 pound : — 
 
 Hydrogen Chlorine _ Chlorhydric Acid 
 1 vol. 1 vol. — 2 vols. 
 
 Hydrogen Bromine _ Bromhydric Acid 
 1 vol. 1 vol. — 2 vols. 
 
 Hydrogen . Iodine _ lodohydric Acid 
 1 vol. 1 vol. ~ 2 vols. '■ 
 
 Nitrogen , Oxygen _ Nitric Oxide 
 1 vol. + 1 vol. - 2 vols. ' 
 
 Tt has further been demonstrated that the following compounds 
 of two elements contain two volumes of one element and one 
 
 H , CI 
 
 HCl 
 
 1 +85-5- 
 
 36-5 
 
 H ^Br 
 
 1 +80 = 
 
 HBr 
 81. 
 
 H , I _ 
 
 1 +127- 
 
 HI 
 
 128 
 
 N , 
 M + 16 - 
 
 NO 
 
 30 
 
204 COMBINATION BT TOLTDHS. 
 
 volume of the other, but that these three volumes are condensedj 
 during the act of combination, into two volumes : — 
 
 Hydrogen . Oxygen Steam „,. H2 j. _ H2O 
 
 2 vols. + 1 TOl. = 2 vols. ' °^ 2 + 16 - 18 
 
 Hydrogen , Sulphur Sulphydric Acid „, H^ S _ H^S 
 2 vols, + 1vol. = 2\ols. '"' 2+32-84 
 
 Hydrogen , Selenium Selenhydric Acid „„ Hj , Se _ HjSe 
 2 vols. + 1 vol. = 2 vols. ' *"^ 2 +79-5- 81-5 
 
 Hydrogen , Tellurium Tellurhydric Acid „^ Hj , Te _H2Te 
 2vok + 1vol. = 2 vols. '""^ 2 +128- 180 
 
 Chlorine , Oxygen Hypochlorous Acid „^ Clj , O _0l20 
 2 vols. + 1 vol. = 2 vols. >°^ 71 + 16 - 87 
 
 Chlorine Oxygen Hypochloric Acid CI , Oj _ CIO, 
 
 1 vol. + 2 vols. - 2 vols. ' °^ 35-5 "^ 32 - 67 -S 
 
 Nitrogen Oxygen _ Nitrous Oxide Nj , O _ NjO 
 
 2 vols. + 1vol. - 2 vols. '°'^ 28 + 16- 44 
 
 Nitrogen , Oxygen Hyponitric Acid „^ N , Oj _ NOj 
 1 vol. + 2 vols. = 2 vols. '°^ 14 + 32 - 46 
 
 Sulphur Oxygen _ Sulphurous Acid S , Oj _ SOj 
 
 1 vol. + 2 vols: - 2 vols. ' "' 32 + 32 - 64 
 
 Selenium Oxygen _ Selenious Acid Se , O2 _ SeOj 
 
 1 vol. + 2 vols. - 2 vols. ' °^ 79-5+ 32 -111-6 
 
 Tellurium , Oxygen _ Tellurous Acid Te , O2 _ TeOj 
 
 1vol. + 2 vols. - 2 vols. ''"^128+32-160 
 
 Lastly, still a third mode of combination by volume with con- 
 densation of four volumes to two has been thoroughly studied in 
 the case of ammonia, and has been further illustrated in the com- 
 position of anhydrous sulphuric acid : — 
 
 Nitrogen .Hydrogen _ Ammonia N H, _ NH, 
 
 1 vol. + 8 vols. - ,2 vols. ' °'" 14+8 " 17 
 
 Sulphur Oxygen _ Sulphuric Acid S 0, _ SO, 
 
 1 vol. + 8 vols. - 2 vols. >°^ 32 + 48 - 80 
 
 Throughout these tables the unit-volume is, of course, the same 
 for every element and compound. What the absolute bulk of 
 this unit- volume may be, is not an essential point ; for the rela- 
 tions remain the same, whatever the unit of measure. Some 
 chemists have thought that an advantage was gained by using 
 the bulk of one gramme of hydrogen at the ordinary pressure 
 
CONDBNSATION-BATIOS. 205 
 
 and temperature, viz. 11-2 litres, as the unit-volume, whUe others 
 prefer to use the litre itself as the unit. 
 
 Three condensation-ratios are exhibited in these tables. In the 
 first the condensation is ; iu the second it is ^, and in the third 
 it is |. The typical character of the three compounds, chlorhy- 
 dric acid, water, and ammonia, is also clearly brought out ; each 
 of these bodies represents a group of compounds which obey the 
 same structural law. The tables also show very clearly the fact 
 that very unequal weights of the compounds tabulated occupy 
 equal spaces, under the same conditions of temperature and pres- 
 sure. The space occupied by the compound molecule is, in each 
 ease, exactly twice the unit- volume. 
 
 259. The symbols H, CI, 0, and N represent the relative 
 weights of the same volume of four elements which are gaseous 
 at common temperatures and pressures ; the symbols Br, I, S, 
 and Se, represent the relative unit-volume weights of four other 
 elements which are not gases under the ordinary atmospheric 
 conditions, but which can be converted into gases at a higher 
 temperature. At this higher temperature their unit-volume 
 weights have been experimentally determined, and from these 
 observed volume- weights, the unit-volume weights which they 
 would possess at the ordinary pressure and temperature have been 
 deduced. The symbols of these eight elements, therefore, repre- 
 sent at once the combining weights and the relative weights of 
 equal volumes (specific gravities) of these substances in the gaseous 
 state. In the present state of the science, these eight symbols 
 are the only ones of which this can be affirmed ; tellurium would 
 undoubtedly make a ninth, if the relative size of its combining 
 weight had been experimentally determined, but until this deter-> 
 mination has been made, the symbol Te represents only the com- 
 bining weight of the element, and not its equal-volume weight as 
 well. 
 
 The relative sizes of the combining weights of four other ele- 
 ments in the state of vapor, have been experimentally ascertained. 
 These four elements are arsenic, phosphorus, cadmium, and mer- 
 cury. When we come to study these elements, we shall find that 
 the symbols of arsenic and phosphorus, namely. As and P, repre- 
 sent only the half- volume weights of tliese two bodies, while the 
 
206 coMBnmfG weight aitd voLnni-WBiGHT. 
 
 symbols of cadmium and mercury represent the two-volume 
 weights of these volatile metals. Coincidence of the combining 
 weight and the volume-weight has been established for eight 
 elements; discrepancy between the combining weight and the 
 volume-weight has been proved for four elements ; of the re- 
 maining elements, constituting more than four-fifths of the whole 
 number, the equal-volume weights are wholly unknown, inas- 
 much as these elements have never been converted into vapor 
 under conditions which permit the experimental determination of 
 the equal-volume weights of their vapors. Eor example, the 
 symbols Na and K represent the combining weights of these two 
 metals ; but they can be held to represent the weights of the 
 unit- volumes of these metals only by pure assumption, or, at best, 
 on the uncertain evidence of analogies, since the unit-volume 
 weights of these metals, when converted by intense heat into 
 gases, have never yet been determined. As the great majority 
 of the known elements cannot be volatilized, or made gaseous, by 
 the highest temperatures as yet at our command, under conditions 
 which permit the chemist to experiment with the gases produced, 
 it is plain that composition by weight is, in the present state of 
 chemistry, of far greater practical importance than composition by 
 volume. The symbols of all the elements represent their com- 
 bining weights, as determined byponderal analysis ; the symbols 
 of eight elements represent also the equal-volume weights of the 
 substances they stand for. These eight elements, though few in 
 number, are nevertheless the leading elements in inorganic 
 chemistry. 
 
 260. The volume of the molecule of every compound gas in the 
 above tables is twice that occupied by the atom of hydrogen. Two 
 volumes of compound gas invariably result from the chemical 
 combination of one volume of hydrogen with one volume of chlo- 
 rine, of two volumes of hydrogen with one of oxygen, of three 
 volumes of hydrogen with one of nitrogen, and these instances 
 are but types of large classes of chemical reactions. In organic 
 chemistry the same law holds good for a great multitude of com- 
 plicated compounds of carbon; the molecule of every organic 
 compound in the state of vapor occupies a volume twice as large 
 as that occupied by an atom of hydrogen, or, in other words. 
 
BOtTBLE OE PEODTTCT-VOITTME. 207 
 
 twice the unit-volmne. This doubled volume is often called the 
 normal or product-Yolnme of a compound gas. Since the com- 
 biaing weight of a compound gas or vapor occupies two unit- 
 volumes, it is obvious that the weight of one volume, which is the 
 specific gravity of the gas or vapor, is deduced from the combining 
 weight by dividing the latter by two. The specific gravity of a 
 compound gas or vapor is, therefore, one-half its combining weight. 
 261. Molecular condition of elementary gases. — Bearing in mind 
 our definitions of atom and molecule (§§ 38, 39), let us inquire 
 what inferences concerning the molecular condition of simple 
 gases in a free state can be legitimately drawn from our know- 
 ledge of the molecular condition of compound gases. To give 
 definiteness to our conceptions, let us assume the unit-volume of 
 the elements to be one litre ; the product- volume of a compoimd 
 wiU then be two litres. Two litres, the product-volume, of chlor- 
 hydric acid gas are made up of one Utre of hydrogen and one 
 litre of chlorine, united without condensation, and each molecule 
 of chlorhydric acid must contain at least one atom of hydrogen 
 and one of chlorine. In these two litres of chlorhydric acid there 
 must be some definite number of molecules ; the number is, of 
 course, indeterminable; but let us assign to it some numerical 
 value, say 1000, in order to give clearness to our reasoning. One 
 litre of chlorhydric acid wiU then contain 500 molecules, and since 
 equal volumes of all gases, whether simple or compound, are 
 assumed to contain, under like conditions, the same numbers of 
 molecules (§ 39), one litre of hydrogen or of chlorine wUl also 
 contain 500 moleeules. But the one Utre of hydrogen and the one 
 Utre of chlorine, which, by uniting, produced 2 Utres =1000 
 molecules of chlorhydric acid, must each have contained 1000 
 atoms of hydrogen and of chlorine respectively, for each molecule 
 of chlorhydric acid demands an atom of hydrogen and an atom of 
 chlorine. The Utre of hydrogen, or of chlorine, then, contains 
 500 molecules, but 1000 atoms, — each molecule of the simple gas 
 being made up of two atoms of the single element, just as each 
 molecule of the compound gas under review is composed of two 
 atoms, one of hydrogen and one of chlorine. It is clear that this 
 train of reasoning is independent of the particular numerical 
 value assumed as the number of molecules iu two Utrea of chlor-^ 
 
208 
 
 MOLECUIES OP BLBMBNXAET (JASES. 
 
 hydric acid. If, therefor^, the molecule of chlorhydric acid is 
 represented by the formula HCl, and the diagram 
 
 + 
 
 CI 
 
 HCl 
 
 there is good reason to assign to /»•«« hydrogen and free chlorine 
 the formulae HH and ClCl, and to represent the constitution of 
 aU uncomhined gases by such diagrams as 
 
 H + H = 
 
 HH 
 
 CI + CI = ClCl 
 
 Upon these models the molecular formulae of aU the elements 
 with which we have become acquainted might readUy be written. 
 It is only in 2, free state that the elementary gases and vapors are 
 thus conceived to exist as molecules ; when they enter into com- 
 bination, it is by atoms rather than by molecules. An atom of 
 hydrogen unites with an atom of chlorine ; three atoms of hydro- 
 gen combine with one of nitrogen. 
 
 If this view of the molecular structure of free elementary gases 
 and vapors be correct, perfect consistency would require that no 
 equation should ever be written in such a manner as to represent 
 less than two atoms, or one molecule, of an element in a free state 
 as either entering into or issuing from a chemical reaction. Thus 
 instead of H,-|-0=H,0, F4.3H=NH3, HCH-Na=NaCl+H, 
 it would be necessary to write 
 
 2HH + 00 = 2Hp, NN -f- 3HH = 2NH3, 
 
 2HC1 + NaNa = 2NaCl -|- HH. 
 
 We have not heretofore conformed to this theoretical rule, and 
 do not propose to do so in the succeeding pages, and this for two 
 reasons : — first, because many equations, representing chemical re- 
 actions, m-ust be multiplied by two in order to bring them into con- 
 formity vrith this hypothesis concerning molecular structure ; the 
 equations are thus rendered unduly complex ; secondly, because, 
 in undertaking to make chemical equations express the molecular 
 constitution of elements and compounds, as well as the equality 
 of the atomic weights on each side of the sign of equality, there 
 is imminent danger of taMng the student away from the sure 
 
PHOSPHOETTS. 209 
 
 ground of fact and experimental demonstration, into an uncer- 
 tain region of hypotheses based only on definitions and analogies. 
 The symbol Na represents 23 proportional parts by weight of the 
 metal sodium ; of the molecular symbol NaNa, the most that can 
 be said is, that some strong analogies justify us in assuming, for 
 the present, in default of any experimental evidence on the sub- 
 ject, that a molecule of free sodium gas, if we could get at it, 
 would be found to consist of two least combining parts by weight 
 of sodium. "We know as much, at least, of the molecular struc- 
 ture of sodium as we do of four-fifths of the recognized chemical 
 elements. Por the present, the biatomic structure of the mole- 
 cule of a simple gas or vapor in the free state must take place, in 
 an elementary manual, as an ingenious and philosophical hypo- 
 thesis, rather than as a general and indubitable fact. 
 
 CHAP TEE XVI, 
 
 PHOSPHOBTTS, 
 
 262. Phosphorus occurs somewhat abundantly and very widely 
 difiused in nature. It is never found in the free state, but almost 
 always in combination with oxygen and some one of the metals. 
 The most abundant of its compounds is phosphate of calcium ; 
 small quantities of this mineral are found in most rocks and soils, 
 and in several localities it occurs in large beds. Phosphate of 
 calcium is the chief mineral constituent of the bones of animals ; 
 it contains one-fifth of its own weight of phosphorus. The pro- 
 portion of phosphorus present in most of the ordinary rocks, and 
 in the soils which have resulted from their disintegration, is 
 usually very small, and phosphorus would be- an- exceedingly 
 costly substance if we were compelled to collect it directly from 
 this source ; but it so happens that the phosphorus-compounds 
 are important articles of food for plants and animals, and it is 
 easy to obtain through their intervention the phosphorus which 
 was before widely diifused, but has been by them concentrated. 
 
210 
 
 OEDINAET PHOSPHOEtrS. 
 
 Growing plants seek oiit and collect the traces of phosphorus- 
 compounds which exist in the soil ; the herbivorous animals in 
 their turn consume the phosphorus which has been accumulated 
 by the plants, and from the bones of animals chemists and manu- 
 facturers derive the phosphorus of which they stand ia need. 
 
 like oxygen and sulphur, phosphorus occurs in several distinct 
 allotropic modifications. Of these, the best-known are called re- 
 spectively ordinary phosphorus and red phosphorus. 
 
 263. Ordinary phosphorus, when perfectly pure, is a trans- 
 parent, colorless, wax-like solid of 1-8 specific gravity, which, when 
 freshly cut, emits an odor like garlic, though under ordinary con- 
 ditions this odor is overpowered by the odor of ozone, which, as 
 has been previously stated (§ 164), is developed when phosphorus 
 is exposed to the air. It unites with oxygen readily, even at the 
 ordinary temperature of the air, and with great energy at some- 
 what higher temperatures (above 60°) ; when ia contact with air 
 it is all the while undergoing slow combustion. 
 
 Exp. 106. Thoroughly wash a piece of phosphorus by rinsing it in 
 successive large quantities of water ; place it, for a moment, upon a 
 sheet of filter-paper, in order that a portion of the water adhering to 
 it may be removed, then lay it upon a clean porcelain capsule, and at 
 short intervals press against it a slip of blue litmus paper. In a very 
 few moments the color of the paper wiU be changed to red ; for the pro- 
 ducts of the oxidation of phosphorus are acid, and they are formed 
 with great rapidity. 
 
 If the temperature of the slowly burning phosphorus be slightly 
 increased in any way, the mass will burst into flame and be rapidly 
 consumed. On account of this extreme inflammabOity, phosphorus 
 must always be kept under water ; it is best also to cut it Tinder 
 water, lest it become heated to the kindling-point by the warmth 
 of the hand or by friction against the knife. When wanted for 
 use, the phosphorus is taken from the water and dried by gently 
 pressing it between pieces of blotting-paper. 
 
 Phosphorus must always be handled with great caution ; for 
 when once on fire, it is exceedingly difiicult to extinguish it, and, 
 in case it happens to burn upon the flesh, painful wounds are in- 
 flicted, which are exceedingly difficult to heal. Whenever phos- 
 phorus is cut or broken, care must likewise to taken that no small 
 
PEICTION MATCHES. 211 
 
 fragments of it fall unobserved into cracks of the table or floor, 
 wbere they migbt subsequently take fire. 
 
 Exp. 107. — Nip a piece of phospliorus, as large as a small pea^ be- 
 tween two bits of wood, in siicb manner that a part of the phosphorus 
 shall project below the wood ; rub the phosphorus strongly upon a sheet 
 of coarse paper ; it will take fire at the temperature developed by the 
 ftiction. 
 
 264. On account of this easy inflammability by friction, phos- 
 phorus is extensively employed for making matches. The matter 
 upon the end of an ordinary friction match usually contains a 
 little phosphorus, together with some substance capable of sup- 
 plying oxygen, such as red-lead, black oxide of manganese, salt- 
 petre, or chlorate of potassium. The phosphorus and the oxidizing 
 agent are kneaded into a paste made of glue or gum, and the 
 wooden match-sticks, the ends of which have previously been 
 dipped in melted sulphur, are touched to the surface of the phos- 
 phorized paste, so that the sulphured points shall receive a coating 
 of it. The sulphur serves merely as a kindling material which, 
 as it were, passes along the fire from the phosphorus to the wood. 
 By rubbing the dried, coated point of the match against a rough 
 surface, heat enough is developed to bring about chemical action 
 between the phosphorus and the oxygen of the other ingredient, 
 combustion ensues, the sulphur becomes hot enough to take on 
 oxygen from the air, and finally the wood is involved in the play 
 of chemical force. 
 
 £xp. 108. — Put a piece of phosphorus, as big as a grain of wheat, 
 upon a piece of filter-paper, and sprinkle over it some lampblack or 
 powdered bone-black. The phosphorus will melt after a time, and will 
 finally take fire. As wiU be more fully explained hereafter, under 
 carbon, the porous, finely divided lampblack has the power of absorb- 
 ino' and condensing within its pores much oxygen fi^om the air j heat 
 is developed by the act of condensation, and, at the same time, oxygen 
 is brought into very intimate contact with the phosphorus, particularly 
 with the vapor of phosphorus which is condensed by the lampblack 
 together with the oxygen, so that chemical action soon results, and 
 ultimately fire. Both the lampblack and the paper are bad conductors 
 of heat ; they prevent the phosphorus from losing the heat developed 
 by the condensation and by the slow action of oxygen. 
 
 It is remarkable that when dry phosphorus, in very thin slices, is 
 
 p2 
 
212 PHOSPHORESCENCE. 
 
 laid upon fine feathers, wool, lint, flannel, dry wood, or other non-con- 
 ducting substances, it quickly melts, and readily inflames upon the 
 slightest friction, heat enough being produced by the slow combustion 
 of the phosphorus to fuse it, if only this heat can be retained by some 
 bad conductor. 
 
 265. At the ordinary temperature of the air, and stiU more 
 at somewhat higher temperatures, phosphorus shines with a 
 greenish-white light, as may be seen by placing the phosphorus 
 in the dark ; hence the name, phosphorus, from Greek words sig- 
 nifying light-bearing. This phosphorescence is seen when an 
 ordinary friction-match is rubbed against any surface in a dark 
 room. Although the phenomena of phosphorescence and of oxida- 
 tion, or slow combustion, occur simultaneously when phosphorus 
 is exposed to the air, it does not appear that the phosphorescence 
 is a consequence of the oxidation; for phosphorus shines not only 
 in the air, but also when placed in an atmosphere of pure hydro- 
 gen, or nitrogen, or carbonic acid, or even in a vacuum, though 
 the light emitted by phosphorus in these inert gases is of different 
 appearance from that developed in presence of oxygen. 
 
 266. In warm weather phosphorus is soft and somewhat 
 flexible ; it may then be bent without breaking, can be scratched 
 with the naU and cut with a knife like wax ; but at 0° it is brittle, 
 and exhibits a crystalline fracture when broken. It melts at 
 44°, forming a viscid oily liquid, which boils at about 290°, and 
 is converted into colorless vapor. Phosphorus can readily be dis- 
 tilled in a retort filled with some inert gas, like hydrogen, nitro- 
 gen, or carbonic acid. The specific gravity of its vapor has been 
 found to be 62' 1. Contrary to all our previous experience, how- 
 ever, the density of phosphorus is not identical with its atomic 
 weight, a point which will be discussed when the compounds of 
 phosphorus and hydrogen are treated of. 
 
 On being heated to about 230°, out of contact with air, it is 
 converted into red phosphorus. (See Exp. 111.) By exposure 
 to light, also, phosphorus undergoes a certain amount of change ; 
 hence it is rarely seen iu the perfectly colorless, transparent con- 
 dition which it exhibits when recently prepared and perfectly 
 •pure. The phosphorus of commerce is usually of a light amber- 
 color. "Wlieu kept for some time under water, phosphorus be- 
 
SOUTTIONS OF PHOSPHOETJS. 213 
 
 comes covered with a white opaque coating, which appears to be 
 a result of the oxidizing action of air held in solution by the 
 water ; the surface of the phosphorus is irregularly corroded by 
 this dissolved oxygen, and is thus roughened and made opaque, 
 in much the same way that the transparency of glass is destroyed 
 by grinding one of its surfaces. It is noti^d, for that matter, 
 that the water in which phosphorus is kept soon becomes strongly 
 acid ; for it dissolves the oxygenated compounds which are pro- 
 duced by the action of the dissolved air upon the phosphorus. 
 The specific heat of solid phosphorus is 0-1788 ; of liquid phos- 
 phorus, 0-2045. It is a non-conductor of electricity, both in the 
 solid and in the liquid state. 
 
 Phosphorus is insoluble in water, but is somewhat soluble in 
 ether, petroleum, benzine, oil of turpentirie, and other oils ; it 
 dissolves abundantly in bisulphide of carbon, in chloride of sul- 
 phur, and in sulphide of phosphorus. 
 
 -Erp. 109. — Pour into a phial of the capacity of 80 or 90 c. c, 10 
 or 12 c. c. of bisulphide of carbon, and throw into this liquid a bit of 
 phosphorus as large as a pea. Cork the phial, and shake its contents, 
 at intervals, imtil the phosphorus has dissolved. Preserve the solution 
 for use in subsequent experiments. 
 
 267. From the solution in chloride of sulphur and from that in 
 sulphide of phosphorus, crystals of phosphorus, usually in the 
 form either of regular octahedrons or of rhombic dodecahedrons, 
 can be obtained ; but, owing to the slowness with which phos- 
 phorus passes from the liquid to the solid state, distinct crystals 
 cannot readily be prepared by the method of fusion, unless a 
 comparatively large quantity of phosphorus be operated upon. 
 
 268. When a solution of phosphorus in ether, or, better, in 
 bisulphide of carbon, is poured upon the surface of any porous 
 substance and left to evaporate in the air, the volatile solvent wiE 
 quickly escape, leaving the phosphorus behind in a very finely 
 divided condition. In proportion as a substance is more finely 
 divided, the greater wiU be the surface which it presents to the 
 oxygen of the air, and the more readily will it combine with this 
 oxygeA. In the case before us, the comminuted phosphorus ab- 
 sorbs oxygen very rapidly, and this chemical action is attended 
 with the evolution of so much heat that the phosphorus wUl take 
 
214 PHOSPHOBTTS A POISON. 
 
 fire, if the material upon which it has been deposited is a bad 
 conductor of heat. 
 
 Bxp. 110. — Pour some of the solution of phosphorus obtained in 
 Exp. 109, upon a sheet of filter-paper, and hang the paper upon the 
 iron stand in such manner that the bisulphide of carbon may freely 
 evaporate. The paper -will soon burst into flame. It will be noticed 
 that the paper is not completely consumed, but that a very considerable 
 residue of carbon remains unbumed. This depends upon the fact that 
 the product of the combustion of the phosphorus, phosphoric acid, 
 quickly covers the paper with a varnish which is not only incombustible 
 in itself, but is quite impervious to air. . 
 
 In lack of bisulphide of carbon, this experiment can be performed 
 with the ethereal solution of phosphorus, prepared in the manner de- 
 scribed in Exp. 109, excepting that common ether is substituted for 
 the bisulphide, and that the mixture is left to digest for a day or two. 
 
 269. Ordinary phosphorus is a violent poison, a few decigram- 
 mes of it being sufficient to destroy human life. It is the efficient 
 ingredient of many preparations used for poisoning rats, cock- 
 roaches, and other vermin. Phosphorus evaporates rather freely 
 at the ordinary temperature of the air ; and the vapor has been 
 found to be exceedingly injurious to persons constantly exposed 
 to it. The makers of friction matches are subject to a horrible 
 wasting disease, one of the symptoms of which is the destruction 
 of the bones of the jaws. 
 
 270. When phosphorus bums with flame in free air, two atoms 
 of it unite with five atoms of oxygen, and there is formed the 
 compound of P^Oj ; this highest oxide of phosphorus is called 
 phosphoric acid. This compound occurs in bones, and from it 
 phosphorus is prepared. Bone-earth, that portion of bones which 
 remains after aU the organic matter has been burnt off in the 
 fire, consists mainly of triphosphate of calcium, CajP^O^. In 
 order to obtain phosphorus from bone-earth, the calcium and the 
 oxygen must both be removed ; the calcium is removed by means 
 of sulphuric acid, the oxygen by means of hot charcoal. Bones 
 are burnt to a white ash (calcined, as the term is), then finely 
 powdered and mixed with a quantity of dilute sulphuric acid. 
 The sulphuric acid removes two of the atoms of calcium and 
 forms sulphate of calcium, while there remains monophosphate of 
 
MAjrUFACIUEE OP PHOSPHOKUS. 215 
 
 calchim (superphosphate of lime) in accordance with the follow- 
 ing reaction : — 
 
 Ca3p,03 + 2H,S0, = CaH^Pp, + 2CaS0,. 
 
 It will be remembered that one atom of calcium replaces two 
 atoms of hydrogen. (See p. 89.) 
 
 The solution of monophosphate of calcium is then filtered off 
 from the insoluble sulphate of calcium, and evaporated to the 
 consistence of syrup ; the syrup is mixed with powdered charcoal, 
 and the mixture dried at a dull red heat ; by this means a quan- 
 tity of water is expelled from the monophosphate ; — 
 
 CaH,P,0, = CaPp, 4- 2H,0. 
 
 The porous dry mixture is finally placed in retorts of fireclay 
 and intensely ignited. At high temperatures, charcoal is a 
 powerful deoxidizing agent; it takes away oxygen from the 
 phosphate of calcium, and forms carbonic oxide, which goes off 
 as a gas ; phosphorus is thus set free, and distilling over into an 
 appropriate receiver, is condensed under cold water, a quantity 
 of triphosphate of calcium is at the same time reproduced and 
 remains in the retort : — 
 
 3CaP,0, -I- IOC = lOCO -|- 4P -|- Ga^Vfi,. 
 
 If a quantity of sand (sOicio acid) be added to the mixture of 
 charcoal and monophosphate, the whole of the phosphorus can 
 be expelled, — the phosphate of calcium, which would otherwise 
 escape decomposition, being entirely converted into silicate of 
 calcium, 
 
 2CaP,0, -I- 2SiO, 4- IOC = 1000 -1- 4P -|- 2CaSi03. 
 Another proposed method is to pass chlorhydric acid gas over a 
 mixture of bone phosphate and charcoal, maintained at a red 
 heat, in a cylinder of fireclay. By this means all of the phos- 
 phorus is set free and chloride of calcium remains : — 
 
 Ca3P,03 -I- 8C -I- 6HC1 = 3CaCl, -t- SCO + 6H + 2P. 
 The crude phosphorus thus obtained is remelted, and purified by 
 filtration, redistillation, and by chemical treatment with a mixture 
 of bichromate of potassium and sulphuric acid, which oxidizes 
 the principal contaminations. The purified phosphorus is finally 
 
216 
 
 EED PHOSPHOETTS. 
 
 remelted and cast into tte sticks or cakes in which it is found in 
 commerce. 
 
 271. Red Phosphorus. — ^This remarkable allotropic modifica- 
 tion of phosphorus is a body as unlike ordinary phosphorus in 
 most respects as could well be conceived. It is of a scarlet-red 
 color, has neither odor nor taste, is not poisonous so far as is 
 known, is not phosphorescent, does not take fire at ordinary tem- 
 peratures, is insoluble in bisulphide of carbon, and in general 
 behaves altogether differently from the ordinary modification. 
 Yet it is no difficult matter to change one of these modifications 
 into the other. For example, if red phosphorus be heated to 
 about 260°, in an atmosphere of nitrogen, or other inert gas, it 
 wiU pass into the condition of ordinary phosphorus without under- 
 going any alteration of weight, or, in other words, without ab- 
 sorbing or disengaging anything. 
 
 Exp. 111. — In a narrow glass tube, No. 6, about 30 cm. long and 
 closed at one end, place a quantity of red phosphorus as large as a small 
 pea ; heat the phosphorus gently over the gas-lamp, and note that a 
 sublimate of a light-colored substance is quickly deposited upon the 
 cold walls of the tube a short distance above the heated portion. This 
 light-colored sublimate is ordinary phosphorus, as may be shown by 
 cutting off the tube just below the sublimate, after the glass has been 
 allowed to cool, and then scratching the coating with a piece of wire ; 
 the coating wiU take fire. The air in the narrow tube employed is de- 
 prived of its oxygen by the combustion of a small portion of the phos- 
 phorus at the moment of its transformation from the red to the ordinary 
 condition; the remaining phosphorus is thus enveloped in nitrogen and 
 so protected from further loss. 
 
 272. Eed phosphorus is itself neither volatile nor inflammable; 
 it neither rises as vapor nor inflames at temperatures lower than 
 260°, the point at which it changes into ordinary phosphorus ; at 
 250° it suffers no alteration. As compared with ordinary phos- 
 phorus, it may be said that red phosphorus can be handled 
 without danger, and that it may be kept in bottles without 
 special precautions, since it is not liable to take fire by moderate 
 friction ; but by powerful friction heat enough may be evolved to 
 convert it into ordinary phosphorus, and if it be even moderately 
 heated, by friction, or in any other way, in contact with oxidizing 
 agents, it instantly bursts into flame 
 
CSTSTAILIZED RED PHOSPHOKUS. 217 
 
 Exp. 113.— In order to oliserve the comparative difficulty of infla- 
 ming^ red phosphorus, lay an inverted cover of a porcelain crucible upon 
 an iron triangle upon the lamp-stand ; place upon the cover, which may 
 be 15 cm. wide, a small bit of ordinary phosphorus, and, at a distance 
 of 12 cm., the same quantity of red phosphorus ; heat the cover gently 
 and gradually over the gas-lamp. The ordinary phosphorus will soon 
 inflame and bum away ; but a considerable space of time will elapse 
 before the red phosphorus takes fire. 
 
 By operating in vessels filled with nitrogen, or some other gas which 
 has no chemical action upon phosphorus, the precise temperature at 
 which the red phosphorus ceases to exist can be noted, and the ordi- 
 nary phosphorus obtained from it can be distilled over and collected. 
 
 273. Eed phosptorus has been obtained in crystals by dissolving 
 common phosphorus in melted lead, and subjecting the fluid mass 
 to a high temperature for several hours in closed tubes. When the 
 lead cools, the phosphorus separates in thin crystals, which have 
 a metallic lustre and a black color ; the crystals, however, trans- 
 mit a yeUowish-red Ught, and the thinnest of them appear, not 
 black, but red. These crystals of red phosphorus are generally 
 enveloped in the lead ; but the lead may be mostly dissolved away 
 by dilute nitric acid, and the phosphorus crystals may thus be 
 obtained in a condition of comparative purity. They are not 
 affected by exposure to the air. These crystals are seen under 
 the microscope to be rhombohedrons ; so that phosphorus, like the 
 succeeding members of the family of elements to which it belongs, 
 is dimorphous, presenting forms both of the monometric and hexa- 
 gonal systems. 
 
 The red variety of phosphorus has been not inaptly called 
 metallic phosphorus, crystallized in the crystals just described, and 
 amorphous in the usual form of red phosphorus. The crystallized 
 metaMic phosphorus is less volatile, and has a higher specific 
 gravity than the amorphous. The power of the so-caUed metallic 
 phosphorus to conduct electricity is small, if compared with that 
 of the common metals, but it is very much greater than the con- 
 ducting-power of colorless phosphorus, for this latter substance is 
 generally classed with the insulators. 
 
 The specific gravity of amorphous red phosphorus is 2-14 ; its 
 specific heat is 0-1698. "When dry, it undergoes no change at the 
 ordinary temperature of the air; but in moist air it oxidizes very 
 
218 
 
 PKEPAKATION OF KBD PH08PH0ETJS. 
 
 slowly. It is easily soluble in nitric acid, which oxidiaes it ; and 
 since it is much more readily dissolved than ordinary phosphorus, 
 the latter can be purified from any contamination of red phos- 
 phorus, by digesting it at a gentle heat in dilute nitric acid. 
 
 274. Amorphous red phosphorus is prepared by maintaining 
 ordinary phosphorus, for some time, at a temperature of 230° to 
 235°, either under water in an air-tight vessel, or in an atmo- 
 sphere of some gas which has no chemical action upon phosphorus. 
 It is manufactured upon the large scale by heating ordinary 
 phosphorus in a cast-iron vessel provided with a gas delivery-tube 
 dipping into mercury outside the vessel, iu such manner that, while 
 the expanded air and some escaping vapors of phosphorus can 
 pass out, no air can enter the vessel. About 200 kilos, of phos- 
 phorus are taken for a single charge ; this quantity of phosphorus 
 is maintained during ten days or more, as nearly as may be, at 
 the temperature of 240°, care being taken that the heat shall, at 
 no time, much exceed this limit. Under these conditions, the 
 ordinary phosphorus slowly changes into the red variety. After 
 the phosphorus has been exposed during the time which the pre- 
 vious experience of the manufacturer has shown to be most advan- 
 tageous, the apparatus is allowed to become cold, and the trans- 
 muted phosphorus is found adhering to the sides of the vessel, in 
 the shape of a hard, brittle, brick-colored coating, which can be 
 removed by means of hammer and chisel, after covering it with 
 water. It is ground to powder under water, and any particles 
 of ordineiry phosphorus which have escaped change are removed 
 from it by means of bisulphide of carbon, or by a solution of 
 caustic soda, which dissolves ordinary phosphorus without acting 
 upon the red modification. 
 
 275. Eed phosphorus is employed, to a certain extent, as an 
 adjunct to the so-called safety-mutehes. Such matches contain 
 no phosphorus in themselves, and will not take fire readily by 
 friction upon an ordinary rough surface, though they burst into 
 flame at once when rubbed upon a surface specially prepared 
 with red phosphorus. The matter upon the tips of safety-matches 
 is usually a mixture of chlorate of potassium and sulphide of 
 antimony, made into a paste by means of glue ; the surface upon 
 which the match is to be rubbed is composed of red phosphorus. 
 
PHOSPHOKTTS A EBDUCING AGENT. 219 
 
 black oxide of manganese, and glue. In favor of tte use of red 
 phosphorus for matches are the facts, that, unlike ordinary phos- 
 phorus, it is not deleterious to the workmen who have to deal 
 with it, and that it is far less liable to be set on fire by accidental 
 friction. For these reasons, the manufacture of safety-matches 
 has been encouraged by the governments of several European 
 countries, and such matches are now much used in France and 
 upon other parts of the continent, though they are manifestly less 
 convenient, in several respects, than the ordinary matches, which 
 can be ignited by friction upon any rough surface. 
 
 276. Phosphorus combines readily with many other elements 
 besides oxygen. The ordinary modification of phosphorus com- 
 bines violently with sulphur at temperatures near the melting- 
 point of sulphur, the act of combination being attended with vivid 
 combustion and loud explosion. Eed phosphorus, on the other 
 hand, does not combine with sulphur at temperatures lower than 
 230°, and the combustion, though rapid, is not explosive. With 
 chlorine, bromine, and iodine, ordinary phosphorus unites directly 
 at the ordinary temperature of the air, the combination being 
 rapid and attended with inflammation. Eed phosphorus also 
 unites with chlorine, bromine, and iodine at the ordinary tem- 
 perature ; and much heat is evolved during the act of combination, 
 though the amount of heat is usually insufficient to produce 
 ignition. 
 
 Phosphorus unites directly with most of the metals also ; and 
 several of the compounds thus formed closely resemble the so- 
 called alloys, or compounds of one metal with another. With 
 hydrogen it forms several interesting compounds, which will be 
 described directly. From the remarkable facility with which it 
 combines with oxygen (§§ 263, 264), it follows necessarily that 
 phosphorus is a powerful reducing agent. Many oxygen com- 
 pounds can be decomposed by means of it. When immersed in 
 the vapor of anhydrous sulphuric acid, phosphorus takes fire after 
 a time, and combines with the oxygen of the acid, while sulphur 
 is deposited. Monohydrated sulphuric acid is reduced to sul- 
 phurous acid, while phosphorous acid is formed : — 
 
 3H,S0, + 2P = 2H,P03 + 3S0,. 
 
220 PHOSPHOEUS AJTD HTBEOGEIT. 
 
 A solution of sulphurous acid, on being heated with phosphorus, 
 yields phosphorous and sulphydrio acids, as follows : — 
 SO^ + 4H,0 + 2P = 2H3PO3 + H,S. 
 When gently heated with chlorate or with nitrate of potassium, 
 or with other highly oxygenated bodies, like the peroxides of lead 
 and manganese, phosphorus combines with their oxygen so rapidly 
 that an explosion ensaes ; heat enough to bring about the reaction 
 can be developed by gentle friction, as when the phosphorus and 
 the other ingredient axe rubbed together upon some hard surface. 
 (Compare § 264.) 
 
 Exp. lis. — Provide a bit of ordinary phosphorus, as large as a pin's 
 head, also an equal quantity of red phosphorus ; add to each of these 
 portions enough finely powdered chlorate of potassium to cover the 
 phosphorus ; fold up each of the mixtures tightly and separately in a 
 small piece of writing-paper ; place the parcels, one after the other, 
 upon an anvil and strike them sharply with a hammer. They will ex- 
 plode with violence. 
 
 277. Compounds of Phosphorus and of Hydrogen. — There are 
 three compounds of phosphorus and hydrogen, one gaseous, PH3, 
 one liquid, PH^, and one soM, PjH, at ordinary temperatures. 
 The gaseous compound, or, rather, the gaseous compound charged 
 with the vapor of the liquid compound, is somewhat interesting, 
 from the fact that it takes fire spontaneously immediately on 
 coming into contact with the air. 
 
 Exp. 114. — In a thin-bottomed flask of about 140 c. c. capacity, put 
 1 gramme of phosphorus and 115 c. c. of potash-lye of 1'27 specific 
 gravity, obtained by dissolving 40 grms. of hydrate of potassium in 
 110 c. c. of water. Pour two or three drops of ether upon the liquid 
 in the neck of the flask, then close the flask with a cork carrying a long 
 gaa-delivery-tube of glass No. 6. Place the flask over the gas-lamp, 
 upon the wire-gauze ring of the iron stand, and immerse the end of 
 the delivery-tube in the water-pan, then gently heat the flask. The 
 ether is added to the contents of the flask in order that the last traces 
 of air may be expelled from the flask by the vapor which arises from 
 this highly volatile liquid so soon as it is warmed. 
 
 As the potash-lye becomes hot, small bubbles of gas will be seen to 
 arise from the sm-face of the phosphorus, and in a short time large 
 bubbles of gas wiU escape from the delivery-tube ; each of these bub- 
 bles, as it comes in contact with the air at the surface of the water. 
 
PEEPAKATION OF PHOSPHtTEETTED HTDEOGEN. 221 
 
 will spontaneously burst into flame, and burn with a vivid light and 
 the formation of beautiful rings of white smoke, if the air be not dis- 
 turbed by draughts. In burning, the phosphuretted hydrogen is con- 
 verted into phosphoric acid and water, or, rather, into hydrated phos- 
 phoric acid ; and of this product the white smoke is, of course, composed. 
 2PH3 -I- 80 = H^PjOj. 
 Exp. 116. — Place a small inverted bottle fuU of water over the end 
 of the delivery- tube from which the phosphuretted hydrogen is esca- 
 ping, as in Exp. 114, and collect 50 or 100 c. c. of this gas. By single 
 bubbles pass the gas thus collected into a litre bottle half-full of oxygen 
 standing inverted upon a shelf in the water-pan. The phosphuretted 
 hydrogen will burn much more vividly in oxygen than in the air. In 
 case, however, several successive bubbles of the gas should fail to in- 
 flame on coming into contact with the oxygen, the experiment must be 
 interrupted and the oxygen thrown away, for the introduction of an- 
 other bubble of phosphuretted hydrogen into this explosive mixture 
 might set fire to it and so shatter the bottle. 
 
 278. The reaction wMch occurs during the preparation of 
 phosphuretted hydrogen is chiefly between water and phosphorus. 
 Phosphorus and water by themselves do not react upon each other, 
 but wien in presence of powerful bases, like soda, potash, lime, 
 or baryta, water is decomposed by phosphorus with formation both 
 of oxygenated and hydrogenized phosphorus compounds : — 
 3(K^0,H,0) + 8P + 6H,0 = 2PH, + 3(K,0,2Hp,P^0). 
 
 Mypophosphite of 
 Potassium. 
 
 Another method of obtaining phosphuretted hydrogen is by 
 decomposing phosphide of calcium with water. 
 
 Exp. 116. — Prepare a number of small balls or sticks of quick lime 
 by moulding moistened slaked lime into these forms and then drying 
 and calcining the product. Select a tube of hard glass. No. 2, close it 
 at one end, and place two or three pieces of phosphorus as large as 
 peas at the closed end ; fill the tube with the pellets of quick lime, 
 and put it in a sheet-iron trough above a wire-gauze gas-lamp, in the 
 manner depicted in Fig. 8. To prevent the melted phosphorus from 
 flowing against the quick lime, an iron nail may be laid beneath that 
 part of the trough which is farthest from the phosphorus. Heat to 
 redness the portion of the tube which contains the lime, and then cause 
 the vapor of phosphorus to pass over it by cautiously heating the closed 
 end of the tube with an ordinary gas-lamp. To ensure the success of 
 
222 PKOPEETIBS OP PHOSPHtTEETTED HTDEOGEN. 
 
 this experiment, that portion of the tube which contains the phos- 
 phorus must be heated so slowly that none of the phosphorus can 
 escape uncombined through the lime. After the phosphorus has all 
 been driven forward from the closed end of the tube, the open end of 
 the tube should be stopped with a cork and the lamps should be ex- 
 tinguished ; the tube is then left at rest until it has become cold. 
 
 When a piece of the impure phosphide of calcium thus obtained is 
 thrown into water, it slowly decomposes with formation of hypophos- 
 phate of calcium and disengagement of phoaphuretted hydrogen ; the 
 bubbles of gas take fire as they reach the sm-face of the water. 
 
 279. Besides the spontaneously inflammable gas, there is another 
 variety of phosphuretted hydrogen vrhich does not take fire of 
 itself in the air. It can be prepared in various ways — for example, 
 by heating hypophosphorous or phosphorous acids (§§ 286, 287)* 
 these acids being resolved by heat into phosphoric acid and phos- 
 phuretted hydrogen : — 
 
 Hypophosphorous I Empirical: 2H,P02 = PH, + H3PO1. 
 
 Acid. 1 Dualistic : GHfi,2Ffi = 2Plt, + 3H20,P205. 
 
 Phosphorous I Empirical: 4H3PO,, = PH + .3H,P04. 
 
 Acid. ] Dualistic : 4(3H20,P203) = 2PH3-(-3(3H20,P20J. 
 
 The non-inflammable gas is regarded as pure phosphuretted hy- 
 drogen, the property of spontaneously inflaming possessed by the 
 other variety being supposed to depend upon the presence of 
 minute portions of some foreign substance ; the vapor of liquid 
 phosphuretted hydrogen, PH^, produces this efi'ect; on adding 
 to the non-inflammable gas so small a quantity as jAnoth of its 
 bulk of nitric oxide, it acquires the property of inflaming spon- 
 taneously. 
 
 Pure phosphuretted hydrogen gas is colorless and highly in- 
 flammable ; its odor is fetid, and has been compared to that of 
 tainted fish ; it is slightly soluble in water, and can be liquefied, 
 but has not yet been solidified. Neither the gas nor its solutions 
 have any action on red or blue litmus. It is a powerful deoxi- 
 dizing agent, and is, in general, easily decomposed. Most of the 
 metals, when heated in the gas, combine with its phosphorus and 
 liberate its hydrogen, just as we have seen the metal potassium 
 set free hydrogen from ammonia. (See p. 77.) This ready de- 
 composition of the gas by hot metals is the basis of the method of 
 determining its composition by weight. 
 
ANALYSIS or PHOSPHTJEETTED HTTEOGEir. 
 
 223 
 
 280. Phosphuretted hydrogen is resolved into its two elements, 
 and the proportional weights of the elements which enter into 
 its composition are simultaneously determined, by the following 
 process: — The gas is passed through a hard-glass tube (A, 
 Kg. 45), filled with copper tumiugs and heated to redness ; the 
 
 Fig. 45. 
 
 copper retains all the phosphorus, and the hydrogen becomes free. 
 This last gas is carried forward through a second tube, B, filled 
 with oxide of copper heated to redness ; the hydrogen combines 
 with the oxygen of the oxide of copper, and the steam thus 
 formed is condensed and absorbed in a third tube, 0, flUed with 
 pumice-stone soaked in sulphuric acid. (Appendix, § 15.) The 
 tubes A and C are weighed both before and after the experi- 
 ment, and the augmentation of weight gives the phosphorus iu 
 A and the water ia C ; from the weight of the water is calcu- 
 lated the weight of the hydrogen required to produce it. Care 
 must be taken that the tube A be heated so moderately as not 
 to distort it, and that nothing be added to its weight by deposi- 
 tions from the lamp-flames used to heat it. Itis also necessary 
 to fiU the tubes with nitrogen gas before beginniag the actual 
 analysis, and to sweep them out with nitrogen at the end. This 
 operation is easily performed by the aid of a small gas-holder 
 full of nitrogen. It has thus been experimentally proved that 
 any given weight of phosphuretted hydrogen contains 8-57 per 
 cent, of hydrogen and 91'43 per cent, of phosphorus. Now it 
 has been determined, as the result of many experiments and of 
 a careful collation of the formulae of aU known compounds of 
 phosphorus, that the least proportional weight of this element 
 which enters into combination is 31, that of hydrogen being 1. 
 The proportion, gj.43 . g.g^ ^ 3^ . \^^ 
 
224 COMPOSITIOlf 05 PHOSPHUEETTED HYDKOGEN. 
 
 gives as the value of x, 2-905. The nearest whole number is 3 ; 
 and the discrepancy may be attributed to defects of the analy- 
 tical process, always specially to be feared in cases Kke the pre- 
 sent, where the quantity of one ingredient is many times as large 
 as that of the other. A loss of matter, or error in weighing, 
 which would amount to only 1 per cent, of 90 centigrammes, 
 would cause an error of more than 11 per cent, on 8 centi- 
 grammes. The analysis clearly points to the formula PHg as 
 representing the composition of phosphuretted hydrogen, inas- 
 much as for every 31 parts by weight of phosphorus, the gas 
 contains three parts by weight of hydrogen. This result is par- 
 tially corroborated by volumetric analysis. If the hydrogen libe- 
 rated from any measured quantity of phosphuretted hydrogen by 
 passing the gas through a tube flUed with hot metal, be accu- 
 rately measured, it wiU be found that, for every two volumes of 
 the compound gas, three volumes of hydrogen are set free. 
 
 Thus far the composition of phosphuretted hydrogen has 
 seemed to be completely analogous to that of ammonia gas ; but 
 at this point the analogy fails. In ammonia, three parts by 
 weight of hydrogen are combined with fourteen of nitrogen, and 
 three volumes of hydrogen are united with one volume of nitro- 
 gen to form two volumes of the compound gas. If the paral- 
 lelism between NH3 and PII3 were perfect, one volume of 
 phosphorus-vapor ought to be united with the three volumes of 
 hydrogen which two volumes of phosphuretted hydrogen invari- 
 ably contain. The densities of phosphorus- vapor and of phos- 
 phuretted hydrogen, as experimentally determined, prove that 
 this is not the case. The unit-volume being that volume of 
 hydrogen which weighs 1, 
 
 From the weight of 2 unit- volumes of PH3 (sp. gr. = 17'09) . . 34-18 
 Subtract the weight of 3 unit- volumes of hydrogen .... 3-00 
 
 And there remains for the weight of the phosphorus-vapor . . 31-18 
 The specific gravity, or relative weight of one unit-volume of 
 phosphorus-vapor, is 62-1, as has been already mentioned. Two 
 volumes of phosphuretted hydrogen, therefore, contain, not one 
 volume, but only half a volume of phosphorus-vapor. The atom 
 of phosphorus weighing 31, combines with the same quantity of 
 
AMMONIA AND PHOSPHUKETIED HTOEOeEN. 
 
 225 
 
 hydrogen by weight as the atom of nitrogen weighing 14 ; but 
 the vohime of the phosphorus atom is only one-half the volume 
 of the nitrogen atom. The combining weights and the unit- 
 volume weights of all the elements previously studied have been 
 identical; but the combining weight of phosphorus must be 
 doubled in order to bring it into coincidence with its unit-volume 
 weight. The volumetric and the ponderal composition of phos- 
 phuretted hydrogen are both exhibited in the annexed diagram : — 
 
 281. This difference be- 
 tween ammonia and phos- 
 phuretted hydrogen is com- 
 pletely outweighed by the 
 essential likeness in com- 
 position of these two gases 
 and by the other striking 
 analogies which exist be- 
 tween them. When one 
 
 H 
 1 
 
 
 
 
 
 
 
 H 
 1 
 
 
 ■ -1- 
 
 31 / 
 P / = 
 
 PH3 34 
 
 
 
 
 
 H 
 1 
 
 / 
 
 
 or more of the hydrogen atoms in phosphuretted hydrogen are 
 replaced by certain groups of elements, which in organic che- 
 mistry play the part of elements, compounds are obtained which, 
 like ammonia, neutralize acids and are strongly alkaline. Phos- 
 phuretted hydrogen itself combines with certain of the acids in 
 definite proportions. With bromhydric and iodohydric acids, for 
 example, it forms crystalline compounds whose composition is 
 represented by the formulae PH^Br and PH^I,^ — formulae which 
 are evidently comparable with NH^Br and NH^^I. 
 
 282. Liquid Phosphuretted Hydrogen (PH^) "^^7 ^^ obtained 
 by passing the spontaneously inflammable gaseous compound 
 obtained in Exp. 114, through a U-tube surrounded by a mix- 
 ture of ice and salt. Under these conditions, the vapor of the 
 liquid compound, which was diffused in the gas, condenses and 
 separates. Liquid phosphuretted hydrogen is colorless, has a high 
 refraeting-power, and is not misoible with water. It does not 
 solidify at —20°; when heated to 30° or 40° it decomposes. It 
 is exceedingly inflammable, and bursts into flame when brought 
 m contact with the air ; when a small quantity of its vapor is 
 mingled with combustible gases, such as carbonic oxide, hydro- 
 gen, or carburetted hydrogen, these gases acquire the property 
 
226 PHOSPHOETJS AND OXTSEN. 
 
 of inflaming spontaneously. When exposed to sunlight, it is 
 resolved into gaseous and soKd phospturetted hydrogen : — 
 
 5PH, = p,h: + 3PH3. 
 
 283. Solid PJiosphuretted Hydrogen (P^H?) is formed by ex- 
 posing liquid phosphuretted hydrogen to sunshine) or by acting 
 upon the liquid with chlorhydric acid, or by dissolving phosphide 
 of calcium in strong chlorhydric acid. It is a compound in- 
 soluble in vrater or alcohol, but soluble in warm potash-lye with 
 liberation of gaseous phosphuretted hydrogen. It takes fire at 
 about 150°, and is of a yeUow color, but becomes red when 
 exposed to light. 
 
 284. Compovmds of Phosphorus and of Oxygen. — Phosphorus 
 unites with oxygen La four different proportions, as follows : — 
 
 Oxide of Phosphorus, P^O. 
 Hypophosphorous Acid, P^O. 
 Phosphorous Acid, P^Oj. 
 Phosphoric Acid, PjO^. 
 
 AH of these compounds exhibit a more or less distinct acid cha- 
 racter, especially when combined with water, and the one con- 
 taining most oxygen, phosphoric acid, is a very important acid. 
 
 286. Oxide of Phosphorus (P^O). — When ordinary phosphorus 
 is burned in a confined volume of air or oxygen, insufficient for 
 its complete combustion, there will be found mixed with the 
 •unconsumed phosphorus, after the chemical action has ceased, 
 a certain quantity of a red powder, which is the oxide of phos- 
 phorus now in question. 
 
 Exp. 117. — ^Repeat Exp. 13, and examine the red mass which re- 
 mains in the porcelain capsule after it has been sunk in the water-pan 
 and thoroughly cooled. 
 
 Since the red oxide of phosphorus is insoluble in bisulphide of car- 
 bon, it can readily be obtained in a state of purity by dissolving in this 
 liquid the free phosphorus with which it is contaminated. 
 
 Although the red oxide is not spontaneously inflammable by 
 itself, a mixture of it with free phosphorus, such as the residue 
 from the preparation of nitrogen (Exp. Ip), takes fire with great 
 ease, being even more readily inflammable than phosphorus alone. 
 Such residues must be handled with special care. 
 
EED OXIDE OF PHOSPHOKXTS. 227 
 
 Eed oxide of phosphorus can he ohtained in larger quantities 
 hy bringing a stream of oxygen gas into contact with phosphorus 
 melted under hot water. 
 
 Exp. 118. — Place about a cubic centimetre of ordinary phosphorus 
 in the bottom of a conical test-glass, or wine-glass, and pour upon it 
 hot water enough to half fill the glass ; the phosphorus will melt, but 
 cannot bum, since the water protects it &om contact with the air, and 
 sLuce phosphorus by itself is incapable of decomposing water. By 
 means of a narrow gas-dehvery-tube of glass, conduct a slow stream of 
 oxygen from a gas-holder to the bottom of the test-glass, so that the 
 oxygen shall come into immediate contact with and bubble through 
 the melted phosphorus. The phosphorus will bum with a vivid light 
 beneath the water ; red oxide of phosphorus will be formed, and will 
 float about in the water, from which it may be separated by filtration. 
 
 In the lack of oxygen, air may be forced down upon the phosphorus ; 
 even the impure air blown from the mouth will answer ; but with air 
 the reaction is less intense than with oxygen ; hence, when it is em- 
 ployed, the experiment had better be performed in a dark room. 
 
 Oxide of phosphorus has neither taste nor smell. On being 
 heated to 350° to 400°, it splits up into phosphoric acid and free 
 phosphorus, the latter, of course, taking fire in case oxygen be 
 present. 
 
 286. EypophospJiorous Acid {^^'PJd^=2R^Y0^).—Th.is com- 
 pound has usually been classed among the oxides of phosphorus, 
 on the supposition that it might be possible to obtain from it an 
 anhydrous oxide, of the composition P^O ; the oxide in question 
 has, however, never yet been obtained. 
 
 When ordinary phosphorus is boiled in a solution of caustic 
 potash, soda, lime, or baryta, water is decomposed, a compound 
 of phosphorus and hydrogen (§ 278) is formed, and a hypophos- 
 phite of the alkali employed remains in solution, from which it 
 may be separated in crystals by cautious evaporation. If baryta 
 be employed, the reaction may be formulated as follows : — 
 Empirical: SBaHjOj + 8P -|- eH^O = SPH, -\- SBaH^P^O^. 
 Dualistic : SCBaOjHjO) -|- 8P -|- GH^O = 2PH3 -f- Z(B&Ofi,Tlf>,Vfi). 
 By cautiously adding sulphuric acid to the solution of the barium 
 salt, sulphate of barium is precipitated and hypophosphorous acid 
 remains in solution : — 
 
 BaO,2H,0,P,0 + H,0,S03 = 230,80, + ZK,0,Vfi. 
 
 a2 
 
228 
 
 HTPOPHOSJ^HITES. 
 
 By evaporating the aqueous solution, after filtration, hypophos- 
 phorous acid is left as a viscid, uncrystaUizable, acid liquid, which, 
 on being strongly heated, splits up into phosphoric acid and 
 phosphuretted hydrogen. It unites with oxygen readily, and is 
 consequently a powerful reduciag agent. Sulphuric acid, for 
 example, is reduced by it, with evolution of sulphurous acid and 
 separation of sulphur. 
 
 The hypophosphites are, for the most part, orystaUizable salts, 
 soluble in water and often in alcohol also ; they can usually be 
 preserved in dry air. Several of them have recently been some- 
 what extensively employed as medicaments. 
 
 287. Pliosphorous Acid (P^Oj).- — This acid is a product of the 
 slow combustion of phosphorus. 
 
 When phosphorus is gently heated in a very slow current of per- 
 fectly dry air, it takes on oxygen enough to form phosphorous acid, 
 which, being volatile, condenses upon the cold walls of the tube beyond 
 the phosphorus as a bulky white sublimate. By conducting the opera- 
 tion in a tube drawn out to a fine point at one end and almost com- 
 pletely closed at the other by a perforated cork carrying a narrow 
 tube, and carefully regulating the supply of air which is admitted into 
 the tube, so that just enough oxygen to form phosphorous acid, and no 
 more, shall come in contact with the phosphorus, a tolerably pure pro- 
 duct can be obtained. For purposes of illustration, however, a simpler 
 arrangement of the apparatus may be employed, as in the following 
 experiment : — 
 
 Exp. 119. — Place a bit of phosphorus, as big as a pea, in the middle 
 of a piece of glass tubing. No. 2, about 30 cm. long, and open at both 
 extremities ; gently heat the phosphorus until it takes fire, and then 
 extinguish the lamp. So long aa the tube is held in a horizontal 
 position, the combustion will be so feeble and imperfect that some red 
 oxide of phosphorus will be formed as well as phosphorous acid. On 
 the other hand, if one end of the tube be inclined upwards, so that the 
 products of combustion can pass ofi' and make way for the entrance of 
 fresh air, the combustion will become more vivid, and there will be 
 produced a quantity of the highest oxide of phosphorus, phosphoric 
 acid. If the tube were held perpendicularly, the draught of air, pass- 
 ing through it as through a chimney, would be so powerful that all 
 the phosphorus would be burned completely to phosphoric acid. 
 
 It is evident, from the foregoing, that if it were only possible to find 
 out the precise angle at which the tube should be inclined, and, at the 
 
PHOSPHOEOUS ACID. 229 
 
 same time, to provide means for continually maintaining a suitable tem- 
 perature witMn the tube, tbe phosphorus might all be converted into 
 pure phosphorous acid, instead of the various and mixed products 
 which are actually obtained. 
 
 288. Hydrated phosphorous acid, H3PO3, or SKfi,F^O^, is 
 readily obtained, though in an impure condition, by exposing 
 sticks of phosphorus to moist air. 
 
 Sxp. 120.-^Select a piece of glass tubing, the diameter of which is 
 so much greater than that of an ordinary stick of phosphorus, that the 
 latter can readily be slipped into it ; from this tubing prepare three or 
 four short tubes 3 or 4 cm. long, open above and below, but drawn in 
 at the bottom to such an extent that a stick of phosphorus placed in 
 the upper part of the tube cannot pass the narrowed portion and fall 
 out of the tube. In each of these short tubes put a stick of phos- 
 phorus, and place them aH in a glass funnel which rests upon a bottle 
 standing in a soup plate full of water; over the funnel and bottle place 
 a tall tubulated beU-jar, from which the stopper has been removed, 
 and allow the apparatus to stand at rest during several days in a cool 
 place where no damage can be done in case the phosphorus take fire. 
 
 Under these conditions, the phosphorus will slowly oxidize and 
 waste away (if time enough be allowed it will completely disappear), 
 and the mixture of phosphorous and phosphoric acids which is formed 
 will flow down through the tube of the funnel into the bottle beneath. 
 The mixture thus obtained is often technically termei phospliatic add. 
 
 The object of the glass tubes employed to envelope the sticks of 
 phosphorus is, to keep the several pieces of phosphorus from touching- 
 one another. If two or three pieces of phosphorus were to be left in 
 contact, in the air, the heat generated during the oxidation of each 
 would be added to that derived from the others, and after a time the 
 mass would become hot enough to take fire spontaneously. But when 
 each stick of phosphorus is placed within a glass tube, the heat gene- 
 rated by its oxidation passes off harmlessly, and a dangerous accumula- 
 tion of heat is very much less likely to occur than if no such system 
 of isolation were resorted to. 
 
 289. The fact that a collection of fragments of phosphorus is 
 thus liable to take fire, so well illustrates the theory of spon- 
 taneous combustion in general, and the precautionary measures 
 taken in the foregoing experiment to prevent the ignition of the 
 phosphorus point so clearly to the methods which must often be 
 resorted to . in order to prevent the spontaneous inflammation of 
 
230 
 
 SPONTANEOUS COMBUSTION. 
 
 many highly combustible substances, that a few words may here 
 be appropriately devoted to this important practical subject. 
 
 As a rule, aU easUy oxidizable substances, when finely divided 
 and thrown into heaps, are liable to take fire spontaneously in 
 the air. Many oils, for example, particularly the so-called dry- 
 ing oils, absorb oxygen from the air and enter into combination 
 with it. Wherever chemical combination occurs, heat is deve- 
 loped, and in case the oU be poured upon some porous substance 
 which is both combustible and a non-conductor of heat, like wool 
 or cotton, paper or cloth, the heat developed during the oxi- 
 dation of the oil may very readily accumulate to the extent 
 necessary to produce inflammation. To prevent this catastrophe, 
 the heap of greasy wool or other matter should be broken up as 
 soon as warmth is perceived in it, and its particles should be 
 scattered about so that air may have free access to them ; the 
 heat will then pass off harmlessly from each of these particles 
 as fast as it is generated. 
 
 This process of subdivision will prove an effectual protection 
 if the subdivision be carried far enough ; but it is a fact not to 
 be lost sight of, that very small parcels of some substances (a 
 hank of oiled twine, for example, or a handful of greasy rags) 
 may take fire when all the conditions are favourable ; and it ig 
 a matter of the first importance that all such matters should be 
 kept in places where no harm can be done in case they inflame. 
 
 A still more familiar instance of the accumulation of heat 
 during chemical action occurs in the ordinary process of hay- 
 making, as when a cock of half-cured hay is left unopened for 
 any length of time ; the green hay combines with oxygen from 
 the air, fermentation sets in, and heat is, of course, evolved ; but 
 when the hay is scattered about the field, this heat passes off into 
 the air as fast as it is generated, and we cannot perceive it. On 
 the other hand, if, instead of the usual small hay-cocks; the 
 farmer were to throw a large quantity of new-mown hay into 
 one great stack, this stack would undoubtedly take fire if left to 
 itself. 
 
 In large heaps of many kinds of bituminous coal also, strong 
 chemical action is induced under very various conditions as re- 
 gards temperature, moisture, and mechanical subdivision, and 
 
PKOPEKTIBS 01' PHOSPHOKOtrS ACID. 231 
 
 the heat evolved becomes at last intense enough to kindle the 
 coal. Protection from the weather, exclusion of moisture, free 
 ventilation, and the avoiding of too large heaps are the most 
 effectual preventives in this case. 
 
 290. Anhydrous phosphorous acid is a white amorphous sub- 
 stance, which rapidly absorbs water from the air, and when 
 sprinkled with water, dissolves rapidly with a hissing noise ; it is 
 volatile, and may easily be driven from one place to another, in 
 a tube filled with nitrogen (see § 287), by applying a gentle heat. 
 Being a product of the incomplete combustion of phosphorus, it 
 is necessarily combustible ; when heated in the air, it undergoes 
 vivid combustion. 
 
 Hydrated phosphorous acid is obtained in the form of rec- 
 tangular prisms, when the aqueous solution is evaporated at 
 temperatures not exceeding 200°. The crystals are deliquescent, 
 and they gradually absorb oxygen from the air ; when strongly 
 heated, they are decomposed into phosphoric acid, and phosphu- 
 retted hydrogen, and at the same time take fire. The aqueous 
 solution of phosphorous acid exhibits a strong acid reaction ; by 
 absorbing oxygen from the air, it is converted into phosphoric 
 acid, quickly in case the solution is dilute, but slowly if it be 
 concentrated. It is a powerful reducing agent; when heated 
 with sulphurous acid, it yields phosphoric and sulphydric acids. 
 Though a very weak acid, it forms salts by combining with those 
 metallic oxides upon which it exerts no reducing action; the 
 phosphites of the alkalies proper are easily soluble in water, but 
 the phosphites of calcium and barium can only be dissolved with 
 difficulty. These salts are more stable than the hypophosphites, 
 but are all decomposed by heat. 
 
 291. Phosphoric Add (P^Oj). — As has been abeady stated, 
 this highest oxide of phosphorus is the product of the rapid 
 combustion of phosphorus in an excess of air or oxygen. 
 
 Exp. 121. — ^Dry thoroughly a large porcelain plate, a small porce- 
 lain capusle, and a wide-mouthed bottle of two litres capacity, by 
 warming them at a fire ; place the capsule upon the plate and put in 
 the capsule a bit of dry phosphorus of the weight of half a gramme 
 or ttiereabouts; light the phosphorus, and cover it at once with the 
 
232 
 
 PHOSPHOEIC ACID. 
 
 inverted bottle. The phosphoric acid, formed by the combustion of 
 the phosphorus, will be deposited as a white powder, like flakes of 
 snow, upon the sides of the bottle, and much of it will fall down upon 
 the plate below. 
 
 The apparatus employed in this experiment can readily be arranged 
 in such manner that fresh portions of phosphorus and of air can be 
 introduced into the bottle as fast as occasion may require ; the process 
 will then be continuous, and any desired quantity of phosphoric acid 
 may be prepared by means of it. 
 
 The flooculent, amorphous, odorless powder tlms obtained 
 unites with water with remarkable facility ; if it be left in the 
 air for a few minutes, it deliquesces completely ; and upon being 
 thrown into water it dissolves, with a hissing noise and develop- 
 ment of much heat. In order to preserve it, it must be placed 
 in a dry tube, and the tube closed by sealing it in the lamp. 
 When touched to the moist tongue, it burns as if it were red-hot 
 metal. On account of this strong affinity for water, it is fre- 
 quently employed by chemists to withdraw the elements of water 
 from other substances ; anhydrous sulphuric acid, for example, 
 can be prepared from oU of vitriol by heating the latter with 
 anhydrous phosphoric acid. On being heated with various or- 
 ganic substances, such as some of the alcohols and essential oils 
 composed of carbon, hydrogen, and oxygen, it decomposes them 
 in such manner that the oxygen of the organic substance, and as 
 much of its hydrogen as is necessary to form water by uniting 
 with this oxygen, combine with the phosphoric acid, whUe a 
 compound of carbon and hydrogen (technically called a hydro- 
 carbon) is set free. 
 
 After the anhydrous acid has once been dissolved in water, it 
 cannot again be completely deprived of water by mere evapora- 
 tion or ignition. When the aqueous solution is evaporated, there 
 is left, not the anhydrous powder, but a transparent glassy mass, 
 which is a hydrate, of the composition 'Sfi,Tfi^. This hydrate 
 is often called glacial phosphoric acid. It is extremely deliques- 
 cent, and, at a bright red heat, sublimes in dense white fumes. 
 Besides the monohydrate, there are two other hydrates of phos- 
 phoric acid, of the compositions, respectively, 2Il20,P 0^ and 
 
HyiKATES OF PHOSPHORIC ACID. 233 
 
 SHjOjPjOj. Of these, the terhydrate is, perhaps, the most im- 
 portant ; it is the substance usually meant when phosphoric acid 
 is spoken of. 
 
 292. Phosphoric acid can be prepared, also, by the oxidation 
 of phosphorus, or of hypophosphorous or phosphorous ' acid, or 
 by the decomposition of some one of its salts, such as the phos- 
 phate of calcium (bone-earth). 
 
 When phosphorus is heated in dilute nitric acid, of V2 specific gra- 
 vity, the nitric acid gives up oxygen to the phosphorus, nitric oxide and 
 phosphoric acid are formed, and the latter goes into solution. When 
 the phosphorus has all disappeared, the solution is evaporated to dry- 
 ness in order to drive off the nitric acid which was employed in ex- 
 cess, and there is obtained a quantity of the monohydrated glacial 
 acid. 
 
 A product less pure than the acid prepared by means of nitric acid 
 is obtained by neutralizing a solution of monophosphate of calcium; 
 prepared from bones in the manner already described when treating 
 of the preparation of phosphorus (see § 270), with carbonate of am- 
 monium, evaporating the filtered solution of phosphate of ammonium 
 to dryness and heating the residue to low redness. Ammonia is ex- 
 pelled and glacial phosphoric acid remains. 
 
 293. It is a remarkable fact that each of the three different 
 hydrates of phosphoric acid possesses properties peculiar to itself,, 
 and unlike those of the other two ; in fact, each of the hydrates 
 must be regarded as a distinct acid. The monohydrated or 
 glacial acid, H^OjPaOj, is usually called metaphosphoric acid ; 
 the bihydrate, 2^^,^^^, is called pyrophosphoric acid ; and 
 the terhydrate, SSfi,7fi., is commonly spoken of as ordinary 
 phosphoric acid, or simply as phosphoric acid. The three hy- 
 drates are sometimes distinguished as a phosphoric acid (meta), 
 b phosphoric acid (pyro), and e phosphoric acid (ordinary). 
 These different hydrates of the acid retain their peculiar cha- 
 racteristics for a considerable time when dissolved in water, 
 though the mono- and bihydrates change, after a while, to the 
 terhydrate ; and in combining with metallic oxides to form salts, 
 they unite with 1, 2, or 3 molecules of the oxide, accordingly as 
 they themselves contain the elements of 1, 2, or 3 molecules of 
 water. There are thus formed three distinct series of salts, each 
 of which corresponds to one of the hydrates, as is seen in the 
 
234 
 
 MBTA- AND PTBOPHOSPHOEIC ACID. 
 
 following formulse, where M stands for any metal wHeli haMtu- 
 
 ally replaces one atom of hydrogen. 
 
 Monohydrated Acid. BihydrOted Add. Terliydrated Acid, 
 
 H^OjPjO, mfi;pfi, safi,vfi, 
 
 MfiiPfi, m.fi,-pja, sM^OjPjO, 
 
 Metaphosphaie of M. Pyrophosphate of M, Phosphate of M. 
 
 This behavior is very different from that of the hydrates of nitric 
 or of sulphuric acid ; when either of the hydrates of nitric acid, 
 for example, is made to combine with a base, like soda, there is 
 formed always one and the same salt, nitrate of sodium. In 
 each of the three series of salts formed by phosphoric acid, 
 the acid exhibits peculiar properties. A salt of the formula 
 SMjO.PjOj will behave very differently towards many reagents 
 from a salt contaiaing the same metal but in the proportions 
 M^O.P.O,, or 2M.fi,Tfi.. As an example of the kind of dif- 
 ferences here alluded to, it may be mentioned that, whUe meta- 
 phosphoric acid, on being added to a solution of albumen, will 
 cause the albumen to coagulate, no such coagulation can be 
 brought about by either pyrophosphoric acid or the ordinary ter- 
 hydrate. Metaphosphoric acid gives a white precipitate when 
 its solution is mixed with a solution of nitrate of silver by either 
 of the other hydrates, unless they are first neutralized with an 
 alkali, in which event a white precipitate is produced by pyro- 
 phosphoric acid, and a yellow precipitate by the ordinary acid. 
 These peculiarities will be examined in detail when we come to 
 treat of the phosphates of sodium in the chapter upon sodimn 
 and its compounds. 
 
 From the formulse given in the above table, it is apparent that 
 metaphosphoric acid is a monobasic acid, that pyrophosphoric acid 
 is bibasic, and that ordinary phosphoric acid is terbasio. Since 
 each of the atoms of M, in either of the formulae, can be re- 
 placed by an equivalent atom of any other metal, or by hydrogen, 
 it follows that the composition of some of the salts of phos- 
 phoric acid is rather complex ; thus there is a phosphate of potas- 
 sium and sodium of the composition (Kfi,^a.J^,^fi)Ffi^, or 
 KNaHPO,. 
 
 Although we have here studied the acids which contain phos- 
 phorus, oxygen, and hydrogen, as if they were in reality composed 
 
PEOPEETIES OF PHOSPHORIC ACID. 235 
 
 of water and the anhydrousoxide of phosphorus, as the manner of 
 their derivation would suggest, yet it must not he forgotten that 
 we have absolutely no knowledge of the actual structure of the 
 molecules of these compounds, and that the empirical formulae 
 HPO3, H^PaO,, and H^PO^ express all that is absolutely known 
 of their composition. 
 
 294-. In whichever way prepared, and in all its varieties, 
 phosphoric acid is a very strong acid. Although a less powerful 
 agent, at the ordinary temperature, than sulphuric acid, yet, from 
 being much less volatile than sulphiiric acid, it can expel the 
 latter, and most other acids, from their compounds on being 
 heated with them. The behavior of the two acids towards cal- 
 cium, or its oxide, furnishes an instructive example of the influence 
 of extrinsic or physical circumstances upon the play of the chemi- 
 cal force. "When triphosphate of calcium (bone-earth) is treated 
 with dilute sulphuric acid at the ordinary temperature, a quan- 
 tity of phosphoric acid is set free from the calcium and goes into 
 solution. From this result it might, at first sight, be thought 
 that the calcium was removed from the phosphate of calcium 
 simply by force of the superior chemical power of sulphuric as 
 contrasted with phosphoric acid ; but, in reality, the water which 
 is present plays an important part in the reaction. Monophos- 
 phate of caJoium is readily soluble in water, sulphate of calcium , 
 on the other hand, being well-nigh insoluble. Hence it happens 
 that when triphosphate of calcium is digested in dilute sulphuric 
 acid, monophosphate of calcium goes into solution, while sulphate 
 of calcium is deposited as an insoluble powder. But if the mix- 
 ture of solid sulphate of calcium and of dissolved monophosphate 
 of calciimi, thus obtained, be evaporated to dryness and the 
 residue be strongly heated, all the sulphuric acid wiU be expelled 
 from the calcium ; it will evaporate and pass off into the air, and 
 nothing will finally be left in the vessel but triphosphate of cal- 
 cium, precisely similar in quality and quantity to that with which 
 the experiment started. In the same way, if a mixture of sulphate 
 of calcium and glacial phosphoric acid be strongly heated, the sul- 
 phuric acid, being readily volatile, as compared with phosphoric 
 acid, will all be expelled from its combination with the calcium : — 
 SCaSO, -I- P,0, = Ca3Pp3 +3SO3. 
 
236 IEECHI,0E1DB OP PHOSPHORUS. 
 
 295. Chlorides of Phosphorus. — Phosphorus and chlorine 
 unite readily and directly even at temperatures as low as 0°, 
 the act of combination being attended with evolution of light and 
 heat. If the chlorine be in excess, as regards the phosphorus, 
 there will be formed a solid quinquichloride of phosphorus, while, 
 if an excess of phosphorus be present, a liquid terchloride of 
 phosphorus will be obtained. 
 
 296. Terchloride of Phosphorus (PCI3) is a colorless liquid 
 of about 1-5 specific gravity, which boils at about 75°. It fumes 
 in the air, and is decomposed by moist air. When heated in the 
 flame of the gas-lamp, it takes fire and burns with a bright hght. 
 When mixed with water it decomposes, yielding clorhydric and 
 phosphorous acids : — 
 
 2PCl3t6H20=6HCl+3H20,P203, or PCl3+3H20 = SHCl+H3P03. 
 
 This reaction is particularly interesting, in view of the fact that 
 by means of it we are enabled to obtain phosphorous acid in a 
 condition of purity. It will be remembered that by the method 
 of direct oxidation (§ 287) it is no easy matter to obtain pure 
 phosphorous acid from phosphorus. But by simply treating ter- 
 chloride of phosphorus with water and evaporating the solution, 
 so that the chlorhydric acid which results from the reaction may 
 be expelled, hydrated phosphorous acid is obtained as the sole 
 product. The process is a good example of the indirect methods 
 to which chemists are frequently compelled to resort. 
 
 Terchloride of phosphorus can be prepared by passing a slow 
 stream of dry chlorine through melted, almost boiling, phospho- 
 rus contained in a tubulated retort which has previously been 
 filled with chlorine in the cold, and condensing the chloride in 
 an appropriate receiver as fast as it distils over. The process, 
 like all operations with phosphorus, requires special care. 
 
 297. It wUl be observed that the formula of terchloride of 
 phosphorus is that of phosphuretted hydrogen in which all the 
 hydrogen has been replaced by chlorine. The two substances 
 have a perfectly similar volumetric composition. In phosphu- 
 retted hydrogen, three volumes of hydrogen in combination with 
 half a volume of phosphorus, produce two volumes of the com- 
 pound gas ; if, in terchloride of phosphorus, 
 
QiriNaTJICHLOEIBE OF PHOSPHORUS. 237 
 
 Half a unit-volume of phosphorus-vapor, weighing . , 31 -00 
 And 3 unit-volumes of chlorine, weighing (35-5 x 3) . 106'50 
 
 Produce 2 volumes of PCI3 vapor, weighing .... 137 -50 
 One unit-volume of PCI3 vapor should weigh . . . 68-75 
 
 The speciiic gravity of the vapor of terchloride of phosphoras 
 has been found, by experiment, to be 69-12, — a number so 
 nearly identical with, the above result of calculation as entirely 
 to confirm the assumption on which the calculation rests, viz. 
 that in terchloride of phosphorus three volumes of chlorine are 
 united with half a volume of phosphorus-vapor. 
 
 298. QuinquicMoride of Phosphorus (PCI5) is a white or 
 straw-colored crystalline solid, which volatilizes at a temperature 
 below 100° without previously fusing ; but when subjected to 
 pressure, it melts at 148°, and boils at a temperature somewhat 
 higher. It bums in the flame of a candle with production of 
 phosphoric acid and evolution of chlorine. It is very deliques- 
 cent, and is decomposed by the moisture of the air ; by a large 
 excess of water it is immediately resolved into chlorhydric and 
 phosphoric acids : — 
 
 PCI5 + 4H^0 = 5HC1 + H3P0^ ; 
 with a smaller quantity of water it yields chlorhydric acid and 
 oxychloride of phosphorus : — 
 
 PCI, -t- H^O = 2HC1 + POCl,. 
 Sulphydric acid decomposes it in like manner, with production of 
 chlorhydric acid and sulphochloride of phosphorus : — 
 
 PCa, -I- H,S = 2HC1 + PSCI3. 
 Quinquichloride of phosphorus reacts upon many organic com- 
 pounds also, with formation of very interesting products, and is 
 hence an important agent of research in the department of 
 organic chemistry. 
 
 299. In order to prepare quinquichloride of phosphorus, a 
 current of dry chlorine may be passed into terchloride of phos- 
 phorus until the latter has been completely solidified ; the 
 product is then distilled in a current of chlorine. The quinqui- 
 chloride may be obtained directly from phosphorus in one opera- 
 tion, if a rapid stream of chlorine be conducted into a retort 
 
238 DissociATiosr. 
 
 containing phosphorus, kept so cool that the terchloride of phos- 
 phorns at first produced shall not distil over. Again, if powdered 
 red phosphorus is exposed to the action of a rapid stream of 
 chlorine, it mU. all be quickly converted into the soUd quinqui- 
 chloride. 
 
 300. The formula above given for quinquichloride of phos- 
 phorus represents the following composition by volume : — 
 
 Half a unit- volume of phosphorus-vapor, weighing . . 31 -00 
 And 5 unit-volumes of chlorine, weighing (SoSxS) . 177'50 
 
 Should produce 2 vols, of PClj vapor, weighing . . . 208-50 
 One imit-volume of PClj vapor ought then to weigh . 104-25 
 
 The specific gravity of the supposed vapor of quinquichloride of 
 phosphorus, as determined by experiment, does not accord -with 
 this calculated result ; it is 52-81, almost exactly one-half of the 
 theoretical unit-volume weight above given. If four volumes of 
 vapor, instead of two, resulted from the union of half a voliune 
 of phosphorus-vapor with five volumes of chlorine, the calcu- 
 lated and the actual vapor-density would coincide. But hitherto 
 we have never found a single compound gas in which the pro- 
 duct volume was four unit-volumes ; two •unit- volumes have in- 
 variably resulted from the union of the constituent volumes, 
 whatever the character and number of the constituents. It 
 would be necessary to admit this substance as presenting an ex- 
 ceptional volumetric composition, were it not for a well-founded 
 distrust of the experimental determination of the vapor-density 
 of this compound. It not infrequently happens that all attempts 
 to determine the vapor-density of volatile compounds of two or 
 more elements are bafiled by their splitting up, at the tempera- 
 ture of vaporization, into their constituent gases or vapors, which, 
 in the act of separating, resume their own proper volumes, how- 
 ever much they may have been condensed during combination. 
 This splitting up of compoimd vapors, at high temperatures, 
 into less complex compounds, or into the elementary constitu- 
 ents, is termed dissociation. Thus, at the elevated temperature 
 necessary to convert quinquichloride of phosphorus into vapor, 
 it is probable that the quinquichloride splits into terchloride 
 of phosphorus and free chlorine, and that it is the specific 
 
DISSOCIAIIOIf. 
 
 239 
 
 gravity of this mixture wHch has heen determinerl, instead of 
 the specific gravity of the real unaltered vapor of the quinqui- 
 chloride. 
 
 Two unit-volumes of PCI, weigh 138'24 
 
 Two unit-volumes of 01 weigh 71- 
 
 209-24 
 52-31 
 
 Four unit-volumes of the mixture weigh 
 One unit-volume of the mixture weighs . 
 
 The specific gravity which has been assigned to the quinquichlo- 
 ride is 52-81,— a number very nearly coincident with the above 
 calculated density of the mixture of terchloride-vapor and free 
 chlorine. At the high temperature of vaporization it is there- 
 fore probable that quinquichloride of phosphorus undergoes 
 dissociation into terchloride of phosphorus and chlorine ; but if 
 this be the case, these constituents recombine when the tempera- 
 ture falls, for by lowering the temperatiu:e the quinquichloride is 
 recovered. 
 
 As we advance, we shaU meet with several other examples of 
 the dissociation of compound gases and vapors ; for the present 
 it wiU be sufficient to give one more illustration of the meaning 
 of this term. When equal volumes of dry ammonia and dry 
 chlorhydric acid gas are mixed (Exp. 65), the two gases are 
 completely condensed to a white solid, which we are famiUar 
 ■with as chloride of ammonium. Since this ammonium -salt is 
 readily volatUizable, there would be no difficulty in determining 
 the product-volume of the compound of ammonia and chlorhy- 
 dric acid, were it not for the fact that the vapor of chloride of 
 ammonium undergoes dissociation at the temperature of vaporiza- 
 tion. If the real vapor of the compound could be measured, the 
 facts would undoubtedly be correctly represented by the dia- 
 gram, 
 
 HCl 
 
 + 
 
 NH3 
 
 = 
 
 NH.Cl 
 
 * 
 
 but the vapor of the compound is resolved into its constituent 
 gases at the high temperature necessarily employed, so that the 
 following diagram really fig-ures the actual state of things : — 
 
240 
 
 BROMIDES AirB lODIBES OF PHOSPHOEFS. 
 
 HCl 
 
 + 
 
 ISTH. 
 
 When the dissociated vapor cools, the parted gases recombine to 
 form solid chloride of ammonium. 
 
 It is obvious that the phenomena of dissociation interfere 
 fatally with one of the common methods of arriving at the 
 weight and structure of the molecule of a volatile compound; 
 the indirect method of getting at the volumetric composition of 
 a substance from its ponderal composition and the specific gra- 
 vity of its vapor becomes impracticable whenever the vapor of 
 the compound under examination is liable to dissociation, inas- 
 much as experiment cannot determine beyond a doubt the real 
 vapor-density of such a body. 
 
 301. Bromides of Phosphorus. — When a piece of phosphorus 
 is dropped into bromine, the two elements combine with explo- 
 sive violence, the burning phosphorus being thrown about in a 
 highly dangerous manner. There are two bromides of phos- 
 phorus, PBTj and PBr^, corresponding to the two chlorides. 
 The terbromide is liquid at ordinary temperatures and the quin- 
 quibromide solid. 
 
 302. Iodides of Phosphorus. — Iodine and phosphorus unite 
 directly, when brought in contact with one another, and so much 
 heat is developed by their union, that a portion of the phospho- 
 rus will take fire if the mixture be in contact with the air. 
 There are two iodides of phosphorus, both of them soKd at the 
 ordinary temperature ; their composition is respectively PI^ and 
 PI3 . It wiU be noticed that, while the teriodide corresponds to 
 the terchloride and terbromide, the other compound is a bin- 
 iodide, of which there is known neither a bromine nor a chlorine 
 analogue. The fact is interesting as illustrating the general 
 truth that, when iu any group or family of elements we compare 
 the behavior of its several members, analogy ceases to be a sure 
 guide, in proportion as the individuals compared are more widely 
 separated in the natural series. Chlorine and bromine stand 
 next to one another in the family or series of elements to which 
 
SULPHIDES OE PHOSPHORUS. 241 
 
 ttey belong ; and as we have just seen, their behavior, as regards 
 phosphorus, is well-nigh identical ; but iodine, one step further 
 removed from chlorine than bromine is, enters into new combina- 
 tions not altogether conformable to those of chlorine. 
 
 303. Sulphides of Phosphorus. — There is a definite sulphide 
 of phosphorus corresponding to each of the oxides, and in addi- 
 tion to these there are two other compounds, which may be repre- 
 sented by the formulae P^S, and P^S^^ . Sulphur and phosphorus 
 may also be melted together in any proportion. The sulphides 
 of phosphorus are exceedingly inflammable, taking fire even 
 more readily than phosphorus itself, and they are all more readily 
 fusible than either of the two elements of which they are com- 
 posed. They may be prepared by heating sulphur under water 
 in contact with melted phosphorus. The union of the two ele- 
 ments is attended with development of much heat, and sometimes 
 with dangerous explosions. It ia well, therefore, to operate only 
 upon smaU. quantities, and to add the sulphur gradually to the 
 phosphorus. 
 
 CHAPTEK XVIL 
 
 AESENIC. 
 
 304. Compounds of arsenic have been known from very early 
 times. The element is sometimes foimd native, but much more 
 frequently associated with other metals and with oxygen and 
 sulphur. The metals in connexion with which it most commonly 
 occurs are iron, cobalt, nickel, and copper. Ferruginous ores 
 and deposits, in particular, are rarely free from traces of arsenic. 
 In small quantity, arsenic is very widely distributed. 
 
 The greater part of the arsenic of commerce is prepared from 
 a native arsenide and sulphide of iron (arsenical pyrites) corre- 
 sponding to the formula FeAsS, and from the arsenides of nickel 
 and cobalt. Metallic arsenic is obtained directly from the 
 mineral of the formula FeAsS by heating it in earthen tubes laid 
 
 B 
 
242 
 
 PEOPEKTIES OP ARSENIC. 
 
 horizontally in a long furnace ; a tube, made by rolling up a 
 piece of tMn sheet iron, is inserted in the mouth of each earthen 
 retort, and an earthen receiver is luted on to this iron tube. 
 The arsenic condenses principally in the iron tube, in the form 
 of a compact, whitish, crystalline mass, which is detached, when 
 cold, by unroUing the sheet iron. The metal is also indirectly 
 obtained by reducing the arsenious acid (Asfi^) which results 
 from roasting (heating in a current of air) arsenides, like those 
 of cobalt and nickel ; this oxide is heated with charcoal in earthen 
 crucibles covered with conical iron caps, or inverted crucibles, 
 into which the reduced metal sublimes. The metal obtained by 
 the second process is gray and pulverulent, instead of whitish 
 and coherent. 
 
 FeAsS = FeS + As ; As,03 + 30 = 2A8 + SCO. 
 
 305. Arsenic is a brittle solid, of a steel-gray color and a me- 
 tallic lustre. Its specific gravity has been variously given at 
 from 5-62 to 5-96. Like the metals, it is a good conductor of 
 electricity. It crystallizes in acute rhombohedrons, and in octa- 
 hedrons also, thus taking on forms of both the monometrie and 
 hexagonal systems, as do phosphorus, the preceding member, and 
 antimony, the succeeding member of this family. At a dull red 
 heat it volatilizes without previous fusion ; the vapor is colorless, 
 and possesses a characteristic odor resembling that of garlic. 
 The specific gravity of this vapor is 150, while the atomic 
 weight of the element is 75 ; arsenic, therefore, resembles phos- 
 phorus, and difiers from all the other elements heretofore studied, 
 in that its atomic weight is not identical with its unit-volume 
 weight ; two combining proportions by weight of arsenic occupy 
 the same volume as one combining proportion of hydrogen ; its 
 symbol, As, represents its atomic weight, but only half the 
 weight of the unit-volume of its vapor. At the ordinary tempe- 
 rature the compact metal does not tarnish by exposure to dry 
 air, but a moistened powder of arsenic is slowly converted by the 
 air into a mixture of arsenious acid and metallic arsenic. At a 
 red heat the metal burns with a whitish flame, producing a white 
 smoke of arsenious acid. When thrown, in fine powder, into 
 chlorine gas, it takes fire spontaneously and is converted into 
 
ARSENIC AND HTBEOGEN. 243 
 
 chloride of arsenic (AsClj). Bromine, iodine, and sulphur also 
 combine readily with arsenic, when aided by a gentle heat. 
 Nitric acid and aqua regia convert the metal into arsenic acid 
 (ASjOj) ; ehlorhydric acid has little action upon it. Dilute sul- 
 phuric acid has no action upon the metal ; but the concentrated 
 acid has the same effect upon arsenic as upon phosphorus (§ 276) ; 
 arsenious acid is formed and sulphurous acid escapes : — ■ 
 
 3H,80, + 2As = As^O, + 3S0, + 3H,0 . 
 Some fatty oils dissolve arsenic to a slight extent, as they do 
 phosphorus. Metallic arsenic unites by fusion with most metals, 
 forming alloys which the arsenic tends to make hard or brittle. 
 In the manufacture of shot a little arsenic is added to the lead 
 to faciEtate the formation of regular globules. 
 
 306. Arsenic and Hvdrogen.^Axsema forms two combinations 
 with hydrogen ; one of these is an unstable, brown solid of un- 
 certain composition ; the other is a well-known gas whose con- 
 stitution is represented by the formida AsH,, and which is 
 therefore analogous in composition to ammonia (NH^) and phos- 
 phuretted hydrogen (PH3). The solid hydride is so obscure a 
 substance that nothing need here be said of it, except that it is 
 supposed to contain two atoms of hydrogen and one of arsenic 
 (AsHJ). 
 
 307. Arseniuretted Hydrogen. — This very dangerous gas may 
 be prepared in an impure state by decomposing, with sulphuric , 
 acid diluted with three parts of water, an arsenide of zinc ob- 
 tained by fusing together equal weights of powdered arsenic and 
 granulated zinc : — 
 
 3H,S0, + ZUjAs = 3ZnHS0,-f- AsH, . 
 As it is not possible to prepare the precise alloy Zn^As, the 
 arseniuretted hydrogen thus obtained is always mixed with hy- 
 drogen. The arsenide of sodium can be decomposed by water, 
 with evolution of arseniuretted hydrogen : — 
 
 3H,0 + -Sa.^Aa = 3NaH0 + ASH3 . 
 The same remark, however, applies to this reaction as to the pre- 
 ceding one ; the product is contaminated with an indeterminate 
 quantity of free hydrogen. Arseniuretted hydrogen seems also 
 to be formed whenever the oxides of arsenic, or compounds of 
 
 ■B.2 
 
244 ABSENTOBETIED HTDROGEN. 
 
 these oxides, are brought in contact with nascent hydrogen. A 
 mixture of arseniuretted hydrogen and hydrogen may be readUy 
 obtained by acting upon ziuc by dilute chlorhydric or sulphuric 
 acid in which arsenious acid has been dissolved. 
 
 308. Arseniuretted hydrogen is a colorless gas, having a fetid 
 odor ; even when very much diluted with air, it is intensely 
 poisonous, and fatal results have repeatedly followed its acci- 
 dental inhalation. In experimenting with this deadly gas, the 
 greatest care is required not to inhale the least portion of it. 
 It has been condensed at —40° to a transparent liquid, but it 
 has never been solidified. The gas is soluble in water at the 
 ordinary temperature only to the extent of one-fifth of its volume, 
 and neither the gas nor its aqueous solution has any action upon 
 blue or red litmus-paper. In spite, therefore, of its strong resem- 
 blance to ammonia in composition, some of its physical proper- 
 ties are strikingly unlike those of that very soluble and intensely 
 alkaline gas. Arseniuretted hydrogen burns in the air with a 
 whitish flame, forming water and a white smoke of arsenious 
 acid ; but if a cold body, like a piece of porcelain, for example, 
 be introduced into a jet of the burning gas, the hydrogen alone 
 wiU bum, and the arsenic will be deposited in the metallic 
 state upon the porcelain siirface, forming a lustrous black spot. 
 This effect is precisely similar to the deposition of soot on a cold 
 body held in the flame of a candle. It is also decomposed when 
 • caused to pass through tubes heated to dull redness, metallic 
 arsenic being deposited as a brown or blackish mirror, while 
 hydrogen gas escapes. This decomposition is a good illustration 
 of the dissociation of gases (§ 300). Chlorine in excess reacts 
 violently upon it, forming terchloride of arsenic (AsClj) and 
 chlorhydric acid : — 
 
 ASH3 -I- 6C1 = ASCI3 + 3HC1. 
 
 When, however, chlorine acts on an excess of arseniuretted hy- 
 drogen, there are formed chlorhydric acid and metallic arsenic ; 
 flame accompanies this reaction. The reactions of bromine and 
 iodine are similar to, but less violent than, those of chlorine. 
 We recall, in this connexion, the decomposition of ammonia by 
 chlorine, with formation of chlorhydric acid and liberation of 
 
AESENITTRETTBD HTBEOGElf. 245 
 
 nitrogen. Arseniuretted hydrogen decomposes the solutions of 
 the salts of many of the heavy metals, but the products are 
 somewhat various ; sometimes a metallic arsenide is precipitated ; 
 sometimes the heavy metal is precipitated, while arsenious acid 
 remains ia the solution. As we shall shortly see, the chemical 
 properties of this gas are of great importance in the processes 
 nsed for detecting arsenic in cases of poisoning. 
 
 309. Arseniuretted hydrogen may he analyzed by precisely 
 the same method which was used for the analysis of phosphu- 
 retted hydrogen (§ 280) ; but the results can only be approxi- 
 mate, because of the extreme difficulty, not to say impossibility, 
 of obtaining the gas in a state of tolerable purity. The compo- 
 sition of the analogous gases, ammonia and phosphuretted hydro- 
 gen, and the specific gravity of the gas, lead us to the following 
 statement of its composition. Two volimies of the gas contain 
 
 3 unit-volumes of hydrogen, weighing 3x1 =3 
 5 unit-volume of arsenic-vapor, weighing J X 150 = 76 
 
 2 unit-volumes of arseniuretted hydrogen weigh 78 
 1 unit-Tolume of arseniuretted hydrogen weighs 39 
 
 The actual specific gravity of arseniuretted hydrogen, as deter- 
 _ mined by experiment, is as nearly as possible 39, — a fact which 
 makes it certain that two volumes of the gas do not contain one 
 volume of the heavy arsenic- vapor, which is 150 times as heavy 
 as hydrogen, but only half a volume. Herein this gas differs 
 from ammonia, but resembles phosphuretted hydrogen. The 
 weight of the quantity of arsenic which combines with three 
 atoms of hydrogen is 75, just as the weight of the quantity of 
 nitrogen which combines with three atoms of hydrogen is 14 ; 
 but 75 parts by weight of arsenic-vapor only occupy one half the 
 space which 14 parts of nitrogen fill. 
 
 310. Arsenic and Oxygen. — Arsenic forms two weU-defined 
 oxides, arsenious acid, As^Oj, and arsenic acid, As^Oj. The 
 black film which forms on the surface of the metal when ex- 
 posed to the air is by many supposed to be a suboxide, while 
 -others think it is more probably a mixture of metallic arsenic 
 with arsenious acid. The first of the above-mentioned acids cor- 
 responds with nitrous and phosphorous acids, the second with 
 
246 
 
 AESENIOTTS ACID. 
 
 nitric and phosphoric ; but arsenious acid is very stable, in com- 
 parison with arsenic acid, while the reverse is true of the analo- 
 gous acids containing nitrogen and phosphorus. The element 
 arsenic possesses many properties which ally it to the metals ; but 
 in its compounds its close connexion with nitrogen and phos- 
 phorus is clearly exhibited. Its oxides, for example, are both 
 acids, and these acids unite with the oxides of the metals proper 
 to form stable, crystallizable salts, which are in many cases 
 isomorphous with the corresponding salts containing phospho- 
 rus. 
 
 311. Arsenious Acid (As^Oj). — Arsenious acid, known in com- 
 merce as arsenic, or white arsenic, is obtained as a secondary pro- 
 duct in the roasting of arsenical ores of nickel, cobalt, and tin, 
 and as a principal product in the roasting of arsenical pyrites. 
 The volatile matters which escape from the roasted ores consist 
 mainly of sulphurous and arsenious^acids ; the first is allowed to 
 pass off into the atmosphere, the second condenses to the solid 
 state in the chambers and long passages through which the vapors 
 are forced to pass in order that they may deposit their arsenious 
 acid. A second sublimation purifies the raw product. Accord- 
 ing to the temperature at which the arsenious acid is sublimed 
 and condensed, the prsduct is either in powder or in transparent 
 masses ; a low temperature with sudden condensation yields a ' 
 white powder of minute crystals; a higher temperature with 
 gradual soUdifioation produces a transparent glass. 
 
 312. Arsenious acid is a white solid, which occurs not only iu 
 two conditions, one amorphous and the other crystalline, but also 
 in two distinct crystalline forms. When the vapor of the acid is 
 cooled so quickly that it soKdifies at once, without passing 
 through the semifluid state, each particle of the solid acid 
 assumes more or less perfectly the octahedral form. A hot satu- 
 rated aqueous solution of the acid also deposits regular octahe- 
 dral crystals on cooling. The amorphous, glassy variety of the 
 acid changes spontaneously, when kept in contact with the air, 
 into an aggregation of minute octahedral crystals, thereby be- 
 coming opaque and porcelain-like in appearance. The other 
 crystalline form of arsenious acid is the right rhombic prism ; 
 this form occurs much less frequently than the first, and is con- 
 
ISOMERISM. 247 
 
 verted into the octahedral form by subhmatioa and by solution 
 in hot water. 
 
 The two varieties of arsenious acid, the vitreous and the porcel- 
 laneous, differ decidedly in physical and chemical properties, yet 
 they have precisely the same chemical composition ; and when 
 either variety changes into the other, no alteration of weight, no 
 addition or subtraction of matter accompanies the change. The 
 two varieties contain the same two elements in precisely the 
 same proportions. When two or more compounds, which exhibit 
 essential differences of physical and chemical properties, are, 
 nevertheless, found to be identical in respect to constituent ele- 
 ments and their proportions, the compounds are said to be iso- 
 tneric (equal parts). The term allotropism (§ 162) properly 
 applies to the elements only, the term isomerism to compounds 
 only; both terms, however, refer to one and the same un- 
 questionable, though perplexing, truth — -namely, that the widest 
 diversity of properties may coexist with absolute identity of 
 idtimate chemical constitution. Two aUotropic states of the 
 same element not infrequently present more striking differ- 
 ences than elements recognized as distinct ; and among the 
 numerous complex compounds of carbon with which organic 
 chemistry deals, there are many isomeric compounds which are 
 so entirely dissimilar as to lead almost irresistibly to the belief 
 that it is of as much consequence how the atoms of a compound 
 are arranged as what kind of atoms they are. Arsenious acid 
 does not afford a very striking example of isomerism ; neverthe- 
 less the properties of its two modifications are quite diverse. If 
 it be true that the different arrangement of atoms is the cause of 
 the diversity of isomeric compounds, it is evident that the differ- 
 ences between two varieties of a compound of only two kinds of 
 atoms, united in the simple ratio of 2 to 3, cannot be expected to 
 be so marked as the differences between isomeric compounds 
 which contain four or five elements united in the very compli- 
 cated proportions which frequently characterize the compounds 
 of carbon. Nevertheless the differences between the two iso- 
 meric compounds of arsenic and oxygen are sufficiently distinct. 
 The glassy acid dissolves much more rapidly in water than 
 the porcelain-like variety, being three times as soluble in that 
 
248 
 
 PBOPEETIES OF AESENIOITS ACID. 
 
 liquid. The relation of the two varieties to heat is not the same ; 
 for when the vitrfeous acid changes into the opaque, heat is disen- 
 gaged. As this change generally takes place slowly, from the 
 surface towards the centre of any fragment of the -vitreous variety, 
 the heat evolved is not perceived ; but if the change be suddenly 
 accomplished, not only heat, but light also will be disengaged. 
 
 -Erjo. 122. — Diasolve 4 or 5 grms. of the vitreous acid in a hot mix- 
 ture of 24 grms. of strong chlorhydric acid and 8 c. c. of water, and 
 let the solution cool slowly ; the arsenious acid will crystallize in 
 transparent octahedrons, and the formation of the crystals will be ac- 
 companied by flashes of light. 
 
 The specific gravity of the vitreous acid is 3'738 ; that of the 
 porcellaneous 3'699. The opaque variety may be changed into 
 the vitreous by long boiling with water. It appears, therefore, 
 that the arrangement of atoms which may be supposed to fur- 
 nish the vitreous acid is stable only at high temperatures, and 
 that the arrangement of atoms which is peculiar to the opaque 
 acid is stable only at low temperatures. 
 
 313. Arsenious acid volatilizes without change when heated 
 with free access of air ; if heated in contact with carbon, it gives 
 up its oxygen, and metaUio arsenic is liberated. Copper and 
 many other metals reduce arsenious acid. 
 
 Exp. 123. — Place a few particles of arsenious acid in an open tube 
 of hard glass (No. 5) about 10 cm. long, and heat the acid over the 
 lamp, holding the tube in a sloping position ; the white solid will be 
 volatilized, but it will immediately be deposited again upon the cold 
 part of the tube. By the aid of a lens, this deposit may be seen to be 
 crystalline. 
 
 Fig. 46. Exp. 124. — Drop into the point 
 
 of a drawn-out tube of hard glass, 
 No. 6, a morsel of arsenious acid, 
 and above it place a splinter of 
 charcoal (Fig. 46); heat the coal 
 red-hot in the flame of the lamp, 
 and then volatilize the arsenious acid. The acid will give its oxygen 
 to the coal, and the arsenic will be deposited in a ring on the cold 
 part of the tube, presenting a brilliant metallic appearance. 
 
 Exp. 125. — Throw a particle of arsenious acid upon a piece of red- 
 hot charcoal ; the acid will be partly reduced, and the peculiar garlic 
 odor of the vapor of metallic arsenic will be perceived. 
 
SOLUBILITY or AKSENIOTJa ACID. 249 
 
 Exp. 126. — Dissolve a few centigrammes of arsenious acid in 5 or 6 
 c. c. of chlorhydric acid heated in a test-tube ; in the hot solution 
 immerse a narrow strip of clean copper ; an iron-gray film will be de- 
 posited upon the copper. This coating contains metallic arsenic de- 
 rived from the arsenious acid; it consists of an alloy of arsenic and 
 copper. 
 
 314. It is very difficult to say what the solubility of arsenious 
 acid in water reaUy is. The results of different experimenters 
 present very wide discrepancies, due in part to the fact abeady 
 stated, that the two modifications of arsenious acid are of unlike 
 solubility, and in part also to the circumstance that the acid dis-' 
 solves with extreme slowness. The difficulty of the determina- 
 tion is increased by the readiness with which either modification 
 passes into the other in consequence of changes of temperature ; 
 it is quite possible that both varieties may simultaneously exist 
 in the same solution. A hot aqueous solution usually contains 1 
 part of the acid in 10 or 12 parts of water ; on cooling this solu- 
 tion, a portion of the acid separates, leaving a solution which 
 contains 1 part of acid in 20 to 30 parts of water. The aqueous 
 solution has a feeble acid reaction. No definite hydrate of arse- 
 nious acid is known. The acid is much less soluble in alcohol 
 than in water. Hot chlorhydric acid dissolves it with facility, 
 and when cold retains a large proportion in solution ; other acids, 
 even some vegetable acids, dissolve it readily when hot, though 
 most of them keep but little in solution when cooled. When the 
 solution of arsenious acid in chlorhydric acid is evaporated, a 
 compound of chlorine and arsenic, the terchloride of arsenic 
 (§ 336), is volatilized, and the solution thus loses a portion of 
 its arsenic. This fact is of importance in examinations for arsenic 
 in eases of suspected poisoning. 
 
 315. Solutions of caustic soda and potash readily dissolve the 
 acid, a soluble arsenite of sodium or potassium resulting from 
 the reaction. From these arsenites of sodium and potassium 
 the arsenites of other metals are generally obtained by the way 
 of double decomposition. The arsenites are numerous, but they 
 are not very stable and have been but little studied. 
 
 316. Arsenious acid is oxidized and converted into arsenic 
 acid by digestion with nitric acid. The same transformation is 
 
250 USES OP ABSENIOUS ACID. 
 
 brought about, but quicker, by the action of aqua regia, and by 
 chlorine, bromine, and iodine in presence of water. When 
 iodine is added to a solution of arseiiious acid mixed with a 
 little starch-paste, the whole of the arsenious acid is converted 
 into arsenic acid before any blue coloration of the starch is pro- 
 duced by the iodine. These facts are turned to account in the 
 volumetric determination of chlorine (§ 565). Sulphuretted hy- 
 drogen colors an aqueous solution of arsenious acid yellow, and 
 precipitates a yellow sulphide of arsenic (§ 210) from a solution 
 acidulated with chlorhydric acid. 
 
 Arsenious acid is a violent poison, all the more dangerous 
 because it has neither taste nor odor to warn the victim of its 
 presence ; two decigrammes of it will cause death. All the solu- 
 ble salts of arsenious acid are likewise horribly poisonous. The 
 best antidote to the poison is a mixture of moist, freshly precipi- 
 tated sesquioxide of iron and caustic magnesia. 
 
 317. Arsenious acid is largely used for the manufacture of 
 two green paints, an arsenite of copper and a compound of 
 arsenite and acetate of copper; it is applied as an oxidizing 
 agent in the manufacture of glass ; it is used for poisoning ver- 
 min, and is consumed in considerable quantities for producing 
 the arsenic acid which is used in the dyeing and printing of 
 'cloth, and in the manufacture of anUine colors ; it is used in 
 very small doses as a remedy for asthma, and in some skin-dis- 
 eases. Although the acid is so violent a poison, it seems to be 
 possible, by beginning with smaU. doses and gradually increasing 
 them, to accustom the human body to sustain, without injury, 
 doses of 2 to 3 decigrammes, or even more ; the arsenic thus 
 taken is said to produce a plump and healthy appearance in those 
 who use it, and especially to increase the power of the respira- 
 tory organs. In veterinary practice, it has been found that 
 arsenious acid administered to animals in this manner improves 
 the appearance of the skin. 
 
 318. Arsenic Add (As^Oj). — This compound is produced by 
 oxidizing arsenious acid with nitric acid, aqua regia, hypochlorous 
 acid, or other oxidizing agents. 
 
 Exp. 127. — Add 4 grms. of powdered arsenious acid, little by little, 
 to a mixture of 4 grms. of concentrated nitric acid, and 8 grms. of 
 
ARSENIC ACID. 251 
 
 concentrated cUorliydric acid, contained in a small evaporating dish, 
 and gently heated over a lamp in a strong current of air, or beneath 
 a weU-ventilated hood. The liquid, which at first gives off red fumes 
 in considerable quantity, mxist be evaporated until it assumes a syrupy 
 consistency, resembling that of oil of vitriol. This syrupy liquid is 
 arsenic acid. 
 
 319. The syrupy solution thus obtained deposits, after stand- 
 ing for some days, at the ordinary temperature, transparent 
 elongated prisms or rhomboidal laminse. These crystals, heated 
 to 100°, first melt and then yield the terhydrate of arsenic acid 
 (SSJJjAsfi^ = 2HgA80 J as a crystalline precipitate. The 
 same hydrated acid separates in large prismatic crystals when a 
 concentrated aqueous solution is cooled to a low temperature. 
 There are two other hydrates of the oxide ASjOg,— a bihydrate, 
 2Sfi,Asfi^ = H^As^O^, and a monohydrate, H20,As205 = 
 2B[A80g ; both these lower hydrates are obtained from the ter- 
 hydrate by subjecting the latter to the prolonged action of certain 
 temperatures. If either of the hydrates be heated to duU red- 
 ness, a white amorphous mass remains, which is the anhydrous 
 acid, Aafi. ; this substance has no action upon litmus, and seems 
 to be scarcely soluble in water. After long exposure to moist 
 air, it slowly deliquesces, and if covered with water and soaked 
 for a long time, it at last dissolves, being probably converted into 
 the soluble terhydrate. At a full red heat it is resolved into 
 arsenious acid and oxygen. 
 
 320. In spite of the recognized existence of three solid hy- 
 drates of arsenic acid, there is but one aqueous solution of this 
 acid, inasmuch as the monohydrate, the bihydrate, and the anhy- 
 dride, are all immediately converted into the terhydrate when 
 dissolved in water. The solution has a very sour taste and a 
 strong acid reaction on vegetable colors. The concentrated liquid 
 is highly corrosive and produces blisters on the skin. Arsenic 
 acid and its salts are poisonous, but not in so high a degree as 
 arsenious acid and the arsenites. 
 
 321. Arsenic acid is a strong acid, capable of expelling aU 
 the more volatile acids from their salts at high temperatures. 
 Its three hydrates are strictly comparable with the three hydrates 
 of phosphoric acid. 
 
252 SAIIS OF ARSENIC ACID. 
 
 Sydrates (HPO. HAsOj ) Hydrates 
 
 of -^H^P^O, H.As^O, \ of 
 
 Phosphoric Acid. ( HjPOj H3AsO^ ) Arsenic Acid. 
 
 Either one, two, or all three of the hydrogen atoms in common 
 arsenic acid, HjAeO^, may be replaced by a metal, so that three 
 arseniates of any one metal may exist, as for example, 
 
 NaHjAsO^ Na^HAsOj NajAsO^ 
 
 Acid Arseniate " Neutral" Arseniate Basic Arseniate 
 
 of Sodium. of Sodium. of Sodium. 
 
 If an acid arseniate be suitably heated, a meta-arseniate results, 
 as, for example, NaAsOg = NaH^AsO^ — H^O ; if a neutral 
 arseniate be sufficiently heated, a pyro- arseniate results, as, for 
 example, Na^As^O^ = 2Na2lIAsO^ — H^O ; but such meta- and 
 pyro-arseniates, unlike the corresponding meta- and pyro-phos- 
 phates, have very little stabUity, take up again the molecule of 
 water, which the heat expelled, the moment they are brought in 
 contact with water, and are so changed back again into salts of 
 ordinary arsenic acid. The salts of arsenic acid are isomorphous 
 throughout with the corresponding phosphates. 
 
 322. Arsenic acid is readily reduced to arsenious acid, and, 
 consequently, acts in some cases as an oxidizing agent. Thus 
 sulphurous acid reduces arsenic acid, and is itself converted into 
 sulphuric acid : — 
 
 2H3ASO, + 2S0, = 2H,S0, + As,03 + H,0. 
 Sulphydric acid gas, passed through a not too concentrated solu- 
 tion of arsenic acid, slowly precipitates the yellow tersulphide of 
 arsenic, the action being assisted by heat and by the presence of 
 another acid. Charcoal and the metals at a red heat reduce 
 arsenic acid to the metallic state, just as they do arsenious acid. 
 
 323. Arsenic acid has been extensively used in calico-print- 
 ing, in place of the more expensive tartaric acid, for developing 
 white patterns on a colored ground in the chloride-of-lime vat. 
 It is also an excellent preservative of animal substances, and is 
 accordingly used to defend the specimens and preparations of 
 the anatomist and naturalist from decay and from the attack of 
 insects. 
 
 324. Detection of arsenic in cases of poisoning. — Nearly all 
 compounds of arsenic are poisonous; but arsenious acid is best 
 
BETBCIION OP AESENIC. 253 
 
 known and most easily procured, and is therefore most likely to 
 be met with in cases of poisoning by arsenic, whetlier accidental 
 or intentional. In criminal trials the solubility of arsenious acid 
 in water has often been much discussed ; but this is practically a 
 point of little importance, for the tasteless poison is generally 
 administered in the solid state mixed with soup, gruel, milk, or 
 even with solid food. It thus sometimes happens that small par- 
 ticles of the poison can be found adhering to culinary vessels, 
 cups, plates, or spoons, or even to the coatings of the stomach 
 and intestines after death. If the arsenious acid is too finely 
 divided to be picked out in lumps, it may sometimes be sepa- 
 rated by stirring up the mass, under examination, with water, and 
 leaving the heavier particles to settle. Any solid arsenious acid 
 that may be present will be sure to be found in the residue ; it 
 may be washed with cold water. It is always very satisfactory 
 thus to obtain the solid poison in the condition in which it was 
 administered, because the examination is, in such cases, very 
 direct and conclusive. It is only necessary to try, with the white 
 powder thus obtained, the experiments already given to illustrate 
 the properties of arsenious acid (Exps. 123-126), together with 
 certain other discriminating tests shortly to be described. 
 
 325. It more frequently happens, however, that the arsenic 
 has been dissolved by the acid secretion of the stomach, and has 
 become intimately mixed with th^ food or excretions, or incor- 
 porated into the substance of the organs themselves. The exa- 
 mination then becomes more difficult. The reduction of arsenious 
 acid by copper (Exp. 126) is an available test in such cases. 
 To the suspected matter, if liqiiid, about one-sixth of its bulk of 
 chlorhydrie acid is added, and the mixture is gently boiled. 
 Solid tissues must be cut into small pieces and boiled for some 
 time with dilute chlorhydrie acid (1 part acid to 6 parts water) 
 until the whole is disintegrated ; this solution is finally clarified 
 by filtration. Strips of copper gauze or foil are then immersed 
 in the boiling liquid ; and if any gray deposit is produced, fresh 
 pieces of metal are added so long as the color of the copper is 
 perceptibly changed. They are then removed, washed with 
 water, dried, folded up, placed in a dry tube of hard glass and 
 gently heated. Some of the metallic arsenic in the gray alloy 
 
254 DIALYSIS. 
 
 will be converted into arsenious acid, wMch coUeets on the cold 
 part of the tube in the form of a crystalline sublimate. To this 
 sublimate all tests for the identification of arsenious acid can be 
 applied. This mode of operation is known as Eeinsch's test. 
 The chlorhydric acid employed must be proved to be free from 
 arsenic. 
 
 326. Another method of separating arsenious acid from the 
 orgaaic matters with which it is mixed is that of dialysis, a pro- 
 cess which depends upon the very different rates at which differ- 
 ent substances diffuse through water. 
 
 Exp. 128. — Select two straight-sided bottles of clear glass about 16 
 cm. deep and 8 to 9 cm. wide. Fill them seven-eighths full of dis- 
 tilled water, or any pure soft water. Dissolve 10 grms. of bichromate 
 of potassium in 100 c c. of water ; suck as much of this solution as 
 will fill the remaining eighth of one of the above-mentioned bottles 
 into a pipette (A-ppendix, § 22), and carefully convey the colored fluid 
 to the bottom of the bottle by bringing the fine point of the pipette to 
 the bottom of the bottle and then allowing the liquid to flow very 
 slowly out of the pipette. If time enough (5 or 6 minutes) be taken 
 for this process, no sensible intermixture of the two liquids will take 
 place during the delivery. Dissolve 10 grms. of caramel (melted and 
 partially burnt sugar) in 100 c c of water, and convey to the bottom 
 of the second bottle, in the same manner as before, enough of the 
 dark-colored solution to fill the bottle. 
 
 The two bottles are left at rest for several days in a room where the 
 temperatvire is nearly constant. Spontaneous difiusion immediately 
 begins ; and the very different rates at which the two colored sub- 
 stances diffuse upwards through the water should be from time to 
 time observed. 
 
 327. Substances which have a comparatively high diffusive 
 power have generally, though not invariably, the power of crys- 
 tallizing ; their solutions are generally free from viscosity, and 
 always have taste. Such substances are designated by the term 
 crystalloids. Among crystalloids there are wide differences of 
 diffusive power ; thus caustic potash diffuses twice as fast as sul- 
 phate of potassium, and sulphate of potassium twice as fast as 
 sulphate of magnesium. 
 
 Substances of very low diffusive power have little, if any, 
 tendency to crystallize, and affect a vitreous structure. Such 
 
CBTSTALLOIDS JlSD COILdlBS. 255 
 
 substances are often very soluble in water ; but their solutions 
 have always a certain degree of viscosity when concentrated, 
 and are insipid or whoUy tasteless. By combining with water, 
 these substances are apt to form jellies. Gelatine has been 
 taken as the type of this class ; and they ha-<% hence been 
 called colloids, a name derived from Greek words signifying 
 glue-like. Among the colloids rank hydrated silicic acid, alumina, 
 starch, gums, caramel, albumen, and animal and vegetable extrac- 
 tive matters. 
 
 As we can separate by means of distillation or evaporation two 
 bodies of difierent volatility, so by the aid of difRision we can separate 
 one substance more or less completely from another. Jellies and col- 
 loid membranes are permeable to crystalloids, but are practically im- 
 permeable by coHoida like themselves. By means, therefore, of a 
 colloidal diaphragm, or partition, crystalloids can be separated from 
 colloids by diffusion. The most suitable substance for the dialytic 
 diaphragm is parchment paper, prepared by soaking unglazed paper, 
 for a few seconds, in a mixture of 6 parts of strong sulphuric acid and 
 1 part of water, and immediately washing it, first in water and then in 
 water containing ammonia. The paper subjected to this treatment 
 becomes semitransparent and tough, like parchment. 
 
 A dialyzer, as the apparatus for effecting separation by diffusion is 
 called, consists of two gutta-percha, or wooden, hoops, one of which 
 should be 6 cm., and the other 2'5 cm. deep. The deeper hoop is 
 slightly conical, and the shallower must shp over the small end of the 
 deeper. The hoops may be from 15 to 25 cm. in diameter. The 
 parchment paper, which is to form the bottom, must be about 8 cm. 
 wider than the small end of the 5 cm. hoop. To prepare the dialyzer 
 for use, soak the parchment paper for about a minute in distilled water; 
 stretch it evenly over the small end of «the 5 cm. hoop and strain it 
 on tightly by pushing over it the 2-5 cm. hoop. The paper must be 
 pressed smoothly up round the outside of the deeper hoop, and the 
 bottom must be flat and even. 
 
 There must be no small holes in the paper. To detect such, put 
 distilled water into the dialyser to the depth of 6 m.m., and place the 
 dialyzer on some white blotting-paper. If any wet or dark spots ap- 
 pear, they indicate the existence of small holes. To close such holes, 
 apply to the under surface of the paper about the holes some solution 
 of albumen, put on a small patch of parchment paper, and iron the 
 patch with a hot smoothing-iron. The albumen wiU coagulate, fix 
 the patch, and close the hole. 
 
 Bxp. 129. — ^Into the dial3'zer so prepared pour an aqueous solution 
 
256 BIAITSIS OF AESENIOTJS ACID. 
 
 containing five per cent, of cane-sugar and five per cent, of gum 
 arabic, to the depth of ahout 1-25 cm. Then float the dialyzer on 
 distilled water contained in a flat basin. The volume of water in the 
 basin should be from 5 to 10 times as great as the volume of the fluid 
 in the dialyzer^ The wider the dialyzer and the greater the quantity 
 of distilled water in the outer basin, the more rapid and effective the 
 difiiision. A dialyzer 15 cm. in diameter, serves to operate upon 200 
 to 260 c c of liquid ; one of 20 cm. upon 400 to 450 c c ; one of 25 
 cm. upon 600 c c 
 
 After the lapse of twenty-four hours, the water in the basin should 
 be poured into an evaporating-disli and gently evaporated over a water- 
 bath. Pure sugar will crystallize fi:om the solution. The sugar, a 
 crystalloid, has passed through the diaphragm ; the gum, a colloid, has 
 remained in the dialyzer. It should be remarked that gum is wholly 
 uncrystaUizable, and that the mixed solution of gum and sugar will not 
 yield crystals, but only an amorphous mass, when evaporated. 
 
 328. By means of this dialyzing apparatus, arsenious acid, 
 salts of the metals, Btrychnine, and other crystaUizable poisons, 
 mineral and organic, can be readily separated from organic 
 fluids ; and the process has the very great advantage of intro- 
 ducing no metal, chemical reagent, or other foreign substance 
 into the fluids under examination. After twenty-foijr hotirs, the 
 crystaUizable poison, or a large proportion of it, will have been 
 transferred to the distilled water in the outer basin, and in this 
 solution it may be sought for by the application of the appro- 
 priate tests. 
 
 Exp. 130. — Dissolve 0-1 grm. of arsenious acid in about 80 c. c of 
 hot water, and stir the solution into about 200 c c. of milk, ale, soup, 
 gruel, or other thick organic ^uid ; place the poisonous fluid in a 15 
 cm. dialyzer and float thejdialyzer on two litres of distilled water in 
 a clean basin. Allow the apparatus to stand at rest in a room where 
 the temperature is tolerably uniform for forty-eight hours. At the 
 expiration of this time, transfer the clear solution in the basin to an 
 evaporating-dish, without losing a drop, rinse the basin carefully with 
 distilled water, and add the rinsings to the contents of the dish ; eva- 
 porate the solution over a water-bath (see Appendix, § 14) to the hulk 
 of 50 c c To one-third of this concentrated solution add a few drops 
 of pure chlorhydric acid, and apply Eeinsoh's test for arsenic (§ 325), 
 with due regard to the small scale on which the operation must be con- 
 ducted. About 0-025 grm. of arsenious acid is the quantity which may 
 be expected to respond to the test by copper. Three-quarters of the 
 
EXiMINATION POE AESBWIC. 257 
 
 Griginal decigramme should be transfeiTed by diffusion tlirougb tbe 
 dialyzer in the course of forty-eight hours, and of this solution of this 
 0-075 grm. of arsenious acid we have taken one-third. The rest of 
 the solution is to be reserved for tests hereafter to be described. 
 
 329, When the arsenious acid must be sought in large organs 
 of the body, like the stomach, liver, or intestines, or in consider- 
 able quantities of disgusting semifluid materials, it is sometimes 
 necessary to utterly destroy the organic matters by processes 
 which cannot cause the loss of arsenic. Several methods may be 
 einployed for thig purpose. 1. The organic matter is gently 
 heated in a tubulated retort with strong chlorhydric acid, and 
 strong nitric acid is added from time to time. The organic mat- 
 ter is thus completely destroyed, witji the exception of the fat. 
 A cooled receiver is connected with the retort to condense the 
 distillate from the hot mass. The fat is separated from the clear 
 liquid in the retort by decantation, and weU washed with water ; 
 these washings, togettier with the distillate in the receiver, are 
 added to the main bulk of the fluid. 2. Chlorate of potassium 
 may be added instead of nitric acid. 3. The organic matter, 
 after being made as fine as possible, is stirred up with water, 
 and chlorine gas is passed through tlje liquid until the organic 
 substances are partly destroyed and partly deposited in brown 
 
 All these processes, and there are others based on like prin- 
 ciples, are processes of combustion ; aqua regia, chlorate of po- 
 tassium, and chlorine are oxidizing agents of great power, as we 
 have already seen ; they burn the carbon and hydrogen of the 
 organic materials as UteraUy as the oxygen of the air burns the 
 coal in the grate. The arsenic also is oxidized and converted 
 into its highest oxide, arsenic acid. Whenever chlorhydric acid 
 is used, and heat is applied, there is danger that chloride of 
 arsenic (AsCl ) may be formed ; this chloride is a volatile body, 
 against whose loss precautions inust be taken, by never allowing 
 the temperature of the fluids to rise much above 100°, and by 
 collecting any distillate which may be formed under circumstances 
 which make it possible for this chloride to be evolved. 
 
 330. AH these methods of destroying the organic matters in 
 which arsenious acid is to be sought for are liable to one objec- 
 
258 
 
 DEIBCTION OF AESENIC. 
 
 tion. Considerable quantities, even kilogrammes, of acids must 
 be used, if the quantity of organic substance to be destroyed is 
 large ; cHorhydric and sulphuric acids very commonly themselves 
 contain arsenic, and since the liq\iids, which result from the de- 
 struction of the organic tissues, are finally evaporated to a very 
 small bulk, all the arsenic in several kilogrammes of the acids 
 employed, as -well as aU the arsenic which may have been con- 
 tained in the bodily organs or fluids submitted to examination, will 
 be concentrated into a small cupful of liquid. It is obviously 
 necessary to demonstrate that the arsenic reactions cannot be 
 obtained from the same quantities of the same acids actually 
 employed, subjected to the same series of operations. The best 
 way is to conduct a parallel examination of normal animal 
 organs or fluids ; iu this examination the identical processes and 
 the same weights of the same chemical materials must be em- 
 ployed as in the examination of the suspected substances; if 
 arsenic is found in the latter investigation, but not in the parallel 
 examination of the normal animal substances, it will be quite 
 certain that the arsenic was not derived from the chemicals em- 
 ployed in the research. 
 
 331. "When, by any of the processes above described, a clear 
 arsenical solution, free from organic matter, has been obtained, 
 the identification of the arsenic may be accomplished by many 
 methods, of which the two following wiU serve as examples : — 
 
 1. By precipitation as sulphide of arsenic. — If the clear solu- 
 tion contains arsenic acid, it is necessary to reduce this oxide to 
 arsenious acid before the precipitation can be efiected. This re- 
 duction may be accomplished by passing a slow stream of washed 
 sulphydric acid gas (§ 202) through the solution for several 
 hours, but may be immediately effected by saturating the solu- 
 tion with sulphurous acid gas, the superfluous gas being finally 
 expelled by gentle heating. After the reduction has been 
 effected, a slow stream of washed sulphydric acid gas precipitates 
 the yellow sulphide of arsenic from the liquid. 
 
 JExp. 131. — ^Acidulate one-half of the liquid reserved from Exp, 
 130 with pure chlorhydiic acid, place it ia a small beaker glass and 
 pass a slow stream of washed sulphydric acid gas through the solution. 
 The delivery-tube of the gas should be small and the current slow; a 
 
maesh's iest. 259 
 
 piece of unglazed paper shovild be used as a cover, in order to keep 
 the beaker full of the gas. A yellow precipitate (Aa^Sj) will appear, 
 indicating the probable presence of arsenic. When no more precipi- 
 tate seems to form, stop the current of gas, and let the beaker stand in 
 a warm place till the odor of the gas has nearly disappeared. Collect 
 the precipitate on a small filter (see Appendix, § 14), wash it tho- 
 roughly with water, and dry it. 
 
 Exp. 132. — ^Mix Ultimately the dry precipitate obtained in the last 
 experiment with its bulk of dry carbonate of sodium and its bulk of 
 dry cyanide of potassium, and introduce this mixture into a hard glass 
 tube (No. 5), the end of which has been closed and expanded to a small 
 bulb. If the precipitate stick to the filter-paper, it must be scraped 
 ofi". Warm the bulb and its contents over the lamp to expel moisture, 
 then wipe the tube out with a tuft of cotton on the end of a wire, and 
 bring the bulb to a red heat. A ring of metallic arsenic, like that of 
 Exp. 124, will be deposited in the tube. Preserve this metallic mirror 
 for subsequent study. 
 
 2. By eonver^on into arseniuretted hydrogen. — When an aqueous 
 or acid solution containing arsenious or arBenic acid is added 
 to the contents of a flask in which hydrogen is being generated, 
 the nascent hydrogen reduces the oxide of arsenic, and there is 
 formed a quantity of arseniuretted hydrogen, which mixes with 
 the uncombined hydrogen evolved. (Compare § 307.) This 
 arseniuretted hydrogen is decomposed, with deposition of metallic 
 arsenic, by being passed through a red-hot tube. The uudecom- 
 posed gas bums with a whitish flame; and if a cold body be held 
 in the flame, a spot of metallic arsenic will be deposited upon it. 
 (See § 308.) Upon these properties and reactions is based the 
 process for detecting arsenic known as Marsh's test. 
 
 Kg. 47. 
 
 Hxp. 133. — To a bottle prepared for generating hydrogen from 
 pure zinc and dilute sulphuric acid, adapt a chloride-of-calcium tube, 
 
 82 
 
260 marsh's ib^t. 
 
 and with the outer end of this drying-tube connect a tuhe of hard glass 
 (No. 4) -which has been twice dra-wn to a fine bore and which termi- 
 nates in a fine open point. (Fig. 47.) Support this long tuhe at 
 three or four points, in such a manner that the softening of the glass, 
 first at the point o, and then at the point 6, shall not distort the tuhe. 
 By adding acid through the funnel-tube of the flask, eTolve hydrogen, 
 and when the whole apparatus is full of hydrogen, %ht the gas at the 
 tip of the hard glass tuhe. By means of an efficient gas-lajiip, heat 
 about 2 cm. of this tube to dull redness at the point a ; just beyond 
 the hot part of the tube, place a small sheet-iron screen, as shown in the 
 figure, to cut off the heat from the adjoining narrow part of the tube. 
 Maintain the apparatus in this condition for ten minutes, the glass 
 tube red-hot at one point and the hydrogen flowing steadily through 
 the tube and burning with a colorless flame at the point. If no de- 
 posit, or only a scarcely perceptible deposit, appears in the fine tube 
 adjoining the heated portion, the zinc and sulphuric acid are pure 
 enough for the experiment, but if a black, shining deposit appears in 
 the fine tube, the materials themselves contain arsenic and are, of 
 course, unsuitable for use in testing for this substance. 
 
 If the zinc and sulphuric acid prove to be sufficiently firee fi-om 
 arsenic, add to the contents of the flask a few drops of the liquid ob- 
 tained by dialysis (Exp. 130). In a moment a mirror of arsenic 
 will be deposited in the fine tube adjoining a ; when this mirror has 
 become large and dense, move the lamp to 6, transfer the screen, and 
 obtain a similar mirror in the second attenuated portion of the tube ; 
 finally, extinguish the lamp and allow the arseniuretted hydrogen to 
 reach the burning jet of gas at the extreme point of the apparatus ; 
 the white coloration of the flame will now, for the first time, be seen f 
 introduce into the jet a bit of cold porcelain, and obtain the character- 
 istic black and lustrous spot of metallic arsenic ; this experiment may 
 be repeated indefiiiitely and a large number of spots obtained for sub- 
 sequent use. Preserve the two mirrors and a number of arsenic spots 
 for future study. In order to prevent the possibility of any arseniu- 
 retted hydrogen escaping into the air of the room, the jet of gas must 
 be kept constantly burning, and when the experiments are ended the 
 flask must be washed out promptly and thoroughly. , 
 
 332. This method is very well adapted for the speedy and 
 certain detection of arsenic in green paints, sncli as are applied 
 to waU-papers, artificial flowers, lamp-shades, and the like ; for in 
 such cases, if any arsenic is present, there is so much as to make 
 any traces of arsenjc which may contaminate the zinc and sul- 
 phuric acid of no consequence whatever. It is only necessary, in 
 
DETECTION OP AESEN3C, 261 
 
 such examinations, to scrape off some of the green coloring-mat- 
 ter, dissolve it in dilute chlorhydric acid, and add the solution to 
 the hydrogen flask of the apparatus described above. Arsenic 
 greens instantly give enormous mirrors and spots under these 
 conditions. 
 
 333. In medico-legal investigations, upon whose results life 
 often depends, it must always be remembered that arsenic is 
 very widely diffused in the mineral kingdom, and that it is a 
 matter of great difficulty to procure reagents absolutely free 
 from it. The substances employed as reagents in Marsh's test 
 are often contaminated with it; and the acids used in destroying 
 organic matter may well contain arsenic enough to become visible 
 after the great concentration of this impurity which inevitably 
 occurs in the evaporation of the liquid which results from the 
 burning of the organic matter. The use of zinc is avoided, and 
 other advantages gained, by obtaining the necessary hydrogen 
 by the electrolysis of acidulated water. (§ 35.) When a solu- 
 tion of arsenious acid, acidulated with chlorhydric or sulphuric 
 acid, is decomposed by the electric current, the greater part of 
 the arsenic eliminated at the negative pole is given off in the 
 form of arseniuretted hydrogen, which may be examined pre- 
 cisely as ^if it were generated in Marsh's apparatus. This method 
 is very delicate, and seems to possess considerable advantages 
 over Marsh's process, but it has not yet (1867) been actually 
 applied in judicial investigations. 
 
 334. To describe the methods by which the analytical chemist 
 purifies his reagents and proves their purity, would involve de- 
 scending into technical detaUs which are unsuitable for this 
 manual. Zinc and acids, pure enough for illustrative experi- 
 ments, can be bought of the dealers in pure chemicals. None 
 but expert analysts should ever be intrusted with the chemical 
 investigation in a supposed case of poisoning by arsenic. A 
 difficulty attending such examinations remains to be discussed 
 under the metal antimony, a substance which combines with 
 hydrogen, as arsenic does, to form a gas which is decomposed by 
 heat, as arseniuretted hydrogen is, with deposition of a metallic 
 mirror which cannot be distinguished by mere inspection from 
 that of arsenic. Since preparations of antimony are much em- 
 
262 
 
 CHLOBITE OF ARSENIC. 
 
 ployed as medicines, and particularly since tartar-emetic, a salt 
 containing antimony, is often administered in cases of poisoning, 
 it is essential to find means of distinguishing between compounds 
 of arsenic and the analogous compounds of antimony. 
 
 335. CMoride of Arsenic. — Only one chloride of arsenic is 
 known, the terchloride (AsClj), corresponding to the terchloride 
 of phosphorus. No quinquichloride corresponding to the quin- 
 •quichloride of phosphorus is known. The chloride of arsenic is 
 formed by passiog dry chlorine gas over finely divided metallic 
 arsenic placed in a retort. The combination is usually attended 
 with combustion ; and the heat developed is sufficient to distil the 
 chloride over into the receiver. It niay also be made by dis- 
 tilling a mixture of metallic arsenic and the mercury compound 
 called corrosive subUmate, in accordance with the following equa- 
 tion, in which Hg stands for mercury (Hydrargyrum): — 
 
 6HgCl, -H 2As = 3Hg,CI^ + 2ASCI3. 
 Corrosive Svhlimate. Calomel. 
 
 Terchloride of arsenic may also be procured by distilling arsenious 
 acid with common salt and sulphuric acid. Small lumps of fused 
 salt should be added from time to time to a mixture of arsenious 
 acid with a large excess of sulphuric acid : — 
 
 As.O, + 6NaCl + 6H,S0, = 3H,0 + 2AsCl, -t- 6NaHS0,. 
 
 336. Terchloride of arsenic is a dense, colorless, oily liquid, 
 whose specific gravity is 2-205. It boils at 132°, producing a 
 vapor whose density is 90'91. It evaporates freely at the ordi- 
 nary temperature, producing fumes of arsenious acid. It is 
 highly poisonous. The chloride is decomposed by an excess of 
 water into chlorhydric acid and arsenious acid, just as the chlo- 
 ride of phosphorus is resolved by water into chlorhydric and 
 phosphorous acids ; this reaction is the basis of the best deter- 
 mination of the atomic weight of arsenic. 
 
 2AbG[, + 3H,0 = 6HC1 + As^O,. 
 All the chlorine in a known weight of chloride of arsenic is con- 
 verted by this reaction into chlorhydric acid ; the weight of the 
 chlorine contained in this chlorhydric acid can be accurately de- 
 termined, and the weight of the arsenic with which this quantity 
 .of chlorine was originally combined is obtained by simple sub- 
 
.SULPHIDES or AESBITIC. 263 
 
 traction. The proportions by weight in which arsenic and chlo- 
 rine combine are thus determined. In terchloride of arsenic, 
 as in terchloride of phosphorus, three volumes of chlorine unite 
 with only half a volume of arsenic vapor to produce two vo- 
 lumes of the terchloride vapor. Indeed aU the volatile compounds 
 of arsenic illustrate the fact, already mentioned (§§ 305, 309), 
 that the unit- volume weight, or specific gravity, of arsenic vapor 
 is the double of its atomic weight. 
 
 337. Bromide and Iodide of Arsenic. It is enough to say of 
 these two compounds that they are crystallizable solids, obtain- 
 able by the direct action of the elements upon each other, and 
 answering to the formulEe AsBr, and Aslg respectively. 
 
 338. Sulphides of Arsenic. — There are three weU-deflned 
 sulphides of arsenic, corresponding to the formulae As^S^, AS2S3, 
 and As^Sj. The first two occur as natural minerals, realgar and 
 orpiment, and may also be obtained in the free state by artificial 
 processes ; the third is known only in combination. 
 
 339. Bisulphide of Arsenic (As^S^). — The native mineral re- 
 algar has this composition. The compound is obtained artifi- 
 cially by meltiag arsenic with sulphur, or arsenic with orpiment 
 (see the next section), or sulphur with arsenious acid, in such 
 proportions in either case as will bring together those parts by 
 weight of the two elements which the above formula requires. 
 The commercial product is a brownish-red opaque substance of 
 variable composition, generally containing free arsenious acid. 
 Kealgar is one of the ingredients of white Indian fire, a mixture 
 of 24 parts of nitre, 7 of sulphur, and 2 of realgar, sometimes 
 used as a signal light. 
 
 340. Tersulphide of Arsenic (As^S^). — This sulphide occurs na- 
 tive in translucent rhombic prisms of a yeUow color. It is 
 obtained artificially by passing sulphydric acid gas through a 
 solution of arsenious acid, or an arsenite acidulated with chlor- 
 hydric acid ; the sulphide falls as a bright yeUow amorphous 
 powder, insoluble in water and dilute acids. It melts easily, and 
 bums in the air with a pale blue flame ; in closed vessels it may 
 be sublimed without change. 
 
 Under the name of orpiment, this sulphide is used as an orange 
 pigment ; a mixture of the sulphide with arsenious acid, called 
 
264 
 
 STTLPHiRSENITES. 
 
 king's yellow, was formerly employed as a yellow pigment. 
 This impure tersnlphide was made by subliming 7 parts of 
 araenious acid with 1 part of sulphur, a proportion of sulphnt 
 not sufficient to convert aU the acid into tersulphide. If a pat- 
 tern be printed upon cotton cloth with a preparation containing 
 arsenious acid, and the cloth be then passed through water con- 
 taining stilphydric acid, orpiment will be deposited in the fibre 
 of the cloth and the pattern will be brought out in orange-yellow. 
 We have already seen (Exp. 132) that the tersulphide of arsenic 
 yields a mirror of metallic arsenic when heated in a closed tube 
 with a mixture of carbonate of sodium and cyanide of potassium. 
 The sulphide is readily dissolved by a cold solution of potash, 
 soda, or ammonia, the oxygen of the alkaK converting part of 
 the arsenic in the sulphide into arsenious acid, while the aliali- 
 metal combines with the sulphur liberated ; this alkaline sulphide 
 then unites with the undecomposed portion of sulphide of arsenic 
 to form a sulphur-salt, whose composition is that of an arsenite 
 in which the oxygen has been replaced by sulphur. 
 
 4As,S3 -f- 5K,0 = 3(E:,S,As,S3) + 2K,0,As,0,. 
 If an acid be added to this solution, no sulphuretted hydrogen is 
 evolved, as is generally the case when an acid is brought in con- 
 tact with an alkaline sulphide, but the sulphur and arsenic re- 
 combine and are separated as tersulphide of arsenic. 
 3(K,S,As,S3) + 2K,0,As,03 + lOHCl = lOKa + 5H,0 -|- 4As,S3. 
 341. Svlpharsenites. — The tersulphide of arsenic unites with 
 basic metallic sulphides in three different proportions, forming 
 with potassium, for example, the three salts 'd^^,ks^^, 2X^8, 
 ASjSj, and 'K^,As^^. One mode of preparing a sulpharsenite 
 has been mentioned in the last section ; another method is to dis- 
 solve arsenious acid ia an alkaline sulphydrate, in which case 
 one-half of the alkali is converted into arsenite : — 
 Dualistic: 2A8,03 -|- 4KHS = K^S,As,S3 + 2:,0,A8,03 + 2H,0. 
 Empirical: A8,03 + 2KH8 = KAsS, -|- KAsO, + H,0. 
 The sulpharsenites of the other inetals are mostly obtaiaed from 
 the sulpharsenites of sodium and potassium by the method 6f 
 double decomposition. The sidpharsenites are either yellow or 
 red ; they are obscure bodies, of no practical importance at pre- 
 
STJLPHAKSENIATES. 266 
 
 sent. They illustrate, however, two points of theoretical in- 
 terest—namely, the existence of sulphur-salts which bear to 
 sulphides the same relation which oxygen salts bear to oxides, 
 and the parallelism of composition between these two classes of 
 salts. We place beside each other the empirical formulae of the 
 sulphur-salts of potassium and arsenic, and the corresponding 
 oxygen-salts : — - 
 
 Sulphur-salts. Oxygen-Salts. 
 
 K3ASS3 k3A803 
 
 K,As,S, K^As^O, 
 
 XAs^ KAsO, 
 
 342. Qiiinquistdphide ofArsenie (As^Sj). — A sulphide of arsenic 
 corresponding to anhydrous arsenic acid is not known in the &Be 
 state. The quinquisulphide is known only in combination with 
 sulphides of the metals in sulphur-salts called sulpharseniates. 
 When a solution of sulphide of sodium is digested with some ter- 
 sulphide of arsenic and sulphur enough to permit the formation of 
 the quinquisulphide, and the solution, after long standing, is con- 
 centrated by evaporation and then cooled, large colorless crystals 
 of sulpharseniate of sodium are obtained, which are not changed 
 by exposure to the air. The crystals have the composition in- 
 dicated by the formula SNa^SjAs^Sj -|- ISH^O. The sulphar- 
 seniate, 21^&^B,Aa^8., may be prepared by saturating the aqueous 
 solution of the corresponding oxygen-salt 2Nafi,Asfi^ with sul- 
 phydric acid gas. The sulpharseniates of the alkah-metals, and 
 a few others, are soluble in water ; but the greater number of sul- 
 pharseniates are insoluble. These insoluble salts are prepared by 
 mixing a solution of an alkaline sulpharseniate with a solution of 
 some salt of the metal whose siilpharseniate is desired. The same 
 parallelism is observable between sulpharseniates and arseniates 
 as between sulpharsenites and arsenites. 
 
266 ANTIMONY. 
 
 CHAPTEE XVIII. 
 
 ANTIMONY. 
 
 343. Antimony is found native, both, alone and alloyed with 
 other metals, especially with arsenic, nickel, and silver. There 
 exist also a considerable number of minerals which consist of, 
 or contain, large proportions of the compounds of antimony with 
 oxygen and sulphur. 
 
 344. All the antimony of commerce is obtained from the 
 mineral tersulphide, Sb^S,. The symbol for antimony is Sb, 
 f^^ the Latin name of the substance, Stibium. This sulphide 
 is very fusible, melting readily in the flame of a candle ; it may 
 therefore be separated from the earthy or rocky gangue in which 
 it occurs by simple fusion at a low temperature. The metal is 
 obtained from the sulphide by several difiierent processes : — 1. By 
 adding to the melted sulphide iron nails, filings, or scraps ; the 
 iron and the antimony change places. 
 
 Sb,83 + 3^0 = SFeS + 2Sb. 
 2. By roasting the sulphide of antimony, reduced to a coarse 
 powder, until the greater part of the sulphur has been burnt off 
 and the antimony converted into the oxide ; this residue is then 
 mixed into a paste with water, charcoal powder, and carbonate 
 of sodium, or some equivalent reducing flux, and heated in co- 
 vered crucibles to full redness ; the metal sinks to the bottom of 
 the crucible. 3. By fusing together a mixture of sulphide of 
 antimony, the scales which fall from hot iron when it is ham- 
 mered (an oxide of iron), carbonate of sodium, and charcoal ; 
 this process is a sort of combination in a single operation of the 
 two preceding methods. Since the sulphides and oxides of anti- 
 mony and the metal itself are somewhat volatile at moderate 
 temperatures^ it has thus far been found impossible to avoid a 
 considerable loss of metal during the melting, roasting, and re- 
 ducing of the ore. Prom one-fifth to one-half of the metal is 
 lost, according to the skill and care of the workmen. 
 
 345. The commonest impurities in commercial antimony are 
 
PEOPEETIES OF ANTIMONT. 267 
 
 sulphur, sodium, arsenic, lead, iron, and copper. These impuri- 
 ties injure the antimony for many of its applications in the arts; 
 and the ^xtensive use of antimonial preparations iu medicine 
 renders the removal of the arsenic a point of particular impor- 
 tance. The purification may be effected by fusing the powdered 
 metal, first, with a mixture of sulphide of antimony and carbo- 
 nate of sodium, and, secondly, with a mixture of carbonate of 
 sodium and nitre. These fusions may be several times repeated ; 
 the impurities are either oxidized or converted into sulphides, 
 and enter the slag. Lead, however, cannot be got rid of by 
 these processes ; this impurity is removed by fusing the anti- 
 mony with oxide of antimony ; the lead changes places with the 
 antimony in the oxide of antimony, and is converted into litharge. 
 346. Antimony is a brittle metal, having a bluish-white color, 
 a brilliant lustre, and a highly crystalline structure. The cakes 
 of the commercial metal usually present upon their upper sur- 
 faces beautiful stellate or fern-like markings. Like phosphorus 
 and arsenic, it is dimorphous, crystallizing both in rhombohedrons 
 and octahedrons. The specific gravity of the metal is from 6-60 
 to 6'85 ; its atomic weight is 122. For a metal, it is a poor con- 
 ductor of heat and electricity. At 450° it melts, gives off vapors 
 at a low red heat, and takes fire at full redness, burning brilliantly, 
 with evolution of white fumes of the teroxide (Sb^Og). If the 
 antimony is contaminated with arsenic, as is often the case, a 
 garlic odor, due to the presence of this impurity, may be im- 
 parted to the vapors. 
 
 Exp. 134. — Melt about 0-5 grm. of antimonyby heating it on a 
 piece of charcoal before the blowpipe. (See Chapter XX.) Throw 
 the white, glowing globule into the middle of a large tray made of 
 coarse paper ; the globule bursts into a multitude of small beads, which 
 fly over the paper, leaving in their trail a white, powdery oxide. 
 
 Exp. 135. — Melt a second small fragment of antimony upon char- 
 coal as before, but, instead of throwing it from the coal, allow it to cool 
 there slowly. The globule will, in this case, become covered with an 
 efflorescence of crystals of the oxide. 
 
 The metal is not oxidized by exposure to dry or moist air at 
 ordinary temperatures. Nitric acid oxidizes it easily, but does 
 not dissolve it; the insoluble quinquioxide, or some mixed 
 ^xide, is formed, according to the strength of the acid employed. 
 
268 
 
 ALLOTS OP ANTIMONY. 
 
 Powdered antimony takes fire when tkrown into cilorine gas, 
 and combines very energetically with, bromine and iodine. 
 When finely powdered, it is dissolved by boiling chlorhydric acid, 
 with evolution of hydrogen ; if a little nitric acid be added to the 
 chlorhydric, the metal dissolves easily, to form a solution of 
 terchloride of antimony (SbClj). The metal, when in fine pow- 
 der, is also dissolved readily by solutions of the higher sulphides 
 of sodium and potassium, with formation of sulphantimonites and 
 sulphantimoniates. 
 
 347. In spite of the strong tendency of this metal to crystal- 
 lize, it can be obtained in an amorphous form by the electrolysis 
 of concentrated antimonial solutions. This amorphous antimony 
 always contains, however, 5 or 6 per cent, of terchloride of an- 
 timony and a trace of chlorhydric acid; whether these foreign 
 substances are retained mecIjanicaUy, or not, within the mass, is 
 not clear. The amorphous metal has a dark steel-color, a smooth 
 surface, a comparatively soft texture, a lustrous amorphous frac- 
 ture and a specific gravity varying from 5'74 to 5-83. "When 
 gently heated or sharply struck, the amorphous antimony sud- 
 denly manifests a great heat, the temperature rising from 15° to 
 230° and upwards, and fumes of terchloride of antimony are 
 evolved. After undergoing this peculiar change, the metal ap- 
 proximates to the crystalline variety ia structure, density, and 
 color. 
 
 348. Antimony enters into the composition of several very 
 valuable aUoys. Type-metal is an alloy of lead and antimony, 
 containing about 20 per cent, of antimony. Por stereotype 
 plates -^ to Jjy of tin is usually added to this alloy. The com- 
 mon white metaUic alloys used for cheap teapots, spoons, forks, 
 and Hke utensils, are variously compounded of brass, tin, lead, 
 bismuth, and antimony ; for example, a superior kind of pewter 
 is made of 12 parts tin, 1 part antimony, and a small proportion 
 of copper ; Britannia metal is sometimes compounded of' equal 
 parts of brass, antimony, tin, bismuth, and lead. The value of 
 antimony in these alloys depends upon the hardness which it 
 communicates to the compounds, without rendering them incon- 
 veniently brittle. 
 
 With zinc, antimony forms two alloys having a definite crys-' 
 
ANTIMONT AND HTDBOGEN. 269 
 
 tallme character. The alloy containing 43 per cent, of zinc 
 crystallizes in silver-white needle-Kke prisms ; it answers to the 
 formula Sb^Zn^. Th-e alloy containing 33 per cent, of zinc 
 crystallizes in broad plates presenting no similarity to the form 
 of the other alloy ; it answers to the formula SbZn. These 
 alloys, «specially Sb^Znj, decompose hoihng water with evolu- 
 tion of hydrogen. The crystals of these two aUoys are obtained 
 by the method of fusion (§ 194). In each of these crystallized 
 alloys, the crystalline form may be preserved, although the pro- 
 portions of the ingredients may vary considerably from the exact 
 atomic proportions indicated by their formnlse. Thus needles may 
 he obtained in which the actual proportion of antimony present 
 varies from 35-77 per cent, to 57 '24 per cent., the exact atomic 
 proportion being 55'7 per cent. ; and the percentage of antimony 
 in the plates may fall as low as 64-57, or may rise as high as 
 79-42, although 65-07 per cent, is the true atomic proportion. 
 These interesting crystalline alloys strikingly illustrate, therefore, 
 a principle of wide applicability, namely, that a definite crystal- 
 line form is not necessarily a guaranty of an unvarying chemical 
 composition. 
 
 349. Antimony and Hydrogen. — The composition of the ga- 
 seous compound of these two elements is not certainly known, 
 inasmuch as it has never yet been prepared free from admixed 
 hydrogen. When a solution of any salt of antimony is poured 
 into a mixture of zinc and dilute acid which is disraigaging hy- 
 drogen, the antimony compound is decomposed; one portion of 
 the antimony, and sometimes even the whole of it, is deposited 
 upon the zinc, while another portion usually combines with the 
 hydrogen, and assumes the gaseous state. When this compound 
 gas is passed through a solution of nitrate of silver, a precipitate 
 is produced which has been found, to conast of antimonide of 
 silver, SbAgj. Since silver is a metal which replaces hydrogen, 
 atom for atom, it is a natural inference that the gas which has 
 produced this precipitate must have the composition represented 
 by the formula SbH^. This supposition derives strength from 
 the analogous formulae of the well-known gases ammonia, NH^, 
 phosphuretted hydrogen, PHj, and arseniuretted hyrogen, AsH^ 
 
 Antimoniuretted hydrogen is a colorless gaSj inodorpus when 
 
270 
 
 ANTIMONITTEETTED HTDROOEN. 
 
 free from arseniuretted hydrogen, and insoluble in water and 
 alkaline liquids. The gas is decomposed at a red heat into anti- 
 mony and hydrogen ; it bums in the air mth a whitish flame, 
 and gives off a white smoke of teroxide of antimony ; when a 
 bit of cold porcelain is held against a burning jet of the gas, a 
 sooty spot of metallic antimony is deposited on the porcelain.. 
 These reactions resemble those of arseniuretted hydrogen (§ 308). 
 Exp. 136. — Dissolve 0-5 grm. of tartar-emetic (tartrate of antimony 
 and potassium) in about 30 c. c. of water. Add a few centimetres of 
 the solution thus obtained to the bottle of the apparatus represented 
 in Figure 48, in which hydrogen is already being generated from zinc 
 
 Fiff. 48. 
 
 and dilute sulphuric acid. Antunoniuretted hydrogen will be produced, 
 and should be submitted to precisely the same series of operations by 
 which arseniuretted hydrogen was examined. (Exp. 133.) By heat^ 
 ing the hard glass tube at a and b successively, two mirrors of antimony 
 will be obtained ; when the gas reaches the jet without decomposition, 
 the white color of the flame will be observable ; when a cold piece of 
 porcelaia is pressed against the burning jet, spots of antimony will be 
 deposited thereon. Preserve these mirrors and spots. 
 
 Exp. 137. — Compare together the spots obtained on porcelain from 
 arseniuretted hydrogen (Exp. 133) and from antimoniuretted hydrogen 
 (Exp. 136). 1. The arsenical spot has a metallic lustre, and a brown 
 color, when thm ; the stain of antimony has a feeble lustre, and is 
 smoky-black. 2. The arsenical stain disappears readily on the appli- 
 cation of a heat below redness ; the stain of antimony is volatile only 
 at a red heat. On account of the comparative want of volatility which 
 characterizes the antimony deposit, the mirrors of antimony obtained 
 in the glass tube (Exp. 136). are always deposited nearer the heated 
 portion of the tube than the arsenic mirrors are. 3. The arsenical 
 stains may be distinguished, moreover, from the antimonial stains by 
 means of a solution of •' chloride of soda " (a mixture of hypochlorite 
 
TESTnfG POK AimMONT. 271 
 
 of sodium with chloride of sodium, prepared by mixing a solution of 
 chloride of lime with carbonate of sodium in excess, and filtering) ; 
 this solution, which is analogous to, and indeed may he replaced by, 
 a solution of chloride of lime (§ 120), immediately dissolves arsenical 
 spots, but leaves antunonial spots unaffected for a long time. For the 
 application of this test it is convenient to produce some spots on the 
 interior of a concave bit of porcelain. 4. On warming an arsenic 
 spot with a drop or two of aqua regia, and evaporating to dryness, a 
 slight residue of arsenic acid is left, recognizable by its ready solubility 
 in a drop of water; if to this drop of arsenic acid solution a drop of 
 ammonio-nitrate of silver be added, a brick-red turbidity, due to the 
 formation of arseniate of silver, will he produced. This ammonio- 
 nitrate of silver is prepared by adding exactly ammonia enough to a 
 solution of nitrate of silver to redissolve the precipitate which forms at 
 first. The antimony spot treated in the same way yields no such red 
 precipitate. 5. An antimony stain will dissolve readily in a few drops 
 of a solution of sulphydrate of ammonium which has become yellow 
 by keeping ; when such a solution is evaporated to dryness, a bright 
 orange stain remains. The arsenical stain, on the contrary, is not per- 
 ceptibly affected by the yellow sulphydrate of ammonium solution, 
 unless heat is applied. 
 
 JExp. 138. — Connect the tube of hard glass in which two arsenic 
 mirrors were formed, in Exp. 133, with a sulphuretted-hydrogen-ge- 
 nerator (Appendix, § 19), interposing between the tube and the gene- 
 rator a suitable drying-tube or bottle filled with chloride of calcium ; 
 then transmit through the tube a vety slow stream of sulphydric acid 
 gas, and heat the mirrors with a small gas-flame, proceeding from the 
 outer to the inner border of the mirrors, in the direction opposite to that 
 of the gas current. 
 
 Kepeat the same process with the tube containing the antimony 
 mirrors obtained in Exp. 136. 
 
 Yellow tersulphide of arsenic is formed in one case, and orange-red 
 or black tersidphide of antimony in the other. "WTien both metals are 
 present in one mirror, the two sulphides appear side by side, the sul- 
 phide, of arsenic as the more volatile lying invariably beyond the 
 sulphide of antimony. 
 
 Erp. 139. — Transmit through the tube which contains the sulphide 
 of arsenic a stream of dry chlorhydric acid gas (§ 95), without apply- 
 ing heat ; no alteration will take place in the yellow sulphide. 
 
 Transmit the same gas through the tube contairdng the sulphide of 
 antimony ; the sulphide of antimony will immediately disappear. If 
 the gaseous current be then passed through some water, the presence 
 
272 T3B0XIDE OP ANTIMONT. 
 
 of antimony in the water can be demonstrated by means of sulphydric 
 acid (§ 210), 
 
 When both sulphides are prie.sent at once, the chlorhydric acid at- 
 tacks and removes the sulphide of antimony, while the sulphide of 
 arsenic remains behind. A drop or two of ammonia- water, drawn into 
 the tube, wUl then dissolve the sulphide of arsenic. This solubility in 
 aramonia distinguishes the yellow sulphide from sulphur itself, with 
 which it might otherwise be sometimes confounded, 
 
 Antimony and Oxygen. — Antimony forms two well-marked 
 oxides, analogous to the oxides of arsenic, the teroxide or anti- 
 monious acid, S\0^, and the quinquioxjde or aatimonic acid, 
 SbgOj ; a compound of these two oxides Sb^Og, Sb^Oj = SSb^O^, 
 is sometimes recognized as a distinct pxide under the name of the 
 quadroxide. 
 
 350. Teroxide of Antimony. — This oxide occurs as a natural 
 mineral, called White Antimony or Antimony Bloom,. Like 
 arsenious acid, it is dimorphous, crystallizing in rhombic prisms 
 belonging to the trimetrio system, and also in regular octahedrons. 
 The artificial, as well as the native, teroxide is dimorphous. 
 Antimonious oxide is produced when antimony is burnt in the 
 air, or heated to full redness in imperfectly covered crucibles. 
 The easiest mode of getting it is to heat the tersulphide (Sb^S,) 
 with strong chlorhydric acid as long as sulphydric acid continues 
 to escape, and pour the resulting solution of the terchloride 
 (SbClj) into a boUing solution of carbonate of sodium :— ^ 
 2SbCl, -1- SNa^CO, = Sb^, + 6NaCl + 3C0,. 
 If the solution of carbonate of sodium be cold or only warm 
 instead of boiling, a hydrate of the teroxide is precipitated; 
 Sb,03,H,0 = 2SbH0,. 
 
 Antimonious oxide is white or grayish-wHte at ordinary tem- 
 peratures, but turns yellow when heated. It melts below a red 
 heat, and sublimes when raised to a higher temperature in a 
 closed vessel. When heated in the air it is partly converted into 
 antimonic acid. It is readily reduced to the metallic state by 
 ignition with hydrogen, charcoal, or potassium. Teroxide of 
 antimony dissolves sparingly in water, but freely in strong chlor- 
 hydric acid ; it also dissolves in a hot solution of tartaric acid, or 
 of acid tartrate of potassium (cream of tartar). The solutioa 
 
ANTIMONTATE OF ANTIMONY. 273 
 
 obtained in the latter case contains the tartrate of antimony and 
 potassium (C^H^KSbO^), commonly called tartar-emetic. Ordi- 
 nary nitric acid does not dissolve the teroxide ; but fuming nitric 
 acid and fuming sulphuric acid both dissolve it, forming solutions 
 which ultimately deposit shining scales of a nitrate in the one case 
 and a sulphate in the other. 
 
 It is obvious, from these facts, that this oxide of antimony dif- 
 fers from all the oxides which we have heretofore studied, in that 
 it is capable of reacting upon strong acids in such wise as to form 
 salts wherein the antimony plays very much the same part which 
 lead plays in nitrate of lead PhN^Oj (Exp. 42), or calcium in 
 'CaSOj (p. 88). This truth is expressed in technical language 
 when we say that the teroxide of antimony is capable of acting 
 as a base ; the oxides heretofore studied have either been acids, 
 like the oxygen acids of the chlorine and sulphur groups, of 
 nitrogen, phosphorus, and arsenic, or they have been indifferent 
 bodies not inclined to form definite, stable compounds by union 
 with other substances. 
 
 But if, on the one hand, teroxide of antimony is thus some- 
 times a base, on the other it also acts as a feeble acid. The arti- 
 ficial teroxide dissolves readily in solutions of caustic potash and 
 soda, forming very unstable antimonites, which are decomposed 
 by boiling, or mere evaporation. These antimonites are analo- 
 gous to the arsenites ; but it is to be observed that arsenious acid 
 is not only a stronger acid than antimonious, but that, unlike 
 antimonious oxide, it never plays the part of a base. 
 
 351. Antimoniate of Antimony or Quadroxide of Antimony 
 (SbjO J . — This oxide occurs as a native mineral. It may be 
 prepared artificially by heating strongly the quinquioxide (Sb^Oj), 
 or by roasting the teroxide or the tersulphide, or by treating pow- 
 dered antimony with an excess of nitric acid. As thus prepared, 
 it is white, infusible, and unalterable by heat, slightly soluble 
 in water, more soluble in chlorhydric acid, and easily resolvable, 
 by boiling with a solution of cream of tartar, into antimonious 
 oxide and antimonic acid. SSb^O^ = Sb^OjjSb^Oj. The oxide 
 may therefore be regarded as a compound of the two other 
 oxides of antimony ; but it is sometimes considered a distinct 
 oxide on the ground that it yields by fusion with caustic potash, 
 
274 ANTntONIC ACID. 
 
 or carbonate of potassium, an amorphous' saline mass whose 
 composition answers to the formula K^OjSb^Oj. This salt itself, 
 however, if such it be, can be regarded as a mixture of an anti- 
 monite and an antimoniate : — 
 
 2(K,0,Sb,0J = K,0,Sb,03 + K,0,Sb,0,. 
 352. Quinquioxide of Antimony or Antimonic Add (Sb^Oj). — 
 This compound is obtained as a hydrate : — 1. By treating anti- 
 mony with nitric acid, or aqua regia containing an excess of 
 nitric acid. 2. By decomposing the quinquichloride of antimony, 
 SbCL (§ 354), with water :— 
 
 2SbCl, + 5H,0 = Sb,0, + lOHCl. 
 
 3. By precipitating a solution of antimoniate of potassium 
 (KjOjSbjOj + SHjO) with a strong acid. This antimoniate of 
 potassium is obtained by fusing one part of antimony with four 
 parts of nitre, digesting the fused mass with tepid water to re- 
 move nitrate and nitrite of potassium, and boiling the residue for 
 an hour or two with water ; the white insoluble mass of anhy- 
 drous antimoniate is thereby transformed into a soluble hydrate, 
 and the solution, treated with a strong acid, yields a precipitate 
 of hydrated antimonic acid. The hydrated antimoniate of po- 
 tassium itself is a gummy, uncrystaUizable salt. 
 
 The hydrated oxide, obtained by either of these methods, gives 
 off its water at a heat below redness, and yields anhydrous anti- 
 monic acid as a yellowish, tasteless powder, insoluble in water 
 and acids. At a red heat it gives off one-fifth of its oxygen, and 
 is converted into the quadroxide. A boiling solution of caustic 
 potash dissolves the oxide. 
 
 The hydrated oxide obtained by the first and third of the 
 above methods is not identical with that which results from the 
 second process. The product of the first and third methods is 
 called antimonic acid ; the product of the second is called met- 
 antimonic acid, a term derived from a Greek adverb which was 
 used in composition to denote a change of place, condition, or 
 quality. Antimonic acid forms normal salts of the composition 
 M^O,SbjO, and acid salts containing M20,2Sb,0„ while met- 
 antimonic acid forms normal salts containing 2M 0,Sb and 
 acid salts answering to the formula 2M20,2Sb ; the acid 
 
TEECHLORIDB OF ANTIMONY. 275 
 
 metantimoniates are isomeric (§ 312) with the normal anti- 
 moniates. 
 
 The metantimoniates of sodium, potassium, and ammonium are 
 crystalline; the antimoniates of the same bases are gelatinous 
 and uncrystallizable. The antimoniates and metantimoniates 
 of sodium, potassium, and ammonium are the only ones which 
 are readily soluble in water ; all other antimoniates and met- 
 antimoniates are insoluble or sparingly soluble. Normal anti- 
 moniates correspond with normal nitrates : — 
 
 Mp,Sbp, = M,Sb,0, = 2MSb03. 
 M,0,N,0, = M,N,0, = 2MNO3. 
 Normal metantimoniates are analogous to pyrophosphates : — 
 2M,0,Sb,0, = M,Sb,0,. 
 2M,0,P,0, = M,Pp,. 
 
 Antimony and Chlorine. — Antimony forms two chlorides, a 
 terchloride, SbClj, and a quinquichloride, SbClj, both of which 
 have their analogues in the chlorides of phosphorus, already 
 studied ; the terchloride is also comparable with the chloride 
 of arsenic. The metal unites directly with chlorine on contact 
 (Exp. 54), and the two chlorides are bodies of considerable sta- 
 bility. 
 
 353. Terchloride of Antimony (SbClj). — This chloride is 
 formed when chlorine gas is passed slowly through a tube con- 
 taiaing antimony in large excess. It may. also be prepared by 
 distilling 3 parts of antimony with 8 parts of corrosive sublimate 
 (chloride of mercury), or 2 parts of the tersulphide of antimony 
 with 4'6 parts of corrosive sublimate : — 
 
 2Sb-t-3HgCl,=2SbCl, -I- 3Hg; 8h,8, + 3HgCl,=2SbCl3 + 3HgS. 
 
 The easiest method of preparing this chloride is to dissolve the 
 tersulphide of antimony in strong, hot chlorhydric acid, or me- 
 tallic antimony in the same acid, to which a little nitric acid has 
 been added ; the resulting liquid, in either case, after evapora- 
 tion to an oily consistency, should be distilled. 
 
 At the ordinary temperature, terchloride of antimony is a 
 translucent yellowish substance of fatty consistency, whence its 
 popular name, butter of antimony. It melts at 72° and boils at 
 about 200°, fumes slightly in the air, is deliquescent and highly 
 
 i2 
 
276 QTriNaiTICHLOErDE OF ANTIMONT. 
 
 corrosive. When thrown into water, it is decomposed into chlor- 
 hydric acid and teroxide of antimony, which, however, remains 
 united with a portion of the chloride, forming a white powder 
 which contains antimony, chlorine, and oxygen, but is somewhat 
 variable in composition. This white precipitate is redissolved 
 by excess of chlorhydric, acid, and the solution thus obtained is 
 the most convenient that can be used for exhibiting the reactions 
 of antimony. The addition of tartaric acid to this solution pre- 
 vents its decomposition by water. 
 
 Exp. 140. — ^In a flask of about 300 c. c. capacity, heat gently 0*5 
 grm. of finely powdered antimony with 3(X c. c. of strong chlorhydric 
 acid, to which 10 drops of nitric acid have been added. When com- 
 plete solution has been efiected, pour a little of the chloride into water, 
 to demonstrate the decomposition just referred to. Evaporate the rest 
 of the solution to the consistency of a thick syrup ; it is the butter of 
 antimony. 
 
 The anhydrous terchloride combines with the chlorides of 
 sodium, potassium, and ammonium, and certain other chlorides, 
 to produce crystalline saline compounds, analogous in composi- 
 tion to those oxygen and sulphur compounds to which the term 
 salt is commonly applied. 
 
 354. Quinquicliloride of Antimony (SbCL). — This compound 
 is formed, with briUiant combustion, when finely powdered anti- 
 mony is thrown into chlorine gas (Exp. 54). It may also be 
 prepared by passing dry chlorine over warm powdered antimony, 
 or over the terchloride. 
 
 Kvp. 141. — Fill a hard-glass tube, No. 2, 150 cm. long with 
 coarsely powdered antimony, and fit one end of the tube so charged 
 into a tubulature of a two-necked glass receiver, the other neck of 
 which is connected with a source of dry chlorine. Support the long 
 tube at an angle of 10° or 15° with the table, so that its open end shall 
 be some 20 cm. higher than the end which enters the receiver. 
 Keeping the tube warm throughout its whole extent, pass chlorine 
 slowly and continuously into the receiver. Combination takes place 
 in the tube and the product flows back into the receiver, where it re- 
 mains in contact with chlorine ; the long layer of antimony prevents 
 the escape of any free chlorine. Preserve the product in a glass- 
 stoppered bottle. 
 
 The quinquichloride is a colorless, or yellowish liquid, which 
 is very volatUe and emits suffocating fumes. Water in small 
 
TEBSTJLPHIDB OP ANTIMONT. 271' 
 
 proportion forms with, it white deliquescent crystals, but ia large 
 quantity water decomposes the chloride into chlorhydric and 
 antimonic acids. 
 
 355. We are familiar with nitric acid (N^Oj) as an oxidizing 
 agent, as a substance which readily yields some of its oxygen to 
 other bodies with which it is brought in contact ; in a perfectly 
 analogous sense, the quinquichloride of antimony and its analogue 
 the quinquichloride of phosphorus, may be said to be chloridizing 
 agents of great power, for they readily impart chlorine to other 
 substances. These two chlorides are much used in organic che- 
 mistry for preparing chlorine compounds ; thus, for example, the 
 compound of carbon and hydrogen called ethylene or olefiant gas, 
 CjH^, is converted by passing through boiling quinquichloride of 
 antimony into an oily bichloride, C^H^Cl^, known as Dutch liquid. 
 The quinquichloride acts as a carrier of free chlorine, being itself 
 reduced to the terchloride. 
 
 Terhromide and Teriodide of Antimony (SbBr^ and SbT,). — It 
 is enough to mention the existence of these compounds, formed 
 by the direct union of the elements. 
 
 Antimony and Sulphur. — Antimony forms two sulphides, Sb^S, 
 and SbjSj, corresponding to antimonious oxide and antimonic 
 acid, and possibly an intermediate sulphide corresponding to the 
 quadroxide. 
 
 356. Tersulphide of Antimony (Sb^Sj). — This compound exists 
 in the crystaJline and in the amorphous state. Crystallized ter- 
 sulphide of antimony is a natural mineral called grey antimony or 
 antimony-glance. It is the source of aU the antimony and anti- 
 mony compounds of commerce. The mineral has a lead-grey 
 color and a metallic lustre ; it is friable and very fusible, melting 
 even in the flame of a candle. At a white heat it may be distUled 
 unchanged in closed vessels, but by roasting in the open air it is 
 converted into a fusible mixture of teroxide and tersulphide of 
 antimony. This oxysulphide, after it has been fused, constitutes 
 the commercial 5'Zas« of antimx)ny, which contains about 8 parts 
 of the teroxide to 1 part of the tersulphide ; the greater the pro- 
 portion of sulphide, the darker the tint of the glass. 
 
 The native tersulphide is seldom pure, being generally con- 
 taminated with lead, copper, iron, and arsenic. To obtain pure 
 
•278 
 
 TERSTTLPHIDE OF ANTIMONT. 
 
 crystallized tersulphide of antimony, it is best to prepare it arti- 
 ficially by fusing pure metallic antimony with sulpbur in the 
 required proportions by weight. The materials must be finely 
 powdered and intimately mixed, and the mixture thrown by 
 smaU portions into a heated crucible. The reactions of crystal- 
 lized sulphide of antimony are the same as those of the amor- 
 phous sulphide, to be presently described ; but they take place less 
 quickly, on account of the greater cohesion of the mass. 
 
 Amorphous tersulphide of antimony can be procured by several 
 processes, from which we may select the two simplest : — 1. The 
 native grey tersulphide is changed into the amorphous variety 
 by keeping it in the fused state for a considerable time, and then 
 cooling it very suddenly by throwing the vessel in which it has 
 been melted into a large quantity of cold water. The product 
 is an amorphous mass, having a conehoidal fracture, and a less 
 specific gravity, but a greater hardness than that of the crystal- 
 line variety. Its color, in thin pieces, is hyacinth -red ; in the state 
 of powder, orange-brown. 2. When sulphydric acid gas is passed 
 into an acidulated solution of an antimony-salt (that of tartar- 
 emetic for example), a bright orange-red precipitate of a hydrated 
 tersulphide of antimony is formed, which may be rendered anhy- 
 drous at a moderate heat without losing its red color. 
 
 U.rp. 142. — Dissolve 2 grms. of tartar emetic in 50 c. c. of water 
 and add to the solution a few drops of acetic acid ; pass a slow current 
 of sulphuretted hydrogen, from a self-regulating generator (Appendix, 
 § 19), through this solution for ten minutes. The precipitate is the 
 hydrated tersulphide of antimony. Collect this precipitate upon a 
 filter and wash it. 
 
 JSxp. 143. — Pour a dilute cold'solution of caustic soda upon the 
 washed precipitate of the last experiment as it lies upon the filter, and 
 collect the filtrate in a test-tube; if the whole precipitate does not 
 shortly redissolve, pour the filtrate a second time upon the undissolved 
 precipitate in the filter, or use an additional quantity of soda^lye, if 
 necessary. There is produced a mixture of stdphantimonite of sodium 
 and teroxide of antimony, which is soluble in the excess of soda-lye. 
 2Sb2S3 + 6NaH0 = SNa^SjSb^S, + Sb^O, + SH^O. 
 
 Uxp. 144. — ^Pour the clear alkaline solution, obtained in the last 
 experiment, into two or three times its hulk of dilute chlorhydric acid. 
 The whole of the antimony wiU he thrown down ag-ain as tersulphide, 
 
BED ST7I.PHIDE OF ANTIMONY. 279 
 
 without any evolution of sulphuretted hydrogen, because the gas 
 evolved from the sulphantimonite is exactly absorbed by the dissolved 
 teroxide : — 
 
 SNa^S^Sb^Sj + 6HC1 = 6NaCl + Sb^Sa + SH^S. 
 SbjOa + SHjS = SbsSg + SHfi. 
 
 When hydrated amorphous tersulphide of antimony is boiled 
 ■with a solution of carbonate of sodium, it is dissolved ; the filtered 
 liquid, on cooling, deposits a reddish-brown substance, formerly 
 much used in medicine, and known as kermes mineral. This sub- 
 stance is not a definite compound, but is a variable mixture of 
 tersulphide and teroxide of antimony, the latter being combined 
 with a small portion of the alkali. Minute crystals of teroxide 
 of antimony have been recognized in this mixture by microscopic 
 examination. A solution of cream of tartar will dissolve out the 
 teroxide, leaving the tersulphide. On acidulating the cold filtered 
 liquid, after the deposition of the kermes, with chlorhydric acid, 
 a particularly bright orange precipitate of sulphide of antimony, 
 known ^s the golden sulpMde, is precipitated. Artificial sulphide 
 of antimony can, indeed, be precipitated of almost any color be- 
 tween a Kght orange and a blackish brown. A vermilion-red 
 sulphide has found some applications as a paint. 
 
 Exp. 145. — Place in a poicelaiu dish 10 grms. of a solution of 
 chloride of antimony of about 1'35 specific gravity; add to this chlo- 
 ride a cold solution of hjrposulphite of sodium made By dissolving 15 
 grms. of the salt in 30 c. c. of water ; heat the dish very slowly, and 
 stir its contents continually so long as any precipitate separates from 
 the liquid. The sulphide of antimony is thrown down of a brilliant 
 red color. The color of the precipitate is darker in proportion as the 
 temperature of the mixture is higher ; when, therefore, a fine red is 
 produced, the lamp may be withdrawn, in order to prevent the color 
 from growing brown. The precipitate is collected on a filter, drained 
 thoroughly, and then washed, first with dilute acetic acid and subse- 
 quently with water. 
 
 Sulphantimonite solutions, similar to those prepared in the wet 
 way, may be obtained by fusing tersulphide of antimony with dry 
 caustic soda or potash, or with the carbonates of sodium or potas- 
 sium, and boiling the residue with water. During the exposure 
 to air of hot sulphantimonite solutions, a process of oxidation 
 takes place, whereby the sulphur set free from one portion of 
 
280 aTjiNauisTJLPHiDE or antimony. 
 
 the salt converts another portion into the state oi sidphantimoniate, 
 so that on aoidillation some quinquisnlphide of antimony is pre- 
 cipitated along with the tersnlphide. 
 
 Like the tersnlphide of arsenic, the tersnlphide of antimony is 
 a sulphur-acid which unites with basic metallic sulphides to form 
 sulphur-salts. The artificial sulphantimonites of the alkalies 
 have been alluded to above ; there are many natural minerals of 
 analogous composition ; among such may be mentioned Miargyrite, 
 Ag^S,Sb,S3, Boumonite, 2Pb,S,Cu,S,Sb,S3, and Berthierite, 3Fe8, 
 2Sb,S3. 
 
 357. Quinqtii sulphide of Antimony (Sb^Sj). — This compound, 
 which is not native, is made by passing sulphuretted hydrogen 
 through qxdnquichloride of antimony dissolved in tartaric acid. 
 It may also be prepared by acidulating the solution of the sulph- 
 antimoniate of sodium, 3Na2S,Sb2S5 : — 
 
 3Na,S,Sb,S, -I- 6HC1 = GNaCl -|- Sb.S^ + 3H^S. 
 The quinquisulphide is an orange-yellow, anhydrous, amorphous 
 powder, and is chiefly remarkable for the facility with which it 
 unites with the sulphides of the metals to form sulphantimoniates ; 
 on this account this sulphide is often called sulphantimonic acid. 
 It is readily soluble in the sulphides, sulphydrates, and hydrated 
 oxides of sodium, potassium, and ammonium. 
 
 The sulphantimoniates have generally the composition repre- 
 sented by the general formula 3M2S,Sb2Sj=2MgSbS^, analogous 
 to that of the tribasic phosphates 3M,0,P,Og=2M,PO^. The 
 sulphantimoniates of sodium, potassium, and ammonium are very 
 soluble in water, and erystaUize with facility ; those of the heavy 
 metals are insoluble. The latter are precipitated by adding solu- 
 tions of metallic salts to a solution of the sulphantimoniate of 
 sodium, keeping the latter in excess. The sodium salt may be 
 prepared as follows : — 
 
 In a wide-mouthed bottle, or other vessel which can be closed, mix 
 thoroughly 22 grms. of elutriated tersulphide of antimony, 26 grms. 
 of crystallized carbonate of sodium, 2 grms. of flowers of sulphur, 10 
 grms. of quicklime, slaked after weighing, and 40 c. c. of water. Let 
 the mixture digest at the ordinary temperatm-e for 24 hours, with 
 frequent fetirring ; then filter the liquid, wash the residue several times 
 with water, and evaporate the filtrate and the wash-water in a poroe- 
 
BISMUTH. 281 
 
 lain dish or clean iron pan, until a sample yields crystals on cooling. The 
 formation of the salt is accelerated by boiling. The whole is then left 
 to cool ; the deposited crystals are washed two or three times with 
 cold water and dried under a bell-jar over a dish of an absorbent like 
 quicklime or oil of vitriol. The salt is sulphantimoniate of sodium 
 NasSbS^+OHjO ; it forms transparent, colorless or pale yellow, regular 
 tetrahedrons. 
 
 CHAPTEE XIX. 
 
 B I S M T7 T H T HE NITBOSEN GROTTP. 
 
 358. The metal bismuth is found chiefly in the metallic state, 
 but also occurs in combination with sulphur, oxygen, and tellu- 
 rium. It is prepared for the arts almost exclusively from native 
 bismuth. The process of extracting the metal from the gneiss 
 and clay-slate in which it generally occurs is very simple, the 
 mineral being merely heated in closed iron tubes, inclined in such 
 a, manner that the melted bismuth runs down into earthen pots, 
 which are heated sufficiently to keep the metal in a state of fusion. 
 It is then ladled out and run into moulds. The impure metal, 
 which often contains sulphur, arsenic, copper, nickel, and iron, 
 may be purified by melting it two or three times with about ^ 
 its weight of nitre. 
 
 Bismuth is a tolerably hard, brittle metal, of a grayish-white 
 color with a reddish tinge. When pure, it crystallizes more 
 readily than any other metal ; by the method of fusion (§ 188) 
 it may be obtained in most beautiful crystals, made highly iri- 
 descent by the thin film of oxide which forms on their surfaces 
 while they are stUl hot ; these crystals look like cubes, but are 
 really rhombohedrons. Bismuth, like phosphorus, arsenic, and 
 antimony, is dimorphous, presenting forms both of the mono- 
 metric and hexagonal systems. The metal melts at 264° and 
 expands about -^ in solidifying; hence its specific gravity is 
 greater in the liquid than in the solid state. When the metal is 
 subjected to strong pressure, its specific gravity, normally 9'83, 
 
282 TEEOXIDE OF BISMUTH. 
 
 has been said to become less. At a high temperature bismuth 
 may be distilled. Of all metals it exhibits in the highest degree 
 the phenomena of diamagnetism. Its atomic weight is 210. 
 
 Exposed to dry or moist air the metal does not alter ; but ■when 
 exposed to the combined action of air and water, it is super- 
 ficially oxidized. When heated in the air, it bums with a bluish 
 flame, forming yellow fumes. Strong chlorhydric acid acts on it 
 with difficulty ; sulphuric acid attacks it only when hot and con- 
 centrated ; nitric acid attacks it immediately, and effects complete 
 solution, with formation of nitrate of bismuth and evolution of 
 nitric oxide. 
 
 359. Bismuth promotes the fusibility of metals with which it 
 is alloyed to an extraordinary extent. The most remarkable 
 alloy of bismuth is that known as " fusible metal." When com- 
 posed of 1 part of lead, 1 part of tin, and 2 parts of bismuth, this 
 alloy melts at 93°-75. Solid fusible metal, like liquid water, 
 undergoes an anomalous contraction by heat. It expands regu- 
 larly from 0° to 35°, then contracts gradually as the temperature 
 rises to 6-5°, at which point it is less bulky than at 0°, again 
 expands rapidly to 80°, and beyond that temperature continues 
 expanding regularly up to its melting-point. On account of this 
 property of expanding as it cools while stiU in the soft state, the 
 aUoy is much used for taking impressions from dies ; the finest 
 and faintest lines are reproduced with great accuracy. It is ob- 
 vious that an alloy possessing such properties must be something 
 more than a mere mixture of the constituent metals. 
 
 No compound of bismuth and hydrogen is as yet known. 
 
 Bismuth and Oxygen — Bismuth forms two principal oxides, 
 a teroxide (BiPg) and an acid oxide (Bi^OJ ; besides these, there 
 is an intermediate oxide (B\OJ which may be represented as a 
 compound of the other two Bi^Oj, 'Bifi^=2'BiJJ^. 
 
 360. Teroxide of Bismuth (BijOJ. — This oxide is formed when 
 the metal is roasted in the air, but is best obtained by gently 
 igniting the nitrate or subnitrate. It is a pale-yeUow, insoluble 
 powder, which melts at a red heat, and is easily reduced to the 
 metallic state by heating it with charcoal. A white hydrate of 
 this oxide, 'Siif),,'S.p=2'&i^0^, may be precipitated from a salt 
 of bismuth by an excess of ammonia. Teroxide of bismuth com- 
 
BISMTJTHIC ACID. 283 
 
 bines with acids to form the bismuth salts ; in the normal salts 
 one atom of bismuth replaces three atoms of hydrogen, thus : — 
 
 Bi,03 + 3(H,N,0,) = 3H,0 + Bi,3(N,0J. 
 Basic salts of bismuth are also known, in which a larger propor- 
 tion of bismuth is present. Some of the normal salts crystallize 
 well from acid solutions, but they cannot exist in solution unless 
 an excess of acid is present. On diluting solutions of the nor- 
 mal salts with water, insoluble basic salts are precipitated ; this 
 reaction recaUs the behavior of antimony solutions. The nitrate 
 of bismuth, Bi2 3(N20j,) + 9Hp, is the commonest soluble salt of 
 bismuth; it is procured by dissolving the metal in nitric acid. 
 To the basic nitrate, which is precipitated when water is added 
 to the solution of the normal nitrate, the formula SBiJ)^,4'Nfi^ 
 -l-QH^O has been assigned. Bismuth salts are heavy compounds, 
 which are colorless unless the acid be colored ; they are poisonous 
 in large doses. 
 
 361. Quinquioxide of Bismuth, or Bismuthic Acid (Bi^Oj). — 
 When chlorine gas is passed through a concentrated solution of 
 potash holding teroxide of bismuth in suspension, a blood-red 
 solution is obtained, from which there soon separates a red pre- 
 cipitate ; this substance is a mixture of hydrated bismuthic acid 
 and teroxide of bismuth. Cold dilute nitric acid dissolves the 
 oxide, but does not attack the acid. The hydrated acid gives up 
 its water at a temperature of 130°, and the anhydrous quinqui- 
 oxide remains as a brown powder, which, in contact with acids, 
 parts very readily with a portion of its oxygen and falls back to 
 the state of teroxide. The anhydrous quinquioxide may be also 
 converted by a gentle heat into the intermediate oxide Bi^O^. 
 Bismuthic acid combines with caustic soda and potash, but the 
 compounds are decomposed by mere washing. The bismuthates 
 are little known, and are of interest only in so far as they go to 
 show the feeble acid character of the quinquioxide. 
 
 362. Ter chloride of Bismuth (Bid J. — ^This compound maybe 
 obtained by heating bismuth in chlorine, or by mixing the metal 
 in fine powder with twice its weight of corrosive sublimate (chlo- 
 ride of mercury) and distilling. The same substance is produced 
 when bismuth is dissolved in aqua regia, and the excess of acid 
 evaporated. It is a very fusible, volatile, deKquescent body, 
 
284 CHLORIDE OF BISMUTH. 
 
 which, was called butter of bismuth, from its resemblance to the 
 butter of antimony, long before the relationship now established 
 between bismuth and antimony had been recognized. The terchlo- 
 ride is decomposed by water into ohlorhydric acid, which dissolves 
 a portion of the chloride, and a precipitate containing bismuth, 
 chlorine, and oxygen, and called oxyehloride of bismuth. 
 
 3BiCl3 + 3H,0 = 6HC1 + 'B,\C\% 
 The same oxyehloride is precipitated when a solution of nitrate 
 of bismuth is poured into a solution of common salt. It is used 
 as a pigment, and is known as " pearl-white." It may be distin- 
 guished from the analogous oxyehloride of antimony by the fact 
 that it is insoluble in tartaric acid and in potash, both of which 
 dissolve the antimony compound. Terchloride of bismuth forms 
 crystallizable double salts with the chlorides of sodium, potas- 
 sium, and ammonium. These chlorine salts are analogous in 
 composition to, and isomorphous with, the corresponding double 
 chlorides of antimony. 
 
 363. Tersulphide of Bismuth (Bi^Sj). — Bismuth glance, a 
 somewhat rare mineral which occurs in acioular prisms isomor- 
 phous with the native tersulphide of antimony, is a tersulphide 
 of bismuth. The same compound may be formed artificially by 
 fusing the pulverized metal vrith one-third its weight of sulphur. 
 Heated in close vessels, the sulphide evolves sulphur ; heated 
 with access of air, it forms teroxide of bismuth and sulphurous 
 acid. The tersulphide is also obtained as a brown-black preci- 
 pitate when sulphuretted hydrogen is passed through a solution 
 of a bismuth salt. 
 
 Exp. 146. — Dissolve 0"5 gnn. of finely powdered bismuth in aqua 
 regia, in a small flask ; the aqua regia should be added by small por- 
 tions at a time, so as to avoid an unnecessary excess of acid, and the 
 mixture should he gently heated. When complete solution has been 
 effected, pour one or two drops of the acid solution into a tumbler iull 
 of water, and observe the precipitation of white oxyehloride of bismuth 
 (§ 362). To the remainder of the solution add water, drop by drop, 
 with constant stirring, until a slight cloudiness appears ; add a drop of 
 ohlorhydric acid to clear the solution, and through the slightly acid 
 liquor, thus obtained, pass a slow stream of sulphuretted hydrogen 
 until the solution has become so thoroughly charged with this gas 
 that it oontiaues to smell of sulphuretted hydrogen even after it has 
 
JTHE NITROGEN GEOTTP. 285 
 
 been removed from the soxirce of the gas. Filter the brownish-black 
 precipitate of tersulphide of bismuth and wash it with water upon the 
 filter; scrape off a portion of the precipitate from the filter, with a 
 smooth slip of wood, and place it in a teat-tube together with a few 
 drops of a solution of caustic soda ; it wiU not dissolve. Test another 
 portion of the precipitate in the same way with a solution of sulphy- 
 drate of ammonium; it will not dissolve. The last two reactions 
 establish distinct differences between the sulphides of bismuth and 
 antimony, in addition to their difference of color. Again filter, and 
 wash the undissolved sulphide and heat a little of it moderately on 
 platinum foil over the gas-lamp ; sulphurous acid will be given off, 
 and the oxide of bismuth remains ; this oxide readily melts to darlj- 
 yellow globules. 
 
 364. The Nitrogen Group of Elements. — The five elements, 
 nitrogen, phosphorus, arsenic, antimony, and bismuth, form a 
 well-marked natural group of elements. In the first place, the 
 elements themselves exhibit a definite gradation of properties ; 
 and secondly, the analogy in composition and properties, mani- 
 fested by the similar compounds of the five elements, is most 
 striking and complete. 
 
 Nitrogen is a gas, phosphorus a solid whose specific gravity 
 varies from 1'8 to 2-2, arsenic has the specific gravity of 5-6, 
 antimony of 6'7, while that of bismuth rises to 9'8. The metallic 
 character is most decided in bismuth, is somewhat less marked in 
 antimony, is doubtful in arsenic, and almost vanishes in phos- 
 phorus. All four of these elements are dimorphous, presenting 
 forms both of the monometric and hexagonal systems. The series 
 of corresponding hydrides, oxides, chlorides, and sulphides which 
 the elements of this group form are very perfect ; they prove the 
 general chemical likeness of the five elements : — 
 
 Hydrides. 
 
 Oxides. 
 
 Oxides. 
 
 Oxides. 
 
 CTilorides. 
 
 Sulphides. 
 
 NH3 
 
 N.O3 
 
 N.O. 
 
 N.O, 
 
 NCl3(?) 
 
 ' ^A 
 
 PH3 
 
 P.Oa 
 
 Sb,0, 
 
 P.O, 
 
 PCI3 
 
 As,S3 
 
 AsH, 
 
 As.O, 
 
 Bi.O, 
 
 As,0, 
 
 ASCI3 
 
 Sb,83 
 
 SbH, 
 
 Sb.O, 
 
 
 Sb,0, 
 
 SbCl, 
 
 Bi.S3 
 
 
 Bi.03 
 
 
 Bi.O, 
 
 BiCl3 
 
 PCI, 
 SbCL 
 
 ^A 
 
 A8,S, 
 
286 THE NITKOGBN ftEOTTP. 
 
 The first four members of the group form gaseous terhydrides, 
 in 'which three volumes of hydrogen and one atom of a nitrogen- 
 group element are combined to form two volumes of the com- 
 pound gas. We have already spoken of the similarity of che- 
 mical composition, and the gradation of properties manifested by 
 these four hydrides. Ammonia is a powerful base, and requires 
 a high temperature for its decomposition ; phosphuretted hydro- 
 gen is a very feeble base, whUe the basic character is not per- 
 ceptible in arseniuretted and antimoniuretted hydrogen. Each 
 of the last three hydrides is decomposed by simple exposure to 
 heat, phosphuretted hydrogen requiring the highest temperature, 
 arseniuretted hydrogen decomposing at a lower, and antimoni- 
 uretted hydrogen at a still lower degree of heat. The affinity of 
 bismuth for hydrogen is so feeble that it does not appear to form 
 a hydride. 
 
 The teroxides also show a gradation of physical and chemical 
 qualities. Teroxide of nitrogen (nitrous acid) is a highly vola- 
 tile liquid, that of phosphorus (phosphorous acid) a very volatile 
 solid, that of arsenic a less volatile soHd, that of antimony a 
 solid volatile only at a fuU red heat, and that of bismuth a solid 
 which requires an extremely high temperature for its volatiliza- 
 tion. The teroxides of nitrogen and phosphorus form with water 
 strongly acid liquids ; teroxide of arsenic is but a feeble acid ; 
 teroxide of antimony is sometimes an acid and sometimes a base, 
 while teroxide of bismuth is a decided base. Arsenious and 
 antimonious acids are isodimorphous. The series of quinqui- 
 oxides also shows a very marked gradation of chemical energy, 
 especially when the compounds which they form with the ele- 
 ments of water are considered. Nitric acid is a powerful acid 
 of intense energy; phosphoric acid is stiU. a strong acid, but 
 much less incisive than nitric acid ; arsenic acid has the corrosive 
 properties generally attributed to acids, but it is chemically a 
 rather less vigorous compound than phosphoric acid. The phos- 
 phates and arseniates are, however, isomorphous, and the two 
 acids are very much alike. In the quinquioxide of antimony 
 the acid character becomes comparatively indistinct ; and in the 
 so-called bismuthic acid little remains but the name. 
 
 The terchloride of nitrogen has hardly been examined, on 
 
CARBON. 287 
 
 account of its extreme instability. The other four terchlorides 
 are all volatile substances of analogous composition, since three 
 volumes of chlorine and one atom of the nitrogen-group element 
 unite to form two volumes of the compound vapor. The boiling- 
 points of the terchlorides of phosphorus, arsenic, and antimony 
 are 74°, 132°, and 223° respectively, while that of the terchlo- 
 ride of bismuth is considerably higher still. AU fouj terchlorides 
 are decomposed by an excess of water. 
 
 The tersulphides of antimony and bismuth are isomorphous. 
 
 The elements of this group do not form many combinations 
 among themselves. They combine with hydrogen, metals and 
 compound radicals which replace hydrogen atom for atom, and 
 with the members of the chlorine group, by preference, in the 
 proportion of 1 atom to 3 ; they also combine with oxygen and 
 the members of the sulphur group, by preference, in the propor- 
 tions of 2 atoms to 3, or 2 atoms to 5. 
 
 When the qualities of the corresponding compounds which the 
 members of the nitrogen group form with other elements are duly 
 taken into account, it will be apparent that the relative chemical 
 power of each element of the group may be inferred from its po- 
 sition in the series of elements : — 
 
 N = 14, P = 31, As = 75, Sb = 122, Bi = 210. 
 The chemical energy of these five elements, broadly considered, 
 follows the opposite order of their atomic weights. 
 
 CHAPTER XX. 
 
 C A Ji B N. 
 
 365. Carbon is an extremely important and a very abundant 
 element. AU organic substances, all things which have life, 
 contain it. Large quantities of it occur in the mineral kingdom 
 as well, both in the free state and in combination with oxygen 
 and with other elements. The various forms of coal, graphite, 
 petroleum, asphaltum, and all the different varieties of limestone, 
 
288 THE IHREB TAEIETIES OF CAEBON. 
 
 chalk, marble, coral, and sea shells contain it in large proportion. 
 It is found also in the atmosphere and in the waters of the globe, 
 and though existing therein in comparatively small proportion, it 
 is an ingredient not less essential than either of their other con- 
 stituents for the maintenance of the actual balance of orgauie 
 nature. All vegetable life is directly dependent upon the pre- 
 sence of the compound of carbon (carbonic acid) which exists in 
 the atmosphere. 
 
 366. Three distinct allotropie modifications of carbon are dis- 
 tinguished, namely: — 1. The diamond ; 2. Plumbago or graphite ; 
 and 3. Ordinary charcoal or lampblack. There are many sub- 
 varieties of the modification last named ; but their peculiarities 
 appear to depend chiefly upon physical conditions of aggregation, 
 whereas each of the three principal varieties of carbon above enu- 
 merated is really different from the other two in chemical quality 
 or nature. 
 
 367. The element carbon, in each of its modifications, is an in- 
 fusible, non-volatOe solid devoid of taste and smeU. But the 
 several modifications diifer among themselves in color, hardness, 
 lustre, specific gravity, behavior towards chemical agents, power 
 of conducting heat and electricity, and in various other respects. 
 All the varieties of carbon, however, agree in this, that on being 
 strongly heated in presence of oxygen they unite with it and 
 form carbonic acid (CO^) ; but in the comparative readiness with 
 which this result is attained great differences are noticeable in 
 the different varieties. 
 
 Lampblack and charcoal, as is well known, readily combine 
 with oxygen at the temperature of an ordinary fire ; they burn 
 easily in the air. But graphite burns, so slowly in air that it is 
 used for making the crucibles in which the most refractory metals 
 are melted. (See Appendix, § 26.) On being heated to a very 
 high temperature, however, in oxygen gas, graphite slowly under- 
 goes combustion ; and the same remark is true of the diamond. 
 Both graphite and diamond can be consumed by nascent oxygen, 
 as when heated in the condition of fine powder with a mixture 
 of bichromate of potassium (a substance rich in oxygen) and sul- 
 phuric acid. They can be oxidized also by heating them with 
 nitrate or with chlorate of potassium. 
 
DIAMOND. 289 
 
 368. Diamond. — Of this first variety of carbon, little need here 
 be said. The physical properties which render it so valuable, its 
 high refractive power as regards light, and its extreme hardness, 
 are familiar to all. It the hardest known substance, being capable 
 of scratching aU other substances ; the name diamond is a mere 
 corruption of the word adamant. 
 
 Of the chemistry of the diamond very little is known. It con- 
 sists of pure or nearly pure carbon, crystallized in octahedrons 
 and other forms of the first or regular system ; its specific gravity 
 is about 3-55, and its specific heat 04469. It conducts electri- 
 city and heat but slowly ; and yet it conducts heat so much 
 better than ^lass that this property is sometimes made use of 
 as a test to distinguish false from real diamonds. Its refractive 
 power on light, as compared with that of glass or rock-crystal, is 
 as 2-47 to 1-6. 
 
 Chemists are as yet unable to prepare this variety of carbon 
 artificially ; the only source of it is the natural mineral. It was 
 thought, at one time, that if there could but be devised means of 
 fusing carbon, crystals of the diamond modification might pos- 
 sibly separate out from the molten liquid as it ■ cooled ; but, at 
 present, aU the evidence goes to show that at high temperatures, 
 the second modification of carbon (namely, graphite), and not 
 diamond, is produced. If a diamond be heated white-hot between 
 the charcoal points of a powerful galvanic battery, it softens, and 
 swells up, and, after cooUng, there is found a hard black brittle 
 mass like the coke obtained by heating bituminous coal. So, too, 
 carbon is soluble in melted iron, and a portion of it crystallizes 
 out as the iron becomes cold, but the crystals thus obtained are 
 crystals of graphite and not of diamond. "We can, therefore, only 
 surmise that diamonds crystallize at a low temperature from some 
 unknown solvent of carbon, or, with greater probability, that 
 when carbon is separated by the decomposition of some one of its 
 compounds it is left in the diamond condition. 
 
 The diamond is not attacked by the strongest acids or alkalies, 
 not even by fluorhydric acid ; nor is it acted upon by any of the 
 non-metallic elements, with the exception of oxygen at high 
 temperatures. At the ordinary temperature of the air, diamond 
 undergoes no appreciable change during the lapse of centuries ; 
 
290 GEAPHIIE. 
 
 it appears to be well nigh indestructible, in tbe ordinary sense of 
 the term. Out of contact with the air, or in an atmosphere which 
 has no chemical action upon it, it suffers no alteration at the 
 highest furnace heat. 
 
 369. Graphite or Plumbago, sometimes called " black-lead," is 
 familiarly known as the material of common " lead pencils.'' It 
 is found as a mineral in nature in various localities. It occurs 
 both in the form of crystals (six-sided tables belonging to the 
 hexagonal system) and in the amorphous, massive state. In both 
 forms it is always opaque, of a black or lead-gray color and me- 
 tallic lustre ; its specific gravity varies from 1-8 to 2-1 ; its specific 
 heat is 0-201. 
 
 It conducts electricity nearlj' as well as the metals, and is, on 
 this account, much used for coating surfaces of wood, wax, plaster, 
 and other non-conducting materials so as to render them capable 
 of conducting the galvanic current and so of receiving a metallic 
 film such as is deposited from solutions of the metals when sub- 
 jected to the action of the galvanic current ; it is an important 
 material in the art of electro-metallurgy. The lustre and con- 
 ducting-power of graphite go far to justify the term which has 
 been often applied to it, metallic carbon. 
 
 370. Graphite is very friable ; when rubbed upon paper it 
 leaves a black shining mark, whence its use for pencils. Amor- 
 phous graphite is much more friable than the crystalline variety ; 
 it makes a blacker mark upon paper, and is consequently pre- 
 ferred for the manufacture of pencils ; it is, in fact, so soft and 
 unctuous to the touch that it is often used as a lubricant for di- 
 minishing the friction of machinery. But in spite of aJI this the 
 particles of which the masses of graphite are composed are ex- 
 tremely hard ; they rapidly wear out the saws employed to cut 
 these masses. By powerful pressure the dust of plumbago can be 
 forced into the condition of a coherent solid similar to the native 
 mineral. 
 
 In the air, at ordinary temperatures, graphite undergoes no 
 change ; hence its use for covering iron articles to prevent then- 
 rusting. By virtue of its greasy, adhesive quality, it is easy to 
 cover iron with a thin, lustrous layer or varnish of it ; the com- 
 mon stove-poUshes, for example, are composed of powdered gra- 
 
PROPERTIES OF eRAPHITE. 291 
 
 pMte. Even at very Mgli temperatures it is scarcely at all 
 oxidized by the air; it is, moreover, altogether infusible.; hence it 
 is usefully applied in the manufacture of a highly refractory kind 
 of crucible, known as black-lead crucibles or blue pots. (See 
 Appendix, § 26.) An analogous application of graphite is seen 
 in its use as " foundry-faciugs," a term applied to the infusible 
 dust which the iron-founder sifts over his mould of sand before 
 pouring into it the melted metal ; if the hot metal were allowed to 
 come directly into contact with the sand, a quantity of the latter 
 would melt and remain adhering to the cold metal when the 
 casting was taken from the mould. For this purpose coal-dust 
 is an inferior substitute for graphite. 
 
 371. Pure plumbago is never met with in nature ; when burned 
 in oxygen the mineral leaves from two to five per cent, of ashes, 
 composed mainly of oxide of iron, together with small quantities 
 of silica and alumina. The presence of this impurity is so 
 unvarying that graphite was formerly supposed to be not carbon, 
 but a chemical compound of carbon and iron, a carbide of iron ; 
 this view has now been disproved, and it is known that the iron 
 in the native graphite exists there merely as a mechanical ad- 
 mixture. 
 
 Soft, fine-grained plumbago, suitable for the manufacture of 
 the best pencils, is rare; but the coarse, foliated crystallized 
 variety is abundant, and this may easily be made soft and unc- 
 tuous by the action of certain oxidizing agents. 
 
 Exp. 147. — Mix 7 grms. of coarsely powdered crystallized graphite 
 with 0'6 grm. of chlorate of potassium in fine powder ; add the mixture 
 to 14 grms. of strong sulphuric acid contained in a porcelain dish, and 
 heat the whole over a water-bath as long as yellow vapors of hypo- 
 chloric acid are evolved. Wash the cooled mass with water, and sub- 
 sequently dry it on the water-hath. 
 
 Ignite a fragment of the dry product upon a piece of platinum foil, 
 and observe the extraordinary intumescence. After the graphite has 
 ceased to swell up, rub a little of it upon a porcelain plate and note 
 the condition of exquisite softness to which it has been reduced, and 
 the ease with which it can be moulded by pressure into any desired 
 form. 
 
 372. Eegarded from the chemical point of view, graphite re- 
 sembles the other modifications of carbon inasmuch as it is con- 
 
 u2 
 
292 (JRAPHITIC ACID. 
 
 verted into carbonic acid on being ignited in oxygen, and in that 
 it undergoes no alteration wten heated in close vessels, but 
 differs materially from the other varieties of carbon in its be- 
 behavior towards several of the oxidizing agents. When graphite 
 is repeatedly exposed to the action of a mixture of strong nitric 
 and sulphuric acids, or to that of a mixture of chlorate or bichro- 
 mate of potassium and sulphuric or nitric acid, it is converted 
 into a pecuhar acid, called graphitic add. 
 
 This graphitic acid occurs in thin transparent crystals, some- 
 what soluble in water, but insoluble in water containing acids or 
 salts ; on being heated, it decomposes, with explosion and evolu- 
 tion of light. By analysis, it has been found to contain carbon, 
 hydrogen, and oxygen, in proportions corresponding to the com- 
 plex formula CjjH^Oj ; but some chemists, who regard this body 
 as an analogue of an acid (Si^H^j) obtained by acting upon one 
 of the modifications of silicon with oxidizing agents, have sug- 
 gested that the atomic weight of graphite may be different from 
 that of ordiuary carbon, and that the composition of graphitic 
 acid could be represented by the simpler formula Gr^H^Oj, in 
 which the symbol Gr stands for graphon — ^provided the atomic 
 weight of this graphon were assumed to be 33, instead of 12 (the 
 atomic weight assigned to ordinary carbon). 
 
 The graphitic modification of carbon can readily be obtained 
 artificially. When charcoal is added to melted iron, the iron 
 takes up a considerable quantity of it, and if the iron be then 
 left to cool slowly, a portion of the dissolved carbon will crys- 
 tallize out in the form of graphite ; the crystals can readily be 
 isolated by dissolving away their metallic envelope by means of 
 dilute chlorhydric or sulphuric acid. 
 
 As has been already remarked, the crystals of graphite are 
 six-sided plates of the hexagonal system, altogether imlike the 
 forms of the regular system which are seen in the diamond. In 
 carbon, then, as in sulphur, we have a striking example of 
 dimorphism. (See § 192.) 
 
 373. Gas-Oarbon. — An interesting sub-variety of carbon some- 
 what similar to graphite, and standing, as it were, between it 
 and the ordinary modification of carbon, is obtained from the 
 retorts in which common illuminating gas is manufactured. It 
 
GAS-CAEBON. 
 
 293 
 
 is known as " gas-carbon," or " carbon of tbe gas-retorts," and 
 results from the burning on of drops of tar upon the interior 
 walls of the retort, and the long-continued heating of the crust 
 thus formed. 
 
 Gras-carbon is very hard, compact, and dense ; it has the me- 
 tallic lustre, and conducts electricity like a metal ; its specific 
 gravity (2-356) and specific heat (0-2036) closely resemble those 
 of graphite. On account of its high conductLag-power, it is em- 
 ployed in the manufacture of galvanic batteries and of pencils 
 for the electric lamp ; its infusibUity and power of resisting 
 chemical agents have led to the employment, in various scientific 
 researches, of crucibles and tubes wrought out of it ; it has also 
 been sometimes employed as fuel Lq experiments where higher 
 degrees of heat are needed than can be obtained from charcoal 
 or coke. The intense heat developed by the combustion of this 
 substance is referable to its high specific gravity ; a very con- 
 siderable weight of carbon can here be burned in a small space. 
 As a fuel, it has the farther merit of leaving scarcely any ashes. 
 
 374. Goke and Anthracite Coal are impure sub-varieties of 
 carbon which, from the chemical point of view, may be classed 
 either with graphite or charcoal, or better between the two. 
 They are less like graphite, however, than gas-carbon is. Coke 
 is the residue resulting from the destructive distillation of soft or 
 bituminous coal. 
 
 Fig. 49. 
 
 JExp. 148. — ^Put into a tube of hard 
 glass, No. 1, 12 or 15 cm. in length, 
 enough bituminous coal, in coarse 
 powder, to fill one-third of the tube. 
 Fit to this ignition-tube a large de- 
 livery-tube of glass, No. 4, and sup- 
 port the apparatus upon the iron 
 stand, as shown in the figure. Heat 
 the coal in the ignition-tube, and 
 collect in bottles the gas which will ' 
 be evolved. This gaa is a mixture of 
 several compounds of carbon and hy- 
 drogen ; for the present, it may be regarded as carburetted hydrogen. 
 It is, in fact, ordinary illuminating gas. 
 
 It is infiammable; like hydrogen, but bums with a far more lumi- 
 
294 iLLxramrATiNS eAS. 
 
 nous flame. It is very light withal ; hence many of the experiments 
 described in the chapter upon hydrogen may be performed with this 
 gas. (See Chapter V.) 
 
 As soon as gas ceases to be given ofi" from the coal, take the end of 
 the delivery-tube out of the water and when the ignition-tube has 
 become cold, break it and examine the coke which it contains. The 
 coke used for domestic purposes is obtained as an incidental product in 
 the manufactui-e of illuminating gas. 
 
 In Europe, where anthracite is lacking, immense quantities of coke 
 are prepared for metallurgical uses, the gas resulting from the decom- 
 position of the coal being usually thrown away. 
 
 375. Bituminous coal is a substance of vegetable origin, which 
 appears to have been formed from plants by a process of slow 
 decay going on without access of air and under the influence of 
 heat, moisture, and great pressure. Like vegetable matter in 
 general, it is composed of carbon and hydrogen, together with 
 small proportions of oxygen and nitrogen, and a certain quantity 
 of earthy and saline substances, commonly spoken of as inor- 
 ganic matter. On being heated in the air, it bums away almost 
 completely after a while, leaving nothing but the inorganic com- 
 ponent as ashes. But when heated out of contact with the air 
 (that is to say, when subjected to destructive distUlation, as in 
 Exp. 148), the volatile hydrogen is all driven off in combination 
 with some carbon, either as gas or as a tarry liquid, and there 
 remains, as a residue, only carbon contaminated with the inor- 
 ganic matters originally present in the coal. 
 
 376. Both coke and anthracite are hard and lustrous. As 
 compared with charcoal, they are rather difficult of combustion ; • 
 but in suitable furnaces they burn readily, with evolution of in- 
 tense heat. Both anthracite and coke, the latter in spite of its 
 porosity, conduct heat readily, as compared with charcoal ; hence 
 one reason of the difficulty of kindling them. In building a 
 charcoal fire, the heat evolved by the combustion of the kindling 
 material is almost all retained by the portions of charcoal imme- 
 diately in contact with the kindling agent ; but in the case of coke 
 or anthracite a large proportion of this heat is conducted off and 
 diffused throughout the heap of fuel, so that no portion of the 
 fuel can at once become very hot. It foUows that in both light- 
 ing and feeding fires of coke or anthracite, only small portions 
 
COKE ANTHRACITE CHARCOAL. 295 
 
 of the fuel should be added at any one time, lest the kindling 
 material, or the existing fire, be unduly cooled. Since coke is 
 usually contaminated with a considerable proportion of, inorganic 
 matter, its combustion is apt to be hindered by the accumula- 
 tion of ashes and consequent exclusion of air, unless special pre- 
 cautions be taken. 
 
 377. Charcoal or Lampblack is commonly taken as the repre- 
 sentative of the third or amorphous modification of carbon. This 
 kind of carbon can be obtained in a state of tolerable purity, 
 either by heating in a close vessel sugar, or starch, or some 
 other organic substance which contains no inorganic constituents, 
 or by burning oU of turpentine in a quantity of air insufficient 
 for its complete combustion. A convenient way of obtaining it 
 is to place a vessel filled with ice-water directly in the flame of a 
 lamp fed with oil of turpentine, so that the combustion of the oil 
 shall be impeded, and that soot may be deposited upon the walls 
 of the vessel. In either event, however, the product is liable to 
 be contaminated with traces of hydrogen or of oxygen, or of both 
 these elements, which cannot be expelled even by the application 
 of long-continued and intense heat. 
 
 For such illustrations as are required in this manual, charcoal 
 can readily be prepared from wood in the same way that it is 
 made for manufacturing and domestic uses, namely by subjecting 
 the wood to a process of incomplete combustion. 
 
 Exp. 149. — Light one end of a splinter of dry wood and slowly push 
 the burning portion into the mouth of a test-tube, as shown in Fig. 50. 
 The portion of the splinter which remains 
 outside the tube and in contact with free -P'?' ^^■ 
 
 air will continue to bum with flame, while 
 that within the tube is either extinguished 
 altogether or barely glimmers as the carbon 
 slowly unites with the small portion of air 
 which can gain access to it. 
 
 Exp. 150. — Repeat the foregoing experi- 
 ment, but, instead of the test-tube, provide 
 a cup of sand and slowly thrust the burning splinter into this sand. 
 The flame will he extinguished as fast as the splinter is cut oft' from 
 the air by immersion in the sand, and a residue of carbon will be thus 
 obtained, as before. 
 
296 PBEPAKAUON OP CHAKCOiL. 
 
 378. Whenever wood, or any other vegetable or animal mat- 
 ter, is not completely consumed, there is left a residue of carbon 
 similar to. that obtained in the foregoing experiments. Incom- 
 plete combustion in such cases is really a process of destructive 
 distUlation, or, rather, in any combustion of wood, or of bitumi- 
 nous coal, there is always destructive distillation at first. When 
 the splinter of wood of Exp. 149, is heated in the lamp, in order 
 to set it on fire, there wUl distil off from it, in the beginning, 
 certain volatUe compounds of hydrogen and carbon ; for wood, 
 like coal (§ 375), is composed of carbon, hydrogen, oxygen, ni- 
 trogen, and inorganic or earthy matters, and when exposed to 
 strong heat it gives ofl' in the gaseous form the volatUe elements 
 hydrogen, oxygen, and nitrogen, together with some carbon. 
 The products of the destructive distillation of the splinter will 
 take fire and bum, and the heat generated by their combustion 
 win be sufficient, not only to distil the contiguous portions of the 
 wood, but also to bring the residual carbon to the temperature at 
 which it unites with oxygen. This kindling-temperature of 
 carbon, it should be remarked, is considerably higher than that 
 at which the volatile distillate composed of carbon and hydrogen 
 takes fire. 'Now if, as in Experiments 149, 160, the burning 
 splinter be removed from the air as soon as the act of distillation 
 has been completed, but before the combustion of the carbon has 
 set in, the carbon will be preserved, as has been seen. So, too, 
 when burning wood is extinguished by pouring water upon it ; 
 the distillatory process has occurred and has been more or less 
 thoroughly completed, but the combustion of the carbon is cut 
 short ; for the water not only excludes air but absorbs so much 
 heat that the temperature of the fuel is reduced below the kindling- 
 point. (Compare Exp. 24.) 
 
 379. Charcoal can be obtained also by distilling wood in retorts 
 in the same way that we have seen that coke can be procured 
 from bituminous coal. (See Exp. 148.) 
 
 Uxp. 151. — Provide an ignition-tube and a delivery-tube similar to 
 those employed in Exp. 148. FUl the ignition-tube with shavings or 
 small fragments of wood, arrange the apparatas as in Fig. 51, and light 
 the gas-lamp. Collect in bottles the gas which is given ofi" from the 
 wood, and test it as to its inflammability by applying a lighted match. 
 
nSIILLAIION OP WOOB, 
 
 297 
 
 After the flow of gas has ceased, remove the end of the delivery-tuhe 
 from the water, plug it so that no air can enter the ignition-tuhe, and 
 lay the apparatus aside until it has 
 become cold. Finally remove the 
 cork from the ignition-tube and take 
 out the charcoal which is contained 
 in it. Heat a portion of this char- 
 coal upon platinum foil and observe 
 the manner in which it bums. It 
 will illustrate the fact that solid sub- 
 stances which are incapable of evol- 
 ving volatile or gaseous matter do 
 not bum with flame ; they merely 
 glow. 
 
 Exp. 153. — Pack an ignition-tube with bits of wood, as in Exp. 161, 
 but, instead of the ordinary delivery-tube, insert in the mouth of this 
 ignition-tube a cork carrying a short piece of glass tubing drawn out 
 to a fine open point. By means of wire, tie the ignition-tube to a ring 
 of the iron stand, and place it over the gas-lamp. The gases evolved 
 from the wood will escape through the narrow tube, and on being 
 kindled will bum with a luminous flame. As has been already stated 
 (§ 57), flame is caused by burning gas. 
 
 This experiment, as well as Exps. 148, 1-51, illustrates the principle 
 of the manufecture of illuminating gas. Upon the large scale, bitumi- 
 nous coal, or sometimes dry wood, is distilled in large iron or clay 
 tubes, called gas-retorts, and the gas evolved is freed from tar and 
 other ofiensive impurities by processes of cooling and washing with 
 water, and by passing it through layers of lime or oxide of iron ; it is 
 then collected in large gas-holders, fi-om which it is pressed through 
 subterranean pipes, it may be for mUes. 
 
 380. For use in the arts, charcoal is prepared by both the 
 methods above indicated ; it is manufactured both by charring or 
 partially burning wood with little access of air, and by methodi- 
 cally distilling wood in actual retorts. The first method is 
 employed in countries where wood is abundant, and is carried 
 on in the forest itself. Logs of wood are piled up into a large 
 mound or stack around a central aperture, which subsequently 
 serves as a temporary chimney, and also for the introduction of 
 burning substances for firing the heap. The finished heap is 
 covered with chips, leaves, sods, and a mixture of moistened 
 earth and charcoal dust, a number of apertures being left open 
 
298 
 
 PREPARATION OF CHARCOAL. 
 
 around the bottom of the heap for the admission of air and the 
 escape of the products of distillation and combustion. The heap 
 is kindled at the centre, and burns during several weeks. "When 
 the process is judged to be complete, all the openings are carefully- 
 stopped, iu order to suffocate the fire, and the heap is then left to 
 itself until cold. Kilns constructed of brick are often used instead 
 of the rude heaps here described. The charcoal retains the form 
 of the wood — the shape of the knots and the annual rings of the 
 wood being stUl perceptible in it, — but it occupies a much smaller 
 volume than the wood ; generally its bulk does not amount to 
 more than three-fourths of that of the wood, and its weight never 
 exceeds one-fouxth the weight of the wood. 
 
 Where charcoal is prepared by distilling wood in retorts, the 
 liquid products of distillation, namely tar and acetic acid (" py- 
 roligneous acid"), are saved and utilized. 
 
 381. Lampblack. — Usually when hydrogen is removed from a 
 gaseous compound of carbon and hydrogen, the carbon separates 
 in the form of soft flakes, called lampblack or soot. In Experi- 
 ment 60, we have already seen that lampblack is formed when 
 hydrogen is removed from carburetted hydrogen by means of 
 chlorine, and we know well that oxygen is capable of producing 
 the same result. Hydrogen is more combustible in oxygen than 
 carbon ; hence if carburetted hydrogen be mixed vrith only enough 
 oxygen to consume its hydrogen, and the mixture be then inflamed, 
 the carbon contained in it will be set free. This, is the way in 
 which lampblack is commonly formed ; a lamp " smokes " when 
 the supply of air is insufficient to furnish oxygen to both the car- 
 bon and the hydrogen of the oil or other combustible. 
 
 Upon the large scale, lampblack is manufactured by heating 
 organic matters, such as tar, rosin, or pine knots, which contain 
 volatile ingredients very rich in carbon, until vapors are disen- 
 gaged, and then burning these vapors in a current of air insufficient 
 for their complete combustion. A dark-red, very smoky flame is 
 thus obtained ; a large portion of the carbon of the combustible 
 does not bum, but is deposited as a very fine powder precisely 
 similar to that which constitutes the black portion of common 
 smoke. Lampblack finds important applications in the arts as a 
 pigment and as the chief ingredient of printers' ink. 
 
lAMPBLACK. 299 
 
 Hxp. 153.— Fill an ordinary spirit-lamp (Appendix, § 6) with oil of 
 turpentine, light the wick and place over it an inverted wide-mouthed 
 bottle of the capacity of a litre or more, one edge of the mouth of the 
 bottle being propped up on a small block of wood, so that some air 
 may enter the bottle. As the supply of air is insufficient for the per- 
 fect combustion of the oil of tiirpentine, a quantity of lampblack will 
 separate and be deposited upon the sides of the bottle. 
 
 Hydrogen kindles at a lower temperature than carbon ; hence 
 if the flame of a burning compomid of carbon and hydrogen be 
 cooled down below the temperature at which carbon takes fire, 
 lampblack will be formed, even if there be present an abundant 
 supply of air. 
 
 -Erp. 154. — Press down upon the flame of an oil-lamp or candle an 
 iron spoon or a porcelain plate in such manner that the flame shall be 
 alniost, but not quite, extinguished. The solid body not only obstructs 
 the draught of air, and thereby interferes with the act of combustion, 
 but it also cools the flame by actually conducting away part of its 
 heat ; the temperature is thus reduced to below the kindling- point 
 of carbon, and a quantity of lampblack remains unconsumed and ad- 
 hering to the spoon or plate. This experiment is, of course, compa- 
 rable with Exps. 133, 136, in which spots of arsenic and antimony 
 were obtained upon porcelain, as products of the incomplete combus- 
 tion of their compounds with hydrogen. As has been stated in § 377, 
 lampblack thus prepared usually contains a certain small proportion 
 of hydrogen compounds. 
 
 382. Charcoal is altogether insoluble in water ; it is odorless 
 and tasteless. Unlike the diamond, it is a good conductor of elec- 
 tricity, but a bad conductor of heat, particularly when in the state 
 of powder. It is a better conductor of heat in proportion as it is 
 denser ; when strongly heated out of contact with the air it be- 
 comes heavier, hairder, and closer in texture than /iommon char- 
 coal, and less easily combustible, but a far better conductor of 
 heat and of electricity than before. -The pieces of charcoal, for 
 example, which sometimes fall unconsumed from the bottoms of 
 smelting furnaces, after having passed through a long column of 
 intensely heated fuel, are found to be peculiarly compact and 
 close-grained, and to conduct heat with comparative facility. 
 
 As has been seen in § 376, the combustibility of a fuel is 
 diminished in proportion as the fuel is a good conductor of heat ; 
 
300 PEOPBEIIES OP CHARCOAL, 
 
 and siuce, as has just been stated, charcoal conducts heat the 
 more readily in proportion as it is denser, it foUows that, other 
 things being equal, a given sample of charcoal will take fire 
 more quickly if it be light than if heavy. It wiU appear, more- 
 over, from the foregoing that the combustibility of charcoal should 
 be less, according as the temperature at which the charcoal pre- 
 pared is higher. If, for example, Unen or cotton rags be carbo- 
 nized at low temperatures, there wiU be obtained a very light 
 variety of charcoal, called tinder, which takes fire with especial 
 ease. So, too, a very hght and easily inflammable charcoal is 
 prepared for the manufacture of gunpowder by distiUing light 
 woods, such as wiUow and alder, at low temperatures. Wood 
 charcoal takes fire easily, as compared with coke ; coke as com- 
 pared with anthracite, and anthracite as compared with gas-car- 
 bon. But, inversely, when the charcoal has once been thoroughly 
 lighted, the intensity of the heat obtained from a fire of it wUl be 
 greater in proportion as the charcoal is more dense. As has been 
 already stated (§ 373), a better fire can be obtained by burning 
 gas-carbon than can be had from coke or charcoal ; for in any 
 given space, if the supply of air be ample, more of the dense than 
 of the light fuel can, of course, be burned in a given time. The 
 specific gravity of charcoalis about 1'6 ; but an ordinary fragment 
 of it readily floats upon water, owing to the air within its pores ; 
 if this air be removed, as when the fragment is powdered, the 
 charcoal wiU sink at once. (See Exp. 159.). It is infusible and 
 non-volatile. 
 
 383. In all its varieties, charcoal is a very important chemical 
 agent, chiefly because of the readiness and energy with which it 
 combines with oxygen at high temperatures. Most of the com- 
 mon processes for extracting the useful metals tfrom their ores are 
 based upon the affinity of carbon for oxygen. 
 
 Exp. 156. — Mix five grammes of litharge (oxide of lead) with a quar- 
 ter of a gramme of powdered charcoal ; place a poi-tion of the mixture 
 in an ignition-tube made of No. 3 glass, and heat it strongly in the 
 gas-lamp. The charcoal will imite with the oxygen of the oxide of 
 lead, and the compound thus formed will escape in the form of gas, 
 while metallic lead will remain ia the tube. 
 
 This experiment is analogous to Exp. 124, where arsenious acid 
 
CHAKCOAL A EBDTJCING ASENT. 
 
 301 
 
 was reduced by means of charcoal. Both experiments are typical 
 of the manner in which hot charcoal acts upon metallic oxides. 
 At a white heat it removes oxygen from its combinations with 
 some elements which hold it with great force, such as the oxides 
 of sodium and potassium and phosphoric acid. Even water is 
 decomposed, with liberation of hydrogen, when brought into con- 
 tact with red-hot charcoal. 
 
 Exp. 166. — ^Fill a piece of iron gas-pipe, about 35 cm. long and 1 cm. 
 or more in internal diameter, with fragments of charcoal ; adapt to it 
 a delivery-tube, as represented in Fig. 52, and support it upon a ring 
 of the iron stand over one or two wire-gauze gas-lamps. Attach to 
 
 =^m. 
 
 the other end of the tube a thin-bottomed glass flask half full of water 
 and supported upon the ring of a second iron stand. Light the lamps 
 beneath the tube full of charcoal, and wait until it has become red-hot, 
 then heat the water in the flask and cause it to boil slowly. The 
 steam will react upon the hot carbon in a manner which may be for- 
 mulated as follows : — 
 
 -h H^O = 00 -1- 2H, 
 
 and there wiU be formed a mixture of a compound of oxygen and car- 
 bon called carbonic oxide, and free hydrogen. OoUect the mixed gaa 
 in bottles upon the water-pan and test it as regards its inflammability 
 by applying a lighted match. 
 
 A certain quantity of water may even be decomposed by thrusting 
 pieces of brightly glowing charcoal into water. If the experiment be 
 performed beneath an inverted bottle of water held near the surface 
 of the water-pan, a quantity of gas large enough to be inflamed can 
 readily be obtained. 
 
 At a red heat charcoal deoxidizes bodies which are rich in oxy- 
 gen so readUy that there occurs a pecuKarly rapid and sparkling 
 
302 STABILITY OF CHAECOAI. 
 
 combustion known as deflagration. Deflagration differs from ex- 
 plosion only in degree ; it is less violent than explosion, because 
 tbe combustion is less rapid. 
 
 Exp. 157. — Mix 10 grms. of nitrate of potassium and 5 grms. of re- 
 cently ignited charcoal, both in fine powder ; place the mixture upon 
 a brick, m a current of air, or in any place where the volatile products 
 of the reaction can occasion no inconvenience, and touch it with a 
 lighted stick or red-hot wire. The charcoal will burn violently, with 
 brOliant scintillations, at the expense of the oxygen contained in the 
 nitrate of potassium. 
 
 As a modification of this experiment, heat a couple of pieces of char- 
 coal to redness in the fire and sprinkle upon the one a small quantity 
 of powdered nitrate of potassium, and upon the other a little powdered 
 chlorate of potassium. 
 
 384. This deoxidizing power of charcoal, above illustrated, is 
 exhibited only at high temperatures. At the ordinary tempera- 
 ture of the air, the chemical energy of charcoal is exceedingly 
 feeble. Charcoal is, in fact, one of the most durable of substances. 
 Specimens of it have been found at Pompeii and upon Egyptian 
 mummies, to all appearance as fresh as if just prepared ; the 
 action of the air continued through centiiries has exerted no 
 appreciable influence upon it. Experience has proved that many 
 wooden articles which are to be placed in situations peculiarly 
 liable to cause their decay, may be protected by charring them 
 superficially ; the carbonization of the interior of casks destined to 
 hold liquids, and of those portions of wooden posts and siUs which 
 are to be sunk in the ground, or to remain on or near the surface 
 of the ground, are familiar instances of this custom. 
 
 Not only is charcoal unacted upon by air or water at the ordi- 
 nary temperature, but there are few chemical substances which 
 have any action upon it unless they be hot ; neither the neutral 
 solvents, such as alcohol and ether, nor corrosive agents, such as 
 chlorine or fluorhydric and chlorhydric acids, attack it in any 
 way. It is slowly oxidized, however, by nitric acid, and rapidly 
 by perchloric acid, and it dissolves, to a slight extent, in cold 
 concentrated sulphuric acid. At the ordinary temperature, no 
 one of the elements combines with it directly; but at high tem- 
 peratures it unites directly, not only with oxygen, as we know, 
 but with sulphur as well, forming bisulphide of carbon (OS ). 
 
CHAECOAL ABSOEBS GAS. 303 
 
 At very high temperatures, as when a powerful galvanic battery- 
 is discharged from carbon points immersed in an atmosphere of 
 hydrogen, carbon sombines directly with hydrogen also, and there 
 is formed a gas called acetylene (C^H^). With nitrogen it unites 
 to form cyanogen (CN) when a current of nitrogen gas is passed 
 through a column of ignited charcoal which has previously been 
 charged with carbonate of potassium by soaking it in a solution 
 of this salt ; but it wiU. not unite with nitrogen without the inter- 
 vention of the alkaline carbonate or of some other substance. 
 With chlorine and the other members of the chlorine group it 
 does not unite except indirectly ; but with several of the metals it 
 unites directly to form badly defined compounds called carburets 
 or carbides. Upon the chlorides and their analogues carbon has 
 no action, and the same remark is true of some refractory oxides, 
 such as sUicio acid and oxide of aluminum, which are not decom- 
 posed by charcoal, even at a white heat ; but at a strong red heat 
 it reduces most of the sulphates to the condition of sulphides (for 
 example — 
 
 CaSO, -I- 2C = CaS -f- 2C0,), 
 
 and the nitrates, chlorates, and perchlorates to the state of car- 
 bonates — 
 
 2(K,0,N,0,) + 5C = 2(K,0,C0,) + 3C0, + 4N. 
 
 385. A physical property of charcoal, which is of great prac- 
 tical importance, is its power of absorbing and condensing within 
 its pores a great variety of gases and vapors ; it absorbs coloring- 
 matters also, and various other substances as well, abstracting 
 them from solutions in which they are contained. 
 
 Exp. 158. — Take from the fire a live coal (charcoal) as large as a 
 hen's egg, extinguish it by covering it up tightly in a small metallic 
 vessel or hy covering it with sand, and wait until it has become cold ; 
 weigh it carefully upon a delicate balance, and record the weight. 
 Place the weighed coal in such a situation (in a damp ceIlar,\for example) 
 that it shall be fi-eely exposed to moist air during twenty-four hours ; 
 again weigh it, and note the increase. Boxwood charcoal has been 
 found to increase in weight 14 per cent, in the course of a single day, 
 and any ordinary charcoal will usually increase in weight from 10 to 
 12 per cent. 
 
 Exp. 159. — Take from the fire, as before, a piece of charcoal which 
 has been heated to fuU redness for some time ; thrust it under water, so 
 
304 CHARCOAL ABSOEBS BASES. 
 
 that it may be suddenly cooled, and observe that it sinks in the water 
 and that few or no bubbles of gas escape from its pores. 
 
 Take another piece of charcoal which has long been exposed to the 
 air and has not recently been heated, attach to it a quantity of sheet 
 lead sufficient to sink it in water, and immerse the whole in a large 
 beaker glass two-thirds full of hot water. The mobile water wiU im- 
 mediately enter the pores of the charcoal, and a portion of the air 
 which had preyiously been absorbed by these pores will be driven out, 
 and can be seen escaping in bubbles through the water, chiefly from 
 the broken ends of the coal. 
 
 In a similar way, if a piece of old charcoal be placed in a bottle full 
 of water standing inverted upon the water-pan, a quantity of air will 
 gradually be expelled from it as the water enters its pores, and will col- 
 lect at the top of the bottle. 
 
 The air can at any time be quickly removed by sinking a piece of 
 the charcoal, by means of lead, in water of the ordinary temperature, 
 placing the vessel which contains the water under the receiver of an 
 air-pump and pumping out the air from this receiver ; as the pressure 
 of the atmosphere is removed from the surface of the water a multi- 
 tude of bubbles of air will be seen to issue from the pores of the coal. 
 
 To the presence of air and aqueous vapor, which, has been thus 
 absorbed, is to be attributed the snapping and crackling of old 
 charcoal when it is thrown upon a hot fire. Charcoal which has 
 been recently made, and which has not yet absorbed air and 
 moisture, does not thus snap and crackle ; moreover it kindles 
 much more easily than charcoal which has long been exposed to 
 the air ; for from the latter a quantity of gas and vapor must be 
 expanded and driven out before the coal can ignite, and this ex- 
 pansion, being, of course, attended with absorption of heat, keeps 
 down the temperature of the coal below the kindling-poiat. 
 
 It is not necessary that charcoal be freshly made or recently 
 heated, in order that it may kindle readily, if only it has been 
 kept in closed vessels, and thus prevented from absorbing mois- 
 ture. In the laboratory it is weU to throw the remnants of 
 charcoal &es into an iron kettle, furnished with a tightly fitting 
 cover, in order to have always a store of easily inflammable coal 
 for starting new fires in small hand-furnaces. 
 
 The absorptive power of charcoal for gases can readily be shown 
 directly by placing recently ignited charcoal in a smaU confined 
 volume of almost any gas. 
 
CHAKCOAL ABSORBS GASES. 305 
 
 Exp. 160.— Fill a glass cylinder of 200 or 300 o. c. capacity with 
 dry sulphurous acid gas (Exp. 96), over the mercury trough ; take 
 from the fire a red-hot piece of charcoal as large as can be introduced 
 ihto the mouth of the cylinder ; thrust it heneath the surface of the 
 mercury and hold it there for a moment, in order that it may be ex- 
 tinguished, then pass it up into the jar of sulphurous acid. Mercury 
 ■will rise in the cylinder in proportion as the gas is absorbed, and will 
 soon completely fill it. 
 
 386. As one result of the enormous condensation to which 
 gases are subjected when thus absorbed by coal, heat is neces- 
 sarily developed ; the temperature of the charcoal rises as the gas 
 is condensed in it, and to such an extent that heaps of recently 
 ignited finely divided charcoal often take fire on being exposed 
 to the air. 
 
 Different gases are absorbed by charcoal in very different pro- 
 portions. It has been found, by experiment, that one cubic cen- 
 timetre of dry, compact charcoal, such as that from boxwood, will 
 absorb in the course of twenty-four hours: — 
 
 90c.c 
 
 of Ammonia gas. 
 
 35 CO 
 
 of Olefiant gas. 
 
 85 „ 
 
 „ Chlorhydric acid gas. 
 
 9-4 „ 
 
 „ Carbonic oxide. 
 
 65 „ 
 
 „ Sulphurous acid gas. 
 
 9-3 „ 
 
 „ Oxygen. 
 
 55 „ 
 
 „ Sulphydric acid gas. 
 
 7-5 „ 
 
 „ Nitrogen. 
 
 40 „ 
 
 „ Nitrous oxide gas. 
 
 6'0 „ 
 
 „ Mai-sh gas. 
 
 36 „ 
 
 „ Carbonic acid gas. 
 
 1-8 „ 
 
 „ Hydrogen. 
 
 As one consequence of this diversity of absorbing-power, it 
 follows that, from a mixture of several gases, charcoal can remove 
 some gases more readily than others. Thus, when recently igni- 
 ted charcoal, which has been cooled under mercury, as in the pre- 
 ceding experiment, is passed up into a jar of common air, it 
 absorbs the oxygen more rapidly than the nitrogen. But, on the 
 other hand, it is found that, after the charcoal has become satu- 
 rated with one kind of gas, it can still take up a certain quantity 
 of any other gas which may be presented to it. 
 
 387. This power possessed by charcoal of absorbing gases is 
 evidently a particular case of the physical force called adhesion 
 or capillary attraction, whose manifestations are familiar to us 
 in the drinMng up of water by a sponge, or of oil by a lamp- 
 wick. If the charcoal be moistened with water (that is to say. 
 
306 
 
 COMBISTATION THHOtTGH CHARCOAL. 
 
 if its pores be clogged by the interposition of a liquid), its ab- 
 sorbing-power for gases -will be largely diminished. 
 
 This subject is chiefly interesting to chemists because of its 
 intimate connexion with the power of causing various gases to 
 combine with one another, which is possessed by charcoal as well 
 as by finely divided platinum (§§ 224, 240) and several other sub- 
 stances. In the same way that spongy platinum causes hydrogen 
 and oxygen, or sulphurous acid and oxygen, to unite with one 
 another, chemical combination ensues when mixtures of various 
 gases are brought into contact with charcoal. Though the ab- 
 sorbent power of platinum, as regards gases, can hardly be com- 
 pared with that of charcoal, its power of causing combination is 
 very much greater ; platinum appears to possess, moreover, in a 
 marked degree, the faculty of attracting and attaching to itself 
 small quantities of most gases. 
 
 Charcoal can be made more efficient as an agent for causing 
 combination, by covering it with a film of platinum. ^ If coarsely 
 powdered charcoal be thoroughly impregnated with bichloride of 
 platinum by boiling it for some time in an aqueous solution of 
 this salt, and if it be then heated to redness in a close crucible 
 in order that the platinum salt may be decomposed, there will be 
 left a residue of platinum everywhere attached to the sides of the 
 pores of the coal. Such platinized coal is very effective, both as 
 an absorbent of gases and as an agent for producing combination. 
 But even by itself charcoal has a very decided influence upon the 
 combination of gases. 
 
 If recently ignited charcoal be allowed to become charged with 
 dry sulphydric acid gas and then introduced into an atmosphere 
 of oxygen, the elements of the sulphydric acid will combine with 
 the oxygen so quickly that an explosion ensues, and both water 
 and sulphurous acid are produced. 
 
 If the coal charged with sulphydric acid be brought into contact 
 with air, instead of pure oxygen, combination will occur as before, 
 only more slowly; in this case, however, the hydrogen alone will 
 be consumed, the sulphur of the sulphydric acid being set free in 
 the solid state. 
 
 Charcoal is much employed as a disinfecting agent. It is 
 capable of removing many offensive odors from the air — such, for 
 
CHAfiCOAl, A DlSDrPECTANT. 307 
 
 example as the fetid products given off during the putrefaction 
 of animal and vegetable substances. Animal matter in an ad- 
 vanced stage of putrefaction loses all offensive odor when covered 
 ■with a layer of charcoal ; and the flesh of a dead animal buried 
 beneath a thin layer of charcoal will gradually waste away and 
 be consumed without exhaling any unpleasant smeU. 
 
 Exp. 161. — Place a small quantity of powered charcoal in a bottle 
 containing sulphydric acid gas and shake the bottle. The odor of the 
 sulphydric acid will quickly disappear. In the same way, an aqueous 
 solution of sulphydric acid (Exp. 86) can be deodorized by filtering it 
 through a layer of charcoal. 
 
 Exp. 162. — In a shallow open basket, or in a box through the bot- 
 tom of which numerous holes have been bored, spread a layer of 
 coarsely powdered boneblack about 5 cm. thick, placing a sheet of 
 filtering-paper below, if need be, to prevent the powder from sifting 
 through the holes in the box. Place the body of a rat or of some other 
 small animal upon the layer of boneblack, and pour on more bone- 
 black until the rat is covered with a layer of it about 5 cm. deep. 
 Hang up the basket or box in a warm room, so that air may have free 
 access to it, and leave it at rest. After the lapse of several weeks 
 it will be found, on examination, that all the putrescible portions of 
 the animal have disappeared, and that nothing is left but a mass 
 of hair and bones ; but in the interim no odor wiU have been de- 
 tected arising from the decomposing animal, excepting a faint odor 
 of ammonia. 
 
 In the same way, water can be preserved imtainted in casks which 
 have been charred internally ; and the quality of some kinds of wine is 
 improved if it be stored in such casks. 
 
 In all these cases the use of charcoal £is a disinfectant depends 
 not merely upon its mechanical ability to absorb offensive gases, 
 but also and mainly upon the fact that the absorbed gases are 
 chemically destroyed within the pores of the coal by the oxygen 
 which is sucked into these spaces from the air. The puriiying 
 action depends upon oxidation, upon the burning up of the offen- 
 sive gases as fast as they are formed. The charcoal is in no sense 
 an antiseptic, or preservative agent proper to prevent decay ; on 
 the contrary, it actually hastens the destruction of putrescible 
 organic matters. Under ordinary circumstances, while in con- 
 tact with the air, the pores of charcoal are, of course, always 
 charged with oxygen by virtue of their absorptive power. When- 
 
 x2 
 
308 OHAECOAX REMOVES COLOES. 
 
 ever, therefore, any new gaa is dragged in, and forced into inti- 
 mate contact with this oxygen, it is precisely as if the gas had 
 been carefully coUeeted and then subjected to the action of some 
 corrosive chemical agent. A great merit of charcoal as a disin- 
 fectant is, that it constantly draws in to destruction the offensive 
 matters around it ; pans of charcoal placed about a room (the 
 wards of a hospital, for example) the air of which is offensive, 
 soon remove the unpleasant smell. Sieves of charcoal, placed 
 across the air- vents of sewers in such manner that the out-going 
 air may be filtered through the charcoal, are found to be most 
 efficient instruments for destroying the noxious effluvia which 
 commonly escape from these openings. In this case, where a 
 current of air is constantly passing through the charcoal filter, 
 the latter wUl preserve its efficiency for an indefinite length of 
 time, if only it be kept dry ; for the action of the coal consists 
 merely in bringing about oxidation and destruction of the offen- 
 sive gases of the sewer, and as fast as one portion of these is con- 
 sumed a new portion can be taken in to destruction. 
 
 388. Charcoal not only destroys odors, but it removes colors 
 as well ; and for this purpose it has long been employed in the 
 purification of sugar and of many chemical and pharmaceutical 
 preparations. Almost any coloring-matter can be removed from 
 a solution by filtering the liquid through a layer of charcoal. 
 
 Exp. 163. — Provide four small bottles of the capacity of 100 or 200 
 c. c, and place in each of them a table-spoonful of boneblack (§ 389) ; 
 into the first bottle pour a quantity of the blue compoimd of iodine 
 and starch obtained m Exp. 69, into the second a decoction of cochi- 
 neal, into the third a diluted portion of the blue liquor obtained by 
 dissolving indigo in Nordhausen sulphuric acid, and into the fourth a 
 solution of permanganate of potassium, enough of the solution being 
 taken in each instance to nearly flU the bottle. Cork the bottles and 
 shake them violently, then pour the contents of each upon a filter (see 
 Appendix, § 14), and observe that the filtrate is in each instance color- 
 less or nearly so. In case the first portions of the filtrate happen to 
 come through colored, they may be poured back upon the filter and 
 allowed to again pass through the coal. 
 
 In the purification of brown sugar the coloring-matters are removed 
 in a manner similar to the foregoing, the colored syrup being filtered 
 through layers of boneblack. Many crystallizable organic acids and 
 alkaloids are purified in the same way in the chemical laboratory. But 
 
CHAECOAl REMOVES COLORS. 309 
 
 it must never be fol'gotteii that charcoal can absorb many other sub- 
 stances besides coloring-matters; sulphate of quinine, for example, 
 is removed from its solutions, to a very considerable extent, by char- 
 coal ; and the same remark applies, -with perhaps still more force, to 
 strychnine. The bitter principle of the hop, " lupulin," may be en- 
 tirely removed from ale by filtering the latter through bone-black. 
 The removal of metals, like gold and sHver, from their dUute solutions, 
 by means of charcoal, appears to be a phenomenon of the same ordfe 
 
 In. all ttese cases where coloring-matters, and the like, are re- 
 moved from solutions, the action of the coal appears to depend 
 in the main directly upon the physical property of adhesion, the 
 subsequent oxidizing action being here far less clearly marked 
 than in the instances previously studied (§ 387) where gases are 
 acted upon. Much of the absorbed color or other matter wiE 
 usually be found attached to the surfaces of the coal, undecom- 
 posed and unaltered. Thus, if the coal which has been charged 
 with a solution of indigo in sulphuric acid, in Exp. 163, be 
 digested in a solution of caustic soda, the latter will dissolve the 
 indigo and remove it from the coal ; the alkaloids above men- 
 tioned, which have been removed from their aqueous solutions by 
 means of charcoal, can be again recovered by boiling the coal in 
 alcohol ; and the metals can be dissolved again by means of strong 
 acids. 
 
 When employed to remove coloring-matters, charcoal soon be- 
 comes saturated with the color and ceases to absorb any more of 
 it ; if the spent coal be then collected and redistilled, it will be 
 found that it has regained but little of its decolorizing-power ; for 
 its pores are filled with charcoal resulting from the carbonization 
 of the absorbed coloring-matters and this charcoal is not porous, 
 but, on the contrary, compact and glistening, like the charcoal 
 obtained from sugar or glue, and is almost entirely destitute of 
 decolorizing-power. In order to revivify their coal, the sugar- 
 refiners digest it in chlorhydiic acid, allow it to ferment in order 
 that the absorbed matters may be decomposed, and, finally, after 
 washing and drying, subject it to distillation. 
 , 389. As obtained from different sources, charcoal exhibits very 
 different degrees of decolorizing-power ; but of the varieties com- 
 monly met with and to be procured in commerce, boneblack is 
 the most efficient. Boneblack is prepared for the use of sugar- 
 
310 DECOLOEIZnfe-POWEK OP OHAHCOAt. 
 
 refiners by subjecting bones to destructive distillation in iron 
 cylinders and carefuUy cooling the charcoal out of contact with 
 the air. 
 
 Expi 164. — Repeat Exp. 148, p. 293, but instead of bituminous coal, 
 charge the ignition-tube with coarsely-powdered bone. Distil as long 
 as gas is evolved, then remove the delivery-tube from the water, plug 
 it by means of a bit of caoutchouc tube and a glass rod, and wait until 
 the ignition-tube is cold, before opening it to examine the boneblack. 
 
 Dry bones contain only about one-third their weight of organic 
 matter, nearly 66 per cent, of them consisting of phosphate of 
 calcium, in the interstices of which the animal matter is distri- 
 buted ; hence it happens that the charcoal obtained by distilling 
 bones is in an exceedingly porous and divided condition. The 
 decolorizing-power of bone-charcoal may, moreover, be increased 
 by digesting it in dilute chlorhydric acid, which dissolves out a 
 portion of the phosphate of calcium and leaves the charcoal even 
 more jjorous than before. 
 
 But because boneblack is most commonly employed for de- 
 colorizing, it must not therefore be inferred that it is the most 
 powerful decolorizer of the several varieties of charcoal. A more 
 efficient coal can easily be prepared by mixing nitrogenized organic 
 matters, such as blood, hoofs, horns, or scraps of leather, with 
 carbonate of potassium, distilling the mixture, and finally leaching 
 the product with water. Charcoal of peculiar decolorizing-power 
 may be prepared by igniting a mixture of 4 parts of fresh blood 
 and 1 part of carbonate of potassium in an iron crucible, so long 
 as vapors are evolved, then washing the product with water and 
 boiling it with chlorhydric acid, and again washing, drying, and 
 igniting in a close vessel. A solution of horn-filings in caustic 
 potash, evaporated to dryness and ignited, also yields a very 
 effective charcoal. As with boneblack, the efficiency of this coal 
 prepared with caustic or carbonated potash appears to depend 
 upon the minute subdivision of its particles and the porosity re- 
 sulting from the mixture of the inorganic matter. The decolo- 
 rizing-power of the charcoal obtained from vegetable substances 
 can be in like manner increased by m ixing these substances with 
 lime or clay before the carbonization. A mixture of 100 parts 
 pipe-clay, stirred up with water to the consistence of a thin paste, 
 
DECOLORIZINS-POWBR OF CHAECOAI,. 
 
 311 
 
 20 parts of tar, and 500 parts of powdered bituminous coal yields a 
 charcoal which decolorizes almost as well as boneblack. It is, 
 however, no very easy matter to determine which, of a number 
 of varieties of charcoal, is the most powerful decolorizer, since 
 the decolorizing-power differs with the nature of the coloring- 
 matter as well as according to the quality of the charcoal. It 
 has been found, for example, that with 
 
 BQUAi WEIGHTS OF CHAEOOAi 
 PREPARED By 
 
 THE RELATIVE DECOLOKIZING- 
 POWBR 
 
 Upmi a aohiHon qf 
 indigo m sulphu- 
 ric acid was 
 
 Upon a solution of 
 brown sugar was 
 
 Igniting a mixture of blood and car- 
 bonate of potassium 
 
 Igniting a mixture of blood and car- 
 bonate of calcium 
 
 Igniting a mixture of blood and 
 phosphate of calcium .... 
 
 Igniting a mixture of glue and car- 
 bonate of potassium 
 
 Igniting acetate of sodium . . . 
 
 Digesting boneblack with chlorhy- 
 dric acid 
 
 Ordinary boneblack 
 
 50 
 18 
 12 
 
 36 
 
 12 
 1-9 
 1-9 
 
 1 
 
 20 
 
 11 
 
 10 
 
 16 
 9 
 
 1-3 
 1-6 
 1 
 
 390. Compounds of Carbon and Hydrogen are exceedingly 
 numerous. There are many diiferent series of them, each mem- 
 ber of either of these series differing but slightly from its next 
 neighbors in composition and properties. But aU. these substances 
 are commonly classed as organic compounds ; they constitute a 
 special branch of chemical science called organic chemistry, and 
 are not discussed in works which treat of aU the elements com- 
 monly met with, without special reference to any one. This sub- 
 division of the general subject is resorted to merely for convenience ; 
 there is no inherent reason why the compounds of hydrogen and 
 carbon should not be studied in this manual as well as the com- 
 pounds of hydrogen and oxygen. But since carbon is capable of 
 uniting with hydrogen, oxygen, or nitrogen, or with two of these 
 elements, or with all three of them, in the most varied propor- 
 tions, there are formed so many different compounds, that it has 
 been found advantageous to study them by themselves. 
 
312 
 
 ORGANIC CHEMISTRT. 
 
 The best definition of the so-called organic chemistry which 
 can be given to-day, is, that it is the Chemistry of the Compounds 
 of Carbon. The department of organic chemistry has grown out 
 of ordinary chemistry solely because of the fact that the com- 
 pounds of carbon with hydrogen, oxygen, and nitrogen are more 
 numerous, and often of more complex composition, than the com- 
 pounds formed by any of the other elements. These compounds 
 of carbon with hydrogen, and with the other elements, are all 
 definite chemical compounds conforming to the law of multiple- 
 proportions (§ 76) ; but they count by thousands, and the mere 
 enumeration of their names and properties would fill a volume. 
 
 391. As examples of the series of compounds of carbon and 
 hydrogen, to which allusion was just now made, the following 
 lists may be given : — 
 
 BoOs at ° C. Boik at° C. BoUs at ° C. 
 
 CH^ 
 CH, C^H^ 
 
 gA C3H„ C^, . . 80° 
 
 C.H, . . -30° GiH, . . 6° C,H, . . 110° 
 
 0,H„ . . 0° C,H,„ . . 35° C,H„ . . 140° 
 
 G.H,, . . 30° C3H,, . . 65° C,H,, . . 170° 
 
 C.Hii . . 60° C,H,, . . 95° 
 
 C,H,e . . 90° G,H„ . . 125° 
 
 The first series of the compounds above formulated is found 
 in petroleum, and in the oil known as coal-oil, obtained by distil- 
 ling highly bituminous coals and shales at comparatively low tem- 
 peratures ; the petroleum used for lighting contains aU these 
 different compounds, together with others of the same class. 
 The second series may generally be obtained by the destructive 
 distillation of various organic compounds ; and the members of 
 the third series are found in the most volatile portion of coal-tar 
 — the tar obtained by distilling bituminous coal at high tempera- 
 tures, as in the manufacture of illuminating gas. 
 
 It wiU be observed that there is a constant difference of one 
 atom of carbon and two atoms of hydrogen (CH^) between any 
 two contiguous compounds enumerated in the lists. The boiling- 
 points of the several members exhibit a constant difference of 30° 
 for each increment of CH^, as we go down the lists, so far as has 
 been determined ; and so with aU the other physical properties, 
 such as specific gravity, mobility, expansibility by heat, and the 
 
HOMOLOGOUS SERIES. 313 
 
 like ; the intensity of these properties increases or decreases re- 
 gularly, in a constant ratio, as we pass from one member of the 
 series to the members next in order. Such series are called 
 " homologouB " series (having the same proportion) ; they are 
 clearly analogous to the groups, families, or series of elements 
 which we have already studied in chlorine, bromine, and iodine 
 (§ 152), in oxygen, sulphur, selenium, and tellurium (§ 257), in 
 nitrogen, phosphorus, arsenic, antimony, and bismuth (§ 364), and 
 are now proceeding to study in carbon, boron, and silicon. Just 
 as in these groups of elements the student has seen a true serial 
 arrangement of the different members, and has observed that the 
 different terms of each series differ from one another in atomic 
 weight and exhibit parallel differences in the intensity of their 
 properties, so here in each of the homologous series of hydrocar- 
 bons there have been observed similar constant differences. In 
 the series of hydrocarbons, we know that there is a constant dif- 
 ference of composition of CH^ ; and this difference of composition 
 we believe to be at the bottom of the constant difference of phy- 
 sical properties ; but to the cause of the constant differences in the 
 homologous series of elements we have, as yet, no clew. 
 
 The power of arranging numerous aUied compounds into 
 groups or series, like those enumerated upon page 312, has been 
 of great service to chemists in facilitating the study of the com- 
 pounds of carbon. For every such series a general algebraic 
 expression has been devised which serves as the name of the 
 series. Like any other name, this concise expression brings 
 before the mind of the chemist the general properties of the 
 series. Thus the expression C^^^^^ is general for the first 
 series above mentioned, CJS^ for the second, and C^ ^ jHjn for 
 the third. 
 
 In this manual we shaU. describe only one of the compounds of 
 carbon and hydrogen, a compound which occurs ready formed in 
 nature. 
 
 392. Marsh-gas, or Light CarbureUed Hydrogen (CEJ, is a 
 permanent gas which constitutes a large proportion of the ordi- 
 nary illuminating gas obtained from coal. It is disengaged in 
 large quantities from some sorts of bituminous coal, even at the 
 ordinary temperature of the air, and more rapidly at higher tem- 
 
314 PEEPAEATION OF MAESH-GAS. 
 
 peratures. In coal mines the gas thus given off is known a3 
 " fire-damp ; " hy mixing with air, in the galleries of badly ven- 
 tilated mines, it forms explosive mixtures, which frequently occa- 
 sion frightful accidents when ignited through carelessness. 
 
 The gas is evolved also, in large quantities, from the mud at the 
 bottom of stagnant pools ; it is one of the products of the putre- 
 faction of vegetable matter under water, where the supply of air 
 is insufficient to oxidize the matter completely to carbonic acid 
 and water ; hence the name marsh-gas. 
 
 In hot weather marsh-gas can be obtained by thrusting a pole into 
 the mud at the bottom of a pond and collecting the bubbles of gas as 
 they rise, by holding over them an inverted bottle full of water. 
 When the bottle has been filled with gas it should be corked tightly 
 under water, and carried to the laboratory for examination. The gas 
 thus obtained is contaminated with nitrogen and with a large quantity 
 of carbonic acid, these gases being set free, together with marsh-gas, 
 during the process of putrefaction. Before the gas thus collected will 
 bum, it is usually found necessary to remove from it the carbonic acid; 
 this caq be done by pouring into the bottle a small quantity of a so- 
 lution of caustic soda, or some milk of lime, closing and shaking the 
 bottle, and finally removing the stopper under water. The bottle may 
 then be placed upright and a lighted match applied to the gas ; it will 
 take fire and burn with a blue flame, the size of which may be in- 
 creased by pouring water into the bottle so that the gas shall be driven 
 out into the air. 
 The gas may be prepared artificially as follows : — 
 
 „ _„ Exp. 165. Mis together 2 grms. of 
 
 °' ' crystallized acetate of Bodium,4gnns. 
 
 of caustic soda, and 8 grms. of slaked 
 lime. Heat the mixture gently upon 
 an iron plate, uutU all the water of 
 crystallization of the acetate has 
 been expelled and the mass has be- 
 come dry and friable. Charge an 
 ignition-tube 20 cm. long with the 
 dry powder, heat it above the gas- 
 lamp,and collect thegas at the water- 
 pan, as shown in Fig. 53. Carbu- 
 retted hydrogen is evolved from the mixture at a temperature below 
 redness, and a residue of carbonate of sodium is left in the ignition- 
 tube. The purpose of the lime is to render the mass porous and in- 
 
PKOPEKiraS OP MAESH-GAS. 315 
 
 fusible, or nearly infusible, so that the tube may he heated equably. 
 If caustic soda is heated with the acetate ■without addition of lime, 
 the tube usually breaks, even when the mixture has been dried before- 
 hand. The reaction may be represented as foUows : — 
 
 O^HjNaOs + NaHO = CH, + Na^COa. 
 
 Bry Acetate of Hydrate of ^ , ^ Carbonate of 
 
 Sodium. Sodium. Marsh-bras. Sodium. 
 
 393. Marsh-gas is transparent, colorless, and little more than 
 half as heavy as air. Next to hydrogen it is the lightest known 
 substance, its specific gravity being only 8. It takes fire readily 
 when touched with a lighted match, but is nevertheless more 
 difficult of inflammation than most of the other combustible com- 
 pounds of hydrogen. While free hydrogen and sulphuretted 
 hydrogen can be lighted by a glass rod which has been heated to 
 dull redness, the rod must be raised to the temperature of bright 
 redness, or even to a white heat, in order that it may kindle 
 marsh-gas. As prepared from acetate of potassium, the gas 
 burns with a pale yeUowish-blue flame. It is rather more solu- 
 ble in water than oxygen ; at 0° one volume of water dissolves 
 0-055 volume of it. It has never been condensed to the liquid 
 condition. 
 
 394. We have, thus far, observed three different proportions 
 in which the other elements unite with hydrogen. The members 
 of the chlorine group unite vrith hydrogen, by preference, in the 
 proportion of one volume to one volume; one volume of any 
 member of the sulphur group combines, by preference, with two 
 volumes of hydrogen ; one atom of any member of the nitrogen 
 group unites, by preference, with three atoms of hydrogen. The 
 condensation increases in direct ratio to the increasing proportion 
 of hydrogen, so that, in every case, two volumes only of the re- 
 sultant compound are produced. We have thus become familiar 
 with the fact that the space occupied by the molecule of a com- 
 pound gas is always two unit-volumes (§ 258). An examina- 
 tion of the molecule of marsh-gas will reveal a fourth kind of 
 hydrogen-compound — a compound containing in the product- 
 volume (§ 260) four volumes of hydrogen condensed. It is not 
 difficult to prove experimentally that two volumes of marsh-gas 
 yield, on decomposition, four volumes of hydrogen ; but, unfor- 
 
316 
 
 AlfALYSIS 01' MABSH-GAS. 
 
 tunately, it is not within our power to demonstrate, by experi- 
 ment, the volume of carbon with which these four volumes of hy- 
 drogen are combined ; for carbon is a solid incapable of volatiliza- 
 tion by the intensest heat at present at our command. We are able 
 to determine the combining volume of each constituent of chlor- 
 hydric acid, steam, and ammonia ; but we have no positive know- 
 ledge whatever concerning the manner in which carbon enters 
 iato combination by volume. Its combining proportion by weight 
 can be ascertained ; but it must be carefully observed that all 
 views respecting the volumetric composition of the very numerous 
 compounds of carbon are p\irely speculative, so far as the carbon 
 is concerned, until carbon shall have been actually volatilized and 
 its vapor weighed. 
 
 That marsh-gas reaUy contains hydrogen and carbon may be 
 readily proved by bringing into play, under appropriate condi- 
 tions, the strong affinity of chlorine for hydrogen. Chlorine will 
 set free carbon from marsh-gas, just as it liberates nitrogen from 
 ammonia (Exp. 67). 
 
 Exp. 166.— Fill a tall bottle of the capacity of 250 or, better, 500 
 c. c. with water, invert it over the water-pan, and pass marsh-gas into 
 it, until a little more than one-third of the water is displaced ; cover 
 the bottle with a thick towel to exclude the light, and then fill the 
 rest of the bottle with chlorine. Cork the bottle tightly, and shake it 
 vigorously, in order to mix the gases together, keeping the bottle 
 always covered with the towel. Finally, open the bottle and apply a 
 light to the mixture. Ignition takes place, chlorhydric acid is pro- 
 duced, while the sides and mouth of the bottle become coated with 
 solid carbon in the form of lampblack, and a cloud of smoke rises into 
 the air. The presence of the acid may be proved by the smell, by its 
 reaction with moistened blue litmus-paper, and by the white fumes 
 which are generated when a rod moistened with ammonia-water is 
 brought into contact with the escaping acid gas. 
 
 Carbon and hydrogen are therefore elementary constituents of 
 marsh-gas. We should be glad to add the synthetical to the 
 analytical demonstration, and make marsh-gas out of carbon and 
 hydrogen ; but no means are at present known by which these 
 two elements can be directly combined to form marsh-gas. As 
 in the case of ammonia, we are obliged to rely upon the assu- 
 rance of the balance that the sum of the weights of the two con- 
 
ATOMIC WEIGHT OF CARBON. 31 7 
 
 stituents separated from a given quantity of marsh-gas is precisely 
 equal to the weight of the marsh-gas submitted to analysis. The 
 experimental process by which this fact is demonstrated is too 
 complex to be profitably studied at this stage of progress, and 
 the fact must therefore be accepted as the result of experience. 
 
 395. It remains to show how the investigation of the composi- 
 tion of the product-volume of marsh-gas leads to the knowledge 
 of the atomic weight, or least combining weight, of the element 
 carbon. Marsh-gas is the compound best suited for ascertaining 
 the atomic weight of carbon, because experience has proved that 
 it contains proportionally less carbon than any other hydride of 
 the element. We determined the atomic weight of oxygen from 
 steam, the hydrogen compound which contains the smallest pro- 
 portion of oxygen, — of chlorine from chlorhydric acid, the only 
 hydride of chlorine, — of nitrogen from ammonia, the hydride which 
 contains the smallest proportion of nitrogen. So the atomic 
 weight of carbon is the weight of carbon which experiment proves 
 to be contained in two unit- volumes of marsh-gas. By physical 
 determinations, the specific gravity of marsh-gas has been shown 
 to be 8 ; in other words, one unit- volume of marsh-gas weighs 8 ; 
 then two imit-volumes, or the product-volume, must weigh 16. 
 How much of this weight of 16 is hydrogen ? This question can 
 be answered experimentally by ascertaining how many unit- 
 volumes of hydrogen are locked up in two unit-volumes of marsh- 
 gas. 
 
 When a series of electric sparks begin to traverse a measured 
 volume of marsh-gas contained in a TJ-tube, arranged like the 
 U-tube of figure 11, but without the jacket, b c, and its accom- 
 paniments, the gas is found to expand, and in a few minutes a 
 light deposit of carbon appears in the vicinity of the points of 
 the platinum wires. The decomposition of the marsh-gas pro- 
 ceeds slowly; so that a considerable time is required for the 
 execution of the experiment. If the mercury in the U-tube be 
 finaEy brought to a level in the two limbs, it will be seen that 
 the original volume of gas has very nearly doubled. When this 
 point is once attained, the continued transmission of sparks pro- 
 duces no further increase of the volume of the gas. The expanded 
 gas may be shown by the usual tests to be hydrogen. 
 
318 ATOMIC WEIGHT OF CAKBON. 
 
 yhis experiment is rather difficult to perform, and does not 
 yield perfectly exact results, for a minute portion of marsh-gas 
 escapes decomposition ; nevertheless it establishes beyond rea- 
 sonable doubt the fact that marsh-gas contains twice its volume 
 of hydrogen. Two unit-volumes of marsh-gas, weighing 16, 
 must therefore contain four unit-volumes of hydrogen ; but four 
 unit- volumes of hydrogen weigh 4 ; therefore the quantity of 
 carbon contained in the product- volume of marsh-gas must weigh 
 12, which number we admit as the atomic weight of carbon. 
 
 But it may be said. What means have we of knowing that 12 
 represents the least combining weight of carbon ? (for the atom is 
 by definition the least quantity of an element which can be con- 
 ceived to exist in combiaation). If it were possible to demon- 
 stratethat the proportional quantity by weight of carbon which 
 is represented by the number 12 is just the quantity required 
 to fill one unit-volume when converted into vapor, we should 
 have the same reason for believing 12 to be the weight of one 
 atom of carbon that we have for considering 16 to be the weight 
 of one atom of oxygen, or 35-5 the weight of one atom of chlorine. 
 As we cannot convert carbon into vapor at all, it is impossible to 
 ascertain with certainty how many atoms, or how many volumes, 
 12 proportional parts by weight of carbon really represent ; the 
 quantity of carbon which is combined with four atoms of hydro- 
 gen in marsh-gas may be four atoms, each weighing 3, or two 
 atoms, each weighing 6, or one atom weighing 12. As it is 
 necessary to assume some number of atoms as represented by the 
 proportional weight 12, that assumption which wiU conveniently 
 formulate the simplest and most familiar compounds of carbon 
 will be the best. Accordingly it has, of late, been assumed that 
 12 proportional parts by weight of carbon constitute the least 
 quantity of this element which is conceived to enter into chemical 
 combiaation, or, in other words, that the atomic weight of carbon 
 is 12. The atom of carbon, thus understood, can then fix, or com- 
 biae with, four atoms of hydrogen or of any member of the chlo- 
 rine group, and two atoms of oxygen or of any other member of 
 the sulphur group. The following substances, fa mili ar in com- 
 mon life, or subjects of discussion in this chapter, may be men- 
 tioned in illustration of this principle : — 
 
ITPICAI HTBEOSEN COMPOUNDS. 319 
 
 Marsh-gas . . . CH^ Carbonic acid . . . COj 
 
 OMoroform . . . CHOI3 Bisulphide of carbon . CSj 
 Chloride of carbon CCl^ 
 
 If it were assumed that 12 proportional parts by weight, the 
 relative quantity of carbon in each of the above-mentioned com- 
 pounds, represent two or four atoms or volumes of carbon, instead 
 of one, every one of these formulae would become less simple. 
 There are a great multitude of compounds which contain a larger 
 proportional quantity of carbon than the compounds cited above ; 
 but the greater proportional quantity is always some multiple of 
 12 proportional parts, or, in other words, is always an integral 
 number of carbon atoms each weighing 12. 
 
 In marsh-gas we have thus found a new term in the series of 
 hydrogen compounds. Marsh-gas is an example and type of the 
 hydrides richest in hydrogen ; so far as we yet know, hydrogen 
 does not form, with any element whatsoever, any compound 
 whereof the product- volume contains more than four atoms of 
 hydrogen united with one atom of the other element. The fol- 
 lowing brief table comprehends aU the principal types of hj'dro- 
 gen compounds, beginning with chlorhydric acid, the poorest 
 hydride, and passing through water and ammonia, intermediate 
 compounds, to marsh-gas, the hydride richest in hydrogen : — 
 
 Chlorhydric acid HCl = 2 volumes. 
 
 Water B.fi = 2 
 
 Ammonia • . HjN = 2 „ 
 
 Marsh-gas H^C,= 2 „ 
 
 Each of these types of hydrogen compounds characterizes a group 
 of chemical elements. The first type is characteristic of the chlo- 
 rine group ; the second, of the sulphur group ; the third, of the 
 nitrogen group ; and the fourth, of the group which we shall soon 
 know as the carbon group. 
 
 396. The compounds of carbon and hydrogen are of great 
 practical interest, since the flame of all ordinary lamps and fires 
 results from their combustion. Any allusion to their properties 
 at oace suggests the influence which these properties exert in 
 the usual methods of obtaining light and heat, and necessitates a 
 more complete discussion of the subjects of flame and combustion 
 than we have had hitherto. We shall recur to this subject in a 
 
320 lUTTMINATIlfG GAS. 
 
 subsequent section, after having studied the oxides of carbon. 
 For the elucidation of the subject of combustion, ordinary illumi- 
 nating gas, which is a mixture of many hydrides of carbon, will 
 serve as well as any pure hydrocarbon. A brief description of 
 this product may here be given. 
 
 About 94-100th8 of the volume of purified coal-gas consists of 
 a mixture of marsh-gas, free hydrogen, and carbonic oxide, — the 
 marsh-gas usually amounting to about one-third part of the 
 whole gas. These non^luminous, or very feebly luminous gases, 
 serve as carriers of the six or seven per cent, of real light- 
 producing ingredients which are contained in the gas. This 
 mixture of light-giving ingredients is exceedingly complex. The 
 vapor of benzole is, no doubt, one of the most important of these 
 ingredients. Some of the higher homologues of marsh-gas lend 
 their aid ; and a hydrocarbon of composition C^H^, called acety- 
 lene, is important and very generally present. Sometimes a little 
 defiant gas (C^H^) is present, as well as other compounds of the 
 same homologous series ; but the old view, that this substance 
 constitutes the chief luminiferous ingredient of coal-gas, is no 
 longer admitted. 
 
 For all practical purposes, we can here regard this mixture 
 of gases as carburetted hydrogen. That it contains hydrogen, 
 can readily be shown by holding a cold, dry bottle over a burn- 
 ing jet of it, and observing that water is a product of the com- 
 bustion ; and that it contains carbon can be seen by holding in 
 the flame a piece of cold porcelain, and noting the deposition of 
 soot. Coal-gas is only about half as heavy as air. In many 
 respects it resembles hydrogen, and most of the experiments 
 which were performed with hydrogen can be equally, or nearly, 
 as well performed with this gas. The student will do well to 
 repeat, as an example, Exp. 24, substituting, for the hydrogen, 
 common gas drawn from the street mains. In the same way he 
 may repeat Exp. 29, mixing 1 volume of coal-gas with from 8 
 to 12 volumes of air. If, instead of coal-gas, pure light car- 
 buretted hydrogen be taken, the explosion wiU be most violent 
 with 8 to 10 volumes of air ; with only 3 or 4 volumes of air, 
 or more than 15 volumes, the mixture is not explosive ; either 
 too much or too little air prevents the explosion. 
 
CAEBON AND OXTOEir. 321 
 
 Compounds of Carbon and Oxygen. — There are two of these 
 compounds — carbonic acid (CO^), and carbonic oxide (CO). 
 
 397. Carbonic Acid (CO^) is always formed when carbon or 
 any of its compounds is burned in an excess of air or of oxygen 
 gas, or in contact with substances, gaseous, liquid, or solid, which 
 are rich in oxygen and yield it readily to other bodies. 
 
 i:xp. 167. — Place a live coal (charcoal) upon a deflagrating-spoon, 
 and thrust it into a bottle full of aii-, or, better, oxygen gas ; cover the 
 bottle closely, and set it aside for examination. Or invert 
 an empty bottle over a burning lamp or candle, so that the 
 products of the combustion of the lamp may he received in 
 it ; the bottle wiU immediately become clouded upon the 
 inside from deposition of water resulting from the combus- 
 tion (see § 56), and will also be filled with carbonaceous 
 and other gaseous products, simultaneously formed. Cover 
 the bottle and test its contents in the manner described in 
 the succeeding experiment. 
 
 Exp. 168. — Pour some lime-water (a solution of common slaked 
 lime in water) into the bottles filled with gaseous products of com- 
 bustion in Exp. 167, and shake the bottles. The Uquid wiU become 
 mUky and turbid, and, when left at rest, will deposit a white powder 
 (carbonate of calcium). The presence of carbonic acid can readily be 
 detected by means of lime-water, since this insoluble precipitate of 
 carbonate of calcium is formed when the two substances are brought 
 together. 
 
 The bottles of gas obtained in Exp. 167, wiU, of course, con- 
 tain, besides carbonic acid, a quantity of nitrogen derived from 
 the air which took part in the combustion, unless, indeed, as was 
 suggested, the charcoal be burned in pure oxygen. It is to be 
 observed that, in all ordinary cases of combustion, whether of 
 wood, coal, wax, or oil, there result these same gaseous products 
 — carbonic acid and nitrogen; they ascend, as iavisible aerial 
 currents, from every well-regulated flame or fire, and are con- 
 tinually issuing from the chimneys of our houses, though, in the 
 absence of the particles of solid carbon, or of condensed aqueous 
 vapor, which constitute smoke, we can see no product of the 
 combustion. 
 
 Bxp. 169. — As was just now said, carbonic acid may be produced 
 also by heating carbon in contact with solid bodies which contain oxy- 
 gen, such, for example, as the red oxide of mercury. Mix 11 grammes 
 
322 
 
 PEEPARATION OF CABBONIC ACID. 
 
 of red oxide of mercury with 0'83 grm. of charcoal ; place the mixture 
 in an ignition-tube, arranged as in figure 53 ; heat the tube and collect 
 over water the gas which is evolved. Test the product with lime- 
 water, as in Exp. 168. The reaction between the charcoal and the 
 oxide of mercury may be written as follows : — 
 
 2HgO + = 00^ 4- 2Hg. 
 
 The metallic mercury set free condenses in droplets upon the cold 
 upper portions of the ignition- tube. Here, again, as ia Exps. 124, 155, 
 the metallic oxide is reduced by the charcoal. 
 
 398. Carbonic acid may readily be obtained from certain com- 
 pounds called carbonates, several of which are abundant minerals. 
 Common chalk, marble, and limestone, for example, are com- 
 posed of carbonate of calcium ; and carbonic acid can readily be 
 obtained by strongly heating them, or by subjecting them to the 
 action of strong acids. 
 
 Exp. 170. — Place two or three grammes of coarsely-powdered marble 
 in an ignition-tube provided with a gas delivery-tube bent at a right 
 angle ; place the ignition-tube upon the iron stand over the gas-lamp, 
 and dip the outer opening of the delivery-tube into a small bottle 
 containing lime-water ; heat the marble strongly, and observe the white 
 precipitate which forms in the lime-water as the carbonic acid gas 
 comes in contact with it. The carbonate of calcium, thus precipitated 
 by bringing together carbonic acid and oxide of calcium, is chemically 
 identical with the chalk or marble from which the acid was expelled. 
 
 In actual practice enormous quantities of carbonic acid are 
 expelled from limestone in this way for the sake of the quicklime 
 which is left as a residue ; but 
 
 the carbonic acid, thus expelled 
 by heat, is rarely collected, for 
 a more convenient method of 
 procuring it is to treat the lime- 
 stone with some acid capable of 
 expelling the carbonic acid. 
 
 Bxp. 171. — In a gas-bottle of 
 500 or 600 c. c. capacity, arranged 
 precisely as for generating hydro- 
 gen (see Exp. 19), place 10 or 12 
 grms. of chalk or marble in small 
 lumps; cover the chalk with 
 
 Fig. 55. 
 
PEEPAKATION 01' CARBONIC ACID. 323 
 
 water, and pour in througli the thistle-tute concentrated chlorhydiic 
 acid, by small portions, in such quantity as shall insure a continuous 
 and equable evolution of gas. Collect several bottles of the gas over 
 water, then replace the anterior portion of the delivery-tube with a 
 straight tube and collect one or two bottles of the gas by displace- 
 ment ; carbonic acid gas is half as heavy again as air. The reaction 
 between the carbonate of calcium and the chlorhydric acid may be 
 thus formulated : — 
 
 CaCO, + 2HC1 = CaClj + H^O + 00^. 
 
 When chalk is the material operated upon, sulphuric acid may be sub- 
 stituted with advantage for the chlorhydric acid ; for the latter, being 
 rather easUy volatile, is liable to be carried forward by the current of 
 carbonic acid, and to contaminate the product. When carbonic acid 
 is prepared for commercial prnposes by the action of an acid upon car- 
 bonate of calcium, sulphiuic acid is almost always the acid employed, 
 and marble-dust the substance acted upon : — 
 
 CaCO, + HjSOi = CaSO, + HjO -|- CO^. 
 
 With a porous material, like chalk, this action occurs readily ; but in 
 attempting to operate upon compact varieties of carbonate of calcium 
 such as marble, difficulties are encountered, unless the carbonate be in 
 the state of powder. The sulphate of calcium, which is a product of 
 the reaction, is a rather difficultly soluble substance, and, being depo- 
 sited upon the surface of the marble, soon covers it with a coating so 
 thick and impermeable that the action of the sulphuric acid upon the 
 marble is well nigh completely arrested. 
 
 Carbonate of calcium being cheaper than most other carbonates, is 
 more commonly employed than any other as a source of carbonic acid ; 
 but it is sometimes convenient to substitute for it the cai-bonate of 
 sodium, or of potassium (saleratus), or even of ammonium, since car- 
 bonic acid is given off from these compounds very quickly and abun- 
 dantly. A self-regulating gas-generator, such as is represented in Fig. 
 xxviii. of the Appendix, charged with large solid lumps of the com- 
 mercial carbonate of ammonium and chlorhydric acid, is, perhaps, the 
 most convenient apparatus which can be employed for preparing the 
 gas upon the lecture-table. 
 
 399. At the ordinary atmospheric temperature and pressure, 
 carbonitt acid is a transparent, colorless gas, of a slightly acid smell 
 and taste. It is incombustible, being abeady the product of the 
 complete combustion of carbon, and is, moreover, incapable of 
 supporting the combustion of most other bodies, since the oxygen 
 
324 PEOPBBTIES OF CAEBONIC ACID. 
 
 contained in it is very firmly held ; like nitrogen, it immediately 
 extinguishes burning bodies which are immersed in it. 
 
 Uxp. 172. — ^Thrust into a bottle of the gas obtained in Exp. 171, a 
 lighted candle, or, better, a large flame of alcohol burning upon a tuft 
 of cotton; in either case the flame will be instantly extinguished. 
 
 The specific heat of gaseous carbonic acid, between 10° and 
 200°, is 0-2169. Its specific gravity is 22 ; being thus 1-53 as 
 heavy as air, it can be poured from one vessel to another almost 
 as readily as if it were water. 
 
 Krp. 173. — Invert a bottle filled with carbonic acid upon another 
 bottle of equal size filled with air, in such manner that the mouth of 
 the upper inverted bottle shall rest upon the mouth of the lower bottle. 
 After the lapse of several minutes, thrust a burning splinter of wood 
 into each of the bottles ; in the upper bottle the splinter wiU continue 
 to bum, for into this bottle the air from the lower bottle has ascended ; 
 while in the lower bottle, now full of carbonic acid, the splinter will 
 be extinguished. 
 
 JExp. 174. — From a large bottle full of the gas, pour a quantity of 
 carbonic acid upon the flame of a lamp or candle ; that is to say, hold 
 the mouth of the open bottle of carbonic acid obliquely over the candle- 
 flame so that the gas shall fall like water upon it ; the flame will im- 
 mediately be extinguished. 
 
 400. Owing to tbe great weight of carbonic acid, it often fails 
 to rise out of wells and other cavities in the earth, in which it is 
 generated by the decomposition or decay of organic substances. 
 Before allowing workmen to descend into any such place, where 
 there is reason to suspect the presence of carbonic acid, a burning 
 candle should first be lowered ; if the candle be extinguished, or 
 even if it bum feebly, the noxious character of the air is indicated, 
 and measures should at once be taken to purify the locality by 
 ventilation or otherwise. One way of removing the carbonic acid 
 is to absorb it by means of some chemical agent, such as slaked 
 lime (hydrate of calcium) or potash-lye. The slaked lime is most 
 efiioient as an absorbent when neither very wet nor very dry ; it 
 should not be dry enough to be dusty, nor yet noticeably moist. 
 If a quantity of it be suspended in the well, or thrown upon the 
 floor of the cellar containing carbonic acid, this gas wiU quickly 
 combine with the lime to form carbonate of calcium, as inExp. 168. 
 Another good method is to lower down a chafing-dish full of 
 
VENTILATION OP TTELIS. 325 
 
 brightly glowing charcoal ; if the carbonic acid be present in such 
 quantity that the test-candle has been extinguished by it, the 
 charcoal will, in like manner, be immediately extinguished, and, 
 in cooling, will rapidly absorb this gas (see § 385), together with 
 any nitrogen which may be present ; a current of fresh air will, 
 in this way, be induced to flow into the weU. If, by the candle 
 test, but little carbonic acid be found in the well, it would, of course, 
 be best to extinguish the charcoal before lowering it into the im- 
 pure air ; this can readily be done by covering it up tightly in an 
 iron kettle. 
 
 It should be distinctly understood that the accumulation of 
 carbonic acid in wells and caves is a consequence of the low 
 difiPusive power of the gas (see § 53). Carbonic acid mixes with 
 air very slowly ; but when once mixed with air it has no further 
 tendency to settle down, or to separate itself in any way. 
 
 JExp. 175. — Over a bottle flUed with carbonic acid gas, invert an- 
 other bottle full of air, in such manner that the mouth of the air- 
 bottle shall rest upon that of the upright bottle full of carbonic acid. 
 After some hours, pour lime-water into each of the bottles and shake 
 them ; a precipitate of carbonate of calcium will he formed in both 
 cases, for a part of the carbonic acid wiU, by this time, have ascended 
 out of the lower into the upper bottle. The two gases have, in fact, 
 become intimately mixed or blended ; the heavy carbonic acid has 
 difiFused upwards into the air, and the lighter atmospheric air has dif- 
 fused downwards into the carbonic acid, just as, in a previous experi- 
 ment, we have seen hydrogen and oxygen diffuse into each other. 
 (Fig. 20, p. 43.) 
 
 The great importance of this diffusion of gases, in the economy of 
 nature, is well illustrated by the case now under consideration. When- 
 ever, as in the processes of respiration and combustion, oxygen is with- 
 drawn from and carbonic acid thrown into the air, the carbonic acid, 
 and the nitrogen with which it is accompanied, immediately mix with 
 the surrounding air and distribute themselves through the atmosphere. 
 The composition of the atmosphere is thus maintained uniform all 
 over the globe, in spite of the constant removal from it of oxygen in 
 some localities, and the addition of carbonic acid in others. It is only 
 in confined places, where nearly pure carbonic acid is produced more 
 rapidly than it can pass off by diffusion, that the gas accumulates to 
 any appreciable extent. 
 
 The singular facility with which gases, and particularly hydrogen, 
 
326 
 
 DIPFUSION OF GASES. 
 
 traverse porous bodies is very strikinglY illustrated by the following 
 experiment, which our acquaintance with carbonic acid now enables 
 us to perform : — Through a large glass tube, a smaller tube of porous, 
 unglazed earthenware is passed, and the ends of the glass tube are 
 tightly closed by the corks which hold the porous tube. By the tube 
 
 Fig. 56. 
 
 a, a rather rapid stream of carbonic acid is brought from a self-regu- 
 lating generator into the annular space between the two tubes, while, 
 by the tube b, a slower current of hydrogen is introduced into the inner 
 porous tube. It would be expected that hydrogen should be found in 
 the cylinder d, and carbonic acid in the cylinder c ; but, on the con- 
 ti'ary, an inflammable gas is found in c, and in the cylinder d carbonic 
 acid pure enough to extinguish a burning splinter. The hydrogen dif- 
 fuses almost instantaneously into the annular space, and the carbonic 
 acid enters the inner tube to replace the issuing hydrogen. 
 
 401. When pure, or nearly pure, carbonic acid is irrespirable ; 
 it produces spasms in the respiratory passages, and is thus pre- 
 vented from entering the lungs. When so far diluted with air as 
 to admit of being respired, it acts as a narcotic poison ; it is, how- 
 ever, far less poisonous than the other oxide of carbon, carbonic 
 oxide, directly to be described. 
 
 402. Carbonic acid gas is soluble in water to a considerable 
 extent. One measure of water, at the ordinary temperatore and 
 pressure, will dissolve one measure of carbonic acid gas ; but its 
 solubility increases if the pressure be increased. 
 
 Exp. 176. — Into a long-necked flask or phial fiUed with carbonic 
 acid, pour a quantity of water, close the bottle with the finger, and 
 shake it ; immerse the mouth of the bottle in water, and remove the 
 finger, water will rush into the bottle to supply the place of the gas 
 which has been dissolved. Again place the flmger upon the mouth of 
 
SOUJBILIIT OP CARBONIC ACID. 327 
 
 the bottle, shaie the bottle as before, and subsequently open it beneath 
 the surface of the water ; a fresh portion of water will flow into the 
 bottle to supply the new vacuum ; in this way, by repeated agitation 
 with water, all of the carbonic acid in the bottle can be absorbed. 
 
 Owing to this solubility in water, some carbonic acid is always lost 
 when the gas is collected over water as in Exp. 171 ; but since consi- 
 derable time is required to absorb all the gas, there is little objection 
 to collecting it over water. 
 
 403. When subjected to increased pressure, carbonic acid gas 
 dissolves in water much more abundantly than at the ordinary 
 pressure of the air ; under a pressure of two atmospheres, one 
 measure of water vrill dissolve two measures of the gas ; under a 
 pressure of three atmospheres, it will dissolve three measures, and 
 so on. Water thus surcharged with carbonic acid has an agree- 
 able, acid, pungent taste, and effervesces briskly when the com- 
 pression is suddenly removed, as when the liquid is allowed to 
 flow out into the air ; such carbonic acid water, or " mineral 
 water," as it is then called, flows from the earth in many locali- 
 ties, as at Seltzer and Saratoga ; it is also prepared, artiflciaUy, 
 in large quantities, and sold as a beverage under the meaningless 
 name of soda-water. Carbonic acid water possesses solvent 
 powers far greater than those of pure water ; few minerals are 
 capable of resisting its long-continued action ; hence the waters 
 of the springs from which it issues are usually highly charged 
 with saline and mineral ingredients, and are often of medicinal 
 value. 
 
 404. The effervescent qualities of fermented liquors, such as 
 cider, champagne, and beer, are in like manner dependent upon 
 the presence of compressed carbonic acid gas. In all these cases 
 the carbonic acid is of value, not only on account of the agreeable 
 pungency which it imparts to the beverage, but also because of 
 the fact that in escaping from solution and assuming the gaseous 
 condition, it absorbs a very considerable amount of heat, and so 
 cools the Kquid which contained it. 
 
 405. Carbonic acid is widely diffused in nature. Traces of it 
 occur in the air and in water everywhere ; and there are many 
 localities, besides the mineral springs before-mentioned, where it 
 issues from the earth in large quantities, notably in several vol- 
 
328 EBBMENTAIIOlf. 
 
 canio districts. It is produced not only in the actual combustion 
 of all substances which contain carbon, but also during the decay 
 and putrefaction of all animal and vegetable substances. During 
 fermentation it is evolved in large quantities, and it is continually 
 given off during the respiration of animals. 
 
 Exp. 177. — Put one or two table-spoonfuls of coarse meal into a 
 bottle of about 250 c. c. capacity ; cover tbe meal with water, and con- 
 nect the bottle, by means of a cork and glass tube, with a second bottle 
 filled about three cm. deep with lime-water ; the delivery-tube must 
 reach into the lime-water. Out of the top of the second bottle carry 
 a second bent glass tube, whose open end dips into water. The bottle 
 containing the lime-water will, of course, be closed by the cork through 
 which pass the two tubes above described. Keep the apparatus in a 
 warm place ; bubbles of gas will pass from the first into the second 
 flask ; they contain carbonic acid, as may be seen from the precipitate 
 of carbonate of calcium which they produce. 
 
 Exp. 178. — Dissolve 2 grammes of honey or molasses in 200 c. c. of 
 water ; fiU a large test-tube with the mixture, and add to it a few drops 
 of bakers' or brewers' yeast ; close the open mouth of the test-tube 
 with the thumb, and invert it in a small saucer or porcelain capsule 
 filled with the diluted syrup. Place the saucer and tube, with their 
 contents, in a warm place, having a temperature of about 20° or 30°, 
 and leave them there during 24 hours. In a short time, fermentation 
 sets in, and the sugar of the syrup is gradually converted into alcohol 
 and carbonic acid. 
 
 C,H,,0, = 202H„0 + 200,. 
 Sugar. Ahohol. 
 
 The carbonic acid thus formed rises in minute bubbles, causing a gentle 
 effervescence in the liquid, and collects in the upper part of the tube, 
 while the alcohol remains dissolved in the liquid. That the gas ob- 
 tained in this experiment is really carbonic acid, may be proved by 
 transferring some of it into a clean tube at the water-pan, and then 
 testing with lime-water. 
 
 Exp. 179. — Provide two test-glasses or small bottles ; place in each 
 15 or 20 c. c. of lime-water ; through a glass tube blow into the lime- 
 water of one of the bottles air coming from the lungs. By means of 
 bellows, to the nozzle of which a gas-deHvery tube has been attached, 
 force through the hme-water of the second bottle a quantity of fresh 
 air. The clear liquid of the first bottle will quickly become turbid 
 through deposition of carbonate of calcium, while the lime-water of the 
 second bottle wiU remain clear for a long while. 
 
EESPIEATIOJf. 329 
 
 This experiment may be modified by constructing an apparatus 
 with vaJves, in such manner that the air drawn into the lungs shall 
 he made to pass through one bottle of lime-water, while the air ex- 
 pired goes out through another bottle of lime-water. The contents of 
 the first bottle will remain clear, while the liquid in the other imme- 
 diately becomes turbid. 
 
 Ordinary fresh air contains only about one 2000th part of carbonic 
 a«id, while air expired from the lungs contains as much as 3 or 4 per 
 cent, of it. Inbreathing, animals inhale oxygen from the air; this 
 oxygen combines with carbon within their bodies and is exhaled as 
 carbonic acid. A crowd of men consume the oxygen of the air, just 
 as lamps or fires consume it ; to carry ofl^ this product of animal com- 
 bustion is one of the objects of systems of ventilation. Air which con- 
 tains even as little as 1 or 2 per cent, of carbonic acid, exerts a very 
 depressing efiect when breathed for any length of time. 
 
 406. Prom the foregoing statements it appears that, in the 
 several processes called "life," "fermentation," "decay," and 
 " combustion," there is involved chemical action ; in all of these 
 processes oxygen from the air unites with carbon, while carbonic 
 acid is set free and thrown into the atmosphere. The question 
 now arises. What becomes of all this vast amount of carbonic acid 
 which is constantly coming into our atmosphere from the respira- 
 tion of animals, from fires, from decaying and fermenting. sub- 
 stances, from volcanic fissures, and from various other sources ? 
 If this carbonic acid remained in the air, the latter would quickly 
 become unfit to support animal life. But it is not found that the 
 average proportion of carbonic acid in the air does increase ; on 
 the contrary, all the evidence goes to show that there was, at 
 certain earKer geological epochs, more of it in the air than novr. 
 Many geologists believe that, in the early history of. our globe, 
 there was much more carbonic acid in the air than at present ; 
 hence immense forests arose whose carbon is now stored away 
 in the form of coal ; hence also the formation of enormous beds 
 of limestone covering many parts of the earth's surface, — ^processes 
 of which the faint continuations are now seen in the formation of 
 peat-bogs and coral-reefs. On the other hand, it is not found 
 that the proportion of oxygen in the atmosphere undergoes any 
 appreciable change, in spite of the enormous volume of it which 
 is absorbed in the processes of breathing, combustion, and decay 
 
330 LiaUID CARBONIC ACLD. 
 
 above enumerated. For, unlike animals, plants, in breathing, 
 take ia carbonic acid and give out oxygen. The leaves of plants 
 are so constructed that they can decompose carbonic acid, fix car- 
 bon for the buUding up of the plant, and set oxygen free. This 
 reciprocal action of plants and animals, tending to maintain un- 
 changed the constitution of the atmosphere, is one of the most 
 wonderful adjustments of nature. 
 
 407. Carbonic acid can be liquefied by pressure, and the liquid 
 thus obtained can be solidified by exposure to cold. When the 
 gas is generated in a confined space in a strong vessel, it soon 
 exerts so powerful a pressure that a large portion of it condenses 
 to a transparent, colorless, mobile liquid, somewhat resembling 
 water, though it refracts light less powerfully ; or it may be 
 liquefied by mere cooling to — 106°, under the atmospheric pres- 
 sure. A better way of preparing the liquid acid is to pump the 
 gas, by means of a forcing syringe, into a strong wrought-iron 
 vessel surrounded with pounded ice. The pressure can thus be 
 regularly and methodically increased and the receiver finally filled 
 with the liquid. At 0° a pressure of 36 atmospheres is required, 
 in order that the acid shall remain in the liquid state. Liquid 
 carbonic acid does not mix readily with water or with the fixed 
 oils ; . but with alcohol, ether, petroleum, and similar liquids it is 
 miscible in aU proportions. Its specific gravity is 0-83 at 0°; but 
 it expands to such an extent on being heated, that at 30° its 
 specific gravity is only 0'6. It expands to a greater extent, on 
 the application of heat, than any known substance, even to a 
 greater extent than the gases ; 20 volumes of it at 0° become 29 
 volumes when the temperature is raised to 30° ; 150 volumes, at 
 30°, shrink to 100 volumes when the temperature is reduced to 
 — 20°. The liquid acid well illustrates the general fact that 
 liquids expand proportionally much more when heated under a 
 high pressure than under a low one. 
 
 408. If the stop-cock of a vessel containing liquid carbonic 
 acid be opened, in such manner that a stream of the liquid shall 
 be forced out into the air, a portion of it at once assumes the 
 gaseous state, and in so doing absorbs so much heat from the re- 
 mainder that the latter solidifies, and is deposited in the form of 
 white flakes like snow. This snow-like substance is slowly con- 
 
SOLID CAEBONIC ACID. 331 
 
 verted into gas when exposed at the ordinary pressure of the air, 
 and so disappears. Though its temperature is lower than —78°, 
 it may be handled lightly without exciting any special sensation 
 of coldness or pain ; for the gas which it is constantly emitting is 
 a bad conductor of heat, and prevents it from coming into intimate 
 contact with the skin. When, however, the solid acid is forcibly 
 pressed between the fingers, it produces painful blisters, as if it 
 were red-hot iron. In order to use the solid acid for producing 
 low temperatures, it is best to mix it with a small quantity of 
 ether ; in such a mixture quicksilver can readily be frozen, and 
 many gases can be Hquefled or even solidified. If this mixture 
 be placed in the vacuum of an air-pump, a temperature as low as 
 — 100° can be obtained ; and if a tube containing liquid carbonic 
 acid be then placed in the mixture, the liquid will speedily be 
 frozen to a clear transparent mass Uke ice. 
 
 409. Carbonic acid gas, on being heated from 0° to 100°, does 
 not expand at the same rate as air and the other permanent 
 gases, but increases in volume to a greater extent than any of 
 them. Upon being heated one degree, it expands 0-003688 its 
 volume at 0°. This behavior is in accordance with the general 
 rule, that those gases expand the most which are most readily 
 condeusable to the liquid state, while those gases which have re- 
 sisted all eiforts to liquify them scarcely show any appreciable 
 differences in the rate of expansion. 
 
 In the same way, carbonic acid, like the other easily condensable 
 gases (see § 221), does not conform precisely to the law of Mari- 
 otte. At pressures greater than one-third of the pressure of our 
 atmosphere, its volume diminishes more rapidly, with increasing 
 pressure, than would be the case with air and the other permanent 
 gases under the same conditions. 
 
 410. Carbonic acid is one of the compound gases which can be 
 split by heat alone into its proximate constituents ; in other words, 
 it exhibits the phenomena of dissociation (§ 300). When the gas 
 is passed through a strongly heated porcelain tube, the gaseous 
 mixture which escapes from the tube contains, besides undecom- 
 posed carbonic acid, notable quantities of carbonic oxide (CO) and 
 oxygen. 
 
 411. As has been already stated (§ 399), the oxygen in carbonic 
 
332 
 
 BECOMBOSIIION OF CAKBONIO ACID. 
 
 acid is so strongly held that it cannot be withdrawn by combusti- 
 bles under ordinary circumstances ; but at high temperatures car- 
 bonic acid is decomposed by carbon and by several of the metals— 
 such as iron, zinc, and manganese, besides potassium, sodium, and 
 the other metals of the alkalies and alkaline earths. By the 
 alkaU-metals the oxygen is completely removed from carbonic 
 acid, and carbon is set free ; but by the other agents above-men- 
 tioned, only half the oxygen of the acid is taken away, while car- 
 bonic oxide gas is formed : — 
 
 CO, + C = 2C0. 
 Phosphorus, also, at high temperatures and in presence of a fixed 
 alkali, decomposes carbonic acid in the same way, and abstracts 
 part of its oxygen. So, too, if a mixture of equal voliunes of hy- 
 drogen and carbonic acid be passed into one end of a red-hot tube, 
 steam and carbonic oxide gas will escape at the other : — 
 CO, + 2H = CO + H,0. 
 
 The decomposing-power of the alkali-metals, above alluded to, 
 furnishes us one means of partially analyzing carbonic acid. 
 
 £xp. ISO.^To a gas-bottle in which carbonic acid is being steadily 
 evolved, according to Exp. 171, attach a chloride-of-calcium tube, and 
 beyond this drying-tube a short tube of hard glass, from which an 
 exit-tube leads into a small open bottle, as shown in Fig. 57. When 
 
 Fig. 57. 
 
 Ui=c=i=asi 
 
 3f==ri 
 
 the extinction of a lighted match in the open bottle proves the appa- 
 ratus to be full of carbonic acid, thrust into the hard-glass tube a bit 
 of potassium as big as a pea, previously dried between folds of blotting- 
 paper, and then gently heat the potassium with a lamp. The potassium 
 will take fire and bum at the expense of the oxygen of the carbonic 
 acid, and black particles of carbon will be deposited upon the walls of 
 the tube. After the reaction has ceased, and the tube has been allowed 
 
COMPOSITION OF CAEBONIC ACID. 333 
 
 to become cold, place it in a bottle of water so that the saline mas8 
 (carbonate of potassium) may dissolve ; the particles of carbon will then 
 be seen more clearly, floating in the liquid ; they may be collected 
 upon a filter. The potassium in this experiment may be replaced by 
 sodium, but in this case a somewhat higher temperature is required. 
 
 412. The quantitative composition of carbonic acid may be 
 readily ascertained by the method of synthesis. When a quantity 
 of carbon is burned in a confined and measured volume of oxygen, 
 it is found that the volume of carbonic acid gas produced has 
 sensibly the same bulk as the original oxygen. Hence we con- 
 clude that the normal or product-volume of the molecule of car- 
 bonic acid gas contains two volumes of oxygen, 
 
 Now two volumes of carbonic acid weigh 44*152, since the 
 weight of the unit-volume, or the specific gravity of carbonic 
 acid, has been found to be 22-076. 
 
 Subtracting from this weight of the product-volume of the gas 44-152 
 The weight of two unit-volumes of oxygen (15-969 X 2) . . 31-938 
 There remains as the weight of the carbon in the product- 
 volume of the gas 12-214 
 
 The weight of one atom of carbon is 12, as we have seen above 
 (§ 395), and it follows that the formula of carbonic acid is CO^. 
 From these figures the following percentage composition of car- 
 bonic acid may be deduced : — 
 
 Carbon 27-66 
 
 Oxygen 72-34 
 
 100-00 
 But these results must be regarded merely as approximations to 
 the truth, since the deviation of carbonic acid from the law of 
 Mariotte (§ 409) renders it weU-nigh certain that we have not 
 yet been able to precisely determine, by experiment, the true 
 weight of a unit-volume of this gas. 
 
 413. The composition of carbonic acid, however, has been de- 
 termined with very great accuracy by burning a known weight 
 of pure carbon in a stream of oxygen gas and carefully collecting 
 and weighing the carbonic acid produced. 
 
 In order to do this, the product of the combustion of the carbon, 
 together with the excess of oxygen, is made to flow through U-tubes 
 
334 
 
 SYNTHESIS OF CABBONIC ACIH CAKBOJTATBS. 
 
 (Appendix, § 15) filled with fragments of hydrate of potassium, a suh- 
 stance which absorbs only the carbonic acid ; the weig^ht of these tubes 
 is determined before the commencement of the experiment and again 
 at its close, the increase of weight during the experiment being, of 
 course, referable to the carbonic acid absorbed. Knowing, then, the 
 weight of the carbon taken and the weight of the carbonic acid into 
 which it has been converted by uniting with oxygen, a very simple 
 calculation, as before, gives us the percentage composition of the acid. 
 Experiments of this kind have yielded the following result : — 
 
 Carbon 27-27 
 
 Oxygen 7273 
 
 10000 
 It therefore, appears, that, in uniting to form carbonic acid, the 
 elements carbon and oxygen combine in the proportion of 3 parts 
 by weight of carbon to 8 parts by weight of oxygen, or in the 
 proportion of 12 to 32. If the number 72-73 be divided by 16, 
 the number representing the weight of a unit- volume of oxygen, 
 and if the number 100 be divided by 22, the number which, in 
 accordance with the weight of all the evidence thus far accumu- 
 lated must be regarded as the true unit- volume weight of carbonic 
 acid, there will be obtained in each case the same quotient, namely, 
 4-545 volumes ; whence we conclude, as before, that any volume 
 of carbonic acid contains the same volume of oxygen. 
 
 414. Carbonic acid unites with the protoxides of most of the 
 metals to form well-defined salts called carbonates. The greater 
 number of the best-defined carbonates contain only one molecule 
 of base ; but besides the normal carbonates of the general for- 
 mula yLfifiO^ or MjCOg, there are sesquicarbonates of the for- 
 mula 2M,0,3CO^, « bicarbonates " of the formula Mfl,TS.fi,2C0^ 
 or MHCOj, and basic carbonates containing two, three, or more 
 molecules of the base to one of the acid. In general the term 
 basic salt is applied to all salts in which; as in the carbonates last 
 named, the alkaline constituent or base predominates. The ap- 
 pellation " bicarbonate," though ordinarily applied in the manner 
 indicated above, is a name of very doubtful correctness ; strictly 
 speaking, the class of compounds to which it refers should, per- 
 haps, be regarded as double salts of the metal and hydrogen. The 
 normal carbonate, and the so-called bicarbonate of sodium, for 
 
CARBONIC OXIDE. 
 
 335 
 
 example, differ only in that half the sodium in the normal salt 
 has been replaced by hydrogen in the bicarbonate : — 
 Normal Carbonate of Sodium. Bicarbonate of Sodium. 
 
 ISTa^CO,. NaHCO,. 
 
 Carbonic acid is an exceedingly weak acid ; it faUs to neutra- 
 lize (§ 65) completely the causticity of oxides such as those of the 
 alkaline metals ; the normal carbonate of sodium, for example, is 
 decidedly alkaline in its reaction and properties. The so-caUed 
 bicarbonate of sodium is also slightly alkaline ; and even the solu- 
 tion of carbonate of calcium in carbonic acid water exhibits an 
 alkaline reaction when tested with turmeric paper. Almost aU 
 the carbonates are readily decomposed by acids (even by very 
 weak acids), with an effervescence caused by the escape of car- 
 bonic acid. Most of them are decomposed also on being heated ; 
 but from the normal salts of sodium and potassium carbonic acid 
 cannot be expelled by heat alone, however intense. 
 
 415. Carbonic Oxide (CO). — As has been stated in § 411, car- 
 bonic oxide can be prepared by acting upon carbonic acid with 
 hot charcoal. 
 
 Uxp. 181. — In the middle of a tube of hard glass, No. 2 or 2^, about 
 35 cm. long, pack a colunm 15 cm. in length of coarsely-powdered 
 charcoal. Place the tube upon a sheet-iron trough on a ring of the 
 iron stand above wire-gauze lamps, as shown in the figure. Connect 
 
 Fig. 58. 
 
 T 
 
 *■■=« 
 
 the tube either with a gas-holder containing carbonic acid, or with a 
 bottle in which the gas is being generated. Heat the charcoal in- 
 tensely, and from time to time test the gas which is delivered at the 
 water-pan, as to its inflammability. Carbonic oxide takes fire on being 
 
336 PEEPAEATION OF CAEBONIC OXIDE. 
 
 touched with a lighted match, and hums with a bluish flame. In place 
 of the charcoal, small fragments of iron or of zinc may he employed in 
 this experiment. 
 
 Instead of gaseous carbonic acid, the solid compounds called 
 carbonates can be conveniently employed for preparing carbonic 
 oxide. 
 
 E.vp. 182. — Mix powdered chalk (carbonate of calcium) with an 
 equal weight of iron or zinc filings, place the mixture in an ignition- 
 tube, provided with a gas-delivery tube, and heat it to redness over 
 the gas-lamp. The metal will abstract an atom of oxygen from the 
 carbonate of calcium, oxide of iron or of zinc wiU be formed, while 
 carbonic oxide will pass off through the delivery-tube to be collected 
 at the water-pan : — 
 
 CaCO^ -f- Fe = FeO -f OaO -\- CO. 
 In the same way, when a mixture of chalk and finely-powdered 
 charcoal is heated to full redness, carbonic oxide gas is given oflF: — 
 
 CaCOj -1- = OaO -I- 200. 
 It should be mentioned, however, that in all these cases the carbonic 
 oxide obtained is more or less contaminated with carbonic acid, por- 
 tions of which escape reduction by the metal and carbon ; the carbonic 
 acid may always be readily removed by causing the gas topaas through 
 a strong solution of caustic soda or through a U-tube filled with bits 
 of pumice-stone saturated with soda-lye. 
 
 Carbonic oxide can be obtained also by heating charcoal with 
 other solid oxygen compounds, such as the phosphate of calcium, 
 already mentioned (§ 270), or the oxides of almost any of the 
 metals, provided the charcoal be in excess. 
 
 Exp. 183. — Heat in an ignition-tube, as before, a mixtm-e of 1 grm. 
 of finely-powdered charcoal and 8 grms. of red oxide of iron ; collect 
 the gas over water, pour into the bottle a little soda-lye, close the 
 mouth of the bottle tightly and shake it, then open the mouth of the 
 bottle under water, and finally test the gas with a lighted match. 
 
 416. Another easy method of preparing carbonic oxide is to 
 decompose oxalic acid by means of oil of vitriol; this is the 
 method usually employed in the laboratory. Oxalic acid is a 
 solid vegetable acid, to be procured of the druggists ; its com- 
 position may be represented by the formula H^CjO^. On being 
 heated with concentrated sulphuric acid, it suffers decomposition 
 in a manner which may be formulated as follows : — 
 
 H,0,CP3 -f H,0,S03 = 2Hp,S0, -f CO -1- CO,. 
 
PREPAKATION OF CARBONIC OXIDB. 
 
 337 
 
 The elements of water are taken away from the oxalic acid and 
 united with the sulphuric acid, while the remainder of the oxalic 
 acid breEiks up into carhonic acid and carbonic oxide. 
 
 Exp. 184. — ^Place in a flask of about 350 c. c. capacity 9 grms of 
 common oxalic acid and 53 
 
 grms. of concentrated sul- S- "*'• 
 
 phuric acid; connect the 
 flask with a bottle filled 
 with fragments of pumice- 
 stone saturated with a strong 
 solution of caustic soda, as 
 shown in the figure ; heat 
 the contents of the glass 
 gently, and collect the gaa 
 which is evolved over water 
 in the usual way. The car- 
 bonic acid resulting from the 
 reaction will aU be absorbed 
 by the soda-lye, and carbonic 
 oxide win alone be delivered 
 at the water-pan. 
 
 If one of the methods heretofore given jrield pure carbonic oxide 
 directly ; in each of the experiments we are compelled to wash 
 out carbonic acid from the gas obtained, if an absolutely pure 
 product is desired j but there are methods by which pure carbonic 
 oxide may be prepared without the need of any process of purifi- 
 cation. One of the best of these is as follows : — 
 
 JExp. 185. — In a thin-bottomed flask of about 250 c. c. capacity and 
 provided with a suitable gas-deUvery tube, heat a mixture of 5 grammes 
 of finely powdered ferrocyanide of potassium (yellow prussiate of pot- 
 ash) and 40 or 50 grms. of strong sulphuric acid. Collect the gas 
 over water, and test it as to its inflammability. Thrust also a lighted 
 splinter into the gas and observe that it will be extinguished. The 
 reactions which occur between the chemicals employed may be ex- 
 pressed as follows : — 
 
 Ferrocyanide of Potassium. Water. StdphuHc Acid. 
 
 KjFeCjNjHeOj + SH^O -|- eH^SO^ 
 = 600 -I- SKjSO^ 4- FeSO^ + SCNHJ^SO,. 
 Carhonic Sulphate of Sulphate of Sulphate of 
 
 Oxide. Potassium. Iron. Ammonium. 
 
 z 
 
338 PEOPEEIIES OP CAEBONIC OXIDE. 
 
 417. Carbonic oxide is a transparent, colorless gas, having 
 little, if any, odor ; it has never yet been hquefied. It is some- 
 what lighter than air, its specific gravity being 14, while that of 
 air is 14-5. It is but little soluble in water, and may be col- 
 lected and preserved over water without much loss. It extin- 
 gTiishes combustion just as hydrogen does, and destroys animal 
 life. Unlike hydrogen and nitrogen, however, it is a true poison. 
 It destroys Ufe, not negatively by mere suffocation or exclusion 
 of oxygen, but by direct noxious action. Even when largely 
 diluted with air, it is still poisonous, producing giddiness, insen- 
 sibility, and finally death. It is the presence of this gas which 
 occasions the peculiar sensation of oppression and headache which 
 is experienced in rooms into which the products of combustion 
 have escaped from fixes of charcoal or anthracite. Carbonic oxide 
 is very much more poisonous than carbonic acid. Much of the 
 ill repute which attaches to carbonic acid reaUy belongs to car- 
 bonic oxide ; for since both these gases are produced by burning 
 charcoal, many persons are hable to confound them; but car- 
 bonic acid is, comparatively speaking, almost innocuous. Car- 
 bonic acid, it is true, is somewhat poisonous ; it does not merely 
 suffocate, like water, or nitrogen, or hydrogen; but it is very 
 much less poisonous than carbonic oxide. It has been found, by 
 experiment, that an atmosphere containing only 1-lOOth of car- 
 bonic oxide is as fatal to a bird as one containing l-25th part of 
 carbonic acid. 
 
 Carbonic oxide exhibits neither an acid nor an alkaline reac- 
 tion when tested with vegetable colors, and, in general, has but 
 little tendency to combine with other substances. With oxygen, 
 however, it combines readily at comparatively low temperatures ; 
 an iron wire heated to duU redness is sufficient to infiame it in 
 the air. Unlike most other combustible gases, it contains no 
 hydrogen, and therefore produces no water when burned; 
 nothing but carbonic acid results from its burniug. 
 
 Exp. 186. — ^To the apparatus employed for evolving carbonic oxide 
 in Exp. 184, attach a piece of small glass tubing drawn out at the end 
 to a fine point, and bent in such manner that a stream of gas may be 
 delivered upwards from this point. Light the gas as it flows out of 
 the tube, and hold over the pale-blue flame a clean, dry bottle. No 
 
PEOPEKIIES OJf CAESONIC OXIDE. 339 
 
 moisture will be deposited upon the sides of the bottle. That car- 
 bonic acid has been produced by the combustion, may be proved by 
 pouring a little lime-water into the bottle, and shaking it about in the 
 gas therein contained. 
 
 418. Carbonic oxide is a very powerful deoxidizing agent. At 
 high temperatures it is capable of taMng oxygen away from 
 many of the compounds which contain that element. Hence it 
 plays a very important part in metallurgical operations. Much 
 of the reduoing-action which is commonly attributed directly to 
 carbon, is really effected in practice through the mediation of 
 carbonic oxide gas. 
 
 lExp. 187. — In the middle of a tube of hard glass, No. 3, about 20 
 cm. long, place a gramme of black oxide of copper (CuO) ; support 
 the tube upon a ring of the iron stand over the gas-lamp, and connect 
 it at one end with a flask in which carbonic oxide is being evolved, 
 as in Exp. 184, and at the other with a tube bent at a right angle and 
 dipping into a bottle which contains lime-water. After the tube, which 
 contains the oxide of copper, has become full of carbonic oxide, heat 
 it and observe that the oxide of copper is reduced, that metallic copper 
 alone remains in the tube, and that the carbonic acid formed has made 
 turbid the lime-water in the bottle. 
 
 419. The specific heat of carbonic oxide is considerably greater 
 than that of carbonic acid, being 0-245, while that of carbonic 
 acid is only 0-2103. 
 
 When a mixture of carbonic oxide and oxygen, in the pro- 
 portion of two volumes of the former to one of the latter gas, 
 is lighted, it explodes with about the same degree of violence as 
 a mixture of hydrogen and oxygen (§ 58), a very considerable 
 amount of heat being evolved in the act of combination. 
 
 Though considerable heat is evolved during the union of car- 
 bonic oxide and oxygen, the amount is much less than that which 
 results from the complete combustion of charcoal to carbonic acid. 
 One gramme of carbonic oxide disengages in burning 2403 units 
 of heat (§ 55), while one gramme of wood charcoal, in burning 
 to carbonic acid, yields 8080 units. The same amount of heat 
 (2403 units) is reabsorbed when the carbonic acid, obtained by 
 burning one gramme of carbonic oxide, is again reduced to the 
 state of carbonic oxide. (Compare Exp. 181.) 
 
 The gramme of hydrogen yields, as it unites with oxygen, 
 
 z2 
 
340 BISSOCIATIOIf OF CARBONIC OXIDE. 
 
 34,462 units of heat; but since carbonic oxide is 14 times 
 as heavy as hydrogen, about the same quantity of heat is deve- 
 loped by the complete combustion of a given volume of carbonic 
 oxide as by that of the same volume of hydrogen. 
 
 420. Carbonic oxide, unlike carbonic acid, is not decomposed 
 when heated to redness in contact with hydrogen, charcoal, iron, 
 or zinc. Sodium and potassium, however, abstract the oxj'gen 
 from this gas as they do from carbonic acid. 
 
 It unites with chlorine directly, under the influence of sun- 
 light, forming a gaseous compound, the composition of which 
 may be represented by the formula COClj. When left for some 
 time in contact with caustic potash, at the temperature of 100°, 
 it combines with it, and there is produced a compoimd known as 
 formiate of potassium : — 
 
 KHO -h CO = CHKO,. 
 It is absorbed readily by solutions of the salts of dinoxide of 
 copper (Cu^O) in ammonia-water, and by a solution of dichloride 
 of copper (CujCl^) in strong chlorhydric acid, and can thus be 
 separated from a mixture with other gases. Melted metallic 
 potassium also absorbs a certaia amount of carbonic oxide and 
 combines with it. 
 
 421. Carbonic oxide may be resolved into carbon and oxygen 
 by heat alone ; but this dissociation occurs only under very peculiar 
 circumstances. 
 
 A porcelain tube is placed in a furnace where it can be raised to a 
 very high temperature ; the ends of this tube project beyond the fur- 
 nace and are closed by corks ; through these corks passes, in the axis 
 of the porcelain tube, a very thin brass tube, and each cork carries also 
 a small glass tube ; by one of these tubes carbonic oxide enters the por- 
 celain tube, and by the other the products of the reaction escape from 
 the apparatus. Two little screens of porcelain divide internally that 
 part of the porcelain tube which lies in the furnace and is to be heated, 
 from the parts which project beyond the furnace and remain cool. A 
 rapid current of cold water is made to flow through the thin brass tube, 
 in such quantity that in traversing the tube while the furnace is in full 
 action the water shall not be sensibly wai'med. 
 
 The apparatus being thus disposed, and the porcelain tube heated, a 
 slow and regidar current of pure and dry carbonic oxide is passed into 
 the hot tube. The gas, as it issues from the tube, passes immediately 
 
COMPOSITION OF CAEBOOTC OXIDE. 341 
 
 through a strong solution of caustic potash, which will absorb the car- 
 bonic acid formed, so that the experimenter can weigh the c[uantity of 
 acid produced, or through lime-water, which will demonstrate the pre- 
 sence of carbonic acid by becoming turbid. Carbonic acid is formed 
 whenever the porcelain tube is bright-red hot. A portion of the car- 
 bonic oxide is decomposed into oxygen, which unites with another 
 portion of carbonic oxide to make carbonic acid, and carbon, which is 
 deposited in the condition of lampblack upon the cold brass tube which 
 traverses the hot porcelain tube from end to end. The first action of 
 the heat is to set free particles of carbon from the carbonic oxide, and 
 all such particles which happen to fasten upon the brass tube are in- 
 stantly chilled down below the temperature at which they will either 
 unite with free oxygen on the one hand, or reduce carbonic acid on 
 the other. 
 
 We have repeatedly used the electric spark as a means of decom- 
 posing compound gases, such, for example, as ammonia (§ 89) and 
 marsh-gas (§ 395). It is supposed that it is the intense heat of the 
 spark which effects such decomposition, and, in the light of the experi- 
 ment just described, it seems probable that the efficacy of the spark- 
 current is due to the fact that the few particles of gas which each spark 
 heats intensely are immediately in contact with an atmosphere of gas 
 which is in constant motion and is relatively very cold. 
 
 422. The composition of carbonic acid being known, that of 
 carbonic oxide can readily be determined by burning a ^ ^^ 
 definite volume of this gas with an excess of oxygen in _, — ^ 
 a eudiometer. If there be introduced into the eudi- ^^--v 
 ometer 
 
 100 volumes of carbonic oxide, 
 and 100 „ „ oxygen, 
 
 and if through the 200 „ „ mixed gases 
 
 an electric spark be made to pass, combination will 
 
 occur, and the gas which remains wiU occupy only 150 volumes. 
 
 If a small quantity of a solution of caustic soda be now introduced 
 
 into the eudiometer, aU the carbonic acid which has been formed 
 
 will be absorbed; there will remain only 50 volumes of gas, 
 
 which, upon examination, will be found to be pure oxygen. 
 
 If only 50 volumes of the original oxygen are thus left free, 
 50 volumes of oxygen must have been absorbed. It appears, 
 then, that 100 volumes of carbonic oxide have united with 50 
 volumes of oxygen to form 100 volumes of carbonic acid; and 
 
342 COMPOSITION OF CARBONIC OXIDB. 
 
 that the original bulk of the carbonic oxide taken has remained 
 unchanged. Since it is admitted, as we have already seen (§ 412), 
 that the product- volume of carbonic acid contains 2 volumes of 
 oxygen, it foUowB that the double volume of carbonic oxide can 
 only contain 1 volume of oxygen — or, in other words, that 2 vo- 
 lumes of this gas contain 1 volume of carbon-vapor and 1 volume 
 of oxygen united without condensation : — 
 
 12 ^ 
 
 
 16 
 
 = 
 
 CO 28 
 
 It will be noticed that the addition of a certain quantity of oxy- 
 gen to a measured quantity of carbonic oxide converts it into 
 carbonic acid without changing the original measured volume of 
 gas. We have often prepared compound gases from elementary 
 gases by this method, and in such cases there is generally a 
 change of voiume. We are here, however, converting one com- 
 pound gas into another compound gas, and the product-volumes 
 of aU compound gases are the same. 
 
 The specific gravity or unit-volume weight of carbonic oxide 
 has been found, by experiment, to be 13-97. 
 
 From the weight of two unit- volumes of carbonic oxide . 27 '94 
 Deduct the weight of one unit-volume of oxygen .... 16' 
 
 There remains the weight of the atom of carbon .... 11-94 
 
 This result accords very well with the previously given atomic 
 weight of carbon. It wiU be noticed that the specific gravity of 
 carbonic oxide is the same as that of nitrogen. 
 
 423. Combustion. — Now that we have become acquainted with 
 carbon, hydrogen, and oxygen, and with some of the more im- 
 portant compounds formed by the union of these elements, the 
 subject of combustion can be more fuUy discussed than has been 
 possible hitherto. Unlike most of the chemical processes em- 
 ployed by man, which have for their object the preparation of 
 some tangible chemical compound or product, combustion is 
 resorted to merely for the sake of the heat or light which inci- 
 dentally accompanies the chemical action. 
 
 As a general rule, only the compounds of carbon and hydrogen 
 are employed as combustibles — though there are some exceptions 
 
LUMINOSITY OP FLAMES. 343 
 
 to this rule, as when the metal magnesium is burned for light, 
 or the heating of a sulphuretted ore is effected by the combustion 
 of its own sulphur. In the manufacture of sulphuric acid, the 
 sulphur-furnace is often so arranged that the heat from the 
 burning sulphur generates the steam necessary for the operation. 
 In the Bessemer process of making steel from cast iron (§ 633), 
 intense heat is evolved, partly by the combustion of the carbon 
 which cast iron contains, but partly also by the combustion of 
 iron. The carbon compounds are peculiarly well adapted to the 
 purpose, since the products of their combustion are gaseous, and 
 can therefore be readily removed; new portions of the com- 
 bustible are thus continually laid bare, and a way opened for the 
 admission of fresh air. 
 
 424. In almost all cases artificial light results from the intense 
 ignition of particles of solid matter or of dense vapors. When 
 the heat, which is an iavariable accompaniment of chemical com- 
 bination, can play directly upon such solid or semisolid particles 
 with force enough to ignite them, an exhibition of hght will 
 accompany the chemical change. The hydrogen-flame affords no 
 Ught, or as good as none, because in it nothing but a highly 
 attenuated gas is heated. But when a solid body, such as the 
 platinum wire or the piece of lime employed in Exps. 26 and 27, 
 is placed in this non-luminous hydrogen-flame, intense light is 
 radiated from the heated soHd. 
 
 Exp. 188. — Sprinkle fine iron filings into the flame of an alcohol- 
 lamp, or into the non-luminous flame of the gaa-lamp, and observe the 
 light given off by the particles of metal as they become incandescent 
 while passing through the flame. Or rub together two pieces of char- 
 coal above a non-luminous flame, in such manner that charcoal powder 
 shall fall into the flame. Or rub the coat-sleeve beneath a non-lumi- 
 nous flame, or even beneath the luminous flame of an ordinary Argand 
 gas-burner, and observe that the particles of dust detached become 
 incandescent and luminous as they pass upward through the flame. 
 Other things being equal, the hotter the flame the more intense will 
 be the Kght emitted by the ignited solid. 
 
 425. In ordinary luminous flames, such as those of candles, 
 lamps, and illuminating gas, the ignited substance is carbon, or 
 rather a vapor or fog of certain carbon compounds containing 
 more or less hydrogen. 
 
344 
 
 ITTMINOSITT OF PIAMES. 
 
 Exp. 189. — By means of caoutchouc tubing, attach to any small 
 gas-burner a piece of hard-glass tubing, No. 4, about 20 cm. long, the 
 outer end of which has been drawn to a fine open point. Open the 
 cook of the gas-bumer, so that gas may flow into and through the glass 
 tube, and light this gas as it escapes. When the last traces of air have 
 been expelled ham the tube, heat the middle of the latter intensely 
 with the flame of a lamp. Part of the transparent and colorless car- 
 buretted hydrogen, of which the illuminating gas consists (§ 396), will 
 be decomposed by the heat as it passes through the tube, just as sul- 
 phuretted hydrogen (Exp. 91), phosphuretted hydrogen, arseniuretted 
 hydrogen (Exp. 133), and antimoniuretted hydrogen (Exp. 136) are 
 decomposed under like conditions, and a ring of carbon will be depo- 
 sited in the cold portion of the tube a short distance in front of the 
 flame. 
 
 In the open channel afforded by the tube it is not easy to heat the 
 whole of the carburetted hydrogen to the temperature necessary for 
 its decomposition ; but by lighting the gas as it issues from the tube, 
 heat enough to decompose it can readily be obtained. Precisely as in 
 the combustion of wood (§ 378), after the fire is once started the com- 
 bustible sufiers decomposition ; the easily inflammable hydrogen of the 
 gas burns first, and particles of carbon, or, at the first, of hydrocarbons 
 rich in carbon, are set free. These particles are heated to ignition by 
 the burning hydrogen, and as they pass up through the flame emit 
 light ; finally they are themselves completely burned to carbonic acid 
 upon the outside of the flame, provided there be present a sufficient 
 supply of adr. That there are really particles of free carbon in the 
 flame has afready been sufficiently demonstrated in Exp. 154. 
 
 If the supply of air furnished to the flame is insufficient to convert 
 all of the components of the gas into carbonic acid and water, then a 
 number of the carbonaceous particles will escape unburned, and a 
 smoky flame will be the result. If, on the other hand, the supply of 
 air is excessive, then all the carbon will be burned at the instant when 
 it is set free, and no light will be afforded. In the gas-lamps com- 
 monly employed in chemical laboratories for purposes of heating (see 
 Appendix, § 5), illuminating gas is purposely mixed with a considerable 
 volume of air before it is lighted j there is thus obtained an intensely 
 hot non-luminous flame. Such flames deposit no soot upon the vessels 
 which are heated in them j moreover the heat which would be con- 
 sumed in heating the particles of carbon, and so producing light, is in 
 such flames utilized for heating-purposes. 
 
 Exp. 190. — Unscrew the tube / (Fig. 61) from the gas-lamp con- 
 structed as described in § 5 of the Appendix, and light the gas as it 
 
THE BUNSEN BXTENEE. 
 
 345 
 
 Fig. 61. 
 
 escapes &om the holes in the face of the screw d; the flame will he 
 
 luminous, and, if the holes are large enough to permit a rapid exit of 
 
 gas, even smoky. Extinguish the burning jet, screw on the tube /, 
 
 and relight the mixture of air and gas at the top ; the flame will be 
 
 nearly colorless. Sometimes, when the 
 
 gas-cock is too nearly closed, the flame 
 
 of the mixed gas and air is liable to 
 
 pass down the tube /, and ignite the 
 
 feeble jet of gas at the apertures in d. 
 
 The lamp then burns with a sickly 
 
 yellow flame, which is often tinged 
 
 with green coming from the copper in 
 
 the heated brass tube /. The lamp 
 
 must be extinguished, and relit at the 
 
 top of the tube with a freer supply of 
 
 gas. When the tube /is in place, the ffC 
 
 the jets of gas, issuing vertically from 
 
 the face of the screw d, draw in currents of air through the side holes 
 
 near the bottom of the tube/; this air mixes with the gas rising 
 
 through/, and at the top of this tube, where the mixture is inflamed, 
 
 the carburetted hydrogen is in intimate contact with air enough to 
 
 burn it at once and completely. • 
 
 Between the two extremes which, a Bunsen burner may be 
 thus made to illustrate, between a smoky flame, on the one hand, 
 and a non-luminous flame, on the other, there are two points 
 which have special significance — the point of most light, and the 
 - point of most agreeable light. The point of most light may always 
 be hit upon by constructing such a burner as will just not allow 
 the gas to smoke. 
 
 JExp. 191. — Across the top of the chimney of an Argand gas-burner, 
 which is burning with a shorter, flame than usual, place several narrow 
 strips of tin or of sheet iron, so as to obstruct the flow of air through 
 the chimney. The small, low flame with which the experiment began 
 will increase in size as the access of air is diminished, and, at last, the 
 whole interior of the chimney will be filled with a long, smoky flame. 
 The volume of gas burning at any one moment of the experiment is no 
 greater than at another, for the cock which regulates the flow of the 
 gas remains fixed and untouched ; but the amount of light afforded by 
 the large smoky flame is manifestly greater than that yielded by the 
 small bright flame with which the experiment started. If any doubt 
 suggests itself as to this point, it will quickly be dissipated by perform- 
 
346 dTJANTITY AND INTENSIIT FLAMBS. 
 
 ing the experiment in a darkened room and noting the comparative 
 visibility of the more distant objects therein contained, first with the 
 one flame and then with the other ; or the observer may determine at 
 what distances from the two flames fine print can be deciphered. 
 
 A murky flame, such as was just now obtained, before actual smo- 
 king begins, in which the largest possible number of the paiticles of car- 
 bon are heated, though none of them are heated very hot, yields the 
 largest amount of light which the particular sample of gas under exa- 
 mination is capable of afibrding. Such flames are called, technically, 
 quantity flatnes ; they are better adapted than any others for lighting 
 streets and large halls. In practice, such flames are obtained by bm'n- 
 ing the gas at a low pressure, that is, under such conditions that it 
 shall be very gently pressed out into the air, so that air shall mix with 
 it and act upon it but slowly. 
 
 But besides this point of the maximum amount of light, there 
 is another, of the most agreeable light ; and this is something 
 which each individual must determine for himself. Few persons 
 would choose, as a study-lamp, either the murky flame of Exp. 
 191, or the intense lime-light of Exp. 27 ; but between these two 
 extremes no one light is likely to suit many people equally well. 
 
 If a bright intensity flame is required, we have only to arrange 
 matters in such a way that air may come to the gas so quickly 
 and abundantly that a portion of the carbon in the gas, as well 
 as the hydrogen, shall be burned at once in the lower part of the 
 flame, and by the heat of its combustion ignite more intensely 
 the remaining particles of carbon. Among the very great num- 
 ber of gas-burners which have been devised, there may be found 
 those adapted to meet almost any requirement. Each kind of 
 burner brings the gas and the air into contact with one another 
 in some special way, producing a flame of convenient shape, of 
 peculiar economy, or of particular steadiness or brilliancy. It is 
 obvious that the conditions under which gas is most advanta- 
 geously burned are different for different uses, and that no one 
 burner can be equally available under such varying and, in some 
 sense, antagonistic conditions. The Argand burner may, perhaps, 
 be made to fulfil as many of these conditions as any other ; from 
 it there may be obtained, at wiU, either an intensity or a quantity 
 flame, as has been shown in Exp. 191. 
 
 426. The chemical composition of the gas to be burned is, of 
 
. AM FLAMES GAS-FLAMES. 347 
 
 course, an important point to be considered in the construction 
 of the burner. A gas rich in carbon requires, for its combustion, 
 far more air than gas which is less carboniferous. 
 
 Bxp. 192. — Place three small tufts of cotton upon an earthen plate ; 
 moisten one with alcohol, another with petroleum, and the third with 
 henziu ; touch a lighted match to the vapor which arises &om each. 
 In the one case there will be seen hardly any luminous particles of 
 carbon, in the second a bright light ; and in the third so much carbon 
 will be set free that, under the conditions of the experiment, a great 
 deal of it cannot iind air with which to unite, and conseq^uently escapes 
 as smoke. 
 
 The composition of alcohol may be represented by the formula 
 CjHgO ; it contains a large proportion of hydrogen and some oxygen ; 
 hence steam is necessarily produced when it burns; this steam spreads 
 or diffuses the flame, and promotes the prompt union of the alcohol 
 vapor with the oxygen of the air, so that few carbonaceous particles 
 have time to become incandescent before they are consumed. But in 
 benzin, the formula of which may be written OgHj, there is no oxygen, 
 and a far larger proportion of carbon than in alcohol ; hence the 
 necessity of supplying a large amount of air to the lamps in which its 
 vapor is burned. The best way of consuming benzin is to mix its 
 vapor with air in suitable proportions, and to press this mixture through 
 a gas-burner as if it were ordinary illuminating gas. When thus 
 treated, it bums without smoke, and affords a brilliant white light. 
 Petroleum. (O^Hj), like benzin, contains no oxygen, but it contains far 
 less carbon than benzin, though much more than alcohol ; it does not 
 smoke like benzin, and yet it smokes so much that it cannot readily be 
 buraed from a simple wick ; it is commonly burned in lamps provided 
 with a special draught of air. 
 
 427. Ordinary lamps and candles are, strictly speaking, gas- 
 lamps. In all cases their flames are composed of burning gas. 
 
 Exp. 193. — Construct a lamp as follows : — To a wide-mouthed bottle 
 of the capacity pf about 50 c. c. lit a cork loosely ; bore a hole in the 
 cork and place therein a short piece of glass tubing. No. 3, open at both 
 ends ; through this glass tube draw a piece of lamp-wicking, or any 
 loose twine, long enough to reach to the bottom of the bottle. It is 
 essential, either that the cork should fit the bottle loosely, or that there 
 should be a hole in the cork, in order that the pressure of the external 
 air may act upon the surface of the alcohol ; to this end a veiy small 
 glass tube may .be inserted in the cork at some distance from the tube 
 which carries the wick. Fill the bottle nearly full with alcohol, and; 
 
348 
 
 THE COMPOSITION OF ElAMES. 
 
 after a few minutes, toucli a lighted matcli to the top of the wick. The 
 fluid alcohol is drawn up out of the bottle by the oapillaiy attraction 
 exercised by the pores of the vegetable fibre of which the wick is com- 
 posed. When heat is applied to the alcohol at the top of the wick, 
 some of it is converted into vapor ; this vapor then takes Are, and, in 
 burning, furnishes heat for the vaporization of new portions of the al- 
 cohol. From the top of the wick there is constantly arising a column 
 of gas or vapor, and upon the exterior of this conical column chemical 
 combination is all the while going on between its constituents and the 
 oxygen of the air. The dark central portion of the alcohol-flame is 
 nothing but gas or vapor. 
 
 Exp. 194. — Thrust the phosphorus end of an ordinary friction-match 
 directly into the middle of the flame of the alcohol-lamp of Exp. 193. 
 The combustible matter upon the end of the match will not take fire 
 in the atmosphere of carbonaceous gases of which the centre of the 
 flame consists. The wood of the match-stick, of course, takes fire at 
 the point where it is in contact with the outer edge of the flame, for 
 it is there heated in contact with air. In withdrawing the match from 
 the middle of the flame, it is not easy to prevent it from taking flre as 
 it passes through the outer edge of the flame ; for the materials on the 
 tip of the match have been so strongly heated by radiation, during 
 their sojourn within the circle of fire, that they are now ready to burst 
 into flame immediately on coming in contact with the air ; by a quick 
 jerk, however, the match may often be withdrawn from the flame 
 without taking flre. 
 
 Exp. 195. — Hold a thin wire (beat of plathium, though iron will 
 answer well enough) or a splinter of wood across the flame of an alco- 
 hol-lamp, as shown in Fig. 62. The wire will be heated to J'io-. 62. 
 redness, and the wood will burn, only at the outer edges of 
 the flame where the gas and air meet; in the interior of the 
 flame the wire will remain dark and the wood unburned ; for 
 there is no combustion there, and comparatively little heat. 
 If the wire be successively placed at difierent heights in the 
 flame, the size and shape of the internal cone of gas can 
 easily be made out ; it wOl appear, moreover, that the hottest 
 part of the flame is just above the top of the interior cone of gas. As 
 a rule, when glass tubing, or the like, is to be heated in a flame, it 
 should never be placed below this point of the greatest heat. 
 
 428. The flame of an ordinary oil-lamp or of a petroleum- 
 lamp, in the same way as the flame of an alcohol-lamp, is com- 
 posed of an inner cone of gas, or vapor of hydrotiarbons, and an 
 envelope where chemical combination is going on ; and a candle- 
 
CANDLE-FLAMES. 349 
 
 flame is really the flame of an oil-lamp (Exp. 196). The pre- 
 sence of vapor in the candle-flame can be readily shown (Exps. 
 197, 198). In the candle-flame, as in that of the alcohol-lamp, 
 there is a cone of unburnt gas surrounded by a shell of burning 
 substances (Exps. 199, 200). 
 
 Exp. 196. — Touch a lighted match to the wick of a new candle ; the 
 cotton of which the wick is composed takes fire and ia at once con- 
 sumed for the moat part ; but, in burning, the cotton gives off consider- 
 able heat, and some of the wax or tallow of which the candle is 
 composed is thereby melted and converted into oil. The liquid oil 
 ascends the wick by virtue of capillary attraction, and is converted into 
 vapor or gas by the heat of the cotton still burning at the stump of the 
 wick ; this gas then bums precisely like the alcohol vapor in Exp. 193 
 or the illuminating gas in Exp. 189, and by the heat thus disengaged 
 new portions of wax or taUow are continually melted. There is always 
 a little cup of oil at the top of the rod of wax or tallow of which the 
 candle consists, and the apparatus is as truly an oil-lamp as if the oil 
 were held in a vessel of glass or metal. 
 
 Exp. 197. — Let a cajidle, best of tallow, bum until the snuff has 
 become long ; blow out the flame, and observe the cloud of vapor which 
 ascends from the hot wick. Touch a lighted match to this column of 
 vapor, and notice that it takes fire at some little distance from the wick. 
 After the flame has been extinguished, the wick retains heat enough 
 for a few moments to distil off a quantity of gas, although there is not 
 heat enough generated to inflame this gas. To the gas or vapor thus 
 evolved is to be referred the disagreeable odor which is observed when 
 a candle is blown out. 
 
 Exp. 198. — Draw a glass tube (No. 5 or 6) 10 or 15 cm. long to a 
 moderately fine open point ; with a piece of wire bind this tube in an 
 inclined position to a ring of the iron stand, and place the lower end 
 of the tube in the middle of a candle-flame, just below the centre, so 
 that a portion of the gas of the inner cone of the flame may escape 
 through the tube ; light the gas at the point at the top of the glass 
 tube, and observe that it will burn there steadily, if the experiment is 
 performed in a quiet place where there are no draughts of air. 
 
 Exp. 199. — Press down a piece of white Yig. 63. 
 
 letter-paper, for an instant, upon the flame 
 of a candle until it almost touches the wick, 
 then quickly remove the paper before it 
 takes fire, and observe that its upper sur- 
 face is charred in the manner shown in Fig. 63. There will be ob- 
 tained, in fact, burned into the paper, a diagram of the cylindrical 
 
350 
 
 POEM- OP LUMINOUS FLAMES. 
 
 column of unbumt gas and of the shell of buming matter which sur- 
 rounds it. Within the charred ring the paper is unacted upon ; for 
 that part of it was in contact only with the unbumt gas in the centre 
 of the flame. 
 
 £xp. 200. — Replace the paper of Exp. 199 with a strip of glass, so 
 held that the conical flame of the candle shall he cut across horizon- 
 tally by the glass as it was by the paper in Exp. 199. Look down 
 from above through the glass into the hollow cylinder of unbumt gas 
 within the circle of combustion. 
 
 429. In any flame, which is rendered luminous by incandescent 
 carbonaceous particles, three portions can be distin- -p. „. 
 guished : — 1st, the dark interior cone of gas, a, Eig. 64 ; , 
 2nd, the zone of intense chemical action, b, where the 
 hydrogen is burning and the carbonaceous particles are 
 heated to whiteness ; and, finally, upon the very outside 
 a thin, scarcely perceptible film of burning carbonic 
 oxide, c. 
 
 430. From the study of luminous flames we pass to 
 a consideration of flames employed only as sources of 
 heat. In the experiments (25-27) with the oxyhydro- 
 gen blowpipe, it has been already shown that a very 
 intense heat may be obtained by throwing oxygen into 
 the hydrogen-flame, and so localizing the chemical action and the 
 heat with which this action is accompanied. The subject may 
 be here conveniently studied by employing coal-gas and air in 
 place of hydrogen and oxygen. 
 
 Exp. 201. — ^FUl one gas-holder with air, and screw to it a metallic 
 jet, such as is shown in Fig. 65. Fill another gas-holder vrith ordi- 
 nary illuminating gas and connect the opening of this gas-holder with 
 
 Fig. 65. 
 
 the lower opening of the metallic jet. Open the cock of the holder 
 which contains the coal-gas, and inflame the gas at the point of the 
 metallic jet. There will be thus obtained a long stream of gas burn- 
 
THE BLASX-IAMP. 351 
 
 ing at the expense of the air which hathes its surface. The chemical 
 action between the oxygen of the air and the constituents of the coal- 
 gas, and the heat Resulting from this action, are diffused over the entire 
 surface of this long flame. Without touching the cock of the holder 
 which contains the coal-gas, or in any way altering the amount of gas 
 which flows out of this holder, open the cock of the holder which con- 
 tains air, so that air may he thrown into the middle of the coal-gas 
 flame. The latter will he immediately shortened down to almost 
 nothing. The constituents of the coal-gas wiU now all combine with 
 oxygen in a very small space, and the heat of combination, which was 
 diffused before, will be correspondingly concentrated. It is much the 
 same as if the coal-gas and the air had been mixed together beforehand 
 and then lighted. Indeed, in one of the first forms of the oxyhydro- 
 gen blow-pipe, a mixture of the two gases, such as we have exploded 
 in Exp. 30, was first prepared, and then forced out of a single gas- 
 holder of peculiar construction, provided with an exceedingly minute 
 orifice, at the mouth of which the mixed gases were burned. This 
 apparatus was inconvenient and dangerous, and has long since been 
 superseded ; but it well illustrated the local concentration of heat now 
 under discussion. 
 
 431. The principle of the common mouth-blowpipe, of the 
 glass-blower's lamp (Appendix, § 6), and ofall blasts and blowers, 
 is identical with that of the oxyhydrogen blowpipe, which, as has 
 been already stated (§ 55), is the simplest of all intense and con- 
 centrated combustions. Air, or more strictly speaking, oxygen, 
 is thrown into the combustible gas or fuel, in order that the com- 
 bustion may go on in a small space. 
 
 The mouth-blowpipe may be used, with a candle, or with any 
 hand-lamp proper for burning oil, petroleum, or any of the so-called 
 huming-Jluids, provided that the form of the lamp below the wick- 
 holder is such as to permit the close approach of the object to be 
 heated to the side of the wick. When a lamp is used, a wick about 
 1'2 cm. vride and 0"5 cm. thick is more convenient than a round or 
 narrow wick ; a wick of this sort, though hardly so wide, is used in 
 some of the open burning-fluid (naphtha) lamps now in common use. 
 The wick-holder should be filed off on its longer dimension a little 
 obliquely, and the wick cut parallel to the holder, in order that 
 the blowpipe-flame may be directed downwards when necessary 
 (Fig. 67). 
 
 The cheapest and best form of mouth-blowpipe for chemical pur- 
 poses is a tube of tin-plate, about 18 cm. long, 2 cm. broad at one end, 
 
352 
 
 THE BLOWPIPE. 
 
 Fig. 66. 
 
 <F? 
 
 ID 
 
 and tapering to 0-7 cm. at the other (Fig. 66) ; the broad end is 
 
 closed, and a little above this closed end 
 
 a small cylindrical tube of brass about 5 
 
 cm. long is soldered in at right angles ; 
 
 this brass tube is slightly conical at the 
 
 end, and carries a small nozzle or tip, 
 
 which may be made either of brass or 
 
 platinum. The tip should be drilled out 
 
 of a solid piece of metal, and should not 
 
 be fastened upon the brass tube with a 
 
 screw. A trumpet-shaped mouth-piece 
 
 of horn or box-wood is a convenient, 
 
 though by no means essential, addition to 
 
 this blowpipe. 
 
 Exp. 202. — To use the mouthblowpipe, place the open end of the 
 tin tube between the lips, or, if the pipe is provided with a mouth-piece, 
 press the trumpet-shaped mouth-piece against the lips ; fill the mouth 
 vrith air till the cheeks are widely distended, and insert the tip in the 
 flame of a lamp or candle ; close the communication between the lungs 
 and the mouth, and force a current of air through the tube by squeez- 
 ing the air in the mouth with the muscles of the cheeks, breathing, in 
 the meantime, regularly and quietly through the nostrils. The knack 
 of blowing a steady stream for several minutes at a time is readUy ac- 
 quired by a little practice. It will be at once observed that the 
 appearance of the flame varies considerably, according to the strength 
 of the blast and the position of the jet with reference to the wick. 
 
 When the jet of the blowpipe is inserted into the middle of a 
 candle-flame, or is placed in the lamp-flame in the position shown in 
 Figure 67, and a strong blast . j-jg gy^ 
 
 is forced through the tube, a " 
 blue cone of flame, a h, is pro- 
 duced, beyond and outside of 
 which stretches a more or less 
 colored outer cone towards c. 
 The point of greatest heat in 
 this flame is at the point of 
 the inner blue cone, because 
 the combustible gases are there supplied vrith just the quantity of 
 oxygen necessary to consume them ; but between this point and the 
 extremity of the flame the combustion is concentrated and intense. 
 The greater part of the flame thus produced is oxidizing in its efiect ; 
 and this flame is technically called the oxidizing Jlame. From the 
 
OXIBIZISe AND EEBUClNa FLAMES. 
 
 353 
 
 point a of the inner blue cone, the heat of the flame diminishes in both 
 directions — ^towards b, on the one hand, and towards c, on the other ; 
 most substances require the temperature to be found between a and c. 
 Oxidation takes place most rapidly at, or just beyond, the point c of 
 the flame, provided that the temperature at this point is liigh enough 
 for the special substance to be heated. 
 
 A flame of precisely the opposite chemical effect may be produced 
 with the blowpipe. To obtain a good reducing flame, it is necessary 
 to place the tip of the blowpipe, not within, but just outside of the 
 flame, and to blow rather over than through the middle of the flame 
 (Fig. 68). In this manner, the flame is less altered in its general 
 character than in the former 
 tase, the chief part consisting -yi„.^ '°' 
 
 of a large, luminous cone, "v-Jo^ 
 containing carbonaceous va- 
 pors in a state of intense igni- 
 tion and just in the condition 
 for talring up oxygen. This 
 flame is therefore reducing in 
 its effect, and is technically 
 called the reducing flame. The 
 substance which is to be reduced by exposure to this flame should be 
 completely covered up by the luminous cone, so that contact with the 
 air may be entirely avoided. It is to be observed that, whereas to pro- 
 duce an effective oxidizing flame a strong blast of air is desirable, to 
 get a good reducing flame the operator should blow gently, with only 
 enough force to divert the lamp-flame. 
 
 Substances to be heated in the blowpipe-flame, are supported, some- 
 times on charcoal, sometimes on platinum foil or wire or in platinum 
 spoons or forceps, and sometimes on little capsules made of clay or 
 bone-earth. Charcoal is especially suited for a support in experiments 
 of reduction. 
 
 Exp. 203. — The heat of the oxidizing flame may be well shown by 
 melting the extremity of a very fine platinum wire into a little ball. 
 To effect this fusion, bend the wire at right angles at 5 to 6 m.m. from 
 the end, and hold this bent end precisely in the axis of the flame, with 
 the angle outward and the extremity of the wire at the hottest part of 
 the flame. If the wire is kept steadily in position, and the blast is 
 strong and the flame pure, a little knob will soon appear on the end of 
 the wire. The bend in the wire is made in order to keep a certain 
 length of the wire hot, and so to diminish the conduction of heat from 
 the point. 
 
 2a 
 
354 
 
 ACTION OP CHIMNEYS. 
 
 Exp. 204. — Place a kernel of metallic tin, as large as this o, in a 
 little hollow scooped out at one end of a bit of charcoal 8 to 12 cm. 
 long. Melt this tin in the reducing flame of the blowpipe, and en- 
 deavour to preserve the metallic lustre of the fused metal untarnished. 
 A pure reducing flame is necessary for this purpose. A touch of the 
 oxidizing flame upon the metal covers its surface with a white, infu- 
 sible, incandescent ash. 
 
 432. Another method of supplying the burping fuel with air 
 is by means of chimneys. Chimneys, whether of lamps or fur- 
 naces, are simply devices for bringing air in. abtmdance, and there- 
 fore oxygen, into the fire ; that in so doing they, at the same time, 
 carry off the waste products of combustion, is an incidental ad- 
 vantage. 
 
 Hxp. 205. — ^Light a piece of a candle 8 or 10 cm. long and stand it 
 upon a smooth table ; over the candle place a rather tall, narrow lamp- 
 cHmney of glass, the bottom of the chimney being made to rest upon 
 the table, and observe that the candle-flame will soon be extinguished. 
 No fresh air can enter the chimney from Tbelow to maintain the che- 
 mical action, and the small quantity of air which can creep down the 
 chimney from above is altogether insufficient to meet the requirements 
 of the case. 
 
 Eicp. 206. — Relight the candle of Exp. 205, and again place over it 
 the lamp-chimney ; but instead of allowing the chimney to rest closely 
 upon the surface of the table, prop it up on two narrow strips of wood, 
 so that air can have free entrance into the chironey from below. The 
 caudle wiU now continue to bum freely ; for the heavy cold air outside 
 will continually press into the lower part of the chimney, and push 
 out the warm, light products of combustion, and the candle-flame wiU 
 aU the while be supplied with fresh air. 
 
 Exp. 207. — Prepare several strips of " ni- 
 tre-paper" by soaking ordinary brown paper 
 in a strong solution of nitrate of potassium 
 and drying the product. On being lighted, 
 paper thus prepared wUl bum without flame 
 while emitting douds of smoke. Light a 
 piece of the nitre-paper and place it at the 
 foot of the chimney arranged as in Fig. 69. 
 The smoke of the burning paper will in- 
 stantly pass up through the chimney, and 
 so indicate the direction of the invisible air 
 which is all the while entering below and 
 
CHIMNEYS CREiTE DRATTGHTS. 
 
 355 
 
 passing out above at the top of the chimney, as fast as it is heated and 
 made lighter by the burning of the candle. 
 
 Exp. 208. — Repeat Exp. 206, and when the candle is burning 
 quietly, cover the top of the chimney tightly -with a piece of tin or 
 sheet-iron, or with a strip of window glass ; the candle wiU soon 
 cease to burn, precisely as if the chimney were closed at the bottom, 
 for, the escape of the hot products of combustion being prevented, no 
 air can pass into the chimney to reach the candle-flame. 
 
 It is hy inducing the current of fresh air (Exp. 206), or draught, as 
 it is ordinarily termed, that chimneys are specially useful. They give 
 direction and precision both to the incoming cold air and the outgoing 
 hot gas. Where there is no chimney, the hot air from a lamp goes off 
 at a comparatively slow rate, and vaguely ; through the chimney, on 
 the other hand, it flows straight forward and rapidly, and, of course, 
 a correspondingly direct and rapid current of fresh air presses in 
 to supply its place. Owing to this power of rapidly supplying air, 
 chimneys are employed upon lamps buraing petroleum and other 
 highly carbonized oils which are liable to smoke; in general they 
 are made use of upon lamps in all cases where intensity flames are 
 required. 
 
 Exp. 209. — It is not absolutely necessary that the fresh air should 
 flow into a chimney from below. Divide the 
 upper part of the chimney of Exp. 205, into 
 two channels, by hanging in it a strip of 
 sheet-iron or tin, as \ partition at the centre 
 of the chimney. (See Fig. 70.) Place the 
 chimney thiis divided over a burning candle, 
 and observe that the candle will continue to 
 bum as if in a strong draught of air, although 
 no air can enter the chimney from below. 
 Hold a piece of burning nitre-paper (Exp. 
 207) at the top of the divided chimney ; the 
 smoke wiU be drawn down into the chimney 
 on one side of the partition and thrown out 
 again upon the other, as indicated by the arrows in Fig. 70. It ap- 
 pears from this, as well as from the tremuloiis motion of the flame, 
 that a current of cold air passes down upon one side of the division 
 wall and supplies the required oxygen. 
 
 433. One exceedingly important point in chemical philosophy, 
 which we have hitherto taken for granted, may now be readily 
 illustrated. As the result of long- continued experimentation and 
 the most rigid scrutiny of all chemical facts, it is admitted, aa a 
 
 2 a2 
 
 Fig. 70. 
 
356 MAIIER INDESTETjCriBLE. 
 
 fundamental truth, that matter is indestructible. When sub- 
 stances undergo chemical change, none of their ingredients are 
 reaUy destroyed, not an atom of them is annihilated ; nor, upon 
 the other hand, is any new matter created ; it is the form only of 
 the old substances which is changed ; their weight remains in 
 every case unaltered. 
 
 By bringing about chemical combination between two or more 
 bodies, we can entirely change their appearance, their condition, 
 and their properties, but in every case it will be found that the 
 weight of the resulting compounds is precisely equal to the sum 
 of the weights of their components. Thus, when a candle bums 
 in the air and gradually disappears, none of the elements which 
 compose it are either lost or destroyed. Though by uniting with 
 the oxygen of the air, the components of the candle have been 
 converted into compounds which are invisible, it is nevertheless 
 easy to satisfy ourselves of the existence of these compounds. 
 Already, in Exps. 167, 168, it has been demonstrated that carbonic 
 acid and ■v^ater are products of the combustion of the candle ; and 
 we now proceed to show that these products weigh more than the 
 candle. 
 
 Exp. 210. — Take a glass tube 2 or 3 cm. in diameter and 25 or 30 
 cm. long, such, for example, as the neck of a breken retort ; fit a cork 
 to each extremity of the tube, and at a distance of 6 or 8 cm. from its 
 upper,, wider end, fix across the tube a partition of wii-e gauze. Through 
 the upper cork insert a glass tube, No. 3 or 4, bent at a right angle, 
 and in the lower cork bore several open holes, besides a central orifice 
 into which a small wax taper is fastened. Fill the space between the 
 upper cork and the shelf of wire gauze with recently slaked lime, in 
 not too fine powder ; replace the cork, hang the tube, with its contents, 
 at the end of one arm of a balance, and counterpoise the apparatus 
 precisely by placing shot or sand in the pan upon the other side of the 
 scales. Next make an " aspirating flask," by fitting to the upper ori- 
 fice of a bottle with a stopcock, such as is depicted in the upper part of 
 Fig. xvii. in the Appendix, a sound cork, carrying a glass tube. No. 3 
 or 4 ; the tube should reach to the bottom of the bottle and be bent at 
 a right angle a short distance above the cork. 
 
 By means of flexible tubing, connect the upper tube of the aspirating 
 flask with the tube issuing ffom the upper cork of the apparatus upon 
 the balance, and open the stopcock of the aspirator to such an extent 
 that water shall flow out from it slowly. Remove the lower cork from 
 
KINBLING-TEMPEEAnmE. 357 
 
 the apparatus upon the balance, in order to light the taper, then quickly 
 replace it and regulate the flow of water from the aspirator, so that 
 sufiident air shall be drawn in through the holes in the cork which 
 supports the taper to maintain the latter in lively combustion. 
 
 After the taper has burned during 4 or 5 minutes, close the aspirator, 
 remove the flexible tube from the candle apparatus, so that the latter 
 may again hang freely from the arm of the balance, and observe that 
 the weight of the apparatus is now greater than it was at the begiu- 
 ning of the experiment, for the lime within the tube has absorbed the 
 carbonic acid and water which were produced by the combination of 
 the ingredients of the candle with the oxygen of the air. 
 
 434. In order that any combustible substance shall bum, or, 
 in other words, in order that brisk chemical action shall occur 
 between the combustible and the oxygen of the air, it must first 
 be heated to a certain temperature, and then kept at that heat. 
 The temperature at which any substance takes flre is known as 
 the kindling-temperature of that substance. 
 
 Hxp. 211. — Place a small bit of phosphorus and another of sulphur, 
 not in contact with the first, upon a fragment of porcelain 6 or 8 cm. 
 across, and heat them slowly over the gas-lamp. The phosphorus will 
 soon take fire at a temperature of 68°-70° ; but the sulphur will not 
 inflame until the temperature of the porcelain support has risen to 
 about 250°, as can be readUy ascertained by the thermometer. 
 
 As was just now said, the degree of heat necessary to start 
 any fire must be kept up continually, or the fitre will go out. 
 Whenever burning bodies are cooled below the kindling-tempe- 
 rature they are extinguished, — the chemical action which occa- 
 sioned the appearance of heat and light ceases. 
 
 Exp. 212. — Pile up upon an iron grate, thick in metal, and sup- 
 ported in such manner that air may enter beneath it, several pieces of 
 red-hot charcoal. The charcoal wiQ go on burning until nearly all of it 
 has been consumed ; for the heat generated by the combustion of the 
 portions first burned keeps up the temperature necessary to kindle the 
 subsequent portions. 
 
 Upon a cold grate, similar to the one just employed, scatter about 
 several small pieces of red-hot charcoal, taking care that no two pieces 
 of the coal shall come in contact, or be placed so as to heat one 
 another. Each of the pieces of charcoal will soon cease to burn ; for 
 the metallic grate is so good a conductor of heat that it removes heat 
 from the isolated pieces of charcoal more rapidly than these can pro- 
 
358 TLAMES Piri OUT BY GOOD COITDUCTOKS. 
 
 duce it ; consequently the temperature of the charcoal is soon reduced 
 to below the kindling-point. 
 
 A result similar to the foregoing is obtained when any fire is broken 
 up and scattered about to such an extent that its several portions can- 
 not assist in one another's combustion — though if, instead of being 
 placed upon iron, the separate glowing coals be laid upon ashes or dry 
 earth, they will be extinguished only after a much longer time, for 
 ashes and dry earth are very poor conductors of heat in comparison 
 with iron. 
 
 In all ordinary fires the heat evolved by the combustion of 
 the fuel is more than sufiicient to maintain a temperature higher 
 than the kindling-point of the fuel — though, generally speaking, 
 the fuel becomes at last so clogged with ashes, that the oxygen 
 of the air cannot get at the remaining combustible matter in 
 sufficient quantity to maintain lively chemical action. 
 
 435. Precisely as coals can be extinguished by placing them 
 upon cold "metal, so flames may be put out. 
 
 Exp. 213.— Upon a ring of the iron stand place a sheet of clean 
 wire gauze about 10 cm. square ; lower the ring so that the gauze 
 shall be pressed down upon the flame of a lamp or candle almost to 
 the wick, as shown in Fig. 71. No flame will be 
 seen above the gauze, but instead of flame a cloud 8^' 
 
 of smoke. The gauze is a mere open sieve ; there 
 is nothing about it which can prevent the gas, 
 which was just now bm'ning with flame above 
 the wick of the candle, from passing through. 
 Indeed it may be seen from the smoke that the 
 particles of carbon which, in the original undis- 
 turbed flame, were becoming incandescent, and so afibrding light, do 
 now actually come through the gauze. 
 
 The explanation of the phenomenon is simply that the metallic 
 sieve conducts away so much heat that the temperature of the candle- 
 flame is reduced to below the kindling-point. That this is really so is 
 proved by the fact that, after the gauze has become suificiently heated 
 by long-continued contact with the flame below — after it has attained 
 the kindling-point of the candle-gas, it will no longer extinguish the 
 flame. In like manner, a candle-flame may be cooled to such an ex- 
 tent that it win go out, by placing over it a small coil of cold copper 
 wire, while if the wire be previously heated the flame will continue 
 to bum. 
 
 If the smoke and unbumed gas which has passed through the cold 
 
SAFETT-LAMPS. 359 
 
 wire gauze he touched with a lighted match, and so brought to the ' 
 Irindling temperature, it will hurst into flame. 
 
 The power of wire gauze to prevent the passage of flame has been 
 usefully applied in several ways, notably for the prevention of explo- 
 sions in those coal-mines which are liable to accumulations of marsh- 
 gas. For this purpose safety-lamps are constructed by enclosing an 
 ordinary oil-lamp completely in wire gauze, so that the flame within 
 the gauze cannot kindle any combustible or explosive gas into which it 
 may be carried. In case such a lamp be carried into a place fiUed with 
 explosive gas, the latter will, of course, pass into the lamp through the 
 meshes of the gauze and bum within the cage. This combustion gives 
 warning of the presence of the dangerous gas, and indicates to the 
 workman that he should withdraw from the locality ; the gas can then 
 be expelled by appropriate methods of ventilation. 
 
 The wire-gauze lamps employed in. chemical laboratories (for 
 one form of which, see Appendix, Pig. viii.) are simply applica- 
 tions of the same general idea. 
 
 -Erp. 214. — ^Beneath the sheet of wire gauze of Exp. 213, place an 
 unlighted ordinary gas-lamp (Bunsen's burner), at such distance that 
 the gauze shall be 3 or 4 cm. above the top of the lamp ; turn on the 
 gas and light it above the wire gauze ; it will continue to bum on the 
 top of the gauze for an iudefinite period, 'for the gauze will, in this 
 case, always be kept cool by the cold gas which is continually passing 
 through it. Carefully and gradually lift the ring which carries the 
 gauze, and determine how far it is possible to lift the gauze above the 
 gas-jet without extinguishing the flame. 
 
 The student vsdll remember that other experiments illustrating the 
 influence of cooling agencies in extinguishing combustion (Exps. 136 
 and 154), have already been performed. Compare also Exp. 196 and 
 § 200, as regards kindling. 
 
 436. An effect somewhat similar to that produced by wire 
 gauze is often seen in ordinary fires. When a mass of red-hot 
 anthracite, charcoal, or coke is burning freely upon a grate in 
 the open air, there is always a blue flame of carbonic oxide 
 burning above the coal. This gas results from the reduction of 
 carbonic acid by means of hot carbon, precisely as in Exp. 181. 
 Air enters at the bottom of the grate and combines with the hot 
 coal which it finds there to form carbonic acid (00^). This car- 
 bonic acid, as it rises through the hot coal in the middle of the 
 fire, is deprived by the heated carbon of half its oxygen, 
 CO, -f- C = SCO, 
 
360 BLAMING FIEBS. 
 
 SO that two molecviles of carbonio oxide gafi finally emerge at the 
 top of the coal, instead of the single molecule of carbonic acid 
 which was formed at first. The carbonic oxide being combus- 
 tible, will at once take fire on coming in contact with the air, 
 provided the temperature at the siimmit of the fire be equal to 
 the kindling-temperature of carbonic oxide. But if the tempe- 
 rature of the fire is in any way reduced below this point, as, for 
 example, by throwing on too large a quantity of cold fuel, which 
 is, of course, equivalent to covering the fire with a sheet of wire 
 gauze, then the carbonic oxide will be extuiguished, and, escaping 
 into the chimney, will produce no useful eflfect. 
 
 Were it not for the formation. of carbonio oxide, as above men- 
 tioned, neither anthracite coal, nor coke, nor charcoal would burn 
 with flame after having once got weU on fire ; they would simply 
 glow, as a single live coal, or a bar of metal, glows when taken 
 from the fire. 
 
 437. In heating steam-boilers and other large vessels, it is 
 often a point of great importance to obtain from the fael a large 
 flame, in order that the heat from the fuel may be quickly dis- 
 tributed and brought into contact with the matter to be heated. 
 With anthracite and coke this result is efiected by placing be- 
 neath the grate, upon which the fuel is burned, a quantity of 
 water. Prom this water steam gradually rises, as hot ashes and 
 cinders fall into it and as heat radiates down upon it from the 
 fire above. The steam, as it enters the fire, is decomposed by 
 the hot coal (see Exp. 156), in accordance with the following 
 reaction, 
 
 C + HP = CO + 2H, 
 
 and the combustible gases thus obtained are superadded to the 
 carbonic oxide which is formed in due course from the action of 
 air upon the coal. AU these gases burn again to carbonic acid 
 and water above the fire, where air is thrown in to meet them 
 through appropriate orifices. In this use of water as an adjunct 
 to the combustion of coal, the absolute amount of heat given off 
 by the fuel is in nowise increased ; but in many instances much 
 heat may undoubtedly be saved by thus equally distributing and 
 applying it by means of flame. 
 
 438. On the other hand, furnaces are sometimes seen con- 
 
CAEBONIO OXIDE SHOTTLB BE BUENBD. 361 
 
 suming fuel under such conditions that all the carhonic oxide 
 produced -within them escapes unbumed into the chimney. In 
 such cases, more than two-thirds of the amount of heat which 
 the fuel is capable of yielding must necessarily be lost ; for while 
 1 gramme of charcoal gives off in burning to carbonic acid 
 8080 units of heat (§ 55), 1 gramme of carbon in burning to 
 carbonic oxide gives off only 2473 units of heat. The number 
 last given is determined as follows. It has been found, by direct 
 experiment, that 1 gramme of carbonic oxide, on being burned 
 to carbonic acid, yields 2403 units of heat; carbonic oxide is 
 composed (§ 422) of one atom of carbon, weighing 12, and one 
 atom of oxygen weighing 16, — the weight of the molecule of car- 
 bonic oxide being consequently 28. In one gramme of carbonic 
 oxide, therefore, there can be only -1^= 0-4286 of a gramme of 
 carbon; but 0-4286 : 1 = 2403 : a;=5607, whence it appears 
 that there is evolved by one gramme of carbon in carbonic oxide 
 5607 units of heat when this carbon unites with the additional 
 oxygen to form carbonic acid; and the difference between this 
 number (5607) and the number (8080) denoting the amount of 
 heat given off by one gramme of charcoal in burning to carbonic 
 acid will show how much heat is evolved by one gramme of 
 carbon burned to carbonic oxide: 8080 — 5607=2473, as above 
 stated. 
 
 In order to thoroughly bum the carbonic oxide in any case, 
 the stove or furnace should be so arranged that a volume of air, 
 as large as that which has already passed through the fire, can 
 be constantly supplied to the carbonic oxide and nitrogen as they 
 emerge from the coal, and be intimately mixed with these gases 
 whUe they are stiU hot. 
 
 439. The amount of air needed for the complete combustion of 
 coal or other fuel can always be readily calculated. We have 
 only to determine how much oxygen will be needed by the com- 
 bustible, and then how much air must be taken in order to supply 
 this oxygen. Let it be supposed, for example, that we wish to 
 learn how much air is needed in order to bum one kilogramme 
 of charcoal. Having learned the full significance of the formida 
 CO , a moment's consideration" of this formula informs us that, 
 for every 12 parts by weight of carbon, 32 parts by weight of 
 
362 CHLOEIDE OF CARBON. 
 
 oxygen are needed in order to its complete combustion, or, for 
 one part of carbon, 2-67 parts of oxygen. Air contains 23-1 per 
 cent, of oxygen by weight; hence the proportion 23-1: 100= 
 2-67: x= 11-558, from which it appears that to burn 1 kilo, of 
 charcoal, 11'558 kilos, of air are needed. Since the weight of a 
 litre of air, at the ordinary temperature, is only 1'2258 grm., 
 these 11*558 Hlos. of air wiU occupy about 9429 litres, or, in other 
 words, nearly 9| cubic metres. In round numbers, it may be 
 said that about 12 kUos., or 9| cubic metres, of air are required 
 to burn one kilo, of charcoal. For coke and anthracite, correc- 
 tions must, of course, be made for the ashes which they contain, 
 as well as for a certain portion of hydrogen which may also be 
 present. If a gramme of pure carbon will disengage 8080 units 
 of heat, a gramme of weU-burned coke, containing 15 per cent, of 
 ashes, will disengage only 6868 units. 
 
 440. Chloride of Carbon (CCIJ. — Chlorine does not unite di- 
 rectly with carbon ; but several compounds of the two elements 
 can be obtained by subjecting compounds of carbon and hydro- 
 gen to the action of chlorine. Of these compounds, only the so- 
 caUed bichloride (CCl^) need here be mentioned, the others being 
 usually treated of in works upon organic chemistry. Bichloride 
 of carbon may be obtained by the action of chlorine on marsh- 
 gas, by subjecting chloroform or wood-spirit to the action of an 
 excess of chlorine in sunlight, by passing a mixture of bisulphide- 
 of-carbon vapor and chlorine through a red-hot porcelain tube, 
 or by the action of quinquichloride of antimony upon bisulphide 
 of carbon : — 
 
 CS, + 2SbCl„ = CCl, + 2SbCl, -f- 2S. 
 At the ordinary temperature of the air it is a transparent, color- 
 less liquid, of pungent aromatic odor, boiling at 77°, and having 
 a specific gravity of 1-56. At — 23° it solidifies in the form of 
 crystals of pearly lustre. The specific gravity of its vapor has 
 been determined to be 76"96, which would indicate that a mole- 
 cule of the vapor is composed of 1 atom of carbon and 4 volumes of 
 chlorine, condensed to 2 unit-volumes : — 
 
 For, since the weight of one atom of carbon is 12 
 
 And the weight of 4 atoms of chlorjne is 142 
 
 The weight of the two volumes of gas produced would be . , 154 
 
CABBON AND NITEOGEjr. 363 
 
 And the weight of 1 Tolume would be 77, a niunlDer with which the 
 experimental determination very nearly agrees. 
 
 In compositioii, this chloride of carbon (CCIJ is analogous to 
 the hydride CH^ which we have already studied under the name 
 light carburetted hydrogen, or marsh-gas (§ 392), and in the 
 same way that tie hydride may be converted into the chloride by 
 acting upon it with chlorine, so, conversely, the chloride, on being 
 brought into contact with water and sodium-amalgam (§ 97), 
 may be deprived of chlorine and converted back into the hy- 
 dride, — the hydrogen of the water being substituted for the 
 chlorine, which, Kke the oxygen of the water, unites with the 
 sodium. 
 
 441. Compounds of Carbon and Nitrogen. — ^With nitrogen, 
 carbon forms a number of highly interesting compounds, which 
 may be found treated of in works upon organic chemistry. Pro- 
 minent among these compounds are cyanogen, CN (§ 384), and 
 cyanhydric acid, HON. Cyanhydric acid corresponds to chlor- 
 hydric acid and the other hydrides of the chlorine group of ele- 
 ments ; by its action upon metallic oxides there may be formed 
 a series of cyanides of the metals, corresponding perfectly with 
 the metallic chlorides : — 
 
 M,0 + 2H(CN) = 2M(C]Sr) + H,0. 
 M,0 -I- 2HC1 = 2MC1 + H^O. 
 
 The group of atoms (CN) which constitutes cyanogen, acts-, in 
 fact, as if it were a single elem^ijt. In the same way that the 
 group NH^, called ammonium,; is capable of replacing a metal 
 like sodium (see § 91), so the group CN can replace chlorine and 
 the elements allied to chlorine. Groups or knots of atoms, such 
 as these, are often called compound radicals. Cyanhydric acid, 
 or prussic acid as it is sometimes called, is notorious as a violent 
 poison. Many of the cyanides are of great importance in the 
 arts, particularly in processes of gUding, plating, electrotyping, 
 and dyeing, as well £is in the preparation of pigments. Some of 
 them win be described hereafter under the respective metals. 
 
 442. Bisulphide of Carbon (CS^), or sulpho-carbonic acid, as 
 it is often called, is especially interesting from its correspondence 
 with the binoxide of carbon, carbonic acid, in accordance with the 
 
364 BIStTLPHIBE OP CAEBOIf. 
 
 general rule that sulphur compounds are analogous to the com- 
 pounds of oxygen. With the metaUie sulphides this compound 
 forms a series of salts, of the general formula M^CSj, or M^SjCS^, 
 analogous to those formed hy the union of carbonic acid with 
 the metallic oxides, the general formula of which, as we know, is 
 M^CO, or M,0,CO,. 
 
 Bisulphide of carbon may be obtained by bringing th6 vapor of 
 sulphur in contact with red-hot charcoal. It is a mobile, colorless 
 liquid of 1 -27 specific gravity, which refracts light powerfully. It 
 boils at 45° and evaporates rapidly at the ordinary temperature of 
 the air. The density of its vapor is 38-19. It has a peculiarly 
 fetid odor, and is very easily inflammable, burning with a blue 
 flame to carbonic and sulphurous acids. It is not soluble in water, 
 but is easily soluble in alcohol, and is itself a powerful solvent of 
 fats and various other substances ; it has been, of late years, 
 somewhat extensively employed as a solvent of phosphorus (§ 274) 
 and of chloride of sulphur (§ 246) in the cold process of vulcanizing 
 caoutchouc. Mixtures of its vapor with oxygen, air, nitric oxide, 
 and other gaseous oxygen compounds burn, without violent ex- 
 plosion, with a sudden brUliant flash of intensely blue light. This 
 flame is remarkable for its great actinic power ; it acts very ener- 
 getically upon a prepared daguerreotype plate, and causes a mix- 
 ture of hydrogen and chlorine to combine almost as readily as 
 sanhght would (Exp. 53). 
 
 Exp. 215.— Fill a tall bottle, of the capacity of 700 or 800 c. c, with 
 nitric oxide gas, at the water-pan ; cover the bottle with a plate of glass 
 and stand it upright upon the table ; draw the cover aside far enough 
 to admit of the introduction, from a pipette, of 8 or 10 c. c. of liquid 
 bisulphide of carbon ; replace the cover and leave the bottle at rest 
 for a few minutes, in order that the vapor of the bisulphide may have 
 time to diffuse through the nitric oxide. Finally, touch a lighted match 
 to the opened mouth of the bottle and observe the brilliant flame which 
 is produced. 
 
BOBON. 365 
 
 CHAPTER XXL 
 
 443. Boron is an element of the same natural family as carbon. 
 It is found in nature, in combination with, oxygen, as boracio 
 acid, and in combination with oxygen and some of the metals — 
 notably as a biborate of sodium, commonly called borax, and as a 
 double borate of sodium and of calcium. , 
 
 In certain volcanic districts in Tuscany, jets of steam mixed 
 with other vapors escape continually from cracks in the soU, and 
 bring to the surface small quantities of boracic acid. Since boracic 
 add is not volatile, in the ordinary sense of the term, at tempera- 
 tures so low as 100°, it appears that it is transported mechanically 
 by the steam, much in the same way that dust is carried along 
 by a current of air. The jets of vapor, laden with boracic acid, 
 are made to bubble through water as they escape from the earth; 
 this water retains the acid, and so concentrates it to a very con- 
 siderable extent. After the water has become as highly charged 
 with the acid as has been found in practice to be desirable, it is 
 run off into pans, lower down upon the hill -side, beneath which 
 hot jets of vapor from the earth are caused to circulate. The 
 excess of water is thus evaporated by heat which the earth sup- 
 plies, and the solution becomes so concentrated that, on cooling, 
 crystals of boracic acid separate from it. About 120 millions of 
 kilogrammes of water are thus evaporated annually, and 1,300,000 
 kilogrammes of boracic acid produced without the iutervention of 
 any artificial motor or the consumption of any fuel. After having 
 been purified, the boracic acid is sent into commerce as such, or 
 it is treated with a hot solution of carbonate of sodium, and so 
 converted into borax. 
 
 Besides this principal source of the boron compounds, a certain 
 quantity of native borax is obtained from the mud and waters of 
 certain lakes in Tartary, Ceylon, Thibet, and California. In 
 Peru, also, a mineral composed of borate of sodium and borate of 
 calcium is found associated with nitrate of sodium. 
 
366 AliOTKOPISM OF BOEON. 
 
 444. The element boron has been obtained in two distinct allo- 
 tropic conditions (§§ 162, 366) comparable with those of carbon. 
 It can be had amorphous like charcoal, and crystallized Eke the 
 diamond. 
 
 To prepare the diamond-like modification, fused boracic acid is in- 
 tensely heated with metallic aluminum ; a portion of the aluminum 
 takes oxygen away from the boron, while another portion of the molten 
 metal dissolves this boron as fast as it is formed. As soon as the 
 solution has become saturated (that is to say, when the melted alu- 
 minum has dissolved aU the boron that it is capable of dissolving), a 
 portion of this boron is deposited in diamond-Uke crystals. When the 
 crucible and its contents are broken up after cooling, these crystals are 
 found lining cavities within the mass. 
 
 The amorphous modification may be prepared by heating together 
 boracic acid and metallic sodium or potassium beneath a layer of fused 
 chloride of sodium. After having been allowed to cool, the products 
 of the reaction are treated with water, which dissolves away the chlo- 
 ride and the borate of sodium, and leaves the boron as an amorphous 
 powder which may be collected upon a filter. 
 
 A third variety of boron, similar to graphite, was at one time de- 
 scribed ; but recent experiments have shown that the so-called graphi- 
 toidal boron is really a boride of aluminum (AIB2). 
 
 445. Of the properties of these veirieties of boron, little need 
 here be said ; they are analogous to, and closely resemble, the 
 corresponding modifications of carbon, which have already been 
 fully described. The diamond modification is transparent, and 
 sometimes colorless, though usually of a yellow or reddish color. 
 It crystallizes in the same forms as the real diamond, and refracts 
 light very powerfully. Its specific gravity is 2-68. It is almost 
 as hard as the real diamond, being capable of scratching the ruby, 
 and even of polishing the diamond. It is only with extreme 
 difficulty that it can be burned in oxygen, since a coating of boracic 
 acid soon forms which protects it from further action of the oxy- 
 gen. It is remarkable that at the moment of its combustion it 
 swells up as the diamond does when intensely heated. Amor- 
 phous boron is an infusible greenish powder, which readily takes 
 fire on being heated in air or oxygen. It is, in fact, necessary, in 
 preparing it, to take care that the filters upon which it has been 
 collected shall be dried at low temperatures, lest the finely divided 
 
COMPOSITION OF BOEACIC ACID. 367 
 
 boron take fire spontaneously ; if exposed to the sun's rays in 
 summer, the filters containing boron will often take fire as soon as 
 they have become dry. Unlike the other modification of boron, it 
 is readily attacked by most chemical agents. Like the correspond- 
 ing modification of carbon, it is an energetic reducing agent. 
 
 No compound of boron and hydrogen has yet been discovered, 
 but it unites readily with chlorine, bromine, and iodine ; it can 
 be made to combine also with fluorine, nitrogen, and sulphur. 
 
 446. The best-known of the compounds of boron is the oxide 
 BjOj, called boracie acid. This oxide occurs ready formed in na- 
 ture, as has been said, and is the sole product when boron is burned 
 in oxygen. The composition of boracie acid may be determined 
 synthetically by burning amorphous boron in pure oxygen, or by 
 treating it with nitric acid. A certain definite weight of boron 
 being taken in the first instance, the weight of the dry boracie 
 acid obtained is carefully determined, and from these data the 
 percentage composition of the boracie acid is calculated; 100 
 grammes of boracie acid consist of 
 
 Oxygen 68-78 grammes. 
 
 Boron ... * 81-32 „ 
 
 From the specific gravities of the vapors of chloride of boron and 
 of fluoride of boron, as determined by experiment, and from some 
 other rather inconclusive considerations which need not here be 
 dwelt upon, chemists have been led to admit that the atomic com- 
 position of boracie acid may be represented by the formula B^O^. 
 If boracie acid be really composed ,of 3 atoms of oxygen and 2 
 atoms of boron, the weight of the atom of boron wUl foUow from 
 the proportion 68-78 : 31-32=(16 x 3) : x, in which 16 equals the 
 weigtt of an atom of oxygen and a; the weight of two atoms of 
 boron. Upon this assumption, the weight of one atom of boron 
 will be 10-93. 
 
 447. Boracie acid is but a feeble acid at the ordinary tempera- 
 ture, and may be set free from its compounds by almost any of 
 the acids, excepting carbonic acid. 
 
 JExp. 216. — Dissolve 4 grms. of borax in 10 grms. of boiling water, 
 in a beaker glass or porcelain capsule of 30 or 40 c. c. capacity, and 
 add to the solution 2-5 grms. of concentrated chlorhydric acid. After 
 
368 PEOPERTIES OP BOKACIC ACID. 
 
 the lapse of some time, hydrated lioracic acid -will be deposited fiom 
 the solution in the form of glistening, colorless plates or scales. These 
 crystals contain as much as 43-6 per cent, of water ; their formula is 
 H3BO3, or, dualistic, 3H2O, B2O3. 
 
 On being heated in a clean iron spoon, the crystals will first dissolve 
 in the water which they contain, or, as the fact is usually stated, they 
 will " melt in their water of crystallization ; " if the heat be continued, 
 the mass will become pasty, and will swell up as the water is expelled. 
 After aU the water has been driven off by strong heat, the anhydrous 
 acid is left as a clear, viscous liquid, from which long threads of the 
 solid acid may be drawn out by touching the surface of the liquid with 
 the end of a stick or glass rod, and then gently pulling away the stick 
 with the matter which has adhered to it. 
 
 If the fused acid be allowed to cool, it will solidify to a hard, trans- 
 parent glass, which soon cracks in every direction and splits up. into 
 fragments. 
 
 Anhydrous boracie acid is of about 1'8 specific gravity ; it is 
 odorless and destitute of corrosive power ; it has a slightly bitter, 
 but not sour, taste. It is much more soluble in hot than in cold 
 water, and more soluble in alcohol than in water. It imparts to 
 the flame of burning alcohol a peculiar green tint, which is quite 
 characteristic, and affords a vailuablfe test by which the presence 
 of the acid may be detected. Upon litmus and turmeric, boracie 
 acid acts somewhat differently from other acids. 
 
 Bxp. 217. — Dissolve a little of the crystallized boracie acid of Exp. 
 216, in a teaspoonful of alcohol in a small porcelain capsule. Set fire 
 to the alcohol and stir the burning solution with a rod, or agitate it by 
 jarring the dish. Or moisten a tuft of cotton with alcohol, strew upon 
 it some powdered boracie acid, and light the alchohol. In either case 
 the flame of the alcohol will he of a fine green color. 
 
 £xp. 218. — Pour into a test-glass 20 or 30 c. c. of a solution of blue 
 litmus ; in a small quantity of water, contained in another test-glass 
 or tube, dissolve a little of the boracie acid of Exp. 216 ; add the 
 solution of boracie acid to the litmus, and observe that the color of 
 the latter changes to a brownish wine-red, decidedly different from the 
 bright clear red which is obtained by the action of other acids upon 
 litmus. If a large quantity of boracie acid, however, be added to a 
 small portion of the litmus solution, the latter will be colored strongly, 
 as if by a powerful acid. 
 
 Sep. 219. — Dip into a solution of boracie acid a slip of yellow tur- 
 meric paper, and observe that the yellow color is changed to brown, 
 
CHLOEIDB OF BOEOir. 369 
 
 as it would be by ammonia-water or by any other alkaline solution. 
 None of the other acids produce a like effect. 
 
 448. When an aqueous solution of boraeio acid is boiled, an 
 appreciable quantity of the acid goes off with the vapor of water ; 
 but the dry acid, when heated by itself, is nevertheless one of 
 the least volatile of all the acids. It does slowly sublime, however, 
 at a white heat, and may be completely evaporated, if left for a 
 long tune in the hottest part of a porcelain furnace. As a con- 
 sequence of this fixity, or lack of volatility, it foUows that boracic 
 acid is a comparatively powerful acid at temperatures high enough 
 to volatilize the ordinary acids. On being heated with nitrates, 
 or sulphates, for example, it quickly expels nitric or sulphuric 
 acid, and unites with the other ingredients of the salt, though 
 either of these acids would at once decompose the borate thus 
 formed, if they were collected and added to it at the Ordinary 
 temperature. Even phosphoric acid is expelled by it from the 
 phosphates. 
 
 449. Chloride of Boron (BCl,) is a colorless, mobile liquid, of 
 1-35. specific gravity, which boils at 17°- The specific gravity of 
 its vapor has been found to be 58'78, a result which points directly 
 to the formula BCI3 as representing the true composition of the 
 compound. 
 
 From the weight of 2 vols, of chloride of boron (68'78 X 2) . 117-56 
 Subtractthe weight of 3 vols, of chlorine (35'5x 3) . . .106-50 
 
 and the remainder will be 11-06 
 
 a number almost precisdy equal to the weight of one atom of boron 
 as previously determined (§ -446). 
 
 Upon being mixed with water, chloride of boron decomposes, with 
 formation of boracic and chlorhydric acids : — 
 
 2BC1, + 3Hp = B^O, + 6HC1. 
 
 Chloride of boron may be prepared by slightly heating amorphous 
 boron in an atmosphere of ohloriue, or more readily by passing 
 a current of chlorine over a mixture of anhydrous boracic acid 
 and charcoal, heated to redness in a porcelain tube. In presence 
 of the hot charcoal which stands ready to take oxygen from the 
 boracic acid, chlorine can take boron away from boracic aqid ; and, 
 
 2b 
 
370 PLTJOEIBE OF BORON. 
 
 conversely, in presence of the chlorine, ready to combine with the 
 boron, carbon can take away oxygen : — 
 
 B^O, + 3C + 6C1 = 2BCI3 + 3C0. 
 The method here described, of converting an oxide into a chloride 
 through the intervention of carbon, is a method of very general 
 applicability, and is often employed for the preparation of chlorides 
 of the metals. 
 
 450. Fluoride of Boron (BFlj) is a colorless gas of 34-19 spe- 
 cific gravity, as determined by experiment. Upon the assump- 
 tion that an atom of boron weighs 11, its specific gravity would 
 be (11 + 3x19)^2=34. It fumes strongly in damp air, and, 
 by pressure, may be readily condensed to a colorless and very 
 mobile liquid. The gas is exceedingly caustic and corrosive ; it 
 carbonizes and destroys wood and other organic substances, in 
 the same way as concentrated sulphuric acid. As with sulphuric 
 acid (Exp. 104), so here, the fluoride of bOron unites with the 
 elements of water which are contained in the organic matter, and 
 the integrity of the latter is destroyed. 
 
 451. Fluoride of boron is absorbed by water rapidly and in 
 large quantity, 1 volume of water being capable of dissolving 700 
 or 800 volumes of the gas ; but in the act of solution decom- 
 position occurs as well, and there is obtained, not a simple solution 
 of fluoride of boron in water, but a mixture, or rather a com- 
 pound, of fluorhydric and boracic acids : — 
 
 2BF1, + 3H,0 = B,03,6HM. 
 The reaction is interesting in aU its stages, inasmuch as it well 
 illustrates the vagueness and indeflniteness of a considerable class 
 of chemical reactions. When water dissolves fluoride of boron, 
 it increases in bulk to a considerable extent, and in density also, 
 its specific gravity rising as high as 1-77. Upon warming the 
 saturated solution, some fluoride of boron is again disengaged, 
 perhaps as much as one-fifth of all that had been absorbed ; but 
 on continuing to heat the solution, it distils over unchanged, and 
 the condensed liquid presents the appearance of oil of vitriol. In 
 it the elements of boracic and fluorhydric acids are tmdoubtedly 
 held together in a loose condition of chemical combination. By 
 many chemists the compound is called fluoboric acid, though, in 
 
PLTTOBOEIC ACID. 371 
 
 order to avoid confusion, it would, perhaps, be better if the name 
 fluorhydrate of boracic acid were aMotted to it ; for when this 
 compound is largely diluted with water, boracic acid is deposited, 
 and another acid compound is left in solution, the composition of 
 which may be represented by the formula IIFl,B.Fl3. This new 
 acid is caUed indiiferently fluoboric acid or fluorborhydrie acid, 
 and the salts formed by its union with metals are caUed fluobo- 
 rates. It is remarkable that the first-named compound, the fluor- 
 hydrate of boracic acid, upon being neutralized with alkalies, 
 yields, not mixtures of a borate and a fluoride of the alkali em- 
 ployed, but true chemical compounds, double salts, of the general 
 formula M.fij'Bfi^; 6Mri, whence the name fluoboric acid has 
 arisen. The best way of preparing the fluorhydrate of boracic 
 acid is to dissolve boracic acid by small portions in fluorhydrie acid. 
 
 Fluoride of boron may be itself prepared by heating in a glass 
 flask a mixture of 1 part of fused boracic acid, 2 parts of powdered 
 fluorspar, and 10 or 12 parts of concentrated sulphuiric acid : — 
 
 3CaFl, -t- B,0, + 3H,S0^ = SCaSO, + 3H^0 + 2BFI3. 
 On account of its easy solubility in water, the gas must be col- 
 lected over mercury. Fluoride of boron may be employed as a 
 test to determine whether a given sample of any gas is completely 
 dry ; if a few bubbles of it are added to the gas to be tested, the 
 slightest trace of moisture in the gas will be made manifest by 
 the appearance of white fumes of the fluorhydrate of boracic acid 
 above described. 
 
 452. Sulphide of Boron (B^S,) is a white, crystalline solid, de- 
 composable by water, in accordance with the following formula : — 
 
 B,S3 + 3H,0 = B,03 + 3H,S. 
 
 It may be prepared by passing a current of sulphide-of-carbon 
 vapor over a mixture of boracic acid and charcoal strongly heated 
 in a porcelain tube. 
 
 453. Nitride of Boron (BN) is a soft, white, amorphous soM, 
 tasteless, odorless, infusible, and non-volatile. It is, in general, 
 but little acted upon by chemical agents. 
 
 454. It vnll be remarked that while boron is closely analogous 
 to carbon in many respects, it differs from it decidedly in others. 
 Thus, while in their allotropic modifications the two elements are 
 
 2b2 
 
372 SIMOON. 
 
 almost precisely alike in appearance aud properties, and while 
 many of the salts of boradc acid are strikingly similar to the 
 corresponding carbonates, the compounds of boron are not com- 
 parable as regards their composition with the compounds of car- 
 bon. While one atom of carbon unites by preference with four 
 atoms of any member of the chlorine group (as in CCl^), or with 
 two atoms of any member of the sulphur group (as in CO^), an 
 atom of boron unites with only three atoms of chlorine (BCI3), or 
 two atoms of it unite with three atoms of oxygen or sulphur 
 (as in BjOj). The exceptional character of the composition of 
 boron compounds will appear still more clearly in the next chapter, 
 where it will be shown that silicon, the third "member of the car- 
 bon group, resembles carbon as regards the atomic composition 
 of its compounds, as well as in other respects. The atomic weight 
 of boron above given (§ 446) cannot be accepted as established 
 beyond a doubt, and it may happen that farther investigation will 
 show that the boron compounds are really formed upon the same 
 type or pattern as those of carbon and silicon ; but in face of the 
 experimental evidence now at hand, this view cannot be main- 
 tained. In the meantime the student wiU better understand 
 the physical and chemical properties of boron and its compounds, 
 if this element is studied in company with carbon and silicon, 
 which it so closely resembles, than if it were described in con- 
 nexion with arsenic, antimony, and the other elements of the 
 nitrogen group, which form teroxides and terchlorides indeed, 
 but which present not the least other analogy to boron, either in 
 the simple or the compounded condition. 
 
 CHAPTER XXII. 
 
 SILICON. 
 
 455. Like carbon, silicon may be obtained in three distinct 
 aUotropic conditions, which have been designated as amorphous, 
 diamond-like, and graphitoidal. After oxygen, it is the most 
 abundant and widely dififused of aU the chemical elements ; at 
 
MODIMCATIONS OP SILICON. 373 
 
 least one quarter of the solid crust of the earth is composed of it. 
 In combination with oxygen, it occurs in silicic acid, which is one 
 of the commonest substances upon the surface of the globe. 
 Common quartz and flint, as well as rock-crystal, agate, and the 
 like, are pure silicic acid. The yellow sand of sea-beaches and of 
 many sterile tracts of country is silicic acid contaminated with a 
 trace of oxide of iron. In like manner, sandstones and a great 
 variety of other rocks are mainly composed of it. 
 
 In order to obtain pure silicon, the foUowing methods may be em- 
 ployed : — When metallic potassium is heated with a double compound 
 of fluoride of potassium and fluoride of silicon, known as fluosUicate 
 of potassium, a violent reaction occurs, fluoride of potassium is formed 
 and silicon set free in the amorphous state, 
 
 KPl,SiFl^ + 4K = 5KF1 + Si; 
 by washing with water, the silicon may then be readily freed from the 
 fluoride of potassium, which is soluble. The graphitoidal modification 
 of silicon can be prepared either by heating the amorphous variety 
 very strongly, in which event the- powder contracts upon itself and 
 becomes much more dense, or by melting together in a crucible a mix- 
 ture of metallic alumiuum, in excess, and fluosihcate of potassium ; a 
 fusible double fluoride of aluminiun and potassium is formed, and the 
 silicon thus set free dissolves in the melted aluminum. If the alumi- 
 num be dissolved away, after the mass has become cold, by means of 
 chlorhydric acid, the silicon will be left in the form of hexagonal scales. 
 Still a third method must be resorted to, in order to obtain the dia- 
 mond-like modification of silicon; a mixture of dry fluosilicate of 
 potassium, metallic zinc, and metallic sodium is thrown into a hot 
 crucible, the mass is covered with a layer of fluosilicate of potassium, 
 and the crucible covered. A hvely reaction ensues, and the mixture 
 within the crucible fuses ; the fiised mass is then stirred with an iron 
 rod imtil the zinc begins to escape as vapor. The crucible is then re- 
 moved from the fire and allowed to cool ; within it there will be found 
 a button of metallic zinc filled with long crystals of silicon, which can 
 readily be isolated by dissolving the zinc in chlorhydric acid. 
 
 456. The amorphous variety of silicon is a brown powder, 
 which, when touched, soils the fingers. It may be melted at a 
 temperature not far from that at which cast iron becomes liquid. 
 "When mixed with common salt and exposed to a degree of heat 
 strong enough to volatilize the salt, amorphous sihcon changes to 
 the graphitoidal variety, as has been already remarked. Amor- 
 
374 
 
 SILICON AND HTBROGEN. 
 
 phous silicon burns readily in the air and in oxygen. It is not 
 acted upon by acids, excepting fluorhydric acid, whicb dissolves 
 it with disengagement of hydrogen. 
 
 Graphitoidal silicon is very similar to true graphite ; it crys- 
 tallizes in lustrous hexagonal plates of a leaden- gray color, and 
 is an excellent conductor of electricity. It is, however, much 
 harder than graphite. By exposing it to an exceedingly high 
 temperature, it can be transformed to the diamond-like condition. 
 The diamond-like modification of silicon occurs in the form of 
 regular octahedral crystals, exhibiting a decided metaUic lustre. 
 The specific gravity of these crystals is 2-49. They are less 
 hard than the corresponding crystals of carbon and boron, and 
 melt at the same temperature at which cast iron melts. 
 
 Either graphitoidal or diamond-like silicon may be heated to 
 redness in oxygen gas without burning to any appreciable extent, 
 for a film of silicic acid is formed which protects the remainder 
 of the silicon and prevents it from being consumed ; but if the 
 silicon be heated together with a substance capable of furnishing 
 oxygen in presence of a base competent to unite with sihoic acid 
 and form a fusible silicate, it can readily be oxidized and con- 
 verted into a silicate. Thus, when heated to intense redness 
 with carbonate of sodium, it decomposes the latter with evolution 
 of light and heat, and there is produced silicate of sodium, while 
 carbon is set free ; — 
 
 Na,0,CO, -I- Si = Na^CSiO, + C. 
 In a similar way, if silicon be heated in very concentrated solu- 
 tions of caustic potash or soda, water wiU be decomposed and a 
 silicate of potassium or of sodium formed, while hydrogen is set 
 free : — 
 
 2NaH0 -I- HP 4- Si = Na.SiO, + 4H. 
 
 Diamond-like silicon is not attacked at the ordinary temperature 
 by any of the acids, excepting a mixture of fluorhydric and nitric 
 acids, by which it is converted into fluoride of silicon. Hot 
 chlorhydric acid gas, as weU as chlorine, attacks it readily. 
 
 457. Silicon and Hydrogen (SiH^). — A gaseous compound of 
 these elements, called siUciuretted hydrogen, may be obtained, 
 mixed with free hydrogen, by acting upon silicide of magnesium 
 (Mg^Si) with chlorhydric acid ; other methods of preparing this 
 
OXIDES OF SILICON. 375 
 
 gas give a purer product. It is a colorless gas, which takes fire 
 spontaneously on coining in contact with the air, and burns to 
 silicic acid and water. On being heated in a tube, out of contact 
 with the air, it is decomposed into free hydrogen and free silicon, 
 and the latter is deposited upon the walls of the tube as a shining 
 mirror, similar to the mirrors of arsenic and antimony obtained 
 in Exps. 133, 136. 
 
 Silicon and Oxygen. — ^Two compounds of these elements have 
 been discovered, though but one of them is as yet well known. 
 
 4.58. Oxide of Silicon is described as a white, amorphous, 
 hydrated substance, so Ught that it floats upon water ; it may be 
 obtained by treating with water at 0° the compound of silicon, 
 hydrogen, and chlorine described in § 472; its composition is 
 probably that represented by the formula Si^H^Oj. It is scarcely 
 at aU acted upon by cold water ; but in presence of alkalies it 
 decomposes water rapidly, with evolution of hydrogen and forma- 
 tion of the higher oxide of silicon, silicic acid, directly to be 
 described. At temperatures above 300° it suffers decomposition, 
 breaking up into silicic acid and siliciuretted hydrogen. It burns 
 brilliantly in the air, and stiU better in oxygen. None of the 
 acids, excepting fluorhydric acid, have any action upon it. 
 
 459. Silicic Acid (SiO^) constitutes at least one half of the 
 crust'of the earth. Besides being thus abundant, it is one of the 
 most important acids known, regarded merely as a chemical 
 agent.' It is found everywhere, sometimes free, as quartz and 
 sand, sometimes in combination with metallic oxides, ia the form 
 of salts known as silicates. It occurs more or less abundantly 
 in aU soUs, plants, and waters, while rocks like granite and 
 earths like clay are largely composed of it. The common mine- 
 rals feldspar and mica are double silicates of aluminum and 
 potassium, and of aluminum, iron, and potassium respectively. 
 In plants, the silicic acid (or silica, as it is often called) is con- 
 tained particularly in the outer covering of the stalks and the 
 husks of grain. The cuticle of rattan, for example, contains a 
 large proportion of silica, and the same remark is true of most 
 of the grasses and grains. The value of the plant called horse- 
 tail (Equisetum) as a polishing or scouring agent depends upon 
 the large quantity of silica contained in it. 
 
876 SOITTBIE SILICIC ACTD. 
 
 460. Silicic acid occurs in at least two distinct isomeric Modi- 
 fications, — in one of which it is completely insoluble in water and 
 in acids, excepting fluorhydric acid, and is only. slowly soluble in 
 boiling potash-lye ; while, when in the other modification, it dis- 
 solves easily in a solution of potash, and may be retained in solu- 
 tion in considerable quantities both by water and by acids. Eock 
 crystal, as it is found in nature, may be regarded as the type of 
 the first or insoluble modification, and the soluble variety may be 
 prepared artificially by treating the solution of some one of the 
 soluble silicates with ehlorhydric or sulphuric acid. 
 
 Exp. 220. — In a block of charcoal 12 or 15 Cm. long by 4 or 5 cm. 
 wide and thick, scoop out a small cup-shaped cavity large enough to 
 hold a pea ; place in this cavity a fragment of amorphous quartz or 
 flint, and heat it intensely by means of thfe blowpipe (Exp. 202) during 
 several minutes. When the quartz has become red-hot, suddenly 
 throw it from the coal into a dish of cold water ; it will break up into 
 numerous small fragments or become filled With a multitude of cracks, 
 and can hence be readily pulverized. Grind the broken quartz to fine 
 powder in a wedgwood, or, better, in an iron or agate mortar ; weigh 
 out 1 grm. of the powder, also 2 grms. of caustic soda, and to the mix- 
 ture of these ingredients add 8 or 10 c. c. of water. Boil the mixture 
 in a porcelain dish for an hour or two, taking care to add, from time to 
 time, water enough to supply that lost by evaporation ; then pour the 
 solution into a tall, narrow bottle, and leave it at rest untU the undis- 
 solved portions of silica have settled and the liquid has become clear. 
 The highly alkaline solution thus obtained may be regarded either as 
 an aqueous solution of basic silicate of sodium, or as a solution of 
 normal silicate of sodium in the soda-lye. 
 
 Exp. 221. — To one-third part of the solution obtained in Exp. 220 
 add 10 or 12 times its bulk of water, and to this solution add dilute 
 ehlorhydric acid, drop by drop, until the liquor manifests a decided 
 acid reaction (Exp. 33). The liquid will remain clear, and no silicic 
 acid wiU be deposited. All the silicic acid which has been set fr-ee 
 from its combination with the alkali remains dissolved in the acidu- 
 lated water. 
 
 If the clear solution be placed in a dialyzer (§ 327), aU the chloride 
 of sodium, together with the free ehlorhydric acid, will pass ofi^ through 
 the parchment-paper in the com-se of a few days, and there will be left 
 in the dialyzer nothing but pure silicic acid and water. Aqueous solu- 
 tions of silicic acid, containing from 5 to 14 per cent, by weight of the 
 acid, may be thus obtained. This pure aqueous solution of silicic acid 
 
SILICA IN NATTJBAI, WATEKS. 377 
 
 exhibits a decided acid reaction. It lias little or no taste, though when 
 applied to the tongue it occasions an unpleasant sensation. It is by no 
 means so permanent as the solution, above mentioned, acidulated with 
 chlorhydric acid. "When left to itself, the aqueous solution deposits 
 silicic acid after a while as an insoluble gelatinous precipitate. In like 
 manner, it has been observed that when chlorhydric or another acid is 
 added to the aqueoiis solution of basic silicate of sodium in no greater 
 quantity than is sufficient to exactly neutralize the alkali, the liquor, 
 though it remain clear for a considerable space of time, will gradually 
 become cloudy and deposit silicic acid. 
 
 -Bay. 222. — To one-third part of the solution obtained in Exp. 220 
 add at once enough concentrated chlorhydric acid to render the solu- 
 tion acid. All the silicio acid will immediately be thrown down as a 
 thick insoluble jejly. 
 
 &p. 223. — Place in a small porcelain dish a portion of the solution 
 of silicic acid in acidulated water obtained in Exp. 221, evaporate 
 it to dryness upon a water-bath, and heat the residue, over the gas- 
 lamp, to a temperatm'e of 180° or 100°. Add water to the cold dry 
 residue, and observe that the silicic acid does not redissolve ; it remains 
 as a fine white powder, which may be readily collected upon a filter 
 and there washed cleMi by pouring upon it several successive portions 
 of water. After having been once thoroughly dried, silicic acid is 
 completely insoluble in water. 
 
 461, By adding chlorhydric acid to a snffloient quantity of the 
 water of almost any spring or river, and then evaporating the 
 water to dryness, a small quantity of silicic acid wiU be found in 
 the residuum. The silica, in this case, may be combined with 
 an alkali, or may be held in solution by the action of an alkaHne 
 carbonate. Silicic acid which has been finely powdered, or, 
 better, that which has recently been precipitated, is soluble, to a 
 considerable extent, in aqueous solutions of the alkaline carbo- 
 nates, or even of the bicarbonates, only a small proportion of the 
 carbonic acid being expelled by it as it dissolves. It is not im- 
 probable, therefore, that the siKcie acid found in waters may be 
 retained in solution by force of this solvent action of the alkaline 
 carbonates. It is, at all events, a matter of fact that waters 
 highly charged with carbonate of sodium, such as flow from the 
 geysers or boiling springs of Iceland, contain, in solution, Very 
 large quantities of silica, much of which is deposited as the 
 
378 SILICIC ACID. 
 
 ■water becomes cold, upon the rocks and other objects witb which 
 it comes in contact ; siliceous petrifactions are thus formed. 
 
 462. Besides the soluble and insoluble modifications above 
 mentioned, a distinction is made between the variety of silicic 
 acid which is found crystaHLzed in nature and that which occurs 
 in the amorphous state. Crystallized silicic acid is anhydrous, 
 has a specific gravity of from 2*6 to 2'66, and is scarcely at all 
 acted upon by alkaline lyes. The amorphous silicic acid found 
 in nature contains a certain amount of water, has a specific gra- 
 vity of only 2-1 to 2'2, and is soluble in alkaline solutions. 
 
 As it exists in the insoluble modification, either as found in 
 nature or as prepared by calcining the artificial product, silicic acid 
 is a white, tasteless solid, incapable of forming a cohesive plastic 
 mass with water. It is infusible, excepting at very high tem- 
 peratures, such as may be obtained by means of the oxyhydro- 
 gen blowpipe, in the flame of which it melts to a colorless glass. 
 When melted, it is tough and viscous, and, like glass, can be 
 drawn out into fine threads which are exceedingly elastic, par- 
 ticularly if they be dipped, while white-hot, into water. Silicic 
 acid is not volatile by itself; but when exposed to a current of 
 gas or vapor at a white heat, portions of it are carried oif by the 
 vapor; like boracic acid, it can be transported in considerable 
 quantities by superheated steam. 
 
 When in the soluble modification, whether in the gelatinous 
 hydrated condition or in the state of an air-dried powder which 
 has never been exposed to heat, it dissolves readily in solutions of 
 ,the caustic and carbonated alkalies, particularly if these be heated. 
 Some varieties of native silica, such, for example, as the soft, 
 pulverulent, infusorial earth found at the bottoms of many ponds 
 and swamps, are as readily soluble in the alkalies as that which 
 has been prepared artificially. All the varieties of silica can be 
 dissolved by heating them with alkahne lyes in close boilers under 
 a pressure of 4 or 5 atmospheres ; in other words, even crystal- 
 lized sihca is soluble in the alkalies at high temperatures. 
 
 463. At the ordinary temperature silicic acid is but a weak 
 acid ; almost any of the other acids are capable of decomposing 
 the aqueous solution of a salt of silicic acid and of expeUing the 
 
SItlCATDS. 379 
 
 latter from, its combination ■with, the metal. But, as is the case 
 with boracio acid also (§ 448), at high temperatures the reverse 
 of aU this is true, silicic acid being then capable of expelling all 
 acids which are more volatile than itself. Neither variety of 
 silicic acid is acted upon at any temperature by either carbon, 
 hydrogen, phosphorus, or chlorine, if these elements be taken 
 separately ; but when exposed at high temperatures to the com- 
 bined action of carbon and chlorine, chloride of silicon and car- 
 bonic oxide are produced, much in the same way that chloride of 
 boron is formed under similar circumstances, as has been shown 
 in § 449. When silicic acid is heated together with carbon, or 
 other reducing agents, in contact with metals like iron or plati- 
 num, some of it is decomposed, and a sUicide of the metal is 
 formed. Platinum crucibles are often injured in this way by the 
 nascent silicon which forms when certain minerals are fused in 
 them. 
 
 464. Silicic acid combines with many of the metallic oxides 
 to form salts, many of which are of very complex composition. 
 Hundreds of sUicates are found in nature as crystallized minerals, 
 and they may, in general, be formed by fusing together silicic 
 acid and the appropriate metallic oxide, or carbonate, in suitable 
 proportions. Most of the silicates are fusible, and the greater 
 number of them, when in the molten state, have the power of 
 dissolving, either an excess of base, or an excess of silicic acid over 
 and above the quantities corresponding to strict atomic propor- 
 tions ; hence it happens that mixtures of silicic acid and of bases 
 may be melted together in the most varied proportions. The 
 study of the silicates thus becomes difficult, since it is often im- 
 possible to determine whether a given silicate be really a definite 
 chemical compound or a chemical compound contaminated with 
 an excess of silicic acid or of the base ; in very many instances, 
 moreover, it is probably true that the excess of silica, above the 
 normal atomic proportion, or of the base, is really held in combi- 
 nation by virtue of the chemical force, though it be held feebly 
 and indefinitely, as is the case with the ingredients of many solu- 
 tions and metaUic alloys. (See §§ 49, 76.) 
 
 As a general rule, the simple silicates containing but a single 
 base, and no excess of either base or acid, crystallize in passing 
 
380 FORMTTLaE OF SILICATES. 
 
 from the liquid to the solid condition ; but the double silicates 
 (compounds formed by the union of t-ff^o or more simple siEcateSj 
 and therefore containing at least two different metals) usually 
 solidify to a non-crystalline, homogeneous glass. All the common 
 varieties of glass consist essentially of such double salts of silicic 
 acid. In general, those silicates of the alkali-metals and of lead 
 which contain an excess of base are more readily fusible than the 
 normal or acid salts ; those silicates which contain easily fusible 
 oxides melt at correspondingly low temperatures ; and many mix- 
 tures of two or more different silicates fuse at temperatures lower 
 than the melting-point of either of the simple silicates of which 
 the mixture is composed. 
 
 The silicates of potassium and of sodium, containiug 1 or 2 or 
 more molecules of base to one molecule of the acid, are readily 
 soluble in cold water, and compounds containing as many as 4 
 molecules of the acid to one molecule of the alkaline base may be 
 completely dissolved in water when boiled therewith for a con- 
 siderable time. These acid compounds (such, for example, as the 
 sodium-salt of the formula Na^O, 2-4Si0j) are much employed 
 in the arts under the name of Waterglass or Soluble glass. When, 
 however, the proportion of acid is more than 4| molecules to 1 
 molecule of the alkaline base, the eiUcate may, for all practical 
 purposes, be regarded as insoluble in water. The silicates of the 
 metals not included in the alkali group (§ 544) are, in like man- 
 ner, insoluble in water, in the ordinary sense of the word, though, 
 in the last analysis, it would be hard to find any siLicious minerals, 
 or glasses, which are not susceptible of being decomposed and 
 dissolved, to a greater or less extent, by water. Some metalHe 
 silicates may be prepared, not only by the method of fusion, but 
 also by adding the solution of an alkaline silicate to the solution 
 of a salt of the metal whose silicate is desired. 
 
 465, The most commonly occurring silicates may be referred 
 to three or four general classes, similar to the classes of carbo- 
 nates (§ 414) : — Ist. Normal silicates, of the general formula 
 M20,Si0j, such as the crystaUizable silicate of sodium Na20,Si02, 
 or the normal silicate of calcium, CaO,Si02. 2d. BisOicates, of the 
 formula M20,2Si02, such as the bisUicate of calcium, CaO,2Si02. 
 3d. DisUicates (basic silicates) of the general formula 2M20,SiO , 
 
BECOMPOSITION OF SILICATES. 381 
 
 such, for example, as the silicates of iron, SFeOjSiO^, of mag- 
 nesium, 2MgO,SiOj, of manganese, 2Mn0,Si0j, and of zine, 
 2ZnO,SiOj. Also, sesquisilioates, of the formula 2M20,3SiO , 
 to which the mineral meerschaum may, perhaps, he referred its 
 formula being 2M:gO,3SiO ^ + 2Kfi. 
 
 466. Many of the natural siUeates may be decomposed by 
 digestion with the strong mineral acids, such as concentrated 
 chlorhydric acid; and this is especially true of those sUicates 
 which contain a large proportion of base, and of those containing 
 water of crystallization. But many anhydrous normal or acid 
 sUieates are not decomposed by any acid, excepting fluorhydric 
 acid. Fluorhydric acid attacks and dissolves, not only pure siUcio 
 acid in all its varieties, but all sUicates as well, and, other things 
 beiag equal, the rapidity of its action is in proportion to the degree 
 of its concentration. Crystallized silica, however, is much less 
 readily acted upon by fluorhydric acid than the amorphous variety; 
 it dissolves slowly and without development of heat, while amor- 
 phous silica not only dissolves rapidly, but the act of solution is 
 accompanied with the evolution of considerable heat. From those 
 silicates which are decomposed with difficulty by chlorhydric 
 acid the silicic acid separates out ae a soft powder ; but from 
 those which are more readily decomposed the silicic acid sepa- 
 rates as a hydrated gelatinous mass when the finely powdered 
 mineral is digested with chlorhydric acid; -in this case the 
 mineral is said to gelatinize with acids. Some silicious minerals 
 may even be completely dissolved, silica and all, in dilute chlor- 
 hydric acid. 
 
 467. It is remarkable that, whUe some of the hydrated silicates 
 (such, for example, as the class of minerals called zeolites) can no 
 longer be readily decomposed by chlorhydric acid after they have 
 been ignited, there are other silicates (such as the minerals gar- 
 net, epidote, and idocrase) which, though scarcely at aU acted upon 
 by chlorhydric acid when in the natural condition, may be decom- 
 posed thereby with gelatinization after they have been melted. 
 Facts like these would seem, at first sight, to indicate that silicic 
 acid exists in combination, sometimes in the insoluble, and at 
 other times in the soluble modification, and that it may be trans- 
 formed from the one state to the other without being first set free ; 
 
382 COMPOSITION OF SILICIC ACID. 
 
 but some of them admit of being explained in another way. 
 When any sUicate, no matter whether it be decomposable by 
 chlorhydric acid or unacted upon by this agent, is mixed with an 
 excess of one of the fixed alkalies, or alkaline earths, or with a 
 carbonate or nitrate of either of the alkaline or alkaline-earthy 
 metals, and the mixture then heated to intense redness, there will 
 be obtained a melted or agglutinated mass, which decomposes 
 readily on being treated with chlorhydric acid, and yields gelati- 
 nous silica. At the high temperature to which the mixture is 
 exposed, the strong alkaline or alkaline-earthy bases combine with 
 the silicic acid, and there are formed silicates of potassium, sodium, 
 calcium, or the like, easily decomposable by acids. Now, in the 
 case of the minerals garnet, epidote, and idocrase, above men- 
 tioned (which are attacked by chlorhydric acid after they have been 
 melted), it may be conceived that the strong bases (such as lime, 
 magnesia, and protoxide of iron) which are contained in these 
 minerals have acted upon the silicate of alumina (also contained 
 in them) in much the same way that an extraneous alkali would 
 act if it were fused with the powdered mineral. 
 
 468. Sulphuric acid, when concentrated or but slightly diluted, 
 acts much more energetically than chlorhydric acid upon the sili- 
 cates, apparently because of its comparatively high boiling-point. 
 Common clay, for example (silicate of aluminum), which is but 
 little acted upon by chlorhydric acid, may be completely decom- 
 posed when digested with boUing concentrated sulphuric acid, 
 silicic acid being set free and sulphate of aluminum produced. 
 This decomposition, like that of the garnet above mentioned, is 
 in any event very much more readily effected if the clay be first 
 gently roasted or calcined. The mineral feldspar also, when in 
 fine powder, may be decomposed by boiling oil of vitriol. 
 
 469. Contrary to the view formerly held by many chemists, 
 the atomic weight of silicon is now thought to be 28, instead of 
 21, as formerly. This change makes the formula of silicic acid 
 SiOj, in strict analogy to carbonic acid, instead of SiOj which was 
 for a long time the accepted formula. 
 
 The percentage composition of sUicic acid has been determined 
 by direct experiment (by oxidizing a weighed quantity of sili- 
 con to silicic acid) to be 51-92 per cent, of oxygen and 48-08 
 
CHLOEIDE or SILICON. 383 
 
 per cent, of silicon. But since it is difficult in this way to 
 oxidize the whole of the silicon, inasmuch as portions of it he- 
 come covered with sUicic acid, and are so protected from the 
 further action of oxygen, the ahove result can he regarded 
 only as a rough approximation to the truth. These numhers 
 would correspond to 29-63 as the atomic weight of sihcon. For 
 
 51-92 : 48-08 : : (32 = 2 atoms of 0) : (a; = 1 atom of Si = 29-63). 
 
 More accurate experiments, however, upon another plan, have 
 since shown that the real atomic weight of silLcon is 28, or very 
 nearly 28, as will he fuUy set forth in the next section. 
 
 470. Chloride of Silicon (SiClJ is formed when silicon is 
 heated La an atmosphere of dry chlorine, or more conveniently 
 hy heating together finely divided silicic acid, charcoal, and 
 chlorine. 
 
 The experiment may he conducted as foUows : — Mix together inti- 
 mately equal weights of lampblack and dry pulverulent silicic acid, 
 such as is obtained hy decomposing an alkaline silicate with chlorhydric 
 acid and evaporating the residue to dryness, as in Exp. 223. Knead 
 into the mixture enough oil to render it plastic, and from the thick 
 paste thus formed make a number of amaU balls or pellets ; roU these 
 pellets in powdered charcoal, place them in a Hessian crucible, cover 
 the crucible, and heat in a strong fire until all the oil has been distilled 
 ofi' or decomposed. The mixture of silicic acid and charcoal is thus 
 left in an open porous condition, well adapted for the action of the 
 chlorine. Place the dry pellets in a porcelain tube about 2 cm. in 
 diameter, connect one end of the porcelain tube with a U-tube sur- 
 rounded with a freezing-mixture of ice and salt, and to the other end 
 attach a flask in which to generate chlorine, taking care to interpose 
 between this flask and the porcelain tube one U-tube filled with pu- 
 micestone soaked in oil of vitriol, and another filled with chloride of 
 calcium, in order that the gas may be thoroughly dried. Place the 
 porcelain tube in a siiitable stove or furnace ; pass into it a slow cur- 
 rent of chlorine, in order to expel the air, dnd then build around it a 
 hot fire of charcoal or coke ; finally, when the tube has become heated 
 to intense redness, pass in the chlorine as fast as it is absorbed. The 
 chloride of silicon vrill be condensed in the U-tube as a liquid which 
 has usually a yellow color, owing to the presence of dissolved chlorine. 
 In order to purify it, the liquid may he shaken in a dry flask with a 
 quantity of quicksilver in which a little potaasium has been dissolved j 
 
384 coMPOsrrioiir of chloeide of silicon. 
 
 after having been decanted from the mercury and subjected to redis- 
 tillation in dry vessels, it vdll be found to be pure. 
 
 It vrill be noticed that the method here described, of preparing chlo- 
 ride of silicon, is similar to that recommended for preparing chloride 
 of boron (§ 449). Chlorine alone is not capable of decomposing either 
 silicic or boracic acids ; but in presence of carbon combination of chlo- 
 rine and silicon is effected, at the same time that carbon and oxygen 
 unite to form carbonic oxide : — 
 
 SiOj, -1- 20 + 401 = SiOl, + 200, 
 
 471. Chloride of silicon is a transparent, colorless, very mobile, 
 volatile liquid, of pungent, acid, and irritating odor. It fumes 
 strongly in the air, boils at 59°, and is of 1-52 specific gravity. 
 The specific gravity of its vapor has been found to be 85-74, which 
 accords well with the supposition that a molecule of chloride of 
 sOicon contains 4 volumes of chlorine and 1 volume of silicon- 
 vapor condensed to 2 volumes : — 
 
 For if to the weight of 4 volumes of chlorine (4 x 35-5) = . . 142 
 There be added the weight of 1 volume of silicon-vapor = . . 28 
 
 The two volumes of gas produced will weigh , . 170 
 
 The weight of one volume of the gas should, consequently, be equal to 
 170 -=- 2 = 85. 
 
 Chloride of silicon is at once decomposed by water with for- 
 mation of chlorhydrie acid and deposition of gelatinous silicic 
 acid, 
 
 SiCl, + 2H,0 =SiO, + 4HC1, 
 
 no gas of any kind being set free, and no other products being 
 formed. The fact is important, since it shows at once that the 
 composition of chloride of silicon must correspond with that of 
 silicic aqid — that in it four atoms of chlorine simply replace the 
 two atoms of oxygen contained in the silicic acid. Por knowing, 
 as we do, the composition of chlorhydrie acid (§ 98) and of water 
 (§ 36), we are sure that, for every atom of chlorine eliminated 
 from the chloride of sUioon, one atom of hydrogen is required, 
 in order that chlorhydrie acid may be formed, and that for every 
 two atoms of hydrogen thus taken from the water, one atom of 
 oxygen will be detached. But as no oxygen escapes from the 
 solution, all of that derived from the water must evidently have 
 
COMPOSITION or CHtOEIBB OF SILICON. 385 
 
 combined with the silicon to form silicic acid. Now, it is a com- 
 paratively easy matter to determine the amount of chlorine ia 
 any solution by adding to the solution nitrate of silver, and then 
 collecting and weighing the insoluble chloride of silver which is 
 formed. Hence, if a weighed quantity of chloride of silicon be 
 decomposed with water, and the amount of chlorine contained in 
 the solution be determined, the difference between the weight of 
 chlorine found and the weight of chloride of silicon taken wiU 
 give us the weight of the silicon with which the chlorine was 
 combined. By careful experiments,, it has been proved in this 
 way that chloride of silicon contains in 100 parts by weight 16-52 
 parts of silicon and 83"48 parts of chlorine. But 83*48 parts of 
 chlorine are equivalent to 18-81 parts of oxygen, for 
 
 (35-5 X 2 = 71) : 16 : : 83-48 ; (x = 18-81). 
 Weight of two Weight of 
 
 atoms of CI, one atom of 0. 
 
 Hence 18-81 parts of oxygen must have combined with every 
 16'52 parts of silicon contained in the solution ; or, reduced to 
 per cent., every 46-75 parts of silicon must have combined with 
 53-25 parts of oxygen j and if this proportion of oxygen lead 
 to the formula SiOj,, the proportion of chlorine will, in like 
 manner, require the formula SiCl^. Prom the composition of 
 chloride of silicon, as thus determined, the atomic- weight of sili- 
 con may be accurately derived (compare § 469i) i — 
 
 63-25 : 46-75 = 32 : (^ = 28-1) 
 Per cent, of Per cent, of Weight oftwa Weight of one 
 
 Oxygen Silicon atoins of atom of 
 
 V ^/ ' Oxygen. Silicon.. 
 
 in Silicic Acid. 
 
 Or, more directly, by the proportion 
 
 83-48 : 16-52 = 142 : (a; = 28-1) 
 Per cent, of Per cent, of Weight of Weight of 
 
 Chlorine SUican four atoms one atom 
 
 of Chlorine. of Silicon. 
 
 in Chloride of SiUcon. 
 
 At the ordinary temperature, liquid chloride of silicon does 
 
 not act upon potassium ; but if this metal be heated in its vapor, 
 
 chloride of potassium is formed and silicon set free ; the reaction 
 
 2c 
 
386 FLTJOEIDE OF SILICON. 
 
 affords, in fact, a good mettod of olitaimng silicon in the amor- 
 phous state. There is a bromide of silicon (SiBrJ analogous to 
 the chloride in composition and properties ; it may be prepared in 
 a similar way. No compound of iodine and silicon has yet been 
 discovered. 
 
 472. Compound of Silicon, Hydrogen, and CJdorine. — By 
 passing a current of dry ehlorhydrie acid gas over crystallized 
 silicon, heated nearly to redness in a glass tube, and condensing 
 the product in a receiver immersed in a freezing-mixture, there 
 is obtained a colorless, fuming liquid, which boUs at 34° ; the 
 density of its vapor has been determined at 4-64, the calculated 
 value being 4-69. At a red heat it decomposes, yielding chloride 
 of sihcon, ehlorhydrie acid, and amorphous sUicon. Its vapor is 
 very inflammable, and, when mixed with air or oxygen, detonates 
 violently on being lighted ; chloride of sihcon, together with a 
 smoke of ehlorhydrie and silicic acids, are the products of this 
 reaction. Water decomposes it instantly, with production of 
 hydrated oxide of silicon, as has been already set forth (§ 458). 
 
 473. Fluoride of Silicon (SiPl^) is formed whenever dry fluor- 
 hydric acid comes in contact with silicic acid, either free or com- 
 bined. It may be readily prepared by treating a mixture of sili- 
 ceous sand and fluorspar with oil of vitriol. 
 
 In a flask of about 250 c. c. capacity, place an intimate mixture of 
 9 grms. of finely-powdered quartz-sand, 9 grms. of powdered fluorspar, 
 and 53 grms. of concentrated sulphuric acid. Heat the flask, and col- 
 lect the gas which is evolved, in tall bottles of 150 c. o. capacity, at 
 the mercury trough. The sand and fluorspar should both be heated 
 before being used, in order that they may be perfectly dry ; the flask 
 also and the mercury in the trough should be thoroughly dried ; for 
 fluoride of sihcon is decomposed by moisture, and the bulky precipitate 
 of silicic acid which would be formed might elog the delivery-tube of 
 the apparatus or coat the glass vessels and render them opaque. 
 
 The decomposition of the gas by water can readily be shown by 
 causing some of it to pass out from the deliveiy-tube into a bottle 
 inverted upon the mercury-trough, one half of which has been filled 
 with water and the other half with quicksilver. The water in the 
 bottle win soon become filled with gelatinous silica. "With the 
 quantities of material above given, there vsdU he obtained first a bottle 
 of 150 c. c. capacity of air from the flask, which should be thrown 
 away ; a bottle of the same size can then be filled with sufficiently 
 
rlTTOEIDE OE SILICON. 387 
 
 pure fluoride of silicon, and in a third bottle the decomposition with 
 water may he shown. 
 
 Instead of sand, coarsely powdered glass may be placed in the flask 
 as the source of silicon. In any event the glass of the flask will be 
 somewhat corroded ; it is better to conduct the operation in a platinum 
 retort, if such a vessel can be had. 
 
 The reactions which occur among the materials in the flask may be 
 represented by the following equations : — In the first place, fluorhydric 
 acid is formed by the action of sulphuric acid upon the fluoride of 
 calcium, 
 
 OaFlj + HjSOi = OaSO, + 2HF1, 
 
 and the fluorhydric acid then attacks the silica, 
 
 SiO^ + 4IIF1 = 2H2O + SiFl^. 
 The water here formed unites with the sulphuric acid which has been 
 employed in excess, and is thus prevented fi-om acting upon the fluo- 
 ride of silicon. The reaction last named is essentially the same as 
 that which occurs when glass is etched with fluorhydric acid gas 
 (§ 158). When the fluoride of silicon is brought into contact with 
 water, there is produced, together with the silicic acid, fluosUicic acid 
 (2HFl,SiFl4), a compound to be described directly. 
 
 474. Fluoride of silicon is a colorless gas which, fumes strongly 
 in the air, especially if the air be moist. It has an acid odor 
 and taste, extinguishes combustion though, itself uninflammable, 
 has no action, upon glass, can support a high degree of heat 
 without being decomposed, and may be condensed by pressure 
 and cold to a colorless, very mobile liquid. Its specific gravity 
 has been determined to be 51'98, or 3'6 as compared with air. 
 It can consequently be readily collected by displacement, if 
 pains be taken to protect it from contact with moist air by mear.s 
 of drying-tubes. 
 
 The specific gravity of this gas points very decidedly to the 
 formula SiFl^, and consequently to the number 28 as the atomic 
 weight of silicon, and to the formula SiO^ for siUoic acid. For, if 
 a molecule of gas be composed of 
 
 One volume of siUcon-vapor = 28 
 
 And four volumes of fluorine (19 X 4) = . . . . 76 
 
 Condensed to two volumes = 104 
 
 One volume of the gas will weigh 52, or almost precisely as much as 
 has been indicated by experiment. 
 
 2c2 
 
388 FLTTOSILICIC ACID. 
 
 The behavior of the gas -with water is peculiarly interesting. 
 If water be sprinkled into a bottle Med with fluoride of silicon, 
 or if the gas be conducted into water, decomposition occurs in- 
 stantly, and silicic acid is deposited in the gelatinous condition. 
 At first sight it might seem as if the reaction were strictly analo- 
 gous to that which occurs when chloride of silicon is mixed with 
 water (see § 471), and that it could be represented by the formula 
 
 8LF1, 4- 2HjO = SiO, + 4Hri; 
 but if it be remembered that fluorhydric acid, unhke (jhlorhydrio 
 acid, is capable of dissolying silica, it will be at once evident that 
 the reaction between water and fluoride of silicon cannot be 
 directly comparable with the other reaction, in which chloride of 
 silicon is concerned. The reaction which really occurs between 
 water and fluoride of silicon may be represented by the following 
 equation : — 
 
 3SiM, + 2Efi = SiO, + 2(2HFl,SiFy, 
 
 — a double compound of fluorhydric acid and fluoride of silicon, 
 known as Jluosilidc acid, being the other product besides silica. 
 
 Fluosilicic acid may be prepared either in the maimer indicated in 
 § 473, or more conveniently by conducting fluoride of siUcon gas into 
 an upright bottle full of water ; in this case, however, the orifice of the 
 tube which delivers the gas should be immersed in a layer of mercmy, 
 3 or 4 cm. deep, beneath the water, so that the gas may bubble up 
 through the mercury, and the water never come in contact with the 
 mouth of the delivery-tube. In this way the tube may be iept free 
 from the silicic acid which would quickly clog it if it opened directly 
 into the water. As the bubbles of fluoride of silicon escape from the 
 merciiry, each of them becomes covered with a thick crust of gelati- 
 nous silica, which it carries with it to the surface of the water. Some- 
 times one of these crusts will remain adhering to the mercury and vrill 
 be gradually prolonged into the form of a tube extending from the 
 mercury to the surface of the water. Such tubes should, however, be 
 broken up, by stirring the liquor, lest fluoride of sUicon escape through 
 them into the air without coming in contact with water. 
 
 Another modification of the method of preparing fluosilicic acid is to 
 conduct the gas into a large flask containing but little water, and to 
 agitate this flask so that its sides may be continually moistened with 
 water, although no water can come in contact with the opening of the 
 gas delivery-tube. The following quantities of materials have been 
 
piTjosmcic ACID. 389 
 
 found convenient in practice. In a flask of 600 ot 700 c. c. capacity 
 place a mixture of 35 grms. of powdered sand, 35 grms. of powdered 
 fluorspar, and 210 grms. of concentrated sulphuric acid. Place the 
 flask upon a sand-bath over the gas-lamp, and by means of a delivery- 
 tube connect it either with the bottom of a tail bottle containing 
 150 c. c. of water and enough mercury to form the layer above de- 
 scribed, or with the middle of a flask of 700 or 800 c. c. capacity, and 
 containing 160 c. c. of water. In the latter case the receiving-flask 
 must be agitated, as aforesaid, so that its walls may be kept moist. 
 When the evolution of gas has ceased, the gelatinous mass in the bottle 
 should be thrown upon apiece of cotton cloth, and the liquid contained 
 in it separated from the solid matter by pressure. The cloudy liquor 
 thus obtained may be rendered clear by flltering it through paper. 
 The clear liquid is a strong aqueous solution of fluosilicic acid, and the 
 solid matter is hydrated silicic acid. 
 
 475. Fluosilicic acid is known only in aqueous solution. The 
 saturated solution is a transparent, colorless, fuming, and very 
 acid Uquid, which has no action upon glass, and may consequently 
 be kept in glass bottles. It cannot be distilled without suffering 
 decomposition, nor can it be evaporated beyond a certain degree 
 of concentration without breaking up into fluoride of siUcon and 
 fluorhydric acid. If the evaporation is conducted in a glass vessel, 
 the silica of the glass wiU retain the fluorhydric acid, and only 
 fluoride of silicon and water will be set free. The reaction which 
 occurs in this case, 
 
 SiO, -1- 2(2HPl,Sm,) = 2S^0 + SSiFl,, 
 
 is just the reverse of that which takes place when fluoride of sili- 
 con is decomposed by water — 
 
 2H,0 -1- 3SiPl, = SiO, + 2(2HFl,SiFl,). 
 
 "With bases fluosilicic acid unites to form compounds known as 
 fluosilicates, such as the fluosiUcate of potassium, Kj,SlF1j = 
 2KF1,SlF1^, and fluosilicate of barium, BaSiFle = BaFlj.SiFl^, 
 if no excess of the base be present ; but if an excess of the base 
 be added, silidc acid vriU be precipitated, and the whole of the 
 fluorine wiU unite with the metal contained in the base to form 
 a fluoride. In the first case, where no excess of base is employed, 
 the reaction may be thus represented : — 
 
 2KH0 + H^SiFl, = 2H,0 + K^SiFl,. 
 
390 THE CAEBON GEOUP. 
 
 In the second case, ■where an excess of the base is present, 
 
 6KH0 + H^SiFl, = 4H,0 + SiO, + 6KF1.] 
 Most of the fluosilicates are easily solnble in water ; but some of 
 them are so nearly insoluble that the acid is sometimes employed 
 as a precipitant of various oxides. It is remarkable that pre- 
 cisely those bases, namely the alkalies, which form soluble salts 
 with almost all the other acids, should here yield insoluble com- 
 pounds. Fluosilicic acid is in fact a good reagent for the detection 
 of potassium ; and it is valuable as a means of removing potassium, 
 from many of its salts when we desire to obtain in a free state the 
 acids which these salts contain. (Compare § 124.) 
 
 476. Sulphide of Silicon (SiS^) occurs in white, needle-Kke 
 crystals, unalterable in dry air. It is volatile at the temperature 
 of redness, and is decomposed at once by water, with deposition 
 of gelatinous silica and evolution of sulphydric acid : — 
 
 SiS, -t- 2Sfi = SiO, + 2H,S. 
 
 Like sulphide of boron, it may be obtained by passing the vapor 
 of bisulphide of carbon over a mixture of sUicic acid and carbon 
 heated to redness. 
 
 477. As has appeared abundantly from the foregoing, the three 
 elements carbon, boron, and sUicon constitute a distinct natural 
 family. This family differs in character from each and every one 
 of the other natural groups of elements hitherto described (§§ 152, 
 257, 364). The occurrence of carbon and silicon in three di- 
 stinct and extraordinary modifications (as diamond, graphite, and 
 charcoal), and of boron in the diamond and amorphous modifica- 
 tions, distinguishes this group from all others. The eminently 
 refractory nature of the several members, and their fixity as re- 
 gards heat and solvents, are marked characteristics of the three 
 elements. The vitrifiable character of the oxides of boron and 
 silicon (boraoic and silicic acids), and of the borates and silicates 
 of many of the metals, is a noteworthy resemblance between these 
 elements. Eemarkable resemblances between the hydrated car- 
 bonate, borate, and silicate of sodium often manifest themselves 
 to the chemical manipulator. The corresponding compounds of 
 carbon, boron, and silicon, with the members of the chlorine group, 
 and with the members of the sulphur group, have similar proper- 
 
SOBITJM. 391 
 
 ties, result from like reactions, and suffer, for the most part, ana- 
 logous decompositions ; but, in the present state of the science, 
 only the compounds of carbon and silicon can be said to have also 
 the same atomic constitution. The three members of this group 
 are not arranged in the order of their atomic weights, as has been 
 the case with all the preceding groups ; but if, in the future, 
 boracic acid comes to be written BO^, the atomic weight of boron 
 will be 14, and therefore higher than that of carbon. The exist- 
 ing anomaly in the arrangement of the group will then disappear. 
 The collocation of these three elements, and the order in which 
 they now stand, is based upon too many natural resemblances to 
 be lightly set aside. 
 
 CHAPTEE XXIII. 
 
 SOD ITTM. 
 
 478. This abundant element is chiefly found in nature in the 
 state of chloride, nitrate, carbonate, borate, and sUicate. The 
 most abundant of its compounds is common salt, which is the 
 combination of sodium with chlorine (NaCl). Sea-water contains 
 two and a half per cent, of salt, and enormous deposits of the same 
 substance are found in the solid crust of the earth. There are 
 also many natural salt springs, whose waters yield^on evaporation 
 the chloride of sodium which they hold in solution. Sodium also 
 occurs, in the condition of silicate, in very many common minerals 
 and rocks. From the soU which has resulted from the disinte- 
 gration and decomposition of these minerals and rocks, and from 
 its soluble compounds, like common salt, sodium enters into plants, 
 and thence into animals. Its chloride is one of the essential 
 mineral constituents of the food of man and other animals. On 
 account of the inexhaustible abundance of common salt, this sub- 
 stance constitutes the chief source from, which all manufactured 
 compounds of sodium are more or less directly derived ; one other 
 natural sodium-containing mineral, however, deserves mention as 
 a source of sodium compounds — the mineral Cryolite, a double 
 
392 CHLOEIDE OP SODITTM. 
 
 fluoride of sodium and aluminum. Nitrate of sodium (NaNOj), a 
 somewhat deliquescent and very soluble salt, oeeurs abundantly 
 on the surface of the soil in certain desert districts of Peru. 
 When heated, this salt first fuses and then undergoes decomposi- 
 tion. Tt is employed in the manufacture of nitric and sulphuric 
 acids and as a manure ; but as a source of sodium-compounds 
 it is comparatively insignificant. 
 
 479. Chloride of Sodium. (NaCl). — There is but one chloride of 
 sodium — common salt. This natural mineral is, when pur«, a 
 colorless, transparent, anhydrous stone, which crystallizes in cubes, 
 dissolves readily in about three times its weight of cold water, 
 and possesses a specific gravity of 2-lp, and an agreeable taste, 
 which, because familiar, is the representative or type of that pecu- 
 liar savor called saline. A saline taste means a taste suggestive of 
 that of common salt, just as the phrase " saline substance " cha- 
 racterizes a very large class of bodies which resemble more or less 
 in appearance and properties the longest- and best-known of all 
 such substances, common salt. 
 
 There are three sources of salt — the beds of the native mineral, 
 saline springs, and sea- water. In all cases in which the salt is obtained 
 from its solution in water, evaporation by fire, or by the heat of the 
 sun in warm, sunny climates, is necessary. When pure enough, the 
 rock-salt is mined like any other ore ; but when it is mixed with earth 
 or other impurities as it lies in its natural bed, the solubility of the 
 chloride of sodium in water is availed of to free the salt from its in- 
 soluble impurities, and to facilitate the lifting of it to the surface of the 
 earth. Water is let into the bed of salt, and allowed to remain there 
 till it has become saturated ; the brine is then pumped out and evapo- 
 rated. Some natmal brine-springs contain so small a proportion of 
 salt that some cheaper mode of evaporation than by fire is essential to 
 their profitable working. Such waters are concentrated by a process 
 termed graduation. The brine is pumped up to a sufficient height, and 
 then allowed to trickle slowly over large stacks of fagots, which are 
 sheltered by a roof from rain, but are freely exposed to the prevailing 
 wind. The brine, thus difiused over a very large surface, is rapidly 
 concentrated by the draft of air. By repeating the process a moderate 
 number of times, a weak brine may be brought to a degree of concen- 
 tration at which evaporation by fire may be employed. Since almost 
 all brines contain sulphate of calcium (CaSO^) in solution, the surfaces 
 of the fagots employed in the graduation, process become covered with 
 
SOIUBJXITT OF SALT. 393 
 
 a stony coating of this comparatively insohible salt. If the strong brine 
 is boiled dowa rapidly, a fine-grained table-salt is obtained ; if it is 
 slowly evaporated, a hard, coarsely crystallized salt is the product. 
 During the earlier stages of the evaporation a deposit is formed, con- 
 sisting principally of sulphate of sodium and sulphate of calcium. 
 Finally there remains a thick mother-liquor, from v^hich no more 
 chloride of sodium will crystallize, but which contains the more soluble 
 salts of the original brine, such as chloride of calcium, and chloride 
 and bromide of magnesium, besides a large' proportion of common salt 
 which cannot be separated from the liquor. Such mother-liquors are 
 sometimes so rich in magnesium-salts as to be advantageously worked 
 for these substances, and they are also sometimes profitable sources of 
 bromine. Considerable quantities of magnesium-salts and of bromine 
 have also been extracted from concentrated sea-water after all the 
 available chloride of sodium has been withdrawn. The salt of com- 
 merce generally contains a small proportion of chloride of magnesium, 
 which makes it slightly deliquescent and bitter. 
 
 Exp. 224. — Heat a few crystals of coarse salt on a piece of sheet-iron 
 over the gas-lamp. The crystals will decrepitate forcibly, and the 
 greater part of the salt wiU be thrown ofi" the plate ; what remains will 
 melt as the temperature rises, and if the heat be strong enough, it will 
 finally volatilize. The decrepitation is due to little particles of water, 
 mechanically enclosed in the crystals, which, when expanded by heat, 
 burst the crystals asunder. 
 
 Exp. 225. — Dissolve 9 grms. of fine salt in 25 c. c. of water at about 
 20°. Add to the solution another gramme of salt; it vriU not dissolve. 
 Bring the solution to boiling; the added gramme of salt will barely 
 dissolve. Chloride of sodium is scarcely more soluble in hot than in 
 cold water, wherein it diflfers from the great majority of soluble salts. 
 Evaporated brines deposit their salt with almost equal fecUity when 
 hot and when cold ; but the hot liquors will hold ia solution a much 
 greater proportion of the salts with which the chloride of sodium is 
 associated, than the cold brines could retain. In the process of eva- 
 poration by fire, the associated magnesium, calcimu, and sodium-salts 
 therefore do not crystallize with the common salt, but remain ia the 
 hot mother-liquor. 
 
 Exp. 226. — ^Expose a saturated solution of salt in winter weather 
 to a temperature of —10°. Large, transparent, six-sided tables, which 
 contain a considerable proportion of water chemically combined, will 
 crystallize from the solution. The warmth of the hand is sufiBcient to 
 destroy this crystalline compound ; the water separates, and the crys- 
 tals are resolved into a mass of minute cubes. 
 
394 SULPHATE OP SODIXTM, 
 
 480. The uses of common salt are manifold. Since it is a con- 
 stituent of almost all kiads of food, and essential to the life of 
 animals, it is not surprising that salt exists in small quantities in 
 almost every spring, soil, plant, and animal. The antiseptic qua- 
 lity of salt is applied to the preservation of fish, meat, and wood. 
 Salt is extensively employed in glazing earthenware, its volatility 
 at furnace-heat (Exp. 224) combining with other qualities to fit 
 it for this use. Immense quantities of salt are consumed in pre- 
 paring sulphate of sodium, from which in turn common " soda " 
 (carbonate of sodium) is made. From the carbonate of sodium 
 thus obtained the greater number of other sodium compounds are 
 prepared. Salt is also the source from which chlorhydric acid 
 and chlorine are derived (§§ 101, 105). 
 
 481. Bromide and Iodide of Sodium (NaBr and Nal). — ^These 
 salts bear a close resemblance to the chloride of sodium ; they 
 both crystallize in anhydrous cubes, and both occur native in sea- 
 water, though in minute proportion. Many marine plants appro- 
 priate iodide of sodium from sea- water ; sea- weeds are therefore 
 the commercial source of iodine (§ 135). 
 
 482. Sulphate of Sodium (Na^SOJ. — This compound is made 
 in great quantities from common salt and sulphuric acid as a pre- 
 liminary step in the manufacture of carbonate of sodium. 
 
 The process has two stages. The first operation is performed in 
 large, covered, cast-iron pans, capable of holding 250 kilos, of salt, and 
 an equal weight of sulphuric acid of the density of V7. A very gentle 
 heat suffices to disengage from such a mixture enormous volumes of 
 chlorhydric acid gas; this gas, which would be injurious to vegetation 
 if suifered to escape into the air, is all absorbed by being passed through 
 vertical stone towers, filled with lumps of coke, over which water is 
 kept trickling. The reaction in the iron pan is by no means complete, 
 much chloride of sodium remaining undecomposed. The reaction at 
 this first stage may be represented as follows : — 
 
 2NaCl + HjSOi = NaOl + NaHSO^ + HCl. 
 The pasty mass is then pushed into an adjoining fire-brick chamber, 
 which is strongly heated by flues from a furnace. The acid sulphate 
 of sodium of the last reaction decomposes the remainder of the salt, 
 and a further quantity of chlorhydric acid is disengaged to be con- 
 densed by the water in the coke-towers, while sulphate of sodium 
 remains:— j^^gj +NaHS04 = Na^SOi -f- HOI. 
 
Glauber's salt. 395 
 
 The sulphuric acid used in this process is not stronger than can readily 
 be made hy evaporation in leaden pans (compare § 230) ; it is always 
 made on the spot. The crude, weak, chlorhydric acid, which is the 
 incidental product of the manufacture of sulphate of sodiimi, has of 
 cotirse some value in the arts ; a portion of the product is often imme- 
 diately consumed in the same factory in the manufacture of " bleaching- 
 powder " (§§ 105, 120). In some works the smoke and gases from the 
 fires pass through the coke-towers in which the chlorhydric acid is 
 absorbed ; in others, the products of combustion are not suffered to 
 mix with the liberated chlorhydric acid, but are conducted by separate 
 flues around the pans and chambers to be heated, and thence into the 
 main cWmney. The latter mode of construction is the best. 
 
 The sulphate of sodium resulting from this process is a white 
 anhydrous salt which dissolves easily in water at 30°. When a 
 strong solution of the anhydrous salt, made at this temperature, 
 is cooled, there separate large colorless crystals of a transparent 
 salt, bitter and oooUng to the taste. This salt, long known as 
 Glauber's salt, contains, besides the elements of sulphate of so- 
 dium, ten molecules of water ; it therefore answers to the formula 
 Na^SO^jlOH^O. There is another hydrated sulphate of sodium, 
 which contains only seven molecules of water. These hydrated 
 salts effloresce in dry air, and crumble into an opaque powder of 
 the anhydrous salt. 
 
 Exp. 227. — Place 10 grms. of crystallized Glauber's salt in a warm, 
 dry place. When it is completely converted into a white powder, 
 weigh the residue. Since Glauber's salt is more than half water, the 
 dry residue will not weigh more than 4-5 grms. 
 
 Exp. 228. — ^In a flask holding about-250 c. c, heat 50 c. c. of water 
 to a temperature of 33°, and keep the water at this temperature, as 
 determined by a thermometer immersed in it. Add to the warm water 
 161 grms. of crystallized Glauber's salt. If this saturated solution be 
 made hotter, the anhydrous sulphate of sodium crystallizes out in octa- 
 hedrons of rhombic base ; if, on the other hand, the solution be suffered 
 to cool, crystals of the common hydrated Glauber's salt appear. This 
 example forcibly illustrates the general fact that the relations of water 
 to other bodies are greatly affected by temperature. 
 
 Exp. 229.- — Dissolve 10 grms. of crystallized Glauber's salt in water 
 of which the temperature has been previously observed ; during solu- 
 tion the temperature falls ; cold is produced, in consequence of the 
 expenditure of some of the heat of the mixture in overcoming the co- 
 hesion of the crystallized salt. Dissolve a like quantity of effloresced 
 
396 
 
 STrrEEaAIUKAIEI) SOLTTTIONS. 
 
 Glauber's salt (anhydrous sulphate of sodium) in a smaU bulk of -water ; 
 heat will he developed. A part of the water is solidified by combining 
 with the anhydrous sulphate to form the hydrated sulphate, and the 
 heat which before kept that quantity of water fluid, being set fiee to 
 do other work, raises by a certain amount the temperature of the 
 mixture. 
 
 Exp. 230.— Dissolve 50 grms. of Glauber's salt in 25 c. c. of water 
 in a small flask, by heating the contents of the flask until the liquid 
 boUs. Cover the mouth of the flask loosely with a card or piece of 
 glass, and allow the liquid to cool, at perfect rest, to the ordinary tem- 
 perature. No crystals will be deposited fl:om the fluid, although the 
 water holds iu solution a much larger quantity of salt than it could 
 dissolve at the atmospheric temperature. Such a solution is said to be 
 mpersaturated. The crystallization of such a solution may generally 
 be brought about, almost instantaneously, by jarring the vessel which 
 contains it, or by permitting some foreign body, like a glass rod, a wire, 
 a crystal of the salt, or a grain of dust, to come in contact with the 
 fluid. By touching with a stick or glass rod the clear solution pre- 
 pared as above described, this sudden crystallization will be strikingly 
 illustrated, the whole mass becoming solid. 
 
 Crystallized sulphate of sodiimi is rapidly soluble in chlorhydric acid, 
 with great depression of temperature. A convenient refrigerating mix- 
 ture may be prepared in climates where ice is dear, by poming 5 parts 
 of the commercial acid upon 8 of the crystallized sulphate. The effects 
 of solution on temperature, and the phenomena of supersaturated solu- 
 tions, though well exhibited by sulphate of sodium, are by no means 
 peculiar to this substance ; they are manifested to a greater or less 
 degree by a large number of salts. 
 
 483. The Double Sulphate of Sodium and Hydrogen (NaHSO J 
 is a very acid salt, to which, the name of bisrdphate is commonly 
 applied. When heated it first gives up a molecule of water, and 
 subsequently, at a higher temperature, a molecule of anhydrous 
 sulphuric acid; the anhydrous salt is therefore employed as a 
 convenient source of the teroxide of sulphur. 
 
 2(j!faHS0J = H,0 4- SO, + Na^SO,. 
 
 The formation of this double sulphate marks an intermediate 
 stage in the making of sulphate of sodium and chlorhydric acid 
 from common salt ; and it is the residue of the nitric-acid manu- 
 facture whenever nitrate of sodium is employed. 
 
 484. Carbonate of Sodium (Na^COj). — ^The manufacture of this 
 
CAEBONATE OF SODITTM. 397 
 
 substance constitutes one of the most important branches of che- 
 mical industry. Immense quantities of it are consumed in the 
 fabrication of glass and soap, in the preparation of the various 
 compounds of sodium, and in washing, both by the manufacturer 
 of cloth and in the household. The ashes of sea and sea-shore 
 plants were formerly the source of the carbonate of sodium, but 
 it is now chiefly made from common salt by a process called, from 
 the name of its French inventor, the process of Leblanc. 
 
 The first stage of this process we have already studied ; it consists 
 in the preparation of sulphate of sodium from common salt. The 
 second stage consists in the reduction of this sulphate to the condition 
 of sulphide of sodium in presence of carbonate of calcium; by in- 
 terchange of metals there results sulphide of calcium and carbonate of 
 sodium. The siilphate of sodium is ground up with an equal weight of 
 chalk and rather more than half its weight of coal, and the mixture is 
 thoroughly melted by the flame of a reverberatory furnace. The black 
 mass, which is called "black ball " or "black ash," is cast into blocks 
 in iron wheelbarrows, cooled, broken up, and systematically washed 
 with warm water until aU the soluble portions are extracted. The 
 black solution is evaporated in large iron pans by the waste heat of 
 the reverberatory furnaces. The residue contains some caustic soda, 
 mixed with the carbonate ; the residue is therefore mixed with about 
 one-seventh of its weight of sawdust, or like material, and roasted in 
 a reverberatory furnace. The product of this heating is the soda-ash 
 of commerce ; it is almost white, and generally contains about 80 per 
 cent, of pure anhydrous carbonate of sodivmi. 
 
 The so-called crystals of soda are obtained by dissolving the crude 
 soda-ash in hot water, and suffering the hot solution to cool in large 
 pans. In the course of five or six days, large transparent crystals are 
 formed which contain 62'93 per cent, of water, and correspond to the 
 ^formula Na2CO3,10H2O. The impure mother-liquor, drained from the 
 crystals, is used in the manufacture of caustic soda. These crystals 
 effloresce in the air ; they have a disagreeable taste, called alkaline, 
 are soluble in very large proportion both in hot and cold water, and 
 even melt at a moderate temperature in their own water of crystal- 
 lization. The crystals readily part with all their water, and the dry 
 residue melts at a bright-red heat; this residue is anhydrous car- 
 bonate of sodium, purified by the process of crystallization which it 
 has imdergone. In this case, as in all others, the process of crystal- 
 lization consists essentially in the aggregation of Kke particles; the 
 strong tendency is to exclude heterogeneous particles, or, in other 
 
398 BICAKBONATE OF SODIUM. 
 
 words, impurities, from the crystallizing structure. There is no more 
 universally applicable and valuable means of purification than the 
 process of crystallization. 
 
 The purchaser of carbonate of sodium for the sake of the alkali 
 which it contains will prefer soda-ash to soda-crystals, unless the 
 purity of the material be an important consideration. The crystals 
 are purer than the ash ; but more than half their weight is water, 
 which must be transported at the cost of the consumer. Effloresced 
 crystals are more advantageous to buy by weight than crystals which 
 have not lost their water by exposure to the air. There are several 
 hydrates of carbonate of sodium, of different solubilities. 
 
 485. Double Carbonate of Sodium and Hydrogen (NaHCO ). — 
 When masses of crystals of hydrated carbonate of sodium (soda- 
 crystals) are exposed to an atmosphere of carbonie acid gas, they 
 absorb carbonic acid with an evolution of heat sufficient to expel 
 the greater part of their water of crystallization. A white powder 
 remains, whose dualistic formula is Na20,H2O,2C02, whence its 
 most familiar name — bicarbonate of soda. This substance is one 
 of the ingredients in most of the artificial yeasts used for raising 
 bread, cake, and puddings, and is known to grocers and cooks 
 as " soda," although the constituent which is really utilized is its 
 carbonic acid. This carbonate of sodium and hydrogen is much 
 less soluble than the carbonate of sodium ; it may be washed with 
 cold water until it is freed from the sulphates and chlorides which 
 generally contaminate the carbonate. The chemist resorts to this 
 process in order to prepare from the purified bicarbonate pure 
 sodium-salts. At a low red heat the double carbonate loses its 
 water and half its carbonic acid, and is converted into the normal 
 carbonate (NajCOJ. If the aqueous solution of the double car- 
 bonate be heated, it loses one quarter of its carbonic acid. 
 
 Weigh out two separate and equal portions of bicarbonate of sodium. 
 Heat one of these portions for a few minutes in an iron spoon or porce- 
 lain capsule, to a low red heat. Then wrap each portion in a piece 
 of paper and introduce each little roU into a cylindrical jar filled with 
 mercury and standing inverted on the mercury trough. By means of 
 a curved pipette (see Appendix, § 22) pass equal quantities of dilute 
 sulphuric acid into each of the jars. The moment the sulphuric acid 
 comes in contact with the carbonates of sodium, carbonic acid is 
 evolved, and upon comparing the volumes of gas yielded by the two 
 samples, both of which contain the same quantity of sodium, it will be 
 
TEAS! POWBBES. 399 
 
 found that tlie carbonic acid evolved from the unheated Hcarbonate is 
 twice as great as that yielded by the portion which was ignited. 
 
 Bicarbonate of sodium may be deprived of its carbonic acid by 
 almost any acid or acid salt. In the experiment just described 
 sulphuric acid displaced the gaseous carbonic acid ; tartaric acid, 
 or an acid tartrate like cream of tartar (tartrate of potassium), 
 wiU effect the same displacement, as will also the acid sulphate of 
 sodium (NaHSO J, the acid phosphate of calcium (CaO,2H20,PjOj), 
 or common alum. " Soda powders" should be made of bicarbo- 
 nate of sodium and tartaric acid. " Eochelle powders" consist of 
 bicarbonate of sodium in one paper and cream of tartar in another ; 
 when these two materials are mixed in water, carbonic acid is 
 set free, and a double tartrate of sodium and potassium, called 
 Eochelle salt and used as a purgative, remains in the liquid. 
 "When bread or cake is "raised" with "soda" and cream of 
 tartar, the escaping carbonic acid is the agent in puffing up the 
 dough, and the same EocheUe salt remains in the bread. Tar- 
 taric acid and cream of tartar having been dear in late years, a 
 cheaper chemical yeast powder has been made from acid phos- 
 phate of calcium ; when this substance reacts within the dough 
 with bicarbonate of sodium, there remains in the bread a mixture 
 of the phosphates of sodium and calcium. Alum is sometimes 
 used for the same purpose. It is necessary to employ for such 
 purposes, in connexion with the bicarbonate, acids or acid salts 
 which are solid, and not so corrosive as to be obviousfy dangerous 
 and harmful. 
 
 There exists a native sesquiearbonate of sodium called trona or 
 natron ; it is a saline efflorescence, always contaminated with the 
 sulphate and chloride of sodium, and less soluble in water than 
 the carbonate, but more soluble than the bicarbonate of sodium. 
 AU the carbonates of sodium have an alkaline reaction on vege- 
 table colors ; carbonic acid is too weak an acid to overcome the 
 intensely alkaline reaction of caustic soda. 
 
 486. Sulphides of Sodium. — In the conversion of sulphate of 
 sodium into carbonate of sodium (§ 484) one step is the reduction 
 of the sulphate to the sulphide of sodium by coal. The oxygen 
 of the sulphuric acid used in making the sulphate is thus com- 
 bined with carbon and lost ; the sulphur of the acid goes to the 
 
400 STJLPHrDES OF SODIUM. 
 
 waste-heap in a useless combination with calcium. Hereiu lies 
 the wastefulness of the Leblanc process, which the experience of 
 fifty years has failed to remedy. 
 
 Exp. 231. — ^Mix a little powdered anhydrous sulphate of sodium, 
 obtained by drying Glauber's salt, with as much powdered charcoal, 
 and make the mixture into a paste with a drop of water. Place a little 
 ball of this paste, as large as a small pea, in a depression in a piece of 
 charcoal, and heat it strongly with a blowpipe. The mixture eflfer- 
 Tesces and finally melts into a brownish mass. The glowing coal takes 
 all the oxygen out of the sulphate, and the carbonic oxide, which 
 results from the union of the carbon and oxygen, in escaping causes 
 the eflervescence which occurs; the sodium and sulphur alone remain , 
 united. The reaction may be thus formulated : — 
 
 Na^SO^ + 40 = 400 + Na^S. 
 If the brownish solid be removed from the coal, placed in a watch-glass, 
 and moistened with dilute chlorhydric or sulphuric acid, sulphydric 
 acid gas will be evolved, as may be recognized by the smell, or by the 
 use of lead-paper : — 
 
 Na^S + 2H01 = 2NaCl -1- H^S. 
 Sulphur unites with sodium in more than'one proportion ; and 
 it may indeed be doubted whether the actual reaction in the 
 above experiment is so simple as the formula represents it to be. 
 There probably exist five distinct sulphides of sodium — Na^S, 
 Na^Sj, Na^Sj, Na^S^, and Na^S^. All these sulphides have an 
 alkaline reaction to test-paper, and evolve a more or less distinct 
 odor of sulphuretted hydrogen. When they are brought into 
 contact with an acid they are decomposed, sulphydric acid escapes, 
 and a white precipitate of finely divided sulphur falls, in every 
 case except that of the fibrst sulphide, Na^S. Besides these sul- 
 phides, a compound of sodium, hydrogen, and sulphur (NaHS) 
 is known, which is perfectly analogous in composition to the com- 
 bination of sodium, hydrogen, and oxygen with which we are 
 already familiar under the name of caustic soda (NaHO). 
 
 487. Sodium (Na). — The element sodium is never found un- 
 combined in nature, for the reason that in its elementary condi- 
 tion it cannot exist in contact with either air or water. It is, 
 however, artificially prepared from the carbonate of sodium with- 
 out serious difficulty, and it might be produced in considerable 
 quantities, if there were any large use for the element. 
 
METALLIC SODITTM. 401 
 
 A mixture oi 20 parts of carbonate of sodium, 9 parts of coal, and 
 S parts of chalk, placed in an iron bottle or cylinder, ia heated to a 
 very high temperature in a suitable furnace ; a narrow iron tube con- 
 nects the bottle, or cylinder, in the furnace, with a flat sheet-iron box 
 outside the furnace ; this box receives the sodium which distils from 
 the hot mixture, and a hole in the front lower comer of the receptacle 
 permits the melted metal to fall into a vessel containing petroleum- 
 naphtha, beneath which the sodium can be preserved. The reaction is 
 theoretically a conversion of all the oxygen in the carbonate of sodium 
 into carbonic oxide, partly by a new combination with the carbon in 
 the carbonate, and partly by union with the carbon which the coal 
 supplies, 
 
 Na^COj -f- 20 = 300 -I- 2Na; 
 but the amount of sodium practically obtained from a given weight of 
 the materials is by no means as large as this simple formula would indi- 
 cate. The chalk has no chemical effect, but is practically essential to 
 the success of the operation. It prevents the mass from melting, and 
 the gas which it gives off when heated assists in sweeping the sodium, 
 out of the bottle into the receiver. To purify the crude sodium thus 
 obtained, it is melted under naphtha and cast into ingots in iron 
 moulds. It must be kept under naphtha in tightly closed bottles. 
 
 The properties of the element, sodium, are very curious. The 
 substance, when freshly cut, or when melted under naphtha or in 
 an atmosphere artificially deprived of oxygen, has the brilliant, 
 white metaUic lustre of silver. Though possessing so eminently 
 this characteristic property of the class of bodies called metals, 
 and being like them a good conductor of heat and electricity, 
 sodium is far from resembling the ordinary metals in other re- 
 spects. Thus it is lighter than water, having a specific gravity of 
 only 0-972, whereas the common metals are dense and heavy; 
 again, it is as soft as wax at common temperatures, and melts at 
 a temperature below that of boilLag water, while it has none of 
 the comparative permanence which characterizes lead, tin, copper, 
 silver, gold, and other familiar metals. If exposed to the air, 
 even for a few seconds only, it tarnishes, and soon becomes covered 
 with a coating of oxide. Instead of being quenched by water, it 
 takes fire when thrown into warm water. We liave already seen 
 that it decomposes cold water (Exp. 14), setting free its hydrogen, 
 and combining with its oxygen. 
 Exp. 232. — Oover the bottom of a large bottle (at least a litre 
 
 2d 
 
402 
 
 HTBEArE OF SODITJM. 
 
 bottle) with hot water, drop in a piece of sodium as large as a small 
 pea, and immediately cover the mouth of the bottle' with a card or 
 glass plate. The heat of the chemical combination between the so- 
 dium and the oxygen of the water is sufficient to inflame the hydro- 
 gen ; the escaping hydrogen can-ies with it a small portion of the 
 volatilized sodium, and therefore biirns with an intensely yellow flame 
 which is very characteristic of sodium-compounds. The metal swims 
 rapidly about on the surface of the water, and is completely converted 
 into caustic soda ; at a little interval, after the flame has ceased to 
 bum, a globule of caustic soda, which has escaped solution, bursts, and 
 scatters in all directions ; the mouth of the bottle should always be 
 covered to avoid the possible projection of particles of hot soda out of 
 the bottle. The water in the bottle, tested with litmus paper, will be 
 found to possess a strong alialine reaction. If the bit of sodium be 
 previously wrapped up in muslin, it will take fire in cold water or even 
 on ice. The muslin prevents the sodium from moving about, and the 
 heat of combination is therefore concentrated upon one spot. The 
 same effect may be produced without the muslin on cold water made 
 viscid with gum. 
 
 At a high temperature sodium will remove oxygen from almost 
 all bodies which contain it, whether solid, liquid, or gaseous. 
 Hence the necessity of preserving the metal under some liquid 
 which, like naphtha, contains no oxygen. Sodium enters directly 
 into combination with all the elements of the chlorine and sulphur 
 groups, and is capable of withdrawing these elements from nearly 
 all the compounds into which they enter. In this substance, 
 therefore, the chemist possesses a very potent agent for effecting 
 chemical transformations. Its atomic weight is 23. 
 
 488. Hydrate of Sodium (NaHO). — When sodium is burnt upon 
 water, a solution of hydrate of sodium, possessing an intensely 
 alkaline reaction, remains behind ; but in practice the hydrate is 
 generally made from the carbonate. 
 
 Exp. 233. — ^Dissolve 100 grms. of crystallized carbonate of sodium 
 (§ 484) in 400 c. c. of water. Slake 20 grms. of quicklime with water 
 enough to make the slaked lime into a cream. Boil the solution of 
 carbonate of sodium in an iron pan, and add to it, little by little, the 
 cream of lime, until a small portion of the liquor, filtered off, produces 
 no effervescence when poured into dilute chlorhydric or sulphuric acid. 
 The calcium of the lime replaces the sodium in the carbonate of so- 
 
CAUSTIC SODA. 403 
 
 dium ; a white insoluble precipitate of carbonate of calcium is formed, 
 and hydrate of sodium remains in the solution : — 
 
 Na2003 + CaHjOj = 2NaH0 + CaOOj. 
 
 When this reaction is complete, no carbonic acid remains in the clear 
 solution, which, therefore, causes no effervescence when mixed with an 
 acid. When this test shows the reaction to be accomplished, extinguish 
 the lamp ; cover the pan, and let the carbonate of calcium settle to the 
 bottom of the vessel. After several hours, draw off the clear super- 
 natant liquid into a bottle by means of a siphon. A weaker lye may 
 be obtained by boiling up the residue in the iron pan once more with 
 water, and again decanting the clear liquid from the deposited pre- 
 cipitate. 
 
 The lye thus prepared contains a very little lime, inasmuch as the 
 hydrate of calcium is not completely insoluble in a dilute solution of 
 hydrate of sodium. If the lye is needed stronger, it is only necessary 
 to concentrate it by evaporation in a clean iron pan to the requisite 
 strength. Since soda-lye attacks ground glass with facility, the stop- 
 pers of bottles in which the lye is kept are apt to get stuck so fast that 
 they cannot be removed. Such a bottle may be best closed with a 
 caoutchouc-stopper, or a cork soaked in melted wax or paraifine. 
 
 In order to obtain the solid hydrate of sodium, its solution must be 
 evaporated in a silver dish (since iron would color the concentrated 
 lye) until the liquid in the dish flows smoothly like oil at a temperature 
 near to a red heat. This thick, oUy liquid solidifies when turned out 
 upon a cold plate of metal or poured into metal moulds. 
 
 Fused caustic soda is a white, somewhat translucent mass, whose 
 composition corresponds to the formula NaHO. Heat will sepa- 
 rate from it no more water ; if the attempt be made, it volatilizes 
 in caustic vapors without change of constitution. The commercial 
 caustic soda always contains much more water than the formula 
 indicates. The solid hydrate is very soluble in water, and greedily 
 absorbs both water and carbonic acid from the air, until the for- 
 mation of a coating of the non-deliquescent carbonate of sodium 
 arrests the process by protecting the enclosed hydrate. It is the 
 prototype of the class of bodies called bases. It colors litmus blue 
 and turmeric brown, and when mixed in due proportion with 
 oxides of the opposite quality, called acid, a saline compound is 
 formed which is neither acid nor alkaline, and which may bear no 
 
 2t>2 
 
404 REPLACEMENT DIKECT COMBIlfATIOlf. 
 
 more resemblance to its proximate constituents than bread bears 
 to flour and water, or rust to iron and oxygen. 
 
 From such, reactions between acids and hydrate of sodium, water 
 is always disengaged simultaneously with the saline product, and 
 the reaction may almost always be as weU considered an inter- 
 change of place between hydrogen and some other element as an 
 act of combination between one oxide and another oxide, both of 
 which, or one of which, contain also hydrogen. The following 
 formulae will illustrate the meaning of this statement : — 
 
 NaHO + NHO3 == NaNO, + H,0, or 
 
 2NaH0 + H„SO^ = Na^SO, + 2H,0, or 
 
 NaHO + C,H,0, = C,H3NaO, + H,0. 
 Acetic Add. Acetate of Sodium. 
 
 While recognizing the frequent occurrence of such reactions as 
 are above represented between hydrated oxides, it must not be 
 forgotten that many anhydrous saline compounds can be made by 
 the direct combination, under appropriate conditions, of two oxides 
 which contain no hydrogen. By heating one molecule of hydrate 
 of sodium, or 40 parts by weight, with one molecule, or 23 parts 
 by weight, of sodium, an oxide of sodium is obtained which con- 
 tains no hydrogen ; but this body has none of the properties de- 
 scribed by the adjective alkaline, any more than the anhydrous 
 teroxide of sulphur possesses the properties suggested to the mind 
 by the term "acid " : — 
 
 NaHO 4- Na = Na,0 + H. 
 Now the very same sulphate of sodium which results from the 
 second of the above reactions, may be prepared by bringing to- 
 gether this anhydrous oxide of sodium and anhydrous sulphuric 
 acid ; — 
 
 Na^O -I- SO3 = Na^SO,. 
 
 There exists another anhydrous oxide of sodium, corresponding 
 in composition to the formula Na^O^, and the same sulphate of 
 
, PHOSPHATES OF SODITTM, 405 
 
 sodium can be made by heating this oxide with sulphurous acid 
 gas:— 
 
 Na^O, + SO, = Na^SO,. 
 
 These facts show that a knowledge of the constituents from 
 which a salt may be made is not sufficient to establish any pre- 
 sumption concerning the molecular constitution of the salt itself. 
 
 The preparation of solid caustic soda, for household and other 
 uses, has lately become a considerable industry. Soap is made by 
 boiling together grease or oil with caustic soda or potash ; soda- 
 lye yields a hard soap, potash-lye a soft soap. If the maker of 
 soap starts from the carbonate of sodium or potassium, he must 
 first make a solution of caustic lye by the method of Exp. 233, 
 and then boU the lye, so obtained, with the grease which is tie 
 other essential ingredient of soap. The soap-maker is saved the 
 trouble of converting the carbonate into the hydrate of sodium or 
 potassium by the maker of the solid caustic alkalies, which need 
 only to be dissolved in water to yield the requisite lye. The solid 
 alkali is commonly put up for transportation in sheet-iron canis- 
 ters, of all sizes. The manufacturer of caustic soda directly from 
 the sulphate of soda has an advantage, in that he can avail him- 
 self of the caustic soda which the " black ash " always contains. 
 He is not obliged, first to convert this caustic alkali into carbonate, 
 and then to remove all the carbonic acid by lime ; he can there- 
 fore dispense with the heating with sawdust which is necessary 
 in the manufacture of soda-ash. 
 
 489. Phosphates of Sodium. — There are three sets of phosphates 
 of sodium : — 1. Common phosphates, which contain three atoms of 
 hydrogen or an equivalent metal; 2. Pyrophosphates, which oc- 
 cupy an intermediate place between common phosphates and me- 
 taphosphates ; 3. Metaphosphates, which contain only one equiva- 
 lent of hydrogen or an equivalent metal. (See § 293.) 
 
 3Hp,P,0, = 2H3PO,; 3Na,0,P,0, = 2Na3P0, 
 
 2H,0,P,0, = H,P,0, ; 2Na,0,P,0. = Na,P,0, 
 
 H,0,P,0, = 2HPO3 ; Na,0,P,0, = 2NaP03. 
 
 The most famUiar of the ordinary phosphates is the rhombic 
 phosphate of sodium, of the formula 'Ea.^'?0^,l'2R.p, which is 
 the salt commonly called phosphate of sodium. 
 
406 PTEOPHOSPHATB OF SODIUM. 
 
 Exp. 234. — Digest 8 grma. of powdered, white, burnt bones with 
 32 c. c. of water and 6 grms. of sulphuric acid, until a uniform paste is 
 produced ; strain the mass through a piece of muslin, stir up the resi- 
 due with water, and squeeze the liquor through the cloth filter. Eva- 
 porate the filtered solution considerably, again filter ofl^ the separated 
 sulphate of calcium, dilute the filtrate with water until it measures 48 
 c. c, and gradually neutralize the acid solution with solid carbonate of 
 sodium. A slight excess of carbonate may be added, and the solution 
 evaporated until it crystallizes ; the crystals may be almost freed from 
 adherina: sulphate of sodium by washing them. By reorystallizing the 
 salt it may be obtained in large, transparent rhombic prisms, which 
 are decidedly efflorescent. They have a cooling, saline taste, are soluble 
 in four parts of cold water, and readily melt in their water of crystal- 
 lization ; their solution has a faint alkaline reaction. 
 
 Exp. 235. — ^Add to a solution of the purified crystals of the last ex- 
 periment a few drops of a solution of nitrate of silver ; a yellow pre- 
 cipitate appears, and the liquid becomes distinctly acid in its reaction 
 with litmus. The precipitate is phosphate of silver, and the acidity is 
 due to the simultaneous liberation of nitric acid in the solution : — 
 
 Na^HPOj + SAgNOj = SNaNO, + HNO3 -I- Ag3P04. 
 
 From the rhombic phosphate two other terbasic phosphates may be 
 prepared : — by adding caustic soda, a terbasic, or tennetaUic, phosphate, 
 Na3P04,12H20 ; by adding phosphoric acid, a so-caUed " acid " phos- 
 phate, NaH2P04,H20. 
 
 Exp. 236. — Heat 4 or 5 grms. of rhombic phosphate of sodium in a 
 porcelain crucible to bright redness. The water of crystallization first 
 escapes, then another portion of water is driven off at a higher heat, 
 the residue melts, and on cooling solidifies again to an opaque, white, 
 substance — ^the pyrophosphate of sodium, NajPjO^ : — 
 
 2(Na2HP04,12H20) = 24H2O + H^O -|- Na^P^O,. 
 
 Exp. 237. — Dissolve the new salt of the last experiment in water 
 and add a few drops of a solution of nitrate of silver ; a challiy- white 
 precipitate of pyrophosphate of silver wiU be produced, while the 
 supernatant liquid is neutral : — 
 
 NaiP^O, + 4AgN03 = iNaNO, + Ag^P^O,. 
 
 The student will observe, in passing, that the pyrophosphate of 
 sodium dissolves in water with more difficulty than the ordinary 
 phosphate. From its aqueous solution the pyrophosphate crys- 
 tallizes in prisms which contain ten moleculesof water of crystal- 
 lization, Na^P^O,, lOH^O, These crystals are not efflorescent, but 
 
METAPHOSPHATE OF SODIUM. 407 
 
 permanent in the air. Two of the atoms of sodium in neutral 
 pyrophosphate of sodium can be replaced by hydrogen, and we 
 thus obtain a salt of the formula Na^H^P^O^ which, like the neutral 
 pyrophosphate, throws down the white pyrophosphate of silver 
 from a solution of nitrate of silver, but, unlike the neutral salt, 
 leaves behind a liquor acidified with free nitric acid. 
 
 Exp. 238. — Mix a hot solution of 18 grma. of common phosphate of 
 sodiiun with a concentrated solution of 3 grms. of chloride of ammo- 
 nium ; common salt remains in solution, and transparent crystals of a 
 complex phosphate of sodium, ammonium, and hydrogen separate from 
 the liquid as it cools : — 
 
 Na^HPO^ + NH4CI = NaCl + NaNH^HPOi. 
 
 This complex triphosphate is known as microoosmic salt ; it contains 
 only one atom of sodium. 
 
 Exp. 239. — Heat the microcosmic salt obtained in the last experi- 
 ment to redness. Ammonia and water are driven off with a great 
 bubbling, and a glassy substance is left which corresponds to the for- 
 mula NaPOj, and is called the metaphosphate of sodium. This salt 
 cannot be obtained by this process in crystals ; it is deliquescent and 
 very soluble. 
 
 Exp. 240. — Dissolve in water some ofthe metaphosphate just made, 
 and add a few drops of the solution to a solution of nitrate of silver. 
 
 The precipitate produced is white, but gelatinous ; its appearance 
 is quite different from that of the pyrophosphate of silver. The meta- 
 phosphate of silver is soluble in an excess of metaphosphate of sodium, 
 so that a sufficient quantity of the sodium-salt will redissolve the 
 silver-salt precipitate which the first addition of the sodium-salt pro- 
 duced. It may be observed, that the solution of metaphosphate of 
 sodium possesses a feebly acid reaction. 
 
 The metaphosphate of sodium exists in several distinct modifi- 
 cations ; or, in other words, there are several sodium-salts which 
 correspond to the formula NaPO^. The most noteworthy modi- 
 fications are the glassy salt just prepared, a crystaUizable modifi- 
 cation, and a variety which is almost insoluble in water though 
 soluble in acids. Pyrophosphates and metaphosphates are alike 
 converted into common ter-metaUic phosphates by long boiling 
 with water in an acid liquid, or by fusion with an excess of caus- 
 tic alkali. The metaphosphate may also be converted into the 
 pyrophosphate by mere heat in presence of water. The meta- 
 
4oa 
 
 BOSAi. 
 
 phosphate, when dried at 100°, retains a certain portion of water; 
 but this water does not enter into the constitution of the salt, 
 for, on again dissolying the salt, the solution gives the usual re- 
 actions of the metaphosphate. If, however, the water-contaia- 
 ing salt be heated to 150°, the water enters into the constitution 
 of the salt, which becomes the " acid " pyrophosphate of sodium, 
 yielding, on solution, the reaction of the pyrophosphates : — 
 
 ' 2NaP03 + H,0 = NaAP.O,. 
 
 We have here a striking illustration of the fact that two sub- 
 stances, which contain precisely the same elements in the same 
 proportions, may have quite different properties in consequence of 
 the different arrangement of their elements, or, in other words, 
 of their different molecular constitution. 
 
 490. Borax (Na,B^O„10H,O=Na,O,2B^O3+10H^O). — The 
 dualistic formula of this useful salt accounts for its chemical 
 name — ftiborate of sodium. The greater part of the borax used 
 in the arts is prepared by dissolving the native boracic acid of 
 Tuscany (§ 443) in a hot solution of carbonate of sodium. After 
 aU the carbonic acid has escaped, the hot liquid is allowed to 
 settle and cool. Either of two different crystaUine forms of 
 borax may be obtained, at will, by suitably regulating the density 
 of the solution and the temperature at which crystallization takes 
 place. One of these forms, prismatic or common borax, contains 
 10 molecules of water of crystallization; the other, called octa- 
 hedral borax, only 5. Both varieties must be purified by recrys- 
 taUization. The large crystals, in which borax is demanded for 
 the market, can only be obtained by operating on very large 
 masses of the salt, — a remark which applies to most of the crys- 
 talline salts which are used in the arts. The crystals of octa- 
 hedral borax are harder and less fragUe than those of ordinary 
 borax. They are unalterable in dry air, but in a moist atmo- 
 sphere they absorb water and are converted into common borax., 
 When heated, they fuse to an anhydrous glass with less intu- 
 mescence than common borax, and without cracking. For these 
 reasons, octahedral borax is better than prismatic borax for 
 many purposes, and its smaller proportion of water (30 per cent, 
 against 47 per cent.) diminishes the cost of transport. Never- 
 
BOEAX AS A TEST. 409 
 
 theless the prismatic borax is generally preferred, probably be- 
 cause it is sold at a less price, weight for -vreight. The prismatic 
 ciystals are soluble in about half their weight of boiling water, 
 but in twelve times their weight of cold water; as they are 
 slightly efflorescent, they are generally covered with a white 
 dust. Borax has a feebly alkaline taste and reaction. When 
 heated it bubbles up, loses its water, and melts below redness 
 into a transparent glass ; this glass dissolves many oxides of the 
 metals, acquiring thereby various colors characteristic of these 
 oxides. Hence borax is much used as a blowpipe test for deter- 
 mJTiing the presence of certain oxides of the metals. 
 
 JExp. 241. — Make a little loop, about as large as this O, on the end 
 of a bit of fine platinum wire 6 or 8 cm. long. Make the loop white- 
 hot in the hlowpipe-flame, and thrust it while hot into some powdered 
 borax ; a quantity of borax will adhere to the hot wire ; reheat the 
 loop in the oxidizing flame ; the borax wiU puff up at first, and then 
 fuse to a transparent glass. K enough borax to form a solid trans- 
 parent bead within the loop does not adhere to the hot wire the first 
 time, the hot loop may he dipped a second time into the powdered 
 borax. When a transparent glass has been formed within the loop of 
 the platinum wire, touch the head of glass, while it is hot and soft, to 
 a speek of black oxide of manganese no bigger than the period of this 
 type ; reheat the head with the adhering particle of oxide in the oxi- 
 dizing flame ; the black speck will gradually dissolve, and on looking 
 through tbe head towards the light, or a white wall, when the black 
 oxide has disappeared, the glass wiU he seen to have assimied a 
 purplish-red color. 
 
 The same experiment may he performed with oxide of iron, which 
 imparts to the glass a yellow color, or with oxide of copper, which 
 imparts a bluish-green color. The oxidizing flame must be used in 
 both these cases, as with the oxide of manganese. 
 
 The power which borax possesses of dissolving metallic oxides 
 suggests an explanation of its use in brazing, and in soldering 
 the precious metals. The solder will only adhere to a bright and 
 clean metallic surface, and the borax which melts with the solder 
 removes from the pieces of metal the film of oxide which would 
 otherwise prevent the adhesion of the solder. Borax is also used 
 by the assayer and refiner as a flux. In making enamels and 
 glazes, it is frequently added for the purpose of rendering the 
 
410 SILICATES OP SODITTM. 
 
 compound more fusible, and it is largely employed in fixing colors 
 on porcelain. 
 
 There is a normal, or neutral, borate of sodium, NaBO^ or 
 Na^OjB^Oj, which crystallizes with various quantities of water ; 
 and other borates of sodium are known ; but the " biborate " is 
 the only one of any practical importance. 
 
 491. Silicates of Sodium may be prepared by dissolving silicic 
 acid in caustic soda, as in Exp. 220, or by fusing together silicic 
 acid and carbonate of sodium, or a mixture of silicic acid, sul- 
 phate of sodium, and carbon. From alkaline solutions, the single 
 crystaUizable silicate of sodium, !N'a2Si03, can readily be obtained 
 in hydrated crystals. The silicate of sodium of commerce, called 
 waterglass or soluble glass, is, however, a much more siliceous 
 silicate, of varying composition. Some samples of it have very 
 nearly the composition expressed by the formula Na^O, 2Si02, 
 while other specimens approximate to the formula Na^O, 4810^. 
 Between these extremes, the acid and the alkali unite in aU 
 possible proportions to form compounds, all of which are soluble 
 with more or less difficulty in boiling water. 
 
 The normal silicate of sodium (Na^SiOj) is readily soluble in 
 cold water, and, like carbonate of sodium, which it closely re- 
 sembles, may even be melted in its own water of crystallization ; 
 but the acid salt of commerce is as good as insoluble in cold 
 water. Waterglass may, however, be completely dissolved by 
 long-continued boUing in water, and the solution thus obtained is 
 largely employed by calico-printers and by soapmakers. Water- 
 glass is also used for hardening porous stones, or even for bind- 
 ing sand into artificial stone, for painting rough woodwork to pro- 
 tect it from the weather, and for diminishing the combustibility 
 of wood, canvas, and other coarse stuffs, such as are used for the 
 decorations of theatres. It has been suggested that the interior 
 surfaces of wooden-roofed railway bridges might be protected 
 from the sparks of the locomotive by washing them with a solu- 
 tion of waterglass. When employed as paint, the coating of 
 waterglass may be washed over with a solution of chloride of 
 ammonium, which decomposes the sUieate, with deposition of free 
 sUicie acid ; or the silicate may simply be left to the decomposing 
 action of atmospheric carbonic acid. The chloride of sodium 
 
■WATEHeLASS. 411 
 
 resulting from the decomposition in the one case, and the carbo- 
 nate of sodium in the other, are subsequently washed away by 
 the rain. Combustible matters, when covered with a coating of 
 silica, or of silicate of sodium, as above, are prevented from burn- 
 ing freely, in the same manner that the carbon of the paper in Exp. 
 110 was kept from burning by the coating of phosphoric acid. 
 
 492. The chief use of sUicate of sodium, however, is as a com- 
 ponent of common glass. The various glasses of commerce are 
 mixtures of a highly siliceous silicate of sodium, or of potassium, 
 or of both these substances, with silicates of other metals, such as 
 calcium, aluminum, and lead. In green bottle-glass the easily 
 fusible sUicate of iron replaces in part the silicate of sodium or 
 of potassium. 
 
 It is a peculiarity of the alkaline silicates that, in changing 
 from the liquid to the solid state, they pass through an inter- 
 mediate pasty or viscous stage, and finally soUdify in transparent 
 amorphous masses, totally devoid of crystalline structure. "While 
 in this pasty, ductile state, these silicates may readily be moulded 
 into almost any form ; and transparent vessels might doubtless be 
 made from the acid alkaline silicates without admixture of other 
 materials. The alkaline silicates, however, are, by themselves, 
 far too easily acted upon by air and moisture to admit of being 
 used as substitutes for ordinary glass. But it has been found 
 that, by combining the alkaline silicates with the silicates of 
 certain other metals, such as calcium, there may be obtained 
 compound glasses which, while they retain the plasticity of the 
 alkaline sUicates as well as their amorphous character and trans- 
 parency, are capable of resisting the action not only of air and 
 water, but even of acids and alkaUes, to a very great extent. 
 Though the ordinary glasses are so difficultly attacked by water 
 that they may, for most practical purposes, be regarded as alto- 
 gether insoluble, it is nevertheless true, as has been stated in 
 § 464, that glass may be partially dissolved by long-continued 
 contact with water, particularly if the water be hot and the glass 
 in the condition of powder. After the smooth surface of glass, as 
 it comes from the fire, has once been removed, the corrosion of 
 the glass goes on more rapidly. 
 
 It is remarkable that mixtures composed of several different 
 
412. GiAss. 
 
 silicates melt at temperatures considerably lower than the mean 
 of the melting-points of their several ingredients. 
 
 The different varieties of glass vary in composition, according 
 to the pnxposes for which they are prepared ; they cannot be re- 
 garded as chemical compounds, being really indefinite mixtures of 
 various acid silicates. The composition of window-glass may be re- 
 presented approximately by the formula Na^O, 2Si02; CaO^, 2810^ ; 
 and that of the hard, Bohemian glass, suitable for ignition- 
 tubes, by the formula 2(K.fi, SSiO^) ; 3(CaO, 3SiO,). The lus- 
 trous "flint" glass, employed for the nicer kinds of household 
 ware, may, on the other hand, be represented by the formula 
 2(K,0,2SiO,);3(PbO,2SiO,); it is prepared from the purest 
 materials attainable. Bottle-glass is composed of the silicates of 
 lime and of alutaina, together with a smaU proportion of the 
 silicates of iron, of potassium, and of sodium ; in this glass, as in 
 the other varieties above formulated, small quantities of various 
 other silicates, such as the silicates of magnesium and of manga- 
 nese, almost always occur. 
 
 In the preparation of the cheaper kinds of glass the materials 
 are melted in large open crucibles of refractory clay ; but the bet- 
 ter sorts of glass, such as flint-glaas, are made in pots so covered 
 that no smoke or dust from the fire can come in contact with 
 their contents. In both cases the thoroughly melted mixture is 
 kept in the liquid state until it has become perfectly homogeneous 
 and until all bubbles of air have escaped from it; it is then 
 allowed to cool to the temperature at which it possesses the 
 peculiar, pasty, ductile, condition in which it admits of being 
 blown, pressed, and moulded. 
 
 493. After glass has been moulded into the shape desired, it 
 must still be subjected to a process of annealing before it can be 
 used. Glass which has been suddenly cooled after fusion is ex- 
 tremely brittle ; and in general all glass which has been quickly 
 cooled after heatiag is far more fragile than that which has been 
 allowed to cool gradually. The operation of annealing is nothing 
 but a process of slow baking, at a temperature which, though not 
 so high as the melting-point of glass, is nevertheless high enough 
 to allow the particles of softened glass to move among them- 
 selves, and to come into easy and natural positions as regards 
 
HrPOSTJIiPHITE OIT SODIUM. 413 
 
 one another ; after the baking follows a process of slow cooling, 
 during which the heated material contracts uniformly in all 
 directions as it assumes the dimensions proper to it when cold. 
 
 Unlike the silicates of the alkali-metals, most metallic silicates 
 have a tendency to assume crystalline form on coohng, and it is 
 not difficult to bring about crystallization of silicate of calcium, 
 or silicate of aluminum, from ordinary glass, particularly from 
 the coarser kinds, such as bottle-glass. Glass, in which some of 
 the constituents have thus crystallized, has the appearance of 
 porcelain ; it is said to be devitrifled. The devitrification may 
 readily be shown by imbedding bottle-glass in sand, heating the 
 glass almost to the melting-point, and then allowing it to cool 
 slowly. In annealing some kinds of glass care must be taken 
 not to heat the ware too strongly, lest it be devitrifled during the 
 process. 
 
 494. Melted glass, like melted borax (Exp. 241), is capable of 
 dissolving small quantities of many of the metallic oxides, a trans- 
 parent and often colored silicate of the oxide being formed, which 
 imparts its hue to the entire mass of glass. In this way, glass 
 may be obtained of almost any desired color. The green color 
 of bottle-glass is due to silicate of protoxide of iron ; but richer 
 shades of green may be obtained by using protoxide of copper or 
 oxide of chromium. Dioxide of copper gives a ruby-r^ color, 
 and oxide of gold various shades of red, inclining to purple. 
 The oxides of uranium, of antimony, and of sUver yield yellow 
 glasses ; oxide of cobalt affords a beautiful blue, and the binoxide 
 of manganese a violet glass ; while mixtures of the oxides of cobalt 
 and of manganese impart to the glass a black color. 
 
 495. Syposulphite of Sodium (Na^S^Oj, SH^O). — This easily 
 crystallized and tolerably permanent salt is of great use to the 
 photographer, because its aqueous solution is capable of render- 
 ing soluble the chloride, bromide, and iodide of silver, compounds 
 much employed by the photographer, and very insoluble in water. 
 The photographic paper or glass, uniformly coated with some 
 sUver compound, is exposed to light in the camera or press, and 
 then immersed in a strong solution of the hyposulphite, which 
 forms with the sUver compound, in those parts of the picture 
 ■which have not been acted upon by the light, a double salt which 
 
414 POTASSIUM. 
 
 is soluble in water. This double salt and the superfluous hjrpo- 
 sulphite must be washed away by soaking the picture several 
 hours in water which is constantly renewed. Hyposulphite of 
 sodium is also used as an " antichlore," or agent for removing 
 the last traces of chlorine, or hypochlorous acid, from substances 
 which have been bleached therewith. The salt may be best pre- 
 pared by digesting sulphur vnth a solution of sulphite of sodium. 
 
 ^xp. 242. — ^Dissolve 20 grms. of crystallized carbonate of sodium in 
 80-40 c. u. of water. Place the solution in a small Woulfe-bottle, and 
 pass sulphurous acid gas (Exp. 96) through it until all the carbonic 
 acid is expelled from the carbonate and effervescence ceases. The 
 liquid then holds in solution sulphite of sodium (Na2S03). Pour this 
 solution into a bottle which can be tightly closed, and add to it 3 or 4 
 grms. of finely powdered sulphur ; let this mixture stand corked up for 
 several days in a warm place ; the sulphur will gradually dissolve, and 
 form a colorless solution, which on evaporation will yield crystals of 
 hyposulphite of sodium. Time may be saved by keeping the solution 
 of sulphite of sodium hot, but not boiling, during the digestion of the 
 sulphur. The reaction has been already formulated (§ 243). 
 
 CHAPTEB, XXIV. 
 
 POTASSITJH. 
 
 496. The proximate sources of sodium-compounds are the sea, 
 and salt springs and deposits. Potassium-compounds, on the 
 other hand, are derived indirectly from the soil. Arable boUs are 
 produced by the weathering and gradual decomposition of the 
 common granitic rocks. Into the composition of these rocks there 
 enter two minerals, called feldspar and mica, which are mixed 
 silicates of potassium or sodium and aluminum or iron. The 
 element potassium thus becomes a normal constituent of the 
 earthy food of plants. The soil itself is not directly available as 
 a source of potassium-salts, because no cheap and easy method 
 has yet been devised for separating the potassium-compounds 
 
CARBONATE OF POTASSIUM. 415 
 
 from the- other ingredients of the soil. Plants, however, are able 
 to pick out and assimilate the potassium-salts from these rocks 
 and soils ; so that by burning the plants and extracting the ashes 
 ■with water a soluble potassium-salt is obtained. Plants thus con- 
 centrate the potassium from out great masses of earth, and make 
 it accessible to us. The salt which is obtained from the ashes of 
 plants by washing and evaporation, is called potash, or, if refined, 
 pearlash, and it is from this substance_that the bulk of potassium- 
 compounds are obtained. 
 
 Exp. 243. — Place a handful of wood-ashes on a filter, and pour hot 
 water over them, collecting the filtrate in a bottle and returning it upon 
 the ashes two or three times, in order to obtain a stronger solution. 
 To exhaust the ashes of their potash, they must, of course, be treated 
 with successive portions of hot water. This solution has a strong alka- 
 line reaction upon test-paper. A few drops of it, poured into a test- 
 tube containing a little dilute acid, occasion a brisk effervescence, a 
 reaction from which we readily surmise the truth, that the potassium-' 
 salt contained in the solution is the carbonate of potassium. Proof that 
 the gas evolved is carbonic acid can readily be obtained by conducting 
 the gas into lime-water, as in Exp. 170. By evaporating the rest of 
 the solution to dryness in a porcelain dish, we obtain a small sample of 
 crude potash. By treating this potash with a quantity of cold water, 
 insufficient to dissolve any but the most soluble portions of the mass, 
 letting the mixtm-e stand some time, and evaporating the partial solu- 
 tion to dryness, a whiter, purer carbonate is obtained, the pearlash. 
 
 497. Carbonate of Potassium (K^C^Og) is a hygroscopic and 
 very soluble salt. When exposed to damp air it becomes moist, 
 and finally deliquesces. In this respect it does not resemble 
 soda-ash, which is not hygroscopic, and is, for this reason among 
 others, better adapted than potash for transportation, storing, and 
 most commercial uses. Carbonate of potassium fuses at a red 
 heat, but cannot be decomposed by heat alone. At a red heat it 
 is decomposed by silica, as is also the carbonate of sodium, car- 
 bonic acid being expelled with effervescence, whilst the silica 
 unites with the alkali. Advantage is taken of this property in 
 the analysis of minerals which contain a large quantity of silica, 
 and are not easily decomposed by acids. The finely powdered 
 mineral is fused with about three times its weight of carbonate of 
 sodium or of potassium, or, better, with thrice its weight of a 
 
416 HTDBATE OF POTASSrUlt. 
 
 mixture of 5| parts of carbonate of sodium with. 7 parts of car- 
 bonate of potassium. The mixed carbonates produce a more 
 fusible mixture than either alone (§ 492). The fused mass is 
 then treated with dilute chlorhydric acid, which decomposes the- 
 alkaline silicates, and dissolves all the bases of the mineral which 
 were before combined with the silica. 
 
 Carbonate of potassium was the most important source of alkali, 
 until Leblanc's process made soda cheaper than potash. It is still 
 largely consumed in the manufacture of soap, glass, caustic pot- 
 ash, and other compounds of potassium; but sodium-salts have, 
 to a great extent, displaced potassium-salts in commerce and 
 the arts. 
 
 498. Carbonate of Potassium and Hydrogen (KHCO3). — This 
 salt, commonly called the " bicarbonate " of potassium (K^O, 
 H.p, 2C0J, is prepared by passing a current of carbonic acid 
 through a strong solution of carbonate of potassium ; crystals of 
 the bicarbonate will be deposited, which are permanent in the 
 air, and require about 4 parts of cold water for solution. When 
 the solution of this salt is long exposed to the air, or boiled, it 
 loses one-fourth of its carbonic acid ; when the dry salt is fused, 
 it loses half its carbonic acid, and is converted into the carbonate. 
 It is a valuable salt to the chemist and the apothecary, because it 
 can be readily obtained in a state of purity ; when itself made 
 from a refined carbonate of potassium, it may be advantageously 
 used as the material from which to prepare other pure compounds 
 of this important element. 
 
 499. Hydrate of Potassium (KHO). — The manufacture of hy- 
 drate of potassium, from carbonate of potassium, resembles, in 
 every detail, the preparation of caustic soda from carbonate of 
 sodium (Exp. 233). The carbonate of potassium is dissolved in 
 10 or 12 times its weight of water, and decomposed by a cream of 
 lime ; carbonate of calcium is precipitated, and hydrate of potas- 
 sium remains in solution. All that has been said of the concen- 
 tration of the solution of hydrate of sodium (§ 488) is true, also, 
 of hydrate of potassium. 
 
 Hydrate of potassium is a hard, whitish substance, possessing 
 a peculiar odor and a very acrid taste. Like the hydrate of so- 
 dium, it rapidly absorbs moisture and carbonic acid from the air ; 
 
CATTSTIC POTASH. 417 
 
 and since the carbonate of potassium thus formed is a deliques- 
 cent salt, this change wiE go on until the entire mass of hydrate 
 is converted into a syrup of the carbonate ; whereas, in the ease 
 of hydrate of sodium, the absorption of water and carbonic acid 
 is soon arrested by the formation of a coating 6f non-deliquescent 
 carbonate of sodium upon the surface of the lump of hydrate. In 
 chemical industries and speculations, the question of success or 
 failure often turns on such points as this ; the advantage of a new 
 material, for example, often depends upon just such differences as 
 this between caustic soda and caustic potash. 
 
 500. The hydrate of potassium, cast into small sticks, is em- 
 ployed by physicians as a cautery, — a use which illustrates forcibly 
 its destructive effect upon animal and vegetable matters. Like 
 hydrate" of sodium, its solution destroys ordinary paper, and 
 cannot be filtered except through asbestos, or gun-cotton. A 
 clear solution is best obtained by decantation from the subsided 
 impurities. All vessels made of materials which contain silica 
 are attacked by this caustic solution; and even platinum is slowly 
 oxidized in its presence ; vessels of gold and silver resist it best. 
 This hydrate, like that of sodium, forms soaps with oils or fats ; 
 the sodium-soaps are hard, the potassium- soft. At a high tem- 
 perature hydrate of potassium volatilizes without change ; heat 
 alone cannot decompose the caustic alkalies. In the chemical 
 laboratory, solutions of caustic potash and caustic soda are in 
 frequent use for absorbing acid gases, such as carbonic acid, and 
 especially for separating the hydrates of other metals from solu- 
 tions of their salts. 
 
 Sxp. 244. — ^Dissolve a crystal of blue vitriol (sulphate of copper) in 
 a few centimetres of cold water, and add to the solution several drops 
 of a solution of caustic soda (or potash). The hydrate of copper is 
 precipitated as a delicate, blue, insoluble powder, while colorless sul- 
 phate of sodium (or potassium) remains in solution. 
 
 CuSO^ -t- 2NaH0 = CuH^O^ + Na^SO^. 
 Sulphate of Copper. Hydrate of Copper. 
 
 Exp. 245. — Place in a small flask 4 or 5 grms. of chalk or marble 
 (carbonate of calcium), and 7 or 8 c. c. of water ; then cautiously add 
 chlorhydric acid, little by little, imtil effervescence cea=e3 and the 
 chalk is dissolved. When the effervescence is not violent, the flask 
 
 2e 
 
418 STKONG BASES. 
 
 may be warmed to facilitate the process of solution. A rather con- 
 centrated solution of chloride of calcium will thus be obtained. 
 CaCOj + 2HC1 = CaCl^ + HjO + COj. 
 Carbonate of Calcium. Chloride of Calcium. 
 
 Add to this solution»a few drops of a solution of caustic soda, which is 
 free from carbonic acid. A white precipitate of hydrate of calcium 
 will immediately appear, since this hydrate is insoluble in the men- 
 struum, while chloride of sodium will be found in the clear solution. 
 
 CaOlj + 2NaH0 = CaHjOj -|- 2NaCl. 
 Hydrate of Calcium. 
 
 501. On account of this power of precipitating other hydrates 
 from solutions of their salts, the caustic alkalies are often called 
 strong bases, as he is the strongest wrestler who throws his ad- 
 versary ; but this term " strong" is applied to bases and acids so 
 confusedly as to be frequently a hindrance rather than a help in 
 classification. Thus, if the reaction which occurs in the prepa- 
 ration of caustic soda (Exp. 233), between carbonate of sodium 
 and hydrate of calcium, be compared with the reaction last given 
 between chloride of calcium and hydrate of sodium, it wiU be seen 
 that in the first calcium displaces sodium, while in the second 
 sodium displaces calcium ; in the one case hydrate of sodium is 
 eliminated from the reaction, and in the other hydrate of calcium. 
 So of acids ; we have before had occasion to remark that, of two 
 acids, now the one and now the other will be stronger, accord- 
 ing to the temperature at which the contest between them takes 
 place, or other extrinsic conditions. Thus sulphuric acid is at 
 certain temperatures capable of displacing phosphoric acid or 
 boracic acid, but at high temperatures both these acids displace 
 it (§§ 294, 448). It is obvious that the definition of the term 
 " strength " must be very vague and unsatisfactory when applied 
 to relations thus capable of actual reversal. Two general pria- 
 ciples, however, have been arrived at through the comparative 
 study of such reactions ; these are : — 1st. When from all or part 
 of the elements of any mixture of liquefied materials a substance 
 can be formed which is insoluble in the existing menstruum, that 
 substance will separate in the solid state ; 2nd. When frojn aU 
 or part of the elements of a solid or liquid mixture a substance 
 can be compounded which is volatile at the existing, or induced. 
 
AIKALniBTKT. 419 
 
 temperature, that substance will be eliminated in the gaseous 
 state. In either case such interchange of atoms as may be essen- 
 tial to the formation of the eliminated substance, takes place, and 
 the remaining elements necessarily adjust themselves to new re- 
 lations. Such insoluble precipitates often present peculiarities of 
 color or textui'e by which they may be recognized ; and such 
 volatile gases may frequently be identified by their color, odor, 
 or specific gravity, or by the chemical effects which they are 
 capable of producing. If every chemical element were known to 
 yield, under attainable conditions, a characteristic precipitate, or 
 to evolve a peculiar and recognizable gas, the analytical chemist 
 would possess the means of detecting every element with cer- 
 tainty. This is to a great extent the case, and chemical analysis 
 is chiefly based upon a knowledge of the degrees of solubility 
 and volatility which belong to a great variety of chemical sub- 
 stances with whose appearance and prominent properties the 
 analyst has previously made himself acquainted; of these sub- 
 stances many are common, but not a few rare and useless, except 
 to serve the purpose of the analyst. 
 
 There exists an anhydrous oxide of potassiTmi, K^O, and also 
 a peroxide. The anhydrous oxide Xfi is a gray, inodorous, hard, 
 brittle solid ; it melts a little above a red heat, but volatilizes 
 only at a very high temperature. 
 
 502. Alkalimetry. — Since the value of the carbonates and hy- 
 drates of sodium and potassium, as they are manufactured and 
 consumed on the large scale in the chemical arts, is generally de- 
 pendent upon the amount of alkali which they contain ready to 
 enter into chemical combination, it is important to have some 
 quick and easy method of determining how much available alkali 
 any sample of these substances really contains. The impurities 
 which most frequently contaminate the carbonate of potassium 
 are the chlorides and sulphates of potassium and sodium, silicic 
 acid, lime, alumina, and the oxides of iron ; the commonest im- 
 purities of carbonate of sodium are the chloride and sulphate 
 of sodium, as might readily be inferred from consideration of the 
 process by which the carbonate is manufactured. Some sulphite 
 of Bodium^ also is not infrequently present in commercial soda- ash. 
 Both carbonates are apt to contain small proportions of the hy- 
 
 2e2 
 
420 VOLTTMETEIC AFAtTSIS. 
 
 drates ; but as tlie hydrates are quite as valuable for most uses 
 as the carbonates, weight for weight, this admisture is not incon- 
 venient. In the common methods of testing the carbonates, the 
 hydrates present are estimated as available aLkaU, but are made 
 no separate account of. 
 
 It would be foreign to our purpose to enter upon the details of 
 alkalimetry ; the process consists essentially in ascertaining how 
 much dilute sulphuric acid of a known strength is required to 
 neutralize exactly a known weight of the sample examined. The 
 requisites are a graduated burette (Appendix, § 21), a standard 
 acid, pure carbonate of sodium wherewith to prepare this acid, 
 and a colored solution, sensitive to both acid and alkali, to indi- 
 cate the point of neutralization. The following experiment will 
 give some idea of the manipulation required in this sort of analysis, 
 which, on account of its rapidity, is of very general application 
 in technical chemistry. The general method is called volumetric, 
 because, when once the standard liquids are prepared, quantita- 
 tive results are obtained, not by weighing, but by measuring the 
 bulk of Kquid consumed in the testing. 
 
 Exp. 246. — Weigh out accurately 5 grms. of piu-e anhydrous carbo- 
 nate of sodium ; transfer it to a flask or beaker having the capacity of 
 about 400 c. c. ; dissolve it iu about 200 c. c. of water, and color the 
 solution blue with about 2 c. c. of a violet tincture of litmus. To pre- 
 pare this tincture, digest 1 part of litmus in 6 parts of water, on a 
 water-bath, for several hours ; filter ; divide the blue liquid into two 
 equal portions, and stir one half repeatedly with a glass rod dipped in 
 very dilute nitric acid, until the color just appears red ; then add the 
 other blue half, together with one part of alcohol, and keep the tincture 
 in a small open bottle. In a stoppered bottle the tincture fades. 
 
 Mix about 60 grms. of strong sulphuric acid with 500 c. c. of water 
 and let the mixtm-e cool (§ 233). Kll a 50 c. c. Mohr's burette (Ap- 
 pendix, § 21) up to the mark with the cold dilute acid. Place the 
 flaak or beaker containing the soda solution beneath the burette, gently 
 press the spring-clip, and allow the acid to flow gradually into the soda 
 solution, stirring the while, untU the color of the liquid changes to a 
 wine-red ; then place the flask or beaker over a lamp, and bring the 
 liquid to ebullition ;• the dissolved carbonic acid will be driven out, and 
 the liquid wiU again become blue; more acid is then added to the 
 nearly boiling fluid, the vessel being occasionally placed over the lamp, 
 until the color of the liquid becomes red, shghtly inclining to yellow. 
 
TAHTATION OP POT- AUB SODA-ASH. 421 
 
 When the point of saturation is approaching, add the acid two drops at 
 a time, and after each fresh addition dip a fine glass rod into the fluid, 
 and make with it two spots on a slip of fine blue litmus-paper, reading 
 the volume each time, and marking the number of ceutimetiea between 
 the two spots. Continue this operation until the spots on the paper 
 appear distinctly red ; then dry the paper and take for the connect 
 number that figure which stands between those two spots which just 
 remain red when dry. 
 
 For some eyes, tincture of cochineal possesses great advantages over 
 tincture of litmus as a means of recognizing the point of neutralization- 
 The tincture of cochineal is prepared by digesting 3 grms. of powdered 
 cochineal in a mixture of 50 c. c. of alcohol and 200 c. c. of water, at 
 the ordinary temperature, for several days. The tincture, which may 
 be either decanted or filtered from the residue, has a ruby-red color. 
 The caustic alkalies and the alkaline carbonates change the color to a 
 violet-carmine ; solutions of sti'ong acids and acid-salts make it orange ; 
 to carbonic acid it is nearly indifierent. 10 or 15 drops of the tincture 
 are suificient to color 200 c. e. of liquid. 
 
 Dilute the acid which remains of the original 500 c. c. with enough 
 water to give a fluid of which exactly 50 c. c. are required to saturate 
 5 grms. of pure carbonate of sodium. This dilution is eflected as fol- 
 lows : — Suppose that 40 c. c. of the acid have proved suificient to neu- 
 tralize 5 grms. of the pure carbonate, then 10 c. c. of water must be 
 added to every 40 c. c. of the acid. 460 c. c. of the original dilute 
 acid remain ; now, as 40 : 460=10 : number of c. c. water to be added 
 = 115 c. c. Dilute, therefore, the acid with 115 c. c. of water, using 
 some of this water to rinse the burette which contains the undiluted 
 acid, the measuring-glass which may have been used to ascertain the 
 extent of volume of the original acid, and any other vessel into which 
 it may have been temporarily poured. Of this diluted acid, 50 c. c. 
 should exactly neuti'alize 5 grms. of pure anhydrous carbonate of so- 
 dium. It may be tested by again weighing out 5 grms. of the pure 
 carbonate, and repeating the volumetric determination precisely as 
 above described. If the work has been well done, the standard acid 
 will be found ready for use. 
 
 Weigh out 5 grms, of common soda^-ash, and dissolve in about 
 200 c. c. of water whatever of the sample is soluble ; repeat upon this 
 liquid, without filtering, the volumetric operation of the last experi- 
 ment. The number oihalfc. c. of standard acid used gives directiy 
 the percentage of pure anhydrous carbonate of sodium which the 
 sample contains. If 50 c. c. or 100 half c. c. are used, the sample is 
 pure carbonate of sodium ; if 40 c. c. or 80 half c. c. are used, the 
 
422 
 
 POTASSITTM. 
 
 sample is eighty per cent, pure carbonate, and twenty per cent, water 
 and other impurities. 
 
 503. When an acid has been prepared, of which 50 c. c. exactly 
 neutralize 5 grms. of pure carbonate of sodium, it is a matter of 
 simple calculation only to determine how much hydrate of sodium, 
 iow much carbonate of potassium, and how much hydrate of 
 potassium the same 50 c. c. acid will neutralize. The follow- 
 ing are the proportions required, the atomic weight of potassium 
 being 39-1 :— 
 
 80 = 
 
 106 : 
 Combining weigM of 
 NajCO,. 
 
 106 : 
 
 Combining weight of 
 Na^COj. 
 
 106 : 
 Combining weight of 
 Na,CO,. 
 
 Com. wt. of 
 
 138-2 = 
 Com. wt. of 
 K,C03. 
 
 112-2 = 
 Com. wt. of 
 K,H,0, 
 
 5 
 
 Grms. 
 Na2C03. 
 
 5 
 
 Grms. 
 Na^COj. 
 
 5 
 
 Grms. 
 
 Na,CO,. 
 
 x = 3-773 ; 
 Grms. 
 NajHjOj. 
 
 X = 6-519 ; 
 Grms. 
 K3CO3. 
 
 a- = 5-292. 
 Grms. 
 K,H,0,. 
 
 are saturated by 50 c. c. 
 - of one and the same 
 standard acid. 
 
 The following table shows the quantities of these four substances 
 which are equivalent in neutralizing- or combining-power : — 
 5-000 grms. of carbonate of sodium ■■ 
 3-773 „ „ hydrate „ „ 
 6-519 „ „ carbonate of potassium 
 5-292 „ „ hydrate „ 
 
 It is apparent from this table that a given weight of carbonate of 
 sodium will saturate more silicic acid or more fat, or will give off 
 more carbonic acid than the same weight of carbonate of potassium, 
 and that the hydrate of sodium is also more efB^eient, gramme for 
 gramme, than the hydrate of potassium. These facts are to be 
 inferred at once from the atomic weights of sodium and potassium, 
 which are 23 and 39-1 respectively ; they have had their weight 
 in bringing about the rapid substitution of sodium-salts for potas- 
 sium-salts in the chemical arts. 
 
 504. Potassium, (K). — This element, Kke sodium, is made from 
 its carbonate by heating itttensely a mixture of the carbonate and 
 charcoal, in accordance with the reaction, 
 
 KCO, + 2C = 2K + 3C0. 
 
POTASSIUM DECOMPOSES WATER. 423 
 
 The apparatus employed is similar to ttat described in treating 
 of sodium (§ 487) ; and as potassium closely resembles sodium, the 
 same general method is followed, and the same precautions are 
 observed. A second distillation of the crude potassium is abso- 
 lutely essential, because, if it be neglected, a black, detonating 
 compound of uncertain composition is formed, which explodes 
 yiolently upon the slightest friction. 
 
 Potassium is a silver-white substance, of very brilliant lustre, 
 "which is brittle at 0°, soft as wax at ordinary temperatures, fuses 
 at 62°-5, and is volatile at a red heat. In its soft state, two clean 
 surfaces can be welded together like iron. It is lighter than 
 water, having a specific gravity of only 0-865. It is almost in- 
 stantaneously oxidized by air and water at the ordinary tempera- 
 ture, and, when heated, by nearly every gas or liquid which con- 
 tains oxygen. Like sodium, it must therefore be coUeoted and 
 kept under naphtha, out of contact with the air. At moderate 
 temperatures, potassium readily absorbs hydrogen, nitrogen, and 
 carbonic oxide, and enters into direct combination with chlorine, 
 bromine, iodine, sulphur, selenium, and tellurium. We have had 
 occasion to avail ourselves of its intense chemical energy (§§ 85, 
 97, 411). 
 
 Exp. 247. — Throw a piece of potassium, aa large as a small pea, upon 
 some cold water in the bottom of a large bottle, and place a card or 
 glass plate over the mouth of the bottle. The potassium decomposes 
 the water, and evolves heat enough to kindle the hydrogen which is 
 given off; this hydrogen burns with a purplish-red color, imparted to 
 the flame by a minute quantity of vaporized solid. This color is cha- 
 racteristic of potassium compounds, as a yellow color is characteristic 
 of sodium compounds. 
 
 505. It is not a matter of indiiference from what kind of a 
 mixture of carbonate of potassium and carbon potassium is pre- 
 pared. The material which is best adapted to its preparation is 
 the potassium-salt of a vegetable acid rich in carbon, which, when 
 decomposed by heat in a vessel from which air is excluded, yields 
 carbonate of potassium and a large quantity of free carbon. 
 While grape-juice is being converted into wine by fermentation, 
 a stony deposit, called " tartar," which is sometimes gray and 
 sometimes reddish, fastens to the bottom and sides of the casks 
 
424 CHLORIDE OP POTASSIITM. 
 
 which contain the fermented juice. When freed by reorystalliza- 
 tion from adhering coloring-matters, this crystalline and diffi- 
 cultly soluble substance is a white salt, acid and cooling to the 
 taste. It is an acid tartrate of potassium, and is commonly called 
 " cream of tartar." When this substance, or crude tartar, is 
 heated in a covered crucible until it ceases to emit combustible 
 vapors, the cooled residue is found to consist of a porous mass of 
 carbonate of potassium, intimately mixed with very finely divided 
 carbon. This mixture is the best material from which to pre- 
 pare potassium ; it is also an excellent flux, useful in assaying 
 the ores of the common metals. In wine-producing countries 
 considerable quantities of excellent carbonate . of potassium are 
 prepared from the deposits of the wine-vats, by dissolving the 
 carbonate out of the ignited tartar and purifying the salt, so ex- 
 tracted, by recrystallization. The carbonate so obtained is the 
 purest source of hydrate of potassium for laboratory use. 
 
 506. Chloride of Potassium (KCl). — This salt is a subordinate 
 source of potassium compounds. It is extracted in considerable 
 quantity from the ashes of sea-weeds, and is largely used in the 
 manufacture of common alum, which is a sulphate of aluminum 
 and potassium. It occurs native, sometimes pure, but more fre- 
 quently mixed or combined with other chlorides. The chloride 
 of potassium is capable of uniting with most other metallic chlo- 
 rides, forming crystallizable double salts. The native double 
 chloride of potassium and magnesium (KCl,MgCl2,6H20) has be- 
 come of late years a productive source of potassium-salts. This 
 mineral is dissolved in hot water ; from the cooled solution the 
 greater part of the chloride of potassium crystallizes out, while 
 the chloride of magnesium remains in solution. Chloride of 
 potassium occurs also with the chlorides of sodium, magnesium, 
 calcium, and other salts in sea-water and brine-springs, and is 
 obtained as a secondary product in the preparation of chlorate of 
 potassium (§ 517), the purification of nitre (§ 514), and in seve- 
 ral other manufacturing-operations. It may be prepared directly 
 from potassium and chlorine, or from the carbonate or hydrate 
 of potassium and chlorhydric acid. 
 
 Chloride of potassium crystallizes in anhydrous cubes, looks 
 and tastes like common salt, is not acted upon by the air, de- 
 
IODIDE OP POTASSIUM. 425 
 
 crepitates when heated, melts at a low red heat, and volatilizes 
 unchanged at a higher temperature. It is somewhat more vola- 
 tile than common salt, is more soluble in water, and produces a 
 greater degree of cold in dissolving. This chloride enters into 
 some highly crystalline compounds, of curious composition, of 
 which the product of the following experiment may serve as an 
 example : — 
 
 -Erp. 248. — ^By the aid of a gentle heat, dissolve 6 grma. of powdered 
 red chromate of potassium in 8 grms. of strong cUorhydric acid, 
 avoiding evolution of chlorine. "When the powder is dissolved, allow 
 the solution to cool ; flat, red prisms will crystallize from the liquid. 
 This compound answers to the formula KCljCrO^. It is decomposed 
 by solution in water. 
 
 K20,2Cr03 + 2HC1 = 2(KCl,0iO3) + H^O. 
 Red Chromate 
 of Potassium, 
 
 507. Bromide of Potassium (KBr) is a very soluble salt, which 
 crystallizes in cubes, and closely resembles in all its properties 
 the chloride. Potassium and bromine unite directly, with inflam- 
 mation and violent detonation, the bromide being the product of the 
 reaction. When bromine is added to a solution of caustic potash 
 until the hquid acquires a permanent yellowish tinge, a mixture 
 of bromide and bromate of potassium is produced : — 
 
 6KH0 + 6Br = 5KBr + E:Br03 + 3H^0. 
 
 The mixed salts are dissolved in water, and a current of sulphy- 
 dric acid is passed through the solution to reduce the bromate : — 
 
 KBrO, + 3H,S = KBr = 3H,0 + 3S. 
 The liquid is then gently warmed to expel the excess of gas, 
 filtered from the deposited stilphur, and evaporated until the bro- 
 mide crystallizes. The salt has lately come into use in medicine 
 as a sedative. 
 
 508. Iodide of Potassium (KI). — This valuable medicine and 
 photographic material may be procured by adding iodine to a so- 
 lution of hydrate of potassium until the liquid turns brown, and 
 gently igniting the residue obtained by evaporation. The pro- 
 cess and the reaction are the same as in the preparation of the 
 bromide, except that the iodate may be decomposed by heat alone 
 
426 CTANIDB OF POTASSIUM. 
 
 and does not require reduction by sulpturetted hydrogen. A 
 better mode of preparing the iodide of potassium is to be found 
 in the decomposition of iodide of iron by carbonate of potassium. 
 
 Digest 4 grms. of iodine and 2 grms. of iron filings in a stoppered 
 bottle with 20 c. c. of water ; iodide of iron (Felj) is formed under 
 these conditions by direct union of the elements. The liquid is then 
 transferred to a flask and boiled, and a solution of carbonate of potas- 
 sium is added by small portions so long as a precipitate occurs. The 
 solution, filtered from the insoluble carbonate of iron, yields on eva- 
 poration crystals of iodide of potassium. 
 
 Iodide of potassium ordinarily crystallizes in semiopaque cubes. 
 It is permanent in the air, has a sharp taste, melts below a red 
 heat, and volatilizes unchanged at a low red heat. It is very 
 soluble in water, and in dissolving produces a considerable fall of 
 temperature. Alcohol also freely dissolves this salt. The facility 
 with which the salt is decomposed and its iodine liberated by 
 chlorine, ozone, and nitric acid has been already amply illustrated 
 (Exps. 70, 72, 76). 
 
 Iodide of potassium is much used in medicine ; it is not poi- 
 sonous even in doses of 6 to 20 grms. Its solution in water dis- 
 solves iodine to a large extent, acquiring thereby a dark-brown 
 color. This brown solution is sometimes used in medicine as a 
 vehicle for iodine ; it is also useful to the photographer for re- 
 moving from the skin the stains produced by nitrate of silver. 
 Iodide of potassium is, further, employed in the photographic pro- 
 cess upon glass, to produce in the substance of the film of collo- 
 dion a deposit of iodide of silver by double decomposition with 
 nitrate of silver. 
 
 509. Cyanide of Potassium (KCN). — ^The elements which make 
 part of the whitish, soluble, fusible, and deliquescent solid which 
 bears this name are potassium, carbon, and nitrogen. At a bright- 
 red heat these three elements will come together to form this salt 
 out of quite a variety of materials, and under quite various cir- 
 cumstances. When nitrogen gas is passed over a mixture of 
 charcoal and hydrate or carbonate of potassium, at a bright-red 
 heat, cyanide of potassium is formed. When nitrogenous organic 
 matters are ftised with hydrate or carbonate of potassium, the 
 cyanide is formed. In presence of iron scraps or filings, this 
 
SXTLPHIDES OF POTASSIUM. 427 
 
 mixture produces a common cyanide, containing potassium, iron, 
 carbon, and nitrogen, and known in ttearts as " yellow prussiate 
 of potash," and to chemists as ferrocyanide of potassium. If this 
 " prussiate " be ignited at a moderate red heat, it is decomposed 
 into cyanide of potassium, nitrogen, and a compound of iron with 
 carbon : — 
 
 4KCN,Fe(CN), = 4KCN + 2N + TeC,. 
 
 In the blast-furnaces in which iron ores are smelted with coal 
 or coke, a considerable quantity of cyanide of potassium is often 
 produced, the nitrogen being probably derived from the torrents 
 of nitrogen which the blast of air carries into the furnace. In- 
 stead of igniting the yellow prussiate alone, a more economical 
 process is to ignite a mixture of the prussiate with carbonate of 
 potassium. This method saves aU the cyanogen in the prussiate; 
 but the salt thus obtained is always mixed with cyanate and car- 
 bonate of potassium : — 
 Z,re(CN), + KfiO^ = 5K(CN) -|- K(C]Sr)0 -|- CO, + Fe. 
 
 The presence of these impurities does not injure the cyanide for 
 many of its uses. 
 
 Cyanide of potassium is of great use in galvanic gilding and 
 silvering, since the cyanides of gold and sUver are both soluble in 
 a solution of cyanide of potassium. Its solution dissolves the 
 sulphide of silver, and has therefore been suggested for house- 
 hold use in cleaning silver- ware ; photographers sometimes use it 
 for removing stains of nitrate of silver from the hands ; but both 
 these applications of cyanide of potassium are dangerous and in- 
 expedient. The cyanide is intensely poisonous, not only when 
 taken internally, but also when brought into contact with an 
 abrasion of the skin, a cut, or scratch. As a reducing agent, 
 cyanide of potassium has great power ; it is especially useful in 
 blowpipe reactions (Exp. 132). 
 
 510. Sulphides of Potassium. — Potassium, heated in sulphur- 
 vapor, takes fire readUy, and burns brilliantly. There are sup- 
 posed to be five different compounds of potassium and sulphur, 
 corresponding to the formulse K,S, K,S„ K,S3, K,S„ and K^S^; and 
 there is a sulphydrate KHS, analogous to the hydrate KHO. 
 
 Ihp. 249.— Heat, gently, a thorough mixture of 10. grms. of dry 
 
428 SULPHATE OF POTASSIUM. 
 
 powdered carbonate of potassium and 6 grms. of sulphur, in a covered 
 earthen or iron crucible, until eftervescence ceases and the laass flows 
 quietly. The fused mass has a yellowish-brown color, and consists of 
 tersulphide, quinquisulphide, and intermediate sulphides of potassium, 
 mixed with sulphate, and often with carbonate of potassiiun ; it is 
 called "liver of sulphur." This substance, dissolved in water, gives a 
 greenish solution, from which dilute acids liberate sulphuretted hydro- 
 gen, and precipitate milk of sulphur (§ 198). The carbonic acid of 
 the air is strong enough to effect this decomposition ; hence the solid 
 substance and its solution, when exposed to the air, smeU of sulphu- 
 retted hydrogen : — 
 
 K2S3 + H2SO4 = K2SO4 + HjS + 2S. 
 The chief use of liver of sulphur is in the medical treatment of skin- 
 
 511. When sulphydric acid gas is passed to saturation into a 
 solution of caustic potash, a colorless solution is obtained, which, 
 is supposed to contain the sulphydrate KHS. It has no perma- 
 nency, quickly absorbing oxygen and turning yellow. 
 
 All the sulphides of potassium are brown solids, having an al- 
 kaline reaction to test-paper, and smelling of sulphydric acid. 
 Their solutions are oxidized by exposure to the air, and sulphur 
 is deposited from them. 
 
 512. Sulphate of Potassium (K^SOJ. — This anhydrous salt 
 crystallizes in transparent hexagonal prisms, terminated by hexa- 
 gonal pyramids, and consequently bears some resemblance to 
 common quartz crystals. The salt has a strong tendency to 
 form double sulphates ; a double sulphate of potassium and mag- 
 nesium is of importance in the manufacture of potassium-salts 
 from sea-water. It also enters into the composition of many 
 
 . of the double sulphates, which are called alums from the name of 
 the commonest member of the class, the sulphate of aluminum 
 and potassium. 
 
 613. Sulphate of Potassium and Hydrogen (KHSO J. — This salt, 
 commonly called the " bisulphate," is formed on a large scale as 
 a residuary product whenever nitric acid is manufactured from 
 nitrate of potassium. When ignited, its crystals lose half their 
 acid : — 
 
 2(KHS0J = K,SO, + H,SO,; 
 
 and the salt is therefore sometimes used as a flux, in cases where 
 
REFINIIfG or SALTPETRE. 429 
 
 the action of a strong acid is required at a high temperature upon 
 salts or oxides with which it may be fused. Platinum tools may- 
 be cleaned by fusing this salt in or upon them. 
 
 514. Nitrate of Potassium (KNO^). — This valuable salt, com- 
 monly called saltpetre, is very widely diffused as a natural pro- 
 duct, being indeed seldom wholly wanting in a productive soil, or 
 in spring- or river-water. At many localities it is found in 
 caverns or caves in calcareous formations ; but the principal com- 
 mercial source of the salt is the soil of certain tropical regions, 
 especially of districts in Arabia, Persia, and India, where the 
 nitrate is found disseminated through the upper portion of the 
 soil, or forming an efflorescence upon the surface, but never 
 extending lower than the depth to which the air can easily 
 penetrate. 
 
 This natm-al production of nitrates appears to result mainly from the 
 putrefaction of vegetable and animal matters, in presence of the air 
 and of alkaline or earthy bases capable of fixing the nitric acid as soon 
 as it is formed. The well-waters of towns, contaminated by neighbor- 
 ing sewers and cesspools, nearly always contain nitrates. The decay 
 of the luxuriant vegetation of the tropics, promoted by a hot sun and 
 a moist atmosphere, is a never-failing source of ammonia ; but it is not 
 certain that the production of ammonia is a necessary stage in the pro- 
 cess of nitrification. In the artificial production of nitrates in tem- 
 perate climates, the supposed natural conditions have been roughlv 
 imitated. In the old saltpetre " plantations " of European countries, 
 nitrate of calcium Was produced by mixing decomposing vegetable and 
 animal matters with cinders, chalk, marl, and so forth, moistening the 
 mass repeatedly with leachings of manure-heaps, exposing it freely to 
 the air for two or three years, and then lixiviating. The nitrate of 
 calcium, which was the main product, was then converted into salt- 
 petre by double decomposition with carbonate of potassium. 
 
 The saltpetre is extracted from the earth which contains it by lixi- 
 viation, evaporation, and crystallization ; but inasmuch as for most uses 
 it is required in a very pure state, the crude salt must generally be re- 
 fined. The common impurities of crude saltpetre are chloride of so- 
 dium and chloride of potassium. In order to separate these chlorides, 
 advantage is taken of the fact that the nitrate of potassium is four 
 times as soluble in boiling water as the chloride of potassium, and six 
 times as soluble as the chloride of sodium. The crude saltpetre is 
 treated with a quantity of water, sufficient to dissolve at boiling all the 
 nitrate of potassixmi, but not all of the chloride of sodium beside. This 
 
430 PROPBEirES OF SALIPETEE. 
 
 residual salt is scooped out of the vessel in which the solution is 
 effected, and the solution, after being somewhat diluted, is hoUed with 
 a little glue, to coagulate the coloring-matters and other soluble dirt, 
 and sweep the liquid clean by means of the adhesive scum which rises 
 to the surface. The strong, clear solution is then transferred to shallow 
 crystallizing pans, and left at rest if large crystals are desired ; if small 
 crystals are preferable, the liquid is constantly stirred from the moment 
 that crystallization begins ; the saltpetre is then deposited in a crystal- 
 line powder, called saltpetre-flour. The chlorides of sodium and 
 potassium are nearly as soluble in cold water as in hot ; but nitrate of 
 potassium is only one-eighth as soluble in water at the temperature of 
 the atmosphere as in boiling water. Hence the chlorides remain in 
 the mother-liquor, while the nitrate rapidly separates from the solution 
 as it cools. The ciystals of saltpetre are drained, and then washed 
 with a solution of saltpetre saturated in the cold. This solution takes 
 up the adhering chlorides, but leaves the pure nitrate of potassium 
 undissolved. 
 
 Large quantities of saltpetre are now made by decomposing nitrate 
 of sodium with carbonate of potassium. When, through governmental 
 interference, the East-Indian supply of saltpetre is checked, this 
 method is resorted to with advantage. Tartar, and the ashes of the 
 beetroot-sugar manufacture, are good sources of potash to be applied 
 to this purpose. Crude nitrate of sodium contains so much chloride 
 of sodium, that it is desirable to purify it for this use by previous re- 
 crystaUization ; otherwise potash would be unprofitably consumed in 
 converting chloride of sodium into chloride of potassium. One of the 
 processes for converting the nitrate of sodium into nitrate of potassium 
 consists simply in adding the nitrate of sodium to a hot concentrated 
 solution of carbonate of potassium ; a precipitation of carbonate of so- 
 dium takes place, and this precipitate is removed as faat as it forms, 
 until no more appears ; from the cooled liquid saltpetre-flour is de- 
 posited. The carbonate of potassium may be replaced in this process 
 by chloride of potassium. NaNOj -|- KCl = KNOj -|-NaCl. 
 
 515. Nitrate of potassium is white, inodorous, and anhydrous, 
 and has a cooling, bitter taste. When pure, it is permanent in 
 the air, — a fact of great importance, inasmuch as the chief use 
 of this salt is in the manufacture of gunpowder. Were it hygro- 
 scopic, like nitrate of sodium, it would not be applicable to this 
 use. Saltpetre is one of those few potassium-salts which cannot 
 be whoUy replaced in the arts by the corresponding sodium-salt. 
 It is very soluble in water, especially in hot water ; it melts below 
 
SALTPETRE NOT EXPLOSIVE. 431 
 
 a red heat to a colorless liquid without loss of suhstance, but at a 
 red heat it gives oflf oxygen and suffers decomposition. Its 
 most marked chemical characteristic is its oxidizing-povrer. It 
 deflagrates in the fire with charcoal, sulphur, phosphorus, and 
 other combustible bodies ; when ignited in contact with copper 
 or iron (Exp. 46), it converts these metals into oxides ; and it 
 even oxidizes gold, silver, and platinum. It is on the oxidizing- 
 power of saltpetre that its use in the manufacture of gunpowder 
 and fireworks, and in the preparation of matches, depends. 
 
 Arrange 10 grms. of pure nitrate of potassium and 20 or SO grms. of 
 thin copper-turnings, or ^mall bits of sheet copper, in alternate layers, 
 in a covered copper crucible, and expose the mixture for half an hour 
 to a moderate red heat. Dissolve out the cooled mass with water, and 
 let the liquid stand in a tall, closed bottle imtil the oxide of copper has 
 settled to the bottom. The supernatant liquid is a pure solution of 
 caustic potash ; indeed this is an excellent method of preparing pure 
 hydrate of potassium for use in analysis : — 
 
 2KNO3 + 50u + HjO = 2KH0 + SCuO + 2N. 
 
 Hxp. 250. — ^Heat 10 or 12 grms. of saltpetre, gently, in a small 
 porcelain dish, until it melts ; pour the melted salt out on a cold piece 
 of iron or stone; break the fused mass into small fragments,' and fill 
 an ignition-tube, 12-15 cm. long, one-third full with these bits. Heat 
 the tube cautiously, taking pains to keep aU the salt, when once melted, 
 in a state of fusion. At a red heat, oxygen, pure at first, is slowly 
 evolved, and may be collected at the water-pan ; simultaneously nitrite 
 of potassium (KNOj) is formed ; at a second stage this nitrite is itself 
 decomposed, and the escaping oxygen is then contaminated with a 
 certain proportion of nitrogen. A portion of the gas collected may be 
 tested with a glowing splinter (Exp. 6) ; another portion maybe mixed 
 with coal-gas, and, with the mixture, bubbles may be blown, as directed 
 in Exp. 30 ; the mixture will be found to be exceedingly explosive. 
 
 This experiment proves, in the first place, that saltpetre itself is not , 
 explosive, and, in the second place, afibrds an explanation of the fact 
 that frightful explosions do often occur when storehouses containing 
 saltpetre are burned. Carburetted hydrogen, such as was obtained in 
 Exp. 151 (represented by the coal-gas in the last experiment), is 
 evolved from the wood- work of the burning building, wherever the 
 wood is heated out of contact with the air ; meanwhile oxygen is given 
 oiffrom the ignited saltpetre, and whenever these two gases mix in the 
 requisite proportions, and their mixture comes in contact with a flame, 
 a violent explosion inevitably ensues. 
 
432 GtrNPOWBEB. 
 
 Exp. 251.— Dissolve 5 grms. of saltpetre in 20 c. c. of water ; dip 
 strips of bibulous paper in the solution, and dry them ; this paper, 
 once kindled, will smoulder away till consumed. It is used m con- 
 nexion with fireworks, and in the manufacture of pastilles and aromatic 
 fumigating paper. 
 
 Exp. 252. —Mix 6 grms. of powdered saltpetre with 1 grm. of dry 
 powdered charcoal ; place the mixture on a piece of porcelain and ig- 
 nite it with a hot wire. When the deflagration is over, a white solid 
 wiU be found upon the porcelain. Dissolve this sohd in a few drops 
 of water ; the solution will be alkaline to test-paper ; add a few drops 
 of a dilute acid ; a brisk effervescence marks the escape of carbonic 
 acid. The nitrate has oxidized the carbon to carbonic acid, part of 
 which escaped with the nitrogen during the deflagration, while pait 
 entered into combination with the potassium : — 
 
 4KNO3 + 50 = 2K2CO3 -I- 300^ -t- 4N. 
 
 Exp. 253. — ^Place 30 grms. of saltpetre in a small beaker with 110 
 c. c. of water ; insert a thermometer in the mixture, and observe the 
 very considerable fall of temperature occasioned by the solution of the 
 salt. In those countries where saltpetre is cheap and ice dear, this 
 property of the salt is availed of for the refrigeration of drinks. 
 
 516. Gunpowder is an intimate mechanical mixture of soft- 
 wood charcoal (§ 382), sulphur, and nitrate of potassium, in the 
 proportions of 70 or 80 per cent, of the nitrate to 10 or 12 per 
 cent, of each of the other ingredients. Though it is in no sense 
 a chemical compound, we may, for convenience' sake, express 
 the composition of gunpowder by the formula K^N^Os + ^+^C, 
 and may roughly formulate the reactions which occur when it is 
 burned, by the foUowing equation : — 
 
 -K^P, -I- S -F 30 = 300, + 2N + K,S. 
 Speaking in general terms, the oxygen of the nitrate combines 
 with the carbon to form carbonic acid, or, at the least, carbonic 
 oxide, while the sulphur is retained by the potassium, and nitro- 
 gen left free. Gunpowder burns at the expense of the oxygen 
 contained in it ; it has no need of air for its combustion, but can 
 be burned in any closed space — as weU, for example, in canisters 
 under water, or tightly enclosed in the chamber of a gun, as in 
 free air. 
 
 From the formula, it will be seen, at a glance, that a very large 
 proportion of gas, as compared with the bulk of the solid powder. 
 
PEEPAKATION OP eUNPOWBEE. 433 
 
 must be evolved ■when powder is burned. But gunpowder bums 
 rapidly and with great evolution of heat, so that the volume of 
 gas, large at any temperatiire, is enormously expanded at the 
 moment of its formation ; hoDce it happens that the gas set free 
 in the barrel of a gun may be capable of occupying a thousand 
 or fifteen hundred times as much space as the powder which ge- 
 nerated it. An enormous pressure is thus engendered at the spot 
 where the powder burns, and to this pressure some part of the 
 matter which confines the powder must yield. In the case of 
 the gun-barrel, it is the bullet which represents the weakest, or 
 breaking side of the chamber in which the powder burns ; but 
 when rocks are blasted, then the packing, or " tamping," which 
 represents the ball, is made so firm that it shall be stronger than 
 the rocky sides of the drill-hole, which is equivalent to the bar- 
 rel of the gun. In case the walls of the gun can be disrupted 
 more readily than the firmly impacted bullet can be driven out, 
 then, of course, the gun hursts ; and, conversely, the tamping of 
 a drill-hole is thrown out if it be less firm than the rock. In the 
 case of the gun-barrel, a part of the effect of the explosion is felt 
 in the kick or recoil of the gun. 
 
 Though the equation last given is useful in so far as it exhibits 
 the gaseous products evolved during the combustion of gun- 
 powder, it does not truly express the solid products of the reac- 
 tion. The residue of the combustion really contains only a com- 
 paratively small proportion of sulphide of potassium ; it consists 
 mainly of sulphate of potassium and carbonate of potassium, 
 together with some hyposulphite of potassium, and a trace of un- 
 burned carbon. Enough sulphide of potassium is always present, 
 however, to impart the offensive odor which is perceived in wash- 
 ing a foul gun, and in powder- smoke. 
 
 Exp. 254. — Pulverize, separately, 23 grms. of nitrate of potassium, 
 4 grms. of sulphur, and 4 grms. of charcoal. Place a drop or two of 
 water in a porcelain mortar, and grind into it, first, the charcoal, and 
 then the other ingredients, taking care to add enough water to form a 
 plastic dough. After the mass has been thoroughly kneaded, roll out 
 small portions of it between two pieces of board, into long threads, of 
 the thickness of a fine knitting-needle. With a knife, cut the threads 
 into small fragments or granules, and leave the granules ia a warm 
 room to dry. The thoroughly dried product is gunpowder ; and the 
 
 2e 
 
434 CHtOEATE OF POTASSITTM. 
 
 manipulation in tWs experiment does not differ essentially from the 
 mode of manufacture employed in the powder-mills, excepting that the 
 granulation is there effected by passing the moist paste through cul- 
 lenders. 
 
 The sulphur in gunpowder acts mainly as a kindling material 
 (§ 200). In powder intended for use in guns, the proportion of sul- 
 phur is kept comparatively low, since any excess of it would corrode 
 the metal of the gun. 
 
 Hxp. 255.— Knead together, as in Exp. 254, 7 grms. of powdered 
 nitrate of potassium and 1-5 grm. of moistened, finely powdered char- 
 coal. Granulate and dry the product, as before, and compare its in- 
 flammability with that of the gunpowder prepared in Exp. 254, by 
 touching small heaps of each with a red-hot wire. Mixtures of char- 
 coal and nitrate of potassium, such as the foregoing, are much used in 
 the manufacture of fireworks. 
 
 517. Chlorate of Potassium (KCIO3). — The basis of the large 
 use now made of this beautiful salt in medicine, in calico-print- 
 ing, in pyrotechny, in the match-manufacture, and in the chemical 
 laboratory is its large oxygen-contents. It is an oxidizing agent 
 of the most vigorous description. 
 
 It may be prepared by saturating a solution of 1 part of hydrate of 
 potassium in 3 parts of water with chlorine, and heating the liquid 
 some time to the boiling-point. The ultimate result maybe expressed 
 by the formula 
 
 6KH0 -I- 601 = KCIO3 + 5KC1 -|- SH^O; 
 but the process has two stages, which are sufficiently described in § 124. 
 The hot solution, left to itself, deposits the greater part of the chlorate 
 in anhydrous six-sided plates of a pearly lustre ; the chloride of potas- 
 sium remains in the mother-liquor. The chlorate is freed from adhe.- 
 ring chloride by recrystaUization. The success of the process depends 
 upon the very different solubilities of the chlorate and the chloride of 
 potassium. At the temperature of their saturated boiling solutions 
 both salts are about equally soluble ; 100 parts of water will dissolve 
 between 60 and 67 parts of either salt ; but at the ordinary tempera- 
 ture of the air 100 parts of water will dissolve 30-40 parts of chloride 
 of potassium and only 6 or 7 parts of chlorate of potassium. We find 
 here the explanation of the fact that chlorate of sodium has not re- 
 placed chlorate of potassium in the arts. The chlorate of sodium is 
 more soluble in water at all temperatures than the chloride of sodium 
 is, while both are exceedingly soluble, so that the two salts cannot be 
 separated by crystallization. This process of crystallization is the 
 chemical manufacturer's chief reliance in refining both his materials 
 
PEEPAKATION OF CHLORiTE OE POTASSItTM. 435 
 
 and his products ; and the purchaser of chemicals finds his test guaranty 
 of the purity of his commodities in the peculiar form, lustre, color, and 
 degree of transparency which characterize the crystals of every crys- 
 tallizable and permanent chemical compound. Hence an easily crys- 
 tallized permanent salt, of characteristic appearance, like chlorate of 
 potassium, will always have the preference over one which, like chlo- 
 rate of sodium, can be crystallized and purified only with difficulty, 
 and is not permanent when once obtained. The chlorate of sodium is 
 deliquescent. 
 
 The waste product in the making of chlorate of potassium by the 
 process just described is chloride of potassium, a comparatively dear 
 salt. Ad economy is effected by substituting hydrate of calcium for 
 hydrate of potassium, and thus making the secondary product chloride 
 of calcium instead of chloride of potassivim ; one equivalent only of the 
 chloride of potassium is then required instead of six of the hydrate of 
 potassium. An excess of chlorine is passed into a mixture of 300 parts 
 of quicklime, 154 parts of chloride of potassium, and 100 of water. 
 The mass is heated by steam, stirred with agitators, filtered, and then 
 evaporated nearly to dryness by steam-heat ; the mass is then redis- 
 solved in hot water and set to crystallize : — 
 
 SCaO + KCl -I- 6C1 = KCIO3 -|- SCaClj. 
 The mother-liquor, which contains all the chloride of calcium, may be 
 decomposed with sulphate of potassium, in which event a very finely 
 divided sulphate of calcium, available for " stuffing " in the manufac- 
 ture of paper, is precipitated, and chloride of potassiiun is recovered, 
 to be again applied to the production of the chlorate ; or the chloride- 
 of-calcium solution may be decomposed with carbonate of sodium, in 
 order to precipitate a very finely divided carbonate of calcium, which 
 is largely employed by the pharmaceutist and perfumer. In the latter 
 case, chloride of sodium has to be thrown away. The whole manu- 
 facture is a good example of a technical chemical process. 
 
 518. Chlorate of potassium is easily decomposed by heat ; at a 
 moderate temperature it yields perchlorate and chloride of potas- 
 sium (§ 124) ; but at a red heat it is resolved into chloride of 
 potassium and oxygen (Exp. I):- — KC103=KCl+30. Chlorate 
 of potassium is so prompt an oxidizing agent that mixtures of it 
 with combustible bodies often detonate violently when struck or 
 heated (Exps. 113, 157). These combustions are dangerous un- 
 less very small quantities be used. It has been often proposed to 
 replace gunpowder by such mixtures ; a mixture of the chlorate 
 with catechu, or some simUar stable substance rich in tannin, is 
 
 2p2 
 
436 OXTDATION BY CHLOKATE OF POTASSnTM. 
 
 the most promising of these suggestions. Strong acids, like sul- 
 phuric, nitric, and chlorbydric acids, decompose chlorate of potas- 
 sium with evohition of oxides of chlorine, or of chlorine and oxy- 
 gen. The decomposition is often attended with decrepitation, and 
 sometimes with a flashing light ; combustibles, like sulphur, phos- 
 phorus, sugar, and resin, are inflamed by the gases evolved. A 
 mixture of chlorate of potassium and chlorhydric acid is used in 
 toxicological investigations as an oxidizing agent for the destruc- 
 tion of organic matter (§ 329). The following formulae will eluci- 
 date some of these reactions : — 
 3KC103 + 2H„S0,= 2C10, + KaO. + 2KHS0, -|- H^ 
 8KCIO3 -f- 6HN0, = 6KNO3 + 2KC10, -I- 6C1 -|- 130 + 3H,0 
 4KCIO3 -I- 12HC1 = 4KC1 + 3C10, + 9C1 + 6H,0. 
 
 Exp. 256. — Pour into a conical test-glass 26-30 c. c. of water, and 
 throw into the water some scraps of phosphorus, weighing together not 
 more than 0'3 grm., and 3-4 grms. of crystals of chlorate of potassium. 
 By means of a thistle-tube bring 6 or 6 c. c. of strong sulphuric acid 
 into immediate contact with the chlorate at the bottom of the glass. 
 Then withdraw the thistle-tube. In a moment the phosphorus is 
 kindled, and burns with vivid flashes of light beneath the water. An 
 evolution of chlorine accompanies the reaction. 
 
 Exp. 257. — Rub 4 or 5 grms. of clean chlorate of potassium, free 
 from dust, to a fine powder in a porcelain mortar. In powdering chlo- 
 rate of potassium, care must be taken that the mortar and pestle are 
 perfectly clean, and the salt free from organic matter, and that violent 
 percussion and heavy pressure upon the contents of the mortar be 
 wholly avoided. Place the powdered chlorate on a piece of paper, 
 add an equal bulk of dry powdered sugar to the pile, and, with the 
 fingers and a piece of card, mix the two materials thoroughly together. 
 Mixtures of chlorate of potassium and organic matter are liable to 
 explode, if strongly rubbed or but lightly struck. Wrap the mixture 
 in a paper cylinder, and place the cylinder on a brick in a strong 
 draught of air ; let fall upon the mixture a drop of sulphuric acid from 
 the end of a glass rod ; a very vivid combustion will ensue, with the 
 violet-colored flame characteristic of potassium. 
 
 Exp. 258. — ^Mix together, on paper, with the precautions above de- 
 scribed, 1 grm. of black oxide of copper, 1 grm. of sulphur, and 2-5 
 grms. of powdered chlorate of potassium. Place the mixture, inclosed 
 in a paper cylinder, on the top of a brick, and touch it with a hot 
 wire ; it will bum vividly, and with a purple color which is prized in 
 pyrotechny. 
 
AMMONIUM-SALTS. 437 
 
 CHAPTEE XXV. 
 
 A M It N I TTM-S ALTS. 
 
 519. The hypothetical metal ammonium (NHJ is a device for 
 explaining the constitution and properties of one weU-defined 
 class out of the several classes of compounds into which the gas 
 ammonia enters. This class of compounds is that which results 
 from neutralizing an aqueous solution of ammonia with acids, as 
 in tie following reactions : — 
 
 NH3,H,0 + H,SO, = (NHJHSO, + H,0. 
 
 Sulphate of Ammonium 
 and Hydrogen. 
 
 NH„H,0 + HNO3 = (NHJNO, + H,0. 
 Nitrate of Am,monium. 
 According to this hypothesis, the crystalline salts which result 
 from such neutralizations contain a group of atoms (NH^) which 
 is analogous in its action to potassium and sodium, and which 
 forms salts analogous in composition to the potassium-salts. Thus 
 chloride of ammonium (NB[^)C1 is analogous to chloride of potas- 
 sium KCl; sulphate of ammonium (NHj)2S0^ is analogous to 
 sulphate of potassium K^SO^, and so forth (§91). 
 
 All the actual evidence we possess of the separate existence 
 and metallic character of the group NH^ is contained in the fol- 
 lowing curious but inconclusive experiment : — 
 
 Exp. 259. — Pour 8 or 10 c. c. of mercury into a small flask, and 
 warm the mercury over a gas-lamp ; drop upon the mercury six or 
 eight bits of metallic sodium, no one of them larger than a hemp-seed. 
 The sodiimi dissolves with some spattering in the warm mercury, and 
 a sodium amalgam is thus obtained. Transfer the amalgam to a tall 
 glass or bottle of at least 300 c. c. capacity, and pour over it a concen- 
 trated solution of chloride of ammonium. The amalgam immediately 
 begins to swell up, and ultimately increases to 8 or 10 times its original 
 bulk, in the cold, or to 20 or 30 times if the solution be hot, assuming 
 a pasty consistency like that of soft butter, but preserving its metallic 
 lustre. It begins to undergo spontaneous decomposition as soon as it is 
 formed, and if it is placed in water, this decomposition is quite rapid ; 
 
438 HTDEATE OP AMMONHral. 
 
 hydrogen gas is given off' in minute bubbles, and ammonia is found m 
 the solution. This curious substance has been supposed to be a com- 
 bination of ammonium (NH4) with mercury ; all attempts, however, 
 to isolate the ammonium have been unsuccessful. The proportion 
 of ammonium (?) present in the amalgam is extremely minute, not- 
 withstanding the great change of bulk and properties experienced by 
 the mercury. The amalgam is said to contain only 1 part of nitrogen 
 and hydrogen to 1800 parts of mercury. 
 
 520. Ammonium-salts are generally isomorphous with potas- 
 sium-salts. They have mostly a pungent, saline taste ; they are 
 colorless, like sodium- and potassium-salts, unless the acids are 
 colored ; the carbonates, and those salts which, like the chloride 
 and iodide, contain no oxygen, are volatile at a moderate heat 
 without decomposition ; some salts lose their ammonia when 
 heated ; if the acid which neutralized this ammonia is a non- 
 volatile substance, like phosphoric acid, it will remain behind un- 
 decomposed; others, Uke the nitrate (Exp. 34), yield simpler 
 gases than ammonia, as, for example, nitrogen or nitrous oxide. 
 An aqueous solution of an ammonium-salt, when exposed to the 
 air or evaporated, generally loses ammonia and acquires an acid 
 reaction; hence in crystallizing an ammonium-salt, ammonia- 
 water must be occasionally added during evaporation. All am- 
 monium-salts, whether solid or in solution, evolve ammonia when 
 heated with the hydrates of sodium, potassium, calcium and a 
 few other metals (Exp. 48). 
 
 Sxp. 260. — Warm a few centimetres of a solution of chloride of 
 ammonium in a test-tube, add a few drops of a solution of caustic soda, 
 and boU the liquid. The gaseous ammonia can be detected by its odor. 
 If in any case the ammonia evolved be in so smaU. a quantity that its 
 characteristic smell cannot be detected, it may be recognized by its 
 property of restoring the blue color to reddened litmus-paper (§ 83), 
 and of forming white fumes by contact with a rod moistened with 
 somewhat dilute chlorhydric acid (Exp. 65). The reaction may be 
 formulated as follows : — 
 
 NH.Cl -1- NaHO = NaOl + NH3 + Hfi. 
 
 521. The solution of ammonia gas in water (NH^jH^O) may be 
 regarded as a solution of hydrate of ammonium (NH )H0, com- 
 parable with the solution of caustic soda, NaHO, or caustic potash, 
 KHO. This solution produces, indeed, many of the effects which 
 
CHLOKIDE OF AMMOSrilTM. 439 
 
 the solutions of the caustic alkalies produce ; it neutralizes acids, 
 displaces the oxides of many metals from solutions of their salts, 
 and comhines with fats to form a soap ; it is, in short, a powerful 
 base. 
 
 Exp. 361. — Dissolve a small crystal of alum in 6-8 c. c. of water in 
 a test-tube, and add ammonia-water until the solution, after being 
 well shaken, smeUs strongly of ammonia. A gelatinous precipitate of 
 the hydrate of aluminum wiU appear in the liquid. 
 
 Hxp. 262. — Dissolve about 1 grm. of sulphate of zinc in 6-8 c. c. of 
 water in a test-tube ; add 4 or 5 drops of ammonia- water, and shake 
 up the contents of the tube. A white, translucent precipitate of the 
 hydrate of zinc wiU appear. Pour into the turbid liquid in the tube 
 3 or 4 c. c. more of ammonia- water ; the precipitate will redissolve 
 and the liquid again become clear. The zinc is at first displaced from 
 its position in the sulphate by the group (NH4) ; but the hydrate of 
 zinc thus precipitated is soluble in an excess of ammonia- water. The 
 hydrate of ammonia behaves in this way with not a few salts of 
 metals. 
 
 Ammonium-salts are very numerous ; but only the few which 
 are of present importance in the useful arts wiU be here de- 
 scribed. 
 
 622. Chloride of Ammoniwm (NH^Cl). — This salt, commonly 
 called sal-ammoniac, is found native in many volcanic regions. 
 When nitrogenized animal matter and chloride of sodium are 
 distilled together, this salt sublimes from the mixture ; the com- 
 mercial supply of the salt was formerly obtained from the soot 
 resulting from the incomplete combustion of camel's dung. 
 
 The raw material whence ammonium-salts are now manivfactured 
 is derived from gasworks and boneblack-factories. Goal and bones 
 contain a portion of nitrogen, which, during the process of distillation, 
 is partially converted into ammonia (§ 92) ; this ammonia combines 
 with the carbonic acid and sulphydric acid which are likewise products 
 of the distillation, and these compounds are condensed into a some- 
 what watery liquor, contaminated with tarry and oily matters, from 
 which the ammonium-salts are subsequently extracted. The impure 
 carbonate is converted into chloride by the addition of chlorhydric 
 acid, or of the mother-liquor from saltworks (a liquor containing the 
 chlorides of magnesium and calcium) ; on evaporating the clarified 
 solution, crystals of sal-ammoniac are obtained, but they are generally 
 too dirty for use. They are partly freed from tarry matters by heating 
 them to a temperature a little below their subliming-point, but high 
 
440 STTIPHATE OF AMMONnm. 
 
 enough to drive off tlie tai, and are then ledissolved in water ; this 
 solution, decolorized by being filtered through animal charcoal, is 
 recrystallized ; these crystals are sometimes further purified by sub- 
 limation. 
 
 Chloride of ammonium serves for the preparation of ammonia 
 (Exp. 48), and of carbonate of ammonium. It is somewhat em- 
 ployed in dyeing, and also in certain processes with metals, such 
 as tinning, soldering, and silvering copper and brass, and galva- 
 nizing (zincing) iron. The sublimed salt forms semitransparent, 
 tough, fibrous masses ; it is very soluble in water, and a great 
 reduction of temperature occurs during its solution ; hence it is 
 employed as a refrigerant. Its taste is sharp and acrid. When 
 heated, it sublimes much below redness, without undergoing 
 fusion. 
 
 Exp. 263. — Heat a bit of sal-ammoniax; on a piece of porcelain, and 
 observe the low temperature at which the solid is completely con- 
 verted into vapor. 
 
 Exp. 264. — Place a teaspoonful of powdered chloride of ammonium 
 in the hollow of the hand, and pour upon it two or three teaspoonfuls 
 of water. The cold produced by the solution of the salt wiU be very 
 perceptible. 
 
 523. Sulphate of Ammonium {(WE.^^0^. — If the ammoniacal 
 liquor from gasworks or animal-charcoal factories be neutralized 
 with sulphuric acid, or if it be decomposed by gypsum (sulphate 
 of calcium), the sulphate of ammonium will be obtained. In the 
 latter case, the impure carbonate of ammonium in the liquor, 
 on being filtered through powdered gypsum, yields carbonate of 
 calcium and sulphate of ammonium. Another recent mode of 
 utilizing the ammoniacal liquor of gasworks yields a crude sul- 
 phate of ammonium ; the liquor is suffered to flow down the coke- 
 towers which are now often connected with sulphuric-acid cham- 
 bers (§ 228), and there absorbs all the acid-fumes which escape 
 from the chambers. A crude chloride of ammonium may be pre- 
 pared in a similar way, by substituting ammoniacal liquor for 
 water in the coke-towers of sulphate-of-sodium furnaces (§ 482). 
 The absorbent power of the ammoniacal liquor is, of course, mneh 
 greater than that of water. 
 
 Sulphate of ammonium is colorless, and has a very bitter taste ; 
 it is soluble in twice its weight of cold, and in its own weight of 
 
iniEATE OF AMMONIITM. 441 
 
 boiling water. Its crystaUine form is the same as that of sul- 
 phate of potassium, and the commercial article looks very much 
 like sand, just as the crystals of sulphate of potassium have a 
 superficial resemblance to quartz crystals. It forms a consider- 
 able number of double salts, which are isomorphous with the cor- 
 responding salts of potassium. Sulphate of ammonium is em- 
 ployed in the manufacture of ammonium- alum, as an ingredient 
 of artificial manures, and as a source of other ammonium-salts. 
 
 524. Nitrate of Ammonium {(S'K^'EO^. — The method of pre- 
 paring this salt, and its complete decomposition by heat; have 
 been already described (Exps. 33, 34, and § 91). The salt crys- 
 tallizes in long needles ; it has a pungent taste, is soluble m less 
 than half its weight of boiling water, and in dissolving produces 
 sharp cold. Between 230° and 250° it is decomposed into water 
 and nitrous oxide ; if it be heated hotter, or too rapidly, ammonia, 
 nitric oxide, and nitrite of ammonium (NHJNOj are also formed. 
 Nitrate of ammonium is formed by the action of dilute nitric acid 
 on several metals, especially tin. 
 
 525. Carbonates of Ammonium. — Commercial carbonate of am- 
 monium (sal-volatile) is a white, semitransparent, fibrous sub- 
 stance, with a pungent taste and a strong ammoniacal smell ; it 
 is prepared, on a large scale, by the dry distillation of bones, 
 horn, and other animal matters. The product is purified from 
 empyreumatic substances by repeated sublimation. 
 
 Exp. 265. — Mix thoroughly together 10 grms. of chloride of ammo- 
 nium and 20 grma. of powdered chalk ; heat the mixture in a small 
 evaporating-dish placed upon a sand-bath. When white vapors begin 
 to rise from the hot mass, place a wide-mouthed bottle over the fuming 
 mixture. The white sublimate which collects in the bottle is a car- 
 bonate of ammonium ; chloride of calcium remains in the dish. 
 
 This experiment illustrates a second, and very common, method 
 of preparing the commercial carbonate, which simply consists in 
 heating to redness a mixture of 1 part of chloride, or sulphate, of 
 ammonium and 2 parts of carbonate of calcium. When this 
 commercial carbonate is dissolved in strong ammonia-water at 
 about 30°, a solution is obtained which yields large, transparent, 
 prismatic crystals. These crystals, however, have no stability ; 
 they are rapidly decomposed in the air, giving off water and 
 
442 SULPHIDES OF AMMOIfnjM. 
 
 ammonia. " Sesquioarbonate of ammonia " is the name generally 
 applied to this substance — a name deduced from the dualistic 
 formula 2(N'E^\0,3C0^. The commercial carbonate approxi- 
 mates to the composition represented by this formula ; but it is 
 an impure product, and, when exposed to the air, changes gra- 
 dually into a more stable compoTind, the carbonate of ammonium 
 and hydrogen, or " bicarbonate " (NH^)HC03. 
 
 This bicarbonate may be obtained by saturating the solution of 
 ammonia, or sesquicarbonate of ammonium, with carbonic acid ; 
 it forms large, transparent, prismatic crystals. When exposed to 
 the air, it slowly volatUizes, giving off a slight ammoniacal odor. 
 At the ordinary temperature, it is soluble in 8 parts of water ; 
 this solution, if heated above 36°, evolves carbonic acid. Even 
 at the ordinary temperature, the solution gradually becomes 
 ammoniacal on keeping. White crystalline masses of this bicar- 
 bonate have been found in guano deposits. It seems to be the 
 most stable of the carbonates of ammonium ; for the other carbo- 
 nates change into it if left to themselves. 
 
 526. Sulphides of Ammonium. — At a temperature of — 18°, 
 two volumes of ammonia-gas combine with one volume of sul- 
 phydric acid gas to form a crystalline unstable substance, of 
 strong alkaline reaction, which corresponds in composition with 
 the sulphides Na^S and K^S. 
 
 2NH, + H,S = (NH,),S. 
 
 Exp. 266. — Pass a slow stream of washed sulphydric acid through 
 100 c. c. of strong ammonia-water, until the solution has a predomi- 
 nating and persistent odor of sulphuretted hydrogen. This solution is 
 at first colorless, and contains a sulphide of ammonium and hydrogen 
 (NH4)HS; but when kept in contact with air it becomes yellow, 
 owing to the formation of a higher sulphide of ammonium. The solu- 
 tion has the property of dissolving many of the sulphides of the metals, 
 by forming with them double sulphides, and is a very useful reagent 
 in the analytical laboratory. 
 
 The higher sulphides of ammonium are obscure bodies, to 
 which the following formulsB have been assigned, — (NH ) S , 
 (NHJ^S3, (KEJP,, (NHJ,S„ (NHJ^S,. With the exception of 
 the last, the septisulphide, all these sulphides are soluble in 
 water. With the same exception, they correspond with the sul- 
 
LiTErrirM. 443 
 
 phides of sodium and potassium. They are in general unstable ; 
 the most permanent is the septisulphide, which forms ruby-red 
 crystals, capable of resisting temperatures below 300°, and only 
 slowly, decomposable by water and chlorhydric acid. 
 
 CHAPTER XXVI. 
 
 1 1 T H it; m — ^R ir B I D I tr ir — c iE s itt m — t h a i l itj m. 
 
 SPECTEUM ANALYSIS. 
 
 527. Lithium (Li). — This rare metal occurs as a constituent 
 of not a few minerals, especially micas and feldspars, but does 
 not form a large percentage of any of them. The minerals lepi- 
 dolite, triphylline, and petalite "usually contain from 3-5 to 5 per 
 cent, of lithium, and are the chief sources of the element. In 
 much smaller proportion, it has been recognized in sea-water, 
 mineral waters, and almost aU spring-waters, in milk, tobacco, 
 and human blood. It is therefore a widely difiused, but not 
 abundant, substance. The metal, which is obtained by decom- 
 posing the fused chloride by the galvanic current, has the color 
 and lustre of silver on a freshly cut surface, but quickly tarnishes 
 on exposure to the air. It is harder and less fusible than sodium 
 and potassium, but softer than lead ; it may be welded, by pres- 
 sure, at ordinary temperatures. It floats on naphtha, and is the 
 lightest of all known solids which include no air, its specific 
 gravity being only 0-59. The atomic weight of the element is 
 also low, namely 7. 
 
 In its chemical relations, lithium closely resembles sodium and 
 potassium, but is somewhat less energetic ; it combines with the 
 same elements to form analogous compounds to those of sodium 
 and potassium ; but the properties of these compounds, while pre- 
 senting a striking general resemblance to those of the sodium and 
 potassium compounds, nevertheless offer some special points of 
 divergence from them. Thus, the hydrate of lithium (LiHO) 
 
444 
 
 SPECTEXTM AITALTSIS. 
 
 has the same taste, causticity, and alkalinity as the hydrates of 
 sodium and potassium, hut is much less soluhle ia water. The 
 fused hydrate attacks platinum more energetically than, caustic 
 soda and potash do. The carbonate and phosphate of lithium are 
 rather sparingly soluble in water, while the corresponding sodium 
 and potassium-salts are exceedingly soluble. The chloride of 
 lithium (LiCl), produced when lithium burns ia chlorine, or 
 when the hydrate or carbonate of lithium is dissolved in chlor- 
 hydric acid, crystallizes in cubes, and has the taste of common 
 salt ; but it is more volatile than the chloride of potassium, and" it 
 deliquesces faster than any other known salt, whereas the chlo- 
 rides of sodium and potassium are almost permanent when pure. 
 All the volatile lithium-compounds color a gas-, alcohol-, or blow- 
 pipe-flame carmine-red. The most delicate reaction for the de- 
 tection of lithium, the test which has revealed its existence in a 
 great variety of substances which were never imagined to con- 
 tain it, is the presence of one bright line, of a peculiar red, in the 
 spectrum seen on looking through a glass prism at a flame 
 colored with a lithium compound. 
 
 528. Spectrum Analysis. — ;We have had occasion to observe 
 that certain chemical substances, like boraeic acid and salts of 
 sodium, potassium, and lithium, impart peculiar colors to the 
 blowpipe-flame, or to any other hot and colorless flame. If 
 these colored flames are looked at through a prism, a narrow 
 pencil of the colored Ught beiag directed through a slit upon 
 the prism, it will be seen that each different flame produces a 
 peculiar spectrum, consisting of one or more distinct bright lines 
 of colored light, and bearing no resemblance to the continuous 
 band of rainbow-colors which constitutes the common spectrum 
 produced by a pencil from any source of white Ught. Thus the 
 spectrum of the yellow sodium-flame consists of a single, bright, 
 yellow line ; the purple potassium-flame gives a spectrum con- 
 taining two bright lines, one lying at the extreme red and the 
 other at the extreme violet end, and a second, fainter red line ; 
 while the Hthium spectrum consists of a very characteiistio red 
 line and a fainter orange line. 
 
 These peculiar Hues which characterize the spectrum of any 
 element are invariably produced by that element, and never by 
 
SPECTETJM ANAITSIS. 445 
 
 any other substance, and not only the color and number of lines, 
 but their position in the normal spectrum always remains unaltered. 
 When the spectrum of a flame colored with a mixture of sodium 
 and potassium salts is examined, the yellow line of sodium is 
 seen in its place, and the red and purple Hues of potassium are 
 as visible in their respective positions as if no sodium had been 
 present. This example illustrates one great advantage which 
 the use of the prism gives, — ^the unaided eye cannot distinguish 
 the potassium color in the presence of the intense sodium- 
 yeUow, the brighter color hiding the paler ; but with the prism 
 it is easy to detect each of several ingredients of a mixture by 
 the appearance of its characteristic lines. Now, every elemen- 
 tary substance, whether metallic or non-metaUic, soHd, liquid, or 
 gaseous, when heated to the point at which its vapor becomes 
 luminous, emits a peculiar light produced by it alone, and the 
 bright lines of the spectrum of this Hghf are characteristic of this 
 element in number, color, and position. Many metals require 
 a much higher temperature than that of the common gas-flame 
 to convert them into luminous vapors; but by the use of the 
 electric lamp all the metals, even gold, silver, and platinum, may 
 be made to yield peculiar spectra. The permanent gases also 
 give characteristic spectra when they are heated by the passage 
 of the electric spark; the spectrum of hydrogen, for example, 
 consists of one red, one green, and one blue line. 
 
 A new method of analysis, of extreme delicacy, is based upon 
 these facts. Spectrum analysis is competent to detect the 
 Sfaao'^ooooo^ of a gramme of sodium, or the j^ny^m °^ » 
 gramme of lithium, and many other elements in incredibly small 
 proportions. So extreme is the delicacy of the method that it 
 brings into plain sight minute quantities which altogether escape 
 the coarser process of analysis, and reveals, as substances com- 
 mon in familiar things, elements which were long supposed to be 
 of extreme rarity. Thus the presence of lithium, formerly con- 
 sidered a rare element peculiar to a few obscure minerals, has 
 been demonstrated by spectrum analysis in many drinking-waters, 
 in tea, tobacco, mUk, and blood. A stiU more striking illustra- 
 tion of the value of spectrum analysis is to be found in the dis- 
 covery of four new elementary bodies by its means. 
 
446 ETTBIBIUM AND CJSSITJM. 
 
 529. Two new elements wMoh closely resemble sodium and 
 potassium, and are in nature associated with these alkali-metals, 
 have been found in certain mineral waters, and in the mineral 
 lepidohte. One of these elements gives a spectrum containing, 
 among others of less mark, a superb, double, red line, and has 
 thence been called Buhidium ; the other produces a spectrum 
 characterized by two beautiful blue lines, and has thence been 
 called Caesium. These two new metals resemble potassium so 
 closely in all their chemical properties, that it would have been 
 nearly impossible to detect them by the common analytical pro- 
 cesses ; yet their spectra are in the highest degree characteristic, 
 exhibiting bright bands which exist neither in the potassium 
 spectrum nor in any other known spectrum. The recently dis- 
 covered metal Thallium was discovered and traced to its source 
 in certain kinds of pyrites by observing a splendid green line 
 which did not belong to any known substance. The new metal 
 Indium was also detected, traced to its source in certain zinc 
 ores, and successfully isolated, by the help of a dark-blue line 
 which had not been previously observed. 
 
 The methods and processes of spectrum analysis are not appli- 
 cable to colored artificial lights alone ; they have been applied 
 with encouraging success to the lights of various quality which 
 emanate from the sun, the stars, and the nebulae ; but the details 
 of these observations belong rather to physics than to chemistry. 
 
 530. Rubidium and Cmsium (Kb and Cs). — These two elements 
 are always found together, and in association with potassium. 
 Though extensively diffused, they generally occur in very minute 
 quantities. Eubidium seems to be rather the most abundant. 
 Ten kilogrammes of the mineral water in which these metals 
 were first discovered jdeld not quite two milligrammes of chloride 
 of csesium, and about two and a half milligrammes of chloride of 
 rubidium. Since the original discovery of the elements, they 
 have been found in many other springs, in several kinds of mica 
 and in other silicates, and in the ashes of beet-root, tobacco, coffee, 
 and grapes. To separate the metals from potassium the analyst 
 reHes on the greater insolubOity of the double chlorides which 
 they form with platinum ; if a mixture of the chlorides of potas- 
 sium, rubidium, and csesium be completely precipitated by chlo- 
 
THAlLItTM. 447 
 
 ride of platinum, and the yellow precipitate be repeatedly treated 
 "with boiling water, the insoluble residue will contain the new 
 metals. The caesium is separated from the rubidium by convert- 
 ing a mixture of their carbonates into their tartrates, the rubi- 
 dium into the acid, or bitartrate, the csesium iato the neutral 
 tartrate, and then exposing this mixture to very moist air. The 
 neutral tartrate of csesium deliquesces, the acid tartrate of rubi- 
 dium remains solid, and the two salts are separated by filtration. 
 Most of the salts of rubidium and caesium are isomorphous with 
 the corresponding potassium-salts. Their hydrates, EbHO and 
 CsHO, are caustic alkalies, soluble in water and alcohol. Their 
 carbonates are fusible, deliquescent, and strongly alkaline ; the 
 nitrates (EbNO, and CsNO^) and sulphates (Kb.SO^ and Cs.SOJ 
 are anhydrous crystalline salts, soluble in water ; the sulphates 
 form alums with sulphate of aluminum. The chloride of csesium, 
 CsCl, is a deliquescent salt, like chloride of lithium ; the chloride 
 of rubidium, EbCl, is permanent, like the chlorides of sodium and 
 potassium. The fused chlorides are easily decomposed by the 
 galvanic current. 
 
 The metal rubidium is white, and has the brilliant lustre of 
 silver, but it rapidly oxidizes in the air; its specific gravity is 
 1-52, and its atomic weight 85-7, It may be prepared either by 
 the electrolysis of its chloride, or, like potassium, by the reduc- 
 tion of its carbonate by ignition with carbon and chalk. 
 
 The properties of csesium have only been studied in the amal- 
 gam with mercury resulting from the electrolysis of its chloride ; 
 the metal itself has not been isolated. Its atomic weight, de- 
 duced from the analysis of its chloride, is 1-33. There can be no 
 question that the properties of both rubidium and csesium differ 
 from those of sodium and potassium not in kind, but only in 
 degree. They are therefore classed with sodium and potassium 
 as alkali-metals. 
 
 531. Thallium (Tl). — This metal was discovered, by means of 
 spectrum analysis, in Lipari sulphur and in the deposit in the flue 
 of a pyrites-burner — a furnace in which iron pyrites are roasted 
 for the sake of the sulphurous acid they yield. The element is 
 found to occur in not inconsiderable quantities in many specimens 
 of iron pyrites, and appears to take the place of arsenic, which is 
 
448 SILTEE. 
 
 a common impurity of this mineral. Thallium presents the ex- 
 ternal characters of lead ; it is heavier than lead, having a specific 
 gravity of 11-85, and it is so soft that the thumb-nail can indent 
 it; it is very malleable, and ductile enough to be drawn into 
 wire ; it melts at 200° and volatilizes at redness ; its freshly cut 
 surface has a bluish-white lustre ; but it quickly tarnishes and is 
 gradually oxidized in the air, so that it is best preserved under 
 water. Water is not decomposed by it even at 100°. "When 
 strongly heated in oxygen, it takes fire and bums with a bright 
 green flame. 
 
 Thallium dissolves in dilute acids, with evolution of hydrogen. 
 There are several oxides of this metal, of which the most impor- 
 tant is the oxide Tl^O, corresponding in composition, and, to some 
 extent, in properties, with the oxide of sodium Na^O. This oxide 
 is somewhat soluble in water, and yields a caustic alkaline solu- 
 tion, which absorbs carbonic acid from the air, and forms a weU- 
 defined series of salts. The sulphate, Tl^SO^, is a soluble salt, 
 which forms an alum with sulphate of aluminum ; the chloride, 
 TlCl, is only slightly soluble in water, resembling, in this respect, 
 the chloride of lead, and being quite unlike the soluble chlorides 
 of sodium, potassium, rubidium, and csesium. The carbonate of 
 thallium is a soluble salt ; but the sulphide of thallium, Tl^S, is 
 an insoluble black powder, which resembles the sulphide of lead, 
 but is entirely unlike the sulphides of the alkali-metals. The 
 soluble salts of thaUium are very poisonous. In general, the 
 properties of thallium are intermediate between those of lead and 
 those of sodium and potassium. Like the aJkaU-metals, it replaces 
 hydrogen atom for atom ; its atomic weight is 204. 
 
 CHAPTEE XXVII. 
 
 S r L V B E T HE A L K A L I-M E T A I, S Q TJANTIVAIElfCE. 
 
 532. Silver is a widely diffused and quite abundant element, 
 but in its mode of occurrence it differs widely from the alkali- 
 metals which we have just been studying. In the first place, it 
 
OCClmEENCE OF SHVEE, 449 
 
 frequently occurs native, both pure and alloyed with mercury, 
 copper, and gold, — a mode of occurrence quite impossible for the 
 alkali-metals, because of their readiness to combine with the ele- 
 ments of air and water. Native silver is found ia various forms, 
 sometimes crystallized in cubes or octahedrons, sometimes in 
 filaments, both coarse and fine, and sometimes in shapeless masses. 
 The metal more commonly occurs m combination with sulphur, 
 mixed with sulphides of lead, antimony, copper, and iron. It is 
 from argentiferous sulphides that the larger part of the silver of 
 commerce is extracted; among ores of this kind the argenti- 
 ferous sulphide of lead (galena) is the most abundant. Combi- 
 nations of silver with selenium, tellurium, chlorine, bromine, and 
 iodine are also to be enumerated among sUver- containing minerals ; 
 of these the chloride (hom-sUver) occurs in quantities large 
 enough to make it valuable as an ore of the metal. It is notice- 
 able that the only elements which are extracted in any quantity 
 from their chlorides as ores are sodium, potassium, and silver. 
 The chlorides of copper, mercury, and lead do, indeed, occur as 
 natural mmerals ; but as sources of those metals they have no 
 significance. A small proportion of silver exists in sea-water 
 (about 1 milligramme in 100 litres), and its presence has been 
 recognized in common salt, in chemical products in the making 
 of which salt is used, in various sea-weeds, in the ashes of land- 
 plants, in the ash of ox-blood, and probably also in coal. In sea- 
 water it exists, as sodium and potassium do, in the form of chloride. 
 
 When silver is extracted from argentiferous sulphide of lead, the ore 
 is first treated for lead, precisely as it would be if it contained no silver. 
 The lead, so reduced, contains all the silver originally present in the 
 quantity of ore treated. The subsequent separation of the metallic 
 silver from the metallic lead depends upon the chemical properties of 
 lead rather than of silver, for the silver remains unaltered during the 
 whole process ; this separation will therefore be described in the next 
 chapter. 
 
 The mixed sulphides which contain silver have been heretofore ge- 
 nerally reduced by a complicated process which depends ultimately on 
 an amalgamation of the silver with mercury. The ore, after thorougli 
 washing and grinding, is mixed with a portion of common salt, and 
 roasted for several hours ; dming this roasting, white fumes of arsenious 
 and antimonious acids are expelled, the sulphides of copper and iron 
 
 2& 
 
450 EXTEACTION OF SILTBB. 
 
 are partially converted into oxides, chlorides, and sulphates, and chlo- 
 ride of silver and sulphate of sodium are formed. The roasted product 
 is then reduced to a very fine powder, and agitated in revolving casks 
 with water and iron filings, or scraps, to which mercury is soon added. 
 This operation lasts about 20 hours ; during it, the iron decomposes the 
 chloride of silver, and the mercury dissolves the silver to an amalgam ; 
 from this amalgam the excess of mercury is first squeezed out through 
 leather or cloth filters, and the remainder is driven off by distillation. 
 The residual spongy mass is silver, alloyed with a variable proportion 
 of copper, derived from the ore and reduced to the metallic state by 
 the same steps which have reduced the silver. 
 
 This process is European ; the process of amalgamation as practised 
 in Mexico and South America is quite diifereut, and the reactions which 
 it depends upon are somewhat obscure. The ore is not roasted, but, 
 after being ground to powder, moistened Vidth water, and mixed with 
 from 1 to 5 per cent, of common salt, it is sufiered to lie undisturbed 
 for some days. From 5 to 1 per cent, of roasted copper pyrites is then 
 added, together with a considerable proportion of metallic mercury, 
 and the mass is worked together and commingled by the trampling of 
 mules or horses. After an interval of two or three weeks, a second 
 dose of mercury is given, and after a stiU longer interval 5, third. By 
 this last addition, a fluid amalgam is obtained, which is separated by 
 washing and filtering, and distilled for the recovery of a portion of the 
 mercury employed, and the isolation of the silver. In this process 
 there is a great waste of mercury, because much of it is converted into 
 a chloride of mercury (calomel) and lost. The recommendations of 
 the process are mainly these — that it requires no fuel, except for the 
 distiUation of the amalgam, and that it leaves the silver in a condition 
 of great purity. The whole process, though far from economical from 
 the point of view of the theoretical chemist, was doubtless a legitimate 
 outgrowth of the conditions under which it took birth. 
 
 Various processes have been patented for the extraction of silver 
 without the use of the costly merciuy, some of which have been suc- 
 cessfully practised on a large scale. They depend, for the most part, 
 either on the comparative stability, in the fire, of sulphate of silver 
 when once formed, as compared with the sulphates of ii'on and copper, 
 and the consequent possibility of dissolving sulphate of silver out of the 
 roasted ore, or upon the fact that the chloride of silver, which results 
 from the roasting of the ore with chloride of sodium, may be dissolved 
 in solutions of the alkaline chlorides, and, indeed, in aqueous solutions 
 of a great many other soluble salts, though it is by itself insoluble in 
 water. Any aqueous solution containing, among other things, a silver- 
 
IHE TEEM MBTAl. 451 
 
 salt (wtether in the condition of ehloride, sulphate, or nitrate is indif- 
 ferent) may be decomposed by digestion with metallic copper; the 
 silver-salt will be decomposed, the corresponding copper-salt formed 
 and dissolved, and the metallic silver will be precipitated. 
 
 533. Silver (Ag). — The element, silver, is much more familiarly 
 known than any of its compounds ; known from the earliest ages, 
 this metal has always been prized as much for its beauty as for 
 its rarity. White, brilliantly lustrous, susceptible of an admirable 
 polish, wonderfully malleable and ductile, the best known con- 
 ductor of heat and electricity, fusible only at a very elevated 
 temperature and permanent in the air, whether hot or cold, wet 
 or dry, it represents and embodies in the completest sense all that 
 is commonly understood by the term metal. 
 
 This word metal cannot be strictly defined ; it is a conventional 
 term, vaguely used because expressing a vague idea. Thus 
 metals would all be solid were not mercury, and perhaps caesium, 
 fluid ; they are generally heavy > but lithium, sodium, and potas- 
 sium float upon water ; they have all a peculiar lustre, called 
 metallic ; but this lustre does not characterize metals alone, for 
 coke and graphite, galena, molybdenite, and many other minerals 
 often exhibit a similar lustre ; they may all be said to be opaque ; 
 but gold may be beaten out so tmn as to transmit a gTeenish 
 light. While it is not possible to define the term metal with 
 precision from chemical any more than from physical properties, 
 one general chemical fact deserves attention in this connexion. 
 We have seen that bodies which contain a large proportion of 
 oxygen, such as SO3, P^Oj, N^Oj, and CO^, have a common ten- 
 dency to unite with other bodies which are alike in that they 
 contain a much smaller proportion of oxygen, such as Kfi, Na^O, 
 PbO, and CaO, to form more or less stable saline substances. The 
 first class of bodies, which are usually rich in oxygen, have been 
 called acids ; the second class, which are usually poor in oxygen, 
 have been designated collectively as bases. Now those elements 
 which unite with oxygen to form acids alone are, as a rule, non- 
 metallic, and those elements which unite with oxygen to form 
 bases are, in the chemical sense of the term, the metals ; but no 
 sharp line of division between metallic and non-metaLic elements 
 can be established on this principle, inasmuch as some elements 
 
 2g2 
 
4S2 PROPEETIBS OF SUTEB. 
 
 wliich possess the other characteristics of a metal form no hasic 
 oxide, while some metals, like antimony, form oxides which are 
 at one time bases and at another time acids. The metal arsenic, 
 for example, forms no hasic oxide ; and we shall hereafter meet 
 with another iUnstration of the same difficulty of classification, in 
 the element tungsten. 
 
 Melted silver possesses the curious property of absorbing a 
 large volume of oxygen (twenty-two times its bulk), from the 
 air, while it is liquid. This gas it gives out again on solidifying. 
 When a globule of molten silver is cooled suddenly, the filin of 
 soUd metal which forms upon its surface is burst open by the 
 escaping gas, and the liquid silver within is apt to be projected 
 outwards with the gas ; this phenomenon is called spitting ; it 
 often occasions a loss in silver assays. When heated on lime 
 before the oxyhydrogen blowpipe, silver gives off vapors which 
 become oxidized if the blast of gas contain an excess of oxygen ; 
 a fine silver wire is dispersed in greenish vapors when a very 
 powerful electric discharge is sent through it. Silver combines 
 slowly with chlorine, bromine, and iodine, and promptly with 
 sulphur. The tarnishing of silver is due to the formation of a 
 thin film of the black sulphide over the metaUic surface, by com- 
 bination between the silver and the sulphur of the sulphuretted 
 hydrogen which is often present in the air of towns and houses. 
 
 The best solvent for silver is nitric acid diluted with two or 
 three parts of water ; nitric oxide is evolved, and nitrate of sUver 
 remains in solution : — 
 
 3Ag + 4HITO3 = SAgNO, + NO -I- 2H,0. 
 Chlorhydric acid acts upon it but slowly ; for the chloride of sUver 
 is but slightly soluble in chlorhydric acid, whether strong or 
 dilute. Boiling sulphuric acid dissolves silver, and forms the 
 sulphate, sulphurous acid being evolved during the reaction :— 
 
 2Ag -1- 2H,S0, = Ag^SO, + 2H,0 -t- SO,. 
 Neither the alkalies nor their nitrates have much effect on silver, 
 whether they are in solution or are fused by heat ; hence a silver 
 dish is used in concentrating the caustic alkalies, and a silver 
 crucible for fusing refractory minerals with the hydrate of sodium 
 or potassium. The specific gravity of silver is 10-5, and its atomic 
 ■weight 108. 
 
SILTEK COIN. 453 
 
 534. The physical and chemical qualities of silver fit it to serve 
 as a medium of exchange, and as the material of jewellery and 
 plate. But as the pure metal vfould be rather too soft for ordi- 
 nary use, it is hardened by combining with it a small proportion 
 of copper. The proportion of copper in the " standard " silver 
 employed for coinage varies in different countries. In the United 
 States and in France it is 10 per cent. ; in Great Britain it is 7*5 
 per cent. ; in Germany it is 25 per cent. 
 
 Hxp. 267. — Place one or two dimes in a small flask, and cover them 
 with nitric acid diluted with two parts of water. Warm the flask 
 gently in a place where there is a good draught of air ; the coins will 
 gradually dissolve, with evolution of nitric oxide, which, on contact 
 with the air, produces the abundant red fumes which escape from the 
 flask ; add more nitric acid, from time to time, if necessary to com- 
 plete the solution. The blue solution contains both the silver and the 
 copper dissolved in nitric acid. 
 
 Place in the blue solution two or three copper cents, and leave the 
 flask at rest for some days in a warm place. Then collect the little 
 plates of pure silver, which have separated from the solution,, upon a 
 filter, and wash them, first with water, and then with ammonia-water, 
 until the ammonia-water no longer shows any tinge of blue.. This 
 silver, washed finally with water and dried, is well nigh pure ; two- 
 thirds of it may be again dissolved in nitric acid; the solution will 
 contain piu-e nitrate of silver. 
 
 535. Nitrate of Silver (A.gNO^). — This salt, as we have already 
 seen, is obtained in solution by dissolving silver in nitric acid. 
 When such a solution is evaporated to the point of crystallization, 
 the nitrate is obtained in transparent, anhydrous, tabular crystals, 
 which are soluble in their own weight of cold water, and in half 
 their weight of hot water. The salt fuses easily, and when cast 
 into cylindrical sticks is used in surgery as a caustic, under the 
 name of lunar caustic. 
 
 Nitrate of silver, when pure, is not altered by exposure to sun- 
 light ; but if it be in contact with organic matter, light readily 
 decomposes it, and a black, insoluble product is formed of no 
 ordinary stability. Hence the solution of the nitrate stains the 
 skin black, and the salt forms the basis of an indelible ink used 
 for marking linen and other fabrics. 
 
 Hxp. 268. — Dissolve 8 grms. of crystallized carbonate of sodium and 
 
454 
 
 NITRATE OF SILVER. 
 
 1 grm. of gum-arabic in 16 c. c. of hot water. Moisten a bit of linen 
 or cotton-cloth vrith this preparatory solution, dry it, and press it 
 smooth -with a hot iron. 
 
 Dissolve 1 grm. of nitrate of silver and 0-1 grm. of gum-arabic in 
 1'75 c. c. of water, previously colored with India-ink. 
 
 Write with this silver solution upon the prepared surface of cloth, 
 and expose the writing to the direct rays of the sun for a few hours. 
 Then wash out the gum and carbonate of sodium with water ; a very 
 durable mark, which neither soap nor '' soda " will obliterate, wiU 
 remain on the cloth. 
 
 Nitrate of silver is even more completely decomposed by a red 
 beat than nitrate of potassium, for nothing but metaUic silver 
 remains behind ; in decomposing, it gives up a large quantity of 
 oxygen ; hence mixtures of combustibles, like sulphur, phos- 
 phorus, and charcoal, with nitrate of silver, detonate, explode, or 
 deflagrate when struck sharply with a hammer or touched with 
 a hot wire. (Compare §§ 515, 516.) Phosphorus, mercnry, char- 
 coal, grape-sugar, certain essential oils, and many other organic 
 substances reduce metallic silver -from solutions of nitrate of 
 silver. Nitrate of silver is the material from which most other 
 silver compounds are artificially prepared. It is largely con- 
 sumed in photography. 
 
 The precipitation of metallic silver in a beautiful arborescent form 
 is accomplished as follows : — Dissolve 2 grms. of nitrate of silver in 
 60 c. c. of water, and place the solution in a test-glass ; pour 2 grms. 
 of mercury into the liquid, and let the glass stand at rest for several 
 hours. The nitrate of silver may he recovered by dissolving the pre- 
 cipitated silver in nitric acid, and evaporating the solution. 
 
 To illustrate the decomposition of a silver solution by an organic 
 substance, dissolve 2 grms. of nitrate of silver in 60 c. c. of water, and 
 immerse in the solution a horn or ivory paper-knife, which has been 
 cleansed from grease with ammonia-water and rinsed in fresh water. 
 Let the knife remain in the solution about an hour ; it will turn yel- 
 low ; take it out, rinse it in water, and expose it to the direct rays of 
 the sun until it turns jet black ; then burnish it with a piece of leather, 
 and the silver will appear in the metallic state. 
 
 Exp. 269.— Wrap a piece of phosphorus, no bigger than a pin's 
 head, with a small crystal of nitrate of silver, in a bit of paper ; place 
 the packet on an anvil and strike it with a hammer. The explosion 
 will be sharp. The student will remember that nitrate of silver stains 
 the fingers. 
 
OXIDES OF SILTEB nrXMIirATrNG SILTEH. 455 
 
 £xp. 270. — ^Mix 1 grm. of powdered nitrate of silver with 0-2 grm. 
 of dry, powdered charcoal ; place the mixture on a piece of porcelain, 
 and touch it with a red-hot wire. The mixture deflagrates, and there 
 remains behind metallic silver. 
 
 -Ezp. 271. — Add to a solution of nitrate of silver a solution of caustic 
 soda, until no further precipitate is produced. The brownish precipi- 
 tate is a hydrated oxide of silver. 
 
 536. Oxides of Silver. — Silver probably forms three oxides, 
 Ag^O, AgjO, and Ag^O^. The first is a very unstable black 
 powder; the second forms with acids the ordinary silver salts; 
 the third is a crystalline body obtained by electrolysis of nitrate 
 of silver. The precipitate obtained in the last experiment is 
 the hydrate of the oxide Ag^O ; this precipitate readily parts 
 with its water, and at a temperature much below 100° becomes 
 anhydrous. Unlike the oxides of sodium and potassium, this 
 oxide of silver yields up its oxygen below a red heat, and 
 metallic silver remains — as may be demonstrated by heating the 
 product of the last experiment ; light also reduces it, and hydro- 
 gen even at 100° has the same effect. Oxide of silver bears, 
 however, certain striking resemblances to the oxides of the 
 alkali-metals ; thus it is a strong base, uniting with strong acids 
 to form salts which are neutral to test-paper, and which are in 
 some cases isomorphous with the corresponding salts of sodium. 
 The oxide is slightly soluble in water, and the solution has a 
 feeble alkaline reaction. 
 
 The oxide is freely soluble in ammonia- water, and the solution 
 deposits, on exposure to the air, a black, micaceous powder which 
 has received the name ot fulminating silver, because of its explo- 
 sive character. The same dangerous compound is formed when 
 freshly precipitated oxide of silver is digested for some hours in 
 ammonia- water, and it is also produced when an ammoniacal 
 solution of chloride or nitrate of silver is precipitated with a 
 solution of hydrate of sodium or potassium. It is necessary to 
 be aware of these facts in order to avoid the risk of producing by 
 accident this exceedingly dangerous substance. Its composition 
 is not accurately known. Friction or slight pressure, even under 
 water, may cause it to explode. The student should never 
 venture to prepare this substance. 
 
456 PHOTOGKAPHT DAQUEBKBOTTPE. 
 
 JSxp. 272.— Fill three test-tubes one-third full of water, and pour 
 into each a few drops of a moderately strong solution of nitrate ot 
 silver. Add to the first test-tube 2 or 3 c. c. of a solution of chloride 
 of sodium, and shake the tube violently ; a dense, white, curdy preci- 
 pitate of the chloride of silver will be produced. Add to the second 
 test-tube 2 or 3 c. c. of a solution of bromide of potassium, and shake 
 the tube ; a yellowish precipitate of bromide of silver will be thrown 
 down. Add to the third teat-tube 1 or 2 c. c. of a solution of iodide 
 of potassium, and shake up the liquid ; a pale-yeUow flocculent deposit 
 of iodide of sUver will be formed. 
 
 Withdraw from each test-tube a portion of the precipitate it con- 
 tains, and try to dissolve each precipitate in strong nitric and chlor- 
 hydric acids ; the attempt will fail, for these silver salts are insoluble 
 in acids. 
 
 Withdraw from each teat-tube another portion of the precipitate it 
 contains, and treat each precipitate with ammonia- water ; the chlo- 
 ride of silver will dissolve easily, the bromide less easily, the iodide 
 vrith difficulty. Lastly, pour upon the remnants of the original pre- 
 cipitates in the three test-tubes a moderately strong solution of hy- 
 posulphite of sodium (§ 495) ; all three precipitates wiU immediately 
 dissolve. 
 
 Uxp. 273. — Precipitate some curdy chloride of silver by adding 
 chloride-of-"sodium solution, or chlorhydric acid, to a solution of nitrate 
 of silver, so long as any precipitate' is produced. Throw the precipi- 
 tate upon a filter, and wash it with water ; then open the filter, spread 
 the chloride evenly over it, and place it in direct sunlight. The white 
 precipitate rapidly changes to violet on exposure to the sun's rays, the 
 depth of shade increasing as the action of the light continues. This 
 coloration arises from a partial decomposition of the chloride of silver, 
 the change of color being accompanied by a loss of chlorine. Upon 
 the facts illusti-ated in this and the preceding experiments the main 
 processes of photography depend. 
 
 537. Photography.— The chemical changes which the salts of 
 silver undergo, when exposed to light, are the basis of the art of 
 photography — not because these are the only salts which are 
 affected by light, but because none are so advantageous on the 
 whole. There are three different kinds of photographic process 
 — that on silver, that on glass, and that on paper. 
 
 To produce a photograph on silver (a daguerreotype), a highly 
 polished silver plate is exposed in a dark box to the diluted 
 vapor of a mixture of bromine and iodine. A bronze-yeUow film 
 
PHOTOGRAPHY ON GLASS. 457 
 
 of brom-iodide of silver is thus produced upon the plate, -which, 
 at a certain stage, possesses a high degree of sensitiveness to 
 light. The plate is then transferred to a camera, and exposed 
 at the focus of the lens to the light radiated from the object to be 
 copied. After remaining a few seconds in the camera, it is with- 
 drawn, and immediately exposed in a warm box to the vapor of 
 metallic mercury. When the plate is taken from the camera, the 
 film looks as uniform as ever, and no image is visible upon it ; 
 but the exposure to mercury vapor immediately brings out an 
 image. The mercury fixes itself strongly upon those parts which 
 have received the light, while it takes no hold upon those parts 
 of the film which the light has not decomposed. A strong solu- 
 tion of hyposulphite of sodium is then poured over the plate, in 
 order to dissolve off the undecomposed brom-iodide. The highly 
 polished sUver, beneath, forms the shades, and the amalgam of 
 mercury with silver forms the lights. The plate is washed, and 
 a very dilute solution of chloride of gold in hyposulphite of sodium 
 is poured over its surface and gently warmed. A thin film of 
 gold, which, as it were, varnishes the picture, is thus deposited 
 upon the plate ; another washing completes the operation. The 
 daguerreotype is the most perfect of photographs ; but the poUsh 
 of the surface prevents the image from being- seen in all lights, 
 and the plate is liable to be tarnished and ruined by sulphuretted 
 gases. 
 
 In order to get a photograph upon glass, a transparent film 
 capable of holding the necessary silver-salt must first be attached 
 to the glass plate. Collodion (a solution of a variety of gun- 
 cotton in a mixture of alcohol) and ether is the material of this 
 film. To the collodion is added a solution of an iodide, either of 
 potassium, cadmium, or ammonium, or a mixture of these ; the 
 bromides of ammonium and cadmium, or one of them, added 
 in the proportion of one part of the bromides to three or four of 
 the iodides, render the film more sensitive to yellow and red rays 
 — a point of importance in cloudy weather or smoky towns. The 
 collodion thus prepared is poured rapidly over a clean and dry 
 surface of plate-glass ; the volatile solvents evaporate rapidly, 
 and as soon as the film is coherent the glass is plunged into a 
 bath of nitrate of silver very slightly acidified with acetic or dilute 
 
458 PHOTOGfEAPHT. 
 
 nitric acid. This bath must be in a dark place ; the plate re- 
 mains in it for several minutes. A yeUow layer of iodide or 
 brom-iodide of silver is produced in the film, and nitrate of po- 
 tassium, cadmium, or ammonium dissolves in the bath. The plate 
 is then exposed in the camera for a few seconds. When removed 
 no image is perceptible ; but on pouring over the film a solution of 
 gallic or pyrogaUic acid in alcohol and acetic acid, or a solution 
 of the green sulphate of iron, mixed with a few drops of a weak 
 solution of nitrate of silver, the image wiU be developed, slowly or 
 rapidly, according to the nature and strength of the developing- 
 liquid, the degree of exposure, and the intensity of the light. The 
 illuminated portions of the picture will appear, under the action 
 of the developer, more or less black, while the shaded portions 
 will retain the yellow colour of the iodide. As soon as the de- 
 tails of the shaded portions appear, the liquid is washed off and the 
 development arrested. A saturated solution of hyposulphite of 
 sodium is then poured over the film to dissolve off the yellow io- 
 dide of silver where it has not been affected by the light ; only 
 the reduced portions of silver remain, and they appear more or less 
 opaque. The plate must finally be very thoroughly washed to 
 remove aU traces of the hyposulphite, and then dried and var- 
 nished on the collodion side to protect the film from injury. 
 
 Concerning the nature of the change which a film of iodide of 
 silver undergoes when exposed to light, we cannot be said to have 
 any exact knowledge. There is no perceptible alteration in the 
 film ; there is no loss of iodiue ; the iodide retains its solubility 
 in hjrposulphite of sodium ; yet the impression is not of a tempo- 
 rary kind ; for the invisible image produced on a plate may be 
 developed many hours afterwards, if the plate is kept in the dark 
 during the interval. 
 
 The photograph on collodion may be employed directly as a 
 positive picture, if not too strongly developed, by placing it on a 
 black background. Those portions which are opaque to light, or 
 in other words those in which silver is deposited, wiU reflect light, 
 and furnish the lights of the picture ; while those on which the 
 light did not act, and which are therefore transparent, will appear 
 black from the nature of the background, and these wiU form the 
 shades of the picture. In the daguerreotype the finished picture 
 
PHOTOeiUIHT ON PAPEE. 459 
 
 is inTerted ; in the collodion positive it is not inverted. If the 
 development be pushed further, the image becomes so strongly de- 
 fined that the deposited silver will more or less completely inter- 
 cept the Ught. The collodion side of the plate is then placed in 
 contact with the sensitive side of paper impregnated with chloride 
 of silver by a process immediately to be described, and exposed 
 to Ught in a pressure-frame. The light is arrested by the altered 
 parts of the collodion, but is freely transmitted by the other por- 
 tions ; upon the paper, therefore, the lights of the real object are 
 light and the shades are dark. Such a negative coUodion picture 
 may of course be copied on a second sensitive collodion film. 
 
 Two developing-solutions, used one after the other, produce a 
 better effect than one. The green sulphate of iron may be used 
 first, and pyrogaUic acid with nitrate of silver subsequently ; 
 the iron solution must be completely washed off before the other 
 is added. The picture may even be intensified by pyrogallic acid 
 after the plate has been washed in hyposulphite of sodium. 
 
 Photographs were made on paper long before the film on glass came 
 into use ; but the paper process is now chiefly confined to the printing 
 of positive impressions from coUodion negatives on glass. The silver- 
 salt which is preferred for photographic paper is the chloride, with or 
 without albumen, but always accompanied with fi:ee nitrate of silver. 
 The paper is floated for five minutes on a solution of chloride of sodium 
 or ammonium ; when dried, it is floated in a dark room, for five mi- 
 nutes, on its salted surface, in a solution of nitrate of silver ; again 
 dried, it is fit for use. When such paper is used to obtain a positive 
 impression from a collodion negative, or from a paper negative made 
 transparent with wax or a mixture of wax and parafiine, it is exposed 
 to light imder the negative to be copied, until the lights of the picture 
 are of a pale lilac hue, and the shades of a deep bronze color. After 
 being thoroughly washed, the paper is transferred to a "toning "-bath, 
 which consists of a very dilute solution of bicarbonate of sodium, with 
 a minute proportion of chloride of gold. The picture is kept in mo- 
 tion whUe in this bath ; it remains there until its shades have acquired 
 a deep purple-black color. It is only in those parts of the picture in 
 which the silver has been well reduced that this toning effect is pro- 
 duced. The picture is again washed in water, and soaked for fifteen 
 minutes in a solution of hyposulphite of sodium, in order to remove 
 all the chloride of silver which is contained in the substance of the 
 paper. Finally the picture must be soaked for twenty-four hours in 
 
460 CHLOEIDB or STXTER. 
 
 water which is constantly renewed, in order to wash away every trace 
 of the compound hyposulphite of sodium and silver. No photograph 
 will keep long, unless the chloride of silver has been completely dis- 
 solved by the hyposulphite, and the compound hyposulphite washed 
 away with a thoroughness that leaves no trace behind. If the first 
 condition is not fulfilled, difiiised daylight wiU alter the picture ; if 
 the second condition is not complied with, yellow or brown stains will 
 ultimately destroy the picture. 
 
 As in every other art which embraces many details, and demands a 
 trained eye and hand, eminent skill in photography can, as a rule, be 
 acquired only by long practice. 
 
 538. Chloride of Silver (AgCl). — Native chloride of silver 
 occurs, sometimes in cubical crystals, sometimes in compact 
 semitransparent masses, which are sectile, and, from their ge- 
 neral appearance, have given the mineral the name of horn-silver. 
 Chloride of silver may be precipitated from any soluble silver- 
 salt by adding to the silver solution chlorhydric acid, or the solu- 
 tion of any soluble chloride ; or it may be obtained by passing 
 over a dry silver-salt a stream of dry chlorine gas. This last re- 
 action is the basis of a method of preparing anhydrous nitric acid. 
 When a stream of dry chlorine is made to pass over perfectly 
 dry nitrate of sUver heated to 60° or 60°, the following reaction 
 takes place: — 
 
 Ag,NA + 2C1 = 2AgCl -I- N,0, + 0. 
 
 The characteristics of precipitated chloride of silver have been 
 already described (Exp. 272). The presence of an extraordi- 
 narily minute proportion of chloride of silver renders a clear 
 liquid opalescent. It is easy to detect silver in a solution of 
 which it forms only the goSooo V^^^i ^J" adding to the solution 
 a drop of chlorhydric acid or of a soluble chloride. An admira- 
 ble method of determining the amount of silver present in any 
 solution depends upon the insolubility of chloride of silver, the 
 density and peculiar curdy quality of the precipitate, and the 
 visibility of the smallest trace of it -in a clear fluid. This method, 
 now generally employed in mints and assay-offlces, is applicable 
 to the quantitative analysis of silver alloys ; it is volumetric, and 
 depends upon the measurement of the amount of a standard so- 
 lution of chloride of sodium which is required to effect the com- 
 plete precipitation, as chloride, of the silver contained in a given 
 
ATOMIC WEIOHI OP SILTEE. 461 
 
 ■weight of the alloy. In a solution which is acidulated with nitric 
 acid, and which contains no excess of the soluble chlorides, the 
 chloride of silver is easily coagulated into dense flocks by agita- 
 tion ; so that the exact point at which the precipitate ceases to be 
 formed is readily perceived. 
 
 Chloride of silver melts at about 260°. It is not decomposed 
 when heated with carbon, but is easily reduced by hydrogen 
 when heated in a current of the gas ; zinc aud iron reduce moist 
 chloride of silver to metallic silver ; when heated with carbonates 
 or hydrates of sodium, potassium, or calcium, chloride of silver 
 gives its chlorine to the other metal, and pure silver is set free. 
 
 These methods of reducing chloride of silver, except that by hydro- 
 gen, are turned to account in the refining of silver on a large scale. 
 The coin, or buUion to be refined is dissolved in nitric acid, and to 
 the solution chloride of sodium is added ; the precipitated chloride of 
 silver is washed until the washings are tasteless, and is then slightly 
 acidulated with sulphuric acid ; bars of zinc are placed in the moist 
 mass, and the whole left at rest for two or three days. Chloride of 
 zinc and metallic silver are the products. As soon as the reduced 
 silver is entirely soluble in nitric acid, the reduction is complete. 
 The reduced metal is dig-ested for two or three days in dilute sul- 
 phuric acid, to remove adhering zinc-salts, and is then thoroughly 
 washed, dried, and finally melted and cast into ingots. If an abso- 
 lutely pure metal is desired, the first reduction should be made with 
 pure zinc, and this refined silver may be again dissolved in nitric acid, 
 thrown down as chloride, and reduced again from the washed chloride 
 by fusion with carbonate of calcium. 
 
 539. The reduction of chloride of silver by hydrogen is the 
 basis of one of the several determinations of the atomic weight of 
 silver ; and since silver forms a large number of anhydrous salts 
 with acids, and has little or no tendency to form more than one 
 salt with each acid, the silver-salt is often the best one to prepare 
 and analyze whenever the combining-weight of an acid is to be 
 determined. But it is clear that the accuracy of these determi- 
 nations depends upon the accuracy with which the atomic weight 
 of silver is known ; hence extraordinary pains have been taken 
 to arrive at the true atomic weight of silver. It has been found, 
 by the most careful experiment, by heating chloride of silver in 
 a current of hydrogen, that in 132'856 parts of that compound. 
 
462 VERIFICATION OP ATOMIC WEIGHTS. 
 
 100 parts of silver are united with 32-856 of chlorine. If the 
 atomic weight of chlorine be accepted as 35-5, a simple propor- 
 tion leads to the atomic weight of silver. 
 
 432-856 : 35-5 = 100 : ir = 108-07. 
 Amount of 01. At. Weight of 01. A^nt. of Ag. At. Weight of Silver. 
 An entirely different experiment verifies this result ; by burn- 
 ing finely divided silver in a current of perfectly dry chlorine, it 
 is proved that 108 parts of silver combine with 35-505 of chlo- 
 rine. The following round of experiment and simple calculation 
 win Ulustrate the manner in which one atomic weight is derived 
 from another, -and all are verified by mutual comparison. Chlo- 
 rate of potassium, when heated, gives off all its oxygen and 
 chloride of potassium remains. Assuming that the formula of 
 chlorate of potassium is KCIO3 and that the atomic weight of 
 oxygen is 16, we derive the following proportion from the fact of 
 experiment that 100 parts of KCIO3 yield 39-209 parts of oxygen. 
 
 39-209 : 48 = 60-791 : x = 74-4208. 
 Amount of 0. 80. Amt. of KCl. Molecular Weight of KC\. 
 
 It is another experimental fact that 100 parts of chloride of 
 potassium produce, when precipitated with nitrate of silver, 
 192-75 of chloride of sUver. 
 
 100 : 192-75 = 74-4208 : a; = 143-446. 
 Amt. of KCl Amt. of AgCl M. Weight of K0\. Molecular Wt. AgCl. 
 But it has been determined, as above stated, that 132-856 parts 
 of chloride of silver contained 32-856 parts of chlorine, and 
 accordingly 
 
 132'856 : 32-856 = 143-446 : a: = 35-476. 
 Amt. of AgCl. Amt. of CI. M. Weight of AgCl. At. Weight of CI. 
 But if the molecular weight of chloride of silver is . . 143-446 
 we may deduct the atomic weight of chlorine . . . 85-476 
 and so obtain the atomic weight of silver ; . . . . 107-970 
 and if the molecular weight of chloride of potassium is 74-4208 
 we may deduct the atomic weight of chlorine, . . . 35-476 
 and so obtain the atomic weight of potassium . . . 38-9448 
 These numbers wiU be found to be very nearly coincident with 
 those previously given as the accepted atomic weights of these 
 three very important elements. 
 
STOPHIBE OP SILVEK. 463 
 
 540. Bromide and Iodide of Silver (AgBr and Agl) are two 
 rather rare minerals, usually associated with chloride of silver or 
 with native silver. Their artificial preparation and such of their 
 properties as have present importance have heen already alluded 
 to (Exp. 272). They are both easily fusible and insoluble in 
 water, but soluble in concentrated solutions of the bromide and 
 iodide of potassium. 
 
 541. Cyanide of Silver (AgCN) is a white powder, insoluble 
 in water but soluble in ammonia-water, obtained by precipitating 
 nitrate of silver with a soluble cyanide like the cyanide of potas- 
 sium. Cyanide of silver is soluble in solutions of the cyanides of 
 sodium, potassium, calcium, and other metals, forming double 
 cyanides of the formula MAgC^Nj,- When such a solution is 
 subjected to the action of a galvanic battery, metallic silver is 
 deposited at the negative pole, in a compact, adherent layer, 
 while at the positive pole, where a strip or plate of metallic 
 silver is placed, a quantity of the metal equal to that which is 
 deposited at the negative pole continually dissolves. A solution 
 which contains -^ of its weight of silver is found to be of con- 
 venient strength for the ordinary operations of electro-plating. 
 
 542. Sulphide of Silver (Ag^S). — This compound is a principal 
 ore of silver. The native mineral is sometimes crystallized, in 
 cubes or octahedrons, and sometimes massive; it has a leaden 
 lustre and color, and it is so soft that a knife will cut or a die 
 impress it; it is fusible, and when roasted in the air yields 
 silver (which remains in the metallic state) and sulphurous acid 
 (the product of the combination of its sulphur with the oxygen of 
 the air). The pure mineral is very easily recognized by these 
 marked characteristics. Silver is readily tarnished by contact 
 with moist gaseous sulphydric acid, or with a solution of a solu- 
 ble sulphide ; this tarnish is the sulphide of silver (§ 533). The 
 sulphide may be artificially prepared by transmitting a stream of 
 sulphuretted hydrogen through a solution of a salt of silver. 
 
 Exp. 274.^ — Place in a teat-glass 8 or 10 c. c. of water to which 20 
 or 30 drops of a solution of nitrate of silver have been added, and pass 
 through the dilute solution a slow stream of sulphuretted hydrogen. 
 The black precipitate is the sulphide of silver. 
 
 Strong acids, especially when hot, dissolve or decompose this 
 
464 THE ALKAXI GEOUP. 
 
 sulphide. It is not soluble in solutions of the sulphides of the 
 alkali-metals ; but by fusion it may be made to unite with many 
 other sulphides of metals. 
 
 643. Sidphate of Silver (Ag^SO^). — When silver is boiled with 
 strong sulphuric acid, the silver gradually dissolves, and there are 
 formed the sulphate of silver, water, and sulphurous acid : — 
 
 2Ag + 2H,S0, = Ag^SO, + 2H,0 + SO,. 
 The sulphate is dissolved by the excess of acid, but it is deposited 
 in great part on the addition of water, for it is but slightly 
 soluble in water. As gold is not soluble in sulphuric acid, small 
 quantities of gold may be separated from large quantities of silver 
 or silver alloys by boUing the metal, finely granulated, in cast- 
 iron vessels with oil of vitriol ; silver and copper dissolve, and the 
 gold is left behind in a fine powder. The solution of silver is 
 subsequently diluted, and the sUver precipitated from the solution 
 in the metallic state by means of metaUic copper. (Exp.' 267.) 
 Old silver coin, containing not more than Ymru "^ gold, has been 
 profitably worked over by this process. 
 
 544. TJie Alkali Group.- — The metals which must plainly be 
 classed together under this head are sodium, potassium, (ammo- 
 nium,) lithium, rubidium, and caesium. Two other metals are 
 better classed with this group than elsewhere ; but their likeness 
 to the alkali-metals is but partial, and in many respects their pro- 
 perties are quite unlike those of the six metals just enumerated ; 
 these two metals are silver and thallium. The common proper- 
 ties of the alkali-metals are mainly these : — they have the lustre 
 of silver, are soft, easily fusible, and volatUe at high tempera- 
 tares ; they unite greedily with oxygen, and decompose water 
 with facility, forming basic hydrates which are very caustic and 
 intensely alkaline bodies, not to be decomposed by heat ; their 
 carbonates, sulphates, sulphides, and chlorides, and, indeed, the 
 vast majority of their salts, are soluble in water ; and each metal 
 forms but one chloride, one bromide, and one iodide ; they all 
 form basic oxides, and never an acid oxide ; they occur in nature 
 in modes analogous though not the same ; their corresponding 
 salts are often, though not always, isomorphous ; lastly, there is 
 a general, though not absolute, uniformity among the formulse of 
 the compounds into which these elements enter, so that, if a com- 
 
eTTAirrrvAXEifCE. 465 
 
 pound of a giVen composition is proved to exist ■with one of these 
 elements, the strong presumption is that analogous compounds 
 with aU the other elements of the group exist likewise, with pro- 
 perties similar though not identical. 
 
 Silver and thallium present, on the whole, so few points of 
 resemhlance to the alkaU-metals that they would not be compre- 
 hended in the same group with them were it not for one consi- 
 deration weighty enough to turn the balance when the discussion 
 of other properties leaves the matter in doubt. Sodium, potas- 
 sium, (ammonium,) lithium, caesium, rubidium, silver, and thallium 
 aU replace hydrogen, atom for atom. All these elements are ex- 
 changeable for hydrogen and with each other, atom for atom, and 
 in the present state of the science they-must be regarded as the only 
 metals thus equivalent to hydrogen. The atom of the elements 
 of the chlorine group, including fluorine in that designation, and 
 of the seven elements above enumerated, is exchangeable for one 
 atom of hydrogen ; it is worth one in exchange, and these ele- 
 ments are therefore said to be univalent, or, with less verbal pre- 
 cision, monatomie.. 
 
 545. Quantivalence. — The chemical elements have not all the 
 same atom-fixing power ; thus, while an atom of chlorine combines 
 with only one atom of hydrogen, an atom of oxygen has the 
 power to drag two atoms of hydrogen into a molecule ; an atom of 
 nitrogen holds three atoms of hydrogen in firm chemical combi- 
 nation, and an atom of carbon four hydrogen-atoms. In all double 
 decompositions: an atom of sodium, potassium, or silver replaces 
 one atom of hydrogen, but an atom of calcium or lead two atoms 
 of hydrogen (§ 82). To indicate conveniently the atom-flxing 
 power of each element a sign is needed and a name. The con- 
 ventional sign is a Boman numeral, or an equivalent number 
 of accents, placed above and at the right of the symbol of the 
 element, in case its atom be worth more than one of hydrogen ; 
 and for the name to denote this atom-fixing power of the elements 
 the word " qiiantivalence " may be used, or the less descriptive 
 word " atomicity." The elements are called univalent, bivalent, 
 trivalent, and quadrivalent, or monatomie, diatomic, triatomic, and 
 tetratomie, according as their respective atoms are capable of satu- 
 rating, or holding in firm chemical combination, 1, 2, 3, or 4 
 
 2h 
 
466 auAsnvALEifCE. 
 
 atoms of hydrogen. Thus, while the simple symhols CI, Br, K, 
 Ag indicate that chlorine, bromine, potassium, and silver are 
 univalent, the symbols of nitrogen, antimony, and other trivalent 
 elements may be written N'", Sb'", &c. In the same way the 
 symbols 0" and Ca" indicate that oxygen and calcium are biva- 
 lent, and the symbol C"" shows that carbon is quadrivalent. 
 
 The quantivalence of many of the elements is not yet deter- 
 mined with certainty; but the classification into groups of the 
 elements we have thus far studied rests upon the quantivalence 
 of the elements, as well as upon the other chemical resemblances, 
 which have been dwelt upon in connexion with each group. The 
 elements of the chlorine-group and the aliali-group are univalent; 
 the elements of the sulphur-group and the majority of the metals, 
 hereafter to be studied, are bivalent ; the elements of the nitro- 
 gen-group are trivalent, and of the carbon-group quadrivalent. 
 
 It must not be supposed that the atom-fixing power of the ele- 
 mentary bodies is, under all circumstances, and m all compounds, 
 invariably exerted to the fullest extent. Were the combination 
 of the elements governed by any such law as this, it would evi- 
 dently be impossible for any two elements to unite iu more than 
 one proportion. Thus trivalent nitrogen and bivalent oxygen 
 could only combine in the proportions represented by the formula 
 ^J'^s'j proportions which completely satisfy the atom-fixing 
 power of both elements. But we know that these two elements 
 actually form no less than five different compounds (§§ 75, 76), 
 of which only one is marked by the complete equilibrium of the 
 two elements ; and this one is by no means the most stable mem- 
 ber of the series ; on the contrary, it is about the most unstable. 
 The student must not imagine that a bivalent element has twice 
 as strong affinities as a univalent element ; the atom-fixing power 
 of an element is no test or index of the avidity with which it 
 seeks combination. Chlorine, which holds but one atom of hy- 
 drogen, is competent to decompose sulphuretted hydrogen, ammo- 
 nia, and marsh-gas, although sulphur unites by preference with 
 two, nitrogen with three, and carbon with four atoms of hydrogen. 
 
cAiciuM. 467 
 
 CHAPTEE XXVIII. 
 
 C A 1 C I IT M — S T B ir T I T7 M — B A R ITT M — I E A D. 
 
 546. This metal is a constituent of several of the commonest 
 and most importajit minerals ; it forms a very considerable portion 
 (perhaps as much as one-sixteenth) of the solid crust of the 
 earth. Before considering the properties of the metal itself, let 
 us examine some of its familiar compounds. 
 
 547. Carbonate of Calcium (CaCOj) occurs in nature in many- 
 different forms, called by a great variety of names, among which 
 may be mentioned limestone, chalk, marble, calc-spar, and coral. 
 There are whole ranges of mountains composed almost entirely 
 of limestone, whUe in many extensive tracts of country the soU is 
 calcareous and reposes upon limestone rocks. The shells of shell- 
 fish are almost entirely composed of it, and it is an important 
 constituent of dolomite, marl, and many other rocks and minerals. 
 It is formed artificially, as has been seen (Exp. 168), when car- 
 bonic acid is brought into contact with lime-water ; but it is 
 noteworthy that carbonic acid wiU not unite with the anhydrous 
 oxide of calcium (quicklime). 
 
 Carbonate of calcium, though tasteless, is slightly soluble in 
 water, and the solution exhibits a faint alkaline reaction; it 
 is, however, rather freely soluble in water charged with carbonic 
 acid (§403). 
 
 Exp. 275. — Place in a test-tube 20 or 30 drops of lime-water, and 
 as much pure water ; immerse in the mixture the delivery-tube of a 
 bottle &om which carbonic acid gas is being evolved (Exp. 171). Car- 
 bonate of calcium vnll be thrown down, at first ; but after a while, as 
 the water in the test-tube becomes saturated with carbonic acid, the 
 precipitated carbonate will redissolve, and there will be obtained a 
 perfectly clear solution, which, m spite of the large proportion of car- 
 bonic acid contained in it, has a decided alkaline reaction. By boiling 
 the solution, so that a portion of its carbonic acid may be expelled, the 
 carbonate of calcium can be again precipitated. So, too, if the liquid 
 
 2e2 
 
468 CAlCAEEOtrS PETEIFACTIONS. 
 
 be left exposed to the air, it will gradually give off carbonic acid, and 
 become turbid from deposition of carbonate of calcium. 
 
 The phenomena illustrated in this experiment often occur in nature. 
 In many districts where limestone is abundant, the well- and river- 
 waters are highly charged vpith carbonate of calcium held dissolved by 
 carbonic acid ; the water is thus made " hard " (see § 560), and is, com- 
 paratively speaking, unfit for washing and for many other purposes. 
 When employed as a source of steam-power, such waters deposit car- 
 bonate of calcium as an incrustation upon the sides of the boilers as 
 fast as the excess of carbonic acid is expelled by boiling. This scale, 
 or incrustation, forms a more or less coherent coating upon the inner 
 surface of the boiler, and, being a very poor conductor of heat, it greatly 
 interferes with the heating of the water ; the scale keeps the water 
 away from the iron sides of the boiler, and the metal, being thus un- 
 duly heated, is rapidly oxidized, or " burnt out," as the fireman cor- 
 rectly states it. 
 
 The formation of calcareous petrifactions, of stalactites and stalag- 
 mites, of the stones called tufa and travertine, and of many deposits of 
 crystallized carbonate of calcium, is directly referable to the escape of 
 carbonic acid from calcareous waters. Whenever water, charged with 
 carbonate of calcium, flows out from the earth into the open air, or 
 trickles into hollows or caverns within the earth, carbonic acid is given 
 off in the gaseous state, and carbonate of calcium is deposited. Stalac- 
 tites are the pendent masses, like icicles, which hang from the roofs of 
 caverns and the walls of cellars, bridges, and like covered ways ; stalag- 
 mites are the opposite masses which grow up out of the drops of water 
 which fall from the stalactites above them, before all the dissolved 
 carbonate has been deposited. The waters of some mineral springs 
 are so highly charged with carbonate of calcium, that, on being exposed 
 to the air, they quickly deposit a considerable quantity of it upon any 
 solid substance with which they come in contact. In case such waters 
 flow over pieces of wood or other organic matter, the form of the wood 
 will be preserved in the cast or " petrifaction," long after the wood 
 itself has decayed and disappeared. Where such deposits are formed 
 upon a scale so large as to be of geological importance, as is the case 
 in some of the volcanic districts of Italy, the rock formed is called tufa 
 when porous, and travertine if compact. 
 
 548. Carbonate of calcium dissolves also in aqueous solutions 
 
 of several of the salts of ammonium, such as the chloride, nitrate 
 
 and sulphate, especially if it has only recently been precipitated 
 
 and is still moist and incoherent. 
 
 Bxp. 276. — Through 2 or 3 c. c. of lime-water, contained in a test- 
 
CAEBOJfATE OF CAICIUM: STOT rN-SOLTJBLE. 469 
 
 tube, blow, by means of a glass tube, a quantity of air from tbe lungs ; 
 to tbe milky liquid obtained, add, drop by drop, a cold, saturated 
 aqueous solution of chloride of ammonium, until tbe cloudiness in the 
 lime-water has disappeared — that is, until the carbonate of calcium 
 has all been dissolved. 
 
 Bxp. 277. — Place a drop or two of a solution of chloride of calcium 
 in a test-tube, pour upon it several drops of a strong solution of chlo- 
 ride of ammonium ; shake the mixture, and then add to it a few drops 
 of a solution of carbonate of ammonium, and also a few drops of am- 
 monia-water. If enough chloride of ammonium has been added to the 
 liquid, no precipitate will be formed in it, though, in the absence of 
 chloride of ammonium, a precipitate will at once be produced on mix- 
 ing the other ingredients. A precipitate may, however, always be ob- 
 tained by boUing the mixed solutions, unless a large excess of chloride 
 of ammonium be present, or unless the chloride-of-calcium solution be 
 very dilute. 
 
 By repeating this experiment under varied conditions, taking note, 
 in each case, of the number of drops of the solutions of chloride of am- 
 monium, chloride of calcium, and of water employed, and methodically 
 increasing or diminishing each of these, the student wjll quickly per- 
 ceive the real significance of the solvent power of the ammoniacal salt, 
 and wiU appreciate the fact that, in testing for small quantities of 
 either lime or carbonic acid, it is necessary for the analyst to exclude 
 ammonium-salts from his solutions as far as may be practicable. 
 
 When boiled with solutions of the salts of anunonium (with cho- 
 ride of ammonium for example), carbonate of calcium is rapidly de- 
 composed and dissolved, carbonate of ammonium being given off, while 
 the chloride (or some other salt) of calcium remains in solution. 
 
 549. Carbonate of calcium is remarkable not only for the very 
 great diversity of external appearance which is presented by its 
 several massive and amorphous varieties, but it is likewise found 
 in a greater variety of regular crystalline forms than any other 
 substance ; more than 150 native varieties of it have been observed 
 by mineralogists. As ealc-spar, it occurs in rhombohedrons and 
 other derivative forms of the sixth or hexagonal system (§ 191) j 
 but it is found also as the mineral arragonite, in forms of the 
 trimetric system, and is consequently dimorphous. 
 
 The two forms of carbonate of calcium, calc-spar and arra- 
 gonite, present many differences in their physical properties. 
 Some specimens of calc-spar, called Iceland spar, are perfectly 
 transparent and colorless, and exhibit to a remarkable degree the 
 
470 CAIC-SPAB AND AEKASONITB. 
 
 phenomena of double refraciion. Transparent crystals of arra- 
 gonite exhibit also the phenomena of double refraction ; but arra- 
 gonite has two axes of double refraction, calc-spar only one. 
 Crystals of calc-spar are cleavable parallel to the faces of the 
 rhombohedron which is the primary form of the mineral, and 
 masses of it may often be broken up into more or less perfect 
 rhombohedrons. Arragonite, on the contrary, presents two direc- 
 tions of distinct cleavage, parallel to the faces of a right rhombic 
 prism. The fractures of the two minerals are therefore quite un- 
 like. The specific gravity of calc-spar ranges from 2'7 to 2-75, 
 while the specific gravity of arragonite is generally between 2-9 
 and 3'3. Arragonite is considerably harder than calc-spar, but 
 its specific heat (0'1966) is less. When carbonate of calcium 
 crystallizes from hot solutions it takes the form of arragonite, but 
 from cold solutions it crystallizes as calc-spar. In Kke manner 
 the precipitate formed by mixing boiling solutions of chloride of 
 calcium and carbonate of ammonium is seen under the microscope 
 to consist of 9,cicular crystals of arragonite, while the precipitate 
 obtained from cold solutions of the same salts is amorphous. In 
 either ease, however, if the moist precipitate be left to itself for 
 some time in the cold, it will gradually assume the rhombohedral 
 form of calc-spar, no matter whether it was at first acicular or 
 amorphous. 
 
 In all its varieties carbonate of calcium is readily attacked by 
 acids, even if they be dilute ; the action is attended with efier- 
 vesoence, owing to the expulsion of carbonic acid and the escape 
 of this gas through the liquid ; — 
 
 CaO,CO, + 2HC1 = CaCl, + CO, + Kfi. 
 limestone is readily distinguished by this reaction from other 
 rocks. 
 
 550. Oande of Caldum (CaO). — On being heated, carbonate of 
 calcium begins to give off carbonic acid at a low red heat, as has 
 been seen in Exp. 170, and at full redness is completely resolved 
 into oxide of calcium, commonly called quicklime, and carbonic 
 acid. 
 
 JErp. 278. — Place a small fragment of marble upon a piece of char- 
 coal and heat it strongly in the blowpipe-flame during several minutes. 
 Or throw a lump of limestone upon an anthracite fire, and leave it there 
 
OXIDB OP CA1CIT7M. 471 
 
 for half an hour or more. In either case, it will he found, upon exa^ 
 mination, that the calcined product has lost the property of efferves- 
 cing with acids; that it weighs less than the original limestone, and 
 that it exhibits a distinct alkaline reaction when placed on wet test- 
 paper. 
 
 For use in the arts, limestone is burned in special furnaces, of 
 peculiar construction, called lime-kilns, some of which are so 
 arranged that they may be kept in operation for years without 
 intermission. When carbonate of calcium, instead of being 
 heated merely in quiescent air, is heated in a current of air, or 
 of any other gas, such as steam for example, it wiU give off aU 
 its carbonic acid very easily. It has been found in practice that 
 limestone fresh from the quarry can be more readily burned than 
 that which has been long dug out of the ground and has so lost 
 its natural moisture ; in damp weather, moreover, the burning is 
 said to go on more satisfactorily than when the atmosphere is 
 dry. If carbonate of calcium be ignited in a tube of iron, or other 
 metal, closed hermetically, so that no carbonic acid can escape 
 from the tube, the carbonate disengages carbonic acid until the 
 pressure of the confined gas becomes so great as to arrest the 
 further decomposition of the carbonate. Under these conditions, 
 the temperature may be raised high enough to fuse the undecom- 
 posed carbonate ; the cooled mass often presents the appearance 
 of fine-grained marble. K the tube in which the experiment has 
 been performed be very slowly cooled, the carbonic acid will be 
 reabsorbed. 
 
 Of the anhydrous oxide of calcium little need here be said. It 
 is infusible at the most intense heat at present at our command, 
 and is therefore used for making crucibles in which the most re- 
 fractory metals are melted by the aid of the compound blowpipe. 
 It has no power to unite with dry carbonic acid at ordinary tem- 
 peratures, but when exposed at very high temperatures to an 
 atmosphere of carbonic acid possessing a certain tension, some of 
 the gas is absorbed. It unites with water very energetically, and 
 the product of this union combines readily with carbonic acid. 
 When lumps of quicklime are exposed to the air they slowly 
 absorb both water and carbonic acid, and after a while fall to 
 powder. This powder is known as air-slaked lime ; its composi- 
 
472 HTBEAIE OF CALCnTM, 
 
 tion maybe represented by the formula CaHjOjjGaCOg, or, dualis- 
 tic, CaG,CO, ; CaO,H^O. 
 
 551. Hydrate of OaMum (CaH^O^). — ^Wben water is brought 
 into contact with oxide of calcium, the latter swells up and falls to 
 powder ; a large amount of heat is evolved, and there is obtained 
 a compound of calcium, hydrogen, and oxygen, commonly called 
 slaked lime, or in chemical language hydrate of calcium : — 
 CaO + HP = CaHp,. 
 
 ^Exp. 279. — Place a lump of recently bmned quicklime, weighing 
 about 30 gnns., upon a large earthen plate ; pour upon the lime some 
 15 or 20 c. c. of water, and observe how much the lime increases in 
 bulk as it is converted into hydrstte of calcium. The heat of the mass 
 may be shown by thrusting an ordinary friction-match into the middle 
 of it ; or, in case a considerable quantity of quicklime has been em- 
 ployed, by excavating a smaU hole in the drypowder and throwing in 
 a few grains of gunpowder, inflammation will ensue in both cases. 
 That much heat is evolved, may be shown also by covering the mois- 
 tened quicklime with a not too tall inverted beaker glass or bottle, and 
 observing that, after a considerable amount of aqueous vapor has been 
 condensed upon the walls of the glass, the space within the latter will 
 at last become filled with a hot, invisible atmosphere of steam ; when 
 the bottle is Ufted, and the steam thus brought into contact with the 
 cold external air, a dense cloud or fog is immediately formed. 
 
 So much heat is developed during the union of water with lime, that 
 wood will quickly be brought to ^the kindling- temperature and inflamed, 
 if it happen to be in contact with large masses of these substances re- 
 acting upon one another. Fires are very frequently occasioned by the 
 access of water to ships or warehouses in which quicklime is stored. 
 It has been noticed, when large quantities of quicklime are slaked in 
 a dark place, that light as well as heat is evolved from the lime. Even 
 when quicklime is brought into contact with ice,so much heat is evolved 
 that the mixture sometimes becomes hot enough to boil water. 
 
 552. When hydrate of calcium is stirred into water, there is 
 formed not only a true solution, lime-water, which may be ob- 
 tained clear and colorless by filtration (See Erp. 168), but also 
 a turbid liquor consisting of particles of solid hydrate of calcium 
 diffused through the lime-water ; this liquor is known as milk or 
 cream of lime, according to its consistency. In slaking lime, only 
 about half a part' of water is really needed to convert one part of 
 quicklime into hydrate of calcium ; but ia all cases where a fine. 
 
SLAKED IIME. 473 
 
 smooth paste is desired, as in tlie preparation of mUk of lime, 
 or of mortar, and in general wh'enever hydrate of calcium is 
 required iJi a very finely divided condition, it is best to pour two 
 or three parts by weight of water upon one part of quicklime, 
 so tha:t the slaking may be quicHy effected. By using hot water 
 the process may be stiU further accelerated. The proportions 
 of material given at the beginning of Exp. 279 are better -adapted 
 than these last for illustrating the evolution of heat ; but if 
 too little water be employed, the hydrate of calcium formed is 
 liable to be granular and crystalline rather than powdery. Both 
 milk of lime and dry powdery hydrate of calcium are largely 
 employed for pnrifying the illuminating gas made from coal. 
 They remove from the gas sulphydric and carbonic acids. 
 
 Exp. 280. — Provide two gas-bottles, one arranged for genesrating 
 sulphydric acid (Exp. 86), the other for generating carhoriic acid 
 (Exp. 171). Connect with one of the gas-bottles a tube filled loosely 
 with dry hydrate of calcium (Appendix, Fig. 15), and with the other 
 a small bottle containing milk of lime. Pour chlorhydric acid into 
 the gas-bottles, so that sulphydric and carbonic adds shall be freely 
 evolved, and test, from time to time, with lead-paper (Exp. 90), and 
 with lime-water (Exp. 170), as to whether these acids are completely 
 absorbed by the dry hydrate of calcium and the milk of lime. After a 
 while, change the places of the absorbing tube and bottle, so that the 
 milk of lime shall now be where the dry hydrate was before, and again 
 test the efficiency of the absorption, with tead-paper and lime-water. 
 In actual practice it is found that, while the dry hydrate is a more 
 efficient absorbent of carbonic acid than mUk of lime, the latter is 
 capable of taking up far more sulphydric acid than the former. 
 
 553. Hydrate of calcium may be obtained crystallized, in hex- 
 agonal prisms, by evaporating lime-water in the dry exhausted 
 receiver of an air-pump. At a red heat it gives off its water, 
 and is reconverted into quicklime. The residue in this case is 
 left in an open, porous condition which well fits it for many 
 chemical purposes (see § 120). 
 
 It is noteworthy that hydrate of calcium is somewhat less 
 soluble in hot than in cold water. If a eold, saturated solution 
 of lime-water be boiled, nearly half of its solid contents will be 
 deposited ; and in case none of the water has been driven off, the 
 matter thus precipitated will slowly dissolve again after the liquid 
 
474 HOETAK. 
 
 above it has become cold. In studying this point, the experi- 
 menter must take care that the solution is kept out of contact 
 with the air, lest it absorb some of the carbonic acid which is 
 always present in the atmosphere, and become turbid from depo- 
 sition of carbonate of calcium. A familiar instance of this absorp- 
 tion is seen in cases where milk of Ume is employed for white- 
 washing : the loosely adherent white coating, left after the liquid 
 has become thoroughly dry, is no longer hydrate of calcium, but 
 carbonate of calcium in a more or less pure condition. 
 
 554. Slaked Ume is very largely employed for making mortar, 
 as an ingredient of various cements, and for plastering. When 
 mixed with enough water to form a thick paste, it is decidedly 
 plastic, and admits of being spread and moulded like wax or clay. 
 This paste sets, as it dries, to a firm, solid mass, which, when in 
 thin layers, adheres firmly to any rough surfaces upon which it 
 may have hardened. When, however, any considerable mass of 
 the moist paste is allowed to solidify by itself, the dry product 
 will gradually crack and fall to pieces. Lime-paste cannot, there- 
 fore, be employed as a mortar unless it be mixed with some sub- 
 stance like sand, which shall present numerous surfaces upon 
 which the hardened product may adhere ; by the addition of sand, 
 moreover, the moist lime is prevented from shrinking too much 
 as it becomes dry. 
 
 Mortar is commonly prepared by mixing 1 part of qxiicklime 
 with water enough to form a thin paste, then adding 3 or 4 parts 
 of coarse, sharp sand, and thoroughly incorporating these ingre- 
 dients. The paste thus obtained is applied as a thin layer to the 
 moistened surfaces of the bricks or stones to be united. The 
 pasty mortar soon sets to the hard mass above described, and, on 
 continued exposure to the air, it slowly absorbs carbonic acid at 
 its surface, and is there converted into a compact compound of 
 hydrate and carbonate of calcium. The stone-Uke mass thus ob- 
 tained binds firmly together the bricks or stones between which 
 it has been interposed. It has been asserted that the original 
 mortar-paste sets more firmly if it contain a certain admixture of 
 carbonate of calcium, than if it contain only the pure hydrate ; 
 this admixture is, of course, produced when mortar is left for 
 some time in contact with the air before being used. In the 
 
CAUSTIC LIMB. 475 
 
 course of time chemical combination occurs, to a limited extent, 
 between the silicic acid of the sand and the oxide of calcium in 
 the hardened mortar, though the process goes on but slowly ; 
 each grain of sand finally becomes covered with a thin layer of 
 hydrated silicate of calcium, which contributes materially to the 
 solidity of the mortar. The mortar taken from old buildings 
 yields a certain proportion of gelatinous silica on being treated 
 with ehlorhydric acid (§ 466). 
 
 The conversion of the original mortar into hydrocarbonate and 
 silicate of calcium is never completely accomplished ; in the cen- 
 tral portions of the mass, free hydrate of calcium wiU still be 
 found after the lapse of many centuries. Samples of mortar, re- 
 cently taken from the Great Pyramid, were found on analysis 
 to contain a large proportion of the free hydrate. 
 
 555. The plastering used for finishing the walls and ceilings of 
 rooms is mortar to which a quantity of hair has been added to 
 increase its tenacity ; in drying, it is, of course, subject to the 
 same chemical changes as ordinary mortar. By absorbing car- 
 bonic acid from the air, it is gradually converted, in part, into 
 carbonate of calcium, while water is set free : — 
 
 CaO,H,0 -I- CO, = CaO,CO, + H,0. 
 
 Consequently the walls of recently plastered rooms cannot become 
 permanently dry, until enough carbonic acid has been absorbed 
 to expel the chemically combined water from their outside sur- 
 faces ; hence the dampness so often perceived in new houses, 
 when carbonic acid first comes to be freely generated in them by 
 respiration and by burning lamps. In order to dry plastering, it 
 would, doubtless, be better to employ open fires of charcoal, or of 
 coke, and to deliver the products of the combustion directly into 
 the room which is to be dried, instead of relying solely upon hot 
 air, as is now usual, 
 
 556. Hydrate of calcium, like the hydrates of sodium and of 
 potassium, exhibits a strong alkaline reaction when tested with 
 moistened litmus-paper, and exerts a corrosive action upon most 
 organic substances ; hence it is often called caustic lime. 
 
 Exp. 281.— Add a few drops of water to a small quantity of dry 
 hydrate of calcium, and rub it to a paste between the fingers. It will 
 
476 
 
 SULPHATE or CAL0IT7M. 
 
 be felt that the alkali acts upon the sHa ; a little of the cuticle is 
 really dissolved. 
 
 Exp. 282. — Wrap a handful of dry hydrate of calcium in a paper, 
 or, belter, in a piece of linen or cotton cloth, and set the packet 
 aside for a week or two. After a while, the cloth or paper will become 
 rotten and friable : the caustic lime, as the common phrase is, has eaten 
 away their more corruptible portions, and has so destroyed the inte- 
 grity of the whole. As a preliminary operation in tanning leather, 
 hides are soaked in milk of lime to loosen the hair, so that it may be 
 readily scraped otf. The value of lime, as an ingredient of composts 
 to be used as manure, appears to depend, in great measure, upon its 
 power of hastening the decay and disintegration of organic matter. 
 
 Lime has been found to be specially valuable as manure when ap- 
 plied to soils rich in vegetable matter. The organic matters are de- 
 composed or oxidized into carbonic and various other organic acids, 
 which unite with the lime ; sometimes, under special conditions, more 
 or less nitrate of calcium is found among the products. 
 
 Lime is important, also, from being not only the cheapest alkali, 
 but the cheapest of all the bases. Since its compounds with car- 
 bonic and sulphuric acids are nearly insoluble in water, it is 
 largely employed for removing these acids from solutions in which 
 their presence is not desired ; it may itself be removed from any 
 solution by means of -the acids in question. It is used in the 
 manufacture of the caustic alkalies (soda and potash), of ammonia- 
 water and of bleaching-powders, as a flux in many metallur- 
 gical operations, in the refining of sugar, for preparing a lime 
 soap in the manufacture of stearine candles, and for numberless 
 other purposes. A noteworthy property of slaked Ume is its 
 power of dissolving freely in solutions of common sugar. 
 
 557. Sulphate of Calcium (CaSOJ is found native in large 
 quantities, as the minerals gypsum and alabaster. These mine- 
 rals contain one-fifth their weight of water ; their composition 
 may be represented by the formula CaSO^ -|- ^Rfi. The same 
 hydrated salt may be obtained by adding sulphuric acid, or the 
 solution of some sulphate, to a strong aqueous solution of almost 
 any of the salts of calcium. This hydrated compound is the sub- 
 stance commonly meant when sulphate of calcium is spoken of. 
 The anhydrous compound is also important : it is sometimes 
 found in nature as the mineral anhydrite, and may be readily 
 
PLASTEB OF PAEIS. 477 
 
 prepared by heating the hydrated salt. There is still a third 
 compound, the oomposition of which may be represented by the 
 formula 2CaS0^ + H^O, of which, however, but little is known. 
 
 Eocp. 283. — Place in a porcelain evaporating-dish, or, better, in an 
 iron pan, two tablespoonfuls of powdered gypsum ; heat the gyp- 
 sum moderately over the flame of the gas-lamp,, and observe the move- 
 ment of ebullition occasioned by the escaping water; stir the mixture 
 as long as the vapor of water is seen to escape, and then set the residue 
 aside to cool. The dry product is known as calcined gypsum or plaster 
 of Paris. 
 
 As much as nine-tenths of the water which the gypsiun contains 
 may be readily expelled at teiliperatures between 100° and 120° ; but, 
 in order to drive oif the last portions of the water, a temperature of 
 nearly 300° is required. If the dry compound be heated to tempera- 
 tures much higher than 300°, its particles appear to become aggluti- 
 nated, and the chemical properties of the substance are somewhat 
 changed ; the gypsum is then said to be over-burned. At the tempe- 
 rature of redness, sulphate of calcium melts without decomposition, 
 and, on cooling, assumes a crystalline structure similar to that of na- 
 tive anhydrite. 
 
 558. When powdered sulphate of calcium, which has been made 
 anhydrous at a comparatively low temperature, is made into a 
 paste with water, and then left to itself, it soon sets or hardens 
 into a compact, coherent mass. This solidification is a conse- 
 quence of the reassumption by the sulphate of calcium of the 
 two molecules of water of crystallization which were driven off 
 by heat when the substance was made anhydrous. 
 
 Exp. 284. — Place a small coin at the bottom of a cylindrical 
 pasteboard piU-box a little wider than the coia ; smear the coin and 
 the interior of the box with a thin film of oil. Mix intimately two 
 or three teaspoonfuls of the calcined gypsum of Exp. 283, with about 
 half their volume of water, in a small porcelain dish, smd quickly 
 pour the mixture into the box, so that the coin shall be completely 
 covered by it. The mixture, which is of the consistence of cream, 
 should then be immediately stirred or puddled with a hair-pencil, or 
 with a tuft of cotton tied upon a stick, or with the end of the finger, 
 so that the bubbles of air which remain adhering to the siuface of the 
 coin may be pressed out, and the moist paste be made to come every- 
 where into contact with the metal. In the course of a few minutes the 
 paste will solidify and become so hard that the pasteboard envelope 
 may be torn away from it, and the coin removed. A perfect cast or 
 
478 PLASTEB-CASTS. 
 
 copy of the stamp upon the coin will be found impressed upon the 
 hardened gypsum. The impression in this first cast is, of course, re- 
 versed, but by smearing it with oil and then pouring over it a new 
 portion of the gypsum -paste, precisely as was done with the coin, a 
 fac-simile of the original coin may be obtained. 
 
 Plaster of Paris is largely used in this way for taking accurate copies 
 of a great variety of objects. Thus, in the process known as stereo- 
 typing, a thin paste of plaster is poured upon the surface of the printers' 
 types, after they have been set up and made ready for printing; the 
 mould thus formed is dried and baJlfed to expel the water from the 
 gypsum, and is then plunged into a bath of a melted alloy of lead, 
 antimony, and tin, known as stereotype-metal, in such manner that, 
 on withdrawing the mould and allowing the metal withiu it to cool, 
 there is obtained a fac-aimile of the original types. From this durable 
 metallic casting the page is finally printed. 
 
 As has been said above, the moist paste sets as soon as the water, 
 which has been mechanically mixed with the anhydrous sulphate of 
 calcium, enters into chemical combination with it. As in all other 
 instances of chemical action, so here, heat is evolved as the water and 
 plaster combine, as may readily be appreciated by operating upon con- 
 siderable quantities of the materials. Since the plaster assumes crys- 
 talline form aa it becomes hydrated, the paste increases in bulk as it 
 hardens, and is thus pressed into the finest interstices of the moulds. 
 
 Gypsum sets the more quickly in proportion as the temperature at 
 which it has been dehydrated was low. After it has been heated above 
 300°, it will no longer set on being mixed with water. Besides its 
 use in taking casts, plaster of Paris, on account of this power of com- 
 bining with water, is largely employed in the preparation of stucco 
 and of various imitations of marble. The hydrated compound finds 
 application also as a manure, in the manufacture of ammoniacal salts, 
 and for various other purposes. 
 
 JExp. 285. — That the plaster paste expands considerably at the mo- 
 ment of solidification may be shown as follows : — Procure a cracked 
 test-tube, or small flask, and fill it completely with a paste made of 
 calcined gypsum and water, in the proportions of 12 pts., by weight, 
 of the former, to 5 of the latter. In the course of 15 or 20 minutes 
 it will be seen that the original crack in the glass vessel has extended 
 in various directions, in consequence of the expansion of the mass 
 withiu it. It wUl be noticed, also, that the vessel feels warm to the 
 hand (compare Exp. 284). Finally, by breaking away the glass enve- 
 lope, there may be obtained a cast of the glass vessel. 
 
 Uxp. 286. — The power of sulphate of calcium to take up water, 
 
BOILEE-SCATE. 479 
 
 to solidify water as it unites ■with it to form the crystalline compound 
 CaHiSOj, can he made manifest as follows : — ^Prepare two table- 
 spoonfuls of a saturated aqueous solution of chloride of calciimi, by 
 dissolving 1 pt., by weight, of the dry chloride in 1-6 part of water ; 
 also prepare the same quantity of a saturated solution of sulphate of 
 sodium (Exp. 228), and, finally, mix the two solutions. Sulphate of 
 calcium wUl be formed, in accordaace with the reaction 
 
 OaClj + NajiSOi = CaSO< + 2Na01, 
 
 and will unite with the water in which the ingredients from which it 
 has been formed were previously held in solution, so that an almost 
 solid mass of 0aSO4,2BL,O will take the place of the two liquids. 
 
 Ordinary hydrated sulphate of calcium is soluble in about 400 
 parts of water at the ordinary temperature of the air; but, like 
 hydrate of calcium, sulphate of sodium, and a few other salts, it 
 is less soluble in hot water than in cold. When an aqueous so- 
 lution of sulphate of calcium is heated to 100° or more, a precipi- 
 tate will soon be formed in it, even if the solution be very dilute ; 
 and at temperatures as high as 140° or 150° the anhydrous com- 
 pound is completely insoluble in water. In the same way as with 
 sulphate of sodium (Exp. 228), it appears that the bihydrated 
 sulphate of calcium cannot exist at temperatures much superior to 
 100°, and that above that temperature we have to deal with other 
 compounds of different solubility. In other words, the water 
 which is held in chemical combination in ordinary unburned gyp- 
 sum may be expelled by heat even when the gypsum is dissolved 
 in water. Whenever water containing sulphate of calcium in 
 solution is strongly heated, as in steam-boilers, there is precipi- 
 tated the half-hydrated compound, of composition 2CaS0^+H20, 
 which has been mentioned above. Hence the forination of incrus- 
 tations, or scale, of sulphate of calcium upon the walls of boilers 
 fed with sea- water, or with other water containing the sulphate. 
 It should be remarked that the incrustation in this case does not 
 depend upon evaporation ; the sulphate of calcium wUl be de- 
 posited the more rapidly in proportion as the water of the boiler 
 is hot, and as more of the impure feed- water is pumped into the 
 boiler. 
 
 559. Besides occurring in sea-water, sulphate of calQium is a 
 very common impurity in spring- water. Water which contains 
 
480 - TESTINfl WATBK. 
 
 much, of it is " hard," and is not well adapted either for washing 
 or for cooking. 
 
 JExp. 28T. — DissolYe a small bit of soap in hot water, and add to the 
 solution an equal bulk of a solution of sulphate of calcium. The mix- 
 ture immediately becomes turbid, and after a few momenta there will 
 be formed a greasy, fiocculent, adhesive scum upon the surface of the 
 liquor. This precipitate is a lime soap, formed by the union of the 
 fatty ingredients of the soap and the base of the sulphate of calcium. 
 Common soap is a compound of one or more organic acids, known as 
 fatty acids, with caustic soda. This soda soap is soluble in water, but 
 lime soap is insoluble ; hence, when a soluble salt of calcium is added 
 to a solution of soap, precipitation occurs. When soap is added to 
 hard water, it will produce neither permanent froth nor cleansing 
 effect, umtii the sulphate, or other lime-salt present, has all been 
 decomposed ; with such waters, much soap is consumed in removing 
 the calcium compound, before the proper detergent action of the soap 
 can be brought into play. 
 
 560. An excellent process for determining the relative hard- 
 ness of several samples of water has been founded upon the 
 behavior of water towards soap, as set forth in the foregoing 
 experiment : — 
 
 JExp. 288. — Prepare a sample of water, of standard hardness,, as fol- 
 lows : — Dissolve 05 grm. of white marble, or other pure carbonate of 
 calcium, in dilute chlorhydric acid, evaporate to dryness, in order to 
 expel the excess of acid, and dissolve the pure chloride of calcium ob- 
 tained in 2 litres of water. Next prepare a solution of soap by digest- 
 ing 7 grms. of Castile soap, or, better, white curd soap, in 1120 
 grms. of a mixture of 3 parts of alcohol, of 0-83 specific gravity, and 1 
 of pure water, until no more soap dissolves ; filter the solution, and 
 preserve it in a tight bottle. Measure off' 100 c. c. of the water, of 
 standard hardness, place it in a bottle of 200 or 250 c. c. capacity, and 
 by means of a graduated burette (Appendix, § 21), or pipette, add to 
 it the solution of soap by portions of 1 c. c. each. After the addition 
 of each c. c. of the soap solution, replace the stopper in the bottle, and 
 shake the latter violently, then place the bottle upon its side, and 
 observe whether the bubbles, which form upon the surface^ of the 
 liquid, quickly disappear. So long as the bubbles disappear immedi- 
 ately, new portions of the soap-liquor must be added ; but as soon as 
 a permanent froth is formed, the operation is finished. It is customary 
 to consider the operation completed when the bubbles persist durino- 
 three minutes. The nimxber of c. c. of soap-liquor which has been 
 employed in producing this result, is then carefully recorded. 
 
PHOSPHATES OP CAICnjM. 481 
 
 Samples of well- and river- water may readily be compared with the 
 water of known standard hardness. We have only to measure off 100, 
 c. c. of the well- water, place it in a small bottle, as above, and add to 
 it the soap-liquor, whose value has been determined, until a persistent 
 froth is produced. If it be assumed that the standard chloride-of-cal- 
 cium water represent 100° of hardness, the comparative hardness of 
 any other sample of water will follow from the proportion : — As the 
 quantity of soap-liquor required to produce persistent bubbles in the 
 standard water is to 100, so is the quantity of soap-liquor which 
 produces bubbles in any given sample of water to the relative hard-, 
 ness of the sample. 
 
 When the water under examination has a much higher degree of 
 hardness thaji 100°, it is necessary to dilute it with from 1 to 5 times 
 its volume of distilled water before adding the soap-liquor ; for the. 
 curdy precipitate, which would form, if soap were added to the un- 
 diluted liquid, would interfere with the formation of froth, and so 
 make it diificvilt to determine when a suiEcient quantity of the soap- 
 liquor had been used. 
 
 On being ignited in an atmosphere of hydrogen, or in contact 
 with substances containing carbon, gypsum may readily be deox- 
 idized and converted into sulphide of calcium : — 
 CaSO^ + 40 = CaS + 4C0. 
 This reduction is readily effected, also, when aqueous solutions of 
 gypsum are left in contact with decaying vegetable matter. Since, 
 in this case, carbonic acid wiU necessarily come in contact with 
 the sulphide of calcium as soon as it is formed, sulphuretted 
 hydrogen gas wiU be set free, as may be perceived wherever the 
 mud of docks and marshes is wet with sea-water : — 
 CaS -f- H,0 + CO, = CaCO, + H,S. 
 
 561. PJiosphates of Galeivm. — ^There are several of these phos~ 
 phates, comparable respectively with the various phosphates of 
 sodium (§ 489) ; the most remarkable among them is the triphos- 
 phate (3CaO, PjOJ, commonly called bone-phosphate, from being 
 found in bones. It is the chief of the inorganic constituents of 
 which the skeletons of animals are composed. SmaU portions of 
 it are found in most rocks and soils (§262), it being a very widely 
 diffused, though nowhere a very abundant, substance. Consider- 
 able masses of it have been found, however, in Spain, ITew Jer- 
 sey, and Canada, and it is the principal ingredient of some kinda 
 
 2i 
 
482 CHXOKIDE OF CALCIUM. 
 
 of guano. No matter whence obtained, it is a valuable manure 
 when reduced to a fine powder. Though as good as insoluble in 
 water, it dissolves readily in acids and in solutions of various 
 organic substances. 
 
 662. Chloride of Calcium (CaClJ may be prepared by dis- 
 solving chalk or marble in chlorhydric acid (as in Exp. 171), 
 and evaporating the solution to drjmess. It is produced in large 
 quantities in the arts by heating chloride of ammonium with 
 slaked lime in the preparation of ammonia- water (Exp. 48) : — 
 
 2ira,Cl + CaH,0, = CaCl, -|- 2NH3 4- 2H,0. 
 When dried at about 200°, chloride of calcium is left as a porous 
 mass, which is largely employed in chemical laboratories for dry- 
 ing gases (Appendix, § 15). It absorbs water with great avidity, 
 and is one of the most deliquescent substances known. When 
 exposed to air at the ordinary temperature, it soon absorbs so 
 much water that it dissolves completely. At a low red heat the 
 anhydrous chloride melts to a clear liquid; if ignited for any 
 length of time in contact with the air, it suffers decomposition to 
 a slight extent, a little oxide and carbonate of calcium being 
 formed. From highly concentrated aqueous solutions there may 
 be obtained crystals of the hydrated compound CaClj + GH^O. 
 
 Slaked Ume may be dissolved in considerable quantity in a 
 boiling aqueous solution of chloride of calcium, and the filtered 
 solution deposits, on cooling, long, thin crystals of a compound 
 known as oxychloride of calcium (CaCl^, 3CaO + 163^0), which 
 is immediately decomposed when treated with pure water. 
 
 563. Hypochlorite of Caldum (CaCljO^), as has been shown 
 in § 120, is a component of the substance commonly called 
 " chloride of lime." This important bleaching agent is prepared 
 by passing chlorine gas into chambers filled with layers of finely 
 powdered slaked lime, in accordance with the reaction already 
 set forth. Chloride of lime, or bleaching-powder, is a dry, white 
 powder, smelling feebly of hypochlorous acid ; it always contains 
 a certain excess of hydrate of calcium which has been unacted 
 upon by chlorine; it is therefore only partially soluble in 
 water. When exposed to the air, it slowly absorbs carbonic 
 acid, and, at the same time, evolves chlorine ; hence its employ- 
 ment as a disinfecting agent. If, instead of being left to be 
 
HTPOCHLOKITE OF CALCIUM, 483 
 
 slowly acted upon by the carbonic acid of the air, it be treated 
 ■with a dilute acid (such as vinegar), a copious evolution of 
 chlorine will immediately occur. 
 
 JSrp. 289. — Place half a teaspoonful of bleaching-powder in a test- 
 glass, cover the powder with water, and stir in enough of a solution of 
 blue litmus to distinctly color the mixture. By means of a glass tube, 
 blow into the mixture air expired from the lungs, and observe that the 
 blue color of the litmus will soon be destroyed. The carbonic acid 
 from the lungs decomposes the hypochlorite of calcium, and the chlo- 
 rine set free destroys the color. 
 
 Exp. 290. — At the bottom of a large, tall beaker, or other wide- 
 mouthed glass vessel, of the capacity of two or three litres, place a 
 small bottle containing 15 or 20 grms. of bleaching-powder. Cover 
 the beaker with a glass plate, or sheet of pasteboard, provided with a 
 small hole at the centre ; through this hole in the cover pass a thistle- 
 tube down into the bottle of bleaching-powder, and pour upon it several 
 small successive portions of sulphuric acid diluted with an equal volume 
 of water. Chlorine gas will immediately be set free from the bleach- 
 ing-powder, in accordance with the reaction 
 
 CaCl2,CaClA + SH^SO^ = 20aS0i + 2H2O -|- 4C1, 
 and, faUing over into the bottom of the large beaker, will gradually 
 press out and displace the air therein contained, so that after a short 
 time the beaker will be seen to be completely flUed with the green gas. 
 This is by far the easiest and most expeditious method of preparing 
 chlorine. If desirable, the bleaching-powder may, of course, be placed 
 in a flask, together with the acid, and the evolved gas collected at will, 
 by means of suitable delivery-tubes ; but many of the experiments of 
 Chapter "Vlll. may be performed perfectly well in the jar of chlorine 
 obtained as above. The heavy gas may be ladled out of the jar with 
 a dipper made of any small bottle, and poured upon a solution of 
 indigo to show its bleaching-power. 
 
 It will be noticed, in the above reaction, that by the addition of an 
 acid all the chlorine of the bleaching-powder is expelled. The point 
 is important as bearing upon the practical use of this agent. 
 
 Exp. 291. — Soak a bit of printed calico in a half-litre of water, into 
 which 10 or 15 grms. of bleaching-powder have been stirred. Observe 
 that the color of the calico slowly undergoes change ; then transfer the 
 cloth to another bottie Med with very dilute chlorhydric or sulphuric 
 acid, and take note of the rapidity with which the color is discharged. 
 If need be, again immerse the calico in the bleaching bath, and after- 
 wards in the dilute acid. Finally, wash the whitened cloth thoroughly 
 in water. 
 
 2i2 
 
484 OXYGEN FEOlt BLEACHUfG-POWBEE. 
 
 564. When teated, bleaohing-powder gives off oxygen, while 
 chloride of calcium is left as a residue. The reaction furnishes 
 a cheap and convenient method of obtaining oxygen. Another 
 method of procuring oxygen from the hypochlorite is to mix a 
 solution of the latter with black oxide of manganese, red oxide 
 of mercury, oxide of iron, or oxide of copper, or, better, with 
 hydrated sesquioxide of iron, hydrate of copper, of nickel, or of 
 cobalt, and to gently warm the mixture. 
 
 Exp. 292. — ^Fill an ignition-tube one-third fall of bleaching-pow- 
 der, and arrange the apparatus so that the gas may be collected 
 over water. Heat the tube, and observe that the gas is expelled at 
 a comparatively low temperature. 1 grm. of bleaching-powder yields 
 40 or 50 0. c. of oxygen gas. 
 
 Exp. 29.3. — Take as much bleaching-powder as was employed in 
 Exp. 292, dissolve it in a small quantity of water, filter the solution, 
 and place it in a small flask provided with a delivery-tube. Add to 
 the contents of the flask two or three drops of the solution of a cobalt 
 salt, connect the flask with an inverted bottle of water upon the water- 
 pan, by means of the deUvery-tube, then heat the flask to 70^ or 80°, 
 and observe that oxygen is freely evolved. 
 
 The cobalt solution employed amounts to the same thing as hy- 
 drated oxide of cobalt, since the latter is immediately precipitated 
 from the cobalt salt by the caustic lime in the bleaching-powder. 
 The action of the oxide of cobalt, or other metallic oxide, ia this ex- 
 periment, appears to be somewhat analogous to that of the higher 
 oxides of nitrogen in the manufacture of sulphuric acid (§ 228). The 
 oxide of cobalt probably takes oxygen from the solution of bleaching- 
 powder, and combines with it to form a high, unstable oxide, which 
 immediately decomposes again with evolution of oxygen. The oxida- 
 tion and deoxidation of the cobalt compound thus goes on incessantly, 
 and a very small quantity of the latter is sufiicient to decompose any 
 desired amoimt of bleaching-powder. It is important that the solu- 
 tion of the hypochlorite should be filtered as above directed, lest a 
 quantity of it be lost by foaming over out of the fiask. 
 
 565. The proportion of hypochlorite of calcium in bleaching- 
 powder varies widely m. dififerent samples, according to the care 
 with which the sample has been prepared, and to the length of 
 time it has been exposed to the action of the air. The bleaching- 
 power, or in other words, the money value of each special sample, 
 should therefore be determined before it is sold. Of the several 
 
CHIOEIMETET, 485 
 
 methods of ascertaining the value of bleaching-powder, one of 
 the simplest is to determine how much arsenious acid (Ab^Oj) 
 can be converted into arsenic acid (As^Og) by a given weight 
 of the sample : — 
 
 As,03 + 4C1 + 2H^0 = As^O, + 4HC1. 
 
 To this end a weighed quantity of arsenious acid is dissolved in 
 a certain definite quantity of a solution of carbonate of sodium in 
 such manner that each c. c. of the liquor shall contain a known 
 weight of arsenious acid. A considerable quantity of this standard 
 solution may be prepared once for all, and kept for use in tightly 
 closed bottles. A weighed sample of the bleaching-powder under 
 examination is then dissolved in water, and into this solution of 
 bleaching-powder the standard solution of arsenious acid is carefully 
 poured, from a burette, so long as the arsenious acid continues to be 
 oxidized and converted into arsenic acid. 
 
 In order to determine the precise moment when the oxidizing- 
 power of the bleaching-powder solution ceases, a drop of this solu- 
 tion is taken out from time to time upon a glass rod and placed 
 upon paper prepared with iodide of potassium and starch, as has 
 been described in Exp. 71. When the paper no longer becomes 
 blue on being touched with the solution, the operation is known 
 to be completed. Towards the close of the experiment the solution 
 of arsenious acid should only be added drop by drop to the solution of 
 bleaching-powder, and some of the latter should be touched to the 
 test-paper after each addition of the arsenious acid. 
 
 The number of c. c. of the solution of arsenious acid which have 
 been employed is then carefully noted, and the amount of arsenious 
 acid contained in them is computed. From these data the amount 
 of chlorine in the sample of bleaching-powder is obtained by the 
 following proportion : — 
 
 Weight of Weight of 
 198 : 142 = arsenious : chlorine in 
 
 Weight of one Weight, of four acid used. the sample, 
 
 molecule of ar- atoms of chlorine. 
 
 senious acid. 
 
 Of the other compounds of calcium may be mentioned the 
 fluoride (§ 155), bromide, and iodide (analogous to the chloride), 
 the peroxide CaO^, several sulphides (§ 213), and the phosphide 
 (§ 278). Nitrate of calcium (CaNjOJ is a very easily soluble, 
 deliquescent salt, found in many soils, and in other localities 
 where organic matters putrefy in contact ■ydth hydrate or car- 
 
486 
 
 8IK0NTIUM AND BAEIinH. 
 
 bonate of calcium. Sulphydrate of calcium CaS,H,S, analogous 
 to the hydrate, may be prepared by boiliiig monosulphide of 
 calcium with water, or by passing sulphydric acid gas into a cold 
 solution of the sulphide. The solution of this substance possesses 
 a remarkable power of loosening hair from the skins of animals. 
 After a skin has been soaked for a few minutes in a strong solu- 
 tion of this substance, the hair may readily be scraped off with 
 any blunt instrument. A solution of sulphite of calcium (CaSOg) 
 in an aqueous solution of sulphurous acid, is sometimes employed, 
 under the name bisulphite of lime, to check fermentation. 
 
 566. The metal itself may be obtained by decomposing fused 
 chloride of calcium by means of the galvanic current, or by 
 heating iodide of calcium with metallic sodium in a closed iron 
 tube. It is a yeUowish-white, lustrous, ductile metal, of 1-6 
 specific gravity, which sufiers no change in dry air at the ordi- 
 nary temperature. In moist air it oxidizes quickly, and it 
 decomposes water with evolution of hydrogen. At a red heat 
 it melts, and, if oxygen be present, takes fire and burns with a 
 bright Hght. It is a bivalent element ; the weight of its atom 
 is 40. 
 
 SIEONTlTrM AND BAKIint. 
 
 567. The metals strontium and barium closely resemble cal- 
 cium in appearance and properties, and may be prepared by 
 methods similar to those used for calcium, £is described in the 
 last section. The specific gravity of strontium is 2-6, that of 
 barium is 4. The atomic weight of strontium is 87-5, and 
 that of barium 137. Like calcium, strontiuni and barium are 
 both bivalent elements. 
 
 Most of the compounds of strontium and barium are closely 
 analogous to the corresponding compounds of calcium. The 
 oxides, peroxides, hydrates, carbonates, sulphates, nitrates, phos- 
 phates, chlorides, sulphides, &,c. resemble in the main the corre- 
 sponding calcium salts. The hydrates of strontium and barium, 
 however, are more readily soluble in water than the hydrate of 
 calcium, while their sulphates, nitrates, and chlorides are less 
 soluble than those of calcium. Sulphate of barium is almost 
 absolutely insoluble in water, and sulphate of strontium is only 
 
PEROXIDE or BAEirTM. 487 
 
 very slightly soluble. Sulphate of barium is found native, soroe- 
 times in considerable masses, as a very heavy white mineral 
 called barytes, which, when powdered, is largely employed for 
 adulterating white lead. The name barium comes from a Greek 
 word meaning heavy. 
 
 From the carbonates of strontium and barium the carbonic 
 acid cannot readily be driven off by heat alone, though when 
 mixed with charcoal, and then ignited, these carbonates may 
 be reduced to oxides. A better way of preparing the oxides is 
 to heat the nitrates strongly in a porcelain crucible or retort. 
 Unlike hydrate of calcium, hydrate of barium does not give 
 off its water at the temperature of redness, but melts without 
 undergoing decomposition. From hydrate of strontium the water 
 may be expeUed by heat, though with difficulty. Peroxide of 
 barium (BaOJ is of interest, since by means of it peroxide of 
 hydrogen (§ 61) and antozone (§ 177) may be prepared. 
 
 568. In order to obtain peroxide of barium, a mixture of 1 
 part of oxide of barium, and 4 parts of chlorate of. potassium 
 may be thrown, little by little, into a crucible heated to low 
 redness, and the fused mass subsequently washed with water to 
 remove chloride of potassium; or a current of oxygen gas, or 
 of air, may "be made to flow over oxide of barium heated to low 
 redness in a porcelain tube. As thus prepared the peroxide is 
 never pure, being mixed with more or less protoxide. Peroxide 
 of barium decomposes, with evolution of oxygen, at the tempera- 
 ture of bright redness, and in view of this fact it was at one time 
 proposed to employ the substance as a means of obtaining pure 
 oxygen from the air upon the large scale. A considerable num- 
 ber of tubes charged with protoxide of barium, having been 
 suitably arranged in furnaces, half of the tubes were heated to 
 duU redness, and a current of air was made to flow through 
 them, until the protoxide had been converted into peroxide; 
 the current of air was then transferred to the other tubes, while 
 the first series was put in connexion with a gas-holder and 
 heated to bright redness, until the second atom of oxygen had 
 been driven out. The second series of tubes were next deprived 
 of oxygen, while the tubes of the first series were put to their 
 old work of absorbing oxygen from the air. The process thus 
 
400 strontium: salts, 
 
 became a continuous one, and was really capable of furnishing 
 large quantities of oxygen ; it has, however, been superseded by 
 cheaper methods (§ 242). 
 
 Strontium salts are commonly prepared from the native car- 
 bonate, a mineral called strontianite, while the various salts of 
 barium are obtained either from the native carbonate (witherite), 
 or more commonly from the sulphate. The finely powdered sul- 
 phate, after having been mixed with powdered charcoal and oil, 
 is strongly heated in a covered crucible, and so reduced to the 
 condition of sulphide of barium : — 
 
 BaSO, -I- 4C = BaS + 4C0. 
 
 Sulphide of barium is readily soluble in water, and on being 
 
 treated with chlorhydric, nitric, or any other acid, it decomposes, 
 
 sulphuretted hydrogen is given off, and there is formed chloride 
 
 of barium, or some other salt, according to the acid employed : — 
 
 BaS + 2HC1 = BaCl, + H,S. 
 
 Several of the compounds of barium are useful reagents in the 
 chemical laboratory. Sulphate of barium is employed as a pig- 
 ment by artists in water-colors, under the name permanent white, 
 also in the finishing of paper, pasteboard, &c., and for adulterating 
 white lead. As a water-color it is valuable, since it is scarcely 
 at all acted upon by any chemical agent ; but when ground with 
 oU it becomes translucent, and seriously impairs the opacity or 
 covering power of the better pigments with which it is mixed. 
 
 Compounds of barium and of strontium are employed in the 
 preparation of fireworks, for obtaining green and crimson flames 
 respectively; — • 
 
 Th« green barium-flame may be well shown by mixing with the 
 fingers a gramme of powdered chlorate of barium with half a gramme 
 of flowers of sulphm-, and strewing the mixture upon a glowing coal. 
 The green fire of the pyrotechnists may be prepared by mixing together 
 58 parts of nitrate of barium, IS parts of sulphur, 6 parts of chlorate 
 of potassium, and 2 parts of charcoal. 
 
 To exhibit the red strontium-flame, a mixture may be prepared by 
 rubbing together in a mortar 30 parts of anhydrous nitrate of stron- 
 tium, 10 parts of powdered sulphur, and 3 parts of sulphide of anti- 
 mony ; and to this mixture may be added, with the hand, taJring care 
 to avoid all violent friction, 7 pai'ts of powdered, fused chlorate of 
 
THE CAXCrUM GROUP. 489 
 
 potassium. The mixture may then be shaken loosely upon a piece of 
 sheet iron and touched with a lighted stick or glowing coal. 
 
 Or the color may be shown upon a smaller scale by operating as 
 follows : — 
 
 Exp. 294. — By means of iron wire, suspend three small bullets of 
 weU-bumed coke from a ring of the iron stand. Heat the fragments 
 in turn with the flame of the gas-lamp, and observe the slightly yel- 
 lowish flame which wiU be produced in each case ; then moisten one 
 of the pieces of coke with a solution of chloride of calcium, the second 
 with a solution of chloride of barium, and the third with a solution of 
 nitrate of strontium, and again heat them in turn with the gas-flame. 
 The calcium salt will impart a reddish-yeUow color to the flame, the 
 barium salt a green color, and the strontium salt a beautiful crimson. 
 Instead of the bits of coke, platinum wire might of course be employed, 
 as in Exp. 202. 
 
 569. As appears abundantly from the foregoing, the three 
 elements calcium, strontium, and barium are intimately related 
 one to the other, and are, as a family, clearly distinguished in 
 several important particulars from the metals of the preceding 
 group. Even before the metals of this family were discovered 
 and isolated, it had long been customary among chemists to speak 
 of the oxides of calcium, strontium, and barium as the aTkaline 
 earths, in contradistinction from the " alkalies," potash and soda, 
 upon the one hand, and the "earths," such as the oxides of 
 magnesium and aluminum, upon the other. 
 
 Each of the members of the alkaJine-earthy group, now in 
 question, decomposes water, even at the ordinary temperature, 
 taking away its oxygen ; and each of them forms two oxides — a 
 neutral, insoluble binoxide, belonging to the class of antpzonides 
 (§ 182), and a more or less soluble protoxide, acting as a powerful 
 base; their carbonates and sulphates are all difficultly soluble, 
 and, like the other compounds of the three metals, are isomor- 
 phous with one another. In aU their compounds, there may be 
 seen the same progression of properties which has been met with 
 in the groups previously studied. The barium compound will 
 always be found at one end of the scale, the calcium compound 
 at the other, and the strontium compound interposed between the 
 two. The hydrate and the carbonate of calcium are both readily 
 destroyed by heat, while the corresponding strontium compounds 
 
490 r^AB. 
 
 are decomposed with diffictilty, and the barium compounds only 
 at exceedingly high, temperatures. The solubility of the oxides 
 diminishes as we pass from baryta to Ume, while that of the sul- 
 phates and carbonates foUows the inverse order. The specific 
 gravities of the metals are, Ca=l-6, Sr=2-6, Ba=4 ; and their 
 atomic weights are 40, 87-5, and 137 respectively, that of stron- 
 tium being nearly the mean of the other two. The specific 
 gravities of their carbonates and sulphates are as follows : — 
 CaCO, (arragonite) =2-95, SrC03=3-6, BaC03=4-33; CaSO^=: 
 2-33, SrSO^=3-89, and BaS0^=4-4. It should be observed that, 
 in all these cases, the specific gravities of the strontium com- 
 pounds approximate closely to the mean of the specific gravities 
 of the corresponding barium and calcium compounds. The same 
 remark applies also to the specific gravities of the three metals. 
 
 LEAD. 
 
 570. Almost all the lead which is employed in the arts is 
 extracted from sulphide of lead, PbS, the mineral galena. This 
 substance is tolerably abundant in many localities, and is often 
 associated with sulphate of barium, fluor-spar, quartz, and other 
 common minerals ; it almost always contains a small proportion 
 of sulphide of silver. In order to obtain metallic lead from ga- 
 lena, this mineral is mixed with a small quantity of lime, and 
 then roasted at a dull-red heat in the flame of a reverberatory 
 furnace. A portion of the sulphur burns off as sulphurous acid. 
 Some oxide of lead, and more or less sulphate of lead is formed, 
 while much of the ore remains undecomposed. After a time, the 
 roasting-process is interrupted, air is excluded from the furnace, 
 the oxide, sulphate, and sulphide of lead are thoroughly mixed 
 together, and the heat of the furnace is suddenly raised. The 
 undecomposed sulphide of lead then reacts upon the oxide and 
 sulphate, sulphurous acid is given off, and metallic lead produced. 
 The reactions may be thus formulated : — 
 
 2PbO + PbS = BPb + SO,. 
 
 PbSO, + PbS = 2Pb + 2S0,. 
 
 The lime is added for the purpose of forming a fusible slag 
 with any siliceous matter which may be present in the ore. 
 Lead is a remarkably soft metal, of bluish- white color ; it can 
 
MEIAIXIC LEAD, 491 
 
 be readily cut with a knife, and may even be indented with the 
 finger-nail ; it soils paper upon which it is rubbed. Its specific 
 gravity is 11-4, and its atomic weight 207. It may be drawn 
 into wire, and beaten into sheets, though, as contrasted with most 
 of the other metals, it has but little tenacity. In comparison with 
 other metals, it is a rather poor conductor of heat and electricity. 
 It melts at about 325°, and contracts considerably in passing from 
 the liquid to the solid condition. Its specific heat is 0-0314. 
 SoUd lead expands greatly when heated, though the heat be not 
 carried near to the melting-point, and the expanded metal does 
 not return again to its original dimensions when cooled. Melted 
 lead begins to emit vapors at a red heat, and at very high tem- 
 peratures the metal may even be distilled. Lead may be obtained 
 crystallized in octahedrons, by slowly cooling the molten metal. 
 
 The ready crystallization of lead furnishes a very simple method 
 of separating this metal from the sUver with which crude lead is 
 almost always contaminated as it comes from the smelting fur- 
 naces. When melted argentiferous lead is aUowed to cool slowly, 
 and is at the same time briskly stirred, a quantity of solid crys- 
 talline grains separate out after a while, and sink beneath the 
 liquid metal, whence they may be dipped out in cullenders. 
 These crystals are composed of lead nearly free from silver, whUe 
 all but a trace of the silver contained in the original lead is left 
 in that portion of the metal which has not yet sohdifled ; in a word, 
 the alloy of lead and silver melts at a lower temperature than 
 pure lead. By methodically remelting and reerystallizing the 
 lead crystals on the one hand, and the silver alloy on the other, 
 it has been found profitable to extract the silver from lead so poor 
 that it contained less than one thousandth part its weight of the 
 precious metal. 
 
 "When in thick masses, such as the common sheets and pipes of 
 commerce, lead is scarcely at all acted upon by cold sulphuric 
 acid, and is but slowly corroded by chlorhydric acid. Both 
 these acids form, by uniting with lead, diflcultly soluble salts ; 
 and so soon as a layer of the salt has once been deposited upon 
 the surface of the metal, the latter is thereby protected from 
 further corrosion. By hot, concentrated sulphuric acid, however, 
 lead is dissolved rather easily. The best solvent of metaUio 
 
492 
 
 OXIDATION OF LEAD. 
 
 lead is diluted nitric acid ; strong nitric acid -will not dissolve it 
 readily, since nitrate of lead is well nigh insoluble in concen- 
 trated nitric acid. 
 
 671. Oxides of Lead. — When a compact piece of metallic lead 
 is freshly cut, it exhibits considerable lustre, and this lustre may 
 be preserved unimpaired by keeping the lead in perfectly dry air, 
 or beneath the surface of pure water free from air (§ 47). But 
 by exposure to ordinary air the brilliant surface soon tarnishes, m 
 consequence of the formation of a thin coating of suboxide of lead; 
 this incrustation protects the metal beneath from further oxida- 
 tion. Finely divided lead, on the contrary, soon changes com- 
 pletely to suboxide when exposed to the air. If the metal be fine 
 enough, it wiU oxidize instantaneously, with evolution of light 
 and heat, and formation of yellow protoxide of lead. 
 
 Exp. 295. — Prepare a small quantity of tartrate of lead, as follows. 
 Dissolve 0'25 grm. of common sugar of lead (acetate of lead) in 8 or 
 10 c. c. of water, also dissolve O'l grm. of tartaric acid in 4 or 5 c. c. 
 of water, and mix the two solutions. Collect upon a filter the white 
 precipitate of tartrate of lead which will be formed, wash it with 
 water, then unfold the filter and spread it out with its contents to dry 
 in the air, or, better, at a gentle heat upon a ring of the iron stand, high 
 above a single gas-flame. 
 
 Fill an ignition-tube one-third full of the dry tartrate of lead, and 
 heat it upon a sand-bath so long as any fumes escape, then cork the 
 tube tightly and set it aside to cool. Holding the cooled tube high 
 in the air, sprinkle its contents upon a plate, and observe that the black 
 powder takes fire spontaneously, and bums with a red flash. The 
 composition of tartrate of lead may be represented by the formula 
 CjH^PbjOj ; on being heated this substance gives off water and car- 
 bonic oxide, as may be seen by lighting the fumes which escape from 
 the tube, and there is left as a residue an intimate mixture of carbon 
 and of metallic lead, so finely divided that it inflames in ordinary air. A- 
 spontaneously inflammable mixture such as this is called s.pyrophonm. 
 
 572. Lead is far more readily oxidized by the continued action 
 of air and water than by ordinary moist air. When exposed to 
 the simultaneous or alternate action of these agents, a coating of 
 the white hydrated protoxide of lead is rapidly formed ; but as 
 this compound is somewhat soluble in water, it is continually dis- 
 solved away and affords little or no protection to the lead beneath. 
 The corrosive action of water upon lead is modified very mate- 
 
ACTION OF WATERS ON lEAD. 493 
 
 rially by the presence of small quantities of various saline sub- 
 stances. Water containing traces of nitrates, nitrites, and chlo- 
 rides corrodes lead more rapidly than pure water, while the 
 corrosive action of pure water appears to be diminished by the 
 presence of sulphates, phosphates, and carbonates, oxide of lead 
 being scarcely at all soluble ia water which contains these salts in 
 solution. Water containing a solution of carbonate of calcium in 
 carbonic acid, such as is frequently met with in nature, has been 
 found to have remarkably little action upon lead ; in such water 
 a coating of insoluble, or nearly insoluble carbonate of lead is 
 formed upon the metal, which protects it from further action. 
 But, on the other hand, water which contains much free carbonic 
 acid dissolves away the protective coating and exposes fresh sur- 
 faces of lead to corrosion. As a general rule, the acids, even when 
 very dilute, greatly accelerate the oxidation of lead in the air j 
 and the same remark is true of organic substances and of metals, 
 the first by their decay, the second by the galvanic action which 
 their presence excites. 
 
 Since solutions of lead are poisonous, and since the metal is 
 employed to an enormous extent for cisterns and conduits, a 
 knowledge of the action of water upon lead is very important in 
 a sanitary point of view. The question has consequently engaged 
 the attention of many chemists, and has been much discussed. 
 It has been proved by numberless experiments that the action of 
 natural waters upon lead is so general that it is rare to find any 
 sample of water, which has been kept in a leaden cistern, wholly 
 free from traces of that metal. The opinion of most chemists is at 
 this time (1867) decidedly adverse to the use of leaden water-pipes 
 in houses, in spite of the fact that the metal is nowadays employed 
 for this purpose almost everywhere with apparent impunity. 
 
 When lead is melted in the air it oxidizes readily, with for- 
 mation at first of gray suboxide, and afterwards of the yellow 
 protoxide. 
 
 673. Suhoadde of Lead (Pb^O) may be prepared in a state of 
 purity by cautiously heating oxalate of lead at a temperature not 
 exceeding 300° in a retort from which air is excluded, so long as 
 any gas is evolved : — 
 
 2PbC,0, = Pb,0 -f CO + 3C0,.] 
 
494 
 
 CTIPELLATIOS. 
 
 After the retort has hecome cold, euboxide of lead will be found 
 in it as a black velvety powder. It is decomposed by acids, with 
 formation of salts of protoxide of lead, and separation of metallic 
 lead. 
 
 574. Protoxide of Lead (PbO), commonly called litharge, may 
 be obtained as a lemon-yellow powder by gently igniting nitrate, 
 carbonate, or oxalate of lead upon an iron plate, or in an open 
 porcelain crucible. The oxide fuses at a red heat, and when 
 melted in vessels of porcelain or earthenware it rapidly destroys 
 them by combining with their silica, an easily fusible slag or 
 glass composed of double silicates of lead, aluminum, iron, &c. 
 being formed. Sihoate of lead is an actual constituent of the easily 
 fusible variety of glass known as flint glass (see § 492, and Ap- 
 pendix, § 3). 
 
 In the arts, litharge is prepared upon the large scale by heating 
 metallic lead in a current of air ; the color and texture of the pro- 
 duct varies considerably according to the temperature and the 
 other conditions under which it has been prepared. 
 
 -Ecp. 296. — Heat a small ftagment of lead iipon charcoal in the 
 oxidizing flame of the blowpipe, and observe the gray film of sub- 
 oxide which forms at first, and the yellow incrustation of litharge 
 which is obtained subsequently. The litharge may be melted if a 
 strong, hot flame be thrown upon it. 
 
 This property of lead, of rapidly oxidizing when heated in the air, 
 taken in connexion with the easy fusibility of the oxide, is the basis 
 of the common method of separating lead and silver in the large way, 
 known as cvpellation. The iridescent film of litharge continually 
 formed upon the surface of the molten metal as incessantly flows off, 
 exposing new surfaces of the metal to the action of the air. The 
 silver, on the other hand, undergoes little or no change, and when the 
 lead has been completely burned the silver appears in all its brUliant 
 whiteness. 
 
 The cupel is a shallow cup or basin, composed either of marl or of 
 a mixtm'e of bone-ash and wood-ashes firmly compacted and beaten to 
 a smooth surface, which may be placed either in the muffle of an assay 
 furnace, upon the hearth of a reverberatory, or in any position where 
 it can be strongly heated at the same time that a free current of air 
 plays over its surface. A charge of argentiferous lead having been 
 melted upon the cupel, new portions of the lead are added as fast as 
 the melted htharge flows ofi from the convex surface of the metal and 
 
PEROXIDE OP lEAD. 495 
 
 makes room for these additions, until an alloy very rich in silver has 
 been obtained. This alloy is then cupelled until the last traces of lead 
 have been removed, and the silver is left pure and glistening. In 
 cupelling upon the small scale, for purposes of assaying, the cupel is 
 made of bone-ash of such quality that the litharge may be absorbed 
 into the substance of the cupel, and not flow oif through gutters upon 
 its edge, as is the case in large metallurgical operations. 
 
 575. Protoxide of lead unites readily with acids, and forms 
 many important salts. When in the state of powder, it even 
 absorbs a certain amount of carbonic acid from the air ; hence 
 the powdered litharge of commerce always contains more or less 
 carbonate of lead, and therefore effervesces on being treated with 
 acids, as has been seen in Exp. 42. As a general rule, it is far 
 better to prepare the salts of lead by dissolving the protoxide in 
 acids, than to treat the metal itself with acids. Protoxide of 
 lead has a remarkable tendency to form basic salts ; thus besides 
 the normal nitrate (PbO.NjOj) there is a dinitrate (2PbO,N205), 
 a trinitrate (SPbOjN^Oj), a tetranitrate (4PbO,N205)> ^^^ ^ hexa- 
 nitrate (6PbO,N,Oj). 
 
 Though a strong base as regards the acids, protoxide of lead 
 behaves like an acid towards the alkalies and alkaline earths. 
 For example, it dissolves readily in soda or potash lye, with for- 
 mation of plumbite of sodium, or of potassium, as the case may 
 be. The term plumbite, like the symbol of lead, Pb, is derived 
 from plumbum, the Latin name of the metal. 
 
 576. Peroxide of Lead (PbOJ may be prepared by oxidizing 
 the protoxide — ^for exa;mple, by passing a current of chlorine gas 
 through water in which protoxide of lead is kept suspended by 
 agitation, or as follows : — 
 
 Exp. 297. — Place 8 or 10 grms. of very finely powdered sugar of 
 lead in a capacious porcelain dish, cover the salt with a filtered solu- 
 tion of bleaching-powder (§ 663), heat the solution to boiling, and 
 maintain it at this temperature, until the escaping vapors smell 
 strongly of acetic acid ; then pour the contents of the dish upon a 
 filter, and wash with water the dark-brown powder of peroxide of 
 lead which has been formed. 
 
 Peroxide of lead may be easily obtained also by digesting red lead 
 with dilute nitric acid, as will appear in the following paragraph. 
 
 Peroxide. of lead is a powerful oiddizing agent; it readily giyee 
 
496 
 
 BED LEAD. 
 
 up oxygen, to many organic substances, even at the ordinary 
 temperature of the air. On beiag heated to redness, it loses half 
 its oxygen, and is converted into the protoxide. 
 
 JExp. 298. — In a small porcelain mortar, rub together a mixture of 
 1 grm. of oxalic acid, and 1 grm. of peroxide of lead. Decomposition 
 will occur, aqueous vapor and carbonic acid will be given off, and car- 
 bonate of lead, PbCOj, vsdll be left as a residue. When the peroxide 
 is thus mixed with one-eighth its weight of sugar, or with one-sixth . 
 its weight of tartaric acid, so much heat is developed, that the mass 
 in the mortar glows. 
 
 Peroxide of lead is decomposed by chlorhydric acid, with libe- 
 ration of chlorine, and formation of normal chloride of lead — 
 
 PbO, + 4HC1 = PbCl, + 2H,0 + 2C1, 
 — and by hot sulphuric acid, with evolution of oxygen. It com- 
 bines with sulphurous acid readily, and is often employed in the 
 laboratory as an absorbent of this gas ; and it is noteworthy that 
 the product of this combination is sulphate of lead : — 
 PbO, + SO, = PbSO,. 
 It is indifferent, therefore, whether we put together peroxide 
 of lead and sulphurous acid, or protoxide of lead and sulphuric 
 acid; the product will, in either case, be common sulphate of 
 lead; for 
 
 PbO + SO3 = PbSO,. 
 
 As a rule, peroxide of lead does not readUy enter into combi- 
 nation with acids, though compounds of it with acetic, phos- 
 phoric, arsenic, and some other acids have been obtained. With 
 strong bases, however, it combines readily, forming salts known 
 as plumbates. 
 
 577. Bed Lead or Minium. — ^When protoxide of lead is kept 
 at a low red heat for some time, in contact with air, it gradually 
 absorbs one or two per cent, of oxygen, and acquires a brilliant 
 red color. The product of this oxidation is extensively used as a 
 pigment and in the manufacture of some kinds of glass ware ; it 
 may be regarded as a compound of PbO and PbO^, ia varying 
 proportions. By digesting it for some time in dilute nitric acid, 
 the protoxide of lead may all be dissolved out and converted into 
 nitrate of lead, while the peroxide of lead is left as a residue : — 
 
 2PbO,PbO, + 2H,N,0, = 2PbN,0, -1- 2Sfi + PbO,. 
 
STTLPHIBES OP LEAD. 497 
 
 JSxp. 299. — ^Heat in an iron spoon 4 grms. of litharge and 1 grm. of 
 chlorate of potassium, and observe that the color of the mixture soon 
 changes from yellow to red. Throw the cooled product upon a filter, 
 wash it with water, then dry it and compare its color with that of the 
 original litharge. In this experiment, the red lead could he obtained 
 as well by simply heating litharge without admixture in the air for 
 many hours, at a temperature just below its melting-point ; time alone 
 is gained by employing chlorate of potassium as the source of oxygen. 
 For commercial purposes, red lead is obtained by heating metallic lead 
 in reverberatory furnaces, or, when a very pure article is needed, by 
 heating carbonate of lead. 
 
 When heated strongly, red lead is resolved into protoxide of lead 
 and free oxygen. Oxygen gas may be prepared from it in the same 
 manner as from oxide of mercury (Exp. 6), though at a higher tem- 
 perature. 
 
 578. Sesqviooeide of Lead (Pb^Og) is recognized as a distinct 
 oxide by some chemists, but is more generally regarded as a 
 compound of the proto- and peroxides, PbO, PbO^, — a plumbate 
 of lead. 
 
 579. Sulphides of Lead. — There are several of these com- 
 pounds, but the protosulphide, PbS, is the only one whose com- 
 position is accurately known. This sulphide is the native mineral 
 galena (§ 570) ; it may be prepared artificially either by melting 
 together lead and sulphur in atomic proportions, or by treating 
 the solution of any lead salt with sulphydric acid (§ 209). The 
 native mineral, lite the compound obtained artificially by way of 
 fusion, is of a leaden-gray color of 7"5 specific gravity, but the 
 precipitate which forms when sulphydric acid is added to the 
 solution of a lead salt, is black, or brown, or even red if the 
 solution be dilute. On account of the deep color, a& weU as the 
 insolubility of this precipitate, sulphydric acid is often made use 
 of as a means of detecting lead ; the test is, in fact, so delicate 
 that solutions containing only a hundred thousandth of their 
 weight of metaUic lead will assume a brown color on being 
 charged with sulphuretted hydrogen. 
 
 Exp. 300. — Dissolve quarter of a gramme of sugar of lead in 4 litres 
 of water, add to the solution s few drops of nitric acid so that it shall 
 exhibit a faint acid reaction with litmus-paper, pass into the solution 
 a current of sulphydric acid gas until the solution smeUs strongly of it 
 and observe the brown color imparted to the fluid after some time. 
 
 2k 
 
498 CHLOKIDE OF LEAP, 
 
 In testing for the presence of lead in excessively dilute solutions, 
 such, for example, as water drawn from leaden pipes, it is well to 
 evaporate the liquid to a small bulk in a porcelain dish, to acidulate 
 the concentrated liquor very slightly with nitric acid, and then to 
 transfer it to a beaker glass. The liquid should then be saturated 
 with sulphuretted hydrogen gas, the beaker covered with a glass plate, 
 and left to stand during several hours in a moderately warm room. 
 J£ lead be present, it will be indicated after a while either by the 
 brown coloration of the liquid, or by the actual separation of a black 
 powder at the bottom or upon the sides of the glass. 
 
 580. Sulphide of lead is volatile at high temperatures, and is 
 often found in the cracks and upon the walls of smelting fur- 
 naces, in the form of crystals, which have been deposited by sub- 
 limation. By virtue of the volatility of its sulphide, lead may be 
 transported to very considerable distances from furnaces where 
 ores containing galena are roasted or reduced. It has been 
 found, moreover, that growing plants are capable of taking up 
 the lead thus deposited, and of assimilating a certain portion of it 
 in their tissues. Comparative experiments made at very high 
 temperatures have shown that galena may lose as much as 3-7 
 per cent, of its weight by volatilization, while metallic lead, ex- 
 posed to the same conditions, loses less than 0-1 per cent. 
 
 Sulphide of lead, like the sulphides of the alkaU-metals and 
 those of the alkaline-earthy metals, acts as a sulphur base ; 
 with sulphantimonic acid, for example, it unites to form a salt, 
 3PbS,8bS5, analogous to that formed by the union of antimonic 
 acid and oxide of lead, 3PbO,Sb05. 
 
 581. Chloride of Lead (PbClJ. — Metallic lead is but slowly 
 acted upon by chlorine, or by chlorhydric acid, though hot chlor- 
 hydrie acid dissolves a little of it with formation of chloride of 
 lead and evolution of hydrogen, even when out of contact with 
 the air; the chloride may, however, be readily prepared by 
 digesting oxide or carbonate of lead in chlorhydric acid, or by 
 mixing the solution of almost any lead salt with chlorhydric acid, 
 or with a solution of some soluble chloride : — 
 
 PblSr.O, + 2NaCl = PbCl, + m.Nfl^. 
 
 Chloride of lead is but sparingly soluble in cold water, and is 
 still less soluble in water acidulated with chlorhydric acid ; hence 
 
SALTS OF LEAD. 499 
 
 it may readily be precipitated as above described, and collected 
 upon a filter. In hot water, bowever, it dissolves rather easily, 
 and it is somewhat soluble in concentrated acid also. 
 
 Exp. 301. — Boil together, in a small flask, 1 grm. of litharge, 14 
 grms. of strong chlorhydrio acid, and 14 grms. of water, during 15 or 
 20 minutes. Pour the mixture upon a filter supported in a funnel 
 which has been gently warmed by holding it over the flame of the 
 gas-lamp, and collect the clear filtrate in a warm bottle. As the solu- 
 tion cools, lustrous needle-shaped crystals of chloride of lead will 
 form in it. 
 
 Bxp. 302. — Pour ofi'the cold supernatant liquor from the crystals of 
 chloride of lead obtained in Exp. 301, place the crystals upon" a frag- 
 ment of porcelain, dry them at a gentle heat, and finally heat them 
 more strongly. It will be found that the crystals melt very easily, 
 and that on cooling they soHdify to a soft translucent horny mass, 
 whence the old name of this substance, horn-had. 
 
 582. The compounds of lead with iodine, bromine, and fluorine 
 are analogous to chloride of lead. The iodide is remarkable on 
 account of its beautiful yellow color, which may readily be shown 
 by adding a drop or two of a solution of iodide of potassium to a 
 small quantity of a solution of nitrate of lead. 
 
 Of the numerous other salts of lead little need here be said. 
 The nitrate and tartrate have already been prepared (Exps. 42, 
 295) ; we have obtained the sulphate also as a white, nearly 
 insoluble powder by adding water to concentrated sulphuric acid, 
 and it may be had in any quantity by mixing the solution of a 
 lead salt with dilute sulphuric acid, or with the solution of a 
 soluble sulphate. Acetate of lead, one of the most important of 
 the lead salts, and the one most readily to be procured in com- 
 merce in a state of purity, is prepared by dissolving oxide of lead 
 directly in acetic acid such as is obtained in the distillation of 
 wood (§ 380), or indirectly by moistening plates of metallic lead 
 with vinegar in vessels open to the air. It crystaUizes readily, 
 is easily soluble in water, and has a sweet, astringent taste, 
 whence the name, sugar of lead. Like the other lead salts, it is 
 highly poisonous. It is employed for many purposes in the arts, 
 and is in particular much used in medicine. Carbonate of lead 
 (PbCOj), or rather compounds of carbonate of lead and of hydrate 
 of lead in varying proportions, are used to an enormous extent as 
 
 2k2 
 
500 
 
 WHITE lEAB. 
 
 a white paint, under the general name of white had. The com- 
 position of this substance may usually be expressed by a formula 
 lying within the limits PbCOjiPbH^Oj,, upon the one hand, and 
 SPbCOj.PbHjOj on the other. As contrasted with the other 
 white pigments it possesses remarkable covering-power and dura- 
 bility, and is consequently much esteemed iu spite of its high 
 cost, its injurious influence upon the health of workmen who 
 have to do with it, and the fact that it is discolored by air 
 containing sulphuretted hydrogen. "White lead is often adul- 
 terated with sulphate of barium, with oxide of zinc, and with 
 gypsum. It is usually prepared by bringing carbonic acid, ob- 
 tained from decaying vegetable matter, or from the combustion of 
 fuel, into contact with basic acetate of lead,^ — the latter being pre- 
 pared in this case either by mixing litharge and vinegar to the 
 consistence of a paste, or by exposing rolls of sheet lead to the 
 simultaneous action of vapors of vinegar and air, or by actually 
 dissolving an excess of litharge in vinegar. Sometimes the car- 
 bonic acid is made to act upon the subacetate at the very moment 
 when it is being formed, while at other times the acetate is pre- 
 pared by itself, and subsequently treated with carbonic acid. 
 
 583. Silicate of lead is of interest from being an important 
 ingredient of flint glass ; a certain proportion of it renders glass 
 lustrous and very beautiful. Such glass is, however, soft, easily 
 fusible, and incapable of bearing sudden changes of temperature ; 
 it is, moreover, rather easily acted upon by alkalies, acids, and 
 other chemical agents, and is hence comparatively useless in the 
 chemical laboratory. 
 
 684. In many points of chemical behavior the compounds of 
 lead resemble more or less clearly the corresponding compounds 
 of barium, strontium, and calcium. Its compounds are moreover 
 somorphous with those of the metals in question, and its atom, 
 like the atoms of these metals, is bivalent. Lead is therefore 
 classed as a member of the calcium group, though, as is the case 
 with fluorine in the chlorine group, it differs in some respects 
 from the other members of the family. The specific gravity of 
 lead is 11-4, and its atomic weight 207. The specific gravity of 
 carbonate of lead is 6'5, and that of sulphate of lead is 6-2. 
 
MAeNESITrM. ' 501 
 
 CHAPTEK XXIX. 
 
 MAaifESnj M Z I N C C A D M I IT M. 
 
 MAONBSirTM:. 
 
 585. This metal, or rather its oxide, was formerly classed with 
 the group which comprises the alkaline earths, but it is now 
 known to be more closely connected with zinc and cadmium than 
 with any other of the elements. It is found widely diffused, and 
 rather abundantly, in nature. The bitter taste of sea- water and 
 of some mineral waters is due to the presence of magnesium salts, 
 while silicate of magnesium and carbonate of magnesium are con- 
 taiaed in a variety of minerals and in such common rocks as 
 dolomite, serpentine, soapstone, and talc. 
 
 586. Metallic magnesium may be prepared by heating anhy- 
 drous chloride of magnesium with sodium in a crucible of por- 
 celain or platinum, and subsequently dissolving out in cold water 
 the chloride of sodium which results from the reaction. Mag- 
 nesium is a lustrous metal, as white as tin ; its specific gravity is 
 1-75, and its atomic weight 24. It does not tarnish iu dry air, 
 though in damp air it soon becomes covered with a film of hy- 
 drate of magnesium. It melts at a low red heat, and volatilizes 
 at higher temperatures ; it may be readily distilled at a bright 
 red heat. When heated strongly in the air it takes fire and 
 burns with a bluish-white light of great brilliancy and high 
 actinic power. The metal is employed by photographers for 
 illuminating caverns and other places into which sunlight cannot 
 penetrate, and in cloudy weather it is even used by them as a 
 substitute for daylight. The metal can be pressed into wire or 
 into thin ribbons, and a considerable quantity of it is now used 
 in both these forms for purposes of illumination, as above stated. 
 Magnesium lanterns are much used in theatres for illuminating 
 scenery and tableaux. The white light has the advantage of 
 showing colors just as they look by daylight. For scenic effects 
 the light may be modified by transmission through colored glass. 
 Magnesium is only slowly acted upon by cold water, but is 
 
502 OXIDE OF MACfNESITJM. 
 
 rapidly oxidized by hot water and by water acidulated with 
 almost any acid ; oxide of magnesium is formed and hydrogen 
 set free. 
 
 587. Oxide of Magnesium (MgO). — There is but one com- 
 pound of magnesium and oxygen ; it is obtained as a white 
 amorphous powder when magnesium is burnt in the air, or when 
 carbonate, chloride, or nitrate of magnesium is ignited. 
 
 Exp. 303. — Roll 10 or 12 cm. of magnesium wire or thin ribbon 
 into a coU around a small pencil ; withdraw the pencil and place m 
 its stead a piece of iron wire or a knitting-needle ; holding this wire 
 horizontally, apply a lighted match to the end of the magnesium coU ; 
 the magnesium will burn to the white oxide, which coheres in an im- 
 perfect coil, clinging to the iron wire. A portion of the oxide goes off 
 as white smoke. The magnesium wire for this experiment may be 
 procured at toy-shops as well as of dealers in fine chemicals. 
 
 The oxide is tasteless and odorless; it is soluble to a very 
 slight extent in water, and the solution has an alkaline reaction. 
 The specific gTavity of the solid oxide, or magnesia, as it is often 
 called, varies from 3'07 to 3-2 as ordinarily prepared; but on 
 being very strongly ignited it becomes denser, and samples have 
 been prepared in this way of specific gravity as high as 3-61. 
 
 The light powdery oxide of magnesium known as " calcined 
 magnesia," which is prepared by gentle but prolonged ig-nition 
 of the hydrated carbonate, differs materially in several parti- 
 culars from the more compact oxide obtained by calcining nitrate 
 or chloride of magnesium at high temperatures, or by intensely 
 heating the powdery oxide. Common calcined magnesia is, for 
 example, readily soluble in acids ; but after the oxide has been 
 exposed to very high temperatures it dissolves but slowly even in 
 the strongest acids. Similar differences between the products ob- 
 tained at high and at low temperatures are met with among the 
 oxides of almost aU the metals hereafter to be studied. 
 
 588. A compact variety of oxide of magnesium, obtained by 
 heating the nitrate or chloride to bright redness, but no higher, 
 exhibits remarkable hydraulic properties. On being wet it 
 quickly combines with a portion of water, and is converted into 
 a crystallized hydrate of compact texture, harder than marble, 
 and of great durability. 
 
HTBRATJUC MAGNESIA. 503 
 
 A mixture of equal parts of the hydraulic magnesia and of 
 chali, or powdered marble, made into paste with water, yields 
 a slightly plastic mass, which admits of being readily pressed 
 into any desired shape ; if the moulded material be then placed 
 in water it will become, after some time, extremely hard and 
 compact (§ 591). 
 
 Oxide of magnesium is altogether infusible at temperatures 
 short of that of the oxyhydrogen flame. Very excellent cru- 
 cibles for scientific purposes are prepared by compressing oxide 
 of magnesium into suitable forms. These crucibles undergo far 
 less change in the air than those made from lime ; and like the 
 lime crucibles they do not unite with oxide of iron and the other 
 metallic oxides to form the fusible slags or glasses which are so 
 annoying in the ordinary crucibles, of which silicic acid is an 
 essential component. 
 
 589. CMoride of Magnesium (MgClJ is found in sea-water 
 and iu many saline springs. It is formed when magnesium 
 is burnt in chlorine gas, when a current of chlorine is passed 
 over a red-hot mixture of charcoal and oxide of magnesium, 
 and, in combination with water, by dissolving oxide of mag- 
 nesium in chlorhydric acid. It is remarkable that the hydrated 
 chloride last mentioned cannot be made anhydrous by evaporation 
 and ignition without some decomposition of the chloride ; oxide 
 of magnesium is formed and chlorine goes oif in combination 
 with hydrogen as chlorhydric acid. 
 
 590. Sulphate of Magnesium (MgSOJ, or rather the hydrated 
 compound (MgSO^ +73^0), is largely employed as a medicament 
 under the name of Epsom salts. It is obtained not only from 
 the mineral spring at Epsom, in England, and from various other 
 springs, but is also prepared from sea-water, and by dissolving 
 the m^inerals serpentine (siheate of magnesium), magnesite (car- 
 bonate of magnesium), and dolomite (carbonate of magnesium 
 and of calcium), in sulphuric acid. Hydrated sulphate of mag- 
 nesium is a colorless crystaUine salt, readily soluble in water, 
 and possessing the peculiar bitter taste common to most of the 
 soluble magnesium compounds. It is often empl6yed'in labo- 
 ratories as the source from which to prepare other magnesium 
 salts. 
 
504 
 
 ZINC. 
 
 591. Carbonate of Magnesium (MgCOj) is found as a mineral 
 in nature, and with due care may be prepared artificially. As 
 met with in commerce, however, — the magnesia alba of the 
 shops, prepared by mixing hot solutions of sulphate of magnesium 
 and carbonate of sodium, — it is mixed with varying proportions 
 of hydrate of magnesium. This compound is employed as a 
 medicament. A compound of carbonate of magnesium and 
 carbonate of calcium occurs abundantly in nature as the mineral 
 dolomite, constituting extensive beds in various regions. Dolo- 
 mite is much more slowly soluble in acids than true limestone, 
 but when heated with a dilute acid it effervesces readily. When 
 burnt, at temperatures so low that the carbonic acid shall be 
 expelled only from the magnesium salt, while the carbonate of 
 calcium remains unaltered, dolomite affords an hydraulic cement, 
 preferable in many respects to ordinary lime. The product of 
 the calcination "sets" rapidly under water, and is converted 
 into a hard compact stone (§ 588). Citrate of magnesium, a 
 preparation made from carbonate of magnesium and citric acid, 
 is also largely employed as a medicament. 
 
 Of the other salts of magnesium, none are of sufficient im- 
 portance to be described in this manual. Most of them are 
 easily soluble in water; hence the insoluble double phosphate 
 of magnesium and of ammonium (MgNH^PO^+eH^O), obtained 
 by adding ordinary diphosphate of sodium to a mixture of 
 ammonia-water and any magnesium salt, is of importance to 
 the analyst, since by means of it magnesium may be separated 
 from its solutions. It should be observed that the ready 
 solubility of sulphate of magnesium is in marked contrast with 
 the insolubility of the sulphates of the alkaline-earthy group 
 of metals. 
 
 ZHTC. 
 
 592. Ores of zinc occur in considerable abundance in several 
 localities. The metal is extracted from the carbonate, oxide, 
 silicate, and sulphide. The carbonate and sulphide are first 
 roasted in order to convert them into oxides, and the oxide is 
 then reduced by means of hot charcoal, in earthen retorts or in 
 crucibles provided with iron delivery-tubes. Since metalHc zinc 
 
GRANULATED ZINC. 505 
 
 is volatile at high temperatures, it distils over from the retorts 
 as fast as it is formed and is condensed in receivers. 
 
 Zinc is a blnish-white metal of crystalline texture, brittle at 
 the ordinary temperature, and also when heated above 200°, but 
 a temperature of about 130° or 140° it may easily be rolled out 
 or hammered into sheets. The metal melts at 425° and boils at 
 a bright-red heat ; in presence of air the red-hot metal takes fire 
 and burns with a brilliant bluish- white light and formation of a 
 dense cloud of white oxide of zinc. 
 
 Exp. 304. — Melt 200 or 300 grms. of metallic zinc in a small 
 Hessian crucible, or in an iron ladle, placed in an anthracite Are. 
 Remove the crucible from the fire by means of appropriate tongs 
 (Appendix, § 27), and pour its contents in a very fine stream into a 
 pail full of cold water, taking care to hold the crucible at a distance 
 of 5 or 6 feet above the pail. Replace the empty crucible in the 
 fire, in order that it may be ready for Exp. 305. 
 
 The small thin pieces of zinc which will be found in the paU when 
 the water is poured away, are known as granulated ov feathered zinc. 
 This process of granulation may be conveniently applied to any of the 
 other easily tusible metals, such as bismuth, lead, or tin, when they 
 are required in a finely divided condition. 
 
 Granulated zinc is much used in chemical laboratories, for a variety 
 of purposes, hut particularly for preparing hydrogen (§ 50). In order 
 that it may be fit for this purpose, it is best to heat the melted metal 
 nearly to redness before pouring it into the water ; for it has been 
 noticed that when zinc is melted at the lowest possible temperature 
 and then immediately poured into water, the granules obtained are 
 but slowly acted upon by dilute sulphuric acid, while another portion 
 of the same metal, heated nearly to redness, and then granulated, is 
 readily soluble in the acid. If the hot metal be poiu'ed upon a warm 
 iron plate, it wiU be found to be stiU more readily soluble in acids 
 than that which has been suddenly cooled by the water. 
 
 Exp. 305. — Dry 20 grms. of the granulated zinc of Exp. 304, and 
 mix it intimately in a mortar with 40 grms. of crude saltpetre ; remove 
 the empty crucible of Exp. 304 from the fire, and place it in such 
 position that any fumes which may subsequently be evolved from it 
 shall be drawn into the chimney. By means of a spoon or ladle, 
 project into the red-hot crucible the mixture of zinc and saltpetre, 
 taking care to stand away as far aa possible from the crucible. The 
 metal will bum fiercely, at the expense of the oxygen in the saltpetre, 
 for the most part, though a portion of it will be volatilized by the 
 
506 
 
 THE OALTANIC CTJEEENT. 
 
 intense heat of combustion, and converted into oxide of zinc in the 
 air. The residue in the crucible is a soluble compound of oxide of 
 zinc and potash, known as zincate of potassium. 
 
 If a strip of thin sheet zinc be held in the flame of the gas-lamp, 
 it can readily be burned to oxide. The experiment succeeds best 
 with zinc leaf, which instantly burns with a vivid flame and forma- 
 tion of floating flocks of the white oxide. In oxygen gas, zinc burns 
 with peculiar brilliancy. 
 
 Zinc is not much acted upon either by moist or dry air at the 
 ordinary temperature ; but a fresh, bright surface of it, when 
 exposed in a moist atmosphere, soon tarnishes and becomes 
 covered with a thin film of basic carbonate of zinc, which adheres 
 closely to the metal, and protects it from further change. Owing 
 to this durability, the metal is much used in the form of sheets. 
 Sheet iron and iron wire are often covered with a protecting coating 
 of zinc by simple immersion in melted zinc, and are then said 
 (most improperly) to be galvanized. The specific gravity of zinc 
 varies from 6'8 to 7'3; its atomic weight is 65. 
 
 593. Zinc is readily attacked and dissolved by acids, with 
 evolution of hydrogen in most instances. The chemical action of 
 dilute acids upon zinc is a very common source of that peculiar 
 mode of force called a galvanic current. There are few, if any, 
 chemical reactions which cannot be made to produce electricity, 
 and, in general, the more powerful the chemical action, the more 
 powerful is the electrical action which results. 
 
 Exp. 306. — Solder a piece of stout copper wire to one end of a strip 
 of sheet zinc, 4 cm. wide by 10 cm. long. The soldering will be 
 readily effected by rubbing the zinc and the wire, in the vicinity of the 
 proposed place of contact, with a strong solution of chloride of zinc, 
 before applying the melted solder. In the same way, solder a similar 
 wire to a like strip of bright sheet copper. Place the strips of zinc 
 and copper in a tumbler filled with water, acidulated with l-12th to 
 1-lOth its volume of sulphuric acid, in such a way that the two strips 
 shall not touch each other either within or without the liquid. So 
 long as the wires coming from the strips of metal do not touch each 
 other, the copper remains quiescent, while the zinc is attacked, and 
 bubbles of gas rise from its surface ; but if the two copper wires are 
 brought into close contact, by means of a binding-screw, or by the 
 application of solder, the following phenomena occur : — 1st. Minute 
 bubbles of hydi'ogen gas will be evolved from the surface of the copper 
 
COERELATION OS IPOHCES. 507 
 
 plate. 2iid. The zinc dissolves more rapidly than before ; at the 
 close of the experiment sulphate of zinc may be recovered from the 
 liquid in the beaker. 3rd. This transfer of the hydrogen from the zinc 
 to the copper instantly ceases if the contact between the vrires is 
 destroyed. 4th. If the two wires be connected with the two ends of 
 the coU of wire which surrounds the magnetic needle of the common 
 galvanometer, the deflection of the suspended needle will demonsti-ate, 
 the fact that an electric current is passing through the wires from one 
 plate of metal to the other. 
 
 This conversion of chemical force into electrical force is a stri- 
 king illustration of the doctrine that all physical forces are corre- 
 lated. The preceding experiment well illustrates the principle 
 on which a large class of batteries employed in telegraphing and 
 in electro-metallurgy are constructed and worked, except that 
 the corrosion of the zinc is generally hindered by coating it with 
 mercuiy. Artificial products, like metals, acids, and saline solu- 
 tions, are used to supply all the'-'chemical force which is imme- 
 diately converted into and utilized as electrical force in the usefid 
 arts. We have not yet succeeded in realizing as electricity any 
 considerable proportion of the prodigious chemical force which is 
 incessantly active in the common processes of combustion. 
 
 594. Ziuc dissolves in hot solutions of the caustic alkalies as 
 well as in acids ; hydrogen is given off and a zincate of the alkali 
 formed : — 
 
 Zn 4- 2NaH0 = Na.ZnO, + 2H. 
 
 When immersed in the solution of a lead salt, such as the 
 nitrate or acetate, zinc dissolves and lead is deposited in the 
 metallic state : — 
 
 PbN^O, -H Zn = ZnN.O, + Pb. 
 
 Exp. 307. — Dissolve 10 grms. of acetate of lead in 250 c. c. of water, 
 add a few drops of acetic acid in order to dissolve the cloudy precipi- 
 tate of carbonate of lead, which is formed from the carbonic acid in 
 the water, pour the solution into a wide-mouthed bottle and suspend 
 in it from the cork a strip of sheet zinc. The zinc will soon be covered 
 with a brilliant coating of crystalline spangles of metallic lead, and 
 this crystalline vegetation, as it were, will shoot out or grow even as 
 far as the sides of the bottle. In the course of 24 hours all the lead 
 will have been deposited from the solution, and the latter will contain 
 nothing but acetate of zinc. Under the conditions of this experiment. 
 
508 OXIDE 01' zxsc. 
 
 and as a general rule, zinc is, chemically speaking, a stronger or more 
 basic element than lead ; it is capable of displacing lead from its com- 
 pounds. The growth of lead, witnessed in this experiment, is fre- 
 quently spoken of as a lead tree ; the experiment is often performed in 
 chemical laboratories for the sake of the chemically pure lead which 
 it furnishes. 
 
 Many other metals besides lead may be thus thrown down by zinc, 
 and the zinc may itself be replaced by other metallic precipitants. The 
 whole series of experiments of which the one here indicated may be 
 taken as the type, is interesting as illustrating the general law of the 
 replacement of metals one by another in atomic proportions, and from 
 the fact that by means of these experimenta the atomic weight of 
 various metals may readily be determined. For example, if in the 
 foregoing experiment the piece of zinc be weighed before and after its 
 immersion in the acetate of lead, and if the precipitated lead be also 
 weighed, it will be found that the weight of lead obtained is, to the 
 weight of zinc dissolved, very nearly as 207 is to 65, the atomic weights 
 of lead and zinc respectively. The atom of zinc dissolved has replaced 
 in the solution the atom of lead which was precipitated. By the ex- 
 ercise of care in the manipulation, by employing boiled water free from 
 carbonic acid so that the addition of acetic acid to the lead salt shall 
 be unnecessary, and by finally drying the lead in an atmosphere of hy- 
 drogen, a close approximation to the numbers above given can be ob- 
 tained. 
 
 595. Oxide of Zinc (ZnO). — Like magnesium, zinc forms but 
 a single compound with oxygen. This compound may be readily 
 obtained by burning the metal, or by igniting carbonate or hy- 
 drate of zinc. As thus prepared, oxide of zinc is an insoluble, 
 white, amorphous powder, which, under the name of zinc white, 
 has of late years been largely employed as a white paint. It 
 lacks the opacity or covering-power of white lead (§ 582), but, on 
 the other hand, has no injurious action upon the health of the 
 workmen and does not blacken or become discolored when exposed 
 to the fumes of sulphydric acid. When heated in a crucible, 
 oxide of zinc exhibits a yellow color, but it becomes white again 
 on cooling. The oxide dissolves easily in acids, with formation 
 of salts of zinc. 
 
 596. Chloride of Zinc (ZnClj), obtained by dissolving metallic 
 zinc in cblorhydric acid, is a compound readily soluble in water ; 
 it is somewhat extensively employed for preserving timber, and 
 
CABMnjM. 509 
 
 as a disinfecting fluid. It is used also by tinmen as a wash, to 
 cleanse the surfaces of tin-plate before soldering. 
 
 597. Sulpkate of Zinc (ZnSO^) is one of the commonest of the 
 zinc salts. The hydrated compound, ZnS0^-|-7Hp, known as 
 white vitriol, is used to a certain extent in medicine, and for other 
 purposes in the arts. The action of carbon upon sulphate of zinc 
 differs somewhat from its action upon the sulphates previously 
 studied. When a dry mixture of the sulphate of zinc and char- 
 coal is heated to dull redness, carbonic and sulphurous acids are 
 evolved in the proportion of two volumes of the former to one of 
 the latter gas, and pure oxide of zinc remains : — 
 
 2ZnS0, + C = 2ZnO -h 2S0, + CO,. 
 
 It would be quite possible to obtain metallic zinc from the sul- 
 phate in one operation by employing an excess of carbon, heating 
 the mixture gently at first until the sulphuric acid had aU been 
 decomposed, and then urging the fire in order to obtain the tem- 
 perature requisite for the reduction of the oxide of zinc and vola- 
 tilization of the metal. But if the mixture of sulphate of zinc 
 and charcoal be qiiickly raised to a high temperature, then sul- 
 phide of the metal is formed and carbonic oxide set free : — 
 
 . ZnSO, -f- 4C = ZnS + 4C0. 
 Zinc forms several valuable alloys ; brass is an alloy of zinc and 
 copper, and German silver is a brass whitened by the admixture 
 of a small proportion of nickel. 
 
 CABMirrM. 
 
 698. Cadmium is a comparatively rare metal, found associated 
 with zinc in nature ; it is remarkably similar to zinc in its che- 
 mical relations. In the process of obtaining zinc from its ores, 
 the small proportion of cadmium which these ores contain comes 
 over with the first products of the distillation, since cadmium is 
 more readily volatile than zinc. 
 
 Cadmium may be prepared either from this early distillate, or from 
 the residues obtained when metallic zinc is dissolved in chlorhydric 
 acid in the preparation of chloride of zinc for manufacturing purposes. 
 These residues always contain a quantity of lead, which next to cadmium 
 is the commonest impurity of commercial zinc ; and if care has been 
 
510 PKOPEKTIES OF CADMITTM. 
 
 taken to keep an excess of metallic zinc in the dissolving-vat, they wiU 
 contain also all the cadmium with which the zinc was contaminated. 
 
 From either of these sources, cadmium salts may be prepared by 
 dissolving; the crude materials in dilute nitric acid, separating the lead 
 by means of sulphuric acid, and throwing down the cadmium with 
 sulphuretted hydrogen. Sulphide of cadmium is a bright-yellow 
 powder, insoluble in dilute acids, while sulphide of zinc is readily 
 soluble in acids. Once isolated, the sulphide of cadmium may be dis- 
 solved in boiling, concentrated chlorhydric acid ; from the solution of 
 cliloride of cadmium thus obtained, carbonate of cadmium may be pre- 
 cipitated, and from the carbonate any of the other cadmium com^^ounds 
 can readily be prepared. 
 
 Metallic cadmium is of a white color tinged with blue ; it is 
 lustrous and takes a fine polish, but gradually tarnishes upon the 
 surface when exposed to the air. Its specific gravity varies 
 from 8-6 to 8-7. It melts and volatilizes at temperatures below 
 redness. Heated in the air it takes fire and burns to a brown 
 oxide. 
 
 When combined with other metals, such as lead or tin, cadmium 
 forms alloys of remarkable fusibility ; in this respect it far sur- 
 passes bismuth (§ 359). The most fusible alloy yet made contains 
 cadmium, bismuth, tin, and lead ; it melts at 63°-65°. 
 
 599. Cadmium is a volatile substance, and the specific gravity 
 of its vapor has been experimentally determined to be 56-85 ; the 
 weight of a unit-volume of the vapor is 56'85 times the weight 
 of the same volume of hydrogen. Now we have seen that the 
 specific gravity of the elementary gases and of the vapors of the 
 elements included in the chlorine and sulphur groups are the 
 same as the atomic weights of these elements. On the other 
 hand, the specific gravities of the vapors of phosphorus and ar- 
 senic were twice the atomic weights of these elements. Cadmium 
 presents still a new relation between the least combining weight 
 and the unit- volume weight ; for the specific gravity of its vapor, 
 56-85, is about one-half of 112, its accepted atomic weight. The 
 sig-nificance of this fact, may be illustrated from its chloride. 
 Cadmium is bivalent, and forms the chloride CdCl^, containing, as 
 experiment has proved, 112-24 parts, by weight, of cadmium to 
 71 parts of chlorine ; if the unit- volume weight of cadmium were 
 the same as its atomic weight, two unit-volumes of chloride of 
 
THE irAGNESIlTM GEOUr. 511 
 
 cadmium would contain one volume of cadmium and two volumes 
 of chlorine ; but were it possible, by experiment, to resolve the 
 vapor of chloride of cadmium into its component vapors, it would 
 be found that two volumes of cadmium were therein combined 
 with two volumes of chlorine. 
 
 The atom of cadmium when converted into vapor occupies twice 
 as much space as the atom of oxygen, or hydrogen, or chlorine 
 does ; and accordingly the product- volumes of its compounds are 
 packed vrith one volume more than the product-volumes of the 
 corresponding compounds of oxygen or any member of the sulphur 
 group. Whether the bivalent metals in general resemble cad- 
 mium on the one hand or oxygen on the other, in regard to the 
 relation between their vapor-densities and their atomic weights, 
 is a point on which experiment has thus far thrown but little 
 light. Mercury resembles cadmium ; but it is certainly possible 
 that these two elements constitute an exception to some general 
 rule hereafter to be proved — a rule, for example, like that which 
 many chemists are inclined to accept in advance of proof, namely 
 that the combining weights and the unit-volume weights of the 
 ' elements are normally identical. 
 
 Cadmium is so soft that paper may be marked with it ; but it is 
 flexible, malleable, and ductile. In dilute chlorhydric and sul- 
 phuric acids it dissolves with evolution of hydrogen, though less 
 readUy than zinc. Its best solvent is nitric acid. It does not 
 dissolve in the caustic alkalies. 
 
 600. From the foregoing it is apparent that the members of 
 the group of metals now under consideration resemble one another 
 with respect to volatility and several other of their physical 
 properties, besides being very closely related in most of their 
 chemical characters. The order of progression is from magnesium 
 to cadmium, zinc and its compoimds occupying always an inter- 
 mediate position. The specific gravities of the three metals 
 are — ^Mg=l-75, Zn = 7-1, Cd=8-6; and their atomic weights 
 are — Mg=24, Zn=65, Cd=112. Magnesium volatilizes at a 
 bright-red heat, cadmium at a low red heat, and zinc at tempera- 
 tures between these extremes. Cadmium is very fusible, melting 
 at about 360°, zinc melts at 425°, and magnesium at a moderate 
 red heat. All of these metals are bivalent ; each forms but one 
 oxide, sulphide, and chloride. 
 
512 ALUMINUM. 
 
 CHAPTEK XXX. 
 
 A L U M I N U M — -G L U C I N U M C H K M I U M M A N G A N E S E 
 
 I E N C B A L I ^N I C K B 1. U H A N I U M. 
 
 AIUIONUM. 
 
 601. Next to oxygen and silicon, aluminum is perhaps the 
 most abundant element upon the earth's surface. It is the most 
 abundant of aU the metals, as much as a twelfth of the solid crust 
 of the globe being composed of it. It occurs in enormous quan- 
 tities in combination with oxygen and silicon, in all the so-called 
 primitive rocks, and indeed in most other rocks and soils. It 
 is contained in clay, marl, and slate, as well as in feldspar, mica, 
 and many other common minerals. 
 
 Oxide of aluminum, chloride of aluminum, and many salts of 
 the metal may readily be prepared artificially from the native 
 minerals ; they have long been known to chemists, and made use 
 of in the arts ; but the metal itself is less readily obtainable. It is 
 but a few years since metaUic aluminum has been prepared upon 
 a manufacturing scale. The metal is nowadays prepared by heat- 
 ing metaUic sodium either with chloride or fluoride of aluminum, 
 or with a double chloride or fluoride of aluminum and sodium. It 
 is a bluish- white metal, of remarkable lightness. Its specific gra- 
 vity, 2"56, is about the same as that of porcelain, and only about 
 £t quarter of that of silver. The metal is malleable, ductile, and 
 tenacious, and may be beaten into thin sheets, like gold and 
 silver, and drawn into fine wire. It melts at a temperature lying 
 between the melting-points of zinc and silver, but is not volatile. 
 It conducts electricity much better than iron, and heat even better 
 than silver ; after having been heated, it cools very slowly. It is 
 remarkably sonorous, a bar of it suspended by a wire rings with 
 a clear musical note on being struck. 
 
 In the air aluminum undergoes no alteration even at a strong 
 red heat ; it may be melted in open crucibles without oxidation, 
 
ALLOTS OP AITTMINUM. 513 
 
 and readily cast into any desired form. It is not acted upon by 
 water at temperatures short of a white heat, so long as it is in 
 the'ordinary compact condition. Sulphydrio acid has no action 
 upon it. Nitric acid, whether dilute or concentrated, has no 
 action upon aluminum at the ordinary temperature, but when 
 boiling dissolves the metal slowly. Cold dilute sulphuric acid 
 has scarcely any action upon it ; but it is easily soluble in chlor- 
 hydric acid, either^ dilute or concentrated, at all temperatures. 
 It is soluble also in aqueous solutions of caustic potash, soda, or 
 ammonia. The vegetable acids, such as acetic and tartaric acids," 
 exert no perceptible action upon it. Although soluble with evo- 
 lution of hydrogen in aqueous solutions of the fixed caustic alka- 
 lies, aluminum is not acted upon by fused hydrate of sodium, or 
 hydrate of potassium ; nor is it even attacked by fused nitrate of 
 potassium, except at temperatures high enough to decompose the 
 nitre so completely that it gives off nitrogen ; when this limit 
 is reached the aluminum is immediately oxidized with incan- 
 descence. 
 
 602. Aluminum unites readily with many of the metals to 
 form alloys, among which that of copper and aluminum, called 
 alumimmi bronze, promises to be of especial importance. Alumi- 
 num bronze, composed of 90 parts copper and 10 parts aluminum, 
 is exceedingly hard, very malleable, as tenacious as steel, of a 
 beautiful golden color, and susceptible of being highly polished. 
 
 603. By Tiniting with the non-metaUic elements, aluminum 
 forms only one class of compounds, of which the oxide Al^Oj may 
 be taken as the type. The atom Al is trivalent, or, in other 
 words, it is equivalent to three atoms of hydrogen, and of the 
 same value as one and a half atom of oxygen. Since it would 
 be inconvenient to employ fractional expressions in writing che- 
 mical formulse, as well as niogical to speak of half atoms, it is 
 customary to write the formula of oxide of aluminum Al^Og as 
 above, and not AlO^i, as might perhaps at first sight seem best. 
 For the sake of consistency, the formula of the chloride is in 
 like manner written AljClj and not AICI3. Since it contains one 
 and a half atom of oxygen for each atom of aluminum, the oxide 
 is often called a Sesqui (one and a half) oxide. 
 
 If no other element analogous to aluminum were known, if 
 
 2l 
 
514 OXIDE OF ALTTMIKtrM. 
 
 tUs metal were not intimately related to glucinum, iron, chro- 
 mium, and the other metals to he considered in the present 
 chapter, chemists might possibly have taken the atomic wefght 
 of aluminum at one-third of its present value, namely at 9-1 in- 
 stead of 27"4. The formula of oxide of aluminum would then 
 have been written Al^O, and that of chloride of aluminum AlCl, 
 corresponding respectively with the formul® of the oxides and 
 chlorides of the alkali-metals. But, as will appear directly from 
 the study of the other members of the aluminum family of metals, 
 and particularly from the isomorphism of their various com- 
 pounds, the atomic weight 27-4, and the formulae first given, 
 must be regarded as the most probable. The atomic weight 9-1, 
 and the formulae derived from it, are inadmissible, since there is 
 no analogy between the chemical properties of aluminum, whether 
 simple or compounded, and those of the alkali-metals. 
 
 604. O.i'ide of Aluminum (Al^O^), commonly called Alumina, 
 is found crystallized in nature as the mineral corundum. The 
 sapphire and the ruby are also composed of this oxide together 
 with a little oxide of iron. It may be prepared artificially by 
 oxidizing the metal, or by igniting the hydrate, or almost any 
 oxygen salt of aluminiim. Though unalterable in oxygen so 
 long as it is compact, powdered aluminum and aluminum-leaf 
 burn brightly when heated to redness ia the air, with formation 
 of oxide of aluminum. It has been found by careful experiments 
 that 53-3 parts of the metal unite with 46-69 parts of oxygen to 
 form 100 parts of the oxide. Now, since oxide of aluminum is 
 isomorphous with certain oxides of iron and of chromium, which 
 are known to be sesquioxides, and is capable of replacing these 
 oxides in any proportion in their compounds (§ 252), it is inferred 
 that oxide of aluminum is likewise a sesquioxide. Upon this 
 view the atomic weight of aluminum is directly derived from the 
 foregoing experimental data by the equation : — 
 
 46-69 : 53-3 = 48 : 64-8 
 
 wt. of 3 atoms wt. of 2 atoms 
 of oxygen. of aluminum. 
 
 605. Etjdrate of Aluminum (Al^H^OJ may be obtained as 
 a gelatinous, flocculent precipitate, by adding ammonia-water 
 to the solution of an aluminum salt, such as common alum. 
 
AUTMINATES, 515 
 
 When dried at a moderate heat it forms a soft, friable mass, 
 whicli adheres strongly to the tongue like clay; when dried 
 still more thoroughly, it forms a hard, yellowish, translucent, 
 horn-hke substance, and at a red heat gives off all its water. 
 The volume of the original precipitate contracts to an enormous 
 extent during the operation of drying ; the bulk of the final 
 anhydrous oxide is exceedingly small as compared with that of 
 the moist hydrate from which it has been derived. 
 
 606. Anhydrous alumina may be melted in the flame of the 
 oxyhydrogen blowpipe. It is neither decomposable by heat 
 alone, nor can it be reduced by carbon or any of the more 
 common deoxidizing agents. At a white heat, potassium de- 
 composes it partially, and an alloy of aluminum and potassium 
 is formed. Oxide of aluminum is insoluble in water, and after 
 having been strongly heated it is scarcely at aU acted upon by 
 acids, excepting concentrated boiling chlorhydric and nitric 
 acids. The crystallized native oxide is insoluble in all acids. 
 The anhydrous oxide is insoluble in solutions of the caustic 
 alkalies, but dissolves readily in water after having been fused 
 at a red heat with either hydrate or carbonate of sodium or of 
 potassium. Hydrate of aluminum, on the contrary, though 
 insoluble in water, dissolves easily in acids and in solutions of 
 the fixed caustic alkalies. Alumina is in fact capable of acting 
 not only as a strong base, forming weU-defined salts by uniting 
 with acids, but it plays the part of an acid as well (compare 
 § 350), and combines with the alkalies and with other metallic 
 oxides to form salts known as aluminates. Aluminate of potas- 
 sium (Kfi,Alfi^) and aluminate of sodium (Nafi,Alfi^) are 
 substances somewhat extensively used in the arts ; the mineral 
 spinelle is an aluminate of magnesium (MgO,Al203) ; and a native 
 aluminate of zinc (ZnO,Al203) is called gahnite by mineralogists. 
 
 Hxp. 308. — Heat a small fragment of alum with water in a test- 
 tube until it has completely dissolved, pour half the solution into 
 another tube, and add to it, drop by drop, ammonia-water, until the 
 odor of ammonia persists after the mixture has been thoroughly 
 shaken. Hydrate, of aluminum will be precipitated, in accordance 
 with the reaction : — 
 
 AI23SO4 + 6(NH4)H0 = Mfi^BUfi + 3(NH4)2SO<. 
 
 2LiJ 
 
516 
 
 MORDANTS LAKES. 
 
 Pour two or three drops of the moist hydrate of aluminmn into 
 another test-tube and cover them with ammonia- water ; no clear 
 solution will be obtained, for hydrate of aluminum is but little soluble 
 ia ammonia-water. 
 
 Pour two or three drops of the moist hydrate of aluminum into 
 still another test-tube, and cover them with a solution of hydrate of 
 sodium ; the precipitate will dissolve immediately ; aluminate of 
 sodixun is formed, and this salt is easily soluble. 
 
 -Erp. 309. — Take another portion of the clear solution of alum 
 prepared in Exp. 308, and add to it, drop by drop, a dilute solution 
 of caustic soda. A precipitate will soon fall, as in Exp. 308, and 
 if no excess of hydrate of sodium were added over and above that 
 necessary to form sulphate of sodium with the sulphuric acid of 
 the alum, this precipitate would remain undissolved ; but on adding 
 more of the soda solution the precipitate dissolves at once, with 
 formation of aluminate of sodium. 
 
 607. Hydrate of aluminum combines readily -with, many vege- 
 table coloring-matters, forming compounds which are insoluble 
 in water. The fibre of cotton, when impregnated with alumina, 
 can be made to retain colors which, the cotton itself has no power 
 to hold ; hence the use of aluminum salts as mordants in dyeing. 
 
 £xp. 310. — BoU a few crushed granules of cochineal in water until 
 a considerable portion of their coloring-matter has been extracted ; 
 add to the filtered solution an equal bulk of a solution of alum, and 
 to the mixture add ammonia-water. A colored precipitate, consisting 
 of hydrate of aluminum and of the coloring-matter of the cochineal, 
 will be thrown down ; it is the substance called carmine-lake. Similar 
 precipitates may be prepared by substituting almost any other organic 
 coloring-matter for the cochineal of this experiment. Precipitates 
 thus formed by the union of a metallic oxide and a coloring-matter 
 are all classed as lakes. 
 
 608. Chloride of Aluminum (AI^CIJ may be prepared, in 
 the same way that the chlorides of boron and silicon are pre- 
 pared (§§ 449, 470), by passing chlorine over a heated mixture 
 of alumina and carbon. It is formed also when hot finely 
 divided aluminum is brought into contact with chlorine gas. 
 Hydrated chloride of aluminum iAlj:\,12I[fi) can be made 
 very easily by dissolving hydrated oxide of aluminum in chlor- 
 hydric acid ; but the anhydrous chloride cannot be prepared by 
 heating this hydrate, since a great part of the chlorine is expelled 
 
SULPHATE OF ALTTMINTJM:. 517 
 
 from it, together with the water, at a low heat. "When obtained 
 in the dry.way, however, chloride of aluminum is readily volatile. 
 The anhydrous chloride, prepared by the reaction, 
 
 AIP3 + 30 + 6C1 = Al^Cl, + 3C0, 
 previously described, is found condensed ia the cold portions 
 of the tube in which the materials have been heated, apart from 
 the residue of undecomposed alumina and carbon. It occurs 
 either as a flocculent powder, or as a transparent wax-like mass 
 of crystalline texture. It is colorless when pure, very deliquescent, 
 and soluble in water. When large masses of it are heated to 
 duU redness, a portion of it liquefies, but at temperatures near 
 the melting-point it volatilizes rapidly. Unlike oxide of alumi- 
 num, it may be readily decomposed by sodium and potassium at a 
 heat below redness, metallic aluminum being set free. 
 
 Chloride of aluminum combines readily with several of the 
 other metallic chlorides, forming compounds analogous to the 
 chloride of aluminum and sodium (2NaCl,AljClj), from which 
 metaUio aluminum is commonly manufactured. 
 
 609. Sulphate of Aluminum (Al^BSOJ is a salt largely em- 
 ployed in the arts. It is commonly prepared nowadays by 
 acting upon hot roasted clay with sulphuric acid. Clay is a 
 siKeate of aluminum not very easily attacked by acids so long 
 as it remains in the native plastic condition, but after having 
 been exposed for some time to a dull red heat it readily yields 
 its alumina to acids. A solid mixture of sulphate of aluminum 
 and free silicic acid obtained as the product of this reaction is 
 known in commerce as alum-cake. By lixiviating alum-cake, 
 sulphate of aluminum may readily be obtained in solution ; 
 and from this solution the salt crystaUizes as a hydrate, the 
 composition of which may be represented by the formula 
 Al,3SO,-l-18H,0. 
 
 Until a comparatively recent period, sulphate of aluminum was 
 sent into commerce neither in its free state nor mixed with silica, 
 but in combination with sulphate of potassium in the form of 
 alum. Common alum is a hydrated double sulphate of aluminum 
 and potassium; its composition is represented by the formula 
 A1,K,4S0, + 24H,0, or K^0,S03; Aip3,3S03 + 24H,0. 
 
 It crystaUizes very easily in large, compact, well-defined octa- 
 
518 
 
 ALjm. 
 
 hedrons, belonging to the first or regular system. The crystalliTie 
 character of alum is important, since it is solely on account of 
 this character that the salt has come into such general use. 
 Xeither the sulphate of potassium nor the water in alum plays 
 any useful part iu the reactions for which this salt is commonly 
 employed. Since 100 parts of alum contain only about 36 parts 
 of anhydrous sulphate of aluminum, it foUows that 64 per cent, 
 of the alum is, for all chemical purposes, simply iuert matter, 
 which has to be transported and manipulated for the sake of the 
 36 per cent, of real sulphate of alumiuum. The reason why 
 this waste of labor and loss of the potassium salt is tolerated 
 is twofold : — Until a comparatively recent period, sulphate of 
 aluminum could be more readily purified by crystallization in 
 alum than in any other way. At the present time, when it is 
 easy to obtain piire sulphate of aluminum from responsible 
 manufacturers, alum is still prepared because its clean, sharply 
 defined crystals afford a valuable criterion of purity. So long as 
 it is left in the condition of crystals, alum cannot be adulterated 
 with any foreign substance. 
 
 Potash- alum is still the common alum of the American market, 
 but in Europe ammonia-alum (Al2(]SrHj24S0^, 242^0) is at 
 present largely employed ; it is there prepared by adding sul- 
 phate of ammonium obtained from the ammoniacal liquor of the 
 gas-works to sulphate of aluminum resulting from the action of 
 sulphuric acid upon clay. Ammonia-alum crystallizes almost as 
 easily as potash-alum ; but it is remarkable that the correspond- 
 ing double sulphate of aluminum and of sodium (soda-alum) is 
 easily soluble in water, and crystallizes with comparative diffi- 
 culty ; hence it has never come into commerce. 
 
 Sulphate of aluminum is employed as the source of the various 
 compounds of aluminum used in dyeing, calico-printing, and 
 paper-making. Acetate of aluminum, for example, is largely 
 employed by dyers, particularly for the red colors obtained from 
 madder, under the name of red liquor. 
 
 Exp. 311.— Dissolve 3 grms. of sugar of lead in 4 c. c. of hot water; 
 also dissolve 4 gxms. of common alum in 6 c. c. of hot water ; mix the 
 hot solutions and filter oft' the insoluble sulphate of lead which is 
 formed. The solution obtained consists of basic acetate of aluminum 
 
SniCAIES OF ALUMINUM. 519 
 
 together with some sulphate of akimimtm and all the sulphate of potas- 
 sium of the original alum. Such solutions are preferred in practice to 
 those containing normal acetate of aluminum, to prepare which a much 
 larger proportion of acetate of lead would be required than has been 
 given above. 
 
 JSxp. 312. — Soak a small piece of cotton cloth in the solution of 
 acetate of aluminum prepared in Exp. 311, and another piece of simi- 
 lar cloth of equal size in pure water. Hang up both pieces to " age," 
 best in a moist and warm atmosphere, for a day or two. During the 
 process of ageing, a portion of the acetic acid escapes from the salt on 
 the cloth, and there is left within and upon the fibres of the cloth a 
 quantity of hydrate of aluminum, or at least a mixture of highly basic 
 acetate and sulphate of aluminum. This deposit is the true mordant. 
 When cloth impregnated with it is soaked in a solution of coloring- 
 matter, the coloring-matter imites with the alumina precisely as in 
 Exp. 310, and is thereby firmly attached to the cloth. It should be 
 mentioned that several other oxides, besides the oxide of aluminum, 
 are capable of acting as mordants ; the sesquioxides of iron and of 
 chromium for example, as well as the binoxide of tin, are largely used 
 as mordants. 
 
 JExp. 313. — ^Place a quantity of a solution of extract of logwood in 
 two small evaporating-dishes, heat the liquor to 40° or 60°, then place 
 the mordanted cloth in one dish, the unmordanted cloth in the other 
 and boil the liquor in both dishes, , Continue to boU during 10 or 15 
 minutes, then take out the pieces of cloth and wash them thoroughly 
 in water. It will appear that the coloring-matter remains firmly 
 attached to the mordanted cloth, while the cloth which has received 
 no mordant can readily be washed clean or nearly clean. 
 
 610. Silicates of Aluminum.— :-0f all the aluminum compounds 
 the silicates are by far the most important. Clay in all its va- 
 rieties is a hydrated silicate of aluminum, usually mixed with 
 an excess of silica, besides other impurities derived from the rocks 
 from whose decomposition the clay itself has been formed. The 
 purer kinds of clay, such as kaolin or porcelain clay, are products 
 of the decomposition of feldspar, a mineral composed of silicon, 
 aluminum, potassium, and oxygen in the proportions Al^OgjE^O, 
 6810^. When, exposed to the atmosphere, many varieties of 
 feldspar gradually decompose, an alkaline silicate is vfashed away, 
 and silicate of aluminum remains. Clay is remarkable on ac- 
 count of its plasticity when moist, of the facility with which it 
 
520 BKICKS EABIHENWAKB 6LAZES. 
 
 is converted into stone-like masses when strongly heated, and of 
 its infusibility when pure. 
 
 Earthenware, bricks, and ordinary pottery are made from com- 
 mon clay, by mixing the clay with water enough to form a plastic 
 paste, which is then moulded into any desired form, dried and 
 intensely ignited. The porous ware resulting from this operation 
 may be glazed, and so made impermeable to liquids, by coating it 
 over with some fusible substance, such for example as a mixture 
 of litharge and clay, and again heating it so intensely that the 
 coating shall melt to a glass, which either fills up the pores of the 
 clay, or at the least stops their openings. Porcelain proper, and 
 the better kinds of stoneware, are made from the purest varieties of 
 clay, and are glazed with feldspar. Common stoneware, such as 
 is used for jugs, beer-bottles, and the Uke, is covered with the so- 
 called salt-glaae : — Moist chloride of sodium is thrown into the 
 kiln in which the ware is baking, and being volatiUzed by the 
 intense heat, comes in contact with the hot stoneware ; decom- 
 position ensues ; the water and the chloride of sodium are both 
 decomposed, silicate of sodium is formed, and by mixing with the 
 silicate of aluminum, forms a smooth hard glaze upon the surface 
 of the ware. 
 
 For all vessels which are to be employed for chemical or culi- 
 nary purposes the hard and durable salt-glaze is very much to be 
 preferred to the lead-glaze prepared from litharge and clay; for the 
 lead-glaze is readily acted upon by many chemical agents, and is 
 liable to impart its poisonous properties to articles of food which 
 have been left in contact with it. 
 
 Pire-bricks, crucibles, and similar refractory articles fitted to 
 support very high temperatures without undergoing fusion, are 
 prepared from pure vaiieties of clay, free from iron, lime, or mag- 
 nesia, but containing an unusually large proportion of silica. 
 Some varieties of iire-clay contain as much silica as is represented 
 by the formula Al^OjjGSiOj, while the composition of many of 
 the common clays may be approximately represented by the for- 
 mula Al^OgjSSiO^, or better by the formula Al203,2Si02. In the 
 manufacture of fire-bricks, and of many varieties of potters' ware, 
 it is usual to incorporate with the original clay a certain pro- 
 portion of foreign matter which prevents the moulded article 
 
HTDKAtTLIC CEMENT. 521 
 
 from shrinking too much as it dries, and from cracking. In fire- 
 bricks the coarse powder obtained by pulverizing old fire-bricks 
 is employed for this purpose ; in Hessian crucibles it is very easy 
 to detect numerous grains of quartz sand ; and, in general, finely 
 powdered flint or quartz, as well as previously baked clay, is 
 used for the same purpose in many varieties of pottery. 
 
 611. Silicate of aluminum is moreover a very important ingre- 
 dient of the common hydraulic cement employed to replace lime 
 mortar in constructions exposed to the action of water. It has 
 been found that by carefully burning some varieties of impure 
 limestone, containing from 10 or 12 to 30 or 35 per cent, of clay, 
 and mixing the product vidth water, there is obtained, in place of 
 ordinary mortar, a cement capable of " setting " or hardening, 
 even under water, to a compact stone. Hydraulic cements may 
 readily be prepared artificially by mixing with qiiicklime a 
 suitable proportion of roasted clay, or by heating mixtures of clay 
 and limestone ; in fact, some of the best cements now in use 
 are artificial. A porous volcanic stone called pozzolana, from 
 the vicinity of Naples, consisting of silicates of aliuninum, calcium, 
 and sodium, was much used by the Romans to the same end. 
 When powdered and mixed with ordinary lime the pozzolana 
 yields an excellent hydraulic mortar. In many Roman ruins it 
 may be seen to-day far more perfectly preserved than the bricks 
 which it cements. 
 
 When treated with water hydraulic limes simply absorb the 
 water and form a slightly plastic paste without greatly increasing 
 in bulk; they do not slake or evolve much heat like ordinary 
 quicklime. The moist paste soon begins to set, and is then 
 ready for application. In order that the cement may harden pro- 
 perly under water it should not be submerged before it has begun 
 to set ; it should in any event be kept moist until it has become 
 hard ; otherwise it is liable to remain loose and porous. 
 
 The soUdiflcation of hydraulic limes appears to depend upon 
 the formation of insoluble hydrated compounds of Kme with silicic 
 acid and alumina. Cements which contain from 25 to 35 per 
 cent, of clay solidify in the course of a few hours ; but those in 
 which the proportion of clay is no more than 10 or 12 per. cent, 
 become hard only after the lapse of several weeks. 
 
522 CHEOMHTM. 
 
 A mixture of hydraulic cement with coarse gravel constitutes 
 the material known as concrete, employed for the foundations of 
 buildings, and by the ancients for walls which have proved to 
 be of great durability ; this mixture soon concretes or hardens 
 into a firm mass, well nigh impermeable to water. The influence 
 of magnesia in the preparation of hydraulic mortars has already 
 been indicated, in § 588. 
 
 GrLtrCINTJM. 
 
 612. Glucinum is a rather rare metal, found, together with 
 aluminum, in the emerald, in beryl, and a few other minerals. 
 It closely resembles aluminum in its physical properties, and 
 forms compounds analogous in composition to those of aluminum, 
 and of similar chemical deportment. Like aluminum, metallic 
 glucinum may be reduced from its chloride by means of sodium 
 or potassium. There is but a single oxide of glucinum, GljOj, and 
 a single chloride, 61^01,,. The salts of glucinum have a sweet 
 taste, whence the name, from a Greek word meaning sweet. The 
 atomic weight of glucinum is 14, and its specific gravity 2-1. 
 
 CHROMITTM. 
 
 613. Chromium is nowhere found in very large quantities, nor 
 is it very widely disseminated in small portions like iodine and 
 fluorine, but it is nevertheless found in sufficient abundance to 
 admit of its compounds being rather extensively employed in the 
 arts. The chief ore of chromium is a compound of oxide of chro- 
 mium and oxide of iron (FeCr^O^) called chrome iron-ore. Me- 
 tallic chromium may be reduced from its oxide by means of 
 intensely heated charcoal, and from its chloride by means of 
 sodium, potassium, magnesium, or zinc ; but it has as yet been 
 little studied. Its specific gravity is about 7, and its atomic 
 weight 52-5. 
 
 614. Oxides of Chromium. — Chromium forms three well- 
 defined oxides : — a protoxide, CrO ; a sesquioxide, Cr^Oj ; and a 
 teroxide, CrO^, called chromic acid. Besides these there is a com- 
 pound of the protoxide and sesquioxide (CrjO =CrO, Cr ), 
 another of the sesquioxide and teroxide (Cr^OjjCrO =3CrO ), and 
 an ill-defined compound containing more oxygen than chromic 
 
OXIDES OF CHEOMIIIM. 523 
 
 acid, usually spoken of as perchromie acid (Cr^O,). Both the 
 protoxide and the sesquioxide are bases, corresponding respectively 
 to oxide of magnesium and oxide of aluminum ; but the protoxide 
 and all its compounds rapidly absorb oxygen from the air, with 
 formation of the sesquioxide. On account of this instability, they 
 are rarely prepared, and are mainly interesting from their ana- 
 logy to the compounds of the protoxides of manganese, iron, 
 cobalt, and nickel, hereafter to be studied. The sesquioxide, on 
 the other hand, is a stable compound, closely resembhng oxide of 
 aluminum. Chromic acid is a strong, well-characterized acid, 
 which combines with bases to form a great number of salts. 
 
 The most important of the chromium compounds is the bichro- 
 mate of potassium ; this salt is readily procurable in commerce, 
 and is the source from which all the other compounds of chro- 
 mium are commonly derived. Bichromate of potassium is itse 
 prepared by heating finely powdered chrome iron-ore with car- 
 bonate and nitrate of potassium in a reverberatory furnace. The 
 sesquioxide of chromium of the ore is oxidized and converted into 
 the teroxide, chromic acid, which displaces the carbonic acid of 
 the carbonate of potassium. 
 
 615. Sesquioxide of Chromium (Cr^Oj). — Compounds of this 
 oxide are more commonly met with than any other of the chro- 
 mium salts, except the salts of chromic acid. As has been stated 
 already, compounds of the protoxide must be regarded merely as 
 chemical curiosities. By adding ammonia-water to the solution 
 of a salt containing the sesquioxide, a bulky green precipitate 
 of hydrated sesquioxide of chromium is thrown down, which, 
 when collected and ignited, leaves the anhydrous oxide as a bright- 
 green powder, unchangeable at the highest fumaee-heat. It is 
 employed in the decoration of porcelain, and is a valued pigment 
 much iised in painting and printing, under the name chrome green. 
 
 616. Chlorides of Chromium. — There are two of these com- 
 pounds, the protoehloride (CrCl^) and the sesquichloride (Cr^ClJ. 
 The latter compound is the more important, and is the substance 
 usually meant when chloride of chromium is spoken of. Hy- 
 drated sesquichloride of chromium, obtained by dissolving the 
 hydrated sesquioxide in chlorhydric acid, is the chloride most 
 commonly met with. 
 
524 CHROMIUM SALTS. 
 
 617. Sulphate of Chromium (CrPjjSSOj) is sometimes prepared 
 in the pure state ; but, like sulphate of aluminum, it ordinarily 
 occurs in combination with sulphate of potassium or sulphate of 
 ammonium, as a double salt, called chrome alum. Chrome alum 
 is a compound of a beautiful violet color, crystallizing in well- 
 defined octahedrons of the same form as the crystals of ordinary 
 alum ; its composition also corresponds to that of common alum, 
 the formula of the chromium salt being Cr2K24S0^ + 24HjO, or 
 K^CSO,; Cr,03,3S03 + 24H,0. 
 
 Hxp. 314. — Dissolve 15 grma. of powdered bichromate of potassium 
 in 100 c. c. of warm water ; cool the solution, and then add to it 26 
 grms. of concentrated sulphuric acid ; cool the liquor again, and pom- 
 it into a porcelain dish, surrounded with cold water ; slowly stir into 
 the mixture 6 grms. of alcohol, and set the whole aside. In the course 
 of 24 hours the bottom of the dish will become covered with well-de- 
 fined octahedral crystals of chrome alum. 
 
 The alcohol in this experiment deprives the chromic acid, of the 
 bichromate of potaasixun, of half its oxygen, and is itself converted for 
 the most part into acetic acid and water. 
 
 618. It is remarkable that the salts of sesquioxide of chromium, 
 as well as the oxide itself, occur in two isomeric conditions. One 
 modification is known as the green, the other as the violet modi- 
 fication. As a rule, the violet compounds crystallize readily, 
 while the green compounds do not. In the preparation of chrome 
 alum it is important to guard against the formation of a green, 
 soluble sulphate of chromium, which does not crystallize. In 
 general, if the solution of a salt of the violet modification is heated 
 nearly to boiling, the salt passes into the green modification and 
 becomes uncrystaUisable. Hydrated sesquioxide of chromium, as 
 obtained by adding a caustic alkali to the cold solution of a chro- 
 mium salt of either modification, is readily soluble both in acids 
 and in cold solutions of caustic soda or potash ; but on boiling 
 the green alkaline solution, aU of the chromium is precipitated 
 as a hydrate of the green modification. 
 
 &p. 315. — Place in a test-tube a few drops of a dilute solution of 
 chrome alum, or of some other salt of sesquioxide of chrondum ; add, 
 drop by drop, a solution of hydrate of sodium, until the precipitate 
 which forms at first is completely rediasolved. Boil the clear solu- 
 tion, and observe that the precipitate which again forms in the liquor 
 is no longer soluble in alkalies. 
 
CHEOMIC ACID. 525 
 
 By means of this reaction, oxide of chromium may readily be sepa- 
 rated from oxide of alunmnmi ; for, as has been seen in Exp. 309, alu- 
 mina is readily soluble in alkaline solutions, and is not precipitated 
 therefrom by boiling. 
 
 619. Chromic Add (CrO,) may be obtained by decomposing 
 bichromate of potassium with sulphuric acid. 
 
 Exp. 316. — Mix 40 c. c. of a cold, satm-ated, aqueous solution of bi- 
 chromate of potassium with 50 c. c. of oil of vitriol, in a small beaker 
 standing in cold water, and observe that chromic acid is deposited in 
 crystalline needles. It is remarkable that in sulphuric acid of 1-55 
 specific gravity, such, as is obtained in the foregoing mixture, chromic 
 acid is well nigh insoluble, though it is readily .soluble both in water 
 and in strong sulphuric acid. Cover the beaker, and set it aside for 
 some hours ; finally pour ofi" the supernatant liquor with care, scrape 
 out the chromic acid v(dth a glass rod, and place it upon a dry, porous 
 brick, under an inverted bottle, in order that the sulphuric acid which 
 adheres to it may be absorbed. Preserve the dry crystals in a glass- 
 stoppered bottle. Chromic acid deliquesces rapidly when exposed to 
 the air. It is easily brought to the condition of sesquioxide of chro- 
 mium, both by heat and by reducing agents, and is hence an oxidizing 
 agent of considerable power. 
 
 JExp. 317. — Shake up in a smaU bottle enough strong alcohol to 
 moisten its sides; then throw in half a gramme or less of chromic 
 acid ; a portion of the alcohol wiU be oxidized so quickly, and with 
 evolution of so much heat, that the remainder will take fire and. bum 
 in the air. 
 
 '" Several of the salts of chromic acid, as well as the acid itself, 
 are employed as oxidizing agents. A mixture of bichromate of 
 potassium and of sulphuric acid, for example, is employed for 
 bleaching certain fats. Prom the chromates, both oxygen and 
 chlorine may be conveniently prepared. 
 
 Sxp. 318. — Heat a mixture of 6 grms. of powdered bichromate of 
 potassium and 9 grms. of concentrated sulphuric acid in a small flask, 
 provided with a delivery-tube leading to the water-pan, and coUect 
 the oxygen which is freely evolved : — 
 K20,2Cr03 + 4(H20,S03) = Cr203,3S03 -|- Kfi,SO, + Allfi + 30. 
 
 Exp. 319. — Place a mixture of 1 grm. of powdered bichromate of 
 potassium and 6 grms. of chlorhydric acid of 1'16 specific gravity, in 
 a flask provided with a delivery-tube, as in Exp. 318. Heat the flask 
 gently for a few seconds until its contents begin to react upon one 
 
526 ' CHEOMATES. 
 
 another ; tten quickly remove the lamp and attend to the collection 
 of the chlorine, which will continue to he evolved without further 
 heating : — 
 
 E:,0,2Cr03 + 14HC1 = Cr^Clj + 2KC1 + 7B.fi + 9C1. 
 620. Chromates. — As has been already indicated, bichromate 
 of potassium is the commonest and the most important salt of 
 chromic acid. It is the material from which most of the other 
 compounds of chromium are prepared, and is itself important in 
 dyeing and calico-printing. It has of late years been used in the 
 art of photolithography. 
 
 When a mixture of gelatine and bichromate of potassium is exposed 
 to light, the chromic acid is reduced, and an insoluble compound of 
 gelatine and sesquioxide of chromium is formed. In practice, albu- 
 menized paper is covered in a dark room with a mixed solution of 
 bichromate of potassium and gelatine, then dried, pressed smooth, and 
 kept always in the dark until wanted for use. If a sheet of this pre- 
 pared paper be placed beneath a negative photographic picture (ob- 
 tained in the usual way) and exposed to light for a short time, the 
 chromic acid will be reduced in such wise that a positive picture will 
 be obtained upon the gelatine paper. In this positive, as taken from 
 the press, the parts acted upon by the light will be brown, while the 
 other portions of the sheet retain their original yeUow color. The 
 positive is then washed with water in such manner that the unchanged 
 portions of gelatine and of bichromate are dissolved away, and an in- 
 soluble, clearly defined impression of the original picture is left upon 
 the paper. By means of pressure, the design is then transferred to 
 the lithographic stone, and from the stone any desired number of 
 copies may be printed upon paper with ink in the usual way. 
 
 Besides the bichromate of potassium, there are several other 
 chromates important in the arts or useful to the analyst. The 
 normal chromate of potassium (KfifirOJ is a yellow salt, readily 
 obtainable by adding a molecule of carbonate of potassium to one 
 of the bichromate : — 
 
 Kp,2Cr03 + Kp,CO, = 2(K,0,Cr03) + CO,. 
 
 It is isomorphous with normal sulphate of potassium (E^^SO^), 
 chromic acid, like sulphuric acid, being bibasic (§ 238). The 
 salt is hence easQy adulterated. Chromate of barium is insoluble 
 in water and in acetic acid ; chromate of strontium is soluble in 
 acetic acid, though nearly insoluble in water ; while chromate of 
 
MANOANESE. 527 
 
 calcium is soluble both in water and in acetic acid ; hence an 
 easy method of separating compounds of either of the three 
 metals from mixtures which contain compounds of aU three. 
 
 Chromate of lead is the pigment called chrome-yeUow ; it may 
 easily be prepared by mixing solutions of bichromate of potassium 
 and acetate of lead. An orange-colored dichromate (2PbO,CrO ) 
 may be obtained by boiling together yeUow chromate of lead and 
 slaked lime in the proportion of two molecules of the former to 
 one of the latter. This process is used to fix a permanent orange 
 upon calico. A stUl more brilliant color may be obtained by 
 fusing one part of the yellow chromate of lead with five parts of 
 nitre ; chromate of potassium and dichromate of lead are formed, 
 and the former may be washed away. Chromate of mercury, of 
 a brick-red color, may be precipitated by adding bichromate of 
 potassium to nitrate of protoxide of mercury, or, of an orange- 
 yeUow color, by adding the potassium salt to the nitrate of di- 
 oxide of mercury. 
 
 MANGANESE. 
 
 621. Black oxide of manganese, such as has been employed 
 in the preparation of oxygen and of chlorine (§§ 14, 105), is a 
 tolerably abundant mineral. Small quantities of manganese exist 
 also in a great number of other minerals and rocks ; so that the 
 element is really very widely difiFused in nature. It is often 
 associated with ores of iron. By heating oxide of manganese 
 very strongly with charcoal, it may be reduced to the metallic 
 state, though not readily. The metal is of a grayish-white color, 
 and is very hard and brittle. It oxidizes quickly when exposed 
 to the atmosphere ; it melts only at the strongest heat of a blast 
 furnace. The specific gravity of manganese is 8, its atomic 
 weight is 55. It slowly decomposes water at the ordinary tem- 
 perature, and dissolves readily in dilute sulphuric acid with evo- 
 lution of hydrogen. Like iron, it combines with carbon and 
 silicon. MetaUie manganese is not used in the arts; and the 
 alloys which it forms with the other metals are of no commercial 
 importance, except that a small proportion of manganese is prcT 
 sent in a peculiar kind of iron largely used for making steel. 
 
 622. Oxides of Manganese. — Six well-defined compounds of 
 
528 OXIDES OF MANGANESE. 
 
 oxygen and manganese are known ; two of them are bases, two 
 are acids, and two may be regarded as salts, formed by the union 
 of the oxides one with the other. Protoxide of manganese 
 (MnO) is a powerful base, while sesquioxide of manganese (Mn203) 
 is but a weak base. Manganic acid (MnO,) and permanganic 
 acid (Mn^O,) are well characterised as acids, though they are 
 known only in combination ; they have never been obtained in 
 the free anhydrous state. On the other hand, binoxide of man- 
 ganese (Mn203,Mn03=3MnOj) and the red oxide (MnO,Mn203 
 =MnjOJ are both neutral or indifferent bodies ; they exhibit 
 neither acid nor basic properties. 
 
 623. Protoxide of Manganese (MnO) may be obtained by heat- 
 ing carbonate of manganese out of contact with the air, or by 
 heating either of the higher oxides of manganese to redness in 
 contact with charcoal or hydrogen. The protoxide is itself re- 
 duced to the metalKc state by these agents only at a white heat. 
 It unites freely with acids to form salts of considerable stability. 
 The crystallized sulphate MnSO^+SH^O and the chloride MnCl^ 
 + 4H^0 are commonly employed in the laboratory. Both of 
 them may be prepared from the residues obtained in the prepa- 
 ration of chlorine and oxygen (§§ 105, 626). Hydratqd prot- 
 oxide of manganese may be precipitated from the chloride as 
 foUows : — 
 
 Exp. 320. — Dissolve a small crystal of chloride of manganese in 
 water ; add to the solution soda-lye until the liquor exhibits a distinct 
 alkaline reaction when tested with litmus-paper. Collect the gelati- 
 nous white precipitate upon a filter, and observe that it soon becomes 
 brown as it absorbs oxygen from the air; the brown product is sesqui- 
 oxide of manganese. 
 
 Exp. 321. — Heat a portion of the precipitated hydrate of Exp. 320 
 to redness upon a fragment of porcelain ; it will slowly absorb oxygen, 
 and change to the deep-brown-colored sesquioxide. 
 
 Exp. 322. — To a solution of chloride of manganese, such as was pre- 
 pared in Exp. 320, add a few drops of sulphydrate of ammonium (§ 626). 
 A flesh-colored precipitate of sulphide of manganese (MnS) wiU fall 
 down. Like the hydrate above described, this precipitate soon becomes 
 brown by exposure to the air. It is often prepared by the analyst 
 when testing for manganese. 
 
 624. Sesquioxide of Manganese (MnfiJ occurs in nature in 
 
SBSaUIOXIDE OP MANGANESE. 529 
 
 the minerals braunite and manganite. It is prepared artificially 
 by roasting the protoxide obtained from chlorine-residues, and 
 is itself used to a considerable extent in the preparation of 
 chlorine : — 
 
 Mn^O, + 6HC1 = 2MnCl, + 3H,0 + 2C1. 
 It combines with acids to form a series of unstable salts ana- 
 logous to the sesquisalts of iron, though far less permanent. 
 A solution of the sesquisulphate, for example, Mn^O^SSOj, is 
 reduced to the condition of protosulphate by mere boiling. In 
 like manner the sesquiehloride Mn^Cl^ is doubtless formed when 
 the protoohloride is treated with cold chlorine, or the sesquioxide 
 is digested in cold chlorhydric acid ; but the salt is decomposed 
 with extreme readiness, and splits up into free chlorine and the 
 protoohloride even when but slightly heated. In the preparation 
 of chlorine from the sesquioxide as ^bove formulated, there is no 
 doubt an intermediate reaction, 
 
 Mn^O, -I- 6HC1 = Mn,Cl, + SRfi, 
 before the final breaking up of 
 
 Mn,Cl, into 2MnCl, -|- 2C1. 
 625. Of the salts of the sesquioxide, the double compound 
 of sulphate of manganese and of potassium, known as man- 
 ganese alum, is one of the most interesting ; it is of analogous 
 composition to ordinary aluminum alum, and is isomorphous 
 with this body, as it is with the corresponding alums of iron 
 and chromium. The series of double salts known as alums, 
 admirably illustrates the relationship of the several members 
 of the group of metals now under discussion, and the law of 
 isomorphism as well. It is interesting to observe, moreover, 
 that the name alum, originally applied specifically to the com- 
 pound of sulphate of aluminum and of potassium, has with 
 the growth of chemical knowledge come to have a generic sig- 
 nification. Several salts are now classed as alums, into the 
 composition of which neither aluminum nor potassium enters. 
 The following list enumerates some of the best-known potas- 
 sium alums : — 
 
 Common alum = K,S0„A1,3S0, -|- 24H,0, 
 Chrome alum = K^SO^Cr.SSO, + 24H,6, 
 
 2m 
 
530 ALTTMS. 
 
 Manganese alum = K^S0^,Mn,3S0^ + 243^0, 
 Iron alum = K,S0„Fe,3S0, + 243,0. 
 But as has been stated in § 609, the potassium in these com- 
 pounds may be replaced by any metal isomorphous with potas- 
 sium. There are ammonium alums and sodium alums corre- 
 sponding to each of the . potassium alums above enumerated, 
 and there is evidence that potassium may be replaced in these 
 alums by the rarer alkali-metals. Some alums, on the other 
 hand, are composed of mixtures in various proportions of alkali- 
 metals, and of the metals capable of forming sesquioxides. Besides 
 these true alums, there are allied bodies which contain no alkaliT 
 metal whatsoever ; such, for example, are the following : — 
 Aluminum iron alum = reS0j,Al,3S0^ -|- 243,0, 
 Aluminum magnesium alum = MgSO^jAl^SSO^ + 2411,0, 
 Aluminum manganese alum = MnS0^,Al,3S0j + 24H,0, 
 but these afBliated alums do not crystallize in the octahedral 
 form which is characteristic of the alums proper. 
 
 626. Binoxide of Manganese (MnO,) is a black compound 
 found abundantly in nature, and largely employed in the arts for 
 the purpose of evolving chlorine from chloride of sodium or 
 chlorhydric acid (§ 105), as well as for decolorizing glass. It 
 may readily be prepared artificially from the lower oxides by 
 the action of oxidizing agents. By itself, at the ordinary tem- 
 perature, binoxide of manganese is an inert chemical substance, 
 though at higher temperatures it has considerable oxidizing-power. 
 At a strong red heat it gives off one-third of its oxygen : — 
 3MnO, = Mn30, + 20. 
 Formerly oxygen was often prepared in chemical laboratories 
 by heating the black oxide of manganese in iron retorts ; but the 
 process has long been superseded by more convenient methods. 
 The oxide, Mn30^=MnO,Mn,03, which is left as a residue in 
 this experiment, corresponds in composition with the magnetic 
 oxide of iron, an important ore of iron. This oxide is the most 
 easily obtained by artificial means of all the oxides of manganese • 
 it is produced when the protoxide or its nitrate or carbonate is 
 strongly heated in the air, or when either of the higher oxides is 
 intensely ignited. 
 
MANGANIC ACID. 531 
 
 Black oxide of manganese is insoluble in nitric acid, but is 
 decomposed by strong hot cblorhydric acid, with formation of 
 protochloride of manganese and free chlorine, as has been already 
 explained (§ 105), and by hot concentrated sulphuric acid with 
 evolution of oxygen : — 
 
 MnO, + H^SO, = MnSO, + H^O + 0. 
 
 &p. 323. — In a small glass flask, provided with a suitable delivery- 
 tube, heat a mixture of 15 grms. of powdered black oxide of manganese 
 and 10 grms. of concentrated sulphuric acid, and collect the gas over 
 water in the usual way. 
 
 After all the available oxj'gen has been obtained in this experiment, 
 and the flask, together with its contents, has been allowed to cool, 
 pour 15 or 20 c. c. of water into the flask, boil the mixture; pour it 
 upon a filter, and evaporate the filtrate to dryness upon a water-bath, 
 taking care to stir it constantly when nearly dry. Hydrated sulphate 
 of manganese (MnS04,4H20) will be obtained as a reddish-white 
 powder. 
 
 JSxp. 324. — ^For the sake of comparing the old process of making 
 oxygen with methods now in use, charge an ignition-tube, such as 
 was used in Exp. 7, to one-third of its capacity, with black oxide of 
 manganese, connect it with the water-pan- in the usual way, heat it 
 strongly over the gas-lamp, and observe the comparatively slow rate 
 at which oxygen is evolved from it. 
 
 627. Manganic Acid (MnOj) has not yet been obtained in the 
 free state ; it is known only as it occurs in combination with potash 
 or some other base. Of the manganates, those of potassium, 
 sodium, and barium are the best-known ; they are isomorphous 
 with the corresponding chromates, sulphates, and seleniates. The 
 alkaline manganates are important compounds to the analyst. 
 
 JExp. 325. — Place upon a piece of platinum-foil as much dry car- 
 bonate of sodium as could be held upon half a pea ; mix with it an 
 equal quantity of powdered nitrate of potassium and a bit of binoxide 
 of manganese as large as the head of a small pin. Fuse the mixture 
 in the outer blowpipe-flame, and observe the bluish-green-colored 
 manganate of sodium which is produced. 
 
 Uxp. 326. — Melt together in an iron ladle over an anthracite or 
 charcoal fire, 10 grms. of hydrate of potassium, and 7 grms. of chlo- 
 rate of potassium; stir into the pasty liquid 8 grms. of very finely 
 powdered black oxide of manganese, and maintain the mixture for 
 a short time at a temperature jtist below visible redness, taking care 
 
 2m2 
 
532 CHAMELEON muteeal. 
 
 to stir it frequently with an iron rod. When the crumbly mass has 
 become cold, place some of it in a test-tube with a small quantity of cold 
 water and shake the tube. As soon as the solid particles have settled, 
 there will be seen a clear green liquid, which is a, solution of man- 
 ganate of potassium. 
 
 Hx2J. 327. — Pour off half of the green solution of manganate of 
 potassium into another short test-tube, and leave it open to the air ; 
 the green color of the solution will gradually change to blue, then 
 to violet and to purple, and finally to ruby red. The red color is 
 that of a solution of permanganate of potassium, into which the man- 
 ganate is converted by exposure to the air. The intermediate colors 
 are merely mixtures of the manganate green and the permanganate 
 crimson. On account of these remarkable changes of color, the name 
 chameleon mineral has been applied to manganate of potassium, and 
 by this term it is still commonly known. 
 
 Manganate of potassium is a very unstable salt, especially when in 
 solution ; it may be readily decomposed in a great variety of ways. 
 It breaks up into permanganate of potassium and binoxide of man- 
 ganese "when the aqueous solution is mixed with a large quantity of 
 water, and even strong solutions are rapidly decomposed in the same 
 way by boiling : — 
 
 SKjMnO^ -I- SH^O = K^MnjO, + MnO^ -|- 4KH0. 
 
 By means of acids, the change from manganate to permanganate 
 may be almost instantaneously effected ; but by the presence of an 
 excess of alkali the decomposition is always greatly retarded. 
 
 &p. 328. — Add a few drops of sulphuric acid to the remaining 
 portion of the solution of manganate obtained in Exp. 326, and 
 observe that a quantity of the red permanganate of potassium is 
 immediately produced. 
 
 628. Permanganic Acid (Mnfi^), or lather its hydrate H Mn , 
 may be obtained in aqueous solution by decomposing permanganate 
 of barium with sulphuric acid. The solution bleaches powerfully, 
 and the acid is rapidly destroyed by organic matter and other 
 reducing agents. Of the compounds of this acid, that with 
 potassium is by far the best-known. 
 
 Kcp. 329.— Place 300 c. c. of water m a porcelain dish, heat it to 
 boiHng and add to it by portions the remainder of the powdered 
 green manganate of Exp. 326; from time to time add small portions 
 of hot water to replace that which evaporates, and continue to boU 
 until the green color of the solution has changed to deep violet red 
 and the manganate of potassium has all been changed to permanganate! 
 
PEEMANGANIC ACTD. 533 
 
 In case the manganate contains a large excess of free alkali it cannot 
 readily be converted into permanganate by boiling ; it will therefore 
 often be found necessary to neutralize with nitric acid a portion of the 
 alkali which is in excess. As soon as the transformation has been 
 completed, pour the mixture into a tall bottle, leave it at rest until 
 the binoxide of manganese and other insoluble matters have settled ; 
 then decant the clear liquor into a glass-stoppered bottle, and preserve 
 it for use in subsequent experiments. The insoluble deposit may be 
 again boiled with water and allowed to settle ; the clear liquor thus 
 obtained may be added to that previously prepared. 
 
 In order to obtain crystals of the permanganate, a clear solution 
 like that above described should be rapidly evaporated to a small bulk, 
 then decanted from the binoxide of manganese which is precipitated 
 during the process, and set aside to cool. Needle-shaped crystals of a 
 dark purple-red color will soon be formed ; they are soluble in 16 parts 
 of water at 15°, and are permanent in the air. It is well to purify the 
 first crop of crystals by washing them with a little cold water, then 
 dissolving in the least possible quantity of boiling water, and again 
 crystallizing in the cold. Neither the crystals nor the solution should 
 ever be brought into contact with paper. Decautation will ordinarily 
 be sufiicient in order to separate the crystals from the mother-liquor; 
 but if filtration be necessary in any case, an asbestos filter shoiild be 
 employed (Appendix, § 14). 
 
 629. The permanganates are isomorphous with the perchlorates 
 (§ 125), and the potassium salts of the two acids are capable of 
 crystallizing together in all proportions. These compound crystals 
 are red-colored when, they contain much perchlorate of potassium, 
 but are black if they contain as much as half their weight of the 
 permanganate. 
 
 In the same way that perchloric acid is a more stable acid than 
 chloric add, so permanganic acid is less readily decomposed than 
 manganic acid. Both manganic acid and permanganic acid, how- 
 ever, give up oxygen to other substances with remarkable faci- 
 lity, and are much used as 'oxidizing agents. Even a piece of 
 wood or paper thrown into the green or red solution of a manga- 
 nate or permanganate, will quickly abstract oxygen from the 
 solution and destroy its color. In filtering the colored solutions, 
 paper is consequently inadmissible, as has been stated in Exp. 
 329 ; asbestos, sand, or some other inert filtering-material must 
 be resorted to. Permanganate of potassium is largely employed 
 
534 IRON. 
 
 for disinfecting putrid water and animal or vegetable matters 
 in a condition of putrefaction. A solution of it, such as has been 
 prepared in Exp. 329, is of great use in volumetric analysis, 
 especially for testing the value of iron ores. 
 
 lEON. 
 
 630. Although iron is one of the most widely diffused and 
 most abundant of the metals, it is rarely found native in the me- 
 tallic state. Meteors, however, fall upon the earth from outer 
 space, which consist mainly of metaUic iron, contaminated with 
 several other elements in small proportions. Minerals containing 
 iron occur in great numbers j and there are iadeed few natural 
 substances, whether organic or inorganic, in which iron is not 
 present. It is found iu the ashes of most plants, and in the blood 
 of animals. The natural compounds of iron which are available 
 as ores of the metal, are chiefly oxides and carbonates. The most 
 important varieties of these ores of iron are the following: — 1. 
 Magnetic iron-ore, the richest of the ores of iron, containing when 
 pure, 72"41 per cent, of iron, and not infrequently approximating 
 closely to this composition in large masses. 2. Red Hcematite, 
 consisting, when pure, of anhydrous sesquioxide of iron contain- 
 ing 70 per cent, of iron ; this ore often yields from 60 to 69 per 
 cent, of the metal. 3. Specular iron-ore, which is a crystalline 
 form of the same anhydrous sesquioxide of iron. 4. Limonite, or 
 Brown iron-ore, which consists essentially of hydrated sesquioxide 
 of iron, containing 59-89 per cent, of iron; yeUow ochre is a 
 clayey variety of this very abundant ore ; the numerous ores 
 classed under this head yield from 25 to 55 per cent, of iron. 5. 
 Spathic iron-ore, or Carbonate of iron, which contains in its 
 purest state 48-27 per cent, of iron, but is so generally contami- 
 nated with manganese, calcium, and magnesium as to yield very 
 various quantities of iron, ranging from 14 to 43 per cent. 6. Clay 
 iron-ore, a name appKed to a mixture of clay and carbonate of 
 iron, which occurs very abundantly in the coal-measures ; as this 
 ore is a mixture in imcertain proportions, it yields various per- 
 centages of iron, ranging from 25 to 40 per cent. 
 
 From the richer iron-ores, like the magnetic and specular 
 oxides, a very excellent iron can be obtained by simply heating 
 
THE BLOOMAET. 535 
 
 the broken ore with charcoal in an open forge fire, urged by a 
 blast. The ore is deoxidized by the carbon of the fuel, and the 
 reduced iron is agglomerated into a pasty lump called a " bloom," 
 while the earthy impurities contained in the ore combine with a 
 portion of the oxide of iron to form a fusible glass or slag. The 
 spongy bloom is freed from slag and rendered homogeneous and 
 solid by hammering while still red-hot ; by reheating and ham- 
 mering, the iron is then converted into bars or shaped into any 
 other desired form. This process is not economical in the che- 
 mical sense, for much iron is lost in the slag, and much fuel is 
 burnt to waste in an open fire ; but when well conducted, it yields 
 an admirable quality of iron ; and since the original outlay for 
 the construction of a bloomary is small, and repairs upon it are 
 always easy, the method has many advantages in regions where 
 transportation is dear while rich ores, charcoal, and water-power 
 abound. The bloomary process, in its crudest form, is easUy 
 practised by people possessing but little mechanical skiU and no 
 chemical knowledge ; it is undoubtedly the oldest method of ex- 
 tracting iron from its ores. 
 
 631. In the extraction of iron from its common ores, the metal 
 is usually obtained, not pure, but in a earburetted fusible state, 
 known as cast iron or pig iron. The main features of the pro- 
 cess are, first, a previous calcination or roasting to expel water, 
 carbonic acid, sulphur, and other volatile ingredients of the ore ; 
 secondly, the reduction of the oxide of iron to the metallic state 
 by ignition with carbon ; thirdly, the separation of the earthy 
 impurities of the ore by fusion with other matters into a crude 
 glass or slag ; and, lastly, the carbonizing and melting of the re- 
 duced iron. With the purer kinds of iron-ore, the preliminary 
 calcination is not always essential ; but with the majority of ores 
 it is very desirable ; not unfrequently all the drying necessary is 
 effected in the upper part of the blast furnace itseK, within which 
 the three last steps of the process always take place. 
 
 The blast furnace for iron consists essentially of a huge cylin- 
 drical structure of masonry, 15 to 25 m. in height, and 6 to 6 m. 
 in diameter at the central portion of the cylinder, but contracted 
 to a less diameter both at the top or throat and at the bottom or 
 hearth. Air is forced in at the bottom of the furnace to support 
 
536 THE BLAST ET7RNACE. 
 
 the combustion, and it has been found advantageous in the ma- 
 jority of oases to heat this blast of air to about the melting-point 
 of lead before it enters the furnace. The reduction of the oxides 
 of iron beuig effected by the carbonic oxide resulting from the 
 combination of carbonic acid with hot carbon (Exp. 181), it is 
 not diflcult to calculate the amount of carbon and the amount of 
 air requisite to reduce to metaUic state the iron contained in a 
 given weight of an iron-ore of known composition. Thus the 
 formula of specular iron-ore, or of red haematite, is Fe^O^, and, 
 since the atomic weight of iron is 56, these ores are 70 per cent, 
 iron ; accordingly the following quantities are equivalent one to 
 the other : — 
 
 1 = 1-429 = 0-3214 = 0-4286 = 1-863. 
 
 Iron. Fe203. Requisite weight Weight of oxygen Air. 
 of carbon in requisite to convert 
 state of CO. so much C to CO. 
 
 For every kilogramme of iron produced, nearly two kilogrammes 
 of air must be supplied, and at least ^ kilogramme of fuel, merely 
 to accomplish the chemical reaction. The reduction of the oxide 
 of iron, however, is not alone sufficient to secure the metal ; iron- 
 ores almost always contain earthy admixtures, consisting chiefly 
 of silica, clay, and carbonate of calcium; and these substances are 
 so intimately mixed with the reduced metal, that it is essential 
 to melt them before the iron can separate by virtue of its greater 
 specific gravity. Any one of these substances taken alone is in- 
 fusible at the temperature of the furnace ; they must be converted 
 into fusible double sUicates ; and as it is rarely the case that the 
 natural impurities of an ore are present in the proportions requi- 
 site for the formation of such double silicates, it is generally 
 necessary to mix with the ore a substance intended to effect this 
 result, and therefore called the flux. With ores in which the 
 earthy admixture is chiefly calcareous, the flux must be clay or 
 some sUieeous material ; but in the more frequent case of ores con- 
 taining clay or silica, the flux will be limestone or quicklime. 
 In either case, a fusible double silicate of aluminum and calcium 
 is the essential constituent of the slag. With sUiceous ores there 
 is another reason for the addition of Hme ; the double sUieate of 
 aluminum and iron is very fusible, and a considerable quantity 
 
THE BLAST EUKNACE. 537 
 
 of iron might be lost in the slag, were not lime enough added to 
 prevent the formation of this iron-containing silicate. Sometimes 
 both calcareous and sUiceous ores are within reach of an iron- 
 fumace, and the smelter, by mixing the two varieties iu due pro- 
 portion, may avoid the necessity of adding a flux. 
 
 The blast furnace is charged at the top with alternate layers of 
 the fuel (which may either be charcoal, anthracite, or coke), the 
 ore, and thfe flux, which is generally lime ; these materials are 
 constantly supplied at the top, and air is constantly supplied in 
 immense quantities at the bottom of the furnace, the actual weight 
 of the air forced ia being greater than the sum of the weights of 
 the ore, the fael, and the flux. "Where the blast first touches the 
 ignited fuel, carbonic acid is formed; this gas, rising with the 
 unused nitrogen through the furnace, comes in contact with white- 
 hot carbon, and is reduced to carbonic oxide (Exp. 181). The 
 layers of soUd material thrown in at the top of the furnace gra- 
 dually sink down, and as soon as a stratum of ore has descended 
 sufficiently to be heated by the hot mixture of nitrogen and car- 
 bonic oxide it becomes reduced to spongy metallic iron, which, 
 mixed with the flux and the earthy impurities of the ore, settles 
 down to hotter parts of the furnace, where it enters into a fusible 
 combination with carbon, while the flux and earthy impurities 
 melt together to a liquid slag. The liquid carburetted iron settles 
 to the very bottom of the furnace, whence it is drawn out, at 
 intervals, through a tapping-hole, which is stopped with sand 
 when not in use. The viscous slag flows out over a dam, so placed 
 as to retain the iron, but to permit the escape of the slag which 
 floats on the iron, as fast as it accumulates in sufficient quantity. 
 The fusion of the materials in the lower part of the furnace re- 
 quires a great heat ; and the amount of fuel consumed in getting 
 this high temperature is much greater than the amount requisite 
 for the reduction and carbonization of the metal. As charcoal 
 is a much purer carbon than coal or coke, iron smelted with char- 
 coal is generally purer than that smelted with coal; but as 
 charcoal crumbles under great pressure, the furnaces in which 
 charcoal is used are usually much smaller than those intended 
 for anthracite or coke. The consumption of fuel in smelting 
 1000 k. of iron varies with the nature of the furnace, the blast. 
 
538 CAST IRON. 
 
 and the fuel, between 500 k. and 3000 k. The gases which issue 
 from the mouth of the blast furnace are charged with an enor- 
 mous heating-power ; for besides being themselves intensely hot 
 they contain, even after having effected the reduction, a large 
 proportion of combustible gases, such as carbonic oxide, carbu- 
 retted hydrogen, and hydrogen. This gaseous mixture takes fire 
 whenever it comes in contact with the air ; a part of its heat may 
 be utilized in heating the air-blast and generating steam. 
 
 Two distinct varieties of cast iron exist, which differ in color, 
 texture, and fusibility ; these are white cast iron and gray cast 
 iron. White iron is hard and brittle, of crystalline texture and 
 shining fracture. Gray iron is slightly malleable, and has a 
 granular texture ; its fracture may be either coarse or fine-grained, 
 and minute particles of black graphite are visible upon the broken 
 surface. White cast iron melts at a lower temperature than gray, 
 but does not become so liquid as the gray. Gray oast iron, when 
 rapidly cooled, is converted into white iron ; when a casting is 
 made in an iron mould, the layer of metal in contact with the 
 mould is chilled and converted into the hard white iron, while the 
 interior of the casting will retain the condition of the stronger 
 gray iron. Excellent shot and shell for rifled cannon have lately 
 been cast on this plan. The chief chemical difference between 
 white and gray cast iron consists in the different condition of the 
 admixed carbon. In white iron the carbon seems to be dissolved 
 in or combined with the iron, while in gray cast iron, on the 
 other hand, the greater part of the carbon seems to be mechanically 
 diffused through the solid iron, in the state of graphite. The two 
 varieties, however, shade off into each other through a great va- 
 riety of intermediate mixtures. White cast iron rusts much more 
 slowly than gray cast iron. When white iron is heated with 
 strong chlorhydric acid it entirely dissolves, but the combined 
 carbon enters into combination with a portion of the nascent 
 hydrogen, forming hydrocarbons which impart a peculiar smell to 
 the gas evolved. Gray iron does not whoUy dissolve in hot chlor- 
 hydric acid ; a residue of graphite remains ; but the gas evolved 
 has the same smell as the gas evolved from white iron. When 
 bars, plates, or implements of common cast iron are exposed 
 to the slow action of dilute acids or of saline solutions such 
 
IMPTTKITIES OP lEON. 539 
 
 as sea-water, the iron is not infrequently wliolly dissolved 
 away, whUe the graphitic carbon remains untouched — a light, 
 soft, sectile substance which often retains the color and form 
 of the original article, but possesses neither hardness nor tena- 
 city. The largest proportion of carbon found in cast iron is 
 5-75 per cent. ; this large percentage occurs La a lustrous variety 
 of white iron which contains manganese and is called specular 
 iron. In gray iron the amount of carbon varies from 2 to nearly 
 5 per cent. 
 
 Silicon, sulphur, phosphorus, manganese, and copper are very 
 common impurities in cast iron. The silicon comes from sUiea 
 deoxidized in the furnace ; its amount varies from 0-1 to 3-5 per 
 cent. There is more of it in gray than in white iron, and more in 
 hot-blast iron than in cold-blast. Sulphur is almost always pre- 
 sent in cast iron, but only in very smaU quantity ; its presence 
 is supposed to conduce to the formation of white iron. The pre- 
 sence of phosphorus to the extent of 1 or 2 per cent, is not un- 
 common, and does not iajure iron iutended for castings, inasmuch 
 as the phosphorus makes the iron more fusible, and more liquid 
 when melted. Manganese is frequently present in cast iron, as 
 is not unnatural considering the common association of manganese 
 ores with iron-ores. Cast iron containing manganese appears to 
 be especially suitable for the production of steel. 
 
 The production of malleable or " wrought " iron from cast 
 iron, consists essentially in burning out the carbon, silicon, sul- 
 phur, and phosphorus which cast iron contains. This oxidation 
 of the impurities of cast iron is effected either by blowing upon 
 the melted metal with an air-blast in a smaU charcoal furnace 
 called a " finery," or by stirring the melted iron in a reverbera- 
 tory furnace in which the fuel does not come in contact with the 
 metal, and into which air can be admitted at vrill ; the latter pro- 
 cess, now much the most important method of manufacturing 
 wrought iron, is called "puddling." In puddling it is customary 
 to add to the charge of pig iron a quantity of iron scale or other 
 oxide of iron. The oxidation of the silicon, carbon, phosphorus, 
 and other impurities is effected partly by the air and partly by 
 the oxide added to the charge ; the carbon bums to carbonic 
 oxide, which heaves the seething mass as it escapes and burns in 
 
540 STEEL. 
 
 jets of blue flame ; the other impurities form, with the oxides ol 
 iron and manganese, a cinder or slag which ordinarily contains 
 sulphur, silicic acid, and phosphoric acid. When the cast iron ig 
 so far decarbonized as to be pasty in the fire, it is gathered into 
 lumps on the end of an iron bar and carried from the furnace to 
 a hammer or squeezer which expresses the liquid slag and welds 
 into a coherent mass the tenacious iron. The hammered lump 
 may be reheated and rolled or forged into any desired shape. 
 The waste of iron in converting cast into malleable iron amounts 
 to from 13 to 30 per cent. 
 
 Ordinary malleable iron has a gray color, and a specific gravity 
 of about 7-6. Though less malleable thaii gold and silver, its 
 malleability is very great, and the greater the purer the metal 
 and the higher the temperature to which it is raised. At a red 
 heat, separate pieces may be firmly united by hammering or 
 rolling ; the operation is called welding. Sulphur is said to ren- 
 der wrought iron brittle whUe hot or " red-short ; " silicon and 
 phosphorus render iron brittle at the ordinary temperature, or 
 " cold-short," in technical phraseology. These common impu- 
 rities of cast iron are therefore very prejudicial to wrought iron. 
 Wrought iron is hammered or rolled while in a doughy condition; 
 and the uniform, close, fibrous texture which is valued in mal- 
 leable iron depends much upon the nature of this mechanical 
 treatment, and the extent to which it is carried. Common mal- 
 leable iron still contains from 0-25 to 0-5 per cent, of carbon ; the 
 smaller the amount of carbon the softer the iron. Wrought iron 
 dissolves almost completely even in dilute acids ; but the hydrogen 
 evolved has the peculiar smell attributed to the presence of car- 
 bonaceous vapor. 
 
 632. Steel. — This invaluable substance is in composition inter- 
 mediate between cast and wrought iron, containing less carbon than 
 cast iron, but more than vrrought. It may be made from wrought 
 iron by heating bars of iron to redness for a week or more in con- 
 tact with powdered charcoal in close boxes from which air is care- 
 fully excluded. Though the iron is not fused, nor the carbon 
 vaporized, yet the carbon gradually penetrates the iron and alters 
 its original properties ; when the bars are withdrawn from the 
 chests in which they were packed, the metal has become fine-grained 
 
THB BESSEMEE PEOCESS. 541 
 
 in fracture, more brittle, and more fusible. The bars, how- 
 ever, are far from uniform in composition, the outside being more 
 highly carbonized than the interior ; they are apt to show blisters 
 of various sizes on the surfaces, and the steel thus prepared is 
 called " blistered " steel. To obtain steel of a uniform quality, it 
 must be cast into ingots. This process of preparing steel is called 
 the " cementation " process ; it is a curious instance of chemical ac- 
 tion between solid materials which are apparently in a state of rest. 
 Since the materials used in this process are the purest attainable 
 — the best iron and the best charcoal — the steel obtained is of 
 the best quality. Cheaper methods of preparing an inferior steel 
 are, however, of great industrial importance. If the " puddling '' 
 process for preparing malleable iron should be arrested when the 
 cast iron had lost from one-half to two-thirds of its carbon, the 
 product would be an impure steel, impure because the silicon, 
 phosphorus, sulphur, and other impurities of the cast iron would 
 only be incompletely removed. Nevertheless there are uses in 
 the arts for a steel of this quality which may be cheaply manu- 
 factured. 
 
 633. A new and very rapid method of preparing cast steel 
 directly from east iron is that known as the Bessemer process. 
 From two to six tons of cast iron, previously melted in a suitable 
 furnace, are poured into a large covered crucible, made of the 
 most refractory materials, and swung on pivots in such a manner 
 that it can be tipped up and emptied by means of an hydraulic 
 press. Through numerous apertures in the bottom of the crucible 
 a blast of air is forced up into the molten metal; an intense 
 combustion ensues involving the carbon in the iron and a portion 
 of the metal itself, and generating a most intense heat, which 
 keeps the mass fluid in spite of its rapid approach to the con- 
 dition of malleable iron. Such a quantity of specular iron or 
 white cast iron is then added to the iron in the crucible as is 
 necessary to give carbon enough to convert the whole mass into 
 steel, and the melted steel is immediately cast into ingots. Six 
 tons of cast iron can thus be converted into tolerable steel in 
 twenty minutes. This steel is suitable for the manufacture of 
 axles, cranks, rails, boiler-plates, and many other articles in which 
 
542 OXIDES OP lEON. 
 
 great strength should be combined with hardness. A pure steel 
 cannot at present be made by this process, inasmuch as the com- 
 bustion ia the crucible does not get rid of the sulphur and phos- 
 phorus in the cast iron nearly as perfectly as does the puddling 
 process ; for the same reason the manufacture of wrought iron 
 by this method, though the original object of the invention, has 
 been thus far found impracticable. It deserves mention that the 
 nailer who keeps his nail hot, while hammering it, by a carefully 
 regulated blast of cold air, applies the chemical fact involved in 
 Bessemer's process. This ancient practice was indeed a prophecy 
 of Bessemer's invention. 
 
 634. The two qualities of steel which are of greatest importance 
 are its hardness and its elasticity. These qualities are deve- 
 loped by quickly cooling the heated metal; the delicate pro- 
 cesses by which steel tools and springs are hardened, tempered, 
 and annealed are exceedingly curious, but are rather physical 
 than chemical phenomena. Many implements are sufficiently 
 well made by converting their exterior surfaces into steel, leaving 
 the interior of cast or wrought iron. Thus cast-iron tools may 
 be heated with oxide of iron to remove a part of the carbon from 
 their exterior and thus coat them, as it were, with steel. Tires 
 for wheels are well made of wrought-iron bars which have been 
 superficially converted into steel by the cementation process; 
 such tires combine the toughness of malleable iron with the 
 hardness of steel. 
 
 635. Oxides of Iron. — There are several definite compounds of 
 iron and oxygen. The best-known of these oxides are the pro- 
 toxide (FeO), or ferrous oxide, as it is often called, and the ses- 
 quioxide (Fe^Oj), often called ferric oxide, and sometimes spoken 
 of as peroxide of iron. There is another oxide, ferri(iacid Fe , 
 which is an exceedingly unstable substance, known only as it 
 exists in combination with potassium, as ferrate of potassium 
 (KjFeOJ, or with some other powerful base. Besides these 
 oxides, there are several compounds of intermediate composition 
 which may be supposed to result from the union of ferrous and 
 ferric oxides, in various proportions ; they are called collectively 
 ferroso-ferric oxides; the most important among them is the 
 
PEEROUS AND EEEBIC OXIDES. 543 
 
 magnetic oxide Fe^O^ = ¥eO,Fefi^, -which, is the black oxide 
 formed when iron is oxidized at high temperatures -in oxygen 
 gas, in air or steam (§§ 9, 18, 34). 
 
 636. Ferrous Oxide or Protoxide of Iron (FeO). — This com- 
 pound is not easily obtained pure, since it absorbs oxygen from 
 the air with great avidity and thus becomes contaminated with 
 the sesquioxide. But by dissolving a ferrous salt (that is, a salt 
 of protoxide of iron) in recently boUed water, and adding to the 
 liquid a solution of caustic alkali, which has likevnse been boiled 
 to expel air, there wiU be precipitated a white ferrous hydrate, 
 provided the operation be conducted out of contact with the air. 
 If this hydrate be exposed to the air, as when the solution of a 
 ferrous salt is mixed with the alkali without the precautions 
 above enumerated, it will rapidly absorb oxygen and wUl ex- 
 hibit various shades of light green, bluish green, and black, till, 
 finally, it assumes the red color of hydrated ferric oxide (Exp. 
 341). The anhydrous oxide obtained by igniting ferrous oxalate 
 in close vessels, absorbs oxygen so rapidly that it takes fire when 
 brought into contact with the air. 
 
 Hydrated ferrous oxide is readily soluble in acids, forming salts 
 known as the protosalts of iron or ferrous salts ; many of these 
 salts are of a pale green color ; like the hydrate, they rapidly 
 suffer decomposition by absorbing oxygen from moist air. 
 
 637. Ferric Oxide (Fe203).^This oxide, called also red oxide, 
 sesquioxide, or peroxide of iron, occurs very abundantly and 
 widely distributed in nature. Several of its varieties have been 
 already mentioned as ores of iron (§ 630). It may be obtained 
 also by igniting metallic iron or either of the lower oxides or 
 hydrates in contact with the air. For use in the arts, it is pre- 
 pared by igniting ferrous sulphate vdth or without addition of a 
 small proportion of nitrate of potassium, or by roasting the native 
 hydrate (yeUow ochre). The better sort, known as rouge, is 
 largely employed for polishing glass and jewelry, and all grades 
 of it are extensively used as pigments. Red ochre is impure 
 ferric oxide. As commonly met with, the oxide is amorphous 
 and has a red, brown, or nearly black color, according to the 
 method of its preparation. At a fuU white heat, it gives off a 
 portion of its oxygen, and magnetic oxide of iron is formed. It 
 
544 OXIBATIOlf BY raOlf-ETJBT. 
 
 is easily reduced to the metallic state by hydrogen gas, even at 
 temperatures below redness, and by carbon and carbonic oxide at 
 a red heat, as has been stated in § 631. Ammonia gas reduces 
 it also at a red heat. 
 
 Exp. 330. — In the middle of a tube of hard glass, No. 3, 10 c. c. 
 long, and provided at both ends with corks carrying short, straight 
 delivery-tubes, place a teaspoonful of red ochre or igrSted iron-rust. 
 Attach to one end of the tube a hydrogen-generator or gas-holder 
 provided with a chloride-of-calcium drying-tube, and connect with 
 the other end a U-tube. Support the tube containing oxide of iron 
 upon a ring of the iron stand, cause a current of hydrogen to flow 
 through it, immerse the U-tube in a bottle of cold water, and finall y 
 heat the oxide of iron. The hydrogen will combine with the oxygen 
 of the red oxide of iron, water will be formed and will condense in the 
 U-tube, while finely divided metallic iron will be left behind. After 
 the reduction has been completed, allow the tube to become cold, and 
 then scatter its contents through the air upon an earthen plate. They 
 will take fire and bum again to the condition of red oxide. 
 
 Exp. 331. — Repeat Exp. 330, using carbonic oxide instead of hy- 
 drogen, the products will be iron and carbonic acid instead of iron 
 and water. 
 
 638. The facility with which red oxide of iron gives up oxy- 
 gen, taken in connexion with the readiness with which metallic 
 iron and the protoxide take on oxygen, is a fact of great practical 
 importance. It has been found that organic substances may be 
 more rapidly incinerated by heating them in the air in contact 
 with a small quantity of ferric oxide than in air alone ; the oxide 
 of iron appears to act as a carrier of oxygen, as it is alternately 
 reduced by the combustible and again oxidized by the air. Even 
 at ordinary temperatures, and with the hydrated oxide, the same 
 reactions are witnessed, though in a less degree. The iron 
 nails employed in the construction of ships, bridges, fences or 
 shoes, actually corrode, "eat up" or "bum out" the organic 
 matter in contact with them, by absorbing oxygen from the air 
 and transferring it to the carbon compound with which they are in 
 contact. The rotting"'of canvas by iron-rust, or of a fishing-line 
 by the rusty hook, are familiar instances of corruption by rust. 
 
 These reactions doubtless play an important part in the forma- 
 tion of soils by the oxidation of vegetable remains. 
 
HTBRAIE OF lEON. 545 
 
 In the same way ferric oxide converts snlphide of calcium 
 (CaS) into sulphate of calcium (CaSOJ at the expense of the 
 oxygen of the air. A useful cement has been prepared by mixing 
 the residual oxysulphide of calcium of Leblanc's soda process with 
 an equal weight of the ferric oxide left as a residue in burning 
 iron pyrites for sulphuric acid. Hydrated sesquioxide of iron 
 (Fe203,3H20) may readily be prepared by adding an excess of 
 ammonia-water to the solution of almost any ferric salt. 
 
 Exp. 332. — Cover a teaspoonful of fine iron filings or small tacks 
 with three or four times as much dilute sulphuric acid in a small 
 bottle ; wait until the evolution of hydrogen ceases, then decant the 
 clear liquor into a small flask or beaker, add to- it a few drops of strong 
 nitric acid, and heat it to boiling. The liquor will soon be colored 
 dark brown by the nitrous fumes resulting from the decomposition of 
 the nitric acid, which are for a short time held dissolved by the liquid ; 
 but this deep coloration soon passes away, and there is left only the 
 yellowish -red color of the ferric sulphate which has been formed. 
 Add to the solution ammonia-water, until the odor of the latter per- 
 sists after agitation, and collect upon a filter the flocculent red preci- 
 pitate of ferric hydrate. 
 
 Besides this normal hydrate (Yefi^fi'Kjy) there are several 
 other ferric hydrates, containing smaller proportions of water. 
 They are found in nature, and may be obtained by heating the 
 normal hydrate, or by suffering it to remain for a long while 
 under water, or by boiling it for some time in water. 
 
 639. Generally speaking, hydrated sesquioxide of iron is easily 
 soluble in acids, though some peculiar varieties of it dissolve only 
 with difficulty. The anhydrous oxide also dissolves in acids,, 
 though less easUy in proportion as it has been more strongly ig- 
 nited ; its best solvent is concentrated boiling chlorhydric acid. 
 
 By long-continued heating at 300° or 320°, ferric hydrate can 
 be deprived of all its water, and stiU be readily soluble in acids ; 
 but when heated to duU redness, this powder suddenly glows 
 brightly for a moment and contracts in bulk, without either 
 losing or gaining weight, and is then attacked by acids only 
 slowly and with difficulty. It has been observed, however, that 
 the ignited oxide may still be dissolved rather easily by a hot 
 mixture of chlorhydric acid and ferrous chloride, protochloride of 
 tin, zinc, or some other reducing agent. 
 
 2n 
 
546 PEOPEETIES OF FEEKIC HTDEAIE. 
 
 Ferric hydrate is somewhat used as a mordant in dyeing, and 
 is largely employed for purifying coal-gas. As has been stated 
 under arsenic, the recently precipitated hydrate acts as an anti- 
 dote to arsenious acid, since when given in sufficient quantity it 
 forms a basic arsenite of iron scarcely at aU acted upon by water. 
 
 Exp. 333. — ^Dissolve half a gramme of arsenious acid in 40 or 50 c. c. 
 of boUing water. Divide the solution into two portions, and stir into 
 one of these portions a considerable quantity of moist ferric hydrate, 
 such as was obtained in Exp. 332 ; filter the mixture, acidulate the 
 filtrate with chlorhydric acid, and test it for arsenic by means of sul- 
 phydric acid (§ 340). 
 
 If a sufficient quantity of ferric hydrate has been employed, no pre- 
 cipitate of sulphide of arsenic will be obtained in the filtrate, though 
 on adding a drop of chlorhydric acid, and afterwards sulphydric acid, 
 to the original solution of arsenic, an abundant yellow precipitate will 
 be at once thrown down. 
 
 Exp. 334.— rm a tube, 30 cm. long, with alternate tufts of cotton 
 and loose layers of dry ferric hydrate, pass a slow current of siilphy- 
 (iric acid (Exp. 86) through the tube, and observe that the oxide 
 gradually becomes black ; it appears to be converted into ferrous sul- 
 phide, while water and sulphur are set free : — 
 
 Y^fi„m.fi + 3H2S = 2FeS 4- S 4- 6H2O. 
 
 After a good part of the ferric oxide has become black, remove the 
 contents of the tube to a porcelain plate, and leave them exposed to 
 the air in a place where no harm can be done in case they take fire. 
 By the action of the air, sesquioxide of iron will be reproduced and 
 sulphur set free within the mass ; some sulphurous acid is given ofi"at 
 the same time, and heat is evolved, as will readily be perceived if the 
 quantity of material be large. The following equation, though it does 
 not fully express the complete reaction which really occurs, may stiU 
 serve to give a general idea of these chemical changes : 
 
 SFeS -I- 50 = Fe^Oa + S -f- SO^. 
 In practice the impure illuminating gas is made to pass through 
 layers of ferric oxide, often made porous by an admixture of sawdust ■ 
 as soon as the oxide ceases to absorb sulphuretted hydrogen it is 
 " revivified " by forcing or dravring through it a current of fresh'air or 
 by spreading it in the air. The oxide is thus used over and over agam 
 until so much sulphur has accumulated within it as to interfere, me- 
 chanically, with its absorbent power. The sulphur may readily be 
 recovered from this mixture by distiUation ; or the spent oxide may be 
 
STTLPHUIIIS OF IKON. 547 
 
 used instead of pyrites for maJring sulphuric acid, wherever enough of 
 it can be obtained to repay the trouble of collecting. 
 
 The ferric salts are usually of a yellowish-brown or red color 
 when, hydrated, though some of them have a violet tinge ; they 
 are white when dry. The normal salts are usually soluble in 
 water and deliquescent; and there are numerous soluble basic 
 salts, besides other basic salts which are insoluble. 
 
 In the ferric salts iron plays the part of a trivalent element 
 like aluminum, while in the ferrous salts it is bivalent like cal- 
 cium or lead. The ferric salts closely resemble salts of aluminum, 
 and are for the most part isomorphous with them. Besides act- 
 ing as a base, ferric oxide, like oxide of aluminum, combines 
 with several of the more powerful Bases to form salts called 
 ferrites ; magnetic oxide of iron, for example, may be regarded 
 as the ferrite of iron. 
 
 It is remarkable that ferric oxide may be displaced from many 
 of its compounds by the protoxide of iron ; thus, when hydrated 
 ferrous oxide is added to a solution of ferric sulphate, hydrated 
 sesquioxide is precipitated : — 
 ^ Fe,03,3S03 + 3(reO,H,0) = Fe.O^SH.O + 3(reO,S03). 
 
 In like manner, carbonate of barium precipitates anhydrous 
 ferric oxide from ferric salts, but upon ferrous salts it has no 
 action : — 
 
 Fe.Cl, + SBaCO, = Fe,03 + 3BaCl, + 3C0,. 
 
 Sulphides of Iron. — There are several sulphides of iron, the 
 most important of which are the protosulphide (FeS) and the 
 bisulphide (FeSJ, found native as iron pyrites. There is a 
 sulphide, FBjS^, which is magnetic like the oxide to which it 
 corresponds. 
 
 640. Ferrous Sulphide (FeS) is a substance of great value to 
 the chemist as the cheapest source of the important reagent 
 sulphydric acid (§§ 202, 210). 
 
 This sulphide may be prepared by igniting pyrites in a covered 
 crucible, by rubbing roll brimstone against a white-hot iron bar, or by 
 fusing together sulphur and iron turnings. The second method is to 
 be recommended if the student have ready access to a blacksmith's 
 forge. The sulphide is a waste product in those chemical works where 
 
 2n2 
 
648 PEOTOSULPHIBE OE IKON. 
 
 sulphate of lead, obtained from dye-houses, is reduced to the metallic 
 state by fusion with iron and coal. In the laboratory it may be pre- 
 pared as follows : — 
 
 JEicp. 335. — Heat a common Hessian crucible to redness in a fire of 
 coke or anthracite, and project into it from an iron spoon successive 
 smaU portions of a mixture of 7 parts of iron turnings and 4 parts of 
 powdered sulphur, replacing the cover of the crucible after each addi- 
 tion of the mixture. The sulphur and iron combine with great energy, 
 and the sidphide formed melts down to the liquid state. Since the 
 molten sulphide is capable of dissolving both iron and sulphur, accord- 
 ing as the one or the other may be present in excess, it is impossible to 
 prepare a pure protosulphide by this method. But the product ob- 
 tained as above described, though of variable composition, answers 
 perfectly well for all ordinary purposes. When the crucible has be- 
 come half-full of the molten sulphide, remove it from the fire, pour 
 out its contents upon a brick floor, and, if more of the sulphide be 
 desired, replace the crucible in the fire and proceed as before. 
 
 Where comparatively large quantities of the sulphide are required, 
 it is well to bore a hole through the bottom of a plumbago crucible 
 and set the latter upon the grate-bars of the furnace in such manner 
 that the hole may remain open ; fill the crucible with iron turnings ; 
 heat it to redness and throw in lumps of sulphur upon the hot iron! 
 As fast as sulphide of iron forms it will melt and flow through th§ 
 hole in the crucible into the ashpit below, which should be kept clean 
 to receive it. In the preparation of sulphide of iron, wrought iron 
 should always be employed. From the filings of cast iron, but little, 
 if any, of the fusible sulphide can be prepared. 
 
 The foregoing experiment illustrates the practical methods of making 
 ferrous sulphide; but several other reactions which produce it are of 
 scientific interest (compare Exp. 85). 
 
 Exp. 336.— AiTange a bottle for generating sulphuretted hydrogen, 
 as in Exp. 86, but in place of the delivery-tube in Fig. 41 attach to 
 the bottle a, jet for burning the gas. After the air has been com- 
 pletely expelled from the bottle, light the sulphydrio acid gas at the 
 jet, and hold in its flame a piece of fine iron wire ; the iron will bum 
 to ferrous sulphide, and if the wire he held in the axis of the flame so 
 that a considerable portion of it shall be kept red-hot, the globule of 
 sulphide of iron formed will melt and flow backward upon the wire as 
 fast as the end of the latter is consumed. 
 
 Exp. 337.— Mix 20 grms. of fine iron filings, 14 grma. of flowers of 
 sulphur, and 7 grms. of water in a smaU bottle, and heat the mixture 
 gently upon a sand bath, or set it aside in a warm place. Chemical 
 
IKON PYRITES. 549 
 
 action will soon set in, much heat -will be evolved, and in the course 
 of half an hour the mixture will become black from formation of sul- 
 phide of iron. If the porous black sulphide be left exposed to the air, 
 it wiU absorb oxygen, and will be partially converted into ferrous 
 sulphate. 
 
 A firm packing or lute for the joints of iron vessels is prepared by 
 mixing together 60 parts of fine iron filings, 1 part of flowers of sul- 
 phur, and 2 parts of powdered chloride of ammonium. The mixture 
 is made into a stiff paste with water, and immediately applied to the 
 iron. It soon becomes hot and swells up, and sets to a hard compact 
 mass, while ammonia and sulphuretted hydrogen are disengaged. 
 
 Exip. 338. — Dissolve a small crystal of ferrous sulphate (copperas) 
 in water,. and add to the liquid a drop or two of sulphydrate of ammo- 
 nium (§ 526). Black sulphide of iron wiU be thrown down (compare 
 Exp. 334). 
 
 The finely divided ferrous sulphide obtained in the wet way, as in 
 the last two experiments, dissolves much more quickly in acids than 
 the compact sulphide obtained by the way of fusion ; in contact with 
 acids it evolves gas so tumultuously that it would be inconvenient as 
 a source of sulphydric acid. 
 
 The black earth between the stones of the pavements of cities, and 
 at the bottoms of drains and cesspools, owes its color to sulphide of 
 iron formed by the putrefaction of sulphuretted compounds in contact 
 with ferric oxide contained in the earth. 
 
 641. Bisulphide of Iron (FeS^) occurs abundantly in nature 
 as the well-known mineral iron pyrites. Two distinct forms of 
 it are met with : — the yellow cubical pyrites, crystallized in forms 
 of the monometric system ; and the white pyrites or marcasite, 
 which crystallizes in trimetric forms. A third variety of sulphide 
 of iron, called magnetic pyrites, is of different composition from 
 the foregoing, and contains less sulphur than the bisulphide. 
 Iron pyrites appears to have been sometimes formed in nature by 
 the deoxidation. of sulphates, such as the sulphate of calcium, by 
 means of organic matter in presence of chalybeate waters. The 
 formation of pyrites has often been noticed in solutions of sul-- 
 phate of iron into which organic matters have fallen. But bisul- 
 phide of iron may be readily formed in the dry way also. 
 
 The compact forms of yellow pyrites, whether natural or arti- 
 ficial, are permanent in the air; but when finely divided the 
 mineral oxidizes rather easily, with evolution of considerable heat. 
 
550 rEEEOirs chxoeibb. 
 
 White iron pyrites oxidizes rapidly in the air, no matter whether 
 it be compact or friable. The spontaneous combustion of many 
 kinds of coal is due to the oxidation of iron pyrites disseminated 
 through the combustible. Alum and copperas are often prepared 
 from pyritous shales, either by firing heaps of the shale artifici- 
 ally, or by allowing the heaps to take fire spontaneously through 
 oxidation of the pyrites, and then regulating the combustion so 
 that the largest practicable yield of sulphate of iron or of sulphate 
 of aluminum shall be obtaiaed. So long as the temperature of 
 the burning pyrites remains comparatively low, ferrous sulphate 
 and sulphuric acid are the principal products, the latter uniting 
 with the alumina of the shale, if such be present ; when the heap 
 has become cold, the sulphates can be separated by lixiviating 
 the mass with water. When pyrites is roasted at higher tem- 
 peratures, as in the manufacture of sulphuric acid, sulphurous 
 acid is given off, and ferric oxide left as the principal residue. 
 
 When distilled in close vessels, one atom of the sulphur in 
 iron pyrites is expelled, and ferrous sulphide remains. Sulphur 
 has sometimes been prepared in this way in a dearth of native 
 sulphur. 
 
 642. Ferrous Chloride (FeCy may be obtained by passing 
 chlorine or dry chlorhydric acid gas over hot iron ; in case chlor- 
 hydric acid, be employed, hydrogen wiU be evolved. As commonly 
 met with, however, the chloride is in the form of a hydrate 
 (YeCl^+^B. fi) obtained by dissolving metallic iron in dilute 
 chlorhydric acid. It crystallizes easily, forms double salts by 
 uniting with many other chlorides, and may be deprived of its 
 water without decomposition when heated carefully out of con- 
 tact with the air. 
 
 643. Ferric Chloride (Fe^ClJ. — As obtained by burning me- 
 tallic iron in an excess of dry chlorine, this compound occurs in 
 anhydrous, glistening scales, which volatilize easily when heated. 
 It dissolves readily in water, with evolution of heat, and deli- 
 quesces rapidly in the air. It hisses when thrown into water. 
 Once dissolved in water, it cannot be freed from the water by 
 evaporation, since chlorhydric acid goes off with the water, and a 
 basic compound of ferric oxide and ferric chloride remains. Hy- 
 drated ferric chloride may readily be obtained by boiling a solu- 
 
lEEEOirS STTLPHATE. 551 
 
 tion of ferrous chloride with a small proportion of nitric acid, or 
 by passing chlorine gas through a solution of ferrous chloride. 
 From concentrated solutions, ferric chloride crystallizes with 
 several different proportions of water. Ferric chloride combines 
 with many of the metaUic chlorides to form double compounds, 
 among which the ammonium salts are perhaps the most stable. 
 
 644. Ferrous Sulphate (FeSOJ. — A hydrate of this compound, 
 of composition FeSO^+TH^O, usually called copperas or green 
 vitriol, is the most common of all the compounds of iron. It may 
 readily be prepared by dissolving metallic iron or protosulphide 
 of iron in dilute sulphuric acid. On the large scale it is commonly 
 prepared by roasting iron pyrites at a gentle heat, or aluminous 
 shales containing pyrites in the manner already indicated. Some- 
 times, -however, it is manufactured directly from metaUic iron 
 and sulphuric acid ; and it is obtained as a secondary product in 
 certain metallurgical operations where copper is precipitated, by 
 means of iron, from a solution of copper. The reaction is analo- 
 gous to those employed for obtaining pure sUver (Exp. 267) and 
 pure lead (§ 594). 
 
 Exp. 339. — Dissolve 6 grms. of common blue vitriol (sulphate of 
 copper) in 50 or 60 c. c. of water, acidulate the liquor with a few drops 
 of sulphuric acid, pour it into a bottle, and place in it a rod of thick 
 iron wire. Copper will immediately begin to be precipitated as a 
 coating upon the iron, and in the course of an hour or two will be 
 completely removed from the solution. The original blue color of the 
 solution wiU disappear and be replaced by the faint green color of 
 copperas, while a spongy mass of metallic copper will be obtaiued : — 
 OuSOj + Fe = FeSO^ + Cu. 
 
 Decant the solution of ferrous sulphate from the precipitated copper, 
 place in it a fragment of iron, and evaporate it to a small bulk ; pour 
 the concentrated solution into a wide-mouthed phial, cork the phial 
 tightly, and set it aside in a cool place ; the liquid wUl be converted 
 into a mass of copperas crystals. 
 
 It has been proposed to prepare copperas from the "finery 
 slag " of the puddling-fomaces (where cast iron is converted into 
 wrought iron) by treating this slag with dilute sulphuric acid. 
 The finery slag consists chiefly of basic silicate of protoxide of 
 iron (2FeO,SiOJ. 
 
 645. When perfectly pure, the crystals of ferrous sulphate are 
 
S52 PROPEETIBS OF PBEEOTTS SULPHATE. 
 
 compact, transparent, and of a bluish-green color ; but in dry air 
 they effloresce and become covered with a ■white incrustation, the 
 color of which subsequently changes to rusty brown through ab- 
 sorption of oxygen. The common commercial article is of a 
 grass-green color, and is contaminated with more or less ferric 
 sulphate. Besides the common hydrate containing 7 molecules 
 of water, there are hydrates which contain 4, 3, and 2 molecules 
 ■of water respectively. From all of these hydrates the water can 
 •easily be expelled by heat, and if the anhydrous salt thus obtained 
 be still further heated it will decompose ; two stages in this de- 
 composition may be formulated as follows : — 
 
 I. 2FeS0^ = SO, -I- Fe,03,S0,. 
 11. Fe,03,S03 = Fe,03 + SO,. 
 Basic ferric sulphate is at iirst formed, while sulphurous' acid is 
 given off; and finally the ferric salt is itself decomposed into an- 
 hydrous sulphuric acid and feme oxide. Upon this reaction the 
 preparation of Nordhausen sulphuric acid depends (§ 239). Like 
 ferrous hydrate, ferrous chloride, and all the ferrous salts, moist 
 copperas, or an aqueous solution of copperas, rapidly absorbs oxy- 
 gen from the air. 
 
 Exp. 340. — Pour a solution of copperas into an open capsule and 
 leave it exposed to the air for a day or two ; the solution will gradually 
 become yellow as the oxidation proceeds, and after a while a rusty 
 precipitate of ferric oxide, or of highly basic ferric sulphate, will fall. 
 The oxide of iron which separates under these conditions is not readily 
 soluble in dilute acids. It- appears to be an isomeric modification of 
 the easily soluble hydrate which is precipitated from cold ferric solu- 
 tions by alkaline lyes. At all events the sulphuric acid of the cop- 
 peras is insufficient to dissolve all of the ferric oxide formed during its 
 oxidation. In most cases where a ferrous salt is to be converted into 
 a ferric salt, it is best to add a certain proportion of free acid to the 
 mixture, in order to prevent the separation of the oxide. 
 
 A difficultly soluble deposit, similar to the foregoing, may readUy he' 
 obtained by hoiliQg an exceedingly dilute solution of almost any of the 
 soluble ferric salts. It is possible that these sediments should be re- 
 garded rather as highly basic salts than as mere hydrates. Their 
 inertness may perhaps be due to the presence of small proportions of 
 the acids of the salts from which they have been derived, still held in 
 chemical combination ; but there is at present less evidence in favor of 
 this view than of the one previously stated. 
 
INK. 553 
 
 Eocp. 341. — To a teaspoonful of a solution of copperas add a few drops - 
 of soda lye, and observe that the hydrate rapidly absorbs oxygen, and 
 changes color as has been set forth in § 636. 
 
 Escp. 343. — Mix a few drops of a solution of copperas with a drop or 
 two of a solution of tannic acid, such for example as tincture of nut- 
 galls, or of oak- or hemlock-bark ; a light violet-colored precipitate 
 will be formed and will remain suspended in the liquid; by exposure 
 to the air this color soon changes to black. The violet precipitate is 
 ferrous tannate, and the black precipitate ferric tannate ; if tbese finely 
 divided precipitates were produced in liquids made slightly viscous by 
 the addition of gum or sugar, they would remain suspended in the 
 liquor, which could then be used as writing-ink. 
 
 Ink may be prepared as follows :— Powder separately 12 gTms. of 
 nutgalls, 5 grms. of copperas, and 5 grms. of gum-arabic. Boil the 
 nutgalls two or tbree hours in a flask with 75 c. c. of water, taking 
 care to add hot water, by small portions, to supply that lost by evapo- 
 ration. Allow the mixtiu:e to settle, and decant the clear liquor into a 
 clean bottle. Dissolve the giun-arabie in a small quantity of water, 
 and mix the mucilage thoroughly with the solution of nutgalls. Dis- 
 solve the copperas in another portion of water, and incorporate this so- 
 lution with the mixture of nutgalls and gum. Add enough water to 
 make the volume of the mixture equal to 100 c. c. Preserve the ink 
 in a tight bottle. If the color of the product be lighter than is de- 
 sired, the liquid may be left exposed to the air until it has acquired a 
 deeper tint. Wben first applied to paper, the color of fresh ink is 
 comparatively pale, but the writing darkens gradually in proportion as 
 it absorbs oxygen. 
 
 In the course of the foregoing experiments, dip a small piece of cot- 
 ton cloth in the solution of nutgalls, and allow it to become dry ; then 
 dip it in the solution of copperas and hang it up in damp air. Black, 
 insoluble tannate of iron wiU be so firmly precipitated in and upon the 
 fibres of the cloth, that it cannot be washed away. 
 
 The experiment illustrates one general method of dyeing, by means 
 of which blacks and grays of various shades may be applied to cloth or 
 leather, though in practice other astringent dye-stufl's, such as catechu, 
 cutch, or gambler, are commonly employed in place of nutgalls. 
 
 Ferrous sulphate is largely employed in dyeing, sometimes diretftly, 
 as in the foregoing experiment, but often as the source of other com- 
 pounds of iron which are employed as mordants ; ferrous acetate, for 
 example, obtained by decomposing ferrous sulphate with acetate of 
 calcium, is a compoimd much used by dyers. It should be remarked, 
 however, that acetate of iron is sometimes made directly by dissolving 
 scraps of iron in vinegar or pyroligneous acid (§ 380). 
 
554 NITKAIES OP lEON. 
 
 646. Ferric Sulphate (Fe^SSOJ is interesting chiefly from its 
 analogy with sulphate of aluminum. Like sulphate of aluminum, 
 it comhines with the sulphates of the alkali-metals to form well- 
 defined alums. (Compare § 625). Ferric sulphate occurs as a 
 waste product in the mother -liquors from which copperas and 
 alum have crystaUized. By drying these liquors and igniting 
 them, red ochre of excellent quality can be obtained, in accor- 
 dance with the second reaction of § 645. Fuming sulphuric acid 
 is commonly manufactured nowadays by distilling pure ferric 
 sulphate, instead of copperas as formerly at Nordhausen. The 
 ferric salt is obtained by dissolving ferric oxide in weak 
 sulphuric acid, and evaporating the solution to dryness ; the 
 residue of ferric oxide left after the ignition of the sulphate is 
 thus reconverted into ferric sulphate, and is used over and over 
 agaiu as often as it is decomposed. 
 
 647. Ferrous Nitrate (FeN^O,, -|- 6II2O) is a compound of con- 
 siderable scientific interest, which may readily be procured by 
 dissolving ferrous sulphide in cold dilute nitric acid, or by de- 
 composing a solution of copperas with an equivalent quantity of 
 nitrate of barium. It may also be obtained, mixed with nitrate 
 of ammonium, by dissolving iron in cold dilute nitric acid. The 
 metal dissolves without evolution of gas, in a manner which may 
 be thus formulated : — 
 
 4Fe + lOHNO, = 4FeN,0, + (WKJl^O^ + 3H^0. 
 
 The aqueous solution of ferrous nitrate decomposes readily when 
 heated, and in warm weather changes spontaneously to a ferric 
 compound. 
 
 648. Ferris Nitrate (Fe^SN^ J may be obtained in hydrated 
 crystals containing 1 8 molecules of water, by dissolving metallic 
 iron in nitric acid, of 1-29 specific gravity, till the liquor has 
 taken up about 10 per cent, of the metal, and then adding an 
 equal volume of nitric acid of specific gravity 1'43. The solution 
 will deposit, on cooling, rhombic prisms of ferric nitrate, which 
 are sometimes colorless, but often of a faint lavender-blue color. 
 They are slightly deliquescent, and very soluble in water, but are 
 only slightly soluble in cold nitric acid. By adding nitric acid to 
 a syrupy solution of ferric nitrate, there may be- obtained another 
 
CTANIBES OF lEON. 555 
 
 hydrate, containing only 12 molecules of water, crystallized in 
 cubes or square prisms. By mixing a solution of ferric nitrate, or, 
 for that matter, almost any other of the normal ferric salts, with 
 recently precipitated ferric hydrate, or by partially abstracting 
 the acid of the salt by means of an alkaJi, deep-red solutions of 
 various basic compounds may readily be obtained. A basic ferric 
 nitrate is employed in dyeing, under the name iron mordant. 
 
 649. Silicates of Iron. — Several native silicates of iron are 
 known; but none of them are of special interest. The green 
 tinge of ordinary glass is due to the presence of a ferrous sOicate, 
 and by increasing the proportion of the ferrous salt, a deep bottle- 
 green colour may be imparted to glass. Ferric silicate, on the 
 other hand, has comparatively little coloring-power, though when 
 a considerable quantity of it is present it imparts a yellow color 
 to glass. It is sometimes used for coloring porcelain. To de- 
 stroy the green color of the ferrous silieate, binoxide of man- 
 ganese, or some other oxidizing agent, is often added to glass in 
 the process of manufacture ; the ferrous silieate is thus converted, 
 for the most part, into ferric silicate, and a nearly colorless glass 
 produced. 
 
 650. Cyanides of Iron. — There is a ferrous cyanide (Fe(CN)2), 
 known as a yellowish-red precipitate, which takes up oxygen 
 and becomes blue when exposed to the air ; and a ferric cyanide 
 (Fe2(CN)j) has been obtained in solution. But by far the best- 
 known of the cyanides of iron are certain double compounds, 
 which constitute the peculiar pigments known collectively as 
 Prussian blue. Common Prussian blue, for example (Pe,CjyN'jg+ 
 ISH^O), may he regarded as a double compound of ferrous and 
 ferric cyanides, 3re(CNX, 2(re2(CN)j) -1- ISH.O ; it may be pre- 
 pared as follows : — 
 
 Eocp. 343. — ^Add to an exceedingly dilute solution of almost any 
 ferric salt, such, for example, as the ferric sulphate of Exp. 332, a 
 drop of ferrocyanide of potassium (§ 609). A beautiful blue precipitate 
 will form, and wUl remain suspended in the liquor for a long whUe. 
 Another variety of Prussian blue, known as TumbuU's blue, may be 
 obtained by mixing a solution of red prussiate of potash, known to 
 chemists as ferricyanide of potassium, with a solution of copperas or 
 other ferrous salt. 
 
 Since the yellow prussiate of potash wiU give no blue coloration 
 
556 DISTnf&UISHING THE TWO OXIDES OF rEON. 
 
 with ferrous salts, and since the red prussiate yields no blue witli 
 ferric salts, it is e\ident that the two solutions may be used as 
 tests by which to detect the presence of ferrous and ferric salts, 
 respectively, in any solution. 
 
 Exp. 344. — Soak a piece of cotton cloth in a solution of ferric sul- 
 phate (Eip. 332), and then immerse it in an acidulated solution of 
 yellow prussiate of potash. Prussian blue will be precipitated upon 
 the cloth and will remain firmly attached to it. Prussian blue is 
 largely employed in dyeing and calico-printing in a variety of ways. 
 
 Now that we have discovered a ready means of detecting 
 ferrous and ferric salts, it will be well to determine experimentally 
 how easily the members of either of these classes may be changed 
 to salts of the other class. 
 
 Exp. 345. — ^Dissolve 4 or 6 grms. of iron tacks or wire in dilute 
 chlorhydric acid in a test-tube, pouring ofi" the liquid from time to 
 time as it becomes nearly saturated. Test a few drops of the solution 
 first with ferro- and then with ferricyanide of potassium, in order to 
 prove that it is pure ferrous chloride. BoU the rest of the liquid with 
 a few drops of nitric acid to convert it to ferric chloride, and determine 
 when the conversion has been completed by testing as before. Finally, 
 divide the ferric solution into three portions. Through the first portion 
 pass sulphydric acid gas ; sulphur wiU be deposited and ferrous chloride 
 formed, 
 
 Fe^Cle + H^S = 2FeCl2 4- 2HC1 -|- S; 
 to the second portion add small fragments of protochloride of tin, until 
 a drop of the mixture, tested with the ferrocyanide, will no longer give 
 a blue coloration, 
 
 Pe,Cle + SnClj = SFeClj -|- SnCl,; 
 boil the third portion with a fragment of metallic zinc, and determine 
 the fact of reduction as before, 
 
 Fe^Cle + Zn = 2FeCl2 + ZnCl,. 
 By leaving either of these reduced solutions in the air, or by heating 
 them with a little chlorate or nitrate of potassium, nitric acid, or 
 other oxidizing agent, they may be readily converted again to the 
 condition of ferric salts. 
 
 COBALT AND NICKEL. 
 
 651. Cobalt and nickel are two metals remarkably similar 
 to one another both in physical and chemical properties. They 
 are found together in nature in the same ores, in combination 
 
eOBALI AM) NICKEL. 557 
 
 with, sidphur and arsenic, and are both, ingredients of meteoric 
 iron. They can be reduced from their oxides by charcoal and 
 by hydrogen at high temperatures, and the metals thus obtained 
 can be melted about as readily as pure iron. Both cobalt and 
 nickel resemble iron more closely than any other common metal ; 
 they are very tenacious, hard, and refractory ; like iron they are 
 magnetic, and when hot they may be forged ; they rust less 
 readily than iron, but resemble it closely in most of their 
 chemical properties. The atomic weights of cobalt and of nickel 
 are identical; the same number (58-8) applies to both. The 
 specific gravities of the two metals also are equal or nearly so, 
 varying in different samples from 8'2 to 8-9. Cobalt is not used 
 in the metallic state ; but several of its compounds are remarkable 
 for the beauty of their color, and find important applications in 
 the arts as pigments, especially for coloring glass and porcelain. 
 A blue glass containing silicate of cobalt, obtained by fusing 
 oxide of cobalt with ordinary glass, is largely employed, under 
 the name of smalt, as a vitrifiable pigment. This coloration may 
 readily be exhibited by adding a minute particle of any cobalt 
 compound to a borax bead (§ 490) upon a loop of platinum wire, 
 and again placing the bead either in the oxidizing or in the 
 reducing flame of the blowpipe. Nickel, on the other hand, is 
 used in the metallic state as an ingredient of various alloys, of 
 which the alloy known as German silver, composed of copper, 
 zinc, and nickel, is one of the most important. A whitish alloy, 
 obtained by adding nickel to copper, is sometimes employed for 
 coin of low denominations. 
 
 652. Both cobalt and nickel form protoxides (CoO and N'iO)^ 
 protochlorides, and protoxide salts, like those of iron, except that 
 the protosalts of cobalt and nickel are far more stable than the 
 salts of protoxide of iron ; so that the protoxides of cobalt and 
 nickel must be regarded as the principal oxides of these metals. 
 Like iron, chromium, and the other metals of the family now 
 under discussion, cobalt and nickel also unite with oxygen to 
 form sesquioxides (Co^Oj and M^Oj), and these sesquioxides, or 
 at least the sesquioxide of cobalt, combine with bases to form 
 salts ; but these salts and the sesquioxides themselves are com- 
 paratively unstable bodies ; they are far more easily decomposed 
 
558 TTRANITTM. 
 
 than compounds of the protoxides of cobalt and nickel, or than 
 compounds of the sesquioxides of the other metals of the group. 
 Hence, in the matter of nomenclature, the salts of the protoxides 
 of cobalt or nickel take precedence of the salts of the sesquioxides. 
 When, for example, nitrate of cobalt is spoken of, nitrate of 
 protoxide of cobalt is the substance referred to ; whereas when 
 nitrate of iron or of chromium is mentioned, without further 
 specification, we must infer that the nitrate of the sesquioxide 
 is the substance meant. The use of terms in the loose manner 
 referred to in the foregoing examples is of course always to be 
 deprecated ; but, in order to avoid the chance of being misun- 
 derstood, some chemists have extended to all metals having two 
 salifiable oxides the use of the terminations ous and ic, which 
 has been exemplified under iron by the terms ferrous and ferric 
 oxides. Thus the terms cobaltous and cobaltic oxides, and 
 nickelous and nickelic oxides have been applied by some writers 
 to the oxides of cobalt and nickel; and there is at present a 
 tendency to adopt and amplify this system of names ; but they 
 are as yet too little employed in the Uterature of science to find 
 appropriate place in an elementary manual. 
 
 TTEAIflUM. 
 
 653. Uranium is a rare metal, found in but few localities. It 
 can be reduced from its chloride by means of hot potassium, 
 but not from its oxide by means of hydrogen. Metallic uranium 
 is of a steel-white color, and is somewhat malleable ; it does 
 not oxidize in air or in water at ordinary temperatures, but 
 bums brilliantly when strongly heated in air. It dissolves in 
 chlorhydric or sulphuric acid, with evolution of hydrogen, and, 
 in general, is closely analogous to iron and manganese in its 
 chemical behavior. The atomic weight of uranium is 120 j its 
 specific gravity is 18'4. 
 
 There are two priacipal oxides of uranium, capable of uniting 
 with acids to form salts (a protoxide UrO, and a sesquioxide 
 TJr^Og), and two other intermediate oxides, formed by the union 
 of the proto- and sesquioxides in different proportions. The 
 sesquioxide also plays the part of a weak acid towards strong 
 bases. Uranium is never used as a metal ; but compounds of it 
 
SESQiriOXtDB SALTS. 559 
 
 are somewhat extensively employed for coloring glass, and to a 
 certain extent in photography also. Sesquioxide of uranium 
 imparts a beautiful greenish-yellow color to glass, and the glass 
 thus colored is to a high degree fluorescent ; the protoxide, on 
 the other hand, gives a fine black, highly esteemed for painting 
 porcelain. 
 
 654. The salts of sesquioxide of uranium are remarkable in 
 that they constitute an exception to the general rule, that, to 
 form a normal salt, as many molecules of the acid are required 
 as there are atoms of oxygen in the base employed. The normal 
 sulphate of calcium, for example (§ 241 ), may be formed by the 
 union of CaO and SO3, and the normal sulphate of sesquioxide of 
 iron is composed of Fe^Oj and 3S0g ; but in sulphate of sesquioxide 
 of uranium we find only UrjOjjSOj, and analogous formulae ex- 
 press the composition of the nitrate and other salts of this oxide. 
 But in spite of this peculiarity, uranium has many properties in 
 common with the other members of the sesquioxide group of 
 metals. One characteristic, for example, of this aluminum-iron 
 group, which is shared by uranium, is that the sesquioxides are 
 capable of uniting with acids, not only in the fixed and definite 
 proportions requisite for the normal, crystallized salts already 
 described, but also in very numerous indefinite proportions to 
 form soluble basic compounds, incapable of crystallization for the 
 most part, and solidifying in tough shining masses like gum 
 when their solutions are allowed to evaporate spontaneously ia 
 the air. Nitrate of iron, for example, may be made as basic as 
 the compound SFeJd^j^fi^, and still be soluble in water; and 
 between this limit, on the one hand, and that of the crystallized 
 normal salt (Eefi^iSNfi^ + ISH^O) upon the other, sesquioxide 
 of iron and nitric acid can combine chemically in every con- 
 ceivable proportion. The compounds of sesquioxide of iron with 
 other acids, and the nitrates and other salts of the sesquioxides 
 of the other metals of the group, all behave in a similar way, the 
 compounds of uranium being no exception to the rule. This ten- 
 dency to form soluble, gummy, polybasic sesquisalts, so strikingly 
 exhibited by the members of the group of elements now under 
 discussion, is evidently one of those obscure manifestations of 
 the chemical force which we have already met with when dis- 
 
560 . THE SESainOXIDB fiKOTJP. 
 
 cussing the phenomena of solution (§ 49), and the law of multiple 
 proportions (§ 76, end). 
 
 655. The most important point of difference between uranium 
 and the other members of the sesquioxide group of elements is 
 the fact, already alluded to, that one molecule of its sesquioxide 
 unites with but one molecule of base to form crystallized salts, 
 whereas the sesquioxides of the other members of the group all 
 unite with acids in the proportion of one molecule of base to 
 three molecules of acid to form their normal crystallized salts. 
 Since the alums are formed by the union of a normal sulphate 
 of some metal of the alkali group with a teracid sulphate of some 
 metal of the sesquioxide group, there is no such thing as a 
 uranium-alum, because the teracid uranium-sulphate is wanting. 
 Sesquioxide of uranium, in fact, behaves among bases somewhat 
 as metaphosphoric acid does among acids ; it stands in much the 
 same relation to the other teracid bases of its class, as meta- 
 phosphoric acid to the ordinary terbasic phosphoric acid. 
 
 656. The Sesquioxide Group. — The bond of union between 
 the metals included in this class is the fact that they all form 
 salifiable sesquioxides. Most of them form also salifiable prot- 
 oxides; and if we arrange the metals in the order of their 
 atomic weights, 
 
 Gl = 14, Al = 27-4, Cr = 52-5, Mn = 55, Fe = 56, 
 Ni = 58-8, Co = 58-8, Ur = 120, 
 it win be apparent that the sesquioxides of the metals at the 
 head of the list are the most stable of the sesquioxides, and that 
 the protoxides of nickel and cobalt are the most stable of the 
 protoxides, while with manganese and iron both forms of oxide 
 are weU represented ; uranium does not conform to this ar- 
 rangement. Glucinum and aluminum have no protoxides at all ; 
 and the protoxide of chromium is very unstable. Some of the 
 metals of the group are usually bivalent, others trivalent, while 
 others are both hi- and trivalent. 
 
 The class of salts caUed alums affords strong evidence of 
 the existence of a natural relation between the members of the 
 alkali group, on the one hand, and the members of the sesqui- 
 oxide group, on the other. These highly crystallized isomor- 
 phous salts are all moulded upon one pattern, and their atomic 
 
Alums. 
 
 Specific 
 
 Atomic 
 
 Gravity. 
 
 Volume. 
 
 1-722 
 
 275-6 
 
 1-641 
 
 279-2 
 
 1-621 
 
 279-6 
 
 1-845 
 
 270-7 
 
 1-736 
 
 275-5 
 
 1-712 
 
 281-4 
 
 ATOMIC TOLUMB OF AITJMS, 561 
 
 volumes (§ 252) are very nearly equal, as the following table -will 
 illustrate for some of the alums : — 
 
 Atomic 
 
 Weight. 
 
 KAISAASH^O 474-5 
 
 NaAlSjO^lSHjO 458-4 
 
 (NHJA1S20„12H20 453-4 
 
 KCrS203,12H20 499-6 
 
 (NH„)CrS20„12H20 478-5 
 
 (NH^)reS20„12H20 482-0 
 
 It is a fact not unworthy of notice, that the compounds of this 
 group of metals, with the exception of those of gluoinum and 
 aluminum, ai'e for the most part colored, independently of the 
 colors of the substances with which they are united. The metals 
 of the sodium, calcium, and magnesium groups produce colorless 
 compounds, unless when joined with an acid possessing a color of 
 its own. Glucinum and aluminum produce, in like manner, 
 colorless compounds ; but the oxides, hydrates, chlorides, bromides, 
 iodides, sulphides, and oxygen-salts of chromium, manganese, 
 iron, nickel, cobalt, and uranium are aU more or less colored in 
 themselves, and every color of the spectrum, from the violet at 
 one extremity to the red at the other, can be matched from 
 among the innumerable tints exhibited by the various compounds 
 of the last six members of the sesquioxide group. 
 
 657. With the members of the group now under discussion 
 are commonly classed a number of rare metals, more or less 
 nearly related to aluminum and iron. They are all, however, 
 of subordinate interest, and need only be named in this manual. 
 The following is a list of these elements, together with their 
 symbols and their atomic weights, so far as the latter have 
 been determined: — ^Yttrium, Tt= 68; Erbium, Er=(?); Terbium, 
 Tb=(?); Zirconium, Zr=90 (?); Norium, No=(?); Cerium, 
 Ce=92; Lanthanum, La= 92-8; Didymium, Di=95; Thorium, 
 Th= 231-5 (?). 
 
 2o 
 
562 EXTRACTION OF COPPBK. 
 
 CHAPTEJR XXXI. 
 
 COPPER AND MERCTJET. 
 
 658. Though by no means one of the most abundant metals, 
 copper is nevertheless very widely diffused in nature, and is 
 largely employed by man. Traces of it exist in almost every 
 soU, whence it is taken up by plants, in which it may almost 
 always be detected by refined testing. Traces of it have re- 
 peatedly been found also in the various animal organs and 
 secretions. Many natural waters contain minute quantities of 
 copper ; its presence may often be recognized in the deposit of 
 oxide of ii'on which separates from chalybeate waters. Since 
 the metal occurs native in many localities, several of its valuable 
 properties were early recognized and made use of. Long before 
 the discovery of methods of reducing iron from its ores, tools 
 and weapons made of native copper were employed by many 
 barbarous nations. 
 
 Besides occurring in the native state, copper is fomid in a great 
 variety of combinations; the most common of its ores, however, is 
 the sulphide, or rather a compound of sulphide of copper and sulphide 
 of iron in varying proportions, knovra as copper pyrites. The processes 
 of obtaining copper from its ores vary greatly, according to the quality 
 of the ore. The oxides and carbonates may be readily reduced by 
 heating the ore in contact with some carbonaceous material and a 
 flux suitable to remove the impurities of the ore. The treatment of 
 ores containing sulphur is far more coraplicated. Such ores are roasted 
 in the iirst place, in order to convert a considerable portion of the 
 sulphides of copper and iron into oxides ; a proper flux is then added 
 to the roasted ore, and the whole is melted down in either a rever- 
 beratory or blast furnace. The oxide of copper formed by roasting is 
 reconverted into sulphide, while much of the sulphide of iron wMch 
 had escaped oxidation before is now changed to oxide and passes off 
 in the slag. Sulphide of cqpper comparatively free from ii-on is thus 
 obtained ; in other words, the copper ore is very much concentrated 
 by the operation. If need be, the concentrated product is subjected 
 
PBOPERTIES OP COPPER. 563 
 
 to a series of roastings and meltings, until it has been almost com- 
 pletely freed from sulphide of iron and other impurities. The pure or 
 nearly pure sulphide of copper is then roasted in a current of air, until 
 a certain proportion of the sulphide has been converted into oxide. 
 Finally the mixture of sulphide and oxide is strongly heated to a 
 temperature at which its ingredients react upon one another in such 
 manner as to yield sulphurous acid and metallic copper : — 
 
 OujS + 2CuO = SO2 + 4Cu. 
 
 Sometimes copper is obtained by precipitating it with iron from 
 solutions of its salts, as has been shown in Exp. 339. The copper 
 thus thrown down by iron is known as cement-copper, and is fre- 
 quently obtained from the drainage-water of certain mines, in which 
 a small proportion of sulphide of copper is oxidized by the air to sul- 
 phate of copper, and so carried into solution. In some localities, low- 
 grade copper-ores are lixiviated with chlorhydric acid, obtained as a 
 waste product from the manufacturers of soda-ash, and the copper 
 solution subsequently made to flow over fi-agments of scrap iron. 
 
 The common method of assaying copper-ores is another application 
 of the precipitation of copper by means of iron. 
 
 659. Copper is a rather hard metal, of a well-known red 
 color ; it is very tenacious, ductile, and malleable. The specific 
 gravity of the metal when free from air-bubbles varies between 
 8-92 and 8-95. Copper melts less readily than silver, but more 
 readily than gold ; its melting-point has been estimated to be 
 about 1170°. At an intense heat it volatilizes, though for aU 
 ordinary purposes it may be regarded as non-volatile. It is one 
 of the best conductors of heat and electricity known. Its spe- 
 cific heat is 0-09515. Copper combines with oxygen far less 
 readily than iron. Even at a bright-red heat it is not capable of 
 decomposing water, excepting to a very slight extent. Finely 
 divided copper, however, soon becomes oxidized on being exposed 
 to the air, though, as is well known, solid masses of the metal 
 suffer little or no change, at the ordinary temperature, in air free 
 from sulphydric and carbonic acids. When strongly heated in 
 the air, copper quickly becomes covered with a coating of black 
 oxide of copper (see Exp. 12). Metallic copper is not very 
 readily acted upon by acids, excepting those rich in oxygen. 
 The weaker acids, such as acetic acid, have no action upon it, 
 unless air be present, in which event the metal is soon corroded ; 
 
 2o2 
 
564 AILOXS OF COPPER. 
 
 and the same remark applies to dilute ctlorhydric and sulplmric 
 acids. Finely divided copper, however, slowly dissolves with 
 evolution of hydrogen in hot concentrated chlorhydric acid ; and 
 in hot oil of vitriol the metal dissolves readily, as has been seen 
 in the preparation of sulphurous acid. (See Exp. 96.) 
 
 Copper is readily soluble iu somewhat diluted nitric acid, such 
 as is commonly found in commerce (see Exp. 37) ; but the 
 strongest nitric acid, of specific gravity 1-52, does not act upon 
 it. When immersed in such acid the metal remains bright, and 
 no bubbles of gas arise from its surface. The phenomenon is 
 explained by the fact that nitrate of copper is insoluble in mono- 
 hydrated nitric acid, though readily soluble in water and in 
 dilute acid. Ammonia-water and many salts, such as chloride 
 of sodium and the various salts of ammonium, corrode copper 
 rather rapidly when in contact with air. Finely divided copper 
 takes fire in chlorine gas ; and at a red heat the metal imites 
 directly with bromine, iodine, sulphur, silicon, and the various 
 metals. It does not appear to unite directly with carbon or with 
 nitrogen at any temperature. 
 
 Several of its compounds with other metals are of great im- 
 portance iu the arts. Brass and the yellow metal used for 
 sheathing ships are aUoys of zinc and copper ; bronze, gun-metal, 
 and bell-metal are alloys of tin and copper ; and various compo- 
 sitions are produced by mixing these alloys with brass. German 
 silver iu its various forms is an aUoy of nickel, zinc, and copper ; 
 and copper is an essential ingredient of all the common coins, 
 implements, and ornaments of gold and silver. 
 
 660. Dioxide of Copper (Cu^O) is sometimes found in nature 
 as Ruby copper ; it may readily be obtained by heating protoxide 
 of copper with finely divided metallic copper, or other reducing 
 agents ; so, too, when masses of metallic copper are gently heated 
 in the air, they become covered with a thin film of the dioxide. 
 
 Mxp. 346. — Dissolve in a test-tube a few drops of honey or a bit of 
 grape-sugar in a little water. Add to the solution two or three drops 
 of a rather dilute solution of sulphate of copper, and then pour in 
 enough soda-lye to redissolve the precipitate which is at first pro- 
 duced by the lye. 
 
 Slowly heat the clear blue solution, and observe that a yellow pre- 
 
PEOTOXIDB or COPPBE. 565 
 
 cipitate of hydrated dioxide of copper soon separates, first at the 
 uppermost part of tlie column of liquid, but soon in all parts of the 
 tube, as its contents become sufficiently hot. When the liquor is 
 heated to boUing, the hydrated yellow precipitate changes after a 
 time to anhydrous red dioxide. 
 
 Most of the dilute acids decompose dioxide of copper with 
 formation of salts of the protoxide and separation of metallic 
 copper. But it dissolves in concentrated chlorhydric acid and in 
 ammonia- water, forming colorless solutions. The ammoniacal 
 solution may be employed as a test for the presence of oxygen in 
 any mixture of gases ; oxygen is immediately absorbed by the 
 solution and a compound of protoxide of copper and ammonia 
 (Exp. 352) of characteristic deep blue color is formed. Dioxide 
 of copper is employed to a certain extent for coloring glass 
 ruby-red. 
 
 661. Protoxide of Copper (CuO) may be prepared by heating 
 the metal or the dioxide in a current of air, or by igniting car- 
 bonate, hydrate, or nitrate of copper. 
 
 Exp. 347. — Bind a bright copper coin with wire, in such manner 
 that a strip of wire 8 or 10 cm. long shall be left projecting from the 
 coin ; thrust the free end of the wire into a long cork or bit of wood, 
 and by means of this handle hold the coin obliquely in a small flame 
 of the gas-lamp. A beautiful play of iridescent colors will appear 
 upon the surface of the copper, particularly if it be moved to and fro. 
 Thrust the hot coin into water, and observe that it is at this stage 
 covered with a coating of red suboxide of copper. Replace the coin 
 in the lamp and hold it in the hot oxidizing portion of the flame 
 (Exp. 195) ; it will soon become black from the formation of prot- 
 oxide- of copper. After a rather thick coating of oxide has been 
 formed, again quench the coin in water ; the black coating or scale of 
 oxide will fall ofi) and beneath it wiU be seen a thin film of the di- 
 oxide firmly adhering to the metal. This film of dioxide is inten- 
 tionally produced upon the surfaces of many copper implements by the 
 manufacturers. If the coin were heated long enough it would all be 
 converted, first into the red dioxide, and then into black protoxide of 
 copper. The scales which fall oif when hot metallic copper is beaten 
 or rolled, like those obtained from the coin in this experiment, always 
 consist of a mixture of the two oxides. 
 
 Exp. 348. — Evaporate to dryness in a porcelain dish upon a sand- 
 bath some of a solution of nitrate of copper prepared from copper as 
 in Exp. 37. There will b3 left as a residue a green basic nitrate of 
 
566 PROIOXIDB OP COPPEE. 
 
 copper. Place a small quantity of this residue upon a iragaxent of 
 porcelain, and ignite it until red nitrous fumes are no longer given off. 
 Pure protoxide of copper will he left upon the porcelain. 
 
 Though no oxygen can be expelled from protoxide of copper 
 by mere exposure to heat, all its oxygen may, nevertheless, be 
 removed with great facility by means of reducing agents. Oxide 
 of copper is, in fact, one of the most convenient oxidizing agents 
 in the chemist's possession, and is largely employed to this end 
 in the analysis of organic compounds. When heated with car- 
 bonaceous substances, it converts all their carbon into carbonic 
 acid ; and, in like manner, hydrogen is immediately oxidized by 
 it and converted into water. Since carbonic acid and water can 
 readily be collected and weighed, and since their composition is 
 accurately known, the determination of the amounts of carbon 
 and hydrogen in any substance, through the agency of oxide of 
 copper, is merely a matter of mechanical detail. 
 
 JExp. 349. — Repeat Exp. 330, with the exception that a teaspoonful 
 of black oxide of copper (Exp. 348) is placed in the tube' instead of the 
 iron rust. Water may be collected in the U-tube as before, and me- 
 tallic copper will be left in the reduction -tube. But, unlike the easily 
 oxidizable iron, the reduced copper will not take fire in the air. 
 
 662. Protoxide of copper is soluble in most acids, with forma- 
 tion of salts which are blue or green when hydrated, but white 
 when thoroughly dried. From the solutions of most of these 
 salts hydrated oxide of copper may be precipitated by means of 
 any of the strong soluble bases. 
 
 IJxp. 350. — Place in a test-tube, or smaU bottle, 8 or 10 c. c. of a 
 cold dilute solution of sulphate of copper, and add to it enough of a 
 solution of caustic soda to render the mixture alkaline to test-paper. 
 A light-blue precipitate will fall ; hydrate of copper is insoluble in 
 water and in soda-lye. 
 
 &p. 351. — Repeat Exp. 350, with the difference that the solutions 
 of caustic soda and sulphate of copper fc both heated to boiling and 
 are mixed while hot. Instead of the blue hydrate, black protoxide of 
 copper win now be thrown down ; for hydrate of copper readily parts 
 with its water when heated, even if it he all the while immersed in 
 water ; it does not again combine with water after it has become cold. 
 Instead of mixing boiling solutions of the alkaU and copper salt the 
 moist precipitated hydrate of copper of Exp. 350 mio-ht be chano-ed 
 
SULPHIDES OF COPPEK. 567 
 
 to black oxide by simple boiling; but the transformation would be, 
 comparatively speaking, slow, and tbe experiment less striking than 
 the one here described. 
 
 Exp. 362. — Again repeat Exp. 350, but instead of soda-lye add to 
 the copper salt amnionia- water, drop by drop, and shake the tube after 
 each addition of the ammonia. Hydrate of copper will be precipitated 
 as before, in accordance with the reaction 
 
 CuSO, + 2(NH,)H0 = (NHJ2SO4 + CuH^O^; 
 for, as has been said, this hydrate is insoluble in water ; but, since hy- 
 drate of copper is readily soluble in ammonia-water, the precipitate 
 will redissolve as soon as more of this agent than is needed to decom- 
 pose the copper salt is added. The animoniacal solution of copper has 
 a magnificent azure-blue color. 
 
 663. The Sulphides of Copper (Cu^S and CuS) are interesting 
 from their occurrence as ores, and from the reactions already 
 briefly explained, which are so important in the industry of 
 copper-smelting (§ 658). The protosulphide, as obtained by add- 
 ing sulphydric acid to acidulated solutions of the salts of copper, 
 is an important substance to the analyst ; it is a black powder, 
 insoluble in water, in dilute acids, and in alkaline lyes. 
 
 664. Dichloride of Copper (Cu^Clj) may be obtained by treat- 
 ing a mixture of protoxide of copper and finely divided metallic 
 copper with concentrated chlorhydric acid, or by boiling a solution 
 of the protochloride with sugar or some other reducing agent. 
 It is a white compound, insoluble in water, but soluble in strong 
 chlorhydric acid, and in aqueous solutions of chloride of sodium, 
 chloride of potassium, and many other chlorides. 
 
 665. Protochloride of Copper (CuClj) is formed when copper is 
 burned in an excess of chlorine. It may readily be prepared in 
 the hydrated condition (G\iC\.^-\-2'KJJ) by dissolving oxide, hy- 
 drate, or carbonate of copper in chlorhydric acid, and evaporating 
 the solution upon a water-bath. Anhydrous chloride of copper 
 is brown ; but the hydrated salt forms green, needle-shaped crys- 
 tals. The concentrated aqueous solution is green ; when diluted 
 with water it becomes blue, but turns green again on being boiled. 
 The dry salt fuses when heated, and at a red heat gives off half 
 its chlorine and is changed to the dichloride. Chloride of copper 
 is soluble in alcohol and ether ; if some of the alcoholic solution 
 
568 STOPHATE OP COPPEE. 
 
 is poured upon a tuft of cotton and then ignited, it will burn with 
 a green flame, which is characteristic of copper. 
 
 666. Sulphate of Copper (CuSOJ has been already obtained 
 in solution as a secondary product in Exp. 96. It may also be 
 readily prepared by dissolving oxide of copper, copper-scale for 
 example, in moderately dilute sulphuric acid. Much of it was 
 formerly prepared in this way for use in the arts ; it is' an inci- 
 dental product also in the process of refining gold and silver, and 
 in certain metallurgical operations. As it crystallizes from aqueous 
 solutions, sulphate of copper holds in chemical combination 5 mo- 
 lecules of water, and may then be represented by the formula 
 CuSOj-fSHjO. This hydrated salt, known as blue vitriol, is the 
 commonest salt of copper ; most of the various pigments and other 
 preparations of copper, medicinal or chemical, are made from it ; 
 and it is itself used to a considerable extent by dyers and calico- 
 printers, and largely by the electrotypers. 
 
 Bxp. 3f>3. — Tie a piece of bladder over one end of a lamp-chinmey, 
 or over the mouth of a vFide-mouthed bottle or beaker, off which the 
 bottom has been somewhat evenly broken. Solder a piece of thick 
 copper wire to a strip of stout sheet zinc, just wide enough to enter 
 the chimney or bottle, and a Uttle longer than the bottle is deep. 
 Place the zinc in the bottle or chimney, and sink the bottle or chimney, 
 with the closed end down, in a beaker or large tumbler containing a 
 strong solution of sulphate of copper. Fill the bottle or chimney with 
 dilute nitric acid, attach to the copper wire a clean medal or coin, of 
 which one side has been varnished, and the other rubbed over with 
 plumbago, and bend the vrire so that the medal or coin may be im- 
 mersed in the sulphate-of-copper solution contained in the beaker or 
 tumbler. Thorough contact must be secured between the copper wire 
 and the unvarnished side of the coin or medal. In a few hours a co- 
 herent film of solid, malleable copper will be firmly deposited on that 
 face of the coin or medal which was not protected by the non-conduct- 
 ing varnish. The shell of copper may be readily detached from the 
 coin or medal, the plumbago ensuring the ready separation of the two 
 metallic surfaces; it is a perfect reverse of the object copied. 
 
 This experiment illustrates on a small scale the important art of 
 electro-metaHurgy. Plating in gold and silver, as well as in copper, 
 is extensively performed by a process perfectly analogous to that of 
 this experiment. Woodcuts, type, medals, maps, and engravings are 
 
ACETATES OF COPPBE. 569 
 
 accurately copied by means of this deposition of metals from their solu- 
 tions under the action of the galvanic current. 
 
 It is remarkable that the blue color of sulphate of copper de- 
 pends upon the presence of water. 
 
 &p. 354. — Heat 1 c. c. of powdered blue sulphate of copper upon 
 a piece of porcelain ; as it loses its water, the light-blue powder will 
 turn white. A drop of water upon the anhydrous powder will restore 
 its blue color. 
 
 If concentrated sulphuric acid be poured over the blue crystals, it 
 wiU abstract water from them, and a quantity of the white anhydrous 
 salt win be formed. 
 
 Since the protoxides of iron and of copper are isomorphous, or 
 rather since the metals iron and copper are capable of replacing 
 one another in many of their compounds, it is not surprising that 
 the sulphates of iron and copper should crystallize together to 
 form a compound which may contain almost any proportion of 
 either salt. This isomorphous mixture of the two salts was 
 formerly largely employed in the arts, and is still somewhat used 
 to meet the requirements of old receipts for dyeing. In a similar 
 way, sulphate of copper crystallizes together with the sulphates 
 of nickel, cobalt, zinc, and magnesium. 
 
 667. Nitrate of Copper (CuN^O,,) may be obtained crystallized, 
 by allowing the blue solution, obtained in Exp. 37, to evaporate 
 spontaneously in dry air. It is interesting as an example of a 
 salt ready to give up oxygen on slight provocation. If a piece 
 of tin-foil about 20 cm. square be twisted firmly around a rather 
 large crystal of nitrate of copper, then pierced in several places 
 with a needle, and moistened with water, or with a few drops of 
 common spirits of wine, a powerful reaction will soon ensue. The 
 tin will be oxidized, at the expense of the oxygen of the nitrate 
 of copper, much heat will be evolved, and smoke, or even flame, 
 produced. 
 
 668. Acetates of Copper are formed by the action of acetic acid 
 upon metallic copper, exposed to the air. They are commonly 
 called verdigris. Purified verdigris is the normal acetate of cop- 
 per ; and common verdigris is a hydrated basic acetate. Verdi- 
 gris is usually prepared by packing plates of copper between 
 wooUen cloths steeped in vinegar ; but sometimes, in wine-grow- 
 ing countries, the refuse of the wine-press is suffered to ferment 
 
670 MBECITRT. 
 
 in contact with the copper plates. Prom time to time the ver- 
 digris is removed from the surface of the copper, the plate of 
 metal being agaia and again subjected to the action of acetic acid 
 so long as any of it remains. 
 
 In ordinary language, the term verdigris is often iacorrectly 
 applied to the green coating of carbonate of copper, vs^hich forms 
 upon copper long exposed to damp air, or to the rust formed 
 upon copper by the combined action of air and almost any acid. 
 A compound of acetate of copper and arsenite of copper consti- 
 tutes the beautiful and vivid green color known as Schweinfurt 
 green. 
 
 669. Small globules of metallic mercury are sometimes found 
 in nature; but the principal ore of this metal is the sulphide 
 (HgS), called cinnabar. From this sulphide the metal is readily 
 extracted, by distiUing a mixture of it and quicklime, or iron- 
 turnings, in cast-iron retorts. The sulphur is retained by the 
 Ume or iron, as the case may be, while metallic mercury passes 
 off in the state of vapor into receivers contaiaing water, beneath 
 which it condenses to the liquid state. 
 
 A rougher method of manufacture is to heat the coarsely 
 broken sulphide on a perforated brick arch, by a quick fire of 
 brush- wood ; the sulphur in the ore is kindled, and, by its com- 
 bustion, maintains the heat necessary to continue the distillation. 
 The liberated mercury is condensed in wide and long earthen 
 pipes, which slope first down, and then up. 
 
 670. At the ordinary temperature of the air, mercury is a 
 brilliant, mobile liquid, of IS- 6 specific gravity, which vaporizes 
 slowly, even at ordinary temperatures, and boils at about 360°. 
 The vapor-density of mercury does not coincide with its atomic 
 weight. As is the case with the metal cadmium (§ 599), the atomic 
 weight of mercury is the weight of two unit- volumes of its vapor, 
 and is therefore double the vapor-density, instead of identical 
 with it. Into the product-volume of any compound of mercury, 
 one more volume is condensed than would be contained in the 
 product- volume of a corresponding compound of oxygen or sul- 
 phur. The atomic weight of mercury is 200, and two unit- 
 
MEKCTJRT. 571 
 
 volumes of its vapor 'weigli 200 times as much as one unit- volume 
 of hydrogen ; its vapor-density should, theoretically, be 100 ; and 
 the results of experiment approximate closely to this number. 
 (Compare § 259.) 
 
 When cooled to — 39°-4 mercury freezes. In solidifying, 
 liquid mercury contracts considerably, and there results a ductile 
 metal of tin-white color and granular fracture, which may be cut 
 with a knife. Perfectly pure mercury undergoes no change in 
 air or in oxygen gas at the ordinary temperature, even when 
 shaken about in the gas for a long while ; but if mercury con- 
 taining traces of foreign metals, such, for example, as that ordi- 
 narily met with in commerce, be exposed to the air, a gray pul- 
 verulent coating wUl, after a while, appear upon its surface. 
 This coating is composed of oxides of the contaminating metals 
 mixed with finely divided metallic mercury. A similar gray 
 powder of finely divided mercury may be obtained by triturating 
 mercury with sulphur, tallow, and a variety of other substances, 
 or simply by shaking it with water or oil of turpentine. When 
 heated in the air to temperatures near its boiling-point, even 
 pure mercury absorbs oxygen, and is converted into the red oxide 
 (§ 672). MetaOic mercury combines directly with chlorine, bro- 
 mine, iodine, and sidphur. 
 
 Chlorhydric acid has no action upon mercury, not even when 
 it is hot and concentrated. Dilute sulphuric acid has scarcely 
 any action upon it ; but hot concentrated sulphuric acid converts 
 it into solid sulphate of mercury, while sulphurous acid is evolved 
 (Exp. 96). Nitric acid, even when dilute, dissolves it easily. 
 
 Large quantities of mercury are used in extracting gold and 
 silver from their ores, for silvering mirrors, and in the process of 
 fire-gHding. Preparations of mercury are employed also as me- 
 dicaments, and for various purposes in the useful arts. The 
 fluidity of the metal makes it valuable in the construction of 
 certain philosophical instruments, of which the thermometer and 
 barometer are familiar examples. 
 
 There are two oxides of mercury — a black dioxide, and the red 
 protoxide ; each of these oxides unites with acids to form a pecu- 
 liar class of salts. 
 
 671. Dioxide of Mermry or Mercurous Oxide (B.gfi) is best 
 
672 BED OXTDB OP MEECaET. 
 
 prepared by decomposing one of its salts, calomel for example 
 (§ 674), by means of caustic soda. Thougb a rather powerful 
 base when in combination, it decomposes readily when in the free 
 state, mere exposure to light or to gentle heat being sufficient to 
 decompose it into metallic mercury and the red oxide. With 
 acids it combines readily, with formation of salts of the dioxide 
 of mercury, or mercurous salts as they are often called. 
 
 672. Protoxide of Mercury or Mercuric Oxide (HgO) may be 
 prepared by heating metallic mercury in the air as above described, 
 or, better, by heating nitrate of mercury at a temperature high 
 enough to drive off oxides of nitrogen, but at the same time too low 
 to decompose the oxide of mercury, or, again, by. precipitating the 
 solution of a salt of protoxide of mercury by means of a caustic 
 alkali. As obtained by the first two methods, it is a compact, 
 granular, almost crystalKne, glistening powder, of bright brick- 
 red color ; but when prepared by the last method it is, when dry, 
 a soft, light-orange-colored powder. Very considerable differ- 
 ences in the chemical deportment of these red and yeUow varieties 
 of the oxide have been noticed, though the differences are hardly 
 so great as are usually found between the isomeric modifications of 
 other substances. The precipitated yellow oxide is, for example; 
 more readily decomposed by heat and by chlorine thau the red 
 oxide. The red oxide, however, is the substance knovm as oxide 
 of mercury in commerce and the laboratory. 
 
 Considered as a source of oxygen, red oxide of mercury is 
 peculiarly interesting, since by means of it oxygen may be derived 
 directly from the air (§ 12) ; but it neither affords the gas 
 cheaply, nor yields an abundant supply. Since red oxide of 
 mercury contains only a single atom of oxygen for each atom of 
 mercury, and since the atomic weight of mercury (200) is com- 
 paratively high, any given weight of the oxide can, of course, con- 
 tain but a small proportion of oxygen : — for 
 
 216 : 16 = ] : 0.074' 
 
 Weight of Weight of Grm. Grrm. 
 
 a molecule an atom 
 
 of HgO. ofO. 
 
 Although it contains so small a proportion of oxygen, compared 
 with the nitrates and chlorates commonly employed for effecting 
 
CALOMEL. 573 
 
 oxidation, yet, from the facility with which it gives up its oxygen, 
 mercuric oxide is still an oxidizing agent of considerable power. 
 If a small portion of it be mixed with a little sulphur, and then 
 heated, the mixture will explode ; so, too, if it be mixed with a 
 small fragment of phosphorus, and struck with a hammer upon 
 an anvil, a similar explosion will ensue ; the violent action de- 
 pends upon rapid oxidation in both cases. 
 
 Most acids unite readily with oxide of mercury to form salts, 
 often spoken of as mercuric salts. Both the oxides of mercury 
 are, like the protoxide of lead (§ 575), remarkable for the facility 
 with which they form basic salts. In general, the compounds of 
 mercury unite with one another readily to form a great variety 
 of double compounds and abnormal basic salts, such as the oxy- 
 chlorides a;HgO,HgCl„ and the chlorosulphide 2H:gS,HgCl,.. The 
 properties of several of these complex substances are iuteresting ; 
 but none of them fairly fall within the scope of this manual. 
 
 673. Bisulphide of Merewry (Hg^S) is a compound nearly as 
 unstable as the dioxide ; but the protosuipMde (HgS) is a per- 
 manent substance of considerable importance in the arts. Arti- 
 ficially prepared for use as a pigment, it is known imder the name 
 of vermilion. It is the most important ore of mercury, as has been 
 already stated (§ 669). 
 
 674. Mercurous Chloride (HgCl), commonly called calomel, is 
 extensively used as a medicament. 
 
 It may be prepared either by heating together a mixture of metallic 
 mercury and corrosive sublimate (§ 675) until the dichloride sub- 
 limes, 
 
 Hg + HgClj = 2HgCl, 
 or by subliming an intimate mixture of ec[ual parts of sulphate of di- 
 oxide of mercury and common salt, 
 
 Hg^SO^ -I- 2NaCl = 2Hg01 + Na^SO^. 
 
 By the way of precipitation it may be made by mixing together solu- 
 tions of common salt and nitrate of dioxide of mercury : — 
 
 Hg^N^O, + SNaCl = 2HgCl -t- Na^N^O,. 
 In place of the corrosive sublimate used in the first method, intimate 
 mixtures of sulphate of protoxide of mercury and common salt, or of 
 common salt and black oxide of manganese or sulphate of sesquioxide 
 of iron may be substituted. 
 
574 MBECTTBIC CHLOHIDB. 
 
 Calomel is a heavy white powder, ■which volatilizes at tempe- 
 ratures helow redness without previous fusion. 
 
 The vapor-density of calomel is, hy calculation, 117'75. 
 
 Weight of one atom, or two unit-volumes, of mercury . 200-00 
 Weight of one atom, or one unit- volume, of chlorine . 35 5 
 
 Weight of two unit-volumes of merourous chloride . . 235-5 
 Weight of one unit-volume of mercurous chloride . . 117-75 
 
 The vapor-density has heen determined by experiment at 
 120-49. By slowly cooling its vapor, prismatic crystals of calo- 
 mel may readily be obtained. Unlike metallic mercury, calomel 
 does not volatilize at ordinary temperatures. It is tasteless, odor- 
 less, and as good as insoluble in water. Alkaline lyes decompose 
 it readily, and it is slightly soluble in many saline solutions. 
 
 675. Mercuric Chloride (HgClj), better known by the name 
 corrosive svMimate, may be prepared by burning mercury in an 
 excess of chlorine gas, by dissolving protoxide of mercury in 
 chlorhydric acid, or by dissolving metallic mercury in aqua regia, 
 and evaporating to dryness. 
 
 In practice, it is commonly prepared by sublimation, by carefully 
 heating an intimate mixture of sulphate of mercury and common 
 salt : — 
 
 IIgS04 -I- 2NaCl = HgCl^ -{■ Na^SO^. 
 
 Another method is, to add concentrated chlorhydric acid to a strong 
 boiling solution of nitrate of dioxide of mercury, as long as a preci- 
 pitate is formed, and to subsequently boil this precipitate with a quan- 
 tity of chlorhydric acid equal to that used in preparing it : — 
 HgN03 4- 2HC1 = HgCl^ -1- H^O + NO,. 
 
 Beautiful crystals of mercm-ic chloride wiU be deposited as the hot 
 solution cools. 
 
 676. Mercuric chloride commonly occurs in commerce, in trans- 
 lucent crystalline masses ; but crystals of it may readily be ob- 
 tained, by careful sublimation, as well as by slowly cooling hot 
 solutions. It melts at about 265°, forming a colorless Uquid 
 which boUs at 293° ; the fumes are acrid, and, Kke the salt itself, 
 exceedingly poisonous. 
 
 The vapor-density of corrosive sublimate is, by calculation 
 135. 
 
MERCURIC IODIDE. 575 
 
 Weight of one atom, or two unit- volumes, of mercury , . 200 
 Weight of two atoms, or two unit- volumes of chlorine , . 70 , 
 
 Weight of two unit-volumea of mercuric chloride . . . . 270 
 Weight of one unit-volume of mercuric chloride .... 136 
 The best experiments assign to the vapor of the salt the den- 
 sity of 141. Mercuric chloride is rather easily soluble in water 
 and alcohol ; with the alkaline chlorides it unites to form salts 
 which are easily soluble in water. These double salts are so 
 numerous and well defined, that they are regarded as chlorine 
 salts comparable with the sulphur salts (§ 340) and the oxygen 
 salts. In this view, protochloride of mercury would be called 
 chloromercuric acid, and its compounds with the alkalies chloro- 
 mercurates. The compound NaCljHgCl^, for example, would be 
 called chloromereurate of sodium, and the compound NaCl,2HgCl2 
 the bichloromercurate. Corresponding double chlorine salts are 
 formed by the union of the chlorides of gold and of platinum with 
 the chlorides of other metals and compound radicals, as wUl ap- 
 pear in the sequel. 
 
 677. Mercuric chloride unites with many organic substances to 
 form compounds insoluble in water and imputrescible. It coa- 
 gulates albumen, for example, and the more perishable portions 
 pf wood ; hence the employment of raw whites of eggs as an 
 antidote in cases of poisoning by corrosive sublimate, and the use 
 of the mercury salt for preserving wood, — a purpose for which it 
 would, no doubt, be largely employed were it not for its high 
 cost. Collections of dried plants, and of other objects of natural 
 history, axe preserved both from decay and from the attacks of 
 insects by brushing over them a solution of the chloride in alcohol. 
 It is worthy of mention that the compound of albumen and chlo- 
 ride of mercury, though insoluble in water, is soluble in an excess 
 of albumen. 
 
 Mercurous and mercuric bromides, iodides, fluorides, and cya- 
 nides axe, in general, analogous to the corresponding chlorides. 
 Mercuric iodide undergoes remarkable changes of color when 
 heated or subjected to friction. 
 
 Exp, 355. — ^Dissolve half a gramme of iodide of potassium in a small 
 quantity of water ; also dissolve 0-4 of a gramme of corrosive sublimate 
 in a little water, and mix the two solutions. Collect upon a filter the 
 
576 NITRAIES OP MBECtTET. 
 
 beautiM red precipitate which is formed, wash it carefully with water 
 and dry it in the air. Place a portion of the dry red powder in a por- 
 celain capsule ; invert over the capsule a small glass funnel, and heat 
 the capsule moderately upon a sand-hath ; the iodide will melt, suhlime, 
 and finally he deposited upon the cold walls of the funnel in yellow 
 crystals. On rubbing these crystals with a glass rod, their color wiU 
 change again to red. Indeed the change of color often occurs of itself 
 as the crystals cool, without friction. The composition of the iodide is 
 neither changed by the sublimation nor by the friction ; the change of 
 color is due to a change of crystalline form — mercuric iodide being di- 
 morphous, and exhibiting a red color in its octahedral form, and a yeUow 
 color when crystallized in rhombic prisms. 
 
 The change of coloration may be shown in another way, by dissol- 
 ving some of the precipitated iodide in alcohol. The alcoholic solution 
 is colorless and appears to contain the yellow modification of the 
 iodide ; on pouring it into water, iodide of mercury is precipitated as a 
 yellow powder, which soon changes to red. 
 
 678. Sulphates of Mercury. — There is a sparingly soluble sul- 
 phate of dioxide of mercury (Hg^SO^), a normal sulphate of the 
 protoxide (HgSO,), and a basic sulphate of the protoxide (of com- 
 position SHgOjSOj). Normal mercuric sulphate may be prepared 
 by dissolving metallic mercury in an excess of boiling concentrated 
 sulphuric acid, and evaporating the solution to dryness. It is the 
 material from which many other compounds of mercury are de- 
 rived. It is decomposed by water ; an insoluble trisulphate is 
 thrown down, while but a small proportion of mercury remains 
 dissolved in the dilute sulphuric acid which is formed. 
 
 679. Nitrates of Mercury are numerous. There are at least 
 four nitrates of the dioxide, and as many of the protoxide namely 
 the normal salts and three basic salts in either case. Both of the 
 normal salts are soluble in water, and are commonly kept in the 
 laboratory as examples of the mercury salts. The nitrate of the 
 dioxide is prepared by digesting an excess of metallic mercury in 
 cold moderately strong nitric acid. The solution should be kept 
 in closed bottles containing a few globules of metallic mercury. 
 The nitrate of the protoxide may be readily obtained- by dissolving 
 red oxide of mercury in an excess of nitric acid. 
 
 680. Amalgams. — Mercury unites with most of the other 
 metals, forming alloys, many of which are pasty, or liquid when 
 the proportion of mercury contained in them is large. These 
 
TIIANITTM. 577 
 
 alloys are commonly called amalgams, in contradistinction to the 
 ordinary solid alloys of the other metals, in which mercury has 
 no place. The liquid amalgams are true solutions of other metals, 
 or of solid amalgams, in the fluid mercury. The so-called silver- 
 ing of mirrors is an amalgam of tin. 
 
 Mercury may be detected in almost any soluble salt of the 
 element by introducing into a solution of the salt a piece of clean 
 copper. 
 
 Bxp. 356. — ^Place a drop of a solution of either of the nitrates or 
 chlorides of mercury upon a clean copper coin and rub the liq[uid over 
 its siu-face. A white coating of metallic mercury will be deposited 
 upon the metal. 
 
 681. Copper and mercury axe classed together partly because 
 of certain resemblances between the two metals, but also because 
 neither of them falls naturally into either of the other groups of 
 elements. They are alike in that they are not readily acted upon 
 by air, excepting at high temperatures, that they do not decom- 
 pose water at any temperature, and that they both form two sa- 
 lifiable oxides, and two chlorides of analogous composition. They 
 are both acted upon in the same way by nitric and by sulphuric 
 acids, the acid being reduced to a lower degree of oxidation, 
 while the metal is dissolved, as has been seen in Exp. 96. As 
 the formulae of their compounds have doubtless already suggested, 
 mercury and copper are univalent, like the alkali-metals, in the 
 mercurous and cuprous compounds, but bivalent in the mercuric 
 and cupric compounds. 
 
 CHAPTEK XXXII. 
 
 T I I A N 1 IT M 1 1 N. 
 
 TrrANiim. 
 
 682. This comparatively rare metal is found in several mine- 
 rals, such as rutile and titaniferous iron, in the condition of titanic 
 acid, TiOj. None of its compounds are employed in the arts, and 
 
 2p 
 
578 TIN. 
 
 the element itself is here mentioned mainly on account of the ana- 
 logies which it hears to tin. Titanic acid is isomorphous with stan- 
 nic acid (§ 685), and resembles it closely in its chemical deport- 
 ment. Sesquioxide of titanium, Ti^Og, corresponds to sesquioxide 
 of tin, Sn^O, (§ 685) ; and in the same waythat the latter may be 
 regarded as a stannate of tin, SnO.SnO^, the titanium compound 
 may be considered a titanate of titanium, TiO,Ti02. 
 
 The bisulphide of titanium, and the bichloride, bibromide, and 
 bifluoride, correspond in like manner to the tin. compounds. 
 
 683. Though by no means widely diflPused in nature, and though 
 ores of it occur in but few localities, tin is one of the metals which 
 have longest been known to man. The fact admits, however, of 
 ready explanation ; for the specific gravity of the ores is high, and 
 the metal is easily reduced from them by simple heating with 
 charcoal. From the manner of the occurrence of many of these 
 ores, in the beds of torrents, it is evident that their great weight 
 would be likely to attract attention, and that their behavior to- 
 wards fire would soon be noticed. The simplest possible metal- 
 lurgical operation, and the one most hkely to suggest itself to 
 savage men, is the heating of a heavy stone in a wood fire. 
 
 The principal ore of tin is the binoxide, called tin-stone. In 
 order to extract the metal from it, the tin-stone is mixed with 
 powdered coal and heated upon the hearth of a reverberatory 
 furnace in a reducing flame. The reduced metal melts readily, 
 and is then run out of the furnace into iron moulds. Tin is a 
 lustrous white metal, soft, malleable and ductile, though not very 
 tenacious. Its ductility varies greatly with the temperature ; at 
 100° the metal may be drawn into thin wire, but at 200° it is very 
 brittle. When a bar of tin is bent, it emits a peculiar crackling 
 sound, and if the bending be repeated, the metal becomes de- 
 cidedly warm. These phenomena appear to depend on the 
 disturbance of interlaced crystals contained in the bar, and upon 
 the friction of these crystals one against the other. Tin always 
 exhibits a great tendency to assume crystalline form in passing 
 from the liquid to the solid condition. Upon this peculiarity is 
 founded a method of ornamenting tinned iron. 
 
TUf. 579 
 
 Exp. 357. — ^Heat a piece of common tinned iron over the gas-lamp 
 until the tin has melted, thrust the plate into cold water in order that 
 the tin may harden quickly, then remove the smooth surfece of the 
 metal by rubbing it first with a bit of paper moistened with dilute 
 aqua regia, and then with paper wet with soda-lye. By this treatment 
 there will soon be laid bare a new surface covered with beautiful crys- 
 talline figures, like frost upon a window-pane. The plate should then 
 be washed thoroughly with water, dried qmckly, and covered with 
 some transparent varnish. 
 
 The same crystalline structure can be brought out, though less con- 
 spicuously, by removing the outside polished surface of almost any 
 piece of tin plate by means of warm dilute aqua regia, without first 
 heating the plate as in this experiment. 
 
 Tin does not tarnish in the air at ordinary temperatures, no 
 matter whether the air he moist or dry; hut when strongly heated 
 it oxidizes rapidly, and even hums with a brUliant white light. 
 The specific gravity of tin is about 7-3 ; its atomic weight is 118- 
 It melts at about 230° — at a lower temperature than any of the 
 other common metals. At very high temperatures it is slightly 
 volatile. 
 
 On account of its brilliant lustre, and its power of resisting 
 atmospheric action, tin is largely employed for coating other 
 metals, — copper, for example, as in ordinary pins, cooking-vessels, 
 and bath-tubs — and iron, as in common sheet-tin, of which the 
 so-called tin ware is mannfectured. 
 
 Exp. 358. — Thoroughly clean the surface of a copper coin, or of a 
 small piece of sheet-copper, by means of dilute sulphuric acid ; place 
 the copper over the gas-lamp, and melt upon it a bit of tin as large as 
 a pea. Rub the melted tin over the copper with a rag. It wiU not 
 adhere to the copper ; for although the la.tter was once carefully cleaned, 
 it afterwards became coated with oxide of copper in such manner that 
 the tin could not come in contact with the metal. 
 
 Repeat the experiment as before ; but when the tin has melted, strew 
 over the copper some finely powdered chloride of ammonium. On now 
 rubbing the tin against the copper, the two metals will adhere firmly. 
 The chlorine of the chloride of ammonium unites with the copper of 
 the oxide of copper to form fusible, volatile chloride of copper, while 
 ammonia and water are set free, as may be perceived by the odor. The 
 excess of tin should be wiped ofi" with a rag, so that a smooth surface 
 may be left upon the coin. 
 
 2p2 
 
580 PEOTOxiDE or xna. 
 
 When in contact with dilute acids, or with alkalies, tin slowly 
 absorbs oxygen from the air and goes into solution. Of the 
 strong acids, nitric acid acts upon it violently, with formation of 
 insoluble hydrated binoxide of tin ; a certain amount of water is 
 decomposed as well as the nitric acid, in this reaction, and some 
 nitrate of ammonium is formed ; the ammonium comes from the 
 union of the nascent hydrogen and nitrogen of the deoxidized water 
 and nitric acid (see § 92). Hot concentrated chlorhydric acid gra- 
 dually dissolves tin, and gives off hydrogen. Boiling concentrated 
 sulphuric acid converts it into sulphate of tin, with evolution of sul- 
 phurous acid ; but dilute sulphuric acid has no action upon it out 
 of contact with the air. "When heated with concentrated soda 
 or potash lye, tin slowly dissolves, with formation of soluble stan- 
 nate of sodium or of potassium, and evolution of hydrogen. 
 
 There are two prominent oxides of tin, a protoxide and a bi- 
 oxide, besides intermediate oxides compounded of these two. 
 The binoxide occurs, moreover, in combination, in different iso- 
 meric modifications. 
 
 684. Protoxide of Tin (SnO) may be obtained as a black 
 powder by heating its hydrate in an atmosphere of carbonic acid 
 or other inert gas. The hydrated protoxide is prepared by adding 
 the solution of an alkaline carbonate to a solution of tin in chlor- 
 hydric acid ; the hydrate is thrown down as an insoluble precipi- 
 tate while carbonic acid escapes : — 
 
 SnCl, + Na,C03 -1- H^O = SnH,0, -|- 2NaCl -|- CO,. 
 The hydrate rapidly absorbs oxygen from the air when moist, 
 but is tolerably permanent when dry. The anhydrous oxide 
 undergoes no change in air at the ordinary temperature ; when 
 touched with a glowing coal, it takes fire and burns vividly, 
 being converted into the binoxide. The hydrate also burns in 
 the same way when lighted. It is remarkable that the anhy- 
 drous oxide is more readily soluble in acids than the hydrate ; 
 but in alkaline lyes only the hydrate is soluble. Most of the 
 salts of protoxide of tin greedily absorb oxygen from the air and 
 from many oxygenated substances. They are much employed as 
 reducing agents. 
 
 Hxp. 359.— To 5 or 6 c. c. of a solution of corrosive sublimate add 
 a few drops of protochloride of tiu, and heat the mixture; a gray 
 
BIIfOXIDE OF TIN. 581 
 
 powder will separate; it is metallic mercury, very finely divided, 
 which has been reduced from the mercuric chloride. The powder 
 boiled with chlorhydric acid agglomerates into visible globules :^ 
 HgClj + SnClj = SnOl, + Hg. 
 
 The protoehloride of tin has abstracted the chlorine from the chlo- 
 ride of mercury. 
 
 685. Binoxide of Tin, or Stannic Add (SnO^). — This oxide 
 occurs in nature as the principal ore of tin, as has been stated in 
 § 683, and may readily be prepared artificially by roasting the 
 metal in a free current of air, or by igniting hydrated binoxide of 
 tin. It is insoluble in water, acids, and alkalies, and in general 
 is aot readily acted upon by chemical agents. When fused with 
 caustic soda, however, it combines with it to form a soluble com- 
 pound. Like the hydrated oxides of phosphorus and antimony, 
 hydrated binoxide of tin (SnH^Oj) is remarkable for the dififerent 
 chemical properties it exhibits when prepared in different ways. 
 As obtained by heating metallic tin with concentrated nitric acid, 
 it is almost absolutely insoluble in some acids, and dissolves only 
 with difficulty in others. The hydrate obtained by precipitation 
 from solutions of bichloride of tin and of an alkaline carbonate, 
 is very readUy soluble in acids. By ignition, the soluble hydrate 
 is converted into insoluble anhydrous oxide of tin. 
 
 The difference in chemical behavior above mentioned is not 
 confined to the hydrates alone, it exists as weU in the compounds 
 formed by the union of these hydrates with other substances, 
 both acids and bases ; hence the names stannic acid, applied to 
 the soluble hydrate, and metastannic acid, applied to the in- 
 soluble modification. The generic terms stannate and meta- 
 stannate applied to the compounds of these two varieties of the 
 oxide are employed precisely as in the case of phosphoric and 
 antimonic acids (§§ 293, 352). Both modifications are soluble 
 in alkaline lyes, but the one representing metastannic acid is iar 
 less readily soluble than the other. 
 
 The stannates of the alkaU-metals, sodium and potassium, 
 crystallize readily from their aqueous solutions ; but the corre- 
 sponding metastannates do not crystallize, they are insoluble in 
 saline solutions, and may be precipitated as gelatinous masses by 
 adding almost any neutral salt of an alkali-metal to their aqueous 
 
582 STTLPHIBES OF TIN. 
 
 solutions. Among the stannates, that of tin (SnO,Sn02=Sn203) 
 is worthy of mention, since it is often described as the sesqui- 
 oxide of tin. Stannate of sodium is somewhat extensively em- 
 ployed in the printing of mousseUnes-de-laine. 
 
 A good method of preparing it is to boil granulated tin, or 
 scraps of tinned iron, in a solution of litharge in an excess of 
 caustic soda : — 
 
 Sn + Na,Pb,03 = Na,Sn03 + 2Pb. 
 
 Or a mixture of caustic soda, nitrate of sodium, and metallic tin 
 may be melted in an iron kettle, a certain portion of chloride of 
 sodium, or of stannate of sodium, from a previous fusion, being 
 added to the mixture in order to mitigate the force of the 
 reaction. 
 
 686. The Suljjhides of Tin (SnS, Sn^Sg, and SnS^) correspond 
 to the oxides. The protosidphide (SnS) is precipitated as a dark- 
 brown powder when sulphydric acid is added to the solution of a 
 salt of protoxide of tin. The bisulphide (SnSj) when prepared in 
 the dry way is a beautiful yellow compound, known as mosaic 
 gold, or bronze powder, and is somewhat employed in decorative 
 painting. 
 
 Exp. 360. — Prepare a quantity of tin amalgam by heating together 
 in a glass flask 12 grms. of granulated tin and 6 grms. of merciu-y. 
 Rub the amalgam in a porcelain mortar together with 7 grms. of 
 sulphur and 6 grms. of chloride of ammonium xmtil the diiFerent in- 
 gredients have been thoroughly incorporated one with the other. 
 Place the mixture in a small, long-necked, glass flask, and slowly 
 heat it to low redness upon a sand-bath. After an hour or two there 
 wiU be found at the bottom of the flask a quantity of bisulphide of 
 tin, in the condition of soft, beautiful, golden-yellow powder, of flaky 
 texture, while in the neck of the flask there will be found a deposit of 
 chloride of ammonium contaminated with sulphur, sulphide of mer- 
 cury, and protochloride of tin. 
 
 Instead of the amalgam and the proportions of the other ingredients 
 as given above, there may be heated in the flask an intimate mixture 
 of 2 grms. of dry protosulphide of tin, half a grm. of sulphur, and 
 1 grm. of chloride of ammonium. 
 
 The part played by the chloride of ammonium in these experiments 
 is not well understood ; it is known only that the presence of this salt 
 promotes the formation of a briUiant golden-colored product, though 
 
PROTOCHLOEIDB OP TIN. 583 
 
 there is no evidence that the chloride either undergoes or produces 
 any chemical change. It is hy no means improbable, however, that 
 by volatilizing at the right moment the chloride of ammonium may 
 so moderate the heat engendered by the combination of the sulphur 
 and the tin that the temperaWe of the mixture is prevented from 
 reaching a point at which the bisulphide would be decomposed. 
 
 The Chlorides of Tin are perhaps more important than any 
 other compounds of the metal. 
 
 687. Protochloride of Tin (SnCy is obtained by dissolving 
 granulated tin in boLLLng concentrated ohlorhydric acid. On 
 evaporating the solution, and allowing it to crystallize, prismatic 
 hydrated needles are obtained of the composition 8nClj+2H20. 
 These crystals are largely used by dyers and calico-printers, 
 under the name of tin-salt. Protochloride of tin, whether in the 
 condition of crystals or in solution, rapidly absorbs oxygen from 
 the air, and is converted into a mixture of bichloride of tin, and 
 an insoluble oxychloride. It must therefore be kept in tight 
 packages. The pure salt is completely soluble in a small quan- 
 tity of water; but when this solution is mixed with a large 
 quantity of water, it decomposes ; a highly acid solution of pro- 
 tochloride of tin in chlorhydric acid remains in solution, while a 
 precipitate of oxychloride of tin (SnO,SnCl2+2H20) subsides. 
 
 Protochloride of tin is a powerful reducing agent, as has been 
 shown in Exp. 359; it combines readily either with oxygen or 
 with chlorine, and is frequently employed to remove these ele- 
 ments from their compounds. By means of it, the oxides or 
 chlorides of arsenic, antimony, gold, silver, or mercury may be 
 reduced to the metallic state ; the salts of sesquioxide of iron, 
 and of protoxide of copper, may be reduced to the degree of 
 protoxide and of dioxide respectively, while acids such as chro- 
 mic and manganic are reduced to the condition of basic oxides. 
 Sulphurous acid is reduced by it in such wise that a precipitate 
 of sulphide of tin is formed, when solutions of protochloride of 
 tin and of sulphurous acid are mixed ; it converts blue indigo to 
 white indigo, and is capable of abstracting oxygen from a host of 
 other substances. . 
 
 At the temperature of 100°, all the water may be expelled 
 from the crystallized salt; but some of the chlorhydric acid is 
 
684 BICHLORIDE OF TIN. 
 
 liable to go off at the same time, so that it is not easy in this 
 way to obtain the anhydrous salt in a state of purity. A better 
 way of obtaining the anhydrous salt is to heat together equal 
 weights of finely divided tin and corrosive sublimate : — 
 
 HgCl^ + Sn = SnCl^ + Hg. 
 The dry chloride of tin remains as a residue, while metallic 
 mercury goes off. The anhydrous salt may itseK be distilled at 
 a full red heat. 
 
 Protochloride of tin unites with many of the metallic chlorides 
 to form double compounds, which may be called chlorostannites. 
 
 688. Bichloride of Tin (SnCl^). — When anhydrous, this com- 
 pound is a fuming, volatile, colorless liquid, of 2-7 specific gravity. 
 It does not solidify at —20°, but boils at 115°- When exposed 
 to the air it gradually absorbs water, and, after a while, hydrated 
 crystals are formed. When mixed mth about one-third its 
 weight of water, it solidifies to a mass of hydrated crystals, 
 much heat being at the same time evolved. These crystals are 
 readily soluble in a small quantity of water ; but when treated 
 with much water they decompose, hydrated binoxide of tin is 
 precipitated, and free chlorhydric acid passes into solution. 
 
 In order to prepare anhydrous bichloride of tin, chlorine gas 
 may be passed over hot chloride of tin, or melted metallic tin ; 
 or an intimate mixture of 1 part of tin filings and 4 or 5 parts 
 of corrosive subHmate may be distilled in a retort. The hydrated 
 bichloride and in general aU solutions of the bichloride are ob- 
 tained, either by dissolving tin in dilute aqua regia, by passing 
 chlorine into solutions of protochloride of tin, or by heating the 
 protochloride with chlorhydric acid to which a little nitric acid 
 has been added. The anhydrous salt may be prepared from the 
 hydrate, by distilling the latter with concentrated sulphuric acid, 
 which retains the water. 
 
 Like the protochloride, bichloride of tin is largely employed in 
 dyeing. It combines also with the alkaline and other chlorides 
 to form salts, known as ohlorostannates. The substance called 
 pink salt, in commerce, employed in the preparation of pink colors 
 upon calicoes, is a chloraetannate of ammonium, 2NH Cl,SnCl . 
 There are, of course, many other salts of tin, but none of them 
 are of sufficient interest to be mentioned here. 
 
MOLTBDENITM. 585 
 
 689. The alloys of tin are important. The composition of 
 bronze, bell-metal, &o. has been already mentioned under copper 
 (§ 659), that of stereotype-metal under antimony (§ 348), and 
 that of tin amalgam under mercury (§ 680). Of the other alloys 
 of tin, those formed by its union with lead are most remarkable. 
 Plumber^ solder consists commonly of equal parts of lead and tin, 
 though some kinds of it contain only one-third their weight of 
 lead, and others only one-third their weight of tin. Pewter is 
 composed of tin, together with a small proportion of lead. 
 
 690. With tin and titanium may be classed the two exceed- 
 ingly rare metals Columbium (niobium) and Tantalum. The 
 principal source of columbium is the rare American mineral 
 columbite. Tantalum is procured from the Scandinavian mineral 
 tantalite. The four metals form binoxides and volatile chlorides 
 containing four atoms of chlorine, and are therefore sometimes 
 quadrivalent. In this respect the tin group differs from all the 
 groups heretofore studied, excepting the group composed of 
 carbon, boron, and silicon. Tin and titanium have a like mode 
 of occurrence in nature. 
 
 CHAPTEE XXXIII. 
 
 MOLTBDEWU M V A N A I) ITJ M T IT N a S T E N. 
 
 MOLTBDENXTM. 
 
 691. This rare element is generally found in nature in com- 
 bination with sulphur, as bisulphide of molybdenum. This bi- 
 sulphide is a mineral closely resembling graphite and galena in 
 appearance. The name molybdenum is derived from a Greek 
 word sometimes applied to galena. Molybdenum is a white 
 metal almost as lustrous as silver, of specific gravity 8-6. Its 
 atomic weight is 96. 
 
 There are three oxides of molybdenum — a protoxide (MoO) 
 and a binoxide (MoOJ, both acting as bases, and a teroxide 
 (M0O3), which is a strong acid known as molybdic acid. Molyb- 
 
586 vANADnnn — tungsten. 
 
 date of ammonium is a salt much, valued by the analyst, since by 
 means of its solution very small quantities of phosphoric acid may 
 be detected ; a double compound of molybdate and phosphate of 
 ammonium is deposited as a yellow crystalline precipitate. 
 
 VANADITTM. 
 
 692. Vanadium is a metal somewhat resembling molybdenum 
 on the one hand, and having certain analogies with chromium 
 upon the other. Though nowhere found in large masses, it 
 appears to be rather widely diffused in nature, traces of it often 
 accompanying the ores of iron, for example. It has three oxides 
 — a protoxide (VO) and a binoxide (VOJ, which form salts by 
 uniting with acids, and a teroxide (VO3), which acts as an acid 
 and forms salts by combining with bases. The atomic weight of 
 vanadium is 137. 
 
 TUNeSTEN. 
 
 693. The element tungsten is far less rare than the other mem- 
 bers of the group now under discussion. It is found in consider- 
 able quantities in combination with oxygen, iron, and manganese, 
 in the mineral wolfram, whence the Latin name of the element 
 wolframium, and the symbol W. The mineral scheelite also con- 
 tains tungsten, in combination with oxygen and calcium. Metallic 
 tungsten may be reduced from its oxides by means of hydrogen 
 gas at a bright-red heat, or by charcoal at a white heat. It is a 
 hard iron-gray metal, of specific gravity 17'6, and very refractory. 
 Its atomic weight is 184. The metal has been employed to a 
 certain extent in the preparation of steel ; a small quantity of it 
 added to steel has been found to greatly increase the hardness 
 of the steel, and to impart to it other valuable properties. 
 
 694. There are two oxides of tungsten : — a binoxide (WO^), 
 which does not unite with acids to form salts, but acts rather as 
 an acid; and a teroxide (WO3) called tungstic acid. Tungstic 
 acid by uniting with bases forms a large number of salts, many 
 of which are of very complex composition. The most important 
 ore of tungsten, wolfram, is a mixture in varying proportions of 
 the tungstates of the protoxides of iron and of manganese. The 
 general formula of the mineral may be written EO, "WO , in which 
 
GOLD. 587 
 
 E stands for either iron or manganese ; but there are nevertheless 
 two special varieties of the mineral, one tending to correspond 
 with the formula 2(reO,W03), 3(MnO,W03), in which the pro- 
 portions of iron to manganese are as 2 to 3, and the other to the 
 formula 4(FeO,"W03) ; MnOjWOj, in which the relation of the iron 
 to the manganese is as 4 to 1. The first variety, richer in man- 
 ganese, is of lower specific gravity than the variety rich in iron. 
 But, since the atomic weights of iron and of manganese are nearly 
 equal, the proportion of tungstic acid is almost absolutely the 
 same in both varieties of the mineral. WoKram is a very heavy 
 mineral, its specific gravity being as high as 7'3. Indeed the 
 name tungsten is derived from Swedish words meaning heavy 
 stone. 
 
 Tuogstate of sodium has been employed to a small extent for the 
 purpose of rendering cotton and linen uninflammable. If a weak 
 solution of the tungstate be added to the starch employed to stiffen 
 light fabrics, the cloth therewith impregnated may be exposed to 
 fire without inflaming ; it will simply be slowly charred. 
 
 The compounds of tungsten are remarkably similar to those of 
 molybdenum. The metal resembles both molybdenum and vana- 
 dium in forming an acid teroside, a binoxide, and a volatile ter- 
 chloride. Like molybdenum and vanadium, it decomposes water 
 at high temperatures. 
 
 CHAPTEE XXXIV. 
 
 GOID AND PLATINTJM:. 
 GOLD. 
 
 695. Though generally found only in small quantities, gold is 
 very widely diffused upon the surface of the globe. Traces of it 
 may be found beneath the sandy beds of most rivers, and it 
 occurs in many of the crystalline rocks and in the soils resulting 
 from their decomposition. Many varieties of iron pyrites, in par- 
 ticular, contain appreciable quantities of gold, and silver is never 
 
688 PEOPEEIIES OF GOZD. 
 
 found in nature altogether free from it. It occurs in the lead 
 and copper of commerce, as well as in the ores from whicB. these 
 metals are derived and in many of the salts obtained from them, 
 and has been detected in various other metals ; it is, in short, 
 almost everywhere. The chief source of the metal as an article 
 of commerce is native gold ; this is sometimes found in a condition 
 of purity, but is usually alloyed with more or less silver. It is 
 collected, either directly by mechanically washing away the 
 lighter substances with which it is associated, or, in the case of 
 poorer ores, the gold is dissolved out chemically by means of 
 quicksilver, and is subsequently recovered from the amalgam by 
 filtration and distillation. 
 
 The separation of gold from the rocks and sands in which it 
 occurs is a process attended with much labor ; hence gold is one 
 of the costliest of metals. The price of a gramme of gold is about 
 sixteen times that of a gramme of silver, and twice as great as 
 that of a gramme of platinum. 
 
 696. Pure gold is remarkable as being the most malleable of 
 the metals, and as being the only metal of a decided yellow color ; 
 also for its softness, which is nearly as great as that of lead. It 
 has, however, much tenacity, and may be drawn into extremely 
 fine wire ; 1 grm. of gold can be made to yield as much as 3 kilo- 
 metres of wire. The metal can be beaten into leaves which are 
 not more than one ten-thousandth of a millimetre thick. Very 
 thin leaves of gold are transparent, transmitting a green polarized 
 light. 
 
 Next to platinum, gold is the heaviest of the ordinary metals ; 
 its specific gravity varies from 19-26 to 19-37, according as it 
 has been more or less compressed. Its atomic weight is 196-7. 
 It melts somewhat less readily than copper or silver, at a tem- 
 perature estimated to lie between 1200° and 1250°. Its power 
 of conducting heat and electricity is greatly inferior to that of 
 silver. It is not volatile to any great extent at the melting tem- 
 perature ; but at higher temperatures, such as it is subjected to 
 in the ordinary processes of melting and refining, the metal wastes 
 considerably ; and at the temperature obtained by the oxyhydro- 
 gen blowpipe the metal goes off as a thick vapor. 
 
 697. In the air, gold undergoes no change at temperatures 
 
KEFUriNe OF SOLD. 589 
 
 lower than its melting-point ; and upon this fact, taken in con- 
 nexion with the beautiful color and lustre of the metal, and its 
 comparative rarity, its principal uses depend. 
 
 On account of this indestructibility, gold was regarded by the 
 earlier chemists as the king of metals ; together with platinum 
 and silver, it is still spoken of as a noble metal. Few chemical 
 agents, excepting melted metals, have any action upon gold. 
 None of the common acids, when taken singly, can dissohe it, 
 though the metal is completely soluble in a mixture of chlor- 
 hydric and nitric acids (§ 104), and is not completely insoluble 
 in nitric acid contaminated with nitrous or hyponitric acid. The 
 elements chlorine and bromine, however, unite with it in the cold ; 
 and when hot it is attacked by phosphorus and arsenic. 
 
 As commonly met with in coins or jewelry, gold is far from 
 being pure ; coin, for example, usually contains at least 10 per 
 cent, of copper. 
 
 In order to prepare pure gold, a piece of coin may be dissolved in 
 aqua regia (Exp. 50), the solution evaporated to dryness upon a water- 
 bath, in order to expel the excess of acid, the residue taken up with 
 water and filtered, to remove any chloride of silver which may be 
 present, and the gold finally precipitated as a brown powder, by adding 
 to the solution some sulphate of protoxide of iron dissolved in water : — 
 SAuClj + CFeSO^ = 2Au + Fe^Cl, + SCFe^Oj.SSOg). 
 
 The powder may then be collected and dried, and, if desirable, melted 
 and cast into solid masses. 
 
 Upon the large scale, fine gold is obtained from its alloys by re- 
 moving the baser metal by means of either sulphuric or nitric acid. 
 
 When an aUoy of gold and silver, or copper is boiled with concen- 
 trated sulphmic acid in iron kettles, the silver and copper dissolve with 
 evolution of sulphurous acid, whUe the gold remains undissolved, and 
 the iron vessel is not acted upon. In order to recover the silver from 
 the solution of mixed sulphates, sheets of copper are placed in this 
 solution, and the silver is precipitated upon them, as has been shown 
 in Exp. 267. 
 
 The solution of sulphate of copper is then evaporated, and the salt 
 obtained in the crystallized condition fit for sale. 
 
 The treatment of the alloy of gold and silver with nitric acid is 
 based upon the fact that silver is soluble, while gold is insoluble, in 
 this acid. But it has been found necessary, in order to obtain a com- 
 plete separation of the two metals, that the proportion of silver to 
 
590 GILDING. 
 
 that of the gold in the alloy should be as much as 2 or 3 to 1 ; other- 
 wise portions of the silver would, after a while, hecome so covered 
 with gold as to be protected from the action of the acid, and the two 
 metals could not be completely separated from one another. In prac- 
 tice, whenever the aUoy to be treated is found to contain more than a 
 quarter of its weight of gold, enough silver is added to reduce it to 
 this proportion ; hence the term guartation, by which this method of 
 parting gold and silver is commonly known. 
 
 Finely divided gold obtained by precipitation, as above indicated, 
 is employed to a considerable extent for gilding porcelain. The sur- 
 face to be gilt is first painted with an adhesive varnish, then covered 
 with a mixture of the gold powder and a fusible enamel, and exposed 
 to intense heat; on being subsequently burnished, the gold takes a 
 high polish. 
 
 There are two series of gold salts, corresponding to the two 
 oxides — a protoxide AuO, and the teroxide AuO^. These oxides 
 are rather acids than bases ; the teroxide in particular unites 
 with many metallic oxides to form compounds known as aurates. 
 The chlorides, bromides, and iodides of gold also readUy combine 
 with, other metallic chlorides to form chloraurates, cliloraurites, 
 and the analogous bromine and iodine compounds. 
 
 698. Terchloride of Gold (AuClj) is the compound of gold most 
 commonly employed in the laboratory. The manner of preparing 
 it has been already indicated in § 697. It serves as a valuable 
 test for tin. 
 
 699. Gilding. — There are several methods of attaching a film 
 of metallic gold to surfaces of the baser metals. 
 
 In the old process of fire gilding, the object to be gilt was first 
 heated to redness, then washed with dilute acid to cleanse its surface, 
 and with a solution of nitrate of mercury in order to amalgamate it 
 slightly ; it was then rubbed with a pasty amalgam composed of two 
 parts of gold and one part of mercury. After a portion of the gold 
 amalgam had thus been attached to the siufaoe of the article to be 
 gilt, the latter was heated to drive off the mercury, and the gold left 
 upon it was polished with a burnishing-tool. 
 
 In the more modem method of electro-gilding, the object to be gilt 
 is attached to the negative pole of a galvanic battery, a bar of gold is 
 fastened to the positive pole of the battery, and both the object to be 
 gut and the bar of gold are placed in a mixed solution of cyanide of 
 gold and cyanide of potassium. Under the action of the current, the 
 solution is decomposed; gold is deposited from it upon the object at 
 
ALLOTS OF GOLD, 591 
 
 the negative pole of the battery, while the other ingredients of the 
 solution go to the positive pole, there to dissolve gold from the bar, 
 and thus make good to the solution the metal it has lost. Compare 
 Exp. 353.) Articles of silver, copper, bronze, brass, or platinum, may 
 thus be gilt directly ; but with iron, steel, or tin, it is necessary first 
 to immerse the article attached to the battery in a solution of cyanide 
 of copper and of potassium, in order to cover it with a film of copper 
 to which the gold may adhere. 
 
 Even without a battery, gold can be deposited upon silver or copper 
 by placing either of these metals in a hot solution of the double cyanide 
 of gold and potassium. Copper trinkets are also sometimes gilt by 
 boiling them in a liquor prepared by mixing a solution of chloride of 
 gold with a solution of an alkaline carbonate. 
 
 In general, the compounds of gold have but few properties which 
 are of chemical interest. What has been said of the permanence of 
 the metal implies, of course, that it is a weak chemical agent, having 
 but little affinity for other substances. 
 
 700. Alloys of Gold. — Gold unites with most of the other 
 metals ; but its most important alloys are those of copper, silver, 
 and mercury. Pure gold is so soft that articles of jewelry made 
 of it would quickly wear out if used ; such articles, as weU as 
 coins and watches, are therefore always made of gold which has 
 been alloyed with copper, in order to increase its hardness. The 
 standard alloy for coin in this country and in France is nine 
 parts by weight of gold to one part of copper ; in England it is 
 eleven parts of gold to one of copper. These alloys, as weU as . 
 the alloys of silver and gold, are more fusible than pure gold, but 
 less ductile. Native gold is an aUoy of gold and silver, the pro- 
 portion of the latter metal varying from 0-2 to 62 per cent. 
 Amalgams of gold play an important part in the metallurgy of 
 gold (§ 695), and in the process of fire gilding above described. 
 
 PLATHfTJlI. 
 
 701. Platinum is a metal which, like gold, has little affinity 
 for the other chemical elements. It is commonly found in the 
 native state, alloyed with gold and with other metals. Like gold, 
 it is obtained by washing away the earth and sand with which it 
 is found mixed. It is a very heavy metal, the specific gravity of 
 cast platinum being 21-15. Its atomic weight is 197-4. The 
 color of platinum is intermediate between the white of silver and 
 
592 PLATINUM. 
 
 the gray of steel ; its lustre is far less brilliant thaii t&at of silver. 
 It is as soft as copper, very maUeaHe and very tenacious ; it may 
 he drawn into "wire so fine that its diameter is only j-jtro °^ ^ 
 millimetre. It is not fusible in ordinary furnaces, but may be 
 fused in the blowpipe-flame (Exps. 26, 203), and is nowadays 
 melted in considerable quantities in lime crucibles by means of a 
 blowpipe-flame obtained from common coal-gas and oxygen. At 
 very high temperatures it may be volatilized. Like wrought iron, 
 platinum admits of being forged and welded at temperatures far 
 below its melting-point. When heated, it expands less than any 
 other metal, and is hence well adapted for the construction of 
 apparatus in which metal and glass must be fused together. It 
 conducts heat and electricity much less readily than gold, silver, 
 or copper, standing in this respect not far from iron. 
 
 702. Platinum does not oxidize in the air at any temperature, 
 nor is it attacked by any of the common acids taken separately ; 
 in aqua regia (§ 104) it dissolves slowly — much less readily than 
 gold. Chlorine-water dissolves it, but neither bromine nor iodine 
 has any action upon it. When heated to redness in the air, in 
 contact with the fixed caustic alkalies or alkaline earths, it is 
 slowly corroded, in consequence of the formation of an oxide 
 which unites with the alkali. Phosphorus and arsenic xmite 
 readily with hot finely divided platinum, forming very fusible 
 compounds ; sulphur also combines with it, though far less readily. 
 At high temperatures, platinum is easily acted upon by silicon 
 (compare § 463). A platinum crucible should consequentiy 
 never be placed in direct contact with a hot mixture of a carbon 
 compound and silicic acid. If the crucible is to be heated in a 
 coal fire, it should first be placed in an earthen crucible lined 
 with some infusible earth, such as magnesia. 
 
 With most of the other metals platinum unites readily, form- 
 ing alloys which in many instances are more fusible than pla- 
 tinum itself ; hence, in using platinum vessels in chemical ex- 
 periments, care must be taken not to touch the platinum while 
 hot with easily fusible metals, or to place in the hot vessels any 
 reducible compound of a metal. Most of the alloys of platinum 
 are not only fusible, but they are also soluble in acids. Platinum 
 which has been alloyed with 10 or 12 times its weight of silver. 
 
CHLORIDES OF PLAXINTJM. 593 
 
 for example, is as completely soluble in nitric acid as the sUver 
 itself. 
 
 Prom its comparative inertness as a chemical agent, taken in 
 connexion with its infusibility, platinum is an extremely useful 
 metal to the chemist. It is employed in the scientific laboratory 
 for crucibles, evaporating-dishes, stills, tubes, spatulse, forceps, 
 wire, blowpipe-tips, and the like ; and, in the manufacture of oil 
 of vitriol, large platinum stiUs, together with cooling-siphons of 
 the same metal, are employed in the process of concentrating the 
 acid. 
 
 703. A remarkable property of platinum, of inducing various 
 gases to combine chemically one with the other, has already been 
 repeatedly aEuded to and illustrated (§§ 224, 240, 387). This 
 power of causing combination is possessed even by clean surfaces 
 of the ordinary solid metal, though to a much greater degree by 
 spongy platinum (Exp. 364), and stiU more by the very finely 
 divided powder known as platinum black (§ 706). 
 
 Platinum forms two series of compounds, corresponding respec- 
 tively to the protoxide PtO and to the binoxide PtO^. Its chlo- 
 rides are well-defined compounds ; but with the oxygen acids it 
 forms comparatively few salts, and none of these are at present 
 of much importance. 
 
 704. ProtocTiloride of Platinum (PtCy is a compound insoluble 
 in water, obtained by carefully heating the bichloride to 230° upon 
 an oil-bath. It dissolves in alkaline lyes, and the solution thus 
 obtained may be used for making platinum black (§ 706). At a 
 red heat chloride of platinum is completely decomposed to metallic 
 platinum and chlorine. With the other metallic chlorides pro- 
 tochloride of platinum unites, to form compounds known as ohlo- 
 roplatinites; the general formula of these compounds is 2MCl,PtCl2. 
 
 705. Bichloride of Platinum (PtClJ is the platinum compound 
 most commonly employed in the laboratory. It is a deliquescent 
 substance, readily soluble in water, alcohol, and ether; the 
 aqueous solution is of a reddish-brown color. When heated to 
 230°, or thereabouts, the salt loses half its chlorine, as has been 
 already stated. The aqueous solution of bichloride of platinum 
 is much used as a test for potassium and ammonium, and for pre- 
 paring certain organic compounds suitable for analysis. 
 
 2q 
 
594 vLA'smsmi sponge. 
 
 -Ei^. 361. — Cut half a gramme, or more, of -wom-out platinum foil 
 or ■wire into small fragments, and boil them with a teaspoonful of aqua 
 regia so long as the metal appears to be acted upon, then decant the 
 liquid into a porcelain dish, add to the fragments of platinum another 
 teaspoonful of aqua regia, and proceed as before, repeating the treat- 
 ments until all the metal has dissolved. By the repeated action 
 of successive small portions of the solvent, platinum and other com- 
 paratively speaking insoluble substances can he dissolved much more 
 readily than if all the liquid necessary for its solution- were added at 
 once. Evaporate the solution to dryness upon a water-hath, taie up 
 the residue with water, and preserve the solution in a bottle provided 
 with a glass stopper. 
 
 -Er^. 362. — Pom' a teaspoonful of a solution of chloride of potassium, 
 or of almost any other salt of potassium, into a test-tube, acidulate 
 the liquid with chlorhydrio acid, and add to it a drop of the solution 
 of bichloride of platinum obtained in the preceding experiment. A 
 yellow, insoluble powder wiU soon be precipitated. It is a double 
 chloride of potassium and platinum, and its formula may be written 
 2KCl,PtCl4. This test serves to distinguish potassium from sodium, 
 and, if need he, to separate potassium from solutions in which it is 
 mixed vrith sodium ; for the double chloride produced with chloride of 
 sodium and bichloride of platinum is easily soluble iu water. 
 
 Ilxp. 363. — Repeat Exp. 362, but substitute chloride of ammonium 
 for the chloride of potassium. A yellow precipitate, similar to that 
 obtained in Exp. 362, will separate immediately, or, if the solutions 
 employed are dilute, after a short time. The composition of this pre- 
 cipitate may be represented by the formula 2NH4Cl,PtCl4. Agaia 
 repeat the experiment, and this time take enough of the platinum 
 solution and of the chloride of ammonium to make half a teaspoonful 
 of the yellow precipitate, taking care that at last there shall be a alight 
 excess of free chloride of ammonium rather than of chloride of plati- 
 num in the supernatant liquid. Allow the precipitate to settle, sepa- 
 rate it fi'om the clear liquid by decautation, and dry it partially at a 
 gentle heat. When the precipitate has acquired the consistence of 
 slightly moistened earth, transfer it to a cup-shaped piece of platiniun 
 foil, and heat it to redness in the gas-flame, as long as fumes of chlo- 
 ride of ammonium continue to escape. AH the chlorine, hydrogen 
 and nitrogen will be driven off, and there wUl remain upon the foU a 
 gray, loosely coherent, sponge-like mass of metallic platinum ; it is 
 called platinum sponge. 
 
 Exp. 364.— Hold the dry platinum sponge of Exp. 363 in a stream 
 of hydrogen or of common illuminating gas issuing from a fine jet. 
 
PLATINUM BLACK. 595 
 
 The metal wUl soon begin to glow, and in a moment will become hot 
 enough to inflame the mixture of air and gas in contact with it. Be- 
 fore friction-matches were employed, this property of spongy platinum, 
 of inflaming hydrogen, was sometimes made use of for striking a light. 
 The mode of action of the platinum in this experiment is obscure ; it 
 has already been alluded to in § 387. 
 
 From platinum sponge, solid articles of platinum may be manufac- 
 tured by compression. If the spongy platinum be first rubbed to pow- 
 der under water, the particles of metal of which it is composed can be 
 readily compacted into solid bars by subjecting the powder to powerful 
 pressure in appropriate moulds. The pressed bar is then heated in- 
 tensely in a coke-fire with strong draught, and forged by striking it 
 with the hammer upon its ends — the process of heating and forging 
 being several times repeated, until the bar has become sufficiently con- 
 densed. The metal may then be wrought into any desired shape by 
 heating and hammering, in the same way as any other malleable metal. 
 This process of working platinum was for a long time the common 
 method, and is still employed to a certain extent. 
 
 706. Platinum Black is a term applied to metallic platinum 
 even more finely divided than the sponge above described. 
 
 By dissolving protochloride of platinum in hot concentrated pot- 
 ash-lye, and pouring into the hot liquor alcohol, by small successive 
 portions, platinum will be thrown down as a black powder looking 
 like soot. The powder should be freed from the supernatant liquor by 
 decantation, and then boiled successively with alcohol, chlorhydrie 
 acid, potash-lye, and water, in order to free it from all impurities. 
 
 A capacious vessel must be chosen for the reaction of the alcohol 
 upon the alkaline solution of chloride of platinum ; for much carbonic 
 acid is generated while the components of the alcohol are reducing 
 the solution of platinum, so that lively effervescence occurs. Platinum 
 black is capable not only of absorbing and storing up many times its 
 own bulk of oxygen gas ; it is also capable of giving away this oxygen 
 to many other substances. If easily oxidizable liquids, such as alcohol 
 or ether, are dropped upon platinum black which has previously been 
 exposed to the air, the liquids will be oxidized and converted into new 
 substances, while the powder becomes red-hot from the heat evolved 
 during the act of oxidation. 
 
 707. Besides forming with the chlorides of potassium and am- 
 monium the insoluble compounds above described, bichloride of 
 platinum unites with many other chlorides, both of ruetals and of 
 organic radicals, to form analogous salts of the general formula 
 
 2q2 
 
696 THE PLATHnjM METALS. 
 
 2MCl,PtCl^, or MCa^.PtCl^. These compounds are commoEly 
 called chloroplatinates ; by means of them the composition and 
 combining weights of many organic compounds have been deter- 
 mined. It is only necessary to ignite a weighed portion of the 
 chloroplatinate, and to weigh the residue of pure platinum which 
 is left after the organic matter has all been driven off, in order 
 to ascertain how much platinum is contained in the compound. 
 This fact having been determined, the quantity of the organic 
 radical, or rather of the chloride of the radical, which was com- 
 bined with the chloride of platinum in the chloroplatinate, may 
 be readily calculated. 
 
 708. With gold and platinum are classed several rare metals 
 which are never found except in association with platinum, and 
 which closely resemble that metal. They are commonly called 
 platinum metals, and the group may be appropriately termed the 
 platinum group. The whole group consists of Rhodium (atomic 
 weight =104), Euthenium (104), Palladium (106-5), Gold (196-7), 
 Platinum (197-4), Iridium (198), and Osmium (199). Palladium 
 is used to impart to brass gas-fixtures a peculiar reddish tint, 
 sometimes called salmon-bronze. Iridium is used for the very 
 hard tips of gold pens. Osmium forms, among other oxides, a 
 volatile compound OsO^, whose vapors are intensely poisonous. 
 The metals of this group are noble metals ; they withstand the 
 action of the atmosphere ; none of them are acted upon by nitric 
 acid, though they dissolve in chlorine and in aqua regia. Their 
 oxides part with all their oxygen when simply heated, leaving 
 the metal behind. 
 
SUtBOIiS AND ATOMIC 'WEIGHTS. 
 
 597 
 
 CHAPTEK XXXV. 
 
 ATOMIC WEISHIS OF THE ELEMENTS CLASSIFICATION. 
 
 709. An alphabetical list of the sixty-five recognized elements, 
 with their symbols and atomic weights, is here given for convenience 
 of reference. The names of those elements which are so rare as 
 to be at present of little importance are printed in italics : — 
 
 Aluminum 
 
 Al 
 
 27-4 
 
 Mercury 
 
 . Hk 
 
 200 
 
 Antimony . 
 
 Sb 
 
 122 
 
 Molyhdmum . Mo 
 
 96 
 
 Arsenic 
 
 As 
 
 75 
 
 Nickel 
 
 . Ni 
 
 58-8 
 
 Barium 
 
 Ba 
 
 137 
 
 Nitrogen 
 
 . N 
 
 14 
 
 Bismuth . 
 
 Bi 
 
 210 
 
 Norium 
 
 . No 
 
 ? 
 
 Boron 
 
 Bo 
 
 11 
 
 Osmium 
 
 . Os 
 
 199 
 
 Bromine 
 
 Br 
 
 80 
 
 Oxygen 
 
 . 
 
 16 
 
 Cadmiimi . 
 
 Cd 
 
 112 
 
 Palladium 
 
 . Pd 
 
 106-5 
 
 Cesium 
 
 Cs 
 
 133 
 
 Phosphorus 
 
 . P 
 
 31 
 
 Calcium 
 
 Ca 
 
 40 
 
 Platinum 
 
 . Pt 
 
 197-4 
 
 Carbon 
 
 C 
 
 12 
 
 Potassium 
 
 . K 
 
 39-1 
 
 Cerium 
 
 Ce 
 
 92 
 
 Rhodium 
 
 . Eh 
 
 104 
 
 Chlorine . 
 
 CI 
 
 355 
 
 Buibidium 
 
 . Eb 
 
 . 85-7 
 
 Chromium . 
 
 Cr 
 
 52-5 
 
 Mtdhenium 
 
 . Ru 
 
 .104 
 
 Cobalt 
 
 Co 
 
 58-8 
 
 Selenium 
 
 . Se 
 
 . 79-5 
 
 Columbium {Nio- 
 
 
 
 ■ Silicon 
 
 . Si 
 
 . 28 
 
 Uum) ' , 
 
 Ni 
 
 94 
 
 Silver 
 
 ■ Ag 
 
 . 108 
 
 Copper 
 Didymium . 
 
 Cu 
 
 03-4 
 
 Sodium 
 
 . Na 
 
 . 23 
 
 D 
 
 95 
 
 Strontium 
 
 . Sr 
 
 . 87-5 
 
 Erbium 
 
 E 
 
 ? 
 
 Sulphur 
 
 . S 
 
 82 
 
 Fluorine 
 
 Fl 
 
 19 
 
 Tantalum, 
 
 . Ta 
 
 . 137-6 
 
 Olucinum . 
 
 Gl 
 
 14 
 
 Tellurium 
 
 . Te 
 
 128 
 
 Gold . 
 
 Au 
 
 196-7 
 
 Terbium 
 
 . Tb 
 
 ? 
 
 Hydrogen . 
 
 H 
 
 1 
 
 Thallium 
 
 . Tl 
 
 !204 
 
 Indium 
 
 In 
 
 35-9 (?) 
 
 Thorium 
 
 . Th 
 
 . 231-5 (?) 
 
 Iodine 
 
 I 
 
 127 ^' 
 
 Tin ., 
 
 . Sn 
 
 .118 
 
 Iridium 
 
 Ir 
 
 198 
 
 Titanium 
 
 . Ti 
 
 . 50 
 
 Iron . 
 
 Fe 
 
 56 
 
 Timgsten 
 
 . W 
 
 184 
 
 Lanthanum 
 
 La 
 
 . 92-8 
 
 Uranium 
 
 . Ur 
 
 120 
 
 Lead . 
 
 Pb 
 
 207 
 
 Vanadium 
 
 . V 
 
 .137 
 
 lAthium 
 
 Li 
 
 . 7 
 
 Yttrium 
 
 . Yt 
 
 . 68 
 
 Magnesium 
 
 Mg 
 
 . 24 
 
 Zinc . 
 
 . Zn 
 
 . 65 
 
 Manganese . 
 
 Mn 
 
 . 55 
 
 Zirconium 
 
 . Zr 
 
 . 90 (?) 
 
598 
 
 ITATirBAL GKOtTPS. 
 
 710. In the following table the elements are arranged in what 
 are believed to be natural groups. Without accepting any one in- 
 fallible criterion of classification, or insisting upon any systematic 
 arrangement of the elements in groups with that strenuousness 
 which is apt to make classification rather a hindrance than a help, 
 the student may provisionally use this subdivision of the elements 
 into groups as a help in remembering facts, as a guide to the 
 prompt recognition of general properties and general laws, and as 
 a suggestive compend of his whole chemical knowledge : — 
 
 Fluorine . 
 
 . 19 
 
 Glucinum 
 
 . 14 
 
 Chlorine . 
 
 . 35-5 
 
 Aluminum 
 
 . 27-5 
 
 Bromine . 
 
 . 80 
 
 Chromium 
 
 . 52-3 
 
 Iodine 
 
 . 127 
 
 Manganese 
 
 . 55 
 
 
 
 Iron . 
 
 . 56 
 
 Oxygen . 
 Sulphur . 
 
 . 16 
 
 Cobalt 
 
 . 58-8 
 
 . 32 
 
 Nickel 
 
 . 58-8 
 
 Selenium 
 
 . 79-5 
 
 Yttrium 
 
 . 68 
 
 Tellurium 
 
 . 128 
 
 Erbium 
 
 p 
 
 
 
 Terbium 
 
 ? 
 
 Nitrogen 
 
 . 14 
 
 Zirconium . 
 
 . 90(?) 
 
 Phosphorus 
 
 . 31 
 
 Norium 
 
 ?^ 
 
 Arsenic . 
 
 . 75 
 
 Cerium 
 
 . 92 
 
 Antimony 
 
 . 122 
 
 Tja,Tithanum 
 
 . 92-8 
 
 Bismuth . 
 
 . 210 
 
 Didymium . 
 
 . 95 
 
 
 
 Uranium 
 
 . 120 
 
 Carbon . 
 
 . 12 
 
 Thorium . 
 
 . 231-5 (?) 
 
 Boron 
 
 . 11 
 
 
 
 Sihcon . 
 
 . 28 
 
 Copper 
 
 . 63-4 
 
 
 
 Mercury 
 
 . 200 
 
 Hydrogen 
 
 1 
 
 
 
 Lithium 
 
 7 
 
 Titanium . 
 
 . 50 
 
 Sodium . 
 
 . 23 
 
 Columbium 
 
 . 94 
 
 Potassium 
 
 . 391 
 
 Tin . 
 
 . 118 
 
 Eubidium 
 
 . 85-7 
 
 Tantalum . 
 
 . 137-6 
 
 Silver . 
 
 . 108 
 
 
 
 Caesium . 
 
 . 133 
 
 Molybdenum 
 
 . 96 
 
 ThaUium 
 
 . 204 
 
 Vanadium . 
 
 . 137 
 
 / 
 
 
 Tungsten . 
 
 . 184 
 
 Calcium . 
 
 . 40 
 
 
 
 Sti'ontium 
 
 . 87-5 
 
 Rhodium . 
 
 . 104 
 
 Barium . 
 
 . 137 
 
 Ruthenium 
 
 . 104 
 
 Lead 
 
 . 207 
 
 Palladium . 
 
 . 106-5 
 
 
 
 Gold . 
 
 . 196-7 
 
 Magnesium 
 
 . 34 
 
 Platinum . 
 
 . 197-4 
 
 Zinc 
 
 . 65 
 
 Iridium 
 
 . 198 
 
 Cadmium 
 
 . 112 
 
 Osmium 
 
 . 199 
 
ATOMIC HBAIS OP THE ELEMENTS. 599 
 
 711. Atomic Heats of the Elements. — The power of teat to 
 cause changes of temperature is not the same for any two sub- 
 stances, but varies with the nature of the substance submitted 
 to its action. Each chemical element is peculiarly affected in 
 this respect by heat. The quantity of heat needed to raise the 
 temperature of a certain weight of water from 0° tol° being called 
 unity, the quantity of heat required to raise the temperature of 
 the same weight of any element by the same amount is the specific 
 heat of that element (§ 31). In the second column of the follow- 
 ing table will be found the specific heats of a number of represen- 
 tative elements, selected from each group of elements except the 
 carbon group, and arranged in the order of their atomic weights. 
 (Compare § 710.) 
 
 Name. Specific Heat. Atomic Weight. Atomic Heat. 
 
 Lithium . . 0-94080 7 6-59 
 
 Aluminum -21430 27-5 5-89 
 
 Sulphur .. -20259 32 6-48 
 
 Iron -11380 66 6-37 
 
 Copper.... -09515 63-4 6-04 
 
 Arsenic .. -08140 75 6-11 
 
 SUver .... -05701 108 6-16 
 
 Cadmium '05669 112 6-35 
 
 Tin -05623 118 6-63 
 
 Iodine -05412 127 6-87 
 
 Tungsten.. -03342 184 6-16 
 
 Gold -03244 196 6-36 
 
 Lead .... -03140 207 6-60 
 
 Bismuth . . -03084 210 6-48 
 
 The preceding table contains only solid substances. It has been 
 found that the specific heat of the same body is commonly greater 
 in the liquid than in the solid state, and always less in the gaseous 
 than in the liquid state. Accordingly in instituting any compa- 
 rison between different bodies, based on their specifi^e beats, it is 
 essential to compare them in the same physical condition, solids 
 with solids, liquids with liquids, gases with gases. The second 
 column of the following table contains the specific heats of the 
 four elements which are gaseous at the ordinary atmospheric 
 temperature and pressure. 
 
600 ATOMIC HEATS OF THE ELEMENTS. 
 
 Name. 
 
 Specific Heat. 
 
 Atomic Weight. 
 
 Atomic Heat. 
 
 Hydrogen . 
 
 . 3-4090 
 
 1 
 
 3-4090 
 
 Nitrogen . 
 
 . 0-2438 ■ 
 
 14 
 
 8-4132 
 
 Oxygen. . . 
 
 •2175 
 
 16. 
 
 3-4800 
 
 Chlorine . 
 
 ■1210 
 
 35-5 
 
 4-2955 
 
 On comparing together the ntimbers in the second and third 
 columns of the preceding tables, it will be noticed that the lo-wer 
 the atomic -vreight of an element is, the higher is its specific heat, 
 and vice versd. In the fourth column of the tables, under the 
 name of atomic heat, will be found the product of the specific heat 
 by the atomic weight of each element. The atomic heats of the 
 elements represent the quantities of heat which are required to 
 cause equal alterations of temperature in atomic proportions of the 
 several elements. But the tables show that these quantities of 
 heat are nearly the same for each and all of the solid elements 
 compared in the first table, and are again approximately equal 
 for the gaseous elements which are grouped in the second table. 
 
 This striking principle is dedueible from the foregoing consi- 
 derations — namely, that while the capacities for heat of the same 
 weights of the various elements are very different, the capacities 
 for heat of the atoms, or atomic proportions, of the elements are 
 nearly identical, provided that the elements compared be in the 
 same physical condition. In other words, those weights of the 
 elements which are assumed to represent the relative weights of 
 their atoms require approximately the same amount of heat to raise 
 them through an equal number of degrees of temperature ; while 
 the amounts of heat required to raise equal weights of the elements 
 through an equal number of degrees are expressed by very diffe- 
 rent numbers (the specific heats). It is essential, however, that 
 the elements compared should be in the same physical condition. 
 
 It is true that the numbers representing the atomic heats show 
 considerable discrepancies ; but when it is remembered that there 
 are unavoidable errors attaching to the determinations both of the 
 specific heats and of the atomic weights, that many of the ele- 
 ments cannot yet be obtained in a condition of purity, and that 
 the two factors of the product (specific heat and atomic weight) 
 vary in the proportion of 1 to 30, it vsdU be seen that the ac- 
 cordance is distinct enough to indicate the existence of a general 
 
ATOMIC HEATS OF COMPOUNDS. 601 
 
 law. The atomic heats of carbon, boron, and silicon, however, do 
 not conform to this law. 
 
 712. Atomic Seats of Compounds. — The same kind of relation 
 between the specific heat and the molecular weight obtains within 
 certain classes of compound bodies of like constitution. Only 
 those compounds which have an analogous atomic constitution can 
 possess approximately the same molecular heat ; and there are 
 many admitted exceptions even to this rule. The following table 
 contains the specific and atomic heats of a number of inorganic 
 compounds, arranged in groups according to their chemical com- 
 position. 
 
 T, , Specific Molecular Atomic 
 
 Formula. ^^^ jfr^^^_ j^^_ 
 
 1. Oxides MO. 
 
 PbO 005089 223 11-35 
 
 HgO -05179 216 11-19 
 
 OuO -14201 79-5 11-19 
 
 ZnO -12480 81 10-11 
 
 2. Mfi,. 
 
 Tefi, -16695 160 26-71 
 
 Cr,03 -17960 163 27-47 
 
 BijOj -06053 468 28-33 
 
 SbjOj -09009 292 26-31 
 
 3. Chxobidbs MCI. 
 
 KaOl 0-21401 68-5 12-62 
 
 KOI -17295 74-5 12-88 
 
 HgGl -06206 236-5 12-26 
 
 CuCl -13827 99 13-69 
 
 4. MOlj. 
 
 MgClj -19460 95 18-49 
 
 ZnOlj -13618 136 18-52 
 
 PbClj -06641 278 18-46 
 
 MnCL, -14255 126 17-96 
 
 SnOl2 -10161 189 19-20 
 
 5. MCI4. 
 
 SnOli -14759 260 38-37 
 
 TiCL, -19146 192 36-76 
 
602 TALTJB OF SPECIFIC HEATS. 
 
 „ , Specific Molecular Atomic 
 
 Fornmla. ■|.J_ ^^.^;^_ ji,^_ 
 
 6. Sulphides MS. 
 
 FeS 0-13570 88 11'94 
 
 NiS -12813 90-7 11-62 
 
 Co8 -12512 90-7 11-36 
 
 SnS -08375 150 12-56 
 
 7. MS3. 
 
 FeS2 -18009 120 15-61 
 
 SnSj -11932 182 21-72 
 
 M0S2 -12334 160 19-73 
 
 8. M2S3. 
 
 Sli),S3 -08403 340 28-57 
 
 Bi^Sj -06002 516 30-97 
 
 9. Oabbonatbs M2OO3. 
 
 K2CO3 0-21623 138 29-84 
 
 NajCO, -27275 106 28-91 
 
 10. MOO3. 
 
 BaOOj -11038 197 21-74 
 
 SrCOj -14483 147-6 21-38 
 
 FeC03 -19345 116 22-44 
 
 11. Sulphates MjSOi. 
 
 K2SO4 0-19010 174 3308 
 
 NajSO^ -23115 142 32-82 
 
 12. MSO4. 
 
 CaSOi -19656 1.36 26-73 
 
 MgSOi -22159 120 26-59. 
 
 PbS04 -08723 303 26-43' 
 
 There are considerable departures from equality in the atomic 
 heats of the bodies of similar constitution grouped in the above 
 table ; but when it is observed that the two factors of the product 
 are very wide apart, the close coincidence in most cases will seem 
 much more noteworthy than the occasional discrepancies. 
 
 713. Value of Specific Heats. — The determination of the spe- 
 cific heat of a substance is a difficult experiment in Physics. It 
 is obvious that, if the laws concerning atomic heat which have 
 been above illustrated were invariable and certain, the physicist 
 
IWO SETS OF ATOMIC WEIGHTS IN USE. 603 
 
 would determine for the chemist the atomic -weights of the ele- 
 ments in experimentally fixing their specific heats; he -would 
 also indicate the true classification of chemical compounds by 
 determining the specific heats of these compounds. To obtain 
 the atomic -weight of any element, it -would sufflce to divide the 
 atomic heat common to aU the elements in the same physical state 
 by the specific heat of that element. To determine the class of com- 
 pounds to which a given compound belonged, it would be suffi- 
 cient to know its atomic heat. A given carbonate, for example, 
 would belong to the class M^COj or to the class MCO3, according 
 as its atomic heat were about 29 or about 22. 
 
 Although the principle of the equality of the atomic heats of 
 the elements and of compounds of like constitution is not esta- 
 blished with that certainty which would give to the experimental 
 determination of the specific heat the conclusive weight just in- 
 dicated, yet this equality certainly affords a very strong pre- 
 sumption in favor of the correctness of the atomic weights of the 
 elements contained in the above tables, and of the molecular 
 formulae on which the classification of compounds in the third 
 table is based. 
 
 714. Two Sets of Atomic Weights in use. — The student -wiU 
 find in many books on chemistry weights, other than those used 
 in this manual, assigned to the majority of the elements, and 
 variously called combining, equivalent, or atomic weights. To 
 all the elements, except those of the chlorine, nitrogen, and 
 alkali groups, and the elements boron and gold, are assigned 
 weights which are respectively the halves of the numbers given 
 in §§ 709, 710. The weight assigned to sulphur, for example, 
 is 16, to lead 103-5, to cadmium 56, to iron 28, to copper 31-7, 
 to tin 59, to oxygen 8, and so forth. If these smaller numbers 
 were accepted as the true atomic weights of the elements to 
 which they are respectively assigned, it is obvious that the rela- 
 tion of equaEty between the atomic heats of all elements in the 
 same physical state, presented in the tables of § 711 , would disap- 
 pear ; furthermore, many of the relations indicated in the table 
 of § 712 would be no longer -visible. The atomic heats of the 
 solid elements would be divisible into two classes, in one of 
 which the atomic heat would be about double what it was in the 
 
604 DisotrssiON or atomic weights. 
 
 other. If the atomic weight of lead were 103-5, the formula of 
 the white chloride of lead (§ 581) would be PbCl, analogous to 
 NaCl, and there would be no clear reason why its atomic heat 
 should not be that of the chlorides of the formula MCI, namely, 
 about 12-5 ; but its atomic heat would be only 9-23. If the 
 atomic weight of iron were 28, that of potassium being 39-1, 
 there would be no assignable reason for the marked difference 
 between the atomic heats of the two carbonates ; the formulae of 
 the carbonates of iron and of potassium would be alike — either 
 both M^CO^ or both MCO,. 
 
 Another consequence of using the smaller atomic weights must 
 not pass unnoticed. If the atomic weight of oxygen is 8 and of 
 sulphur 16, the coincidence of the atomic weight and the unit- 
 volume weight of those eight elements for which this equality 
 has been affirmed (§ 259) ceases to be true ; and the simple rule 
 that the molecule of every compound gas or vapor occupies a 
 volume twice as large as the combining volume of hydrogen, 
 oxygen, chlorine, and so forth, will lose the universality which 
 constitutes its chief value. 
 
 The student will remember that the determination of the least 
 combining proportion by weight of any element which cannot be 
 converted into vapor is not a matter of direct experiment simply 
 (§§ 395, 603). The natural analogies of the element and its 
 compounds, the greater or less simplicity of the formulae which 
 result from one assumption or another, the indications of isomor- 
 phism, and of atomic heat, have aU to be consulted. That the 
 best guides have thus far failed to lead to an unquestionable 
 determination of the real least combining weights (or atomic 
 weights) of the majority of the elements, may be inferred from 
 the diversities of usage on this subject in chemical literature. 
 In order to indicate that they mean the atomic weights which 
 have been given in this manual, many chemists write the sym- 
 bols of those elements for which two different weights are in use 
 with a line drawn through them, thus 0, S, Ee, Pb. This prac- 
 tice is almost essential in periodical publications to which writers 
 of different theoretical views contribute. 
 
 715. In the midst of the doubts and discussions which to-day 
 envelope chemical theories, the student will do well to remember 
 
PACT AKD THEORY. 605 
 
 that all these questions lie without the sphere of fact. They do 
 not affect the actual composition or properties of a single element 
 or compound ; they are questions of iaterpretation, classification, 
 and definition. The existence of atoms is itself an hypothesis, 
 and not a probable one ; all speculations based on this hypothesis, 
 all names which have grown up with it, aU ideas which would 
 be dead without it, should be accepted by the student provision- 
 ally and cautiously, as being matter for belief but not for know- 
 ledge. All dogmatic assertion upon such points is to be regarded 
 with distrust. The great majority of chemists, devoted to the 
 applications of chemistry in mineralogy, metallurgy, dyeing, 
 printing, and the manufacture of chemicals, remain completely 
 indifferent to discussions of chemical theories. Hence the student 
 will find that in technical chemical literature the older notation 
 and the corresponding smaller atomic weights are almost in- 
 variably employed. 
 
 Theories, however, are of great importance to the progress of 
 the science and to the clear ordering of the ground already won. 
 It is, on this account, very much to be wished that the great 
 attention now devoted to the discussion of the best methods of 
 representing symbolically the constitution of chemical substances 
 and the changes to which they are subject, may result in the 
 elaboration of a system good enough to command general ac- 
 ceptance. 
 
APPENDIX. 
 
 CHEMICAL MANIPULATION. 
 
 1. Glass tubing. — ^Two qualities of glass tubing are used in chemical 
 experiments — that which softens readily in the flame of a gas or spirit- 
 lamp, and that which fuses with extreme diflicidty in the flame of the 
 blast-lamp. These two qualities are distinguished by the terms soft 
 and hard glass. Soft glass is to be preferred for all uses except the 
 intense heating, or ignition, of dry substances. Fig. I. represents the 
 most convenient sizes of glass tubing, both hard and soft, and shows 
 also the proper thickness of the glass walls for each size. 
 
 Kg- 1. 
 
 2. Cutting and cracking glass. — Glass tubing and glass rod must 
 generally be cut to the length required for any particular apparatus. 
 A sharp triangular file is used for this purpose. The stick of tubing, 
 or rod, to be cut is laid upon a table, and a deep scratch is made with 
 the file at the place where the fracture is to be made. The stick is 
 than grasped with the two hands, one on each side of the mark, while 
 the thumbs are brought together just at the scratch. By pushing 
 with the thumbs and pulling in the opposite direction with the fingers, 
 the stick is broken squarely at the scratch, just as a stick of candy or 
 dry twig may be broken. The sharp edges of the fracture should in- 
 variably be made smooth, either with a wet file, or by softening the 
 end of the tube or rod in the lamp. (See Appendix, § 3.) Tubes or 
 rods of sizes four to eight inclusive may readily be cut in this maimer; 
 the larger sizes are divided with more difficulty, and it is often neces- 
 
11 CVTima AlTD CKACKIN& GLASS. 
 
 sary to make the file-mark both long and deep. An even fracture is 
 not always to be obtained with large tubes. The lower ends of glass 
 funnels, and those ends of gas delivery-tubes which 
 enter the bottle or flask in which the gas is generated, ^"' 
 
 should be filed ofij or ground ofi' on a grindstone, ob- 
 liquely (Fig. II.), to facilitate the dropping of liquids 
 from such extremities. 
 
 In order to cut glass plates, the glazier's diamond 
 must be resorted to. For the cutting of extremely thin 
 glass tubes and of other glass ware, like fiasks, retorts, and bottles, stiU 
 other means are resorted to, based upon the sudden and unequal ap- 
 plication of heat. The process divides itself into two parts — the pro- 
 ducing of a crack in the required place, and the subsequent guiding of 
 this crack in the desired direction. To produce a crack, a scratch 
 must be made with the file, and to this scratch a pointed bit of red- 
 hot charcoal, or the jet of flame produced by the mouth blowpipe, or 
 a very fine gas-flame, or a red-hot glass rod may be applied. If the 
 heat does not produce a crack, a wet stick or file may be touched upon 
 the hot spot. Upon any part of a glass surface except the edge, it is 
 not possible to control perfectly the direction and extent of this first 
 crack ; at an edge a small crack may be started vrith tolerable certainty 
 by carrying the file-mark entirely over the edge. To guide the crack 
 thus started, a pointed bit of charcoal or slow match may be used. 
 The hot point must be kept on the glass from 1 cm. to 0-5 cm. in 
 advance of the point of the crack. The crack will follow the hot 
 point, and may therefore be carried in any desired direction. By 
 turning and blowing upon the coal or slow match the point may be 
 kept sufficiently hot. ^^Tienever the place of experiment is supplied 
 with common illuminating gas, a very small jet of burning gas may 
 be advantageously substituted for the hot coal or slow match. To 
 obtain such a sharp jet, a piece of hard glass tube. No. 5, 10 cm. long, 
 and drawn to a very fine point (see Appendix, § 3), should be placed 
 in the caoutchouc tube which ordinarily delivers the gas to the gas- 
 lamp, and the gas should be lighted at the fine extremity. The burn- 
 ing jet should have a fitne point, and should not exceed 1-5 cm. in 
 length. By a judicious use of these simple tools, broken tubes, 
 beakers, flasks, retorts, and bottles may often be made to yield very 
 useful articles of apparatus. No sharp edges should be allowed to 
 remain upon glass apparatus. The durability of the apparatus itself 
 and of the corks and caoutchouc stoppers and tubing used with it vriU 
 be much greater, if all sharp edges are removed with the file or' still 
 better, rounded in the lamp. 
 
HEATING GLASS TtTBES. Ill 
 
 3. Bending and closing glass ti/hes. — Tubing of sizes five to eight 
 inclusive can generally be worked in the common gas- or spirit-lamp ; 
 for larger tubes the blast-lamp is necessary (see Appendix, § 6). 
 Glass tubing must not be introduced suddenly into the hottest part of 
 the flame, lest it crack. Neither should a hot tube be taken from the 
 flame and laid at once upon a cold surface. Gradual heating and 
 gradual cooling are alike necessary, and are the more essential the 
 thicker the glass ; very thin glass will sometimes hear the most sudden 
 changes of temperature, but thick glass and glass of uneven thickness 
 absolutely require slow heating and annealing. When the end of a 
 tube is to be heated, as in rounding sharp edges, more care is required, 
 in consequence of the great facility with which cracks start at an edge. 
 A tube should therefore always be brought first into the current of 
 hot air beyond the actual flame of the gas or spirit-lamp, and there 
 thoroughly warmed before it is introduced into the flame itself. If 
 a blast-lamp is employed, the tube may be warmed in the smoky 
 flame, before the blast is turned on, and may subsequently be annealed 
 in the same manner ; the deposited soot will be burnt -ofl^ in the first 
 instance, and in the last may be wiped off when the tube is cold. 
 In heating a tube, whether for bending, drawing, or closing, the tube 
 must be constantly turned between the fingers, and also moved a little 
 to the right and left, in order that it may be xmiformly heated all 
 round, and that the temperature of the neighboring parts may be duly 
 raised. If a tube, or rod, is to be heated at any part but an end, it 
 should be held between the thumb and first two fin|;ers of each hand 
 in such a manner that the hands shall be below the tube or rod, with 
 the palms upward, while the lamp-flame is between the hands. When 
 the end of a tube or rod is to be heated, it is best to begin by warming 
 the tube or rod about 2 cm. from the end, and thence to proceed slowly 
 to the end. 
 
 The best glass will not be blackened or discolored during heating. 
 The blackening occurs in glass which, like ordinary flint glass, con- 
 tains oxide of lead as an ingredient. Glass containing much of this 
 oxide is not well adapted for chemical uses. The blackening may 
 sometimes be removed by putting the glass in the upper or outer part 
 of the flame, where the reducing gases are consumed, and the air has 
 the best access to the glass. The blackening may be altogether avoided 
 by always keeping the glass in the oxidizing part of the flame. 
 
 Glass begins to soften and bend below a visible red heat. The con- 
 dition of the glass is judged of as much by the fingers as the eye ; the 
 hands feel the yielding of the glass, either to bending, pushing, or 
 pulling, better than the eye can see the change of color or form. It 
 
 2e 
 
r 
 
 IV BENDING, DEAWUfG, AND CLOSING GLASS TUBES. 
 
 may be bent as soon as it yields in tbe hands, but can be drawn out 
 only when much hotter than this. Glass tubing, however, should not 
 be bent at too low a temperature ; the curves made at too low a heat 
 are apt to be flattened, of unequal thickness on the convex and concave 
 sides, and brittle. 
 
 In bending tubing to make gas-delivery-tubes and the like, attention 
 should be paid to the following points : 1st, the glass should be equally 
 hot on all sides ; 2nd, it should not be twisted, pulled out, or pushed 
 together during the heating ; 3rd, the bore of the tube at the bend 
 should be kept round, and not altered in size; 4th, if two or more 
 bends be made in the same piece of tubing (Fig. IH., a), they should 
 all be in the same plane, so that the finished tube will lie flat upon the 
 level table. 
 
 When a tube or rod is to be bent or drawn _. —-j. 
 
 close to its extremity, a temporary handle may °' 
 
 be attached to it by softening the end of the ff\\ 
 tube or rod, and pressing against the soft glass 
 a fragment of glass tube, which wiU adhere 
 strongly to the softened end. The handle may 
 subsequently be removed by a slight blow, or by the aid of a file. If a 
 considerable bend is to be made, so that the angle between the arms 
 will be very small or nothing, as in a siphon, for example, the curva- 
 ture cannot be well produced at one place in the tube, but should be 
 made by heating, progressively, several centimetres of the tube, and 
 bending continuotisly from one end of the heated portion to the other 
 (Fig. in., h). Small and thick tube may be bent more sharply than 
 large or thin tube. 
 
 In order to draw a glass tube down to a finer bore, it is simply 
 necessary to thoroughly soften on all sides one or two centimetres 
 leng-th of the tube, and then, taking the glass from the flame, pidl the 
 pai'ts asunder by a cautious movement of the hands. The larger the 
 heated portion of glass, the longer will be the tube thus formed. Its 
 length and fineness also increase with the rapidity of motion of the 
 hands. If it is desirable that the finer tube should have thicker walls 
 in proportion to its bore than the original tube, it is only necessary to 
 keep the heated portion soft for two or three minutes before drawing 
 out the tube, pressing the parts slightly together the while. By this 
 process the glass will be thickened at the hot ring. 
 
 To obtain a tube closed at one end, it is best to take a piece of 
 tubing, open at both ends, and long enough to make two closed tubes. 
 In the middle of the tube a ring of glass, as narrow as possible, must be 
 made thoroughly soft. The hands are then separated a little, to cause 
 
BIOWING BULBS. V 
 
 a contraction in diameter at the hot and soft part. The point of the 
 flame must now be directed, not upon the narrowest part of the tube, 
 but upon what is to be the bottom of the closed tube. This point is 
 indicated by the line a in Fig. IV. By with- -— .j-^ 
 
 drawing the right hand, the narrow part of °' 
 
 the tube is attenuated, and finally melted ofi) 
 leaving both halves of the original tube closed 
 
 at one end, but not of the same form; the 
 
 right-hand half is drawn out into a long point, 
 
 the other is more roundly closed. It is not possible to close hand- 
 somely the two pieces at once. The tube is seldom perfectly finished 
 by the operation ; a superfluous knob of glass generally remains upon 
 the end. If small, it may be got rid of by heating the whole md of 
 the tube, and blowing moderately with the mouth into the open end. 
 The knob, being hotter and therefore softer than any other part, yields 
 to the pressure from within, spreads out and disappears. If the knob 
 is large, it may be cut ofi' with scissors while red-hot, or drawn off by 
 sticking to it a fragment of tube, and then softening the glass above the 
 junction. The same process may be applied to the too pointed end of 
 the right-hand half of the original tube, or to any misshapen resvilt of 
 an unsuccessful attempt to close a tube, or to any bit of tube which is 
 too short to make two closed tubes. When the closed end of a tube 
 is too thin, it may be strengthened by keeping the whole end at a red 
 heat for two or three minutes, turning the tube constantly between 
 the fingers. It may be said in general of all the preceding operations 
 before the lamp, that success depends on keeping the tube to be heated 
 in constant rotation, in order to secure a imiform temperature on all 
 sides of the tube. 
 
 4. Blmoing bulbs and piercing holes in tubing. — If the bulb desired 
 is large in proportion to the size of the tube on which it is to be made, 
 the walls of the tube must be thickened by rotation in the flame before 
 the bulb can be blown. If the bulb is to be blown in the middle of a 
 piece of tubing, this thickening is efiected by gently pressing the ends 
 of the tube together while the glass is red-hot in the place where the 
 bulb is to be ; if the bulb is to be placed at the end of a tube, this end 
 is first closed, and then suitably thickened by pressing the hot glass up 
 with a piece of metal until enough has been accumulated at the end. 
 The thickened portion of glass is then to be heated to a cherry-red, 
 suddenly withdrawn from the flame, and expanded while hot by 
 steadily blowing, or rather pressing air, into the tube with the mouth ; 
 the tube must be constantly turned on its axis, not only while in the 
 flame, but also while the bulb is being blown. If too strong or too 
 
 2k2 
 
sudden a pressure he exerted with the mouth, the bulb will be ex- 
 tremely thin and quite useless. By watching the expanding glass, the 
 proper moment for arresting the pressure may usually be determined. 
 If the bulb obtained be not large enough, it may he reheated and en- 
 larged by blowing into it again, provided that a sufficient thickness of 
 glass remain. 
 
 It is sometimes necessary to make a hole in the side of a tube or 
 other thin glass apparatus. This may be done by directing a pointed 
 flame from the blast-lamp upon the place where the hole is to be, 
 until a small spot is red-hot, and then blowing forcibly into one end 
 of the tube while the other end is closed by the finger ; at the hot spot 
 the glass is blown out into a thin bubble, which hursts or may be easily 
 broken oflF, leaving an aperture in the side of the tube. 
 
 It is hoped that these few directions wiU enable the attentive student 
 to perform, sufficiently well, all the manipulations with 
 glass tubes which ordinary chemical experiments require. 
 Much practice will alone give a perfect mastery of the 
 details of glass-blowing. 
 
 5. Lamps. — The common glass spirit-lamp will be under- 
 stood without description from the figure (Fig. V.). This 
 lamp does not give heat enough for most ignitions; for 
 such purposes a lamp with circular wick, of some one of 
 the numerous forms sold under the name of Berzelius's 
 Argand Spirit Lamp (Fig. VI.), is necessary. These argand lamps 
 are usually mounted on a lamp- 
 stand provided with three brass 
 rings; but the fittings of these 
 lamps are all made slender, in 
 order not to carry oif too much 
 heat. When it is necessary to 
 heat heavy vessels, other supports 
 must be used. 
 
 Whenever gas can be obtained, 
 gas-lamps are greatly to be pre- 
 ferred to the best spirit-lamps. 
 For all common chemical experi- 
 ments, except a few for which ig- 
 nition-tubes must be prepared or 
 in which considerable lengths of 
 tubing must be heated, the gas- 
 lamp known as Bunsen's burner is the best lamp. The cheapest and 
 best construction of this lamp may be learned from the following 
 
description with the accompanying figures. (Fig. VII.) The single 
 casting of brass a b comprises the tuhe 6 through which the gas enters, 
 and the block a from which the gas pjc, yjj_ 
 
 escapes by two or three fine vertical 
 holes passing through the screw d, and 
 issuing from the upper face of d, as 
 shown at e. The length of the tuhe 
 6 is 4'5 cm. and its outside diameter 
 varies from 0"5 cm. at the outer end 
 to 1 cm. at the junction with the 
 block a. The outside diameter of the 
 block a is 1-6 cm., and its outside 
 height without the screws is 1'8 cm. 
 By the screw c, the piece a 5 is at- 
 tached to the iron foot g, which may he 6 cm. in diameter. By the 
 screw rf,the brass tube /is attached to the casting a b. The diameter 
 of the face e, and therefore the internal diameter of the tube/, should 
 be 8 m.m. The length of the tube /is 9 cm. Through the wall of 
 this tube, four holes 5 m.m. in diameter are to be cut at such a height 
 that the bottom of each hole will come 1 m.m. above the face e when 
 the tube is screwed upon a b. These holes are of course opposite each 
 other iu pairs. The finished lamp is also shown in Fig. "VH. To 
 the tube 5 a caoutchouc tube of 5 to 7 m.m. internal diameter is at- 
 tached; this flexible tube shoiild be about 1 m. long, and its other 
 eltremity should be connected with the gas-cock through the inter- 
 vention of a short piece of brass gas-pipe screwed into the cock. 
 In cases where a very small flame is required, as, for example, in eva- 
 porating small quantities of liqxiid, a piece of wii-e gauze somewhat 
 larger than the opening of the tube /should be laid across the top of 
 the tuhe, and its proj ecting edges pressed down tightly against the sides 
 of the tube before the lamp is lighted. In default of this precaution 
 the flame of a Bunsen's burner, when small and exposed to currents of 
 air, is liable to pass down the tube and ignite the -p^„ VIII 
 gas at d. 
 
 A lamp to give a powerful flame 8 or 10 cm. long, 
 suitable for heating tubes, may be very simply con- 
 structed by boring two holes, entering the side and 
 issuing at the upper face, through a block of compact 
 hard wood, 10 cm. by 6'5 cm. by 5'6 cm., and fit- 
 ting short pieces of brass tubing into the holes so 
 formed. To the tubes at the side are attached the 
 caoutchouc tubes which deliver the gas, and from the tubes at the top 
 
BLAST-IAMPS AND BLOWEES. 
 
 the gas issues imder a sheet-iron funnel closed at the top with wire* 
 gauze. Above this gauze^ the mixture of gas and air is to be lighted. 
 The iron funnel will be readily understood &om the accompanying figure, 
 and the following dimensions : — Length of the wire gau^e 10 cm. ; 
 width of the gauze 5 cm. ; width at a 6 9 cm. ; height of the Hne a h 
 from the table 8-5 cm. ; whole height of the funnel 21 cm. A par- 
 tition parallel to a J divides the funnel into two equal parts from the 
 gauze to the level of a b. 
 
 6. SlaU-lamps and Blowers. — For drawing, bending, and closing large 
 glass tubes, a blast-lamp is necessary. The best form is that sold under 
 the name of Bunsen's Gas Blowpipe. Its construction and the method 
 of using it may be learned from Fig. IX. ; a 6 is the pipe through 
 
 Fig. X. 
 
 Fig. IX. 
 
 Fig. XI. 
 
 which the gas enters, c is the tube for the blast of au-; the relation of 
 the air- tube to the external gas-tube is shown at d; there is au outer 
 sliding tube by which the foim and volume of the flame can be 
 regulated. 
 
 If gas is not to be had, a lamp burning oil or naphtha must be em- 
 ployed. Fig. X. represents a common tin glassblower's lamp, suitable 
 for burning oil. A large wick is essential, whether oU or naphtha be 
 the combustible. 
 
 For every blast-lamp a blowing-machine of some sort is necessary. 
 To supply a constant blast it is essential that the beUows be of that 
 construction caUed double. Figs. XI. and Xn. represent two fonns 
 
BLOWEES. 
 
 IX 
 
 of blowpipe-table ; their height is that 'of an ordinary table, from 
 which dimension the other proportions may be inferred. A small 
 double-acting bellows is now made for the use of dentists, which is 
 available at any table by the help of a caoutchouc tube to conduct the 
 blast to the jet. These bellows are too small to give a steady flame 
 of large size, but will nevertheless answer for most of the glass- 
 blowing necessary in the execution of the experiments described in 
 this manual. 
 
 Where an abundant supply of water is at command, the following 
 blowing apparatus is very convenient. A tin pipe, a b (Fig. XIII.), 
 
 Fig. xn. 
 
 about one metre long and about IS m.m. in diameter, has two smaller 
 pipes, 12 to 16 cm. long, soldered into it; these small pipes are 8 m.m. 
 in diameter ; one, c d, is inserted at right angles 12 cm. from the end, 
 the other, ef, 2-5 cm. lower, at an angle of 45°. The lower end of 
 the tube passes through the cork of a wide-mouthed five-litre bottle, 
 extending rather more than halfway down. Two glass tubes also 
 pass through the cork of the bottle — a short small tube ff, No. 4, which 
 should reach some 16 cm. above the cork, but should not project into 
 
X CAOtTTCHOTTC. 
 
 the bottle, and a larger tube h, No. 2, extending to the bottom of the 
 bottle. The outer end of the tube h bends over and is connected by 
 caoutchouc tubing -with a straight tube of equal diameter. This last 
 arrangement forms the siphon. To the tube g a caoutchouc tube, g z, 
 is attached to convey the blast to any desired point. To produce a 
 blast, the water-cock is connected with the tube c d hj means of a 
 caoutchouc tube. When the water is turned on, the caoutchouc tube 
 g i is closed for a moment with the thumb and finger. This starts the 
 water through the siphon, and immediately a continuous and powerful 
 blast of air rushes out through the tube g i, and may be carried directly 
 to the blowpipe. The siphon must be capable of carrying off a larger 
 stream of water than that which is allowed to enter, so that there shall 
 never be more than 3 or 4 cm. of water in the bottle. By regulating 
 the water-cock, the proper supply of water may be determined. 
 
 The same apparatus may be used as an aspirator. When the instru- 
 ment is to be used to draw air through any apparatus, the tube g i is 
 closed by inserting a glass rod ; the upper end of the tube a 6 is closed 
 with a cork, and the tube ef is connected with the apparatus through 
 which tbe current of air is to be drawn. The force of the current 
 of air ia to a certain degree affected by the size of the tube ab; to 
 diminish the effective calibre of this tube, in case a gentle current of 
 air is required, a glass rod as long as the tube may be passed down 
 the tube through a cork inserted at a. The same apparatus may thus 
 be made to produce a gentle or a powerful current of air. 
 
 7. Caoutchouc. — ^Vulcanized caoutchouc is a most useful substance 
 in the laboratory, on accoimt of its elasticity and because it resists so 
 well most of the corrosive substances with which the chemist deals. 
 It is used in three forms : — (1) in tubing of various diameters com- 
 parable with the sizes of glass tubing; (2) in stoppers of various sizes 
 to replace corks ; (3) in sheets. Caoutchouc tubing may be used to 
 conduct all gases and liquids which do not corrode its substance, pro- 
 vided that the pressure under which the gas or liquid flows be not 
 greater or its temperature higher than the texture of the tubing can 
 endure. The flexibility of the tubing is a very obvious advantage in a 
 great variety of cases. Short pieces of such tubing, a few centimetres 
 in length, are much used, under the name of connectors, to make 
 flexible joints in apparatus of which glass tubing forms part; flexible 
 joints add greatly to the durability of such apparatus, because long 
 glass tubes bent at several angles and connected with heavy objects 
 like globes, bottles, or flasks fuU of liquid, ai-e almost certain to break 
 even with the most careful usage; gas-delivery-tubes, and all con- 
 siderable lengths of glass tubing, should invariably be divided at one or 
 
CORKS. XI 
 
 more places, and the pieces joined again witli caoutcliouc connectors. 
 The ends of glass tubing to he thus connected should be squarely cut, 
 and then rounded in the lamp, in order that no sharp edges may cut 
 the caoutchouc ; the internal diameter of the caoutchouc tube must be a 
 little smaller than the external diameter of the glass tubes ; the slipping 
 on of the connector is facilitated by wetting the glass. In some cases 
 of delicate quantitative manipulations, in which the tightest possible 
 joints must be secured, the caoutchouc connector is boimd on to the 
 glass tube with a silk or smooth linen string ; the string is passed as 
 tightly as possible twice round the connector and tied with a square 
 knot; the string should be moistened, in order to prevent it from 
 slipping while the knot is tying. 
 
 Caoutchouc stoppers of good quality are much more durable than 
 corks, and are in every respect to be preferred. The German stoppers 
 are of excellent shape and quality ; the American, being chiefly in- 
 tended for wine-bottles, are apt to be too conical. Caoutchouc stoppers 
 can be bored, like corks (see the next section), by means of suitable 
 cutters, and glass tubes can be fitted into the holes thus made with a 
 tightness unattainable with corks. German stoppers may be bought 
 abeady provided with one, two, and three holes. It is not well to lay 
 in a -large stock of caoutchouc stoppers; for, though they last a long 
 time when in constant use, they not infrequently deteriorate when 
 kept in store, becoming hard and somewhat brittle with age. These 
 stoppers must not be confounded with the very inferior caps which 
 were in use a few years ago. 
 
 Pieces of thin sheet caoutchoTic are very conveniently used for 
 making tight joints between large tubes of two different sizes, or be- 
 tween the neck of a flask, or bottle, and a large tube which enters it, 
 or between the neck of a retort and the receiver into which it enters. 
 A sufficiently broad and long piece of sheet caoutchouc is considerably 
 stretched, wrapped tightly over the glass parts adjoining the aperture 
 to be closed, and secured in place by a string wound closely about it 
 and tied with a square knot. 
 
 8. Corks. — ^It is often very difficult to obtain sound, elastic corks of 
 fine grain and of size suitable for large flasks and wide-mouthed bottles- 
 On this account, bottles with mouths not too large to be closed with a 
 cork cut across the grain should be chosen for chemical uses, in pre- 
 ference to bottles which require large corks or bungs cut with the 
 grain, and therefore offering continuous channels for the passage of 
 gases, or even liquids. The kiads sold as champagne-corks and as 
 satin corks for phials are suitable for chemical use. The best corks 
 generally need to be softened before using; this softening may be 
 
PTTTIUfG TUBES THEOTJGH CORKS. 
 
 effected by rolling the cork under a board upon the table, or under the 
 foot upon the clean floor, or by gently squeezing it on all sides with 
 the well-known tool expressly adapted for this purpose, and thence 
 called a cork-squeezer. Steaming also softens the hardest corks. 
 
 Corks must often be cut with cleanness and precision ; a sharp, thin 
 knife, such as shoemakers use, is desirable for this purpose. When a 
 cork has been pared down to reduce its diameter, a flat file may be 
 employed in finishing ; the file must be fine enough to leave a smooth 
 surface upon the cork; in filing a cork, a cylindrical, not a conical 
 form should be aimed at. 
 
 In boring holes through corks to receive glass tubes, a hollow 
 cylinder of sheet brass sharpened at one end is a very convenient tool. 
 Fig. XIV. represents a set of such little cylinders 
 of graduated sizes, slipping one within the other 
 into a very compact form ; a stout wire, of the 
 same length as the cylinders, accompanies the 
 set, and serves a double purpose. Passed trans- 
 versely through two holes in the cap which ter- 
 minates each cylinder, it gives the hand a better 
 grasp of the tool while penetrating the cork ; and 
 when the hole is made, the wire thrust through 
 an opening in the top of the cap expels the little 
 cylinder of cork which else would remain in the 
 cutting cylinder of brass. That cutter whose 
 diameter is next below that of the glass tube to 
 be inserted in the cork is always to be selected ; 
 and if the hole it makes is too small, a round file 
 must be used to enlarge the aperture ; the roimd 
 fide, also, often comes into play to smooth the rough sides of a hole made 
 by a dull cork-borer. Cutters which have been dulled by use may be 
 sharpened by filing or grinding down their outer bevelled edges and 
 then paring off any protuberance or roughness which may remain 
 upon the iaside of the edge with a sharp penknife. A pair of small 
 callipers is a very convenient, though by no means essential tool in 
 determining which size of cutter to employ. A flask which presents 
 shai-p or rough edges at the mouth can seldom be tightly corked, for 
 the cork cannot be introduced into the neck without being cut or 
 roughened; such sharp edges must be rounded in the lamp. In 
 thrusting glass tubes through bored corks, the foUowing directions are 
 to be observed :— (1) The end of the tube must not present a shai-p 
 edge capable of cutting the cork. (2) The tube should be grasped 
 very close to the cork, in order to escape cutting the hand which holds 
 
STTPPOETS FOE TESSELS. XUl 
 
 the cork, should the tube break ; by observing; this precaution the 
 chief cause of breakage, viz. irregular lateral pressure, will be at the 
 same time avoided. (3) A funnel-tube must never be held by the 
 funnel in driving it through a cork, nor a bent tube grasped at the 
 bend, imless the bend comes immediately above the cork, (4) If the 
 tube goes very hard through the cork, the application of a little soap 
 and water wiU facilitate its passage ; but if soap ia used the tube can 
 seldom be withdrawn from the cork after the latter has become dry. 
 (5) The tube must not be pushed straight into the cork, but screwed 
 in, as it were, with a slow rotary as well as onward motion. Joints 
 made with corks should always be tested before the apparatus is used, 
 by blowing into the apparatus and at the same time stopping up all 
 legitimate outlets. Any leakage is revealed by the disappearance of 
 the pressure created. To the same end, air may be sucked out of an 
 apparatus and its tightness proved by the permanence of the partial 
 vacuum. To attempt to use a leaky cork is generally to waste time 
 and labor and to insure the failure of the experiment. When, how- 
 ever, a leak is only discovered during the actual progress of the expe- 
 riment, it is sometimes possible to save the experiment by using a 
 lute ; for this purpose wax applied with a warm knife, or a paste made 
 of rye-meal and water may be used; common sealing-wax also is 
 sometimes a useful makeshift. 
 
 9. Iron Stand, Sand-bath, and Wire Oauze. — To support vessels over 
 the gas-lamp, an iron stand is used consisting of a stout vertical rod 
 fastened into a heavy cast-iron foot, and three iron rings of graduated 
 sizes secured to the vertical rod with binding-screws ; all the rings may 
 be slipped off the rod, or any ring may be adjusted at any convenient 
 elevation. The general arrangement is not unlike that of the stand 
 which makes part of the Berzelius lamp (Fig. VI.), although simpler 
 and cheaper. As a general rule, it is not best to apply the direct 
 flame of the lamp to glass and porcelain vessels; hence a piece of 
 wire gauze is stretched loosely over the largest ring, and bent down- 
 wards a little for the reception of round -bottomed vessels ; on this 
 gauze, flasks, retorts, and porcelain dishes are usually supported. In 
 a few cases, in which a very gradual and equable heat is required, the 
 wire-gauze is replaced by a small shallow pan, beaten out of sheet- 
 iron, and filled with dry sand. This arrangement is called a sand-bath. 
 With the aid of annealed iron wire, the iron stand may be made avail- 
 able for supporting tubes over the lamp. Crucibles, or dishes, too small 
 for the smallest ring belonging to the stand, are conveniently supported 
 on an equilateral triangle made of three pieces of soft iron wire twisted 
 together at the apices ; this triangle is laid on one of the rings of the 
 
XIV PNET7MAIIC lEOITGrH. 
 
 stand. An iron tripod (that is, a stout ring supported on three 
 legs) may often be used instead of the stand above described ; but 
 it is not so generally useftd, because of the difficulty of adjustmg 
 it at various heights; with a sufficiency of wooden blocks wherewith 
 to raise the lamp or the tripod as occasion may require, it may be 
 made available. 
 
 10. Pneumatic Trouffh.—The pneumatic trough is a contrivance 
 which enables us to coUect and confine gases in suitable vessels, and 
 to decant them from one vessel to another. Its efficiency depends on 
 the pressure of the atmosphere, which, as we know, is capable of sup- 
 porting a column of water 10-33 metres long or a column of mercury 
 76 cm. long (see § 7), provided that the liquid column be so arranged 
 that the atmospheric pressure shall be fully felt upon the foot of the 
 column, but not at all upon its head. If a tube, closed at one end 
 and open at the other, and of any length less than 10-33 m., be com- 
 pletely filled with water, and then inverted so that its open end shall 
 dip beneath some water held in a basin or saucer, the tube will remain 
 full of water when the thumb or cork, which closed the open end while 
 the immersion was efiected, is withdrawn. What is true of a tube is 
 equally true of a bell, or other vessel closed at one end, of any diameter 
 or shape, provided its height be not greater than 10-33 m. ; and the 
 principle which applies to water is equally applicable to mercury, 
 except that the height of the mercury column which the average 
 atmospheric pressure can hold up is only 76 cm., because mercury is 
 13-596 times as heavy as water. If a few bubbles of any gas insoluble 
 in water should be delivered beneath the open end of a tube, or bell, 
 thus standing f uU of water in apparent defiance of gravitation, the gas 
 would rise to the top of the tube, by virtue of being lighter than the 
 water, and the exact volume of water displaced by the gas, small or 
 large, wotdd drop into the baSin or saucer beneath. If the gas were 
 thus delivered continuously beneath the tube or bell, we should finally 
 get the tube or bell full of gas, without admixture, of air, and sealed 
 at the bottom by the water in the basin or saucer. If mercury were 
 the liquid, the operation would be precisely the same, except as 
 regards the height of the tube or bell. Even this difierence of possible 
 height is not noticeable in practice, because beUs and bottles more 
 than 50 cm. high are very seldom used with either liquid. On accotmt 
 of its costliness, mercury is rarely used, unless the gas to be' collected, 
 or experimented upon, be soluble in water. A trough for mercury is 
 made as small as possible for the same reason. It is obvious that the 
 object of a pneumatic trough may be accomplished under a great 
 variety of forms. Any bucket or tub with a hanging shelf in it may 
 
PNETTMAHC TEOtreH. XV 
 
 be made to serve. It -will be sufficient to describe two convenient 
 forms of the apparatus. 
 
 A cbeap pnemnatic trough is represented in Fig. XV. Its materials 
 are durable and its capacity sufficient. jrjg, XV. 
 
 It consists of two pieces, 1st, a stone- 
 ware pan, about SO cm. in diameter on 
 the bottom, with sides sloping slightly out- 
 wards and rising to the height of about 10 
 cm.; 2nd, a deep flower-pot saucer about 
 15 cm. in diameter, with one hole bored 
 through the middle of the bottom, and a 
 second arched hole nipped out of its rim ; 
 this saucer is inverted in the pan. If this 
 second piece be made expressly for this purpose, it should be made 
 about 5 cm. high, and its interior should be rounded to the hole in the 
 centre, while the outside is left flat like the flower-pot saucer. For 
 the saucer may be conveniently substituted two slabs or blocks of any 
 stone, like soapstone, sandstone, or marble, made of even thickness and 
 laid side by side in the water-pan with an interval between them which 
 permits the gas-delivery-tube to come beneath the mouth of an inverted 
 bottle or cylinder supported on the two blocks over the intervening 
 crack. To use this apparatus, the pan is filled with water to a level 
 about 2 cm. above the top of the inverted saucer ; the bottle, cylinder, 
 or bell which is to receive the gas is completely filled with water from 
 a pitcher or water-cock, then closed with the hand of the operator or 
 with a flat piece of glass or wood, inverted into the pan, and placed 
 on the saucer over the hole in its centre ; the end of the gas-delivery- 
 tube is thrust through the side hole in the saucer ; and the gas, rising 
 through the centre hole, bubbles up into the bottle or cylinder placed 
 to receive it. While one bottle is filling with gas, another is made 
 ready to replace it ; and when the first is full, it is pushed oflf the centre 
 hole of the saucer, and the second bottle is brought over the hole. A 
 bottle full of gas may be removed from the trough by slipping beneath 
 the mouth of the bottle a shallow plate or dish, and then lifting plate 
 and bottle out of the pan together in such a manner that water enough 
 to seal the mouth of the bottle shall remain in the plate. The gas in 
 one bottle maybe decanted upwards into another, by flUing the second 
 bottle with water, and then carefully inclining the bottle containing the 
 gas so as to bring its mouth under the mouth of the bottle which is 
 fall of water, keeping the mouths of both bottles all the time beneath 
 the surface of the water in the pan. If the gas which has been col- 
 lected is heavier than air, a bottle of it may be withdrawn from the 
 
XVI 
 
 COLLECTING GASES. 
 
 water-pan and got at for use, by simply slipping a flat piece of glaas or 
 wood beneath its moutli so as to close it rather tightly, and then 
 standing the bottle, mouth upward, upon the table. If the cover be 
 then removed from the bottle, the gas will not flow out, though it will 
 slowly difiiise into the air. As the water with which the bottles or 
 cylinders are filled falls into the pan when displaced by gas, it is possible 
 that the pan may become inconveniently full if many large bottles are 
 used ; this difiiculty must be remedied by dipping water out of the 
 pan, and so restoring the true level. 
 
 Where considerable quantities of gas are frequently to be handled, 
 and large vessels are therefore necessary, a large apparatus, shown in 
 Fig. XVI., is much more conve- pjg XVI. 
 
 nient than the small pan, which 
 suffices for all common experi- 
 ments. The form of this larger 
 pneumatic trough and the mode 
 of using it will readily be under- 
 stood from the fig-ure ; the depth 
 and width of the tank or well 
 must be determined by the size 
 of the beUs and cylinders which 
 are to be sunk in it, and the length and breadth of the shallow part or 
 shelf by the number of bells or jars of gas which are likely to be in 
 use at any one time. The deep groove in the shelf permits a glass or 
 caoutchouc tube to pass without compression under a bell whose rim 
 projects over the groove. Such a trough is best made of zinc or lead. 
 It is very convenient to have it sunk in a table, and permanently pro- 
 vided with a water-cock and drain-pipe. A chief merit of this instru- 
 ment is that the glass vessels used can be filled with water by sinking 
 them in the well much more conveniently than from a pitcher or 
 water-cock. 
 
 A pneumatic trough for mercury may be made either of wood, iron, 
 or stone. For all common uses, it is very well cut out of a solid block 
 of compact hard wood, which will not split. Small cylinders or bells 
 only can be used, and the well of the trough should be scooped out 
 but a little larger than the bell or cylinder selected, with its principal 
 dimension horizontal, and its bottom curved to fit the cylindrical bell 
 which is to be laid in it ; the shelf, too, should have but a small area, 
 siifficient only for four or five bells of 3 or 4 cm. diameter. 
 
 In using a pneumatic trough, of any construction or dimensions, the 
 student should be on his guard against two difficulties of possible occur- 
 rence — against the sucking hack of the liquid in the trough into the 
 
STTCKDfG BACK AUD LEASAGB. XVU 
 
 gas-generating apparatus, and against the leakage sometimes induced 
 by the pressure created by thrusting the gas-delivery-tuhe deep under 
 water or mercury. The first of these difficulties is the most serious. 
 When the flow of gas from a heated flask or tube is suddenly arrested, 
 in consequence of some reduction of temperature, or from any other 
 cause, it often happens that the volume of gas in the generating appa- 
 ratus contracts, and the cold water or mercury from the trough rises 
 in the deliverj'-tube to fill the void ; if the contraction is so considerable 
 as to suffer the cold liquid to penetrate into the hot flask or tube, an 
 explosion almost inevitably ensues, which fractures the apparatus, if it 
 does no worse damage. In collecting over water a gas somewhat solu- 
 ble in that liquid, this danger is especially imminent. The occurrence 
 of si)f h accidents may be efiectually guarded against by paying atten- 
 tion to the following directions : — (1) Whenever it is proposed to stop 
 an evolution of gas which has been going on from a hot flask or tube, 
 withdraw the delivery-tube from the water hefore extinguishing the 
 lamp, and shake ofi' from the bent end of the tube the drops of water 
 which are apt to adhere to it ; the lamp may then be safely put out, 
 for air can enter the apparatus through the open tube. (2) When the 
 flow of gas from a hot apparatus is observed to slacken, watch closely the 
 escape of the gas from the delivery-tube, and as soon as any tendency 
 to reflux of water is detected, lift the delivery- tube quickly out of the 
 water, or, better, slip ofi" the caoutchouc connector, which should always 
 be found between the flask and the water-pan on every such piece of 
 apparatus ; if there be no connector, the cork must be loosened in the 
 neck of the flask. Air will thus be admitted to the hot flask or tube. 
 
 These precautions apply more particularly to the cases where gas is 
 evolved from dry materials, as in maJring oxygen or nitrous oxide ; 
 when a liquid is contained in the generating flask, a safety-tube is a 
 sure protection against the danger of sucking back. The atmospheric 
 pressure can force air into a flask, in which a partial vacuum has been 
 created, through the safety-tube, by lifting and displacing a column of 
 the liquid whose height is the length of that portion of the safety-tube 
 which dips beneath the liquid. Unless the liquid in the flask be extra- 
 ordinarily dense, the force required to do this will be very much less 
 than that required to lift a column of water whose height is determined 
 by the elevation of the highest point of the delivery-tube above the 
 level of the water in the pan. 
 
 When the gas coming from the generating flask has to force out and 
 keep out of the delivery-tube a column of water measmed from the 
 lowest point of the tube to the surface of the water in the pan, a pres- 
 sure determined by the height of this column is established upon the 
 
xvm 
 
 GAS-HOLDBES. 
 
 interior of the flask and upon every joint of the apparatus. Hence an 
 apparatus will sometimes leak, and refuse to deliver gas at the desired 
 point, when its delivery-tuhe is deeply immersed, while it does not 
 leak if the tube merely dip beneath the surface of the water. With 
 mercury the pressure of a few centimetres is very considerable, on 
 account of the high specific gravity of the fluid, so that this difliculty 
 is more likely to occur with this metal thanvsdth water. Tight joints 
 prevent the occm'rence of this difficulty. A partial remedy is to dip 
 the delivery-tube as little as possible below the surface of the fluid in 
 the trough. 
 
 11. Gas-holders. — A small gas-holder, very convenient for many uses, 
 is made from a common glass bottle in the following manner: — A. 
 
 Fig. xvn. 
 
 (Fig. xvn.) is a bottle of 4-6 litres 
 capacity; through the cork in its 
 neck pass two glass tubes (No. 6), of 
 which one reaches the bottom of the 
 bottle, while the other merely pene- 
 trates the cork ; with the outer end 
 of the first tube a caoutchouc tube c 
 is coimected, with the outer end of 
 the second a common gas-cock a. 
 The bottle being first completely 
 fiUed with water, the apparatus 
 which generates, or contains, the 
 gas to be introduced into the holder 
 is connected with the tube carrying 
 the cock a ; this cock is open. As 
 the gas presses in, the water mounts 
 in the long tube, and flows out by 
 the siphon^ c. In order to relieve 
 the gas from this pressure at the 
 beginning, it is only necessary to 
 suck a little at c. The tube c should 
 of coiu'se be thrust into a sink or 
 drain-pipe. 
 
 To get gas out of the bottle, thus charged, the cock a is closed, and 
 the flexible tube c is lifted up and connected, as shown in the figure 
 with a bottle of water B placed on a shelf, or stand, somewhat above 
 the bottle A. When the cock h is opened, the gas in ^ is pressed upon 
 by the weight of the superincumbent column of water, and may there- 
 fore be made to issue at vpiU from the cock a. The higher B is placed 
 above A, the g-reater wiU be the force with which the gas will issue. 
 
GAS-HOLDEKS. 
 
 Fig. xvin. 
 
 6=a 
 
 If a moderate or easily regulated water-pressure is at liand, supplied 
 by city water-works or a reservoir in the upper part of the building, 
 tbe bottle B is unnecessary, and tbe flexible tube c may be connected 
 with, such a water-supply whenever gas is to be pressed ou.t of the 
 gas-holder A. 
 
 When larger quantities of gas are to bo stored for use, a metallic gas- 
 holder, whose construction and proportions are shown in Fig. XVIII., is 
 advantageously employed. The open cistern 
 -Bis supported over the vessel A on two co- 
 lumns c c, and two tubes a and h ; of these 
 tubes the first, a, reaches from the bottom 
 of B nearly to the bottom of A, while the 
 second, 6, starts from the bottom of B and 
 just enters the arched top of A without 
 projecting into it; d\as. short large tube, 
 sloping iipwards and outwards, and capable 
 of being tightly closed with a cork or caout- 
 chouc stopper; jr is a glass gauge to show 
 the height of the water in the vessel A ; e 
 is the discharge-pipe. To fill the gas-holder 
 with water, close d, open the stopcocks a, 
 b, and e, and pour water into the cistern B ; 
 the water entering A will expel the air 
 throug;h b and e; when the water begins 
 to flow through e, close that stopcock and 
 expel the rest of the air through b. The 
 gas-holder may now be fiUed with gas by 
 displacing the water in the following manner: — Close aU the stop- 
 cocks, withdraw the cork or stopper from d, and introduce the tube 
 which delivers the gas through that opening. A short piece of caout- 
 chouc tubing makes the best end for the gas-delivery-tube ; but glass 
 tubing wiU answer the purpose if the end be slightly bent upward. 
 The water flows out at d as fast as the gas enters, and the gas-holder 
 should therefore stand in a shallow metal tray provided with a drain- 
 pipe. When the desired quantity of gas has been introduced, close d. 
 To draw gas out of a gas-holder of this construction, the cistern B is 
 filled with water and the cock a is opened ; under the pressure thus 
 established the gas may be drawn off through e, or allowed to rise 
 through b into bottles or bells filled with water and held over the 
 mouth of the tube b in the cistern B; in this last case B answers the 
 purpose of a pneumatic trough. 
 
 This gas-holder may be cheaply made of zinc; any gas-fitter can 
 
 2s 
 
GAS-HOLDEES. 
 
 supply the necessary stopcocks; care must be taken that the glass 
 tube which constitutes the gauge ia fitted air-tight to the gas-holder. 
 The stopcock e need not end in a screw ; tubes may be as well con- 
 nected with it by caoutchouc. The available pressure under which 
 the gas in the holder streams out at e is of course limited by the ele- 
 vation of B above A, which must always be moderate. When a 
 stronger pressure is desirable, as in getting- the oxyhydrogen blowpipe- 
 flanie, for example, a heavier water-column maybe obtained by screw- 
 ing a tall tube with a capacious funnel on the top of it into the tube a, 
 where it opens into the bottom of the cistern B. A piece of common 
 iron or copper gas-pipe about a metre long, answers this purpose very 
 well ; the funnel at the top should hold two or three litres, and must 
 be kept full of water from a cask or tub provided with a cock and 
 placed just above the funnel. Where a water-supply, with moderate 
 pressure, is obtainable, it may be used to keep the funnel full, or to 
 replace the funnel altogether, if directly connected with the tube a. A 
 gas-holder, measuring not more than 60 cm. in total height, is not too 
 heavy to be portable, and during the process of filling may be placed 
 over a tub ; but a gas-holder of much larger proportions is better made 
 a fixture, and provided in a permanent manner with drain-pipe and 
 water-supply. The gas-holder thus described is that which is the most 
 generally useful ; it may be charged from any 
 glass flask, retort, or bottle, without any pres- 
 sure being exerted upon the glass vessel ; and 
 imused gas contained in any sort of bell, bottle, 
 or flask can be very readily transferred to such 
 a gas-holder without waste and with very little 
 trouble. 
 
 A cheaper gas-holder may be made on the 
 plan of the large gas-holders, improperly called 
 gasometers, used in gas-works. Fig. XIX. re- 
 presents a gas-holder of this sort. Over a tank 
 of water, which may be a cylinder of zinc as 
 shown in the figure, or a headless pork- or oil- 
 barrel, or any other water-tight tub, is balanced 
 by pulleys and weights a tight bell of zinc, not 
 too large for complete immersion in the tank. 
 The U-tube, shown in the figure, which may 
 be either of lead or brass, serves both to intro- 
 duce and deliver the gas. To fill such a gaso- 
 meter, open the cock, lift the counterbalajicing weight, and let the bell 
 sink into the water j then connect the vessel from which the gas is 
 
DEFIiAQaATINQ-SPOON. XXX 
 
 delivered -with the tube of the holder, counterpoiae the bell, and the 
 gas coming- from the generator -will gradually lift the bell out of the 
 water. To force the gas out of the holder it is only necessary to remoTO 
 the counterbalancing weight ; the weight of the bell forces out the gas ; 
 and if this pressure be not sufficient, additional weights may be 
 placed on the top of the bell. Gas-holders of this construction, unless 
 very small, are too heavy, when filled with water, to be carried about ; 
 but this difficulty may be obviated, when economy is not specially to 
 be regarded, by placing within the lower cylinder, or tank, a second 
 aijr-tight cylinder as a core, so as to leave only a narrow space between 
 the inner and outer cylinders for the water into which the upper beU 
 dips. Elegant, but not cheap, gas-holders are thus made, which are 
 convenient for some uses, but are not so generally to be recommended 
 as those of the construction first described. The vessel from which a 
 gas-holder with counterpoised beU is charged is always subjected to 
 some pressure, slight if the pulleys, cords, and weights are in perfect 
 order, but more frequently considerable on account of the difficulty of 
 maintaining such an apparatus in perfect condition, 
 
 12. Deflagrating-Spoan. — The little cup which holds combustible 
 material, to be burnt in a bottle or jar of gas, is called a defliagrating- 
 spoon ; it may be cheaply made by hoUowiug a hemispherical cup out 
 of a cube of chalk about 3 cm. on a side, and attaching a stout iron or 
 brass wire to the chalk, in such a manner that the cup wUl be right 
 side up when hung by the wire in a jar of gas ; the upper end of this 
 wire should be straight, that it may be thrust through the cork or piece 
 of wood which covers the mouth of the bottle or jar. The piece of 
 chalk may be replaced by a bit of the cylindrical chalk crayon com- 
 monly used with blackboards. A piece of crayon 1'5 cm. in length 
 will make a sufficient spoon. A small cupel is a convenient ready-made 
 substitute for the chalk cup. Brass deflagrating-spoons are also tp be 
 had of philosophical-instrument-makers. 
 
 13. Platimtm Foil and Wire.~~A piece of platinum foil about 3 cm. 
 square is useful in experiments involving the evaporation of a drop or 
 two of liquid and the ignition of the residue ; it is an essential tool in 
 qualitative analysis. The foil should be at least so thick that it does not 
 crinkle when wiped ; and it is more economical to get foil which is tog 
 thick than too thin, for it reqliu'es frequent cleaning. A bit of platinum 
 wire, not thicker than a No. 10 needle, and 20 cm. long, will last a long 
 time with careful usage. No other metal, and no mixture of substances 
 from which a metal can be reduced, must ever be heated on platinum 
 foil or wire, for platinum forms alloys with other metals which are 
 much more fusible than itseE If once alloyed with a baser metal, the 
 
 2s2 
 
XXll riLIEEISG. 
 
 platinum ceases to bo applicable to its peculiar uses. Platinum may 
 be cleaned by boiling it in either nitric or chlorhydric acid, by fusing 
 the acid sulphate of sodium or potassium upon it, or by scouring it 
 with fine sand. Aqua regia and chlorine-water dissolve platinum; 
 the sulphides, cyanides, and oxides of sodium and potassium, when 
 fused in platinum vessels, slowly attach the metal. 
 
 14. -P(/tenra(/.— Filtration is resorted to in order to separate a finely 
 divided solid from a liquid. The filter may be made of paper, cloth, 
 tow, cotton, asbestos, and other substances. Paper is the substance 
 oftenest used. A good filtering-paper must be porous enough to filter 
 rapidly, and yet suiSciently close in textm-e to retain the finest pow- 
 ders ; and it must also be strong enough to bear, when wet, the pres- 
 sure of the liquid which must be poured upon it. For delicate experi- 
 ments it is also necessary that filtering-paper should contain no soluble 
 salts, and but a very small proportion of incombustible material, which 
 would remain as ash were the filter to be burned. Filtering-paper 
 (which is generally sold in sheets) is first cut into circles of various 
 diameters, adapted to the various scales of operation -pj yy 
 and quantities of liquids to be filtered. To prepare a 
 filter for use, one of these circles is folded over on its 
 own diameter, and the semicircle thus obtained is 
 folded once upon itself into the form of a quadrant ; 
 the paper thus folded is opened so that three thick- 
 nesses shall come upon one side, and one thickness 
 upon the other, as shown in Fig. XX.; the filter is 
 then placed in a glass funnel, the angle of which 
 should be precisely that of the opened paper, viz. 60° ; 
 after being wetted, it is ready to receive the liquid to be filtered. The 
 paper may be so folded as to fit a funnel whose angle is more or less than 
 60° ; but this is the most advantageous angle, and glass funnels should 
 be selected with reference to their correctness in this respect. 
 
 Coarse and rapid filtering can be effected with cloth bags, j^- -jry-r 
 also by plugging the neck of a funnel loosely with tow or 
 cotton. If a very acid or very caustic liquid, which would 
 destroy paper, cotton, tow, or wool, is to be filtered, the best 
 substances wherewith to plug the neck of the funnel are 
 asbestos and gun-cotton, neither of which is attacked by 
 such corrosive liquids. 
 
 The glass funnel which holds the filter generally requires 
 an independent support; for it is seldom judicious, or pos- 
 sible, to support the funnel directly upon the vessel which 
 receives the JiUrate, as the clear liquid which runs through the filter is 
 
DETING GASES. 
 
 called. The iron stand may be used for tWs purpose ; and wooden 
 stands, of a similar construction, adapted expressly for holding- funnels, 
 ai-e very convenient and not expensive. In general, care should he 
 taken that the lower end of the funnel touch the side or edge of the 
 vessel into which the filtrate descends, in order that the liquid may 
 not fall in drops, but run quietly down without splashing. Sometimes 
 there is no objection to thrusting a funnel directly into the neck of a 
 bottle or flask ; but in this case an ample exit for the air in the bottle 
 must be provided (Fig. XXI.). 
 
 15. Drying Gases. — It is often desirable to remove the aqueous vapor 
 .which is mixed with gases, collected over water or prepared from 
 materials containing water. It very seldom happens that a gas can be 
 prepared at one operation in so dry a state as to contain no vapor of 
 water; this vapor must ordinarily be removed by a subsequent or 
 additional process. Experience has shown that some gases are more 
 easily dried than others ; thus air, hydrogen, and common oxygen are 
 thoroughly dried with great ease, but gaseous mixtures which con- 
 tain antozone only with great difficulty ; chlorine is three times as 
 hard to dry as carbonic acid. These and similar facts must be borne 
 in mind in constructing drying-apparatus. The common drying-pro- 
 cess depends upon bringing the moist gas into contact with some liquid 
 or solid which greedily and rapidly absorbs aqueous vapor. The three 
 substances most used for this purpose are concentrated sulphuric acid, 
 chloride of calcium, and dry quicklime. Sulphurio acid may be used 
 in two ways : the gas may be made to bubble through a few centi- 
 metres depth of the liquid acid, or it may be forced to pass through 
 the interstices of a column of broken pumice-stone which has been 
 previously soaked in the acid. The latter method is the most eiFectual, 
 because it secures a more thorough contact of the gas with the hygro- 
 scopic acid than is possible during 
 the rapid bubbling of the light gas 
 through a shallow layer of the dense 
 liquid. The column of fragments 
 of pumice-stone may be held in a 
 U-tube, arranged like that shown 
 in Fig. XXII. ; but the vertical cy- 
 linder shown in the same figure is 
 better adapted for this use, because 
 the acid as it becomes dilute from 
 absorption of moisture, gradually 
 trickles from the pumice-stone, and^^^^^'*'^ 
 is apt to collect in such quantity at 
 
 Fig. XXII. 
 
 33= 
 
XXIV CHLOEIDB-OF-OAICITJM tr-TXTBE. 
 
 the bottom of the U-tube as to completely cloae tbe tube. In preparing 
 the upright cylinder for use, the portion below the contraction is not 
 filled with pumice-stone ; it receives the drippings from the pumice- 
 stone column. The gas to be dried enters by the lower lateral opening, 
 and goes out at the top of the cylinder. Though especially adapted 
 to the column of acid-soaked pumice-stone, this cylinder may very 
 well be used with either of the other drying-agents, chloride of cal- 
 cium or quicklime. Either of the forms of drying-tube represented in 
 Fig. XXII. may be employed with these latter substances ; in charging 
 the horizontal tubes, bits of loose cotton-wool should first be placed 
 against the exit-tube to prevent any particles of the chloride of cal- 
 cium, or quicklime, from entering that tube ; pieces of the perfectly 
 dry solid are then introduced in such a way that the tube may be com- 
 pactly filled with fragments which leave room for the gas to pass very 
 deviously between them, but offer no direct channels through which 
 the gas could find straight and quick passage. Quicklime must be 
 charged much more loosely than chloride of calcium, because of its 
 great expansion when moistened. Fused chloride of calcium is not so 
 well adapted for drying gases as the imfused substance. It is not at 
 all necessary that the fragments of chloride of calcium, or quicklime, 
 should be of uniform size. When the tube is nearly fuU, a plug of 
 loose cotton should be inserted before putting in the cork. A chloride- 
 of-calcium tube, once filled, will often serve for many experiments ; 
 whenever out of use, its outlets should be covered with paper caps; or, 
 better, caoutchouc connectors may be slipped upon the exit-tubes, and 
 bits of glass rod thrust into these connectors. The moisture of the air 
 is thus kept from the chloride of oalciimi. The dimensions of drying- 
 tubes are of course very various ; the bulb-tube shown in Fig. XSH. 
 is seldom used with a greater length than 25 cm. ; when this form of 
 tube is employed the gas should invariably enter by the end without 
 a cork, where the small size of the tube permits direct 
 connexion with a common gas-delivery-tube by means ^S' ^■^■'■■'-'■' 
 of a caoutchouc connector; the other horizontal tube, '^^ 
 shown in the figure, may be of any length ; but when- .pt 
 ever a great extent of drying-surface is necessary, U- tubes 
 have the advantage of compactness; for many can be 
 htmg upon one short frame. The upright cylinder may 
 be from 25 cm. to 40 cm. in height. A good U-tube, 
 with an addition which has the merit of economizing- 
 chloride of calcium, is shown in Fig. XXIII. ; the addi- 
 tion consists of a short test-tube, into which the tube 
 by which the gas comes in barely enters ; a quantity of water is often 
 
WAIEB-BATH. 
 
 XiV 
 
 caught in this test-tube wMch otherwise would wet and spoil a con- 
 siderable amount of chloride of calcium ; the little test-tube may, of 
 course, be taken out and emptied at will. 
 
 The choice between one or other of the three drying-substances is 
 determined in each special case by the chemical relations of the gas to 
 be dried ; thus ammonia-gas, which is absorbed by sulphuric acid and 
 by chloride of calcium, must be dried by passing it over quicklime, 
 while sulphurous acid gas, which would combine with quicklime, must 
 be dried by contact with sulphuric acid. 
 
 Fig. XXV. 
 
 Fig. XXIV. 
 
 16. Spring Clip and Screw Compressor. — ^These are very convenient 
 substitutes for the ordinary stopcock, and as such are in constant use 
 in the laboratory. Their form, and the manner of their use, wUl be 
 readily understood from the figures. As glass stopcocks are expensive 
 and fragile, and metal stopcocks are usually out of the question, be- 
 cause so many gases and liqiuds attack the common metals, these 
 excellent substitutes are used whenever a caoutchouc tube is not inad- 
 missible ; they cannot be used unless a bit of elastic tubing can be 
 inserted into the apparatus which requires a cock. 
 
 Another effective mode of temporarily stopping or partially closing 
 a caoutchouc tube, is to slip over the tube a common brass ring of 
 about the same diameter as that of the tube, and then to thrust a 
 slightly conical plug of hard wood or ivory between the ring and the 
 flexible tube. 
 
 17. Water-hath. — ^It is often necessary to evaporate solutions at a 
 moderate temperature which can permanently be kept below a certain 
 known limit ; thus, when an aqueous solution is to 
 be quietly evaporated without spirting or jumping, 
 the temperature of the solution must never be suf- 
 fered to rise above the boiling-point of water, nor 
 even quite to reach this point. This quiet evapora- 
 tion is best effected by the use of a water-bath — a 
 copper cup whose top is made of concentric rings of ' 
 different diameters to ad^pt it to dishes of various 
 size (Fig. XXVI.). This cup, two-thirds full of water. 
 
 Fig. XXVI. 
 
IKOIf EETOBT. 
 
 is supported on the iron stand over tlie lampj and the dish Contain- 
 ing the solution to be evaporated is placed on that one of the several 
 ring's which will permit the greater part of the dish to sink into the 
 copper cup. The steam rising from the water impinges upon the 
 bottom of the dish, and brings the liquid vrithin it to a temperature 
 which insm-es the evaporation of the water, but will not cause any 
 actual ebullition. The water in the copper cup must never be allowed 
 to boil away. Whenever a constant svipply of steam is at hand, as in 
 buildings warmed by steam, the copper cup above described may be 
 converted into a steam-bath by attaching it to a steam-pipe by means 
 of a small tube provided with a stopcock. 
 
 A cheap but serviceable water-bath may be made from a quart 
 milk-can, oil-can, tea-cannister, or any similarly shaped tin vessel, by 
 inserting the stem of a glass funnel into the neck of the can through 
 a well-fitting cork. In this funnel the dish containing the liquor to 
 be evaporated rests. The can contains the water, which is to be kept 
 just boiling. On account of the shape of the funnel, dishes of various 
 sizes can be used with the same apparatus. 
 
 The copper vessel first described may be conveniently employed 
 when it is requii'ed to expose substances to a constant temperature 
 higher than 100°. For this purpose the cup is filled with oil, wax, 
 paraiEne, or a solution of chloride of zinc or chloride of calcium ; the 
 flask or dish containing the substance to be heated should, in this case, 
 be immersed in the fluid to about two-thirds of its depth ; a thermo- 
 meter must be used to indicate the temperature of such a bath. "When 
 oil, wax, or paraffine is used, the temperature must not be carried so 
 high as to bum or decompose these organic matters, else a very dis- 
 gusting vapor will be produced. 
 
 18. Iron Retort. — A retort, made of iron, of the form shown in 
 Fig. XXVU., is a convenient utensil 
 
 in making large quantities of oxygen, ^io- -^-^"^ ^• 
 
 and in preparing illuminating-gas or 
 marsh-gas. The iron top is fitted to the 
 retort with a ground joint, fastened bj' a 
 screw-clamp. When the top is removed, 
 the whole inner surface of the retort is 
 exposed — a decided advantage wherever 
 the residue left in the retort after use is 
 solid. A retort of about 300 c. c. capa- 
 city Ls amply large for most uses. A small iron kettle makes a serviceable 
 retort ; the lid must be luted on, and the nose becomes the exit-tube. 
 
 18, Self-regulating OaH-generator.—An appai'atus which is always 
 
SEL]?-EEGrri.AIIN(} aAS-GENEBATOR. 
 
 Fig. xxvnr. 
 
 ready to deliver a constant stream of hydrogen, and yet does not 
 generate the gas except when it is immediately -wanted for use, is a 
 great convenience in an active laboratory or on a lecture-table. The 
 same remark applies to the two gases sulphydric acid and carbonic 
 acid, which are likewise used in considerable quantities, and which can 
 be conveniently generated in precisely the 
 same form of apparatus which is advan- 
 tageous for hydrogen. Such a generator 
 may be made of divers dimensions. The 
 following dii'ections, with the accompany- 
 ing figure (Fig. XXVIIL), will enable the 
 student to construct an apparatus of con- 
 venient size. Procure a glass cylinder 20 
 or 25 cm. in diameter and 80 or 35 cm. 
 high; ribbed candy-jars are sometimes to 
 be had of about this size ; procure also a 
 stout tubulated bell glass 10 or 12 cm. 
 wide and 5 or 7 cm. shorter than the cy- 
 linder. Get a basket of sheet-lead 7'5 cm. 
 deep and 2o cm. narrower than the bell- 
 glass, and bore a number of small holes in 
 the sides and bottom of this basket. Cast 
 a circular plate of lead 7 m.m. thick and of a diameter 4 cm. larger 
 than that of the glass cylinder ; on what is intended for its under side 
 solder three equidistant leaden strips, or a continuous ring of lead, tq 
 keep the plate in proper position as a cover for the cylinder. Fit 
 tightly to each end of a good brass gas-cock a piece of brass tube 8 cm. 
 long, 1'5 to 2 cm. wide, and stout in metal. Perforate the centre of 
 the leaden'plate, so that one of these tubes will snugly pass through 
 the orifice, and secure it by solder, leaving 5 cm. of the tube project- 
 ing below the plate. Attach to the lower end of this tube a stout hook 
 on which to hang the leaden basket. By means of a sound cork and 
 common sealing-wax, or a cement made of oil mixed vsith red and 
 white lead, fasten this tube into the tubulature of the bell glass air- 
 tight, and so firmly that the joint will bear a weight of 2 or 3 kilos. 
 Hang the basket by means of copper wire within the bell 6 cm. above 
 the bottom of the latter. To the tube which extends above the stop- 
 cock attach by a good cork the neck of a tubulated receiver of 100 or 
 150 c. c. capacity, the interior of which has been loosely stuffed with 
 cotton. Into the second tubulature of the receiver fit tightly the de- 
 livery-tube carrying a caoutchouc connector ; into this connector can 
 he fitted a tube adapted to convey the gas in any desired direction. 
 
GLASS WAEE. 
 
 To charge the apparatus, flU the cylinder with dilute acid to -snthrn 
 10 or 12 cm. of the top, place the zinc, sulphide of iron, or marble, as 
 the case may be, in the basket, hang the basket in the bell, and put 
 the beU-glaas full of air into its place with the stopcock closed. On 
 opening the cock, the weight of the acid expels the air from the bell, 
 the acid comes in contact with the solid in the basket, and a steady 
 supply of gas is generated until either the acid is satura,ted or the 
 solid dissolved; if the cock be closed, the gas accumulates in the boU, 
 and pushes the acid below the basket so that all action ceases. In 
 cold weather the apparatus must be kept in a warm place. For gene- 
 rating hydrogen, sulphuric acid diluted with four or five parts of water 
 is used; for sulphydric acid, sulphuric acid is diluted with fourteen 
 parts of water ; for carbonic acid, chlorhydric acid diluted with two or 
 three parts of water is to be preferred. 
 
 20. Glass Retorts, Flasks, Beakers, Test-tubes and Test-glasses.— All 
 glass vessels which are meant for use in heating liquids must have 
 uniformly thin bottoms. Tubulated retorts are much more generally 
 useful than those without a tubulature. As retorts are expensive in 
 comparison with flasks, they are less used than formerly. 
 
 The neck of a flask should have such a form that it can be tightly 
 closed by a cork, and the lip must be strengthened to resist the force 
 used in pressing in the cork, either by a rim of glass added on the 
 outside, or, 'better, by causing the rim itself to flare outward. The 
 actual edge of the rim must never be sharp or rough, but always smooth 
 and rounded by partial fusion. The thin-bottomed flasks in which 
 olive-oil is sometimes imported from Italy are excellent for chemical 
 uses ; their edges always require, however, to be rounded in the lamp. 
 These Florence flasks, which are very much to be recommended both 
 on the ground of cheapness and of durability, may be cleaned by 
 soaking them 24 hours in a weak caustic lye, and then washing them 
 with boiling water. 
 
 BeaJjers are thin flat-bottomed tumblers with a slightly flaring rim. 
 They are to be bought in sets or nests which sometimes include a large 
 range of sizes. The small sizes are very useful vessels ; the large are 
 so fragile as to be almost worthless. Up to the capacity of about a 
 litre, beakers are to be recommended for heating liquids whenever it is 
 an object to have the whole interior of the vessel readily accessible. 
 
 Test-tubes are little cylinders of thin glass, with round, thin bottom.s, 
 and lips slightly flared. Their length may be from 12 cm. to 18 cm., 
 and their diameter 1 cm. to 2 cm. ; they should never have a dia- 
 meter so large that the open end camiot be closed by the ball of the 
 thumb. To hold the tubes upright a wooden rack is necessary. Be- 
 
MEASt7KING-GLAS8E3 AND BITKEITES. xxix 
 
 sides the row of holes to receive a dozen test-tubes bottom down, the 
 rack should have a row of pegs on which the test-tubes may be in- 
 verted when not in use ; in this position the water in which they are 
 rinsed drains off, and dust cannot be deposited within the tubes. Test- 
 tubes are much used for heating small quantities of liquid over the gas- 
 or spirit-lamp ; they may generally be held by the upper end in the 
 fingers without inconvenience, but if a liquid is to be boiled for some 
 minutes in a test-tube, the tube must be held in wooden nippers, or in 
 a strip of thick folded paper, nipped round the tube and grasped be- 
 tween the thumb and fore finger just outside the tube. The wooden 
 nippers above mentioned are made of two bits of wood about 30 cm. 
 long hinged together at the back, and at once connected and kept apart 
 by a sliding steel or brass spring, somewhat like those used on certain 
 pruning-shears and some kinds of steel nippers. When a liquid is 
 boiling actively in a test-tube, it sometimes happens that portions of 
 the hot liquid are projected out of the tube with some force; the 
 operator should therefore hold the tube in an inclined position, rolling 
 it to a slight extent between the thumb and fore finger in order that 
 all sides of the tube may be equally exposed to the flame ; while thus 
 using the tube, he should be careful not to direct it either towards 
 himself or towards any other person in his neighbourhood. Test-tubes 
 are cleaned by the aid of cylindrical brushes made of bristles caught 
 between twisted wires, like those used for cleaning lamp-chimneys : 
 they should have a round end of bristles. 
 
 Two precautions are invariably to be observed in heating glass and 
 porcelain vessels of whatever form : first, the outside of the vessel to 
 be heated must be made perfectly dry ; secondly, the temperature must 
 not be raised too rapidly. When a large flask or beaker containing a 
 cold liquid is first warmed over a lamp, moisture almost invariably 
 condenses upon the bottom of the vessel : this moisture should be 
 wiped off with a cloth. 
 
 Stout conical glasses with strong stems and feet are convenient 
 for many uses not involving the application of heat. They are called 
 test-glasses, and may be had of various shapes and sizes. It is obvious 
 that cheap wine- or beer-glasses and common jelly-tumblers would 
 answer the purposes which these test-glasses serve. 
 
 21. Meamrmg-glassea and Burettes. — Measuring-glasses, divided into 
 cubic centimetres, are made in the Cylindrical form, and also in the 
 flaring shape common in druggists' measuring-glasses ; the cylindrical 
 form is to be preferred. Such a glass of 250 c. c, or better of 600 
 c. c. capacity, is a very useful implement ; a flask holding just one 
 litre when filled to a mark upon its neck is also convenient. Smaller 
 
:sxs 
 
 BEADING BUEETIES. 
 
 — - 
 
 4ia i 
 
 §20 1 
 
 ~ ^ 
 
 = ' f 
 
 i-3Q ^ 
 
 ■=" ■■' 1 
 
 ~riO ] 
 
 3. '" 
 
 Ira i 
 
 to 3 
 
 jm. J 
 
 quantities of liquid are measured with burettes. Mohr's burette is 
 -the most generally useful of all forms of this instru- i-jct. XXIX. 
 ment (see Fig. XXIX., the right-hand instrument) ; 
 it is a graduated tube di'awn to a small bore at the 
 bottom ; a caoutchouc connector is slipped upon the 
 bottom of the tube, a short bit of tube drawn to a 
 fine point is thrust into the lower end of the con- 
 nector, and a spring clip nips the connector between 
 the two glass tubes. The spring clip closes the bot- 
 tom of the burette, but it can of course be opened 
 at will to permit the liquid in the bm-ette to flow or 
 drop out. The caoutchouc affects injm-iously some 
 of the liquids which are used in burettes ; so that this 
 common form of Mohr's burette is not always appli- 
 cable. To avoid this difficulty the instrument may 
 be made with a glass cock, but is then rather costly. ''fe==^ °! 
 Gay-Lussac's burette is available whenever the caoutchouc in Mohr's 
 burette is objectionable. The construction of Gay-Lussac's bm-ette is 
 plainly to be seen in the figure (see Fig. XXIX., the left-hand instru- 
 ment); a narrow tube rims up beside the large graduated tube to the top 
 of the latter, and the liquid can be poured out in drops by gently in- 
 clining the instrument. Its fragility is a serious objection to this form 
 of bm'ette ; the danger of breaking off the small tube is lessened, if a 
 small piece of cork be inserted between the two tubes at the top, and 
 a string tied round them both. A wooden foot in which it may stand 
 upright upon a table is a convenient addition to Gay-Lussac's burette. 
 Mohr's burette must be held upright in a suitable screw clamp, or 
 be fastened on to a wooden frame in such a manner that the tube shall 
 be vertical, firm, and at the same time easily .detached. The fineness of 
 measurement maybe increased, without impairing the distinctness of the 
 scale, by reduciug the bore of the bm'ette. For delicate work, burettes 
 divided into tenths of a cubic centimetre are employed. The way in 
 which the reading-off is effected is a matter of importance in using a 
 burette ; it is essential, 1st, that the burette should be vertical ; 2nd, 
 that the eye should be brought to a level with the surface of the fluid; 
 3rd, that a fixed standard should be adopted of what is to be consi- 
 dered the surface. K a burette, partly filled with a liquid, be held 
 between the eye and a white wall, the surface of the liquid presents 
 a light line which is nearly level, and just below this line a second 
 line, which is dark and curved with the convexity downward. If a 
 sheet of white paper be held immediately behind the tube, these two 
 lines, though somewhat altered in appearance, are still distinctly 
 
WHnfG BUEETIES. XXXI 
 
 visible. They may be made still mOre distinct by using instead of 
 wUte paper a card half white, half black, with a straight di-viding line 
 between the two colors. On holding this card with the white half 
 uppermost, and the border line between white and black from 2 to 3 
 m.m. below the lowest visible dark line, two zones are brought out, 
 a light zone and a dark zone, and the lower limit of the dark zone is 
 made very distinct. Care must be taken to hold the card invariably 
 in the same relative position, since, if it be held lower down, the lower 
 border of the dark zone will move higher up. In practice the lower 
 border of the dark zon6 is read oif as the surface of the liquid, this 
 being the most distinctly marked line. There is one exception to this 
 rule ; when an opaque solution of permanganate of potassium is to be 
 measured in Gay-Lussac's burette, the upper border of the dark zone 
 must be held to be the surface of the liquid ; in this case it is best to 
 place the burette against a white background. 
 
 The zero of the graduated scale on a burette is always near the top 
 of the tube. In order to fill Mohr's bm-ette, the point of the instru- 
 ment is dipped into the liquid, the spring clip opened, and a little liquid, 
 sufficient at least to reach into the burette tube, is sucked up by ap- 
 plying the mouth to the upper end ; the spring clip is then closed, and 
 the liquid poured into the burette through the upper end until it has 
 risen a little above the zero-line. By opening the spring clip, the 
 liquid is then allowed to drop out until the exact level of the zero-line 
 is reached. The instrument is then ready for use. When a quantity 
 of liquid has been allowed to flow out of a burette thus fiUed, and the 
 operator desires to read off the amount used, he must wait a few 
 Inoments to give the particles of fluid adhering to the sides of the 
 emptied portion of the tube time to run down. This remark applies 
 to all forms of burette. Erdmann's swimmer is an excellent addition 
 to Mohr's burette. It is a cylindrical glass float of such a width as 
 nearly to fill the burette, but yet so loosely as to float Fig.XXX. 
 freely up and down with the liquor. To set the instrument f\ -g y 
 at zero a ring cut round the swimmer is brought to coin- '' ^ 
 cide with the line engraved on the burette. The abso- 
 lute height of the liquor in the burette is to be disregarded. 
 In order to read the height of the liquor in the burette at 
 any time, it is only necessary to note that line on the scale 
 with which the mark cut round the float coincides. 
 
 22. Pipettes. — Pipettes are tubes dravra to a point, and n^ 
 
 sometimes furnished with a bulb or a cylindrical enlarge' 
 ment. They are chiefly used to suck small quantities of fluid out of 
 a vessel without disturbing the bulk of the liquid. Figure XXX, re- 
 
XXXU POECELAIN WAKE. 
 
 presents three forms of pipette ; the form with the lower end bent 
 upwards is used to introduce liquids into a hell or bottle of gas stand- 
 ing over mercury. Pipettes graduated into cubic centimetres, or holdmg 
 a certain number of cubic centimetres when filled to a mark on the 
 stem, are often convenient. 
 
 23. Wash-bottle.— A wash-bottle is a flask with a uniformly thin 
 bottom, closed with a sound cork or caoutchouc stopper, through 
 which pass two glass tubes as shown in Fig. XXXI. The outer 
 end of the longer tube is drawn to a moderately -p. XXXI 
 fine point. A short bend near the bottom of this 
 longer tube in the same plane and direction as the 
 upper bend is of some use, because it enables the 
 operator to empty the flask more completely by inclin- 
 ing it. By blowing into the short tube, a stream of 
 water will be driven out of the long tube with consi- 
 derable force. This force with which the stream is 
 projected adapts the apparatus to removing precipitates 
 from the sides of vessels as well as to washing them on 
 filters, For use in analytical operations, it is often 
 convenient to attach a caoutchouc tube 12 or 16 cm. 
 long to the tube through which air is blown; this 
 flexible tube should be provided with a glass mouthpiece about 3 cm. 
 long. As the wash-bottle is often filled with hot or even boiling 
 water, it may be improved by binding about its neck a ring of cork, or 
 winding closely round the nook a smooth cord. It may then be handled 
 without inconvenience when hot. 
 
 24. Porcelain Dishes and Cnidbles. — Open dishes which will bear 
 heat without cracking- are necessary implements in the laboratory for 
 conduotiug the evaporation of liquids. The best evaporating-dishes 
 are those made of Berlin porcelain, glazed both inside and out, and 
 provided with a little lip projecting beyond the rim. The dishes made 
 of Meissen porcelain are not glazed on the outside, and are not so 
 durable as those of Berlin manufacture ; but they are much cheaper, 
 and with proper care last a long time. The small Berlin dishes will 
 generally bear an evaporation to dryness on the wire gauze over the 
 open fiame of the gas-lamp ; the Meissen dishes do not so well endure 
 this severe treatment. Evaporating-dishes are made of all diameters, 
 from 3 cm. to 45 cm. ; they should be ordered by specifying the dia- 
 meter desired. The large sizes are expensive, and not very durable ; 
 they should never be used except on a sand-bath. Dishes of German 
 earthenware are as good as porcelain for many uses, and are much to 
 be recommended in place of the large sizes of porcelain dishes. 
 
CEtrciBiES, xxxm 
 
 Very thin, HgLIy glazed porcelain cruelties with glazed covers are 
 made both at Berlin and at Meissen near Dresden ; they are indispen- 
 sable implements to the chemist. In general, the Meissen crucibles are 
 thinner than the Berlin, but the Berlin crucibles are somewhat less 
 liable to crack ; both kinds are glazed inside and out, except on the 
 outside of the bottom. Crucibles should be ordered by specifying the 
 diameters of the sizes desired ; they are to be had of nearly a dozen 
 different sizes, with diameters varying from 2 cm. to 9 cm. The 
 smallest and largest sizes are little used ; for most purposes the best 
 sizes are those between S cm, and 5 cm. in diameter. As the covers 
 are much less liable to be broken than the crucibles, it is advantageous 
 to buy more crucibles than covers, whenever it is possible so to do. 
 Porcelain crucibles are supported over the lamp on an iron- wire tri- 
 angle ; they must always be gradually heated, and never brought sud- 
 denly into contact with any cold substance while they are hot. 
 
 25. jRings to svpport round-bottomed vessels.— It is often necessary to 
 support globes, round-bottomed flasks, evaporating-dishes, and round 
 receivers in a stable manner upon the table or other flat surface. For 
 this purpose rings are used made of braided straw, or of straw wound 
 about a core of straw, or of tin wound with listing or coarse woollen 
 cloth. The material of which these rings are made, or with which 
 they are covered, ought to be a substance which does not conduct heat 
 well, because one of the chief uses of these rings is to receive hot 
 vessels just removed from the lamp or sand-bath. A hot flask or 
 dish would almost certainly be broken, if it were placed upon the cold 
 surface of a good conductor of heat. The student must never touch 
 a hot vessel with cold water, or bring it into sudden contact with a 
 surface of marble, iron, copper, or other conductor of heat. 
 
 26. Crucibles. — ^For use in a coal fire there are three good kinds of 
 crucibles, each of which has its own merits which recommend it for 
 certain purposes. The Hessian crucibles are sold in nests containing 
 from 3 to 10 crucibles ; there are 10 sizes, which vary from 3 to 25 
 cm. in height. They generally have a triangular form, and wiU with- 
 stand a very high temperature, if they are warmed before being put 
 in the fire. They are not sold with covers ; but covers may be bought 
 separately, or a triangular piece of soapstone maybe very conveniently 
 used as a cover for these crucibles. Hessian crucibles are cheaper 
 than any other kind, and are therefore the most used. The French 
 crucibles, called Beaufay crucibles, are admirable, but too dear for 
 common use. They have a tall, narrow form, a smooth surface, and a 
 small lip ; covers for the crucibles are sold separately. The crucibles 
 are sold; not in nests, but singly ; there are 22 sizes, which vary from 
 
XXSIV 3I0RTAKS. 
 
 4 to 40 cm. in lieight. They are highly refractory. Plumbago cru- 
 cibles are used for the fusion of the most refractory metals — gold, silver, 
 copper, brass, steel, iron, and so forth ; they resist better than any 
 other crucibles the combined action of a very high temperature and a 
 strong flux ; and as they are not liable to crack, they may often be 
 used many times without risk. Their first cost is higher than that 
 of any other crucibles. Crucibles are mainly used for the fusion and 
 reduction of metals; but there are also many chemical compounds 
 which can only be prepared at the very high temperatm'es which by the 
 use of crucibles we are able to command. Although crucibles often 
 withstand the most sudden changes of temperatm-e, it is nevertheless 
 expedient as a general rule to heat up a crucible gi'adually, and to pre- 
 viously warm a charge which is to be placed in a crucible already hot. If 
 a cold crucible is to be introduced into a fire, it should first be placed in 
 the least hot part of the fire and gradually brought into the hottest part. 
 
 27. Tongs and Pincers. — Hot -p- XXXII 
 crucibles are handled by means 
 of tongs of various shapes and 
 sizes, according to the weight and 
 nature of the vessels to be lifted. 
 Fig. XXXn. represents two good 
 forms of stout iron tongs for lifting 
 large crucibles out of a coal fire. The manner of using them is readily 
 understood from the figure. 
 
 SmaU porcelain crucibles are handled, when Fig. XXXIII. 
 hot, by means of small steel or iron tongs, such 
 as are represented in Fig. XXXIII. 
 
 SmaU steel pincers (jewellers' tweezers) are 
 applied in the laboratory to a great variety of uses. 
 
 28. Mortars. — ^Iron, porcelain, and agate mortars are used by che- 
 mists to reduce solids to powder. An iron mortar is useful for coarse 
 work, and for efiecting the first rough breaking up of substances which 
 are subsequently powdered in the porcelain or agate mortar. If there 
 be any risk of fragments being thrown out of the mortar, it should be 
 covered with a cloth or piece of stiff paper, having a hole in the 
 middle through which the pestle may be passed. Pieces of stone, 
 minerals, and lumps of brittle metals may be safely broken into frag- 
 ments suitable for the mortar by wrapping them in strong paper, 
 laying them so enclosed upon an anvil, and striking them with a heavy 
 hammer. The paper envelope retains the broken particles which 
 might otherwise fiy about in a dangerous manner and be lost. 
 
 The best porcelain mortars are those known by the name of Wedge- 
 
PTJLVEBIZINO. XXXV 
 
 wood-ware ; but there are' many cheaper substitutes. Porcelain mor- 
 tars will not bear sharp and heavy blows ; they are intended rather for 
 grinding and tritm'ation than foriammering ; the pestle may either be 
 formed of one piece of porcelain, or a piece of porcelain cemented to a 
 wooden handle ; the latter is the less desirable form of pestle. Un- 
 glazed porcelain mortars are to be preferred. In selecting mortars, the 
 following points should be attended to : — 1st, the mortar should not be 
 porous ; it ought not to absorb strong acids or any colored fluid, even 
 if such liquids be allowed to stand for hours in the mortar ; 2nd, it 
 should be very hard, and its pestle should be of the same hardness ; 
 3rd, it should be sound ; 4th, it shoiUd have a lip for the convenience 
 of pouring out liquids and fine powders. As a rule, porcelain mortars 
 will not endure sudden changes of temperature. They maybe cleaned 
 by rubbing in them a little sand soaked in nitric or sulphuric acid, or, 
 if acids axe not appropriate, in caustic soda. 
 
 Agate mortars axe only intended for tritm'ation; a blow would break 
 them. They are exceedingly hard, and impermeable. The material is 
 BO precious and so hard to work, that agate mortars are always small. 
 The pestles are generally inconveniently short, — a difficulty which may 
 be remedied by fitting the agate pestle into a wooden handle. 
 
 In all grinding-operations in mortars, whether of porcelain or agate, 
 it is expedient to put only a small quantity of the substance to be 
 powdered into the mortar at once. The operation of powdering will 
 be facilitated by sifting the matter as fast as it is powdered, returning 
 to the mortar the particles which are too large to pass through the 
 sieve. 
 
 29. SpatidcB. — For transferring substances in powder, or in small 
 grains or crystals, from one vessel to another, spatulse and scoops 
 made of horn or bone are convenient tools. A coarse bone paper- 
 knife makes a good spatula for laboratory use. Cards free from glaze 
 and enamel are excellent substitutes for spatulse. 
 
 30. Thermometers. — Thermometers intended for chemical use must 
 have no metal, and no wood or other organic material upon their outer 
 surfaces; their external surfaces must be wholly of glass. The best 
 thermometers are straight glass tubes, of uniform diameter, with cy- 
 lindrical instead of spherical bulbs, and having the scale engraved upon 
 the glass ; such instruments can be passed tightly through a cork, and 
 ^re free from many liabilities to eiTor to which thermometers with paper 
 or metal scales are always exposed. A cheaper kind of thermometer, 
 having a paper or, better, enamel scale enclosed in a glass envelope, will 
 answer for most experiments. 
 
 31. Furnaces.—'For all common fusions, an anthracite or coke fire 
 
 2 T 
 
XXXVl THE METEICAL SYSTEM. 
 
 in an ordmary cylinder stove will suffice. The chafing-dish, or open 
 portable stove, such as is used by plumbers for example, is very con- 
 venient for operations which require less heat. The clay buckets used 
 as open furnaces are better than the iron ones, because they hold the 
 heat better. 
 
 Charcoal is the fuel used in these open fiies. A very useful accom- 
 paniment to these portable furnaces is a piece of straight stove-pipe, 
 about 60 cm. long and 10 cm. wide, and flaring out below like a fun- 
 nel until it is vride enough to cover the top of the furnace. This con- 
 trivance powerfully increases the draught, and is used to urge the fire 
 during kindling, or to intensify it while a fusion is in progress. With 
 a furnace of this description there is no difficulty in keeping a small 
 crucible white-hot for a short time. 
 
 THE METRICAL SYSTEM OF WEIGHTS AND MEASUEES. 
 
 The metrical system, employed in the afiairs of every-day life by 
 most of the nations of continental Europe and by scientific writers 
 throughout the world, is based upon a fundamental uait or measure 
 of length, caUed a metre. This metre is defined as the 40-millionth 
 part of the circumference of the earth, or, in other words, of a "great 
 circle " or meridian ; its length was originally determined by actual 
 measurement of a considerable arc of a meridian ; but the varioxis mea- 
 surements heretofore made of the length of the earth's meridian diflfer 
 slightly from each other, and it is to be expected, and indeed hoped, 
 that the steady improvements of methods and instiimients will make 
 each successive determination of the length of the meridian better 
 than, and therefore different from, the preceding. It is therefore 
 necessary to define the standard of length, by legislation, to be a certain 
 rod of metal, deposited in a certain place under specified guaranties, 
 and to secm-e the vmiformity and permanence of the standard by the 
 multiplication of exact copies in safe places of deposit. 
 
 From this single quantity, the metre, all other measures are deci- 
 mally derived. Multiplied or divided by 10, 100, 1000, and so forth, 
 the metre supplies all needed linear measures, and the square metre 
 and cubic metre, with their decimal multiples, supply all needed 
 measures of area or surface on the one hand, and of solidity or capa- 
 city on the other. 
 
 From the unit of measm'e to the unit of weight the ti'ansition is 
 adnm-ably simple and convenient The cube of the 1 -hundredth of the 
 linear metre is, of course, the millionth of the cubic metre; its bulk is 
 
THE METEICAI, SYSTEM!. 
 
 xxxvu 
 
 about that of a large die of tlie common back-gammon board. This 
 little cube of pure water is the universal unit of weight, a gramme, 
 which, decimally multiplied and divided, is made to express all weights. 
 The numbers expressing all weights, from the least to the. greatest, 
 find direct expression in the decimal notation ; the weights used in 
 different trades only differ from each other in being different decimal 
 multiples of the same fundamental unit; and in comparing together 
 weights and volumes, none but easy decimal computations are ever 
 necessary. 
 
 The nomenclature of the metrical system is extremely simple ; one 
 general principle applies to each of the following tables. The Greek 
 prefixes for 10, 100, and 1000, viz. deca, hecto, and kilo, are used to 
 signify multiplication, while the Latin prefixes for 10, 100, and 1000, 
 viz. deci, centi, and milli, are employed to express subdivision. Of the 
 names thus systematically derived from that of the unit in each table, 
 many are not often used ; the names in common use are those printed 
 in small capitals. Thus, in the table for linear measure, only the 
 metre, kilometre, centimetre, and millimetre are in common use, — 
 the fijst for such purposes as the English yard subserves, the second 
 instead of the English mile, the third and fourth in lieu of the fractions 
 of the English foot and inch. 
 
 LINEAE MEASITBE. 
 
 {Millimetre 
 Centimetre 
 Decimetre 
 Unit Metre 
 
 {Decametre 
 Hectometre 
 Kilometre 
 
 01 
 1- 
 10- 
 100- 
 1,000- 
 
 Metre. 
 
 0-001 or 11000th of a metre. 
 0-01 or 1100th of a metre. 
 
 or HOth of a metre. 
 
 SUBFACE MEASUEE. 
 
 {Millimetre square 
 Centimetre square 
 Decimetre square 
 TTnit Metre square 
 
 CUBIC MEAStTEE. 
 
 ■ Cubic Millimetre 
 Divisions. . . Cubic Centimetre 
 Cubic Decimetre 
 ■pnit Cubic Metre 
 
 {Cubic Decametre 
 Cubic Hectometre 
 Cubic Kilometre 
 
 0-000,001 of a metre square. 
 
 0000,1 of a metre square. 
 
 01 of a metre square. 
 
 !• metre square. 
 
 Cubic Metre. 
 0000,000,001 
 0000,001 
 0-001 
 1- 
 1,000- 
 1,000,000- 
 1,000,000,000- 
 2t2 
 
-THE METRICAL SYSTEM. 
 
 The .table for land-meagure we omit, as haying no connexion with 
 our subject. For the measurement of wine, beer, oil, grain, and simi- 
 lar wet and dry substances, a smaller unit than the cubic metre is 
 desirable. The cubic decimetre has been selected as a special standard 
 of capacity for the measurement of substances such as are bought and 
 sold by the English wet and dry measures. The cubic decimetre thus 
 used is called a litre. 
 
 CAPACITY MEASUHE. 
 
 litres. Cubic Metre. 
 Millilitre = 0001 = 0-000,001 = 1 cubic centimetre. 
 DiTLsions... .{ Centilitre = 
 
 [ Decilitre 
 Unit Litre 
 
 0-01 
 
 0-000,01 
 
 Multiples . 
 
 f Decalitre = 
 
 ■! Hectolitre = x\j^ 
 
 [Kilolitre = 1,000 
 
 0-1 
 
 = 0000,1 
 
 
 1- 
 
 LO- 
 X)- 
 
 = 0-001 
 = 001 
 = 0-1 
 
 = 1 cubic decimetre 
 
 X)- 
 
 = 1- 
 
 = 1 cubic metre. 
 
 Divisions.. 
 
 The table of weights bears an intimate relation to this table of 
 capacity. As already mentioned, the weight of that die-sized cube, a 
 cubic centimetre or millilitre of distilled water (taken at 4°, its point of 
 greatest density) constitutes the metrical unit of weight. This weight 
 is called a gramme. From the very definition of the gramme, and from 
 the table of capacity-measure, it is clear that a litre of distilled water 
 at 4° will weigh 1000 grammes. 
 
 WEIGHTS. 
 
 Grammes. 
 
 0-001 
 
 001 
 
 01 
 
 1" =1 cubic centimetre of water at 4°. 
 10- 
 100- 
 [ Kilogramme = 1,000- = 1 cubic decimetre of water at 4°. 
 
 The simplicity and directness of the relations between weights and 
 volumes in the metrical system can now be more fuUy explained. 
 The chemist ordinarily uses the gramme as his unit-weight, and for 
 his unit of volume a cubic centimetre, which is the bulk of a gramme 
 of water. For coarser work, the kilogramme becomes the unit of 
 weight, and the corresponding unit of measure is the litre, which is 
 the bulk of a kilogramme of water. In commercial dealings, in ma- 
 nufacturing-processes, and, above all, in scientific investigations, these 
 simple relations between weights and measures have been found to be 
 an inestimable advantage. The numerical expressions for metrical 
 weights and measm-es may always be read as decimals, Thus 5-126 
 
 ' MiLLIGRAlIME = 
 
 Cestiqramme = 
 
 \ Decibeamme = 
 
 Unit G-EA3IME = 
 
 C Decagramme = 
 Multiples..-^ Hectogramme = 
 
IHEEMOMETEES COMPAEED. 
 
 xxsix 
 
 metres will be read five metres and one hundred and twenty-six thou- 
 sandtlis, and not five metres, one decimetre, two centimetres, and six 
 millimetres.' The expression 10-5 gxammes is read ten and five-tenths 
 grammes ; just as we say one hundred and five dollars, not ten eagles 
 and five dollars ; or sixty-five centS) not six dimes and five cents. All 
 computations under the metrical system are made,wi|th decimals alonei 
 The abbreviations commonly met with in chemical literature are : — 
 
 m.m. for millimetre ; cm. for centimetre ; 
 
 m. for metre ; c. c. for cubic centimetre ; 
 
 grm. for gramme ; kilo, for kilogramme. 
 
 The use of the metrical system of weights and measures in thd 
 arts and trades has been legalized both in the United States and in 
 Great Britain. The United States coin, composed of copper and 
 nickel, of the denominations cents, and date 1866, is 2 cm. in diame- 
 ter, and weighs 5 gnns. 
 
 TABLE for the Conversion of Degrees on the Centigrade Thermometer 
 into Degrees of Fahrenheit's Scale. 
 
 Cent. 
 
 Fahr. 
 
 Cent. 
 
 Falir. 
 
 Cent. 
 
 Fahr. 
 
 Cent. 
 
 Fahr. 
 
 -50 
 
 -58-0 
 
 -2& 
 
 -26-2 
 
 -§ 
 
 if 6 
 
 1§ 
 
 6E-4 
 
 -49 
 
 -56-2 
 
 -28 
 
 -18'4 
 
 - 7 
 
 19-4 
 
 14 
 
 67-2 ; 
 
 -48 
 
 -54-4 
 
 -27 
 
 -16-6 
 
 - 6 
 
 21-2 
 
 15 
 
 69-0 
 
 -47 
 
 -52-6 
 
 -26 
 
 -14-8 
 
 - 5 
 
 23-0 
 
 16 
 
 60-8 
 
 -46 
 
 -50-8 
 
 -25 
 
 -13-0 
 
 - 4 
 
 24-8 
 
 17 
 
 62-6 
 
 -45 
 
 -49-0 
 
 -24 
 
 -11-2 
 
 - 3 
 
 26-6 
 
 18 
 
 64-4 
 
 -44 
 
 -47'2 
 
 -23 
 
 - 9'4 
 
 - 2 
 
 28-4 
 
 19 
 
 e6'2 
 
 -4.3 
 
 -45-4 
 
 -22 
 
 - 7-6 
 
 - 1 
 
 30-2 
 
 20 
 
 68'0 
 
 -42 
 
 -43-6 
 
 -21 
 
 - 5-8 
 
 
 
 32-0 
 
 21 
 
 69-8 
 
 -41 
 
 -41-8 
 
 -20 
 
 - 4-0 
 
 + 1 
 
 33-8 
 
 22 
 
 71-6 
 
 -40 
 
 -40'0 
 
 -19 
 
 - 2-2 
 
 2 
 
 36-6 
 
 23 
 
 73-4 
 
 -39 
 
 -38-2 
 
 -18 
 
 - 0-4 
 
 3 
 
 37-4 
 
 24 
 
 75-2 
 
 -38 
 
 -36-4 
 
 -17 
 
 4- 1-4 
 
 4 
 
 39-2 
 
 25 
 
 77-0 
 
 -37 
 
 -34-6 
 
 -16 
 
 3-2 
 
 5 
 
 .41-0 
 
 26' 
 
 78'8 
 
 -36 
 
 -32-8 
 
 -15 
 
 5-0 
 
 6 
 
 42-8 
 
 27 
 
 80'6; 
 
 -35 
 
 -810 
 
 -14 
 
 6-8 
 
 7 
 
 44-6 
 
 28 
 
 82-4 
 
 -34 
 
 -29-2 
 
 -13 
 
 8-6 
 
 8 
 
 46-4 
 
 29 
 
 84-2 
 
 -33 
 
 -27-4 
 
 -12 
 
 10-4 
 
 9 
 
 48-2 
 
 30 
 
 86-0 
 
 -32 
 
 -25-6 
 
 -11 
 
 12-2 
 
 10 
 
 50-0 
 
 31 
 
 87-8 
 
 -31 
 
 -23-8 
 
 -10 
 
 14-0 
 
 11 
 
 51'8 
 
 32 
 
 89-6 
 
 -30 
 
 -22-0 
 
 - 9 
 
 15'8 
 
 12 
 
 53'6 
 
 33 
 
 91-4 
 
xl 
 
 IHERMOMEIEKS COMPAKED. 
 TABLE (continued). 
 
 Cent. 
 
 Fahr. 
 
 Cent 
 
 Fahr. 
 
 Cent. 
 
 Fahr. 
 
 Cent. 
 
 rahr. 
 
 34 
 
 9§-2 
 
 7§ 
 
 17§-4 
 
 122 
 
 251-6 
 
 166 
 
 336-8 
 
 85 
 
 95-0 
 
 79 
 
 174-2 
 
 123 
 
 253-4 
 
 167 
 
 832-6 
 
 36 
 
 96-8 
 
 80 
 
 176-0 
 
 124 
 
 255-2 
 
 168 
 
 334-4 
 
 37 
 
 98-6 
 
 81 
 
 177-8 
 
 125 
 
 267-0 
 
 169 
 
 336-2 
 
 38 
 
 100-4 
 
 82 
 
 179-6 
 
 126 
 
 258-8 
 
 170 
 
 338-0 
 
 39 
 
 102-2 
 
 83 
 
 181-4 
 
 127 
 
 260-6 
 
 171 
 
 339-8 
 
 40 
 
 104-0 
 
 84 
 
 183-2 
 
 128 
 
 262-4 
 
 172 
 
 341-6 
 
 41 
 
 105-8 
 
 85 
 
 1850 
 
 129 
 
 264-2 
 
 173 
 
 343-4 
 
 42 
 
 107-6 
 
 86 
 
 186-8 
 
 130 
 
 266-0 
 
 174 
 
 346-2 
 
 43 
 
 109-4 
 
 87 
 
 188-6 
 
 131 
 
 267-8 
 
 175 
 
 347-0 
 
 44 
 
 111-2 
 
 88 
 
 190-4 
 
 132 
 
 269-6 
 
 176 
 
 348-8 
 
 45 
 
 1130 
 
 89 
 
 192-2 
 
 133 
 
 271-4 
 
 177 
 
 350-6 
 
 46 
 
 114-8 
 
 90 
 
 194-0 
 
 134 
 
 273-2 
 
 178 
 
 352-4 
 
 47 
 
 116-6 
 
 91 
 
 196-8 
 
 135 , 
 
 275-0 
 
 179 
 
 354-2 
 
 48 
 
 118-4 
 
 92 
 
 197-6 
 
 136 
 
 276-8 
 
 180 
 
 3660 
 
 49 
 
 120-2 
 
 93 
 
 199-4 
 
 137 
 
 278-6 
 
 181 
 
 357-8 
 
 50 
 
 122-0 
 
 94 
 
 201-2 
 
 138 
 
 280-4 
 
 182 
 
 359-6 
 
 51 
 
 123-8 
 
 95 
 
 203-0 
 
 139 
 
 282-2 
 
 183 
 
 361-4 
 
 52 
 
 125-6 
 
 96 
 
 204-8 
 
 140 
 
 284-0 
 
 184 
 
 363-2 
 
 53 
 
 127-4 
 
 97 
 
 206-6 
 
 141 
 
 285-8 
 
 185 
 
 365-0 
 
 54 
 
 129-2 
 
 98 
 
 208-4 
 
 142 
 
 287-6 
 
 186 
 
 366-8 
 
 56 
 
 131-0 
 
 99 
 
 210-2 
 
 143 
 
 289-4 
 
 187 
 
 368-6 
 
 56 
 
 132-8 
 
 100 
 
 212-0 
 
 144 
 
 291-2 
 
 188 
 
 370-4 
 
 67 
 
 134-6 
 
 101 
 
 213-8 
 
 145 
 
 293-0 
 
 189 
 
 372-2 
 
 68 
 
 136-4 
 
 102 
 
 215-6 
 
 146 
 
 294-8 
 
 190 
 
 374-0 
 
 59 
 
 138-2 
 
 103 
 
 217-4 
 
 147 
 
 296-6 
 
 191 
 
 375-8 
 
 60 
 
 140-0 
 
 104 
 
 219-2 
 
 148 
 
 298-4 
 
 192 
 
 377-6 
 
 61 
 
 141-8 
 
 105 
 
 221-0 
 
 149 
 
 300-2 
 
 193 
 
 379-4 
 
 62 
 
 143-6 
 
 106 
 
 222-8 
 
 150 
 
 302-0 
 
 194 
 
 381-2 
 
 63 
 
 145-4 
 
 107 
 
 224-6 
 
 161 
 
 303-8 
 
 195 
 
 383-0 
 
 64 
 
 147-2 
 
 108 
 
 226-4 
 
 152 
 
 305-6 
 
 196 
 
 384-8 
 
 65 
 
 149-0 
 
 109 
 
 228-2 
 
 153 
 
 307-4 
 
 197 
 
 386-6 
 
 66 
 
 150-8 
 
 110 
 
 230-0 
 
 154 
 
 309-2 
 
 198 
 
 388-4 
 
 67 
 
 152-6 
 
 111 
 
 231-8 
 
 156 
 
 3110 
 
 199 
 
 390-2 
 
 68 
 
 154-4 
 
 112 
 
 233-6 
 
 166 
 
 312-8 
 
 200 
 
 3920 
 
 69 
 
 156-2 
 
 113 
 
 235-4 
 
 157 
 
 314-6 
 
 201 
 
 393-8 
 
 70 
 
 168-0 
 
 114 
 
 237-2 
 
 158 
 
 316-4 
 
 202 
 
 395-6 
 
 71 
 
 159-8 
 
 115 
 
 239-0 
 
 159 
 
 318-2 
 
 203' 
 
 397-4 
 
 72 
 
 161-6 
 
 116 
 
 240-8 
 
 160 
 
 320-0 
 
 204 
 
 399-2 
 
 73 
 
 163-4 
 
 117 
 
 242-6 
 
 161 
 
 321-8 
 
 205 
 
 401-0 
 
 74 
 
 165-2 
 
 118 
 
 244-4 
 
 162 
 
 323-6 
 
 206 
 
 402-8 
 
 75 
 
 167-0 
 
 119 
 
 246-2 
 
 163 
 
 325-4 
 
 207 
 
 404-6 
 
 76 
 
 168-8 
 
 120 
 
 248-0 
 
 164 
 
 327-2 
 
 208 
 
 406-4 
 
 77 
 
 170-6 
 
 121 
 
 249-8 
 
 165 
 
 329-0 
 
 209 
 
 408-2 
 
IHBKMOMETEBS COMPARED. 
 
 TABLE (contmued). 
 
 xli 
 
 Cent. 
 
 Fahr. 
 
 Cent. 
 
 Fahr. 
 
 Cent. 
 
 Faht. 
 
 Cent. 
 
 Sahi. 
 
 210 
 
 4100 
 
 238 
 
 460-4 
 
 266 
 
 6l6-8 
 
 294 
 
 561-2 
 
 211 
 
 411-8 
 
 239 
 
 462-2 
 
 267 
 
 612-6 
 
 295 
 
 663-0 
 
 212 
 
 413-6 
 
 240 
 
 464-0 
 
 268 
 
 514-4 
 
 296 
 
 664-8 
 
 213 
 
 415-4 
 
 241 
 
 465-8 
 
 269 
 
 516-2 
 
 297 
 
 666-6 
 
 214 
 
 417-2 . 
 
 242 
 
 467-6 
 
 270 
 
 518-0 
 
 298 
 
 568-4 
 
 215 
 
 4190 
 
 243 
 
 469-4 
 
 271 
 
 519-8 
 
 299 
 
 570-2 
 
 216 
 
 420-8 
 
 244 
 
 471-2 
 
 272 
 
 521-6 
 
 300 
 
 572-0 
 
 Sir 
 
 422-6 
 
 245 
 
 473-0 
 
 273 
 
 523-4 
 
 301 
 
 573-8 
 
 §18 
 
 424-4 
 
 246 
 
 474-8 
 
 274 
 
 525-2 
 
 302 
 
 676-6 
 
 219 
 
 426-2 
 
 247 
 
 476-6 
 
 275 
 
 627-0 
 
 303 
 
 677-4 
 
 220 
 
 428-0 
 
 248 
 
 478-4 
 
 276 
 
 528-8 
 
 304 
 
 579-2 
 
 221 
 
 429-8 
 
 249 
 
 480-2 
 
 277 
 
 630-6 
 
 305 
 
 681-0 
 
 222 
 
 431-6 
 
 250 
 
 482-0 
 
 278 
 
 532-4 
 
 306 
 
 682-8 
 
 g^ 
 
 433-4 
 
 251 
 
 483-8 
 
 279 
 
 534-2 
 
 307 
 
 584-6 
 
 ■2M 
 
 435-2 
 
 252 
 
 485-6 
 
 280 
 
 636-0 
 
 308 
 
 586-4 
 
 225 
 
 437-0 
 
 253 
 
 487-4 
 
 281 
 
 537-8 
 
 309 
 
 588-2 
 
 226 
 
 438-8 
 
 254 
 
 489-2 
 
 282 
 
 539-6 
 
 310 
 
 590-0 
 
 227 
 
 440-6 
 
 255 
 
 491-0 
 
 283 
 
 641-4 
 
 311 
 
 591-8 
 
 228 
 
 442-4 
 
 256 
 
 492-8 
 
 284 
 
 543-2 
 
 312 
 
 593-6 
 
 229 
 
 444-2 
 
 257 
 
 494-6 
 
 285 
 
 645-0 
 
 313 
 
 595-4 
 
 230 
 
 446-0 
 
 258 
 
 496-4 
 
 286 
 
 546-8 
 
 314 
 
 697-2 
 
 231 
 
 447-8 
 
 259 
 
 498-2 
 
 287 
 
 648-6 
 
 315 
 
 599-0 
 
 232 
 
 449-6 
 
 260 
 
 500-0 
 
 288 
 
 650-4 
 
 316 
 
 600-8 
 
 233 
 
 451-4 
 
 261 
 
 501-8 
 
 289 
 
 652-2 
 
 317 
 
 602-6 
 
 234 
 
 453-2 
 
 262 
 
 503-6 
 
 290 
 
 654-0 
 
 318 
 
 604-4 
 
 285 
 
 455-0 
 
 263 
 
 605-4 
 
 291 
 
 655-8 
 
 319 
 
 606-2 
 
 236 
 
 466-8 
 
 264 
 
 607-2 
 
 292 
 
 557-6 
 
 320 
 
 608-0 
 
 237 
 
 458-6 
 
 265 
 
 609-0 
 
 293 
 
 669-4 
 
 
 
xlii 
 
 THE JIEIKICAI SYSTEM. 
 
 m 
 
 -W 
 o 
 
 o 
 
 CO 
 
 H 
 
 h-t 
 
 O 
 
 P 
 
 <! 
 
 o 
 
 o 
 
 CO 
 
 < 
 
 a 
 
 f^ 
 o 
 
 o 
 
 hH 
 CO 
 
 W 
 
 o 
 o 
 
 o 
 
 B 
 
 <l 
 
 :i S..2 ^ 
 .2 t, "^ 
 
 ^ O fH 
 
 OJ ^ r-H 
 
 m g » 
 
 •SP " =3 
 
 O "H C3 
 
 - § -a -if 
 •s ^ .g 
 
 « ^ g 
 
 ;3 ffi o 
 2 .a 
 28 
 
 bp 54-1 
 
 ■S ^ o 
 *^ t3 to 
 
 X g ci 
 
 t^ • rH CD 
 
 ■I-. cj> 
 
 ^ ^^ I 
 
 r— < P a> 
 
 g a ,a • r3 
 
 •I " "-^l 
 
 a> .S a =^ 
 
 ^ ^1 S 
 
 ^.S §^ 
 o o 53 
 
 01 
 
 -5l( 
 
 I-H 
 
 05 . 
 
 a 
 
 I-H 
 1—1 
 
 
 do 
 
 
 
 
 TO 
 
 
 
 
 rH 
 
 
 60 
 
 00 
 
 00 
 CD 
 
 00 
 
 1 
 
 
 CO 
 
 
 ^ 
 
 
 c<t 
 
 
 1— 1 
 
 
 I— 1 
 
 
 TO 
 
 I> 
 
 Si 
 
 3 
 
 t- 
 
 CI 
 
 
 do 
 
 
 lO 
 
 
 
 
 
 IV 
 
 
 r-H 
 
 
 CT 
 
 
 
 
 ^ 
 
 
 CO 
 
 
 t- 
 
 
 l^ 
 
 
 -^( 
 
 
 
 
 <M 
 
 
 
 
 CO 
 
 CM 
 
 
 
 
 CD 
 CO 
 
 
 
 
 
 
 
 
 a 
 
 
 CO 
 
 
 on 
 
 
 t^ 
 
 
 1C> 
 
 
 
 i-H 
 
 
 
 
 
 1> 
 
 
 rH 
 
 
 
 
 
 
 
 -f( 
 
 
 I— 1 
 
 
 00 
 
 
 00 
 
 
 CO 
 
 
 00 
 
 -* 
 
 b- 
 
 'di 
 
 ^ 
 
 
 CO 
 
 
 
 
 
 
 t~ 
 
 
 
 
 CO 
 
 
 
 
 (M 
 
 
 
 
 I— t 
 
 n 
 
 
 CO 
 
 I— 1 
 
 
 ^ 
 
 
 CO 
 rH 
 
 (M 
 
 1 
 
 CT 
 
 CO 
 I— 1 
 
 
 6 
 
 
 CO 
 
 
 CO 
 
 
 l^ 
 
 
 
 
 
 ~<S 
 
 r-H 
 
 ■^ 
 
 i-H 
 
 co 
 
 
 lb 
 
 
 Oi 
 
 
 rH 
 
 
 CO 
 
 § 
 
 
 g 
 
 
 g 
 
 '3 
 
 
 
 CD 
 
 g 
 
 ,::3 
 
 PI 
 
 1— 1 
 
 
 
 
 ^ 
 
 
 
 
 
 'a 
 
 (D 
 
 
 .1 
 
 p^ 
 
 
 
 
 
 
 
 
 
 
 
 
 t 
 
 •^ 
 
 "* 
 
 " 
 
 
 
 
 JLO 
 
 
 C^ 
 
 
 Q 
 
 S 
 
 l^ 
 
 Q 
 
 1^ 
 
 i-H 
 
 J^ 
 
 CO 
 
 
 t^ 
 
 
 b- 
 
 ^ 
 
 T^ 
 
 (M 
 
 <N 
 
 I- 
 
 »o 
 
 
 
 
 
 II II II 
 
 
 
 
 
 
 a CO 
 
 
 
 
 
 
 ^-73 
 
 
 
 
 
 
 ffl a 
 
 
 
 
 
 
 a .tJ 
 
 
 
 
 
 
 5; a 
 
 
 
 
 
 
 Sf 
 
 
 
 
 
 
 ?^ 
 
 OT 
 
 
 
 
 
 
 
 
 &. 
 
 
 s 
 
 Sa 
 
 'd 
 
 
 3 
 
 
 ^■-;; 
 
 1 
 
 1 
 
 1 
 
 
 
 
 r^ CD 
 
 a 
 O 
 
 id CT< Ph 
 
 1 
 
 r; 
 
 R 
 
 
 :: 
 
 S 
 
 
 
 
 
 
 
 I-) 
 
 C3 
 
 01 
 
 t— 
 
 CD 
 
 CO 
 
 CO 
 
 
 
 r^ 
 
 iH 
 
 
 CO 
 
 CO 
 
 r^ 
 
 r~^ 
 
 
 
 
 I-H 
 
 
 
 
 
 
 CO 
 
 CO 
 
 
 
 
 
 <N 
 
 00 
 
 t^ 
 
 10 
 
 T—t 
 
 
 
 
 
 
 
 rH 
 
 a 
 O 
 
INDEX. 
 
 j(*jf Compound names are to be found under the first, word of the name — 
 chloride of sodium, for example, under chloride, sulphuric acid under sul- 
 pliurio. Occ. stands for occurrence, prep, for preparation, prop, for pro- 
 perties, comp. for composition. The numbers refer to pages. The Eoman 
 numerals refer to the Appendix. 
 
 Acetate of aluminum, 518. 
 
 lead, 499. 
 Acetates of copper, 569. 
 Acetic acid, prep, from wood, 298. 
 Acid, jneanings of the term, 53, 191, 
 
 451. 
 Acids, monobasic, bibasic, &c., 191. 
 Affinity, use of the term, 101. 
 Air, comp. of, 6-10. 
 not an element, 10. 
 displacing of, 5. 
 a mixture, 67- 
 physical prop, of, 6. 
 presence of, 4. 
 quantity necessary for complete 
 
 combustion, 361. 
 reaction with nitric oxide, 59, 67. 
 weight of, 5. 
 Alabaster, 476. 
 Alcohol, from the fermentation of 
 
 sugar, 328. 
 Alcohol-lamp flame, 347. 
 Altalies, the caustic, 4(12, 416, 418. 
 
 definition of, 53. 
 Alkalimetry, 419. 
 Alkahnetearths, 489. 
 Alkaline reaction, 53. 
 Alkaloids, organic, absorbed by char- 
 coal, 308. 
 Allotropism, 139. 
 Alum, 517. 
 
 in bread, 399. 
 ammonium, 518. 
 Alum-cake, 517. 
 . Alumina, 514. 
 Aluminates of tlie alkalies, 515. 
 
 Aluminum, abundance of, 512. 
 alloys of, 513. 
 bronze, 513. 
 prop, of, 512. 
 Alums, atomic volumes of, 500. 
 
 class of, 529. 
 Amalgam of ammonium, 437. 
 gold, 588, 500. 
 sodium, 94. 
 . tin, 577. 
 Amalgams, 576. 
 Ammonia, analysis of, 77. 
 comp. of, 81. 
 electrolysis of, 78. 
 occ. of, 83. 
 
 physical prop, of, 76, 77. 
 prep, of, 75. 
 solubility in water, 76. 
 sources of, 84. 
 synthesis of, 79. 
 Ammoniacal liquor of gas-works, 84. 
 Ammonia- water precipitates metallic 
 oxides, 439. 
 prep, of, 84. 
 uses of, 84. 
 Ammonium, 82. 
 
 amalgam, 437. 
 the supposed metal , 437. 
 Ammonium-salts, prop, of, 438. 
 test for, 594. 
 Analysis,' definition of, 3. 
 qualitative, 419. 
 
 a method of se- 
 parating Ca, 
 Sr, and Ba, 
 526. 
 
xliv 
 
 INBEX. 
 
 Analysis of organic compounds, 566. 
 
 volumetric, 420. 
 Animal charcoal, decolorizing power 
 
 of, 309. 
 Animals and plants, reciprocal ac- 
 tion of, 330. 
 Annealing, 412. 
 Anthracite, 293, 294. 
 
 conducts heat, 294. 
 getting flame &om, 360. 
 Antimoniate of antimony, 273. 
 Antimoniates, 275. 
 Antimonio acid, 274. 
 Antimoniuretted hydrogen, 269. 
 Antimony, aUoys, 268. 
 
 alloys ■with zinc, 269. 
 amorphous, 268. 
 bloom, 272. 
 
 distinguished from arse- 
 nic, 270. 
 extraction of, 266. 
 glance, 277. 
 mirrors, 270. 
 occ. of, 266. 
 prop, of, 267. 
 the commercial metal, 
 
 267. 
 vermilion, 279. 
 Antozone, 139, 147. 
 
 distinguished from ozone, 
 
 153. 
 fogs and smokes, 149, 151. 
 makes air hard to dry, 150. 
 oridizes water, 152. 
 prep, of, 148. 
 Antozonides, 153. 
 Aqua regia, 104. 
 Argand burner, 345, 346. 
 Arragonite and calc-spar compared, 
 
 469. 
 Arseniates, isomorphous with phos- 
 phates, 252. 
 Arsenic, detection of the poison, 252. 
 determination of its atomic 
 
 weight, 262. 
 distinguished from anti- 
 mony, 270. 
 eating, 250. 
 extraction of, 241. 
 greens, 260. 
 mirrors, 260. 
 occ. of, 241. 
 prop, of, 242. 
 imit-volume weight, 242. 
 
 Arsenic acid, hydrates of, 251. 
 prep, of, 250. 
 reduction of, 252. 
 salts of, 252. 
 uses of, 252. 
 Arsenical pyrites, 241. 
 Arsenious acid, antidote for, 250. 
 a poison, 250. 
 reduction of, 248. 
 solubiUty of, 249. 
 sources of, 246. 
 two varieties of, 246. 
 uses of, 250. 
 Arseniuretted hydrogen, analysis of, 
 245. 
 decomposed 
 by heat, 260. 
 prep, of, 243. 
 prop, of, 244. 
 Asbestos, platinized, 193. 
 Atom, definition of, 29. 
 Atomic heats of compounds, 601. 
 
 elements, 599. 
 Atomic volume, 201. 
 Atomic weight, analogy a guide in 
 
 determining, 614. 
 Atomic weights, defl nition of, 31. 
 
 mutual comparison 
 
 of, 462. 
 practical use of, 100. 
 table of, 597. 
 two sets in use, 603. 
 value of, 64. 
 Atomicity of the elements, 465. 
 
 Barium, 486. 
 
 compounds, 486-488. 
 flame, 489. 
 Barytes, 487, 488. 
 Beakers, xxviii. 
 BeU-metal, 564. 
 Bessemer steel, 541. 
 Biatomic metals, 73. 
 Bibasic acids, defined, 191. 
 Biborate of sodium, 408. 
 Bicarbonate of ammonium, 442. 
 potassium, 416. 
 sodium, 398. 
 Bichloride of platinum, 593. 
 
 tin, 584. 
 Bichromate of potassium, 523. 
 
 , use in 
 photolithography ,526. 
 Binoxide of manganese, uses of, 530. 
 
INDEX. 
 
 xlv 
 
 Binoxida of tin, 581. 
 Bismuth, extraction of, 281. 
 
 makes fusible alloys, 282. 
 prop, of, 281. 
 salts, 283. 
 Bismuthio add, 283. 
 Biaulphate of potassium, 428. 
 Bisulphide of carbon, 363. 
 
 and nitric oxide, 
 364. 
 Bisulphide of iron, 549. 
 Bisulphite of calcium, checks fermen- 
 tation, 486. 
 Bivalent metals, 73. 
 Blaek.ball, 397- 
 Black-lead, 290. 
 Blast furnace, iron, working of, 535- 
 
 538. 
 Bleaching by chloride of lime, 483. 
 chlorine, 112. 
 ozone, 143. 
 sulphurous acid, 180. 
 Bleaching-powder, 482. 
 Blistered steel, 541. 
 Bloom, 535, 
 Bloomary, 535. 
 Blowers, viii. 
 
 Blowpipe with gas and air, 350. 
 Blowpipe, Bunsen's gas-, viii. 
 mouth-, 351. 
 oxidizing iiame of, 352. 
 oxyhydrogen, 46. 
 reducing flame of, 353. 
 Boiler-scale, 468, 479. 
 Bone-ash, 214. 
 ■Bone-black, prep, of, 310. 
 Bone-phosphate of calcium, 481. 
 Bones, distillation of, 84, 310. 
 Boraoio acid, comp. of, 367. 
 
 extraction of, 365. 
 prop, of, 368. . 
 strong at high 
 temperatures, 369. 
 Borax, as a blowpipe-test, 409. 
 two forms of, 408. 
 uses of, 409. 
 Boron, allotropic states of, 366. 
 occ. of, 365. 
 
 resemblance to carbon and 
 silicon, 372. 
 Brass, 564. 
 
 Bread, raising with chemicals, 399. 
 Breaking up stones, xxxiv. 
 Britannia metal, 268. 
 Bromhydric acid, 120. 
 
 Bromic acid, 122. 
 
 Bromide of ammonium, used in 
 photography, 457. 
 arsenic, 263. 
 cadmium; used in pho- 
 tography, 457. 
 nitrogen, 123. 
 
 potassium, 425. 
 silicon, 386. 
 silver, 463. 
 sodium, 394. 
 Bromides, formation of, 120. 
 of iodine, 133. 
 phosphorus, 240. 
 Bromine, mother-liquors of salt- 
 works, a source of, 393. 
 occ. of, 119. 
 prop, of, 119. 
 uses of, 120. 
 Bronze, 564. 
 Bronze-powder, 582. 
 'Bulbs, blowing, v. 
 Bunsen's burner, 344, vi. 
 Burettes, xxix. 
 
 how to fiU, xxxi. 
 read, xxx. 
 
 Cadmium, extraction of, 509. 
 
 makes fusible alloys, 510. 
 prop, of, 510. 
 imit-volume weight half 
 its atomic weight, 510. 
 Caesium, 446. 
 
 Calcareous waters, 468, 479. 
 Calcined magnesia, 502. 
 Calcium-flame, 489. 
 light, 47. 
 the metal, 486. 
 Calo-spar and arragonite compared, 
 
 469. 
 Calomel, 573. 
 Caudle-flames, 349. 
 Candles are gas-burners, 347. 
 Caoutchouc in sheets, xi. 
 stoppers, xi. 
 tubing, X. 
 Carbon, aUotropio modifications of, 
 288. 
 atomic weight of, 317. 
 its atom hypothetical, 318. 
 compounds with nitrogen, 
 
 363. 
 dimorphous, 292. 
 for galvanic batteries, 293. 
 occ. of, 287. 
 
xlvi 
 
 INDEX. 
 
 Carbon, vapor-density hvpothetioal, 
 
 316. 
 Carbonate of ammoniuni,commercial, 
 441. 
 calcium, dissolves in wa- 
 ter containing 
 carbonic acid, 467. 
 dissolves in 
 ammonium- 
 salts, 468. 
 occ. of, 467. 
 lead, 499. 
 magnesium, CO-1. 
 potassium, prop, of, 415. 
 pure, source 
 
 of, 424. 
 uses of, 416. 
 and hydro- 
 gen, 416. 
 sodium, sources and 
 uses, 396. 
 and hydrogen, 39S. 
 Carbonates, 334. 
 
 alkaline, impurities of, 
 419. 
 Carbonic acid, 321. 
 
 absorbents for, 324. 
 comp. of, 333. 
 decomposed by 
 carbon, 335. 
 potassium, 332. 
 dissociation of, 331. 
 formed in combustion , 
 321. 
 fermentation ,328. 
 respiration, 328. 
 generator, 323. 
 liquid, 330. 
 obtained from carbo- 
 nates, 322. 
 occ. of, 327. 
 prop, of, 323. 
 solid, 330. 
 solubiHty of, 326. 
 sources of, in the air, 
 
 329. 
 synthesis of, 333. 
 test for, 321. 
 Carbonic oxide, comp. of, 341. 
 
 dissociation of, 340. 
 economy in burning 
 
 it, 361. 
 heating value of,339, 
 
 361. 
 a poison, 338. 
 
 Carbonic oxide, prep, of, 33o. 
 prop, of, 338. 
 a reducing agent, 
 339. 
 Carburetted hydrogen, decomposed 
 
 by heat, 344. 
 Carmine-lake, 516. 
 Cast iron, impurities of, 539. 
 
 varieties of, 538. 
 Caustic alkalies, strong bases, 418. 
 Caustic potash, 417. 
 soda, 403. 
 
 advantageous use of, 
 405. 
 Cement copper, 563. 
 Cement, Roman, 521. 
 Cerium, 561. 
 Chalk, .323, 467. 
 Ciameleon-mineral, 532. 
 Charcoal absorbs gases, 303. 
 
 different gases in 
 different propor- 
 tions, 305. 
 Kiuses combination of gases, 
 
 306. 
 a disinfectant, 307. 
 hot, decomposes steam, 301. 
 physical prop, of, 300. 
 prep, of, 296, 297. 
 a reducing agent, 301. 
 removes colors, 308. 
 satbility of, 302. 
 Chemical changes, 2. 
 
 combination, 32. 
 
 and solution 
 compared,38. 
 force, 32. 
 strength, 418. 
 Chemistry, subject-matter of, 1. 
 Chili-sall^etre, 51. 
 Chimneys create draughts, 355. 
 
 on fire, how to put out, 
 
 178. 
 use of, 354. 
 Chlorate of potassium, an ingredient 
 of explosive 
 mixtures, 
 435. 
 prep, of, 434, 
 435. 
 Chloraurates, 590. 
 Chlorhydrio acid, 40. 
 
 analysis of, 92. 
 comp. of, 96. 
 electrolysis of, 94. 
 
IXDES. 
 
 xlyii 
 
 Clilorliydric acid gaa, prep, of^ 
 
 92. 
 Chlorhydric acid, prep, of, 102. 
 prop, of, 92. 
 synthesis of, 98. 
 uses of, 103. 
 Chloric acid, 117. 
 Chloride, definition of term, 109. 
 of aluminum, 516. 
 ammonium, 86. 
 
 dissociation 
 
 of, 239. 
 prep, of, 
 
 114. 
 sources of, 
 
 439. 
 uses of, 440. 
 arsenic, 262. 
 boron, 369. 
 bromine, 123. 
 ealciimi, 482. 
 
 used for dry- 
 ing gases, 
 482. 
 tube, xny. 
 carbon, 362. 
 gold, used in photogra- 
 phy, 457, 459. 
 lead, 498. 
 lime, 482. 
 magnesium, 503. 
 nitrogen, 114. 
 potassiimi, 424. 
 silicon, decomposed by 
 water, 384. 
 prep, of, 383. 
 sUyer, effect of light on, 
 456. 
 occ. of, 460. 
 reduction of, 
 
 461. 
 solyents for, 456. 
 sodium, 392. 
 
 solubility of, 
 393. 
 sulphvir, 197. 
 zinc, 508. 
 
 a disinfectant, 509. 
 Chlorides of antimony, 275. 
 
 terchloride, 
 
 275. 
 quinquichlo- 
 ride, 276. 
 ehropiium, 52.3. 
 
 Chlorides of gold, 589, 590. 
 iodine, 132. 
 iron, 550. 
 mercury, 573, 574. 
 phosphorus, 236. 
 
 terchloride, 
 
 236. 
 quinquichlo- 
 ride,237. 
 platinum, 593. 
 selenium, 201. 
 tin, 583. 
 Chlorimetry, 485. 
 Chlorine, action on ammonia, 113. 
 atomic weight of, 97. 
 bleaches, 112. 
 bums in hydrogen, 110. 
 combustion in, 110. 
 decomposes water. 111. 
 disinfects, 113. 
 eiplosive mixture with hy- 
 drogen, 108. 
 occ. of, 106. 
 oxidizing action of, 112. 
 physical prop, of, 107. 
 prep, of, 105, 106. 
 prep, from bleaching-pow- 
 
 der, 483. 
 prep, with bichromate of 
 
 potas.sium, 525. 
 unites with metals, 109. 
 -water, 107. 
 Chloroform, formula, of, 319. 
 Chloroplatinates, 596^ 
 Chlorous acid, 117. 
 Chromates, 526. 
 Chrome-alum, 524. 
 -green, 523. 
 -iron ore, 522. 
 -yellow, 527. 
 Chromic acid, 525. 
 Chromium, occ. of, 522. 
 Cinnabar, 570. 
 Citrate .of magnesium, 504. 
 Classification, 598. 
 Clay, 519. 
 Cleavage, 157. 
 Coal, bituminous, 294, 
 distillation of, 293. 
 Tarieties of, 293, 294. 
 Coal-gas, comp. of, 320. 
 
 purification of, 473, 546. 
 Coal-tar, 312. 
 Cobalt, 550. 
 
xlviii 
 
 INDEX. 
 
 Cochineal, tincture, preparation of, 
 
 421. 
 Coke, 293, 294. 
 
 conducts heat, 294. 
 Cold, greatest artificial, 67. 
 Collodion, 457. 
 CoUoids, 255. 
 Columbium, 585. 
 Combination hj Tolume, 203. 
 Combining weights of compounds, 
 71. 
 of organic com- 
 pounds, de- 
 termination 
 of, 596. 
 and unit-TO- 
 lume weights 
 
 205, 206. 
 Combustion, definition of, 15. 
 
 ordinary, 342-362. 
 spontaneous, 229. 
 Compound radicals, 363. 
 Condensation-ratios, 205. 
 Condenser, 34, 35. 
 Cooling flames by good conductors, 
 
 358. 
 Copper, alloys of, 564. 
 
 extraction of, 562. 
 oco. of, 562. 
 prop, of, 563. 
 pyrites, 502. 
 Copperas, 551. 
 Cork-cutters or borers, xii. 
 Corks, xi. 
 
 Correlation of force, 507. 
 Corrosiye sublimate, 574. 
 
 antidote for, 575. 
 Cream of tartar, 424. 
 Crucibles, Beauiay, Hessian, plum- 
 bago, xxxiii. 
 porcelain, xxxii. 
 how to use, xxxiv. 
 material of, 520. 
 CryoHte, 391. 
 
 Crystalline form, a guaranty of 
 purity, 435. 
 structure, 157. 
 Crystallization, the chief means of 
 purification, 397, 
 434. 
 by fusion, 156. 
 six systems of, 158. 
 Crystalloids, 254. 
 
 Crystals, four methods of obtaining, 
 
 161. 
 Cupellation, 494. 
 Cyanhydric acid, 363. 
 Cyanide of potassium, formation of, 
 ^ 426. 
 
 in blast fur- 
 naces, 427. 
 uses of, 427. 
 iron, 555. 
 silver, 463. 
 Cyanogen, 363. 
 
 Daguerreotype, 456. 
 Decolorizing power of charcoal, 308- 
 
 311. 
 Deflagrating-spoon, xxi. 
 Deflagration, 302. 
 Deodorizing by charcoal, 306. 
 chlorine, 113. 
 Destruction of organic matter in casfes 
 
 of poisoning, 257. 
 Detection of arsenic, 252-262. 
 Developers, a term of photography, 
 
 458. 
 Devitrification, 413. 
 Dialysis, 254. 
 
 applied to defection of poi- 
 sons, 256. 
 Dialyzer, 255. 
 Diamond, 289. 
 Dichloride of copper, 667. 
 sulphur, 197. 
 Dichromate of lead, 527. 
 Didymium, 561. 
 Diffusion of carbonic acid, 325. 
 gases, 43, 326. 
 
 rapidity of, 325. 
 Dimorphous substance, defined, 159. 
 Dioxide of copper, 564. 
 
 mercury, 571. 
 Direct combination, 404. 
 Disinfectant, charcoal, 306. 
 
 chloride of zinc, 508. 
 chlorine, 112, 113. 
 hypochlorite of cal- 
 cium, 482. 
 ozone, 144. 
 
 permanganate of potas- 
 sium, 533. 
 sulphurous acid, 181. 
 Displacement, collection of gases by, 
 
 Dissociation, 238. 
 
INDEX, 
 
 xlii 
 
 Distillation, the process of, 34. 
 Dolomite, 503. 
 Drying-apparatus, xsiii. 
 gases, xxii. 
 
 substances used for, 
 xxiii. 
 plastering, 475. 
 Dualistic formula), 87. 
 
 Earthenware, 520. 
 Effervescing liquids, 327. 
 Electrolysis of ammonia, 78. 
 
 ohlorhydric acid, 94. 
 marsh-gas, 317. 
 water, 24. 
 Electro-metallurgy, 568. 
 
 batteries, 507. 
 silTer-plating, 
 
 463. 
 use of graphite, 
 290. 
 Electro-plating, 463, 568, 590. 
 Element, definition of, 3. 
 Elements are bodies incapable of de- 
 composition, 33. 
 Empirical formulae, 86. 
 Epsom salts, 503. 
 Equations, chemical, 90. 
 Erbium, 561. 
 
 Erdmann's swimmer, xxxi. 
 Etching glass, 138. 
 Evaporating-dishes, xxxii. 
 Explosion of oxygen and hydrogen, 
 
 48. 
 Explosions in coal-mines, 314. 
 
 Feldspar, 375, 519. 
 Fermentation, 328. 
 Ferric chloride, 550. 
 
 hydrate, used in purifying 
 
 gas, 646. 
 nitrate, 554. 
 oxide, 543. 
 
 corrodes organic mat- 
 ter, 544. 
 
 reduction of, 644. 
 salts, 647. 
 sulphate, 564. 
 Ferricyanide of potassium, 555. 
 Ferrocyanide of potassium, 427. 
 Ferrous chloride, 660. 
 nitrate, 554. 
 oxide, 643. 
 salts,changedintoferrio,566. 
 
 Ferrous sulphate, 551. 
 
 dyeing black with, 653. 
 sulphide, prep, of, 547-549. 
 Filtering, xxii. 
 Filters, how to fold, xxii. 
 Filtrate, definition of, xxii. 
 Fire-brick, 620. 
 Firedamp, 314. 
 Fireworks, a green color, 488. 
 purple, 436. 
 red, 488. 
 white, 263. 
 Flame, dissection of, 348-350. 
 intensity, 346. 
 luminosity of, 343. 
 oxidizing, 352. 
 put out by good conductors, 
 
 357-369. 
 quantity, 346. 
 reducing, 363. 
 structure of, 48, 348-350. 
 Flaming fires, 360. 
 Flasks, xxyiii. 
 Florence flasks, xxviii. 
 Fluoboric acid, 371. 
 Fluorhydric acid, 136. 
 
 • action on silica, 
 137. 
 Fluoride of boron, 370. 
 calcium, 136. 
 silicon, its reaction with 
 
 water, 388. 
 prep, of, 386. 
 Tolumetriocomp. of, 387. 
 Fluorine, 135. 
 
 hard to get and keep, 136. 
 occ. of, 136. 
 Fluosilicates, 389. 
 FluosUicic acid, prep, of, 388. 
 
 a reagent for potas- 
 sium salts, 390. 
 a use of, 118. 
 Flux, used in smelting iron-ores, 636. 
 Fluxes — alkaline carbonates, 415. 
 borax, 409. 
 
 cyanide of potassium, 427. 
 limestone, 536. 
 sulphate of potassium and 
 
 hydrogen, 428. 
 
 tartar, ignited, 424. 
 
 Formula, empirical and rational, 86. 
 
 molecular, 208. 
 Foundry-facings, 291. 
 Free gases exist as molecules, 208. 
 
Freezing-apparatus, 77. 
 
 mixtures, see Befrigerating. 
 Priotion- matches, 211. 
 Pulmiuating-silver, 455. 
 Fusible alloys, 510. 
 Furnaces, xxxt. 
 
 Galbsa, 490, 497. 
 Galyanio current, 506. 
 Gas, illuminating, 293, 297, 320. 
 Gas-burners, 346. 
 -carbon, 292. 
 
 -generator, self-regulating, xxvi. 
 -holders, xviii. 
 -lampa for "heating, 344. 
 Gay-Lussao's burette, xxx. 
 German silver, 557, 564. 
 Gilding, 590. 
 Glass of antimony, 277. 
 Glass, colored, 413. 
 comp. of, 412. 
 etching of, 138. 
 not insoluble, 411. 
 varieties of, 412. 
 Q-hss beakers, xxviii. 
 
 cutting and cracking of, i. 
 
 , xxvm. 
 retorla, xxviii. 
 
 tubing, bending, drawing and 
 closing, iii.-v. 
 heating of, iii. 
 sizes and qualities of, i. 
 Glauber's salt, 395. 
 
 solubility of, 395. 
 supersaturated solu- 
 tion of, 396. 
 Glazes — ^lead, feldspar, salt, 520. 
 Gluoinum, 522. 
 Gold, .alloys of, 591. 
 coin, 591. 
 oco. of, 587. 
 prop, of, 588. 
 salts, 590. 
 
 separation from siLver alloys, 
 464. 
 
 silver and 
 copper, 589. 
 solution of, 689. 
 Golden sulphide of antimony, 279. 
 Graduation, 392. 
 
 Grainme, definition of, 19, xxxviii. 
 Graphite, .290. 
 
 artiacial, 292. 
 in cast iron, .53.?. 
 
 Graphite, use in eloctro-metallargy, 
 
 290. 
 Graphitic acdd, 292. 
 Graphon, 292. 
 Gray iron, 538. 
 Green vitriol, 551. 
 Grey antimony, 277. 
 Group, the alkali, 464. 
 
 calcium, 489. 
 
 carbon, 390. 
 
 chlorine, 133. 
 
 magnesium, 511. 
 
 nitrogen, 285. 
 
 platinum, 596. 
 
 sesquioxide, 560. 
 
 sulphur, 202. 
 
 tin, 585. 
 Groups, principles concerning, 135. 
 
 table of, 598. 
 Gun-metal, 564. 
 Gunpowder, comp. of, 432. 
 
 manufactm-e of, 433. 
 products of combustion 
 of, 432. 
 Gypsum, 470. 
 
 Hard water, 468, 479. 
 Hartshorn, 84. 
 
 Heat, relation to chemical force, 
 418. 
 unit of, 45. 
 Homologous series, 313. 
 Hydrate of aluminum, 514. 
 
 calcium, 472. 
 
 copper, 566. 
 
 iron, 545. 
 
 potassium, 416. 
 
 sodium, prep, of, 402. 
 type of bases, 403. 
 Hydraulic cement, 504, 521. 
 Hydrocarbons, 312. 
 Hydrogen, chemical eifect of, 129. 
 
 derived from water, 22. 
 
 diffusive power of, 43, 44. 
 
 explosive mixture with 
 oxygen, 48, 49. 
 
 heating power of, 45. 
 
 inflammable, 44. 
 
 lightness of, 42. 
 
 peroxide of, 50, 51. 
 
 physical prop, of, 41. 
 
 precautions in making, 
 40, 
 
 prep, of, 39. 
 
Hydrogen, standard of specific gra- 
 vity for gases, 41. 
 
 Hypobromous acid, 122. 
 
 Hypoehloric acid, 117. 
 
 Hypochlorite of calcium, 482. 
 
 Hypochlorous acid, 116. 
 
 Hyponitric acid, comp. of, 61. 
 prep, of, 62. 
 prop, of, 62. 
 
 Hypophospliites, 228. 
 
 Hypophosphorous acid, 227. 
 
 Hyposulphite of sodium, prep, of, 
 414. 
 use in pho- 
 tography, 413, 456. 
 
 Hyposulphites, 196. 
 
 Hyposulphurous acid, 196. 
 
 Ice, crystals of, 21. 
 
 lighter than water, 21. 
 Ignition-tube, definition of, 8. 
 
 manner of using, 8,11. 
 Illuminating gas, 293. 
 
 description of, 320. 
 manufacture of, 
 
 297. 
 purification of,473, 
 546. 
 Incrustations in boilers, 468, 479. 
 Indelible ink, 453. 
 Indestructibility of matter, 356. 
 Indian fire, 263. 
 Ink, 553. 
 
 indelible, 453. 
 Intensity flames, 346. 
 Iodic acid. 130 
 Iodide of arsenic, 263. 
 lead, 499. 
 nitrogen, 131. 
 potessium, 425. 
 silver, 463. 
 sodium, 394. 
 Iodides of phosphorus, 240. 
 Iodine, extraction of, 124. 
 
 manufacture of, 132. 
 occ. of, 123. 
 prop, of, 124. 
 reaction with starch, 126. 
 testing for, 126. 
 uses of, 125. 
 lodohydric acid, prep, of, 128. 
 
 prop, of, 128, 129. 
 Ipdo-starch paper, 127. 
 Iridium, 596. 
 
 Iron, oast, impurities of, 539. 
 varieties of, 538. 
 extraction of, 535. 
 galvanized, 506. 
 mordant, 555. 
 ooc. of, 534. 
 
 ores — brown, clay, red hffi- 
 matite, magnetic, spathic, 
 specular, 534. 
 puddling of, 539. 
 pyrites, 549. 
 replaces copper, 551. 
 wrought, 5,39. 
 Iron retort, xxvi. 
 Iron stand for supporting vessels, 
 
 xiii. 
 I.somerism, 247. 
 Isomorphism, 200. 
 
 Kaolin, 519. 
 
 Kelp, 124. 
 
 Kermes mineral, 279. 
 
 Kindling-temperature, 357. 
 
 Lakes, 516. 
 Lampblack, 295. 
 
 manufacture of, 298. 
 Lamp-flames are gas-flames, 347. 
 Lamps for laboratory use, vi-viii. 
 Lanthanum, 561. 
 Laughing-gas, 57. 
 Lavoisier, his analysis of air, 9. 
 Lead, action of acids on, 491. 
 water on, 492. 
 classed with the calcium group, 
 
 500. 
 crystallization of, 491. 
 extraction of, 490. 
 forms basic salts, 495. 
 metallic, prop, of, 490. 
 testing for, 497. 
 tree, 507. 
 
 use of, for water-pipes and cis- 
 terns, 493. 
 Leblanc's process, 397. 
 
 wastefulness of ,400. 
 Light, action of, on silver salts, 458. 
 bichromate of po- 
 tassium, 526. 
 Light carburetted hydrogen, 313. 
 Lime, air-slaked, 471. 
 
 the cheapest base, 476. 
 heat evolved in slaking, 472. 
 milk or cream of, 472. 
 ■2v 
 
lii 
 
 Lime, slaked, absorbs carbonic and 
 sulphydric acids, 473. 
 uses of, 476. 
 
 Limestone, 467. 
 
 Litharge, 494. 
 
 Lithium-flame, 444. 
 oco. of, 443. 
 
 resembles sodium and po- 
 tassium, 443. 
 
 Litmus-paper, 53. 
 
 tincture, prep, of, 420. 
 
 Liver of sulphur, 428. 
 
 Luminosity of flames, 343. 
 
 Luminous flames, form of, 3.50. 
 
 Lunar caustic, 453. 
 
 Magnesia alba, 504. 
 
 crucibles, 503. 
 hydraulic, 302. 
 Slagnesite, 503. 
 Magnesium light, 501. 
 
 the metal, prop, of, 501. 
 occ. of, 501. 
 
 salts.from mother-liquor 
 of salt-works, 393. 
 Manganate of potassium, 531. 
 Manganates, 531. 
 Manganese, oco. of, .">27. 
 Manganese-alum, 529. 
 Manganic acid, 531 . 
 Marsh-gas, 313. 
 
 analysis of, 316. 
 prep, of, 314. 
 two vols, yield four vols, 
 of hydrogen, 315. 
 Marsh's test for arsenic, 259. 
 Matches, 211, 219. 
 Matter, indestructibility of, 355. 
 Measuring-glasses, xnx. 
 Mercuric chloride, 574. 
 
 an antiseptic, 575. 
 forms double chlo- 
 rine salts, 575. 
 iodide, changes of color of, 
 
 575. 
 oxide, 572. 
 
 as a source of oxygen, 
 572. ^^ 
 
 Mercurous chloride, 573. 
 
 oxide, .571. 
 Mercury, alloys of, 576. 
 
 detection of, 577. 
 extraction of, 570. 
 pneumatic trough, xvi. 
 
 Mercury, tendency to form double 
 compounds, 573. 
 
 unit-volume weight half its 
 atomic weight, 570. 
 
 uses of, 571. 
 Metal, meaning of the term, 451. 
 Metantimoniates, 275. 
 Metantimonio acid, 274. 
 Metaphosphate of silver, 407. 
 
 sodium, 407. 
 Metaphosphoric acid, 233. 
 Metastannic acid, 581. 
 Meteoric iron, 534. 
 Metre, definition of, xxxvi. 
 Metrical system of weights and mea- 
 sures, xxxvi. 
 Mica, 376. 
 
 Microcosmic salt, 407. 
 5V[inium, 496. 
 Mohr's burette, xxx. 
 Molecular condition of elementary 
 gases, 207. 
 hypothesis, 30. 
 Molecule, definition of, 29. 
 Molybdate of ammonium, 586. 
 Molybdenum, 585. 
 Monoatomio metals, 73. 
 Mordant, use of, 519. 
 Mordants, 516. 
 Mortar, 474. 
 Mortars, xxxiv. 
 Mosaic gold, 582. 
 Multiple proportions, law of, 66. 
 Muriatic acid, 40, 91. 
 
 manufacture of, 99. 
 
 Nascent state, 80. 
 Neutralization, 54. 
 Nickel, 556. 
 Nitrate of ammonium, 441. 
 
 prep, of, .53. 
 calcium, 485^ 
 copper, 569. 
 lead, decomposition of, 62. 
 
 made, 61, 62. 
 potassium, ooc. of, 429. 
 
 prop, of, 430. 
 silver. 453. 
 
 stains of, removed. 
 426, 427. 
 sodium, 392. 
 Nitrates of iron, 554, 
 
 mercury, 576. 
 Nitre, 429. 
 
im 
 
 Nitre-paper, 354, 432. 
 Nitric acid, analysis of, 63. 
 
 anhydrous, 69, 70. 
 
 prep, of, 460. 
 combining weight of, 73. 
 monohydrated, 70. 
 prep, of, 62. 
 sources of, 51. 
 uses of, 71. 
 Nitric oxide, analysis of, 60. 
 prep, of, 58. 
 a test for free oxygen, 
 59, 60. 
 Nitride of boron, 371. 
 Nitrogen, a constituent of air, 10. 
 
 dilutes the oxygen in air, 
 
 obtained from air, 16. 
 physical prop, of, 17. 
 prep, by copper, 16. 
 
 phosphorus, 17. 
 widely diffused, 18. 
 Nitrous acid, 63. 
 
 oxide, comp. of, 55, 56. 
 
 physical prop, of, 57. 
 prep, of, 54. 
 supports combustion, 
 58. 
 Nomenclature, prefixes derived from 
 Greek and Latin nu- 
 merals, 174. 
 the prefix hypo-, 61. 
 the termination ide, 
 
 174. 
 the terminations ous 
 and ie, 60. 
 Nordhausen acid, 192. 
 Norium, 561. 
 
 OcuKE, red, 543. 
 
 yellow, 543. 
 Oil-bath, xxvi. 
 Oil of vitriol, manufactiu-e of, 184^ 
 
 186. 
 Organic analysis, 566. 
 
 chemistry, defined, 312. 
 Orpiment, 263. 
 Osmium, 596. 
 
 Oxidation by platinum-black, fiO."!. 
 Oxide of aluminum, 514. 
 
 calcium, 470. 
 
 magnesium, 502. 
 
 silicon, 375. 
 
 silver, a strong biiM.*, 45.3. 
 
 Oxide of zinc, 508. 
 Oxides, definition of, 14. 
 of antimony, 272. 
 
 teroxide, 272. 
 quadroxide,273. 
 quinquioxide, 
 274. 
 arsenic, 245. 
 bismuth, 282. 
 
 teroxide, 282. 
 quinquioxide, 
 
 283. 
 chlorine, series of, 116. 
 chromium, 522. 
 cobalt, 557. 
 iron, 542. 
 lead, 492. 
 manganese, 527. 
 mercury, 571. 
 molybdenum, 585. 
 nickel, 557. 
 nitrogen, series of, 65. 
 platinum, 593. 
 silver, 455. 
 
 sulphur, series of, 175. 
 tiu, 580. 
 tungsten, 586. 
 uranium, 558. 
 Oxidizing agents, defined, 71 . 
 Oxychloride of bismuth, 284. 
 Oxygen, abvmdance and importance 
 of, 15. 
 burning charcoal in, 13. 
 iron in, 13. 
 phosphorus in, 13. 
 sulphur in, 13. 
 burns in hydrogen, 50. 
 a constituent of an", 9. 
 explosive mixture with hy- 
 drogen, 48, 49. 
 physical properties of, 12. 
 precautions in making, 11. 
 prepared from bichromate of 
 potassium, 
 525. 
 bleachiug-pow- 
 
 der, 484. 
 chlorate of po- 
 tassium, 11. 
 peroxide of ba- 
 rium, 487. 
 sulphuric acid, 
 196, 
 supports combustion, 13. 
 
liv 
 
 Oiyhydrogen blowpipe, 46. 
 Ozone, 139. 
 
 atmospheric, 145. 
 
 a disinfecting agent, 144. 
 
 distinguished from antozone, 
 
 153. 
 influence on liealth, 146. 
 prep, by electricity, 141 . 
 ether, 142. 
 permanganate of po- 
 tassium, 142. 
 phosphorus, 140. 
 prop, of, 143. 
 resembles chlorine, 143. 
 tests for. 143, 144. 
 Ozonides, 147. 
 
 Palladium, 696. 
 Paraiime-bath, xxvi. 
 Parchment paper, 25o. 
 Fearlash, 41.'5. 
 Pearl-white, 284. 
 Perchloric acid, 118. 
 Periodic acid, 131. 
 Permanganate of potassium, 532. 
 
 a disinfectant, 
 533. 
 Permanganates, 533. 
 Permanganic acid, 532. 
 Peroxide of barium, prep, of, 487. 
 
 hydrogen, prep, of, 152. 
 lead absorbs sulphurous 
 acid, 496. 
 an oxidizing agent, 
 
 495. 
 prep, of, 495. 
 Persulphide of hydrogen, 173. 
 Petrifactions, calcareous, 468. 
 
 siliceous, 378. 
 Pewter, 585. 
 
 Phosphate of magnesium and ammo- 
 nium, 504. 
 silver, 406. 
 
 sodium, ammonium,aud 
 hydrogen, 407. 
 Phosphates of calcium, 481. 
 sodium, 405. 
 
 rhombic, 405. 
 pyro-, 406. 
 meta-, 407. 
 varieties of, 234. 
 Phosphide of calcium, 221. 
 Phosphorescence. 212. 
 Phosphoric acid, anhydrous, 231. 
 
 Phosphoric acid, anhydrous, afiinity 
 of, for water, 232. 
 glacial, 232. 
 hydrates of, 232. 
 strength of, 235. 
 terbasic, 234. 
 Phosphorous acid, 228. 
 
 hydrated,229,231. 
 Phosphorus, allotropism of, 210. 
 
 burnt under water, 436. 
 combinations of, 219. 
 common, 212. 
 comparison of red with 
 
 common, 216. 
 compounds with hydro- 
 gen, 220. 
 inflammability of, 210. 
 manufacture of, 214. 
 occ. of, 209. 
 oxides of, 226. 
 poisonous, 214. 
 red, 216. 
 
 converted into eam- 
 
 mon, 216. 
 crystallized, 217. 
 oxide of, 226. 
 prep, of, 218. 
 used on 
 matches, 218. 
 shines in the dark, 212. 
 solutions of, 213. 
 unit-Toliune weight of, 
 224. 
 Phosphuretted hydrogen, analysis of, 
 223. 
 comp. of, 224. 
 liquid, 225. 
 prep, of, 220. 
 from 
 phosphide 
 of calcium, 
 221. 
 soUd, 226. 
 Photography, 456-460. 
 
 on glass, 457. 
 paper, 459. 
 Photolithography, 526. 
 Physical changes, 1. 
 Pincers, xxxiv. 
 Pink salt, 584. 
 Pipettes, xxxi. 
 
 Plants and animals, reciprocal ac- 
 tion of, .S.30. 
 Plaster of Paris, 477 
 
Iv 
 
 Plaster-casts, 477. 
 Plastering, comp. of, 475. 
 
 dampness of, 475. 
 Platinized asbestos, 193. 
 Platinum, alloys of, 592. 
 black, 595. 
 cleaning, rxii. 
 foil and wire, xii. 
 induces combination, 182, 
 
 193, 306, 593, 595. 
 melting of, 353. 
 metals, 596. 
 occ. of, 591. 
 prop, of, 592. 
 sponge, prep, of, 694. 
 uses of, 593. 
 vessels, precautions in 
 
 using, 592. 
 working, one method of, 
 595. 
 Plumbate of lead, 497. 
 Pneumatic troughs, construction and 
 
 use of, xiy-xriii. 
 Porcelain, 520. 
 
 dishes, xxxii. 
 Potash, obtained from ashes of plants, 
 
 415. 
 Potassium-flame, 423. 
 
 metaUic, 422. 
 occ. of, 414. 
 salts, test for, 594. 
 Product-Tolume, defined, 207- 
 Protochloride of copper, 567. 
 tin, 583. 
 
 a reducing a- 
 gent, 583. 
 Protoxide of chromium, salts of, 523. 
 copper, 565. 
 lead, 494. 
 manganese, 528. 
 tin, 580. 
 Prussian blue, 555, 556. 
 Prussic acid, 363. 
 Puddled steel, 541. 
 Puddling iron, process of, 539. 
 PulTerdzing, xxxv. 
 Pyrites, 549, 562. 
 Pyritous shales, use of, 550. 
 Pyroligneous acid, 298. 
 Pyrophorus, of carbon and lead, 492. 
 Pyrophosphate of silyer, 406. 
 
 sodium, 406. 
 Pyrophosphoric acid, 233. 
 
 QuASTiTV flame, 345. 
 Quantivalence, 465. 
 Quartatiou, 590. 
 Quartz, 375. 
 Quicklime, 470. 
 
 manufacture of, 471. 
 Quicksilver, 570. 
 
 Quinquichloride of antimony, 276. 
 phosphorus, 237. 
 dissocia- 
 tion of, 238. 
 Quinquichlorides of antimony and 
 phosphorus, chloridizing agents, 
 277. 
 Quinquioxide of antimony, 274. 
 bismuth', 283. 
 Quinquisulphide of antimony, 280. 
 
 Radicals, compound, 363. 
 Eational formube, 87, 89. 
 Realgar, 263. 
 Red lead, manufacture and uses of, 
 
 496. 
 Reducing agent, defined, 71. 
 Reduction of metalsby carbonic oxide, 
 339. 
 charcoal, 300, 
 321. 
 Refrigerating mixture — ice and salt, 
 180. 
 nitric oxide 
 and bisulphide of carbon, 57. 
 saltpetre, 4.'!2. 
 sulphate of sodium 
 and chlorhydric acid, 396. 
 Reinsch's test for arsenic, 253. 
 Replacement, 41, 404, 508. 
 Respiration, 329. 
 Retort, iron, xxvi. 
 use of, 34. 
 Retorts, xxviii. 
 
 Revivification of animal cliarcoal, 309. 
 Rhodium, 596. 
 Rochelle-powders, 399. 
 Rock-crystal, 376. 
 Rouge, jewellers', 543. 
 Rubidium, 446. 
 Ruby, 514. 
 
 Rust, of tin, iron, mercury, &c., con- 
 tains sometliing derived from the 
 air, 7-9. 
 Rusts are oxides, 14. 
 Ruthenium, 596. 
 Rutile, 577. 
 
Ivi 
 
 SAFETY-lamps, iJ59. 
 
 -matches, 218. 
 Saline taste, and substance, 3il2. 
 Salt, decrepitation of, 393. 
 glaze, 394. 
 manufacture of, 392. 
 solubility of, 393. 
 sources of, 391. 
 use? of, 394. 
 Saltpetre, 429. 
 
 manufactured from nitrate 
 
 of sodium, 430. 
 not explosive, 431. 
 plantations, 429. 
 purification of, 429. 
 Sand-bath, xiii. 
 Sapphire, 514. 
 Saturated solutions, 37. 
 Schweinfurt green, 670. 
 Screw compressor, xxv. 
 Selenhydric acid, 201 . 
 Selenites and seleniates isomorphous 
 with sulphites and sulpliates, 200. 
 Selenimn, occ. of, 198. 
 prop, of, 199. 
 sources of, 199. 
 Sovpentine, 503. 
 
 Sesquicarbonate of ammonium, 442. 
 Sesquioxide, the term, 513. 
 
 of chromium, 523. 
 
 salts of, 
 524, 
 iron, 543. 
 manganese, 528. 
 Shot, arsenic added to, 243. 
 Silicates, 379. 
 
 altaUne, soluble, 380. 
 classes of, 380. 
 decomposition of, 381. 
 fused with alkaline car- 
 bonates, 415. 
 in glass, 412. 
 of aluminum, 519. 
 iron, 555. 
 
 sodium, making of, 410. 
 Siliceous petrifactions, 377. 
 Silicic acid, composition of, 382. 
 double salts of, 380. 
 in natural waters, 377. 
 isomeric modifications 
 
 of, 376. 
 occ. of, 375. 
 prop, of, 378. 
 soluble, 370. 
 
 Siliciurctted hydrogen, 374. 
 Silicon, abundance of, 372. 
 
 allotropic conditions of, 372. 
 atomic weight of, 382, 385. 
 compound with hydrogen 
 
 and chlorine, 386. 
 prep, of the three modifica- 
 tions of, 373. 
 prop, of, 373, 374. 
 Silver, atomic weight of, 461. 
 coin, 453. 
 extraction of, 449. 
 melted, absorbs oxygen, 4."i2. 
 occ. of, 448. 
 precipitation of, 454. 
 quantitative determination of, 
 
 460. 
 separation from lead by crys- 
 tallization, 491. 
 separation from lead by cupel- 
 
 lation, 494. 
 solvents for, 452. 
 Silvering of mirrors, 577. 
 Slag, finery, 551. 
 
 of iron furnaces, 536. 
 Smalt, 557. 
 Soap, hard, 405. 
 soft, 417. 
 Soda-ash, manufacture of, 394, 397. 
 -crystals, 397. 
 grocers', 398. 
 -powders, 399. 
 -water, 327. 
 Sodium-amalgam, 94. 
 -flame, 402. 
 000. of, 391. 
 prep, of, 400. 
 prop, of, 401. 
 Solder, 585. 
 
 Soldering, use of chloride of zinc in, 
 506, 509. 
 sal-ammoniac in, 
 579. 
 Soluble glass, 380. 
 Solution and chemical combination 
 compared, 38. 
 defined, 36, 37. 
 heat either absorbed or set 
 j free diu-ing, 395. 
 
 I how to apply the solvent, 
 
 I 37,594. 
 
 of gases in water, 67. 
 Spatulje, XXXV. 
 Specific gravity, definition of, 2ti. 
 
Ivii 
 
 Specific heat, definition of, 20. 
 
 heats, vahie of, 602. 
 Spectrum-analysis, 444. 
 Spongy platinum, 5'04. 
 Spontaneous combustion, 229. 
 
 of coal, 550. 
 Spring clip, xxv. 
 Stalactites, 468. 
 Stalagmites, 468. 
 Stannate of sodium, prep, of, 582. 
 Stannates, 581. 
 Stannic acid, 581. 
 Starch-paste, prep, of, 126. 
 Steam, physical prop, of, 21. 
 superheated, 21. 
 volumetric comp. of, 29. 
 Steel, Bessemer, 541. 
 blistered, 540. 
 cast, 541. 
 puddled, 541. 
 tempering, 542. 
 Stereotype-metal, 268. 
 Stone, artificial, 410. 
 StoTe-polish, 290. 
 Straw rings, xndii. 
 Strontianite, 488. 
 Strontium, 486. 
 
 compounds, 486-488. 
 flame, 489. 
 Stucco, 478. 
 Suboxide of lead, 493. 
 Substitution, defined, 41. 
 Sugar, purification of, 308. 
 Sugar of lead, 499. 
 Sulphantimoniates, 280. 
 Sulphantimonic acid, 280. 
 Sulphantimonites, 278, 279. 
 Sulpharseniates, 265. 
 Sulpharsenites, 264. 
 Sulphate of ahmiinum, 517- 
 ammonium, 440. 
 barium, 487. 
 calcium, 476. . 
 
 reduction of, 
 
 481. 
 stuffing for pa- 
 per, 435. 
 chromium, 524. 
 jcopper, 568. 
 lead, 499. 
 magnesium, 503. 
 potassium, 428. 
 
 and hydro- 
 gen, 428. 
 
 Sulphate of silver, 464. 
 
 sodium, manufacture of, 
 394. 
 and hydrogen, 
 396. 
 zinc, 509. 
 
 reduction of, 509. 
 Sulphates, 191. 
 
 of iron, 551-554. 
 mercury, 576. 
 Sulphide of arsenic, precipitation of, 
 . 258. 
 
 reduction j>{, 
 259. 
 boron, 371. 
 
 lead, volatility of, 498. 
 .silicon, 390. 
 silver, 463. 
 Sulphides of ammonium, 442. 
 antimony, 277. 
 
 tersulphide, 
 
 277. 
 qainquisul- 
 phide,280. 
 arsenic, bisulphide, 263. 
 tersulphide, 
 
 263. 
 quinquisul- 
 phide, 265. 
 calcimn, 173. 
 copper, 567. 
 iron, 547. 
 lead, 497. 
 mercury, 573. 
 phosphorus, 241. 
 potassium, 427. 
 sodium, 399. 
 tin, 582. 
 Sulphites, 183. 
 
 Sulphur, change of prismatic into 
 octahedral, 160. 
 crystallizatiou of, 156, 157. 
 dimorphous, 159. 
 extraction of, 155. 
 a kindling material, 165. 
 melting of, 156. 
 metals burn in, 164. 
 milk of, 163. 
 occ. of, 154. 
 salts, 264. 
 
 compared with oxy- 
 gen salts, 265. 
 soft, 162. 
 solutions of, 163. 
 
Iviii 
 
 Sulphur, uses of, 165. 
 Sulphuretted hydrogen, see Sulphy- 
 
 drio acid. 
 Sulphuric acid, absorbs water, 188. 
 action on metals, 190. 
 organiomat- 
 ter, 190. 
 anhydrous, 192. 
 
 decompo- 
 sition 
 of, 196. 
 prep, of, 
 
 193. 
 prop, of 
 194. 
 bibasic, 191. 
 freezing by, 189. 
 fuming, 191. 
 how to distil, 187. 
 how to mix with wa- 
 ter, 188. 
 hydrates of, 189. 
 importance of, 184. 
 manufacture of, 184- 
 186. 
 Sulphurous acid, antiseptic, 181. 
 bleaches, 180. 
 comp. of, 176. 
 liquid, 180. 
 oxidation of, 182. 
 prep, of, 176, 177, 
 
 178. 
 prop, of, 178. 179. 
 stops combustion, 
 179. 
 Sulphydrate of calcium, 486. 
 Sulphydrie acid, 165. 
 
 analysis of, 168. 
 comp. of, 169. 
 decomposition of, 
 
 172. 
 inflammable, 170. 
 m mineral waters, 
 
 169. 
 poisonous, 169. 
 prep, of, 166. 
 prop, of, 167. 
 pure, 168. 
 as a reagent, 171. 
 solution in water, 
 170. 
 Supersaturated solution, 396. 
 Swimmer, Erdmann's, rxxi. 
 Symbolic formuliP, value of, 90. 
 
 Symbols, chemical, 41. 
 Synthesis, definition of, 3. 
 Systems of crystallization, 158. 
 
 Table of atomic heats of compounds, 
 601. 
 gaseous ele- 
 ments, 600. 
 solid ele- 
 ments, 599. 
 atomic weights and sym- 
 bols of the elements, 597. 
 for conversion of centigrade 
 into Falirenheit degrees, 
 Y-rgiT — t1i 
 for conversion of French into 
 English mea,sures and 
 weights, xlii. 
 of groups of the elements, 598. 
 Tables of metrical weights and mea- 
 sures, xxxvii, xsxviii. 
 Tantalum, 585. 
 Tar, product of the distillation of 
 
 wood, 298. 
 Tartar, 423. 
 Tartar-emetic, 273. 
 Tartrate of lead, 492. 
 Tellurium, compounds of, 202. 
 occ. of, 201. 
 prop, of, 202. 
 Terbium, 561. 
 
 Terbromide of antimony, 277. 
 Terchloride of antimony, 275. 
 bismuth, 283. 
 phosphorus, 236. 
 Teriodide of antimony, 277. 
 Terminations ous and ic, 558. 
 Teroxide of antimony, 272. 
 
 both an a«id 
 and a base, 
 273 
 bismuth, 282. 
 
 a base, 283. 
 Tersulphide of antimony, 277-280. 
 
 bismuth, 284. 
 Test-glasses, xxix. 
 Test-tubes, xxviii. 
 Thallium, 447. 
 Thermometers, xxxv. 
 Thermometer-scales, centigrade and 
 
 Fahrenheit, compared, ixxix-xli. 
 Thionic acids, 175. 
 Thorium, 561. 
 Tin, allovs of, .'iB.i. 
 
lix 
 
 Tin, crystallization of, 578. 
 
 extraction of, 578. 
 
 occ. of, 578. 
 
 prop, and uses of, 578, 579. 
 Tin-salt, 583. 
 Tin-stone, 578. 
 Titanic acid, 577. 
 Titanium, oco. of, 577. 
 
 resembles tin, 578. 
 Tongs, xxxiy. 
 
 Tubing, sizes and qualities of, i. 
 Tungsbite of sodium, 587. 
 Tungstates, 586. 
 Tungsten, 586. 
 
 steel, 586. 
 Tungstic acid, 586. 
 Type-metal, 268. 
 
 Types — chlorhydric acid, water, and 
 ammonia, 205. 
 doctrine o^ 88. 
 Typical hydrogen compoimds, 319. 
 
 TInit of heat, 45. 
 Unit-Tolume not absolute, 204. 
 
 the bulk of 1 grm. of 
 
 hydrogen, 204. 
 a litre, 205. 
 weights, 205. 
 Univalent metals, 73. 
 Uranium, 558. 
 
 salts, peculiarity of, 559. 
 
 Vanadium, 586. 
 
 Vegetable parchment, 255. 
 
 Ventilation of wells, 324. 
 
 Verdigris, 569. 
 
 Vemulion, 573. 
 
 Volume, combination by, 203. 
 
 Wash-Bottle, xxxii. 
 Water, analyzed by iron, 23. 
 
 sodium, 22. 
 
 blue color of, 19. 
 
 densest at 4°, 19. 
 
 dissolves air, 35. 
 
 what it dissolves from air 68. 
 
 Water, distillation of, 33. 
 electrolysis of, 23. 
 hardness of, 468, 480. 
 method of determining hard- 
 ness of, 480. 
 occ. of, 33. 
 
 removal of gases from, 35. 
 the common solvent, 37. 
 standard of specific gravity, 
 20. 
 heat, 20. 
 symbol of, 32. 
 synthesis of, 25-29. 
 volumetric comp. of, 29. 
 Water-bath, xxv. 
 Waterglass, 380. 
 
 uses of, 410. 
 Wedgewood mortars, xxiiv. 
 Weights and measures, metrical, 
 
 xxxvi. 
 Weights, table of, < x x viii. 
 White iron, 538. 
 lead, 500. 
 vitriol, 509. 
 White-wash, 474. 
 Wire gauze, use of, xiii. 
 Witherite, 488. 
 Wolfram, 586. 
 Wood, distillation of, 296. 
 Woulfe-bottles, 85. 
 Wrought iron, 539. 
 
 impurities of, 540. 
 making of, 539. 
 
 YEAST-powders, 399. 
 Yellow-metal, 564. 
 Yttrium, 561. 
 
 Zinc, alloys with antimony, 269. 
 
 extraction of, 504. 
 
 granulated, 505. 
 
 prop, of, 505. 
 
 replaces lead, 507. 
 
 white, 508. 
 Zirconium, 561. 
 
 Printed by Taylor and Francis, Red Lion Court, Fleet Street, London.